# Homework Help: Furnace Heat transfer question

1. May 12, 2010

### ash-kennard

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

a furnace wall has an area of 3m^2. a thickness of 250mm and a thermal conductivity of 1.5 W m^-1 K^-1. calculate the rate of heat transfer through it when the temperature is 40K

2. Relevant equations

Q/t=KxAx(T2-T1)/L

3. The attempt at a solution

This isn't homework as such, it was given in a list of questions aimed at helping with revision for my module exam. I've done the other 11 questions but this one is doing my head in. the furthest I've gotten to is (Q/18t)-40=T2 but without knowing T2 or the transfer rate is it impossible to progress to an answer?

2. May 12, 2010

### RTW69

40K must be the temperature difference (delta T) it surely isn't -233 C for a furnace.

3. May 12, 2010

### ash-kennard

i was talking to my dad about it earlier today too. but thats the exact question, havent re worded it at all. a furnace implies very hot temperatures, and the 40k must have to be a difference. but i wanted to see if i was overlooking something so posted on here.

is there anyway to get any further on this question with the lack of information?

4. May 12, 2010

### RTW69

I don't see any other way to solve this problem rather than to assume a delta T of 40 K. But actually that value seems to low. Furnace temperatures get very high, I would have expected a delta T of about 350 K assuming an exterior surface temperature of about 40 C (100 F) and an inside wall temperature of 380 C (800 F). Might be a typo.

5. May 12, 2010

### ash-kennard

right cheers for that then. i know how to do it providing that is is delta 40, i also know how to do it given 2 temperatures so cheers for the help. was annoying me greatly

much appreciated, ash