# Homework Help: Heat transfre for a domestic radiator

1. Aug 5, 2007

### nickbone59

Any suggestions anyone??? Really struggling with this one !!
1. The problem statement, all variables and given/known data
A domestic radiator is 2.5 m long and 0.6m high and is sited in a room whose temperature is 14C. Hot water is circulating through the radiator at a temperature of 90c. The radiator is convecting heat from both sides but only radiating from one side. Given that the surface emissivity is 0.7, calculate the total heat transfer from radiator to the room.

2. Relevant equations
Stefan-Boltzmann Constant = 5.67x10^-8

Nu = 0.59(Gr.Pr)^0.25 for laminar flow (GR.Pr)<10^9
Nu = 0.129(Gr.Pr)^0.33 for turbulent flow (GR.Pr)>10^9
where,
Grashof no. Gr= ($$\rho$$^2$$\beta(\theta$$1-$$\theta$$2)l^3)/$$\mu$$^3

Nusselt No. Nu= hl/k

Prandtl No. Pr=Cp$$\mu$$/k

3. The attempt at a solution

Q= $$\sigma\epsilon$$A(T1^4-T2^4)

= 5.67x10^-8 x 0.7 x 1.5 x (1.736x10^10-6.785x10^9)

= 629.8W
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 5, 2007

### Astronuc

Staff Emeritus
Looks like you got the radiated heat correct. It would be preferable to include units with the numbers.

Now find the convective heat. One needs a formula for the convective heat transfer coefficient.