Solar Drier Final

Solar Crop Dryer Project Report-2011

Abstract

A multi-purpose solar crop dryer was developed for drying various

agricultural products such as fruits, vegetables, medicinal plants etc. The

newly developed system consists of a small fan, a solar air heater and a

tunnel dryer. The simple design allows production either by farmers

themselves, using cheap and locally available materials, or by small scale

industries. Due to the low investment required, the solar dryer is

predestined for application on small farms in developing countries.

Depending on the crop to be dried and the size of the dryer 100–1000 kg

of fresh material can be dried within 1–7 days to safe storage conditions.

The solar dryer was successfully tested in Greece, Yugoslavia, Egypt,

Ethiopia and Saudi Arabia drying grapes, dates, onions, peppers and

several medicinal plants. Compared to traditional sun drying methods,

the use of the solar dryer reduces drying time significantly and prevents

mass losses. Furthermore, product quality can be improved essentially.

During drying, the crop is protected completely from rain, dust, insects

and animals. All these features contribute to the desired high product

quality. The energy cost required for operating the fan features

contribute to the the additional earnings from reduced mass losses and

improved quality. On-farm tests also showed that the dryer can be easily

operated by farmers. However, at present the dissemination of the solar

dryer is limited to electrified areas.

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Chapter – 1

Introduction

Drying is an excellent way to preserve food and solar food dryers

are appropriate food preservation technology for sustainable

development . Drying was probably the first ever food preserving

method used by man, even before cooking. It involves the removal of

moisture from agricultural produce so as to provide a product that can

be safely stored for longer period of time.

“Sun drying” is the earliest method of drying farm products ever known

to man and it involves simply laying the agricultural products in the sun

on mats, roofs or drying floors. This has several disadvantages since the

farm products are laid in the open sky and there is greater risk of

spoilage due to adverse climatic conditions like rain, wind, moist and

dust, loss of products to birds, insects and rodents (pests); totally

dependent on good weather and very slow drying rate with danger of

mould growth thereby causing deterioration and decomposition of the

products. The process also requires large area of land, takes time and

highly labour intensiv.

With cultural and industrial development, artificial mechanical drying

came into practice, but this process is highly energy intensive and

expensive which ultimately increases product cost. Recently, efforts to

improve “sun drying” have led to “solar drying”.

In solar drying, solar dryers are specialized devices that control the

drying process and protect agricultural produce from damage by insect

pests, dust and rain. In comparison to natural “sun drying”, solar dryers

generate higher temperatures, lower relative humidity, lower product

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moisture content and reduced spoilage during the drying process. In

addition, it takes up less space, takes less time and relatively inexpensive

compared to artificial mechanical drying method. Thus, solar drying is a

better alternative solution to all the drawbacks of natural drying and

artificial mechanical drying.

The solar dryer can be seen as one of the solutions to the world’s food

and energy crises. With drying, most agricultural products can be

preserved and this can be achieved more efficiently through the use of

solar dryers.

Solar dryers are a very useful device for:

Agricultural crop drying.

Food processing industries for dehydration of fruits and vegetables.

Fish and meat drying.

Dairy industries for production of milk powder.

Seasoning of wood and timber.

Textile industries for drying of textile materials, etc.

Thus, the solar dryer is one of the many ways of making use of solar

energy efficiently in meeting man’s demand for energy and food supply.

Air is commonly used as a heat transfer fluid in many types of

energy conversion systems. In drying applications and space heating

solar energy can take part in a major role because which can be done

with warm air alone. Nearly any black surface which is heated by the

sun will transfer heat to air when the air is blown over it. Air is

distributed over the black radiation-absorbing surface and the air

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stream should be in contact with the complete collector surface to

achieve higher temperatures. Air collector is usually over-laid by one or

more transparent covers to reduce the heat loss. A good review of solar

air heaters and their applications has been reported.

Conventional, fuel-operated artificial dryers are more efficient,

providing uniform high quality products. But such units are beyond the

reach of the farmers with limited crop volume and high requirements of

financial resources with respect to the cost of equipment. The increasing

rate of fuel consumption in agriculture has made it necessary not only to

save energy by intensifying the drying processes and improving their

designs and where these solar energy systems can play a major role.

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Chapter – 2

Literature Survey

Sunlight

Sunlight, in the broad sense, is the total frequency

spectrum of electromagnetic radiation given off by the Sun. On Earth,

sunlight is filtered through the Earth's atmosphere, and solar

radiation is obvious as daylight when the Sun is above the horizon.

When the direct solar radiation is not blocked by clouds, it is

experienced as sunshine, a combination of bright light and radiant heat.

When it is blocked by the clouds or reflects off of other objects, it is

experienced as diffused light.

The World Meteorological Organization uses the term "sunshine

duration" to mean the cumulative time during which an area receives

direct irradiance from the Sun of at least 120 watts per square meter.

Sunlight may be recorded using a sunshine

recorder, pyranometer or pyrhelio meter. Sunlight takes about 8.3

minutes to reach the Earth.

Direct sunlight has a luminous efficiency of about 93 lumens per watt

of radiant flux, which includes infrared, visible, and ultraviolet light.

Bright sunlight provides illuminance of approximately

100,000 lux or lumens per square meter at the Earth's surface.

Sunlight is a key factor in photosynthesis, a process vital for life on

Earth.

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Calculation

To calculate the amount of sunlight reaching the ground, both

the elliptical orbit of the Earth and the attenuation by the Earth's

atmosphe- re have to be taken into account. The extraterrestrial solar

illuminance (Eext), corrected for the elliptical orbit by using the day

number of the year (dn), is given by

where dn=1 on January 1; dn=2 on January 2; dn=32 on February 1,

etc. In this formula dn-3 is used, because in modern times Earth's

perihelion, the closest approach to the Sun and therefore the

maximum Eext occurs around January 3 each year. The value of

0.033412determined knowing that the ratio between perihelion.

(0.98328989AU) squared and the aphelion (1.016710033 AU) should be

approximately 0.935338.

The solar illuminance constant (Esc), is equal to 128×103 lx. The direct

normal illuminance (Edn), corrected for the attenuating effects of the

atmosphere is given by:

where c is the atmospheric extinction coefficient and m is the relative

optical airmass.

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Solar constant

The solar constant, a measure of flux density, is the amount of incoming

solar electromagnetic radiation per unit area that would be incident on a

plane perpendicular to the rays, at a distance of one astronomical unit

(AU) (roughly the mean distance from the Sun to the Earth). When

solar irradiance is measured on the outer surface of Earth's

atmosphere, the measurements can be adjusted using the inverse square

law to infer the magnitude of solar irradiance at one AU and deduce the

solar constant. The solar constant includes all types of solar radiation,

not just the visible light. It is measured by satellite to be roughly

1.366 kilo watts  per square meter (kW/m²).

