Thermoeletric Air Cooling System

MINI PROJECTTHERMOELECTRIC AIR CONDITIONING SYSTEM

Div – U Project Guide – Prof. Dr. J.P. Shete

Name Roll No. GR. No.Shubham Lakhotia 26 141546Keshav Kumar Jha 19 141569

Shreyas Saste 48 141480

INTRODUCTIONThermoelectric effect (also known as peltier effect) is the

directconversion of electric voltage to temperature differences and

viceverse. The direction of heat flow can be controlled by

changingthe polarities of the voltage source.

• Thermoelectric cooling incorporates both semiconductors and electronic assembly techniques.

• In a TEC (eg: Peltier device) one side gets hot and the other side gets cold. Therefore, they can be used to either warm something up or cool something down, depending on which side we use.

• Thermoelectric coolers (TEC) create a temperature differential on each side. • They are an excellent cooling alternative to vapor compression coolers for

systems that are sensitive to mechanical vibration.

OUR MODELOur project is a Thermoelectric Peltier Module. It is based on the

‘Peltier Effect’ (named after Jean Peltier).Advantage of using such a device for the purpose of cooling is

that it is solid state (no moving parts), vibration free, noise-free. They are modular devices, So are simple to install and operate.

Characteristics of the Peltier Module:• Its ability to lower temperature below ambient.• Heat transport controlled by current input.• Compact size make them useful for applications where size or

weight is a constraint.• Ability to alternate between heating and cooling.

Some Essential featuresOn an industrial level, this kind of a setup is used

widely in the field of Electronic, Medical, Aerospace, Telecommunications.

For Cooling, this module is used in :• Refrigerators• Telecommunications equipment• Laboratory instruments• Electronic enclosures• Temperature control in missiles and space

systems

Some Essential featuresThe standard specifications for a thermoelectric

module are :1.) The heat pumping capacity, or Qmax 

in Watts2.) The maximum achievable difference in

temperature between the hot and cold sides of the module, known as the δTmax or ∆Tmax 

3.) The maximum (optimal) input current in amps or Imax 

4.) The maximum input voltage or Vmax when the current input is optimal (Imax ). In mathematical formulae, temperatures are typically expressed in Kelvin (K) units

COMPONENTS USEDComponent Quantity Description Cost (Rs.)

Battery 1 12V, 7.5 Amp-hr

-

Battery 6 9V 240Peltier Device 1 12V, 6 Amp 450

Heat Sink 2 L Shape, Al 120DC Fan 1 12V, 6.8 Watt 80Epoxy 1 Araldite (90 g) 160

Thermocol 1 100 x 50 cm 60Connecting

Wires2 1 metre 30

SPDT Switch 1 - 12Insulation Tape 1 Red 20

Glass Vessel 1 15 x 15 cm -Extras - Blade, Glue,

etc100

Working PrinciplesPeltier Effect:Jean Peltier discovered that the opposite was also

possible. By sending a current through 2 metals, you could create a temperature difference in them.

Seebeck Effect (vice verse) :In the 1820’s, Thomas Seebeck discovered that if 2

metals at different temperatures were touching, an electric current can be generated.

Peltier EffectThe Peltier effect is a

temperature difference created by applying a voltage between two electrodes connected to a sample of semiconductor material. The Peltier effect occurs whenever electrical current flows

through two dissimilar conductors. The flow of electricity causes one side to get hot and the other to get cold. The degree of heating or cooling that you get is determined in large part by the type of metal that is used. Bismuth Telluride is a very commonly used Peltier element metal. 

Peltier Device•When a voltage or DC current is applied to two dissimilar conductors, a circuit can be created that allows for continuous heat transport between the conductor’s junctions.

