13 - Radiation Heat Transfer

Question 1

Assumptions for radiation heat transfer

Answer 1

Uniform
Isothermal
Diffuse
Medium has no impact

Question 2

Define view factor

Answer 2

Purely geometric quantity and is independent of the surface properties and temperature
(also called ‘shape factor’, ‘configuration factor’ and ‘angle factor’)

Question 3

Define diffuse view factor

Answer 3

View factor based on the assumption that the surfaces are diffuse emitters and diffuse reflectors

Question 4

Define specular view factor

Answer 4

View factor based on the assumption that the surfaces are diffuse emitters but specular reflectors

Question 5

Summation rule

Answer 5

Sum of the view factors from a surface i of an enclosure to all surfaces of the enclosure, including to itself, must equal unity

Question 6

Superposition rule

Answer 6

The view factor from a surface i to a surface j is equal to the sum of the view factors from surface i to the parts of surface j

Question 7

Symmetry rule

Answer 7

Two (or more) surfaces that possess symmetry about a third surface will have identical view factors from that surface

Question 8

Define radiosity

Answer 8

Total radiation energy leaving a surface per unit time and per unit area

Question 9

When are some surfaces modelled as being adiabatic?

Answer 9

If their back sides are well insulated and net heat transfer through them is zero