FABRICATION OF SOLAR REFRIGERATOR GUIDED BY SUBMITTED BY

FABRICATION OF SOLAR REFRIGERATOR GUIDED BY: - SUBMITTED BY: - KIRAN RAJ K RAVI KANT PANDEY DEPARTMENT OF RAVISH KUMAR MECHANICAL ENGG. RAJEEV KUMAR VIKASH KUMAR SANTOSH ABHISHEK

CONTENTS • • • OBJECTIVE INTRODUCTION CONSTRUCTION PARTS WORKING OF EQUIPMENTS POWER CALCULATION OPERATING SPECIFICATION ADVANTAGES LIMITATIONS APPLICATIONS

OBJECTIVE • To design and develop a thermoelectric refrigerator in order to produce a small quantity of refrigerating effect by using Solar energy. • To effectively use the low grade Solar energy rather than using high grade energy. • To design a refrigerating unit which will work without any moving parts. • To develop a vibration less refrigerator.

INTRODUCTION • Freezing action means transfer of heat from low temperature to a high temperature body • Freezing effect can be produced by vapour compression, vapour absorption, and thermoelectric effect • Solar fridge works on the principle of thermo electric refrigeration • It is non conventional type of refrigeration used to produce small amount of refrigeration • The working principle is based on peltier effect

FIG-1. SOLAR FRIDGE

CONSTRUCTION PARTS • • Solar panel Battery Thermoelectric device Air blower

SOLAR PANEL • Solar panel consists of solar photovoltaic cells which converts solar energy into electrical energy • One cell in the panel is capable of producing 0. 45 v is when current is 0. 27 A /mm 2 • V=(P-Q)(T 2 -T 1) where v=voltage induced, P, Q are photovoltaic coefficient of two voltaic materials T 1&T 2 are temperatures of two materials

SOLAR CELL

BATTERY • The device consist of lead-acid cell • Sulphuric acid is used as electrolyte • Gives high load current of current rating (100 -300) A -hr • The following chemical phenomena takes place • Pb. O₂ + 2 H₂SO₄ 2 Pb. SO₄ + 2 H₂O • One cell has nominal output voltage 2. 1 v • Charging can be done to restore o/p voltage

LEAD ACID CELL

THERMOELECTRIC DEVICE • Thermoelectric device are pair of two dissimilar metals, semiconductors or conductor with semiconductor. • The pair should have high electrical conductivity but low thermal conductivity because we are working with low amount of refrigeration. • In this system the device is made of extrinsic semiconductor having p-n junction in series with required no of cells. • The energy difference of conduction band of material should be high for higher refrigeration

THERMOELECTRIC DEVICE

WORKING PRINCIPLE • System works on peltier effect • As d. c supply is provided there is formation of hot and cold junctions • The heat absorbed or expellded is given by Qhor Qc=B*I=A*T*I • Qh or Qc is heat absorbed or expellded • B is diffrential peltier cofficient • I is flowing current in circuit

PELTIER EFFECT

SEMICONDUCTOR MODEL

POWER CALCULATION • Qh = QC + Pin • • COP = QC / Pin Where: • Qh = the heat released to the hot side of thermoelectric (watts).

• QC = the heat absorbed from the cold side (watts). • Pin = the electrical input power to thermoelectric (watts). • COP = coefficient of performance of thermoelectric device, typically is between 0. 4 and 0. 7 for single stage applications. • Estimating QC, the heat load in watts absorbed from the cold side is difficult, because all thermal loads in the design must be considered.

• By energy balance across the hot and cold junction it produces • Qh = (α Th) x I - C (Th - Tc) + I 2 R/2 • QC = (α Tc) x I - C (Th - Tc) - I 2 R/2 (17. 7) • R = RA + RB • C = (k. A+ k. B) (A/L)

• To get the max the heat absorbed from the cold side (QC); by differentiate the Qc to the electric current I, • d Qc /d I = 0 • Then it produces • Iopt. = α Tc /R • Substitute for Iopt. In Equation to get the max the heat absorbed from the cold side • QC (max) = [(Z Tc 2)/2 - (Th - Tc)] C Where, Z = Figure of merit for the material A and B = α 2 / R C

