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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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Construction & Working:
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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Construction & Working:
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