Consider an element with finite dimensions. In general which among the following equations is correct for change in energy of element during a time span dt?

[Heat generated in the element during time dt] – [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]

[Heat generated in the element during time dt] + [Heat flow into the element during time dt] + [Heat flow out of the element during time dt]

[Heat generated in the element during time dt] + [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]

[Heat generated in the element during time dt] – [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]

Consider a plane wall of finite thickness having energy generation in it. The sum of the rate of heat energy generation in the wall and rate of energy transfer by conduction into the wall is equal to

rate of heat transfer by convection out of the wall

rate of heat transfer by conduction out of the wall

rate of heat transfer by convection out of the wall

Consider a plane wall of area A, having a layer of insulation on it. What will happen to the thermal resistance for convection of wall if the thickness of the insulation is increased?

the thermal resistance for convection increases with increase in thickness of insulation

the thermal resistance for convection decreases with increase in thickness of insulation

the thermal resistance for convection remains same with increase in thickness of insulation

Change in momentum is

the result of powers acting on the surface of the control volume

the result of works acting on the surface of the control volume

the result of forces acting on the surface of the control volume

At a given temperature if wavelengths are changed, the quality of radiation per unit wavelength

will be changed sometimes but sometimes be constant

As the radius increases in hollow cylinder the temperature

it depends upon the direction of heat flow

As a radiator, the black body emits the maximum possible thermal radiation

at a constant single wavelength

Aluminum is used as a fin material because

it has lower convection heat transfer coefficient

it has higher convection heat transfer coefficient

it has higher thermal conductivity

it has lower convection heat transfer coefficient

it has lower thermal conductivity

All radiations in a black body are___________________?

partly reflected and partly absorbed

According to the Stefan-Boltzmann law of thermal radiation for a perfect radiator, the rate of radiant energy per unit area is proportional to

the temperature of that radiator

the square of the temperature of that radiator

the cube of the temperature of that radiator

the fourth power of the temperature of that radiator

According to the Nusselt's theory, to determine the heat transfer coefficient for film condensation on surfaces,

the vapour should be pure, dry and saturated

the condensate flow should be laminar

heat transfer should be at steady state

According to the Fourier's law of heat conduction, the rate of heat transfer by conduction depends upon

area of cross section normal to the heat flow

According to the Buckingham π–Theorem, the number of independent dimensionless groups, formed by combining the physical variables of a problem, is equal to

[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n

[total number of physical quantities (n)] – [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantitie

[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n

[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] + [total number of physical quantities (n)]

[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] x [total number of physical quantities (n)]

According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to___________________?

fourth power of absolute temperature

According to Prevost theory of heat exchange ___________________?

heat transfer in most of the cases takes place by combination of conduction, convection and radiation

it is impossible to transfer heat from low temperature source to t high temperature source

heat transfer by radiation requires no medium

all bodies above absolute zero emit radiation

heat transfer in most of the cases takes place by combination of conduction, convection and radiation

rate of heat transfer depends on thermal conductivity and temperature difference

According of Kirchhoff’s law______________________?

radiant heat is proportional to fourth power of absolute temperature

emissive power depends on temperature

emissive power and absorptivity are constant for all bodies

ratio of emissive power to absorptive power is maximum for perfectly black body

ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

Absorptivity of a body will be equal to its emissivity___________________?

when system is under thermal equi-librium

A thorough knowledge of the mechanism is necessary for the estimate of convective heat transfer coefficient so that the process can be adequately represented by mathematical equation. This is a limitation of the method of

analogy between heat, mass and momentum transfer

approximate analysis of the boundary layer equation

dimensional analysis coupled with experimental data

exact mathematical analysis of the boundary layer equation

A steam pipe is to be insulated by two insulating materials put over each other . For best results__________________?

inferior insulation should be put over pipe and better one over it

better insulation should be put over pipe and better one over it

inferior insulation should be put over pipe and better one over it

whether to put inferior OIL over pipe or the better one would depend on steam temperature

A perfect black body is one which_______________?

abslprbs heat radiations of all wave lengths falling on it

A grey body is one whose absorptivity _________________?

varies with the wave length of incident ray

does not vary with temperature and wave length of the incident ray

A grey body is one whose absorptivity_________________?

does not vary with temperature and. wavelength of the incident ray

varies with wavelength of the incident ray

does not vary with temperature and. wavelength of the incident ray

585 + Mcqs in Heat Transfer Questions Page 12 McqOptions

551.	Depending on the radiating properties, a body will be black when_________________?
A.	p = 0, x = 0 and a = 1
B.	p= l,T = 0anda = 0
C.	p = 0, x = 1 and a = 0
D.	x = 0, a + p = 0
E.	a = 0,x + p= 1.
Answer» B. p= l,T = 0anda = 0

552.	Cork is a good insulator because it has___________________?
A.	free electrons
B.	atoms colliding frequency
C.	low density
D.	porous body
E.	all of the above
Answer» E. all of the above

553.	Convective heat transfer coefficient is also known as
A.	film convection factor
B.	film coefficient
C.	film conductance
D.	none of the above
Answer» D. none of the above

554.	Consider the heat is transferred through a wall of surface area A and thickness t at the rate of q, what is the thermal resistance of the system? The thermal conductivity of the wall is k and the heat is transferred normal to the surface area A.
A.	kA
B.	1 / kA
C.	kAt
D.	t / kA
Answer» E.

