If thermal conductivity of a material of wall varies as k0(1 - αT), the temperature at the center of the wall will be (α is +ve)

More than in case of constant thermal conductivity

Less than that in case of constant thermal conductivity

For given combined radiative and convective heat transfer coefficient ‘ht’ and given thermal conductivity k, Critical thickness of insulation for cylinder and sphere is given as

\(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)

\(\frac{k}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)

\(\frac{k}{{{h_t}}}\) and \(\frac{{2k}}{{{h_t}}}\)

\(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)

\(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{{h_t}}}\)

Heat pipe is widely used now a days because

It acts as conductor and insulator

A spherical steel ball of 12 mm diameter is initially at 1000 K. It is slowly cooled in a surrounding of 300 K. The heat transfer coefficient between the steel ball and the surrounding is 5 W /m2K. The thermal conductivity of steel is 20 W/mK. The temperature difference between the centre and the surface of the steel ball is

Large because conduction resistance is far higher than the convective resistance

Large because conduction resistance is far less than the convective resistance

Small because conduction resistance is far higher than the convective resistance

Small because conduction resistance is far less than the convective resistance

For the same heat transfer, the temperature profile between two metal walls joined together is shown in the figure. if l1 = l2, from the figure it can be concluded that

Heat is generated at the interface

Heat conduction in a semiconductor takes place

by the mobility of the carriers

due to energy gap between conduction band and valency band

by the holes and thermal vibrations of atoms

by the electrons and thermal vibrations of atoms

A hot steel spherical ball is suddenly dipped into a low temperature oil bath.Which of the following dimensionless parameters are required to determine instantaneous center temperature of the ball using a Heisler chart?

Nusselt number and Grashoff number

Reynolds number and Prandtl number

A sphere, a cube and a disc all of the same material, quality and volume are heated to 900 K and left in air. Which of these have the lowest rate of cooling

All will have the same rate of cooling

Conduction takes place due to temperature gradients

in a medium which is not vacuum

Critical thickness of insulation yields

No heat transfer rate from a pipe

Minimum heat transfer rate from a pipe

Maximum heat transfer rate from a pipe

As the temperature increases, the thermal conductivity of a gas

increases up to a certain temperature and then decreases

In MLTθ system (T being time and θ temperature), what is the dimension of thermal conductivity?

\(M{L^{ - 1}}{T^{ - 1}}{\theta ^{ - 3}}\)

\(ML{T^{ - 1}}{\theta ^{ - 1}}\)

\(ML{T^{ - 3}}{\theta ^{ - 1}}\)

Metals are good conductor of heat because

Their atoms are relatively far apart

A thin copper wire at 300° is suddenly immersed in water at 30°C. It cools down to 150°C in 70 seconds. It is then reheated to the initial temperature of 300°C and suddenly exposed to air at 30°C where it cools down to 150°C in 200 seconds. This difference in cooling time is due to

Smaller heat transfer coefficient of water

Larger heat transfer coefficient of water

Smaller heat transfer coefficient of water

135 + Mcqs in Conduction Sphere in Heat Transfer Page 2 McqOptions

51.	Lumped heat transfer analysis of a solid object suddenly exposed to a fluid medium at a different temperature is valid when
A.	Biot number < 0.1
B.	Biot number > 0.1
C.	Fourier number < 0.1
D.	Fourier number > 0.1
Answer» B. Biot number > 0.1

Discussion

52.	In a furnace the heat loss through the 150 mm thick refractory wall lining is estimated to be 50 W/m2. If the average thermal conductivity of the refractory material is 0.05 W/mK, the temperature drop across the wall will be:
A.	140°C
B.	150°C
C.	160°C
D.	170°C
Answer» C. 160°C

Discussion

53.	A solid copper ball of mass 500 gm when quenched in a water bath at 30°C, cools from 530°C to 430°C in 10 sec. What will be the temperature of the ball after the next 10 seconds?
A.	300°C
B.	320°C
C.	350°C
D.	Cannot be determine
Answer» D. Cannot be determine

Discussion

54.	If thermal conductivity of a material of wall varies as k0(1 - αT), the temperature at the center of the wall will be (α is +ve)
A.	Depends on other factors.
B.	More than in case of constant thermal conductivity
C.	Less than that in case of constant thermal conductivity
D.	None of the above
Answer» D. None of the above

