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musicmar
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Homework Statement
We wish to size a flat plate collector to provide water for one hot shower per hour. We have determined that a shower uses 80 liters of 40°C water that has been heated from a 15°C supply line. The receiver temperature must be greater than the desired water temperature of 40°C and below 90°C to prevent the risk of pressure build up in the collector due to boiling. Determine the required area (Aa in m2) needed for the collector for the following receiver temperatures Tr=50°C, Tr=60°C, Tr=70°C and Tr=80°C. What conclusions can you draw from your calculations?
Assume the following values:
Gtn=400 W/m2 Total solar radiation on a surface normal to the sun’s beam
=30° Average angle of incidence between the normal to the collector and the beam
of the sun
=0.97 Receiver absorptivity
=0.87 Glass transmissivity
UL=5 W/m2-K Overall loss coefficient including conduction, radiation and convection losses
Ta=20°C Temperature of the air
Homework Equations
I have too many equations and don't know what to do with them.
Qdotu=Qdotin-Qdotloss
Q=ArUL(Tr-Ta)
eta = Qdotu/(AaGt)
but I don't think Gt is anything.
and many more, but these seemed the most relevant
The Attempt at a Solution
mdot = 80kg/3600s
Qdotu=mdotcp(Tout-Tin)
=2330 W
Qdotu is in just about every equation, but in order to find the area of the plate, we need to know eta, I believe.