Am I wrong with my calculations or using wrong formula?

[knight92]

Homework Statement

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.

Homework 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

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 ?

 

[SteamKing]

What is the density of water?

 

[Chestermiller]

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

 

[knight92]

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

 

[rezeew]

As a scientist, it is always important to double check your calculations and equations to ensure accuracy. In this case, it seems that your equations and calculations are correct. The large difference in heat transfer between the two fluids could be due to the difference in specific heat capacities and temperature differences. Water has a higher specific heat capacity compared to air, meaning it takes more energy to change its temperature. Additionally, the temperature difference for air is only slightly higher than that of water, which could also contribute to the difference in heat transfer. It is also important to consider other factors such as the material and design of the radiator, which could affect the heat transfer for each fluid. It is always a good idea to review and analyze your equations and calculations to ensure they are accurate and to consider all possible factors that may affect the results.