Day 5 (Jan 10) Notes

Question 1

Cross - sectional area (A)

Answer 1

The rate of heat transfer is directly proportional to the area of the object. The greater the surface area the greater the heat transfer.

Question 2

Thermal conductivity (K)

Answer 2

Thermal conductivity is the rate of heat transfer for a given thickness of material per unit area per unit temperature difference.

Question 3

The rate of heat transfer is directly proportional to the thermal conductivity. The greater the thermal conductivity the greater the heat transfer.

Question 4

Heat transferred can be summarized in to the following formula:

Answer 4

Q = K A (T, -T,) Δt
————————-
d

Δt= change in time
A= area

Question 5

Thermal Resistance

Answer 5

The inverse of thermal conductivity is thermal risistance- a measure of the ability of a given thickness of material to prevent heat transfer. In everyday life this is more useful than thermal conductivity, Thermal resistence tells us how well our homes are insulated.

Question 6

As thermal resistance in creases less head passes through the materal for equal temperature differences. Bags of insulation hare thermal resistance in st units marked on them- RSI. The wits for RSI are (m^2K)/W. For simplicity the units are omitted on a bag at insulation.

Question 7

Thermal resistance is determined by dividng the thickness of a material by its thermal conductivity

Answer 7

RSI: ÷ d/K