Engineering :: Heat Transfer

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41.

For pure metals the thermal conductivity (k) and the electrical conductivity (ke) are related approximately as

A.	L = k T/ke	B.	L = k/ke
C.	L = ke /k	D.	L = k /keT

42.

The critical radius for curved insulation

A.	increases with decreasing insulation thickness	B.	decreases with decreasing insulation thickness
C.	is independent of insulation thickness	D.	depends on the thermal conductivity of insulating material

43.

Convection is the method of heat transfer in which

A.	the heat is sent out or emitted in waves	B.	the heat is transferred along a chain of molecules
C.	the heat is carried along by a movement of warmed matter	D.	all of the above

44.

Heat transfer by convection is described by

A.	Ficks law	B.	Fouriers law
C.	Newtons law of cooling	D.	Stefan-Boltzmann law

45.

The unit of heat transfer coefficient is

A.	W/(m.K)	B.	W/(m2.K)
C.	J/(m2.K)	D.	J/(m.K)

46.

According to Newtons law of cooling (provided the difference of temperature is small). The rate of heat transfer is proportional to

A.	the excess temperature	B.	the square of the excess temperature
C.	the cube of the excess temperature	D.	the fourth power of the excess temperature

47.

When crude oil is pumped through the furnace the first heat transfer to the tubes occurs when the hot flue gases rise and heat the tubes. The oil tubes are heated first by the process of

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

48.

The Prandtl number (NPr) is defined as

A.	Cp?/?	B.	k C ?/?
C.	C ? ?/k	D.	C ? ?/k

49.

The Nusselt number (NN?) is defined as

A.	C ? ?/k	B.	h D/k
C.	k D/h	D.	C ? ?/h

50.

The Reyleigh number (NRa) is given by

A.	NGr NRe	B.	NGr NPr
C.	NGr Npe	D.	NGr NSt