•A typical Peltier module is composed of two ceramic substrates sandwiching many pairs, or "couples" of Bismuth Telluride dice. The (pairs of) dice are connected electrically in series, and thermally in parallel, between the ceramics. One of these ceramics will be the "hot-side" and the other, the "cold-side.“

For example, when n- and p-type semiconductors are biased in the same direction, their charge carriers flow in opposite directions. As a result, n- and p-type Peltier elements create opposite temperature gradients .

Peltier DeviceAlumina ceramic substrates are commonly used for making TE modules.  They're  ridged, thermally conductive and excellent electrical insulators.  In addition to providing a sturdy foundation, the ceramics insulate the electrical elements within the module from a heat-sink on the hot-side of the module, and the object being cooled on the cold-sideHeat transfer occurs in the direction of charge carrier movement.

Peltier Device SpecificationsType TEC1-12706

Dimensions 40 x 40 x 4mmCouples 127

Qmax (Watts) 50Delta Tmax (ºC) 66

Imax (Amps) 6.4Vmax (Volts) 14.4

Module Resistance (Ohms)

1.98

Fully sealed for protection against moisture

Basic Principles• To increase heat transport, several P type or N

type thermoelectric(TE) components can be hooked up in parallel.

• However, the device requires low voltage and therefore, a large current which is too great to be commercially practical.

• The current should always be DC and not AC.

Seebeck Effect• The Seebeck effect is a phenomenon in which a

temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.

The Seebeck Coefficient is given by:

where is the electric field.dxdT

x

/

Battery• We have used a 12V rechargable lead acid battery with a current

rating of 7.5 Amp hours.• Lead acid batteries provide a good amount of power and are

compact. They are widely used for storage in backup power supplies.

• Excessive charging of the lead acid battery Causes electrolysis, i.e. Release of Hydrogen and O² gas. Accumulation of these gasses leads to explosion of the Battery.

Heat Sink• A heat sink is an

electronic device that incorporates either a fan or a peltier device to keep a hot component such as a processor cool.

• There are two heat sink types: Active and Passive.

• Heat Sink prevents a device from overheating by absorbing its heat and dissipating it into the air.

HEAT SINK• WHAT IS A HEAT SINK? A heat sink is an environment or object that absorbs and

dissipates heat from another object using thermal contact. Heat sinks are used in a wide range of applications wherever efficient heat dissipation is required; major examples include refrigeration, heat engines, cooling electronic devices and lasers.

Thermal resistance is defined as temperature rise per unit of power, analogous to electrical resistance, and is expressed in units of degrees Celsius per watt (°C/W).

We Have used an L-Shape Heat Sink

HEAT SINK• PRINCIPLE OF HEAT SINK: Heat sinks function by efficiently transferring thermal energy

from an object at a relatively high temperature to a second object at a lower temperature with a much greater heat capacity. This rapid transfer of thermal energy quickly brings the first object into thermal equilibrium with the second, lowering the temperature of the first object, fulfilling the heat sink's role as a cooling device.

epoxy

HEAT SINK• Performance:

Heat sink performance is a function of material,

geometry, and overall surface heat transfer coefficient. Generally, forced convection heat sink

thermal performance is improved by increasing the thermal conductivity of the heat sink

materials,increasing the surface area and by increasing the overall area heat transfer

coefficient .

HEAT SINK• Construction and Materials: A heat sink usually consists of a base with one or more flat

surfaces and an array of comb or fin-like protrusions to increase the heat sink's surface area contacting the air, and thus increasing the heat dissipation rate. Heat sinks are made from a good thermal conductor such as copper or aluminum alloy. Copper (401 W/(m·K) at 300 K) is significantly heavier and more expensive than aluminum (237 W/(m·K) at 300 K) but is also roughly twice as efficient as a thermal conductor.

Aluminum has the significant advantage that it can be easily formed by extrusion, thus making complex cross-sections possible.

HEAT SINK• Explanation:

In common use, a heat sink is a metal object brought into contact with an electronic component's hot surface — though in most cases, a thin thermal interface material mediates between the two surfaces.

