Engineering :: Thermodynamics

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131.

Cut of ratio in a steam engine is the ratio of

A.	Pressure at cut off to supply pressure	B.	Pressure at cut off to exhaust pressure
C.	Pressure at cut off to mean effective pressure	D.	Fraction of piston stroke which the piston has travelled when cut off occurs
E.	Work done by piston after cut off to total work done per cylinder

132.

The rate of heat flow from a 50 mm thick wall of material having thermal conductivity of 40 W/m?C for a temperature difference of 10?C will be

A.	80 kcal/m2 hr	B.	800 kcal/m2 hr
C.	8000 kcal/m2 hr	D.	80000 kcal/m2 hr
E.	2000 kcal/m2 hr

133.

The ratio of heat flow QA/QB from two walls of same thickness having thermal conductivity kA = 2 kB, for the same temperature difference will be

A.	1
C.	2	D.	0.5
E.	None of the above

134.

A wall 50 mm thick (thermal conductivity k = 40 W/m?C) has temperature difference on two surfaces of 100?C. What could probably change if the temperature difference of this wall drops to 100?C

A.	Thermal conductivity changes to 400 W/?C	B.	Area of heat transfer increases 10 times
C.	Thickness of wall increases to 500 mm	D.	Thickness of wall reduces to 5 mm
E.	Rate of heat flow drops to one tenth of the original

135.

If the rate of heat flow in aboves case remains constant, the ratio of temperature difference (?t1) (?t2) would be

A.	1 ; 4	B.	1 ; 8
C.	8 ; 1	D.	16 ; 1
E.	1 ; 16

136.

Steady state heat transfer occurs when

A.	The flow of heat is negligible	B.	The flow of heat is uniform
C.	The flow of heat is independent of time	D.	The flow of heat is uniformly increasing
E.	The flow of heat is uniformly decreasing

137.

Pipes are insulated so that

A.	They may not break under pressure	B.	There is minimum corrosion
C.	Capacity to withstand pressure is increased	D.	Heat loss from the surface is minimized
E.	None of the above

138.

Identify the correct statement

A.	Thermal conductivity increases with molecular weight	B.	Thermal conductivity increases with time
C.	Thermal conductivity increases as the rate of heat flow increases	D.	Thermal conductivity is independent of temperature
E.	Thermal conductivity varies with temperature

139.

In unsteady state, heat transfer occurs when

A.	The body through which heat flow is in motion	B.	The source of heat is in motion
C.	The heat flow changes with change in temperature	D.	The heat flow changes with time
E.	None of the above

140.

Out of the following materials which may be expected to have higher value of thermal conductivity?

A.	Clay	B.	Wood
C.	Asbestos	D.	Refractory brick
E.	Nichrome