Radiation: Exchange between Surfaces

This quiz contains problems on black body heat exchange, shape factor concepts, non-black body heat exchange, radiation shield, gaseous radiation, fouling factor, physical and geometrical property symbols, adiabatic surface, reradiating surface and other network approaches

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The interchange factor is also known as

Equivalent emissivity Irradiation Radiosity Shape factor

For the same type of shapes, the value of the radiation shape factor will be higher when

Surfaces are closer Surfaces are larger and held closer Surfaces are moved further apart Surfaces are smaller and held closer

The grey body shape factor for radiant heat exchange between a small body (emissivity = 0.4) in a large enclosure (emissivity = 0.5) is

0.1 0.2 0.4 0.5

Two long parallel surfaces, each of emissivity 0.7 are at different temperatures and accordingly have radiation exchange between them. It is desired to reduce 75% of this radiant heat transfer by inserting thin parallel shields of equal emissivity 0.7 on both sides. What should be the number of shields?

2 4 1 3

An enclosure consists of four surfaces 1, 2, 3 and 4. The view factors for radiation heat transfers are F 11 = 0.1 F 12 = 0.4 F 13 = 0.25 The surface areas A 1 and A 2 are 4 m2 and 2 m2. The view factor F 41 is

0.50 0.75 0.1 0.25

The value of shape factor depends on how many factors?

4 1 2 3

The total radiant energy leaving a surface per unit time per unit surface area is represented by

Radiation Radiosity Irradiation Interchange factor

Determine the radiant heat flux between two closely spaced, black parallel plates radiating only to each other if their temperatures are 850 K and 425 K. The plates have an area of 4 m2

.040 .030 .020 .010

Which one of the following is true for the opaque non-black surface?

J = E +2 p G J = E + p G J = 2 E + p G J = ½ E + p G

The total radiant energy incident upon a surface per unit time per unit area is known as

Shape factor Radiosity Radiation Irradiation

Consider the above problem, if temperature difference is doubled by raising the temperature 480 K to 540 K, then how this heat flux will be affected?

1803.55 W/m2 1703.55 W/m2 1603.55 W/m2 1503.55 W/m2

Two opposed, parallel, infinite planes are maintained at 420 K and 480 K. Calculate the net heat flux between these planes if one has an emissivity of 0.8 and other an emissivity of 0.7

534.86 W/m2 634.86 W/m2 734.86 W/m2 834.86 W/m2

Engineering problems of practical interest involve heat exchange between two or more surfaces, and this exchange is strongly dependent upon
(i) Radiative properties
(ii) Temperature levels
(iii) Surface geometrics
Identify the correct factors.

i and ii

i and iii

ii and iii

i, ii and iii

The fraction of the radiative energy diffused from one surface element and striking the other surface directly with no intervening reflections is called
(i) Radiation shape factor
(ii) Geometrical factor
(iii) Configuration factor
Choose the correct answer.

i only

ii only

i, ii and iii

iii only

A thin shield of emissivity E{3} on both sides is placed between two infinite parallel plates of emissivities E{1} and E{2} and temperatures T{1} and T{2} respectively. If E{1} = E{2} = E{3}, then the fractional radiant energy transfer without shield takes the value

0.25

0.50

0.75

1.25

Quiz/Test Summary

Title: Radiation: Exchange between Surfaces

Questions: 15

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