# Homework Help: Temperature(thermal radiation transfer)

1. Mar 1, 2010

### Ajwrighter

1. A solid cylinder of radius r1 = 2.3 cm, length h1 = 4.2 cm, emissivity 0.88, and temperature 24°C is suspended in an environment of temperature 55°C. (a) What is the cylinder's net thermal radiation transfer rate P1? (b) If the cylinder is stretched until its radius is r2 = 0.52 cm, its net thermal radiation transfer rate becomes P2. What is the ratio P2/P1?

2. P1 = ($$\sigma$$) ($$\epsilon$$) A1(Tenv4 - T4)

A1 = 2($$\pi$$) r12 + 2 ($$\pi$$) r h

3. A1 = 9.393362*10-3m2
P1 = (5.67*10-8)(.88)(9.393362*10-3)((273+55)4-(273+24)4)) = 1.77W

I have (b) .. but for some reason (a) is wrong.. here is answer for (b) $$\frac{P2}{P1}$$ = 2.87
.

Last edited: Mar 2, 2010
2. Mar 1, 2010

### Ajwrighter

Ok I just did it in mathmatica .. and it gave the same answer .. If
my intuition is incorrect then the only possible solution would be
that P1 is somehow =($$\sigma$$) ($$\epsilon$$) A1((24+273)4) ... but thats not how the question reads

3. Mar 2, 2010

### Ajwrighter

I asked a friend he agrees with me.. but are we both wrong? not sure why the answer is considered wrong

4. Mar 2, 2010

### Ajwrighter

had another person agree.. anyway I could get someone to review this problem and confirm?

5. Mar 3, 2010

### Ajwrighter

any attempts?

6. Mar 25, 2010

### Ajwrighter

ok I've resolved the problem. Both the book, and their online website have two distinct wrong equations to use.. The correct one would involve flipping the Tenv^4 with the T^4.. so it would read (T^4 - Tenv^4). So, I dub this problem as resolved in case anyone was interested.