Sunlight intensity in the Solar System

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Different bodies of the Solar System receive light of an intensity

inversely proportional to the square of their distance from Sun. A rough

table comparing the amount of light received by each planet on the Solar

System follows -

PlanetPerihelion - Aphelion

distance (AU)

Solar radiation

maximum and minimum

(W/m²)

Mercury 0.3075 – 0.4667 14,446 – 6,272

Venus 0.7184 – 0.7282 2,647 – 2,576

Earth 0.9833 – 1.017 1,413 – 1,321

Mars 1.382 – 1.666 715 – 492

Jupiter 4.950 – 5.458 55.8 – 45.9

Saturn 9.048 – 10.12 16.7 – 13.4

Uranus 18.38 – 20.08 4.04 – 3.39

Neptune 29.77 – 30.44 1.54 – 1.47

The actual brightness of sunlight that would be observed at the surface

depends also on the presence and composition of an atmosphere. For

example Venus' thick atmosphere reflects more than 60% of the solar

light it receives. The actual illumination of the surface is about 14,000

lux, comparable to that on Earth "in the daytime with overcast clouds".

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Sunlight on Mars would be more or less like daylight on Earth wearing

sunglasses, and as can be seen in the pictures taken by the rovers, there

is enough diffuse sky radiation that shadows would not seem particularly

dark. Thus it would give perceptions and "feel" very much like Earth

daylight.

For comparison purposes, sunlight on Saturn is slightly brighter than

Earth sunlight at the average sunset or sunrise (see daylight for

comparison table). Even on Pluto the sunlight would still be bright

enough to almost match the average living room. To see sunlight as dim

as full moonlight on the Earth, a distance of about 500 AU (~69 light-

hours) is needed; there is only a handful of objects in the solar system

known to orbit farther than such a distance.

Composition

The spectrum of the Sun's solar radiation is close to that of a black

body with a temperature of about 5,800 K. The Sun emits EM radiation

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across most of the electromagnetic spectrum. Although the Sun

produces Gamma rays as a result of the Nuclear fusion process, these

super high energy photons are converted to lower energy photons before

they reach the Sun's surface and are emitted out into space. So the Sun

doesn't give off any gamma rays to speak of. The Sun does, however,

emit X-rays, ultraviolet, visible light , infrared, and even Radio waves.

When ultraviolet radiation is not absorbed by the atmosphere or other

protective coating, it can cause damage to the skin known as sunburn or

trigger an adaptive change in human skin pigmentation.

Solar irradiance spectrum above atmosphere and at surface.

The spectrum of electromagnetic radiation striking the Earth's

atmosphere is 100 to 106 nanometers (nm). This can be divided into five

regions in increasing order of wavelengths

Ultraviolet C or (UVC) range, which spans a range of 100 to 280 nm.

The term ultraviolet refers to the fact that the radiation is at higher

frequency than violet light (and, hence also invisible to the human eye).

Owing to absorption by the atmosphere very little reaches the Earth's

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surface (Lithosphere). This spectrum of radiation

has germicidal properties, and is used in germicidal lamps.

Ultraviolet B or (UVB) range spans 280 to 315 nm. It is also greatly

absorbed by the atmosphere, and along with UVC is responsible for

the photochemical reaction leading to the production of the Ozone layer.

Ultraviolet A or (UVA) spans 315 to 400 nm. It has been traditionally

held as less damaging to the DNA, and hence used

in tanning and PUVA therapy for psoriasis.

Visible range or light spans 380 to 780 nm. As the name suggests, it is

this range that is visible to the naked eye.

Infrared range that spans 700 nm to 106 nm [1 (mm)]. It is responsible

for an important part of the electromagnetic radiation that reaches the

Earth. It is also divided into three types on the basis of wavelength:

Infrared-A: 700 nm to 1,400 nm

Infrared-B: 1,400 nm to 3,000 nm

Infrared-C: 3,000 nm to 1 mm.

SOLAR RADIATION – THE ENERGY

SOURCE FOR SOLAR DRYING

The sun is the central energy producer of our solar system. I has

the form of a ball and nuclear fusion take place continuously in its

centre. A small fraction of the energy produced in the sun hits the earth

and makes life possible on our planet. Solar radiation drives all natural

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cycles and processes such as rain, wind, photosynthesis, ocean currents

and several other which are important for life. The whole world energy

need has been based from the very beginning on solar energy. All fossil

fuels (oil, gas, coal, etc.) are converted solar energy.

The radiation intensity of 6000oC solar surface corresponds to

70,000 to 80,000 kW/m2. Our planet receives only a very small portion of

this energy. In spite of this, the incoming solar radiation energy in a year

is about 200,000,000 billion kWh; this is more than 10,000 times the

yearly energy need of the whole world. The solar radiation intensity

outside the atmosphere is in average 1,360 W/m2 (solar constant). When

the solar radiation penetrates through the atmosphere some of the

radiation is lost so that on a clear sky sunny day in summer between 800

to 1000 W/m2 (global radiation) can be obtained on the ground.

Solar energy will be extremely expensive as compared to other

energy sources. However there is an unlimited amount of power across

different countries in summer. There will not be enough input from

other sources and therefore we must work extremely hard on solar

energy. It will be indispensable. The only problem is that the public is

unwilling to make the huge investments in solar that are needed, and if

we wait too long to make these investments it will be too late. In order to

use this energy, we will have to have seasonal industries that take

advantage hat when the sun doesn’t shine, the factory won’t work and it

might be necessary to go to bed early because there is no electricity.

Capital costs of solar will be very high because the percentage of time

that it is available is so small. A lot of labour will be required but labour

will be cheap after oilo depletion power needs for an economic one. The

information gained can then be used in large power plants or in house

sized installations.

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Global Radiation

The duration of the sunshine as well as its intensity is dependent on

the time of the year, weather conditions and naturally also on the

geographical location. The amount of yearly global radiation on a

horizontal surface may thus reach in the sun belt regions over 2,200

kWh/m2. In north Europe, the maximum values are 1,100 kWh/m2. The

global radiation composes of direct and diffuse radiation. The direct

solar radiation is the component which comes from the direction of the

sun. The diffuse radiation component is created when the direct solar

rays are scattered from the different molecules and particles in the

atmosphere into all directions, i.e. the radiation becomes un-beamed.

The amount of diffuse radiation is dependent on the climatic and

geographic conditions. The global radiation and the proportion of

diffuse radiation is greatly influenced by clouds, the condition of the

atmosphere (e.g. haze and dust layers over large cities) and the path

length of the beams through the atmosphere.

Solar energy

Solar energy, radiant light and heat from the sun, has been harnessed by

humans since ancient times using a range of ever-evolving technologies.

Solar radiation, along with secondary solar-powered resources such

as wind and wave power, hydroelectricity and biomass, account for most

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of the available renewable energy on earth. Only a minuscule fraction

of the available solar energy is used.

