Chapt 11

Question 1

What factors govern the cooling rate of an object?

Answer 1

1) film resistance at surface (h)
2) rate of heat flow out from object

Question 2

What is the Fourier number equation?

Answer 2

Fo= (alpha)(time) / (Lc)^2

Question 3

Characteristic length (general)

Answer 3

Volume / Surface Area

Question 4

Lc for a cylinder

Answer 4

R/2

Question 5

Lc for a sphere

Answer 5

R/3

Question 6

Biot number (def & eqn)

Answer 6

Resistance ratio: Bi = (Interior resistance / surface resistance) = hLc / ks

Question 7

What does a small Bi number mean (< .1)

Answer 7

Main resistance is in the film

Question 8

What does an intermediate Bi number mean? ( .1 > Bi < 40)

Answer 8

Both resistances are important

Question 9

What does a large Bi number mean? (>40)

Answer 9

All resistance is in the conduction through solid

Question 10

What is the equation for fractional cooling? Aka fraction of heat remaining in the solids

Answer 10

Q / Qmax = (Ts - Tg) / (Ts0 - Tg) = e^-FoBi = e^-(ht/LcpsCs)

Question 11

What is the instantaneous rate of heat loss from an object?

Answer 11

•
-q = hA(Ts0-Tg)e^-FoBi