Design and development of solar air dryer for medicinal and aromatic plants

DESIGN AND DEVELOPMENT OF SOLAR AIR DRYER FOR MEDICINAL

AND AROMATIC PLANTS

Group Members: NS Abdullah Bin Masood

PC Mubashar Sharif

NS Haider Iqbal

Project DS: Asst. Prof. Ahmed Sohail

Introduction

There are several MAPs that naturally grow in northern areas of Pakistan.

These are in wet conditions when they are harvested.

These are conventionally being dried in open.

Our purpose is to dry these MAPs utilizing the solar energy, in a controlled environment.

Key Objectives

Literature Review

Quality assessment of MAPs

Analysis of Metrological data

Design Phase

Fabrication

Results

Future works

Literature Review

Quality assessment of MAPs

Selection of Ambient Temperature for Solar Dryer:

No Botanical name Local name Part Harvesting months Drying Temperature (0C)/Drying condition

1 Biostorta amplexicaulis

Anjabar Roots/Rhizomes April to august 45-50/ Sunlight

2 Valariana jatamansi Mushk bala Roots/Rhizomes July to September 45-50/ Shade

3 Viola Spp (flowers) Banafsha Flowers March - April 45-50/ Shade

4 Paeonea emodi Mamekh Roots July to September 50-55/ Sunlight

6 Berberis lycium Kwaray Root Bark October to December 45-50/ Sunlight

6 Matricharia chamomilla

Babona Flowers March to April 45-50/ Shade

7 Morchella spp Gochai Plant (stalk+pilus) March to April 40-45/ Diffused Sunlight

8 Trillium govanianum Matar jari Roots May to June 45-50/Sunlight

Dryer Load

No Botanical name Local name Part Average Produce in Kg/Cluster

1 Biostorta amplexicaulis Anjabar Roots/Rhizomes 300

2 Valariana jatamansi Mushk bala Roots/Rhizomes 200

3 Viola Spp (flowers) Banafsha Flowers 5

4 Paeonea emodi Mamekh Roots 100

6 Berberis lycium Kwaray Root Bark 30

6 Matricharia chamomilla Babona Flowers 1

7 Morchella spp Gochai Plant (stalk+pilus) 5

8 Trillium govanianum Matar jari Roots 15

Final Moisture Content of the Product:No Botanical name Local name Part Recommended Moisture

contents after drying

1 Biostorta amplexicaulis Anjabar Roots/Rhizomes Less than 15%

2 Valariana jatamansi Mushk bala Roots/Rhizomes do

3 Viola Spp (flowers) Banafsha Flowers Less than 10%

4 Paeonea emodi Mamekh Roots Less than 15%

6 Berberis lycium Kwaray Root Bark do

6 Matricharia chamomilla Babona Flowers Less than 10%

7 Morchella spp Gochai Plant (stalk+pilus) do

8 Trillium govanianum Matar jari Roots Less than 15%

Design Parameters for Solar Dryer

Drying Temperature:variable can be changed as desiredHowever, drying air temperature between 50 and 60°C is feasible for drying a large variety of medicinal plants.

Dryer Load:Lab scale model, drying 6 Kg of MAPs

Moisture Content: from 70% to 10%

Design Phase

Meteorological Data

Meteorological data obtained from PMD and METEONORM Satellite based data shows that annual average PSH (peak sun hours) available are sufficient to be utilized for solar drying operation.

Average clear sunny days: 270-300.

Average solar intensity: 4.5 kWh/m2-day.

Calculation of Average Irradiation Ф= 33.67ᴼ Slope of collector= β=30ᴼ Collector is faced towards south

For winter (from Duffie and Beckman) β=30-15= 15ᴼ

for summer β=30+15= 45ᴼ

Average β=30ᴼ

Average Monthly Total Irradiation, HT

Solar Absorbed Irradiations, S

Proposed Design of Solar Dryer

Design specifications of Solar Dryer

Load capacity: 500 kg Solar collectors: 30m2

(15x 2m2 collectors)

32 different MAPs can be dried simultaneously

Capable of drying volatile MAPs

No interference of moisture in atmosphere

Negligible energy losses due to walls insulation

Lab Scale/Scaled Down Model

Design specifications of Lab Scale Model

Load Capacity: 6 kg Solar collector: 1m2

2 different MAPs can be dried simultaneously

Capable of drying volatile MAPs Well insulated

Working Principle

Fresh air is heated in Solar Collector Then transferred to chamber via Pipes This heated air is passed over the MAPs

in chamber Thus hot air takes away their moisture

contents

Solar Collector

Thermocol insulation at the bottom

Metal sheet with inclined ribs over thermocol sheet

a low iron content glass

Artificial Roughness and corrugation

Size of Solar Collector

Total load=M= 6kg Initial moisture content= mi= 70%

Final moisture content= mf= 10%

Water to be removed= Now since,

we get approx. 10-12 MJ/m2/day for the solar energy, with an efficiency of 50% of solar collector.