Solar powered electrical generation relies on heat

engines and photovoltaics. Solar energy's uses are limited only by human

ingenuity. To harvest the solar energy, the most common way is to

use solar panels.

Solar technologies are broadly characterized as either passive

solar or active solar depending on the way they capture, convert and

distribute solar energy. Active solar techniques include the use of

photovoltaic panels and solar thermal collectors to harness the energy.

Passive solar techniques include orienting a building to the Sun, selecting

materials with favorable thermal mass or light dispersing properties,

and designing spaces that naturally circulate air.

Energy from the Sun

The Earth receives 174 petawatts (PW) of incoming solar radiation

(insolation) at the upper atmosphere. Approximately 30% is reflected

back to space while the rest is absorbed by clouds, oceans and land

masses. The spectrum of solar light at the Earth's surface is mostly

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spread across the visible and near-infrared ranges with a small part in

the near-ultraviolet.

Earth's land surface, oceans and atmosphere absorb solar radiation, and

this raises their temperature. Warm air

About half the incoming solar energy reaches the Earth's surface.

containing evaporated water from the oceans rises, causing atmospheric

circulation or convection. When the air reaches a high altitude, where

the temperature is low, water vapor condenses into clouds, which rain

onto the Earth's surface, completing the water cycle. The latent heat of

water condensation amplifies convection, producing atmospheric

phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed

by the oceans and land masses keeps the surface at an average

temperature of 14 °C. By photosynthesis green plants convert solar

energy into chemical energy, which produces food, wood and

the biomass from which fossil fuels are derived.

increased food prices by diverting forests and crops into biofuel production.

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Yearly Solar fluxes & Human Energy

Consumption

Solar 3,850,000 EJ [6]

Wind 2,250 EJ[7]

Biomass 3,000 EJ[8]

Primary energy use (2005) 487 EJ[9]

Electricity (2005) 56.7 EJ[10]

The total solar energy absorbed by Earth's atmosphere, oceans and land

masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this

was more energy in one hour than the world used in one year.

Photosynthesis captures approximately 3,000 EJ per year in

biomass. The amount of solar energy reaching the surface of the planet

is so vast that in one year it is about twice as much as will ever be

obtained from all of the Earth's non-renewable resources of coal, oil,

natural gas, and mined uranium combined.

From the table of resources it would appear that solar, wind or biomass

would be sufficient to supply all of our energy needs, however, the

increased use of biomass has had a negative effect on global warming

and dramatically As intermittent resources, solar and wind raise other

issues.

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Solar energy can be harnessed in different levels around the world.

Depending on a geographical location the closer to the equator the more

"potential" solar energy is available.

Applications of solar technology

Average insolation showing land area (small black dots) required to

replace the world primary energy supply with solar electricity. 18 TW is

568 Exajoule (EJ) per year. Insolation for most people is from 150 to 300

W/m² or 3.5 to 7.0 kWh/m²/day.

Solar energy refers primarily to the use of solar radiation for practical

ends. However, all renewable energies, other than geothermal and tidal,

derive their energy from the sun.

Solar technologies are broadly characterized as either passive or active

depending on the way they capture, convert and distribute sunlight.

Active solar techniques use photovoltaic panels, pumps, and fans to

convert sunlight into useful outputs. Passive solar techniques include

selecting materials with favorable thermal properties, designing spaces

that naturally circulate air, and referencing the position of a building to

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the Sun. Active solar technologies increase the supply of energy and are

considered supply side technologies, while passive solar technologies

reduce the need for alternate resources and are generally considered

demand side technologies.

History

There are records of solar collectors in the United States dating back to

before 1900, comprising a black-painted tank mounted on a roof. In

1896 Clarence Kemp of Baltimore, USA enclosed a tank in a wooden

box, thus creating the first 'batch water heater' as they are known today.

Although flat-plate collectors for solar water heating were used in

Florida and Southern California in the 1920s there was a surge of

interest in solar heating in North America after 1960, but specially after

the 1973 oil crisis.

Work in Israel

Main article: Solar power in Israel

Passive (thermisiphon) solar water heaters on a rooftop in Jerusalem

Flat plate solar systems were perfected and used on a very large scale in

Israel. In the 1950s there was a fuel shortage in the new Israeli state, and

the government forbade heating water between 10 p.m. and 6 a.m.. Levi

Yissar built the first prototype Israeli solar water heater and in 1953 he

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launched the NerYah Company, Israel's first commercial manufacturer

of solar water heating. Despite the abundance of sunlight in Israel, solar

water heaters were used by only 20% of the population by 1967.

Following the energy crisis in the 1970s, in 1980 the

Israeli Knesset passed a law requiring the installation of solar water

heaters in all new homes (except high towers with insufficient roof area).

As a result, Israel is now the world leader in the use of solar energy per

capita with 85% of the households today using solar thermal systems

(3% of the primary national energy consumption), estimated to save the

country two million barrels of oil a year, the highest per capita use of

solar energy in the world.

Other countries.

New solar hot water installations during 2007, worldwide.

The world saw a rapid growth of the use of solar warm water after 1960,

with systems being marketed also in Japan and Australia Technical

innovation has improved performance, life expectancy and ease of use of

these systems. Installation of solar water heating has become the norm in

countries with an abundance of solar radiation, like the Mediterranean,

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and Japan and Austria, where there Colombia developed a local solar

water heating industry thanks to the designs of Las Gaviotas, directed by

Paolo Lugari. Driven by a desire to reduce costs in social housing, the

team of Gaviotas studied the best systems from Israel, and made

adaptations as to meet the specifications set by the Banco Central

Hipotecario (BCH) which prescribed that the system must be

operational in cities like Bogotá where there are more than 200 days

overcast. The ultimate designs were so successful that Las Gaviotas

offered in 1984 a 25 year warranty on any of its installations. Over

40,000 were installed, and still function a quarter of a century later.

In 2005, Spain became the first country in the world to require the

installation of photovoltaic electricity generation in new buildings, and

the second (after Israel) to require the installation of solar water heating

systems in 2006.

Australia has a variety of incentives (national and state) and regulations

(state) for solar thermal introduced starting with MRET in 1997 .

Solar water heating systems have become popular in China, where basic

models start at around 1,500 yuan (US$190), much cheaper than in

Western countries (around 80% cheaper for a given size of collector). It

is said that at least 30 million Chinese households now have one, and that

the popularity is due to the efficient evacuated tubes which allow the

heaters to function even under gray skies and at temperatures well

below freezing . Israel and Cyprus are the per capita leaders in the use

of solar water heating systems with over 30%-40% of homes using them.

See Appendix 1 at the bottom of this article for a number of country-

specific statistics on the "Use of solar water heating worldwide".

Wikipedia also has country-specific articles about solar energy use

(thermal as well as photovoltaic)

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in Australia, Canada, China, Germany, India, Israel,Japan, Portugal, R

omania, Spain, the United Kingdom and the United States.