555.	Consider an element with finite dimensions. In general which among the following equations is correct for change in energy of element during a time span dt?
A.	[Heat generated in the element during time dt] + [Heat flow into the element during time dt] + [Heat flow out of the element during time dt]
B.	[Heat generated in the element during time dt] + [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]
C.	[Heat generated in the element during time dt] – [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]
D.	none of the above
Answer» C. [Heat generated in the element during time dt] – [Heat flow into the element during time dt] – [Heat flow out of the element during time dt]

556.	Consider a plane wall of finite thickness having energy generation in it. The sum of the rate of heat energy generation in the wall and rate of energy transfer by conduction into the wall is equal to
A.	rate of heat transfer by conduction out of the wall
B.	rate of heat transfer by convection out of the wall
C.	both a. and b.
D.	none of the above
Answer» B. rate of heat transfer by convection out of the wall

557.	Consider a plane wall of area A, having a layer of insulation on it. What will happen to the thermal resistance for convection of wall if the thickness of the insulation is increased?
A.	the thermal resistance for convection increases with increase in thickness of insulation
B.	the thermal resistance for convection decreases with increase in thickness of insulation
C.	the thermal resistance for convection remains same with increase in thickness of insulation
D.	unpredictable
Answer» D. unpredictable

558.	Change in momentum is
A.	the result of powers acting on the surface of the control volume
B.	the result of works acting on the surface of the control volume
C.	the result of forces acting on the surface of the control volume
D.	none of the above
Answer» D. none of the above

559.	At the critical radius of insulation of a hollow sphere, the heat transfer will be
A.	minimum
B.	maximum
C.	does not change
D.	unpredictable
Answer» C. does not change

560.	At a given temperature if wavelengths are changed, the quality of radiation per unit wavelength
A.	will always be constant
B.	will also be changed
C.	will be changed sometimes but sometimes be constant
D.	unpredictable
Answer» C. will be changed sometimes but sometimes be constant

561.	Assume fluid flowing in a tube forcefully. The velocity boundary layer develops along the tube. Thickness of this boundary layer increases in the flow direction until the boundary layer reaches the tube centre. This region from the tube inlet to the point at which the boundary layers merge at the centerline is called as
A.	laminar entry region
B.	hydraulic entry region
C.	hydrostatic entry region
D.	hydrodynamic entry region
Answer» E.

563.	Assume a natural convection heat transfer on a vertical flat plate surrounded by a fluid. Where will be the fully developed turbulent layer of fluid established, if the plate is hotter than the fluid?
A.	At the bottom of the plate
B.	At the middle of the plate
C.	At the top of the plate
D.	Nowhere
Answer» D. Nowhere

582.	A non-dimensional number generally associated with natural convection heat transfer is________________?
A.	Grashoff number
B.	Nusselt number
C.	Weber number
D.	Prandtl number
E.	Reynold number
Answer» B. Nusselt number

562.	Assume a turbulent flow of a fluid on a flat plate. A very thin region near the plate surface is called as
A.	laminar buffer layer
B.	laminar sublayer
C.	laminar turbulent layer
D.	none of the above
Answer» C. laminar turbulent layer

564.	As the radius increases in hollow cylinder the temperature
A.	also increases
B.	decreases
C.	it depends upon the direction of heat flow
D.	unpredictable
Answer» D. unpredictable

565.	As a radiator, the black body emits the maximum possible thermal radiation
A.	at a constant single wavelength
B.	at the maximum wavelength
C.	at all wavelengths
D.	none of the above
Answer» D. none of the above

566.	Aluminum is used as a fin material because
A.	it has higher convection heat transfer coefficient
B.	it has higher thermal conductivity
C.	it has lower convection heat transfer coefficient
D.	it has lower thermal conductivity
Answer» C. it has lower convection heat transfer coefficient

567.	All radiations in a black body are___________________?
A.	reflected
B.	refracted
C.	transmitted
D.	absorbed
E.	partly reflected and partly absorbed
Answer» E. partly reflected and partly absorbed

568.	According to Wien’s law, the wavelength corresponding to maximum energy is proportion to ________________?
A.	absolute temperature (T)
B.	I2
C.	f
D.	t
E.	1/r
Answer» B. I2

569.	According to the Stefan-Boltzmann law of thermal radiation for a perfect radiator, the rate of radiant energy per unit area is proportional to
A.	the temperature of that radiator
B.	the square of the temperature of that radiator
C.	the cube of the temperature of that radiator
D.	the fourth power of the temperature of that radiator
Answer» E.

570.	According to the Nusselt's theory, to determine the heat transfer coefficient for film condensation on surfaces,
A.	the vapour should be pure, dry and saturated
B.	the condensate flow should be laminar
C.	heat transfer should be at steady state
D.	all of the above
Answer» E.

571.	According to the Fourier's law of heat conduction, the rate of heat transfer by conduction depends upon
A.	area of cross section normal to the heat flow
B.	temperature gradient
C.	both a. and b.
D.	none of the above
Answer» D. none of the above

572.	According to the Buckingham π–Theorem, the number of independent dimensionless groups, formed by combining the physical variables of a problem, is equal to
A.	[total number of physical quantities (n)] – [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantitie
B.	[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n
C.	[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] + [total number of physical quantities (n)]
D.	[the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] x [total number of physical quantities (n)]
Answer» B. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n

Explore topic-wise MCQs in Mechanical Engineering Questions.

Depending on the radiating properties, a body will be black when_________________?

Cork is a good insulator because it has___________________?

Convective heat transfer coefficient is also known as

Consider the heat is transferred through a wall of surface area A and thickness t at the rate of q, what is the thermal resistance of the system? The thermal conductivity of the wall is k and the heat is transferred normal to the surface area A.