Discussion

55.	For given combined radiative and convective heat transfer coefficient ‘ht’ and given thermal conductivity k, Critical thickness of insulation for cylinder and sphere is given as
A.	\(\frac{k}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)
B.	\(\frac{k}{{{h_t}}}\) and \(\frac{{2k}}{{{h_t}}}\)
C.	\(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)
D.	\(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{{h_t}}}\)
Answer» C. \(\frac{{2k}}{{{h_t}}}\) and \(\frac{k}{{h_t^2}}\)

Discussion

56.	One-dimensional steady state heat conduction takes place through a solid whose cross-sectional area varies linearly in the direction of heat transfer. Assume there is no heat generation in the solid and the thermal conductivity of the material is constant and independent of temperature. The temperature distribution in the solid is
A.	Linear
B.	Quadratic
C.	Logarithmic
D.	Exponential
Answer» D. Exponential

Discussion

57.	Consider the following statements about thermal conductivity:1) Thermal conductivity decreases with increasing molecular weight2) Thermal conductivity of non-metallic liquids generally decreases with increasing temperature3) Thermal conductivity of gases and liquids is generally smaller than that of solidsWhich of the above statements are correct?
A.	1 and 2 only
B.	1 and 3 only
C.	2 and 3 only
D.	1, 2 and 3
Answer» E.

Discussion

58.	A refrigerator with COP of 5 is used in a room at 300 K. What will be the heat intake through a section of refrigerator wall of area 100 cm × 100 cm with a thickness of 10 cm, assuming only conduction? Value of thermal conductivity of the wall can be taken as 1 W/cm.K
A.	50000 W
B.	1000 W
C.	7500 W
D.	3000 W
Answer» B. 1000 W

Discussion

59.	A furnace wall made of steel plate 10 mm thick and thermal conductivity 15 kcal/m-hr-°C is lined inside with silica brick of 150 mm thick of thermal conductivity 1.75 kcal/m-hr-°C and on outside with magnesia bricks of 200 mm thick with thermal conductivity of 4.5 kcal/m-hr-°C. The total resistance of the composite wall will be
A.	0.13 °C-hr/kcal
B.	0.23 °C-hr/kcal
C.	0.03 °C-hr/kcal
D.	0.33 °C-hr/kcal
Answer» B. 0.23 °C-hr/kcal

Discussion

60.	Heat pipe is widely used now a days because
A.	It acts as an insulator
B.	It acts as conductor and insulator
C.	It acts as a superconductor
D.	It acts as a fin
Answer» D. It acts as a fin

Discussion

61.	A 40 mm diameter electric cable of an Aluminium conductor of thermal conductivity 240 W/mK is to be insulated with rubber of thermal conductivity 0.15 W/mK. The cable is to be located in the air with a heat transfer coefficient of 6 W/m2K. The critical thickness of insulation will be
A.	5 mm
B.	25 mm
C.	20 mm
D.	15 mm
Answer» B. 25 mm

Discussion

62.	A dimensionless number associated with transient conduction heat transfer is
A.	Reynolds number
B.	Nusselt number
C.	Froude number
D.	Biot number
Answer» E.

Discussion

63.	A spherical steel ball of 12 mm diameter is initially at 1000 K. It is slowly cooled in a surrounding of 300 K. The heat transfer coefficient between the steel ball and the surrounding is 5 W /m2K. The thermal conductivity of steel is 20 W/mK. The temperature difference between the centre and the surface of the steel ball is
A.	Large because conduction resistance is far higher than the convective resistance
B.	Large because conduction resistance is far less than the convective resistance
C.	Small because conduction resistance is far higher than the convective resistance
D.	Small because conduction resistance is far less than the convective resistance
Answer» E.

Discussion

64.	A wall of thickness 0.6 m has a normal area 1.5 m2 and is made up of material of thermal conductivity 0.4 W/mK. The temperature on the two sides are 800°C and 100°C. What is the thermal resistance of the wall?
A.	1 W/K
B.	1.8 W/K
C.	1 K/W
D.	1.8 K/W
Answer» D. 1.8 K/W

Discussion

65.	A hot fluid is flowing through a long pipe of 4 cm outer diameter and covered with 2 cm thick insulation. It is proposed to reduce the conduction heat loss to the surroundings to one third of the present rate by increasing the same insulation thickness. The additional thickness of insulation required will be
A.	2 cm
B.	6 cm
C.	9 cm
D.	12 cm
Answer» E.