Solar air heat

Solar air heat is a type of energy collector in which the energy from the

sun, solar insolation, is captured by an absorbing medium and used to

heat air . Solar air heating is arenewable energy heating technology used

to heat or condition air for buildings or process heat applications.

Solar air collectors can be commonly divided into two categories: .

glazed (recirculating types)

unglazed (ambient air heaters -transpired type)

Glazed Air Systems

Functioning in a similar manner as a conventional forced air furnace,

systems provide heat by recirculating conditioned building air

through solar collectors - Solar thermal collectors. . Through the use of

an energy collecting surface to absorb the sun’s thermal energy, and

ducting air to come in contact with it, a simple and effective collector can

be made for a variety of air conditioning and process applications.

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SPF Solar Air Heat Collector

A simple solar air collector consists of an absorber material, sometimes

having a selective surface, to capture radiation from the sun and

transfers this thermal energy to air via conduction heat transfer. This

heated air is then ducted to the building space or to the process area

where the heated air is used for space heating or process heating needs.

Air Heat Applications

A variety of applications can utilize solar air heat technologies to reduce

the carbon footprint from use of conventional heat sources, such as fossil

fuels, to create a sustainable means to produce thermal energy.

Applications such as space heating, pre-heating ventilation makeup air,

or process heat can be addressed by solar air heat devices. Further

strides are being made in the field of ‘solar co-generation’ where solar

thermal technologies are being paired with photovoltaics (PV) which

increases the efficiency of a typical PV system by generating additional

useful energy in the form of both electricity and heat.

Space Heating Applications

Space heating for residential and commercial applications can be done

through the use of solar air heating panels. This configuration operates

by drawing air from the building envelope or from the outdoor

environment and passes it through the collector where the air warms

from conduction of the absorber and is then supplied to the living or

working space by either passive means or with the assistance of a fan.

Ventilation, fresh air or makeup air is required in most commercial,

industrial and institutional buildings to meet code requirements. By

drawing air through a properly designed unglazed transpired air

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collector or an air heater (such as

an http://en.wikipedia.org/wiki/Energy_recovery_ventilation energy and

heat recovery ventilators ERV/HRV]), the solar heated fresh air can

reduce the heating load during daytime operation. Many applications

are now being installed where the transpired collector preheats the fresh

air entering a heat recovery ventilator to reduce the defrost time of

HRV's.

Process Heat Applications

Solar air heat can also be used in process applications such as drying

laundry, crops (i.e. tea, corn, coffee) and other drying applications. Air

heated through a solar collector and then passed over a medium to be

dried can provide an efficient means by which to reduce the moisture

content of the material.

Unglazed Air Systems

Transpired Air Collector

Transpired air collectors are becoming the most popular type of solar

air heating system in North America. These unglazed solar collectors are

low cost and primarily used to heat ambient air and not building air.

Transpired collectors only require one penetration into the building, or

if existing fan inlets are used, then no additional penetrations are

necessary. The transpired air collectors are generally wall mounted to

capture the lower sun angles in the winter months, additional sun

reflection off the snow and they also capture heat loss escaping from the

building envelope which is collected in the SolarWall air cavity and

drawn back into the ventilation system. As of 2009, there are over 1500

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transpired collector installations with over 300,000 square meters of

collector surface.

Solar Heating Efficiency

Solar air collector heat loss is lowest when the temperature of the air

entering the solar panel is equal to (or less than) ambient temperature.

This occurs with transpired collectors designed to pre-heat outside air

for ventilating a building. Space heating collectors are designed to reheat

inside building air so the air entering the collector is warmer than

outside air resulting in some heat loss through the glazing. Space heating

systems must also heat the air above room temperature whereas with

ventilation heating, it is only necessary to raise the outside air

temperature to room temperature (20 C). On cold, overcast days, there

may be insufficient energy for space heating but ambient air heaters

may still be able to extract a few degrees of useful energy from the

filtered sunlight. Transpired collectors will provide significant energy

savings when heating ventilation air for buildings that have high fresh

air requirements such as factories, schools, hospitals arenas etc.

Transpired collector systems are generally day time solar heaters

without storage. Most homes have low ventilation requiements and need

higher temperature air and thus transpired collectors are not as popular

for residential applications.

Active solar

Active solar technologies are employed to convert solar energy into

usable light, heat, cause air-movement for ventilation or cooling, or store

heat for future use. Active solar uses electrical or mechanical equipment,

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such as pumps and fans, to increase the usable heat in a system. Solar

energy collection and utilization systems that do not use external energy,

like a solar chimney, are classified as passive solartechnologies.

Solar hot water systems, except those based on the thermosiphon, use

pumps or fans to circulate water, an anti-freeze mixture, or air

throughsolar collectors, and are therefore classified under active solar

technology. The solar collectors can be nonconcentrating or 'flat-plate',

or of various concentrating designs. Most solar-thermal collectors have

fixed mounting, but can have a higher performance if they track the

path of the sun through the sky. Solar trackers, used to

orient photovoltaic arrays or daylighting, may be driven by either

passive or active technology.

Solar trackers   may be driven by active or passive solar   technology

Passive solar

Passive solar technologies are means of using sunlight for useful energy

without use of active mechanical systems (as contrasted to active solar).

Such technologies convert sunlight into usable heat (water, air, thermal

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Solar Crop Dryer Project Report-2011

mass), cause air-movement for ventilating, or future use, with little use

of other energy sources. A common example is a solarium on

the equator-side of a building. Passive cooling is the use of the same

design principles to reduce summer cooling requirements.Passive solar

energy is a type of energy.

Technologies that use a significant amount of conventional energy to

power pumps or fans are active solar technologies. Some passive systems

use a small amount of conventional energy to control dampers, shutters,

night insulation, and other devices that enhance solar energy collection,

storage, use, and reduce undesirable heat transfer.

Passive solar technologies include direct and indirect solar gain for space

heating, solar water heating systems based on

the thermosiphon or geyser pump, use of thermal mass and phase-

change materials for slowing indoor air temperature swings, solar

cookers, the solar chimney for enhancing natural ventilation, and earth

sheltering. More widely, passive solar technologies include the solar

furnace and solar forge, but these typically require some external energy

for aligning their concentrating mirrors or receivers, and historically

have not proven to be practical or cost effective for widespread use.

'Low-grade' energy needs, such as space and water heating, have

proven, over time, to be better applications for passive use of solar

energy.

Chapter – 3

Solar Drying

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Solar Crop Dryer Project Report-2011

Food dehydrator

A food dehydrator is an appliance that removes moisture from food to

aid in its preservation. A food dehydrator uses heat and air flow

to reduce the water content of foods. The water content of food is usually

very high, typically 80% to 95% for various fruits and vegetables and

50% to 75% for various meats. Removing moisture from food restrains

various bacteria from growing and spoiling food. Further, removing

moisture from food dramatically reduces the weight of the food. Thus,

food dehydrators are used to preserve and extend the shelf life of various

foods.

