Thermo Electric and Solar

8/4/2019 Thermo Electric and Solar

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Thermo electric refrigeration


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Introduction

Thermoelectric cooling uses the Peltier effect tocreate a heat flux between the junction of twodifferent types of materials.

A cooler is a solid-state active heat pump which

transfers heat from one side of the device to theother side against the temperature gradient (fromcold to hot), with consumption of electricalenergy.

Such an instrument is also called a Peltier device,Peltier heat pump, solid state refrigerator, orthermoelectric cooler (TEC).


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Parts:

1. D.C. source (battery)

2. P & N type semiconductors

3. Electrical conductor (copper)

4. Electrical insulator(ceramic)

5. Heat sink (made of copper)


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Construction & Working:

The typical thermoelectric

module is manufactured using

two thin ceramic wafers with a

series of P and N doped

bismuth-telluride

semiconductor material

sandwiched between them

The ceramic material on both

sides of the thermoelectricadds rigidity and the

necessary electrical insulation.


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The N type material has an excess of electrons, while the P typematerial has a deficit of electrons.

One P and one N make up a couple and thermoelectric couples areelectrically in series and thermally in parallel.

As the electrons move from the P type material to the N typematerial through an electrical connector, the electrons jump to ahigher energy state absorbing thermal energy (cold side).

Continuing through the lattice of material; the electrons flow fromthe N type material to the P type material through an electricalconnector dropping to a lower energy state and releasing energy as

heat to the heat sink (hot side). Heat absorbed at the cold junction is pumped to the hot junction at

a rate proportional to carrier current passing through the circuit andthe number of couples.


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Heat absorbed at the cold junction is pumped

to the hot junction at a rate proportional to

carrier current passing through the circuit and

the number of couples.

The heat sink and cold side mounting surface

should be made out of materials that have a

high thermal conductivity (i.e., copper or

aluminum) to promote heat transfer.


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Advantages

No Moving Parts and no recirculating fluid(refrigerant)

Ability to Cool Below Ambient temperature

Precise Temperature Control

Noiseless and vibration free operation

Small size and flexible shape

Environmentally friendly


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Disadvantages

It cannot simultaneously have low cost and highpower efficiency

Attainable COP is low

The presence of moisture causes an electro-

corrosion that degrades the thermoelectricmaterial, conductors and solders, so propersealing methods has to be used


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Applications

medical and pharmaceutical equipment

spectroscopy systems

various types of detectors

portable refrigerators

chilled food and beverage dispensers

drinking water coolers


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Solar refrigeration system


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Introduction

When most of us think of "solar power," we think of panels of

photovoltaic cells. A refrigerator introduced in 2009 by British

student Emily Cummins used a far more literal version of solar

power.

Cummins' refrigerator uses no photovoltaic cells, no

electricity, no chemical refrigerant and no moving parts to

produce a cooling effect. Instead, it uses an evaporative-

cooling system based entirely on the sun's heat and some

water.


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Construction:

It's made of two cylinders, one inside theother.

The outer cylinder can be made of cardboard,

wood or plastic, typically, with holes in it toallow the greatest possible sun access

The inner cylinder is made of metal.

The space in between the inner and outercylinders is filled with materials like wool,sand or dirt.


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Working

You place food or medicine inside the inner metal cylinderand close it up.

You then pour fresh water into the area between thecylinders, saturating the organic material, and place the whole

setup in the sun.

As the sun warms the outer cylinder and heats up the wetorganic material, the water evaporates. Just like in atraditional fridge, evaporation removes heat

The organic material is touching the inner cylinder, so thisheat transfer pulls heat from the inner cylinder holding thefood.

The result is a very cold inner chamber.


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Advantages

Silent running & Emission free

Virtually maintenance free, annual inspection

only

Inexpensive to produce

Does not use electricity

Easy to operate


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Disadvantages

Dependent on sunlight

Cannot used for high capacity refrigeration

Operates continuously for years

It has no back up battery in case of no sunlight


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Applications

Transport refrigeration system

Water and beverages cooling purpose

Food and medicine cooling purpose

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