OPERATING SPECIFICATION p n α (V/K) 170 x 10 -6 -190 x 10 -6 ρ (Ω. cm) 0. 001 0. 0008 k (W/cm K) 0. 02 Th = 30 o. C = 303 K Tc = 5 o. C = 278 K d = 0. 1 cm L = 0. 125 cm A = (π/4) (0. 1)2 =7. 854 x 10 -3 cm 2 Overall electric resistance (R) = Relement + Rjunction = 1. 1 Relement = 1. 1(ρp + ρn) (L/A)

= 1. 1 (0. 001 + 0. 0008) (0. 125 / 7. 854 x 10 -3) = 0. 0315 Ω • Conduction coefficient (C) = (kp + kn) (A/L) = (0. 02 + 0. 02) (7. 854 x 10 -3 /0. 125) = 2. 513 x 10 -3 W/K • Figure of merit (Z) = (αp - αn) 2/ RC = (360 x 10 -6)2/ (0. 0315 x 2. 513 x 10 -3) = 1. 636 x 10 -3 K-1 • Number of couples required. QC = QC (max) = N C [(Z Tc 2)/2 - (Th - Tc)] 10 = N (2. 513 x 10 -3) [0. 5 (1. 636 x 10 -3 x (278)2) - (25)] N =105 couples

• Rate of heat rejection to the ambient (Qh) Iopt. = (αp - αn) Tc /R = (360 x 10 -6) x 278/ 0. 0315 = 3. 2 A • Qh = N [(αp - αn) Th x Iopt - C (Th - Tc) + I 2 opt R/2] = 105 [(360 x 10 -6) 303 x 3. 2 - 2. 513 x 10 -3 (25) +(3. 2)2 0. 0315/2] = 47 W • COP = QC / Pin (Power input by power source to thermoelectric) = Qh - QC = 47 - 10 = 37 W

• COP = 10 / 37 = 0. 27 • The voltage drop across the d. c. power source. voltage drop (∆V) = Pin / I = 37 / 3. 2 = 12 volt(approx)

2 4 6 8 10 12 14 16 18 20 22 Current-3. 2 amp Voltage-12 V 2 4 6 8 10 12 14 16 18 20 22 • CHANGE IN TEMP OBSERVATION OF WORKING PARAMETERS TIME

ADVANTAGES • • No moving parts, hence operation is noiseless. Simple and fewer parts are required. Less power consumption. Maintenance cost is low. Easily portable. Suitable for low capacity. Compact in size. The weight per unit refrigeration is considerably lower than conventional refrigeration system.

• An interchange of heating and cooling process can be exercised by reversing the polarity. • An important advantage of this refrigeration system is the independence of C. O. P. on the size of thermoelectric refrigerator and this makes it particularly attractive to use peltier cooling when the cooling capacity required is high. • It is free from vibration of any kind unlike the vapour compression refrigeration, which uses compressor making it to vibrate.

LIMITATIONS • • Low C. O. P. Advantageous only for units of smaller capacity. Can not be used for large freezing requirement. Unavailability of suitable materials of high figure of merit.

APPLICATION • Peltier refrigerators are widely used in several western countries. • Serum coolers for preservation of blood plasma and serums. • Photo multiplier cooler. • Dew point hygrometer for determining absolute humidity. • Constant low temperature bath and chambers.

CONCLUSION • In this work, a portable thermoelectric generator unit was fabricated and tested for the cooling purpose. The refrigerator was designed based on the principle of a thermoelectric module to create a hot side and cold side. The cold side of thermoelectric module was utilized for refrigeration purposes whereas the rejected heat from the hot side of the module was eliminated using heat sinks and fans. In order to utilize renewable energy, solar energy was integrated to power thermoelectric module in order to drive the refrigerator.

Furthermore, the solar thermoelectric refrigerator avoids any unnecessary electrical hazards and provides a very environmentally friendly product. In this regard, the solar thermoelectric refrigerator does not produce chlorofluorocarbon (CFC), which is believed to cause depletion of the atmospheric ozone layer. In addition, there will be no vibration or noise because of the difference in the mechanics of the system. In addition the rejected heat from the solar thermoelectric refrigerator is negligible when compared to the rejected heat from conventional refrigerators. Hence, the solar thermoelectric refrigerator would be less harmful to the environment

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