Engineering :: Heat Transfer

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21.

The conductance has the units of

A.	W/m2	B.	W/K
C.	W/(m.K0	D.	1/k

22.

The thermal diffusivity of a material is defined as

A.	k/(pCp)	B.	(pCp)/k
C.	(kCp)/p	D.	(kp)/Cp

23.

The units of the thermal diffusivity of a material are

A.	m2/K	B.	s/m2
C.	W/(m2.K)	D.	m2/s

24.

The thermal diffusivity of a material is the ratio of

A.	the thermal conductivity to the thermal capacity of the material	B.	the thermal capacity to the thermal conductivity of the material
C.	the thermal conductivity to the specific heat of the material	D.	the thermal conductivity to the density of the material

25.

The thermal diffusivity of a material is important in the analysis of problems involving heat transfer by

A.	radiation	B.	natural convection
C.	condensation	D.	conduction

26.

The resistance to heat flow by conduction is

A.	directly proportional to the material thickness	B.	inversely proportional to the material density
C.	inversely proportional to the area normal to the direction of heat transfer	D.	all of these answers

27.

If the thermal conductivity of a wall material varies linearly with temperature the steady state temperature distribution in the very large thin plane wall having steady uniform surface temperature follows

A.	linear law	B.	parabolic law
C.	logarithmic law	D.	hyperbolic law

28.

The thicker the insulation the less is the total heat lost. This statement is

A.	always true for flat insulation only	B.	always true for curved insulation only
C.	always true for both flat and curved insulation	D.	not true for both flat and curved insulation

29.

If the thermal conductivity of a wall material is independent of temperature the steady state temperature distribution in the very large thin plane wall having steady uniform surface temperatures follows

A.	hyperbolic law	B.	parabolic law
C.	linear law	D.	logarithmic law

30.

The maximum heat loss from pipe occurs when the critical radius equals

A.	the ratio of the surface coefficient of heat transfer to the thermal conductivity of the insulation	B.	the ration of the thermal conductivity of the insulation to the surface coefficient of heat transfer
C.	the product of the thermal conductivity of the insulation and the surface coefficient of heat transfer	D.	the radius of the pipe