1. Sep 26, 2011

### jefferson123

Hi guys can anyone help

I have a problem trying to find an equation to work out the heat rejection for a car radiator I have

Heat exchange = u x a x deltaT

But I cannot find u ?

The radiators have flat profile tubes and wave fin they are made from aluminium, the formulae would have to take this into consideration and work at various mass flows through both the airside. And waterside these would be affected by vehicle speed ie the force of air pushed through the radiator. Can anyone help as I have been looking at this for hours and not getting anywhere.

Cheers

Jefferson123

2. Sep 26, 2011

### Allenman

Well first you would need to know the heat entropy of aluminum. That is, how many joules of energy is required to raise (or lower) its temperature by 1 degree... You also need to know the total surface area both exposed to the coolant inside, as well as the air outside...

it's been a while since I've done a problem like that so I'd have to pretty much relearn it myself beyond that. Maybe someone else will chime in.

3. Sep 26, 2011

### Curl

this problem is impossible, i.e. there exists no "formula" that gives heat transfer rate. This goes for any problem with turbulent flow. In a nutshell, water+air+metal combination = game over.

You get a "guess" by guesstimating the area of the fins, guesstimating a heat transfer coefficient and taking the coolant temperature as constant; then do the classic newton's law of cooling. Errors are probably lower if you take an educated guess, let me just warn you on that...