Engineering :: Heat Transfer

@ : Home > Mechanical Engineering > Heat Transfer

241.

If the amount of radiant energy received per unit area per second from the sun is measured at the Earth, Mars and Jupiter it will be

A.	identical on all the three planets	B.	in the decreasing order - Jupiter, Mars, Earth
C.	in the increasing order - Earth, Mars, Jupiter	D.	in the increasing order - Jupiter, Mars, Earth

242.

Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then

A.	equal quantity of wax will meet on the two rods	B.	more wax will melt on copper rod as compared to mild steel rod
C.	more wax will melt on mild steel rod as compared to copper rod	D.	nothing can be predioted as the data is insufficient

243.

The diathermous body is one that

A.	diffuses all the thermal rays in the different directions	B.	absorbs all the thermal rays
C.	negligible absorptivity but high reflectivity	D.	allows all the incident radiation to pass through it

244.

The reflectance of a black body is

A.	infinite	B.	one
C.	less than 1.0	D.	zero

245.

A sphere 15 cm in diameter is covered with 5 cm of insulation (k = 0.057 kcal/m-hr-?C). The inside and outside surface temperature of the insulation are 315?C and 80?C respectively. The heat loss per sq. m of the outside surface will be closer to

A.	40 kcal/hr	B.	80 kcal/hr
C.	160 kcal/hr	D.	320 kcal/hr

246.

The face temperatures of a flat wall are 650?C and 450?C respectively and the thermal conductivity of wall material is 0.30 kcal/m-hr-?C. For a wall thickness of 20 cm, the rate of heat conduction per square meter of wall area will be

A.	150 kcal/hr	B.	300 kcal/hr
C.	600 kcal/hr	D.	3000 kcal/hr

247.

Which dimensionless number correlates the relative thickness of the hydrodynamic and thermal boundary layers?

A.	Prandlt number	B.	Nusselt number
C.	Crash off number	D.	Mach number

248.

Which dimensionless number can be used for convective heat transfer?

A.	Graetz number	B.	Nusselt number
C.	Mach number	D.	Froude number

249.

Grashoff number has significant role in heat transfer by

A.	conduction	B.	natural connection
C.	Forced convection	D.	radiation

250.

Which of the following has higher thermal conductivity as compared to the remaining?

A.	Oxygen	B.	Air
C.	Hydrogen	D.	Water