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%
= 0.75Effective 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= 1.512 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
Some design Factors 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 it without reflectors or just one back reflector only.
plastics with UV rays---use UV stabilized plastic for longer usage
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)