Heat Transfer in Solar Air Heater

Good evening jimmi.

Why do you think that temperature would increase when you are removing heat faster? Ignoring your current analysis methodology for a moment, lets do a thought problem. If I put a flat plate collector under sun, and do not allow any removal of heat by any takeaway fluid, (Velocity = 0) the heat will build up to stagnation temperature, until the collector temperature gets to equilibrium with what it leaks out to the environment.

Now, lets start moving the fluid to takeaway heat, at the slowest rate of removal, the fluid will have the temperature at stagnation, the highest temperature available; Increase velocity, and it will pick up less heat, so lower temperature in the fluid.

Think about it like leaving a car closed up in the hot sun, with the windows up, and the windows down in a breeze and all will be made clear to you.

milo

Milo, are you confusing heat and temperature?

At zero flow in heat exchange, you are correct that the fluid temp will reach a max value. But the heat gain stops when stagnation temerature is reached. Heat gain is fluid mass time temp change.

With flow through the heat exchange, max temp will be lower. But heat gain is increased because the heat gain equals the mass flow rate times the temperature change. Heat gain continues as long as mass flows through the system.

Good morning Ried.

Actually I think I read the question pretty clearly. The Original Poster is asking about temperature increase, not heat.

"But when I increase a inlet velocity the base temperature reduced at the same time outlet temperature has been reduced. Our aim is increase outlet temperature with increase in inlet velocity"

OP asks about increasing temperature as velocity increases.

I answered his question as he worded it.

milo

You're right, I thought the OP was looking for heat, but he does ask about temperature.

Either I misunderstood his post and I gave the answer based on heat not temp, or I accidently interpreted that the OP mis-stated temp and really wanted to increase heat output.

Hopefully the OP comes back and reduces my confusion.

No harm, No foul.

I agree that heat would be likely more useful.

milo