Microprocessors and power handling semiconductors are examples of electronics that need a heat sink to reduce their

temperature through increased thermal mass and heat dissipation .

EPOXY• Stabilizing and mounting of the DC fan and peltier on the

Heat sink was done using epoxy.

Characteristics –• Stress Proof• Heat proof• Water proof• Non-corrosive• Non-Toxic• Resistant to most chemicals.

• Araldite is used as a Standard Epoxy Adhesive.

CALCULATIONS

T cold = 35.8ºF = 2.11ºCT hot = 115.7ºF = 46.5ºC

So,

COP cooling = Tc / (Th – Tc) = 0.8064

COP heating = Th / (Th – Tc) = 1.055

Where,

T cold – Minimum Temp. of Peltier

T hot – Maximum Temp. of Peltier

COP – Coefficient of Performance (measure of success of cooling/heating)

DC FansV = 12V

P = 6.8 Watts

Cooling Container

Material – Thermocol (Polystyrene Foam) Dimensions = 248 x 235 x 285 mm

Thickness = 30 mm

We used Polystyrene Foam due to its high heat and cold resisting property.

Advantages• Thermoelectric modules have no moving parts and do not

require the use of chlorofluorocarbons. Therefore they are safe for the environment, inherently reliable, and virtually maintenance free.

• A thermoelectric cooler permits lowering the temperature of an object below ambient as well as stabilizing the temperature of objects above ambient temperatures. 

Advantages• Ability to lower temperature below ambient.• Heat transport controlled by current input.• Able to operate in any orientation.• Compact size make them useful for applications

where size or weight is a constraint.• Ability to alternate between heating and cooling.• Excellent cooling alternative to vapor compression

coolers for systems that are sensitive to mechanical vibration. 

Dis-Advantages• Able to dissipate limited amount of heat flux.• Lower coefficient of performance than vapor-

compression systems.• Relegated to low heat flux applications.• More total heat to remove than without a TEC.

Problems Faced• We encountered a problem

with one of the dc fans so we decided  to dissipitate the heat energy from hot side i.e hot heat sinks we kept those sinks in water bath.

• Firstly we used 12V lead acid battery 1 AHr which didn’t give a sufficient result of what we have expected. So we used a higher rating battery from a motor bike.

• Stabilizing and mounting of the DC fan and peltier on the Heat sink was done using epoxy

RECOMMENDATIONS• When a laptop is running on batteries, the

electricity used to power the fan comes from the battery. Therefore, to conserve battery life, a thermoelectric power generator is a good alternative.

• We can insulate the surrounding areas of the peltier device with thermofoam (or any other material with high resistance to thermal energy) so as to avoid heat dissipation into the surrounding atmosphere.

• We can use another peltier module at the bottom of the apparatus and convert the heat liberated, into electrical energy using Seebeck Effect.

References• Goldsmid H. (1986). Electronic Refrigeration.London:Pion.• Goldsmid H.(1964). Thermoelectric Refrigeration. New York:Plenum.• Lasance, C.J.M., and Simmons, R.E. (2005) Advances In High-Performance

Cooling For Electronics. Electronics Cooling. Retrieved May2006. http://www.electronics-cooling.com/html/2005_nov_article2.html

• Mollar(2003). Themoelectric Cooler Selection Procedure. Retieved June 2006. http://www.marlow.com/TechnicalInfo/themoelectric_cooler_selection_p.htm

• Tellurex. (2002). The 12 Most Frequently Asked Questions About Themoelectric Cooling. Retrieved May 2006. http://www.tellurex.com/12most.html

• TE Technology, Inc. (2005). Thermoelectric Modules. Retrieved April 2006. http://www.tetech.com/modules/

• Wikipedia the Free Encyclopedia(May 2006). Semiconductor.. Retrieved May 2006. http://en.wikipedia.org/wiki/Semiconductor.

THANK YOU