Tomato slices ready to be dried in a food dehydrator. In this model, multiple trays can be

stacked on top of each other and warm air flows around the food.

A food dehydrator's basic parts usually consist of a heating element, a

fan, air vents allowing for air circulation and food trays to lay food

upon. A dehydrator's heating element, fans and vents simultaneously

work to remove moisture from food. A dehydrator's heating element

warms the food causing its moisture to be released from its interior. The

27

Solar Crop Dryer Project Report-2011

appliance's fan then blows the warm, moist air out of the appliance via

the air vents. This process continues for hours until the food is dried to a

substantially lower water content, usually fifteen to twenty percent or

less.

Most foods are dehydrated at temperatures of 130 °F, or 54 °C, although

meats being made into jerky should be dehydrated at a higher

temperature of 155 °F, or 68 °C, or preheated to those temperature

levels, to guard against pathogens that may be in the meat. The key to

successful food dehydration is the application of a constant temperature

and adequate air flow. Too high of a temperature can cause case

hardened foods; food that is hard and dry on the outside but moist on

the inside.

The first food dehydrator was sold in 1920.

Solar dryers use solar energy to create a flow of warm air through the

tray.

Drying (food)

Drying is a method of food preservation that works by

removing water from the food, which inhibits the growth

28

Solar Crop Dryer Project Report-2011

of microorganisms and hinders quality decay. Drying food using sun and

wind to prevent spoilage has been practised since ancient times. Water is

usually removed byevaporation (air drying, sun drying, smoking or wind

drying) but, in the case of freeze-drying, food is first frozen and then the

water is removed by sublimation.

Bacteria yeasts and moulds need the water in the food to grow. Drying

effectively prevents them from surviving in the food.

A whole potato, sliced pieces (right), and dried sliced pieces (left)

Food types

29

Solar Crop Dryer Project Report-2011

Many different foods are prepared by dehydration. Good examples are

meat such as prosciutto (a.k.a. Parma ham), bresaola, and beef jerky.

Dried and salted reindeer meat is a traditional Sami food. First the meat

is soaked / pickled in saltwater for a couple of days to guarantee the

conservation of the meat. Then the meat is dried in the sun in spring

when the air temperature is below zero. The dried meat can be further

processed to make soup.

Fruits change character completely[clarification needed] when dried:

the plum becomes a prune, the grape a raisin; figs and dates are also

transformed in new, different products, that can be eaten as they are or

else after rehydration.

A collection of dried mushrooms.

Home drying of vegetables, fruit and even meat (to produce jerky) may

be carried out by a do-it-yourself practice, employing electrical

dehydrators (household appliance). If the user does not like to use

additives as potassium metabisulphite, or BHA, BHT for meats, dried

products may be hermetically shelf stored if it is to be consumed soon, or

else in the refrigerator or even freezer if a long storage is to be expected.

Freeze dried vegetables are often found in backpackers food, hunters,

military, etc. The exception to this rule are bulbs, such

as garlic and onion, which are often dried. Also chilis are frequently

30

Solar Crop Dryer Project Report-2011

dried. Edible andpsilocybin mushrooms, as well as other fungi, are also

sometimes dried for preservation purposes, to affect the potency of

chemical components, or so they can be used as seasonings.

For centuries, much of the European diet depended on dried cod, known

as salt cod or bacalhau (with salt) or stockfish (without). It formed the

main protein source for the slaves on theWest Indian plantations, and

was a major economic force within the triangular trade.

Dried shark meat, known as Hákarl, is a delicacy in Iceland.

Grain drying

Hundreds of millions of tonnes of wheat, corn, soybean, rice and other

grains as sorghum, sunflower seeds, rapeseed/canola, barley, oats, etc.,

are dried in grain dryers. In the main agricultural countries, drying

comprises the reduction of moisture from about 17-30%w/w to values

between 8 and 15%w/w, depending on the grain. The final moisture

content for drying must be adequate for storage. The more oil the grain

has, the lower its storage moisture content will be (though its initial

moisture for drying will also be lower). Cereals are often dried to 14%

w/w, while oilseeds, to 12.5% (soybeans), 8% (sunflower) and 9%

(peanuts). Drying is carried out as a requisite for safe storage, in order

to inhibit microbial growth. However, low temperatures in storage are

also highly recommended to avoid degradative reactions and, especially,

the growth of insects and mites. A good maximum storage temperature

is about 18°C. The largest dryers are normally used "Off-farm", in

elevators, and are of the continuous type: Mixed-flow dryers are

preferred in Europe, while Cross-flow dryers in the USA. In Argentina,

both types are usually found. Continuous flow dryers may produce up to

100 metric tonnes of dried grain per hour. The depth of grain the air

must traverse in continuous dryers range from some 0.15 m in Mixed

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Solar Crop Dryer Project Report-2011

flow dryers to some 0.30 m in Cross-Flow. Batch dryers are mainly used

"On-Farm", particularly in the USA and Europe. They normally consist

of a bin, with heated air flowing horizontally from an internal cylinder

through an inner perforated metal sheet, then through a annular grain

bed, some 0.50 m thick (coaxial with the internal cylinder) in radial

direction, and finally across the outer perforated metal sheet, before

being discharged to the atmosphere. The usual drying times range from

1 h to 4 h depending on how much water must be removed, type of grain,

air temperature and the grain depth. In the USA, continuous

counterflow dryers may be found on-farm, adapting a bin to slowly

drying grain fed at the top and removed at the bottom of the bin by a

sweeping auger. Grain drying is an active area of manufacturing and

research. Now it is possible to simulate the performance of a dryer with

computer programs based on equations (mathematical models) that

represent the phenomena involved in drying: physics, physical

chemistry, thermodynamics and heat and mass transfer. Most recently

the evolution of quality indices is beginning to be predicted with some

confidence, in order to add an essential performance parameter with

which to establish a compromise of reasonably fast drying rate, limited

energy consumption, and satisfactory grain quality. A typical quality

parameter in wheat drying is the breadmaking quality and germination

percentage whose reductions in drying are somewhat related.

Attempts to Harness Solar Energy

Some Background to the Concept

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Solar Crop Dryer Project Report-2011

The idea of using solar energy to produce high temperature dates

back to ancient times. The solar radiation has been used by man since

the beginning of time for heating his domicile, for agricultural purposes

and for personal comfort. Reports abound in literature on the 18th

century works of Archimedes on concentrating the sun’s rays with flat

mirrors; Antoine Lavoisier on solar furnace; Joseph Priestly on

concentrating rays using lens. In the 19th century, development of solar

distillation unit covering 4750sq meters of land, operated for 40 years

and, producing 6,000 gallons of water from salt water per day has been

reported. Also, John Ericson’s work on conversion of solar energy into

mechanical energy through a device, which produced 1hp (746 W) for

each 9.3m2 of collecting surface has also been reported.

