Idris,

"B" is any day better, as it will give you easier and more user friendly designs in most respects.

However, particularly if the collector area is large, the ideal conditions of "B" may be difficult to maintain (though so designed !). In such cases, "A" is a more realistic - and somewhat "inevitable" - form.

Hope that helped.

-Sanjay

Thank you very much prof The issue is which design will give the higher energy output..

Depends on the "division" between the two areas that you have in "A", and the three temperature values (two for "A", one for "B"). Difficult to conclude off-hand !

When you calculate, please do not overlook the lateral heat flow between the two parts of "A", and the ambient cooling for the two parts in "A" and one in "B". If you do not include these aspects, the designs will be unrealistic.

With best wishes.

-Sanjay

 Thanks you very much prof..

collector B is an ideal case . in real life conditions it is not easy to obtain such characteristics from a solar collector. Collector A looks more practical and easy to operate. 

Qu = FR. A [Iτα - UL (Ti- Ta)

in this equation I(solar radiation intensity) , Ta( ambient temperature) are independent variables not in your control. @(absorptivity of glass cover) ,UL ( total heat loss coefficient ) are collector design parameters. you cant change them . its factory made issues.

only thing in your control is Ti( inlet fluid temperature ) . now according to your requirement you can vary Ti and get appropriate results as you want.

hi dear,

the efficiency of a solar collector is define as:

Collector efficiency = a0 – [a1 × (Tc-Tamb)/I] – [a2 × (Tc-Tamb)2 /I]

as the temperature difference between collector temperature (Tc) and ambient (Tamb) is higher the efficiency and heat gained by collector will be less. in this case collector B will have less over all heat loss and more efficiency.

 Thanks my friends..

I try to get higher output temperature for solar collector. That why, i'm confusing, if i choose A, it will give high temperature on a part of absorber only..

hi dear,

you have to optimize between temperature, efficiency and  energy gain.

Further to what our colleagues said above, remember that higher temperature does not mean higher efficiency. You are not trying to heat up the collector, but the solar fluid. If your collector has a very high temperature, its losses are increased and it could mean that your fluid is not circulating fast enough to carry heat away, which can lead to stagnation temperatures. 

The actual heat absorption process in solar collector is isofux not isothermal. So the energy output  will be calculated by this equation Qu = FR. A [Iτα - UL (Tav- Ta) ].where Tav is the average temperature between the inlet and outlet heat transfer fluid.

So the higher or lower temperature region will affect only the heat loss and will have no influence on heat absorption . 

hint: utilized heat Qu = heat absorption - heat loss .

You could divide the heating process between two collectors. the first one which is at lower temperature is a single glass cover flat plate solar collector and the second one which is at higher temperature is a double glass cover flat plate or evacuated tube solar collector.