Engineering :: Heat Transfer

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31.

The thermal conductivity of wood depends upon

A.	Density	B.	Moisture content
C.	Temperature	D.	All of the above
E.	None of the above

32.

Which liquid metal is supposed to be the best conductor

A.	Lead	B.	Mercury
C.	Zinc	D.	Sodium
E.	Potassium

33.

Which sample of concrete may be expected to have highest value of thermal conductivity

A.	Dry concrete	B.	Dry concrete having 0.4% rein-forcement
C.	Concrete having 10% moisture by volume	D.	Concrete having 10% meisture by volume and 0.4% reinforcement
E.	Concrete having 10% moisture by volume and 0.6% reinforcement

34.

The value of thermal conductivity of water at room temperature is expected to be

A.	0.001 kcal/m-hr-?C	B.	0.05 kcal/m-hr-?C
C.	0.5 kcal/m-hr-?C	D.	1.0 kcal/m-hr-?C
E.	1.5 kcal/m-hr-?C

35.

Thermal conductivity of air at room temperature is approximately

A.	0.002 kcal/m-hr-?C	B.	0.02 kcal/m-hr-?C
C.	0.2 kcal/m-hr-?C	D.	2.0 kcal/m-hr-?C
E.	20.0 kcal/m-hr-?C

36.

The value of Prandtl number for air is of the order of

A.	1000	B.	67
C.	9.7	D.	0.7
E.	0.065

37.

The numerical value of which property of air generally drops with rising temperature

A.	Density	B.	Dynamic viscosity
C.	Kinematic viscosity	D.	Thermal conductivity
E.	Thermal diffusivity

38.

In which case the value of thermal conductivity drops with rising temperature

A.	Methane	B.	Benzene
C.	Carbondioxide	D.	Ammonia
E.	None of the above

39.

Three rods one made of glass, one of pure aluminium and one made of wrought iron are heated to 150?C. All the rods are 15 mm in diameter and 300 mm long. The lowest temperature at the free end of the rods will occur in case of

A.	Aluminium rod	B.	Wrought iron rod
C.	Glass rod	D.	Temperature will be same for all the three rods at free end
E.	Temperature will depend on the surrounding air temperature

40.

The surface temperatures of a flat wall are 650?C and 450?C respectively and the thermal conductivity of the wall material is 0.30 kcal/m-hr-?C. The heat flux for a wall of 20 cm thickness will be

A.	300 kcal/m2-hr	B.	120 kcal/m2-hr
C.	60 kcal/m2-hr	D.	450 kcal/m2-hr
E.	600 kcal/m2-hr