Modern research on the use of solar energy started during the 20th

century. Developments include the invention of a solar boiler, small

powered steam engines and solar battery, but it is difficult to market

them in competition with engines running on inexpensive

gasoline .During the mid 1970’s shortages of oil and natural gas, increase

in the cost of fossil fuels and the depletion of other resources stimulated

efforts in the United States to develop solar energy into a practical power

source. Thus, interest was rekindled in the harnessing of solar energy for

heating and cooling, the generation of electricity and other purposes

Capturing Solar Energy

Solar radiation can be converted either into thermal energy (heat)

or into electrical energy. This can be done by making use of thermal

collectors for conversion into heat energy or photovoltaic collectors for

conversion into electrical energy. Two main collectors are used to

capture solar energy and convert it to thermal energy, these are flat

plate collectors and concentrating collectors . In this paper, emphasis is

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Solar Crop Dryer Project Report-2011

laid much on the flat plate collectors which are also known as non-

focusing collectors.

 Importance of Solar Dried Food

For centuries, people of various nations have been preserving

fruits, other crops, meat and fish by drying. Drying is also beneficial for

hay, copra, tea and other income producing non-food crops. With solar

drying being available everywhere, the availability of all these farm

produce can be greatly increased. It is worth noting that until around

the end of the 18th century when canning was developed, drying was

virtually the only method of food preservation.

The energy input for drying is less than what is needed to freeze or

can, and the storage space is minimal compared with that needed for

canning jars and freezer containers. It was further stated that the

nutritional value of food is only minimally affected by drying . Also, food

scientists have found that by reducing the moisture content of food to 10

to 20%, bacteria, yeast, mold and enzymes are all prevented from

spoiling it. Microorganisms are effectively killed when the internal

temperature of food reaches 145°F . The flavour and most of the

nutritional value of dried food is preserved and concentrated . Dried

foods do not require any special storage equipment and are easy to

transport . Dehydration of vegetables and other food crop by traditional

methods of open-air sun drying is not satisfactory, because the products

deteriorate rapidly .

Studies showed that food items dried in a solar dryer were

superior to those which are sun dried when evaluated in terms of taste,

colour and mould counts . Solar dried food are quality products that can

be stored for extended periods, easily transported at less cost while still

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Solar Crop Dryer Project Report-2011

providing excellent nutritive value. This paper therefore presents the

design and construction of a domestic passive solar food dryer.

Chapter – 4

Solar Crops Dryer Parts

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Solar Crop Dryer Project Report-2011

Collector types

A solar-thermal-collector is a solar-collector designed to

collect heat by absorb ing sunlight. The term is applied to solar hot

water panels, but may also be used to denote more complex installations

such as solar parabolic, solar trough and solar towers or simpler

installations such as solar air heat. The more complex collectors are

generally used in solar power plants where solar heat is used to

generate electricity by heating water to produce steam which drives

a turbine connected to an electrical generator. The simpler collectors are

typically used for supplemental space heating in residential and

commercial buildings. A collector is a device for converting the energy in

solar radiation into a more usable or storable form. The energy in

sunlight is in the form of electromagnetic radiation from

the infrared (long) to the ultraviolet (short) wavelengths. The solar

energy striking the Earth's surface depends on weather conditions, as

well as location and orientation of the surface, but overall, it averages

about 1,000 watts per square meter under clear skies with the surface

directly perpendicular to the sun's rays.

Due to varying air-ducting methods, collectors are commonly classified

as one of three types:

a) through-pass collectors,

b) front-pass,

c) back pass,

d) combination front and back pass collectors.

Through-Pass Air Collector

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Solar Crop Dryer Project Report-2011

In the through-pass configuration, air ducted onto one side of the

absorber passes through a perforated or fibrous type material and is

heated from the conductive properties of the material and the convective

properties of the moving air. Through-pass absorbers have the most

surface area which enables relatively high conductive heat transfer rates,

but significant pressure drop can require greater fan power, and

deterioration of certain absorber material after many years of solar

radiation exposure can additionally create problems with air quality and

performance.

Combination Passage Air Collector

In back-pass, front-pass, and combination type configurations the air is

directed on either the back, the front, or on both sides of the absorber to

be heated from the return to the supply ducting headers. Although

passing the air on both sides of the absorber will provide a greater

surface area for conductive heat transfer, issues with dust (fouling) can

arise from passing air on the front side of the absorber which reduces

absorber efficiency by limiting the amount of sunlight received. In cold

climates, air passing next to the glazing will additionally cause greater

heat loss, resulting in lower overall performance of the collector.

Fan

The main problem with a PV powered solar crop dryer is the fan: the

fan should be in- expensive, durable and produce high flow rates at a

high pressure while having a low power consumption in order to keep

the prise of the solar crop dryer down and at the same time en- sure an

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Solar Crop Dryer Project Report-2011

efficient drying process. In order to limit the necessary size of the PV-

panel the flow rate through the crop was de- creased considerably

compared to conventional dryers. With the air flow in the design case of

300 m³/h per unit the air speed through the drying bed was 0.06 m/s.

This is very low com- pared to the 0.3-0.7 m/s in conventional cross flow

dryers and also low compared to the 0.1 m/s in conventional platform

dryers. The data sheet for the chosen fan is shown in appendix A. The

fan is type 7212N from Pabst. The characteristic of the fan is shown in

figure 2.8, curve 2. The figure shows that the pressure drop of the system

should be below 50 Pa at a flow rate of 300 m³/h as the flow rate else may

drop to around 200 m³/h. The voltage range of the fan is between 6 and

15 V and the nominal power demand is 12 W.

Chapter – 5

Materials and Method

General Description of the Domestic Passive Solar Food Dryer

The most commonly seen design types are of cabinet form (wooden

boxes with glass cover), some types are even improved making use of

38

Solar Crop Dryer Project Report-2011

cardboard boxes and transparent nylon or polythene.For the design

being considered, the greenhouse effect and thermosiphon principles are

the theoretical basis. There is an air vent (or inlet) to the solar collector

where air enters and is heated up by the greenhouse effect, the hot air

rises through the drying chamber passing through the trays and around

the food, removing the moisture content and exits through the air vent

(or outlet) near the top of the shadowed side.

The hot air acts as the drying medium, it extracts and conveys the

moisture from the produce (or food) to the atmosphere under free

(natural) convection, thus the system is a passive solar system and no

mechanical device is required to control the intake of air into the

dryer.The solar food dryer consists of two major compartment or

chambers being integrated together:

The solar collector compartment, which can also be referred to as the air

heater.

The drying chamber, designed to accommodate four layers of drying

trays made of net cloth (cheese cloth) on which the produces (or food)

are placed for drying.

39

Solar Crop Dryer Project Report-2011

Drawings

40

Solar Crop Dryer Project Report-201141

Solar Crop Dryer Project Report-2011

 Materials Used

The following materials were used for the construction of the domestic

passive solar dryer:

GI Sheet of gauge 16 (1.2mm)- as the casing (housing) of the entire system.

