# Am I wrong with my calculations or using wrong formula?

1. Apr 29, 2014

### knight92

1. The problem statement, all variables and given/known data
I have a radiator through which water is passed at 90 degrees Celsius, the air speed as it passes through the radiator is 4ms-1. Water temperature difference between inlet and outlet of radiator is 28.33 K. Temperature difference between air before and after passing through radiator is 29K. Area of radiator core is 2.88 x 10^-2 m^2.

2. Relevant equations
Equation for heat transfer = W*Cp*ΔT where W is weighted flow and Cp is specific heat capacity of fluid.

For water heat transfer is = WCpΔT = QwpwCpΔT, where Qw is volumetric flow rate of water, pw is density of water and Cp is specific heat capacity of water at 90 degrees celcius.

so Qw = 2.5 x 10-5 m3s-1
pw = 1.0 kgm-3
Cp = 4.21
ΔT = 28.33 K

For air heat transfer is = WCpΔT = = Ar v CpΔT, where Ar is the surface area of radiator core, v is the velocity of air as it passes through the radiator core, Cp is the specific heat of air

so Ar = 2.88 x 10^-2
v = 4.0 ms-1
Cp = 1.0
ΔT = 29.0 K

3. The attempt at a solution

Heat transfer of water = 2.98 x 10^-3 kWatts
Heat transfer of air = 3.34 kWatts.

why am I getting such a huge difference between heat transfer of the two fluids ? are my equations wrong ?

2. Apr 29, 2014

### SteamKing

Staff Emeritus
What is the density of water?

3. Apr 29, 2014

### Staff: Mentor

That water flow rate seems very low. I don't see a water flow rate in the problem statement. What is the actual problem statement?

Chet

4. May 3, 2014

### knight92

thanks for your replies, I figured out I was using the wrong density of water, it should be 1000 instead of 1