Solar Cookers World Network

Calculating efficiency

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It is not based on any actual data.

It shows calculations for two solar cookers of areas of 2.5 Sq Mts and 10 Sq Mts.

Physical constants
Specific Heat of water 1 Calories/gm
Specific Heat of Aluminium 0.21 Calories/gm
Solar Constant 1.94 cal per min per sq cm
Latent heat of Vaporisation of water 540 Calories/gm
Constants Assumed
Ambient Temperature 20 20 20 Centigrade
Area of Reflector Sq Meters 2.5 2.5 10 Sq. Mts.
Variables Assumed
Weight of Water 1000 10000 50000 gms
Weight of Al. Vessel 250 2000 5000 gms
Time required to evaporate above quantity of water 45 480 540 minutes
Input Given
Energy received from Sun in time required to evaporate Area * Solar Constant* Time 2182500 23280000 104760000 Calories
Or in Kilo Calories 2182.5 23280 104760 K Cal
Output Obtained
Calories required to:
Raise Water to Boiling point 'Weight of Water * Specific heat * Temp Difference 80000 800000 4000000 Calories
For Evaporation Weight of Water * Latent Heat of Evaporation 540000 5400000 27000000 Calories Notice that Latent Heat of Evaporation is about 7 times the Heat required to reach the boiling point
Sub Total ( Water) 620000 6200000 31000000 Calories
Raise Aluminium to 100 C Weight of Aluminium * Specific Heat of Aluminium * Temp Difference 4200 33600 84000 Calories This is usually an insignificant amount
Sub Total ( Al) 4200 33600 84000 Calories
Grand Total (Water + Al) 624200 6233600 31084000 Calories
Or in Kilo Calories 624.2 6233.6 31084 K Cal
Efficiency (GT( Water+Al) / Input  % 28.60% 26.78% 29.67% Percent
Efficiency (GT( Water+Al) / Input  %

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