Glass - as the solar collector cover and the cover for the drying chamber. It

permits the solar radiation into the system but resists the flow of heat

energy out of the systems.

Aluminium sheet - of 18gauge - 1mm thickness (dimension 30cm × 30cm)

painted black with mat finish for absorption of solar radiation.

Steel net and Steel rods as frames for constructing the trays.

Thermocol – as insulation in drying chamber

Welding for joining and glue as adhesive for insulation.

Hinges and Magnet for the dryer’s door.

Paint (black and cherry red).

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Solar Crop Dryer Project Report-2011

Chapter – 6

Design Consideration

1. Temperature- The minimum temperature for drying food is 30°C and the

maximum temperature is 60°C, therefore. 45°C and above is considered

average and normal for drying vegetables, fruits, roots and tuber crop chips,

crop seeds and some other crops .

2. The design was made for the optimum temperature for the dryer. T0 of 60°C

and the air inlet temperature or the ambient temperature T1 = 30°C

(approximately outdoor temperature).

3. Efficiency - This is defined as the ratio of the useful output of a device to the

input of the device.

4. Air gap – In this work, a gap of 5 cm should be created as air vent (inlet) and

air passage.

5. Glass and flat plate collector -The glass covering should be 3-4mm

thickness. In this work, 3mm thick transparent glass was used. Here the metal

sheet thickness should be of 0.8 – 1.0 mm thickness; here an Aluminium

sheet of 18gauge (1mm) thickness was used. The glass used as cover for the

collector was 30 × 50cm2.

6. Dimension – It is recommended that a constant exchange of air and a roomy

drying chamber should be attained in solar food dryer design, thus the design

of the drying chamber was made as spacious as possible of average

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Solar Crop Dryer Project Report-2011

dimension of 30 × 30 × 30cm with air passage (air vent) out of the cabinet of

2” diameter.

7.      Dryer Trays – Steel Net was selected as the dryer screen or trays to aid air

circulation within the drying chamber. Two trays were made. The tray

dimension is 30 × 30cm .

The design of the dry chamber making use of thermocol wall sides and

tends to bleach colour, removes flavor and causes the food to dry unevenly.

Design Calculations

1.      Angle of Tilt (β) of Solar Collector/Air Heater.

It states that the angle of tilt (β) of the solar collector should be

β = 100 + lat ф

where lat ф is the latitude of the collector location, Region: Kerala

Country: India Latitude: 10.516667 .

Hence, the suitable value of β use for the collector:

β = 100 + 10.5170 = 20.5170

2.      Insulation on the Collector Surface Area.

A research obtained the value of insulation for Thrissur, Kerala,

India i.e. average daily radiation H on horizontal surface as;

H = 978.69W/m2

and average effective ratio of solar energy on tilted surface to that on

the horizontal surface R as;

R = 1.0035

Thus, insulation on the collector surface was obtained as

44

Solar Crop Dryer Project Report-2011

Ic =HR = 978.69 × 1.0035

Ic = 982.11W/m2                                                       

3.      Determination of Collector Area and Dimension.

The mass flow rate of air Ma was determined by taking the average

air speed

Va = 0.15m/s.

The air gap height was taken as 5cm = 0.05m and the width of the

collection assumed to be 30cm = 0.3m.

Thus, volumetric flow rate of air V'a = Va × 0.05 × 0.3

V'a = 0.15 × 0.05 × 0.3 = 2.25 × 10-3m3/s

Thus mass flow rate of air:

a = vaρa                                                              

Density of air ρa is taken as 1.28kg/m3

Ma = 2.25 × 10-3 × 1.28 = 2.88 × 10-3kg/s

Therefore, area of the collector AC = Ma Cp dT / 0.6 Ic 

AC = (2.88 × 10-3 × 1005 × (60-30)/(0.6× 982.11) = 0.147356m2

The length of the solar collector (L) was taken as;

L = Ac/B = 0.147356m2/0.3 = 0.491m

Thus, the length of the solar collector was taken approximately as

0.5m.

Therefore, collector area was taken as (0.3× 0.5) 2 = 0.15m2

4.      Determination of the Insulator Thickness for the Drying

Chamber

The rate of heat loss from air is equal to the rate of heat

conduction through the insulation. The following equation holds for

the purpose of the design.

FmaCp (T0 – Ti) = Ka(Ta - Ta)/tb                                                  

K = 0.05Wm-1K-1 which is the approximate thermal conductivity for

polyurethane [11].

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Solar Crop Dryer Project Report-2011

F = 10% = 0.1

T0 = 60ºC and Ti = Ta = 30ºC approximately

ma = 2.88× 10-3Kgs-1

Cp = 1005JKg-1K-1

and Ac = 0.09m2

tb =[0.05 × 0.09 × (60-30)]/[0.1×2.88×10-3×1005×(60-30)] = 0.001554m

= 1.554mm

For the design, the thickness of the insulator was taken as 50mm. The side of

the drying chamber was insulated using thermocol (a polymer), the loss

through the side of the collector was considered negligible.

5.      Determination of Heat Losses from the Solar Collector (Air

Heater).

Total energy transmitted and absorbed is given by

IcAcτα = Qu + QL + Qs                                     

where Qs is the energy stored which is considered negligible therefore,

IcAcτα =Qu +QL                                                      

Thus QL the heat energy losses

QL = IcAcτα - Qu                                                                                 

Since

Qu = maCp (T0 – Ti) = maCp∆T                                                

and

QL = ULAc∆T                                                                                     

then

ULAc∆T = IcAcτα - maCp∆T                                                          

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Solar Crop Dryer Project Report-2011

UL = (IcAcτα - maCp∆T)/(Ac∆T)                                                       

α was taken as 0.9 and τ = 0.86

Ta = 0.774

UL  = (982.11×0.15×0.774 – 2.88×10-3×1005×30)/(0.15×30)

= (114.022971 - 86.832)/4.5

UL  = 6.0424W/m2°C

Therefore,

QL = 6.0424 × 0.15 × 30 = 27.19W

This heat loss includes the heat loss through the insulation from the sides and

the cover glass.

