Engineering :: Heat Transfer

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21.

There metal walls of same cross-sectional area having thermal conductivity in the ratio 1 : 2 : 4 transfer heat at the rate of 15000 kcal/hr. For same thickness of wall, the temperature deop will be in the ratio

A.	1 ; 2 ; 4	B.	4 ; 2 ; 1
C.	1 :
E.	1 ; 1 ; 1

22.

Thermal diffusivity is

A.	A mathematical formula only	B.	A physical property of the material
C.	A configuration for heat conduction	D.	A dimensionless parameter
E.	A function of temperature

23.

The unit of thermal diffusivity is

A.	m/hr	B.	m2/hr
C.	m/hr?C	D.	m2/hr?C
E.	kcal/m2-hr

24.

Non-isotropic conductivity is exhibited in case of

A.	Brass	B.	Steel
C.	Copper	D.	Lead
E.	Wood

25.

For glass wool the thermal conductivity varies from sample to sample because of variations in

A.	Structure	B.	Composition
C.	Density	D.	Porosity
E.	All of the above

26.

Which variety of steel may be expected to have lowest value of thermal conductivity?

A.	High carbon steel (0.83% C)	B.	Low nickel steel (1.37% Ni)
C.	Low chromium steel (0.46% Cr)	D.	High chromium steel (0.26% Cr)
E.	Chromium nickel steel (9% Ni, 18% Cr)

27.

The highest value of thermal conductivity is expected for

A.	Solid ice	B.	Melting ice
C.	Water	D.	Boiling water
E.	Steam

28.

Which is not the assumption in Fourier's equation of heat conduction?

A.	Homogeneous substance	B.	Steady heat flow
C.	Constant temperature difference	D.	Thermal conductivity independent of temperature
E.	Uniform area of cross-section

29.

The unit of thermal conductivity in S.I. units is

A.	W/m-hr-?K	B.	W/m-hr?C
C.	W/m?K	D.	KJ/m-hr?C
E.	KJ/m-hr-?K

30.

Which insulating material is suitable for low temperature applications?

A.	Cork	B.	Asbestos paper
C.	Diatomaceous earth	D.	85% magnesia
E.	Fused alumina bricks