Heat gain and loss calculation for a Solar Cooker Presented by: Abdulaziz Barkat Shaheen Alshaheen

Objectives:  Advantage of solar cooker  Purpose  Heat Principles  Box cooker calculation  Heat gain  Heat reflection calculation  Heat loss  Some design Factors  Conclusion

Advantage of solar cooker  Solar cooking can save you time, work and fuel, it is also environmentally friendly.  Smoke free cooking and stirring of food is not required.  Each solar cooker in sunny climates can save one ton of wood per year.  Solar Cookers help two of the world’s most pressing problems :  A growing shortage of cooking fuels  the scourge of water-borne diseases.

Purpose Project  Helps to calculate design parameters for solar cooker/oven  Also, summarize the basic principles that are used in the design of solar box cookers  heat gain,  heat loss  heat storage

Heat Principles  The purpose is to heat things up (cook food and purify water)  Both direct and indirect reflected turns to heat  This heat input causes the temperature inside of the solar box cooker to rise until the heat loss of the cooker is equal to the solar heat gain

Box cooker calculation  Box window area= 2 feet x 2 feet = 4 square feet  Solar flux= 700 watts/square meter (variable)  Heat gain = solar flux x area x transmittance x hours of operation Heat gain = 700 x 4 x 0.75 x 4 = 8.4 KW/Hr  Effective heat gain = heat gain x efficiency (Since heat losses are there by side walls, bottom area /plastic glazing or window  take efficiency = 55%  Net heat gain= 8.4 x 0.55 = 4.62 KW/Hr

Heat gain  Once light is absorbed by materials within the enclosure, it is transformed into longer wavelength heat energy  The more directly the glass faces the sun, the greater the solar heat gain

Heat reflection calculation  Most solar ovens have one or more reflectors  Find total area of reflectors  For 2 reflectors of each 2 Sq feet. Total area= 4 square  Take reflectance = 75% = 0.75 Effective reflector area = 4 x 0.75 = 3 square feet.

Heat loss  The loss of heat from a solar oven is described by the Second Law of Thermodynamics  Heat within a solar box cooker is lost in three fundamental ways: Conduction, Radiation, and Convection

Heat loss calculation  Taking efficiency as 55%, heat loss= 45%  Heat loss= 0.45 x 8.4= 3.78 KW/Hr  The Heat loss occurs through side walls, bottom area and also through the glazing  Insulation reduces loss through walls, nearly 40% = 0.4 x 3.78= KW/Hr  Loss thru glass/plastic window=0.6x3.78=2.268 KW/Hr Loss thru glass/plastic  Note that much loss, nearly 2.268/ 8.4 =27% occurs thru glazing  To reduce loss through window, designers use double glazing  Solar ovens reach higher temperatures with more layers of glazing

Heat Storage  The capacity of a solar box cooker to hold heat increases when more mass is placed inside the cooker  The cooker takes longer to heat with heavy materials inside, but will hold heat longer through periods

Conclusion  A large, flat box, depth not greater than 9 inches is preferred…this reduces the volume of air inside and also side wall area  If you have bright sunlight most of the days, do without reflectors or just one back reflector only  Double glazing may be required for higher temperatures(for baking, roasting, deep fry)

References  king/cooking.htm king/cooking.htm  Cookers_World_Network_(Home) Cookers_World_Network_(Home)  cantinawest.com/solar_oven_comparison s.html cantinawest.com/solar_oven_comparison s.html 