We are having a fictive, non existing heat exchanger with the following parameters:
Outer tube diameters: 20 & 12 mm
Wall thickness inner tube: 1mm, outer tube; 2 mm
flow area hot side: 0.0226m2, cold side; 0.0272 m2
The heatexchanger is going to cool some hot water, with cool water. The hot water is 55 degrees C to start with and we don't really care what it will become. The cool water is 15 degrees to start with and we don't want it to become more than 25 decrees Celsius. The heat exchanger is having max cooling power of 4kW (so Q=4kW) and the hot water is having a flowrate of 215 liter/hour
But we have to use an other heat exchanger with the following properties:
Outer tube diameters: 16 mm & 10 mm and the wall thickness of the inner tube is 12 mm
With that heat exchanger we are to determine the Overall heat transfer coefficient U (q=U*A*Tlm) as a function of the speed of the water (v) or Reynolds (Re=(vDρ)/μ. And then somehow we need to get the length of the non existing heat echanger from that...
So I have like no idea how to measure it... ^^' I think we can measure the flow rate of the water and the temperature at the beginning and ending. The heat exchanger is a counterflow heat exchanger. We were also given the following formula: q=m(with a dot on it)*Cp*(Tin -Tout)
q=m(with a dot on it)*Cp*(Tin -Tout)
The Attempt at a Solution
I think it has something to do with the reynolds number, since if they are the same two flows are the some right? so you could use that one. μ and ρ would stay the same and D would chance if you use an other heat exchanger, but you can't really vary it, so the only thing in that one that you could vary to get the reynoldnumbers the same would be the speed (v)
I'm having q and Tlm I want to know A and to get A I need U. (haha that has two meanings:P) but I really, really don't know how to get that one, all kind of thinks are going trough my head and the one making the most sense would be to first use the dementions of the non existing heat exchanger (because you know everything from that one) and then the only one you don't know would be U... but than you don't need to do the experiment to begin with and I just don't think that it would make sense... So I'm kinda out of ideas...
Someone any ideas how to get U? or some kind of tip or hind? Thanks so much in advance :)