# Homework Help: Flat plate solar collector

1. Sep 16, 2010

### musicmar

1. The problem statement, all variables and given/known data
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

2. Relevant 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

3. 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.

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