Part no: 1 Name:

CollectorOperations

SL

no

Activity Distance

moved

(m)

Time

(min)

1 Material laying

store

2 Moved to

machine shop

5 10

47

Solar Crop Dryer Project Report-2011

3 Welding 2 480

4 Grinding 3 180

5 Painting 1 60

6 Delay time for

drying point

2 300

7 Inspection - 15

Part no: 1 Name:

CollectorOperations

SL

no

Activity Distance

moved

(m)

Time

(min)

1 Material laying

store

2 Moved to

machine shop

5 10

3 Welding 2 480

4 Grinding 3 180

48

Solar Crop Dryer Project Report-2011

5 Painting 1 60

6 Delay time for

drying point

2 300

7 Inspection - 15

° Flow Process Chart

Part no: 2 Name: Drier Operations

SL

noActivity

Distance

moved

(m)

Time

(min)

1Material

laying shop

2Moved to

workshop5 10

3 Welding 2 420

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Solar Crop Dryer Project Report-2011

4 Grinding 3 120

5 Painting 1 60

6Delay time

for drying2 300

7 Inspection - 15

SL

noItem Quantity Specification

Cost

Rs Ps

1 Aluminium Sheet 1no 3mm thickness cross 150 00

2 Thermo coal 1no14*2 Sheet 1.5cm

thickness10 00

3 PVC Pipe 1no4m long*2inch

diameter 400 00

4 Bend 3nos 2inch diameter

5 Steel net 2no0.5inch wire grill

2mm thickness100 00

6 Blower 1no ½HP 1400 00

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Solar Crop Dryer Project Report-2011

7 Reducer 1no 1½

8 Magnet 1no Door Magnet 50 00

9 Paint 250ml 100 00

10 Thermometer 1no 200°c 225 00

11 Glass 1no 5mm thickness 105

12 Adhesive 100ml Synthetic gum 20 00

13 G.I. Sheet 19.5kg2½mm thickness

plate1750 00

Total 4310 00

Estimation & costs

Chapter – 7

Construction

 The solar food dryer was constructed making use of locally

available and relatively cheap materials. Since the entire casing is made

of wood and the cover is glass, the major construction works is

carpentry works (joinery).

The following tools were used in measuring and marking out on the

wooden planks:

Carpenter’s pencil.

Steel tapes (push-pull rule type).

Steel meter rule.

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Solar Crop Dryer Project Report-2011

Vernier caliper.

Steel square.

Scriber.

The following tools were also used during the construction;

Hand saws (crosscut saw and ripsaw).

Hammer.

Pinch bar and pincers.

The construction was made with simple butt joints using nails as

fasteners and glue (adhesive) where necessary. a

The metal sheet used was GI sheet of 16gauge (1.2mm) thickness. It was

cut to the size of 30 × 50cm, 30 x 30cm, and 30 x 20cm according to the

design. It was painted black with mat finish for maximum absorption

and radiation of heat energy. The metal sheet, together with the

insulator of 50mm thickness, was placed inside the air heater (drying

chamber) compartment.

The glass was cut into size of 30 × 50cm size was required as the solar

collector’s cover. The glass used was clear glass with 3mm thickness.

The trays were made with steel rod as frame and steel net to permit free

flow of air within the drying cabinet (chamber). Two trays were used

with average of 10cm spacing arranged vertically one on top of the

other, the tray size was 30× 30cm.

The interior of the solar food dryer was insulated to prevent the heat loss

while the exterior was painted cherry red to minimize the adverse effects

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Solar Crop Dryer Project Report-2011

of weather and insect attraction on the drying chamber and also for

aesthetic appeal.

Chapter – 8

Conclusion

Solar radiation can be effectively and efficiently utilized for drying of

agricultural produce in our environment if proper design is carried out.

This was demonstrated and the solar dryer designed and constructed

exhibited sufficient ability to dry agricultural produce most especially

food items to an appreciably reduced moisture level.

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Solar Crop Dryer Project Report-2011

Locally available cheap materials were used in construction making it

available and affordable to all and sundry especially peasant farmers.

This will go a long way in reducing food wastage and at the same time

food shortages, since it can be used extensively for majority of the

agricultural food crops. Apart from this, solar energy is required for its

operation which is readily available in the tropics, and it is also a clean

form of energy. It protects the environment and saves cost and time

spent on open sun drying of agricultural produce since it dries food

items faster. The food items are also well protected in the solar dryer

than in the open sun, thus minimizing the case of pest and insect attack

and also contamination.

However, the performance of existing solar food dryers can still be

improved upon especially in the aspect of reducing the drying time and

probably storage of heat energy within the system. Also, meteorological

data should be readily available to users of solar products to ensure

maximum efficiency and effectiveness of the system. Such information

will probably guide a local farmer on when to dry his agricultural

produce and when not to dry them.

The performance of a solar air heater without any cover is very

poor and hence at least one cover should be used for better performance.

The performance of the air heater is dependent on the number of covers

used and the temperature difference between the inlet air to the ambient

air. Therefore, the efficiency will be maximum when the inlet air

temperature is more than the ambient air temperature. Even plastic

covers can be used where the inlet temperature rise over the ambient air

temperature is small. The fluid conduction has no effect on the overall

performance of the collector. Increased flow ratio improves the matrix

efficiency. With the addition of side mirrors one can produce the

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Solar Crop Dryer Project Report-2011

maximum output only in the peak hours. The highest output obtained

from the inclined side mirror when compared to the vertical side mirror.

Since the double exposure solar collector unit cost is estimated to be only

70 per cent greater than a conventional air collector it is efficient to go

for the double exposure solar collector. Further work is needed to

optimize the length and inclination angle of the side mirror of the flat

plate collector.

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Solar Crop Dryer Project Report-2011

References

 1.  Scalin D., The Design, Construction and Use of an Indirect, Through-

pass, Solar Food Dryer, Home Power Magazine, 1997, 57, p. 62-72.

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4.  The World Book Encyclopedia (1982). World Book-Childcraft

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5.  Whitfield D.E., Solar Dryer Systems and the Internet: Important

Resources to Improve Food Preparation, 2000, Proceedings of International

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6.  Herringshaw D., All About Food Drying, 1997, The Ohio State University

Extension Factsheet-hyg-5347-97, www.ag.ohio-state.edu/.

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of Cape Coast, Ghana.

9.  Sukhatme S.P., Solar-Energy-Principles of Thermal Collection and

Storage, Tata McGraw Hill Publishing Company Limited, 1996.

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Solar Crop Dryer Project Report-2011

10.  Olaleye D.O., The Design and Construction of a Solar Incubator, 2008,

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Engineering, University of Agriculture, Abeokuta.

11.  Fisk M.J., Anderson H.C., Introduction to Solar

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12. Ambrose, C. W.; Bandopadhyay, P. C. (1970). Asymmetrical heating in

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15. Bliss, R. W. (1955): Multiple gauge flat plate solar air heaters. Proc.,

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16. Buelow, F.H. (1956): The effects of various parameters on the design of

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18. Characters, W. W. S.; MacDonald, R. (1974): Heat transfer effects in

solar air heaters. COMPLES, Revenue Internationale d’

Heliotechnique, 1, pp. 29-38.

19. Characters, W.W.S. (1971): Some aspects of flow duct design for solar

air heater applications. Solar energy, 13(2), pp. 283-288.

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Solar Crop Dryer Project Report-2011

20. Chiou, J. P.: Heat transfer and flow friction characteristics of metallic foil

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the design of solar collectors, University of Wisconsin, USA, 164. Ph. D.

thesis.

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