Collector Specfication

Plate to cover spacing=25mm Plate emittance=0.98 Ta= 30ᴼC = 303K Wind heat transfer coefficient= 10 W/m2 ᴼC mass flow rate = 0.04 kg/sec

volume flow rate

Velocity=

Calculations of Losses in Solar Collector

Thermal losses

Back losses

Edge losses

Edge and Back Losses

Ut

Ub

Ue

Now Total Losses in our collector are accumulated to be:

UL

Outlet Temperature and efficiency of Solar Collector

Pipes

Length of pipe= 1.2 m Pipe inlet temperature= 55 ᴼC = 328 K Pipe outer Dia= 3 in = 0.076m Thickness of pipe= 0.5 cm= 0.005m Pipe inner Dia= 0.066m Ambient temperature=30 ᴼC = 303 k

Heat transfer co-efficient outside the pipe= 18.9 W/m2 ᴼC Velocity of air in the pipe= 2.46 m/sec Heat transfer co-efficient inside the pipe= 31.12 W/m2 ᴼC

Pipe insulation

Ri=1/h1A1R1= [ln(r2/r1)]/[2 (3.14)K1 L]R2= [ln(r3/r2)]/[2 (3.14)K2 L]R3=1/h2A2Rtotal = Ri + R1 + R2 + R0

Thickness of insulation is 0.0095 m = 0.950 cm

Heat loss without insulation= 46 W/mHeat loss with insulation= 15 W/m

Mixing valves

Drying Chamber

Drying Chamber

    Initial moisture = 70% Final moisture = 10 % Total drying load=6 kg Moisture to be removed=4 kg Total energy required=9 MJ

Psychometric Analysis

Inlet air temperature =50ᴼC

Wet bulb temp of inlet air= 38ᴼC

Relative humidity of inlet air= 46%

Dew point temperature= 35.73 ᴼC

Enthalpy= 149.3 kJ/kg Density= 1.07 kg/m3

Specific volume= 0.972 m3/kg

Required mass flow rate in chamber

Quantity of air required for drying can be calculated from energy balance equation as:

maCp (Tb-Tc)= mwL

or, Ma= mass of air

ΔWcb= change in humidity ratio Mw= mass of water to be removed= 4kg n= pickup factor= 0.25 Q= ma x Vs = 0.09 m3/s

Here, Q is the volume flow rate, Vs is the specific volume of drying air.

Drying air conditions

Rate of evaporation= Kg x A x (Ys – Ya)= 1.98 x 10-4 kg/s

hc= 13.6 J/m2s ᴼCwhere, hc is the heat transfer co-efficient from air to

water

Outlet temperature of air from drying chamber= 34ᴼC

Relative humidity of outlet air from drying chamber= 58%

Drying time

 t  =  w (Xo- Xc) / (dw /dt)const.  

where   (dw /dt )const. = k'gA(Ys -Ya)           

the constant drying time comes out to be approx. 4 hours.

t  =  w (Xo- Xc) / f (dw /dt)const.

Falling rate period comes out to be 3.1 hours. So, our total drying time is 7.1 hours.

Responsibility Assignment Matrix

Gantt Chart

Results

After completing the fabrication of our lab scale model, experimental results validated our theoretical deductions and calculations upto an acceptable extent. Collector should increase the temperature by 23 ᴼC theoretically whereas we are getting an increase of 21 ᴼC experimentally.

Furthermore, the drying time that we had calculated theoretically was about 7.1 hours and experimentally we had dried the same load of MAPs reducing moisture contents from 70% to 10%; in approximately 7.5 hours.

The small difference between theoretical and experimental values is because we had not taken certain smaller or lesser affective factors into account theoretically to avoid complexity in our calculations.

Future Works

A biomass air heater along with a heat exchanger can be used in order to keep the plant running even if there is no Solar irradiation.

Also the working operation of this solar dryer can be fully automated; eliminating the need of continuous supervision of an operator, that if the MAPs placed in drying chamber have been dried to desired level or not. This can be done by installing a humidity sensor with an alarm and/or an actuator. The humidity sensor will continuously be checking the humidity of air exiting the drying chamber and when the MAPs have been dried up to a desired limit, the humidity of air exiting the chamber would also have fallen to that particular value. Now when the humidity of air falls to a required value, the alarm should start ringing so that operator comes and takes out the MAPs placed inside drying chamber; whereas the actuator will cut the supply of air to drying chamber by closing a valve on the main supply duct/pipe line.

Furthermore, another automatic system can be added which should load/unload the MAPs as and when required without any human effort.

Thank you