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
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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

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

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

any attempts?

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.