Discussion

66.	A beaker filled with hot water in a room cools from 70°C to 65°C in t1 minutes, 65°C to 60°C in t2 minutes and from 60°C to 55°C in t3 minutes, then
A.	t1 > t2 > t3
B.	t1 = t2 = t3
C.	t1 < t2 < t3
D.	Can not be concluded
Answer» D. Can not be concluded

Discussion

67.	A small metal bead (radius 0.5 mm), initially at 100°C, when placed in a stream of fluid at 20°C, attains a temperature of 28°C in 4.35 seconds. The density and specific heat of the metal are 8500 kg/m3 and 400 J/kgK respectively. If the bead is considered as a lumped system, the convective heat transfer coefficient (in W/m2.K) between the metal bead and the fluid stream is
A.	283.3
B.	299.8
C.	149.9
D.	449.7
Answer» C. 149.9

Discussion

68.	A 1000 kg vehicle travelling at 80 m/s impacts a plunger attached to a piston-cylinder arrangement. If all of the energy of the vehicle is absorbed by the 20 kg of liquid contained in the cylinder, what is the maximum temperature rise of the liquid? (The specific heat of the liquid is 4.0 kJ/kg°C)
A.	55°C
B.	40°C
C.	45°C
D.	50°C
Answer» C. 45°C

Discussion

69.	For the same heat transfer, the temperature profile between two metal walls joined together is shown in the figure. if l1 = l2, from the figure it can be concluded that
A.	Heat flows from A to B
B.	Heat flows from B to A
C.	Heat is generated at the interface
D.	A is bad conductor of heat
Answer» D. A is bad conductor of heat

Discussion

70.	For a current-carrying wire of 20 mm diameter exposed to air (h = 20 W/m2K), maximum heat distribution occurs when the thickness of insulation (k = 0.5 W/mK) is
A.	20 mm
B.	10 mm
C.	2.5 mm
D.	None of the above
Answer» E.

Discussion

71.	An insulated pipe of 50 mm outside diameter with e = 0.8 is laid in a room at 30°C. If the surface temperature is 250°C and the convective heat transfer coefficient is 10 W/m2K, the total heat loss per unit length of the pipe will be
A.	896.6 W/m
B.	818.8 W/m
C.	786.4 W/m
D.	742.2 W/m
Answer» C. 786.4 W/m

Discussion

72.	For conduction through a spherical wall with constant thermal conductivity and with inner side temperature greater than outer wall temperature (one-dimensional heat transfer), what is the type of temperature distribution?
A.	Linear
B.	Parabolic
C.	Hyperbolic
D.	None of the above
Answer» D. None of the above

Discussion

73.	A furnace is made of red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. What is the thickness if it is replaced by a layer of diatomite earth of conductivity 0.14 W/mK under the same heat loss per unit area and same temperature drop?
A.	0.5 m
B.	0.1 m
C.	0.2 m
D.	0.9 m
Answer» C. 0.2 m

Discussion

74.	Heat conduction in a semiconductor takes place
A.	by the mobility of the carriers
B.	due to energy gap between conduction band and valency band
C.	by the holes and thermal vibrations of atoms
D.	by the electrons and thermal vibrations of atoms
Answer» E.

Discussion

75.	Heat is lost steadily through a 0.5 cm thick 2 m × 3 m window glass whose thermal conductivity is 0.7 W/m°C. The inner and outer surface temperatures of the glass are measured to be 12°C to 9°C. The rate of heat loss by conduction through the glass is:
A.	420 W
B.	5040 W
C.	1256 W
D.	2520 W
Answer» E.

Discussion

76.	A hot steel spherical ball is suddenly dipped into a low temperature oil bath.Which of the following dimensionless parameters are required to determine instantaneous center temperature of the ball using a Heisler chart?
A.	Nusselt number and Grashoff number
B.	Reynolds number and Prandtl number
C.	Biot number and Froude number
D.	Biot number and Fourier number
Answer» E.

Discussion

77.	A metal plate has a surface area of 2 m2, thickness 10 mm and a thermal conductivity of 200 W/m-K. What is the thermal resistance of the plate ?
A.	4 × 104 K/W
B.	2.5 × 10-3 K/W
C.	1.5 × 10-4 K/W
D.	2.5 × 10-5 K/W
Answer» E.

Discussion

78.	An air-conditioned room has one of the walls, which is 5 m × 3 m of 3.75 cm thick brick. The conditioned space is maintained at 27°C when the outside temperature is 47°C. Variation of thermal conductivity with temperature of the wall is given by k = 1 + 2 × 10-4 T, where T is in Kelvin and k is in W/mK. The heat gained by the conditioned space through this wall is
A.	8496 W
B.	84.96W
C.	800 W
D.	0
Answer» B. 84.96W

Discussion

79.	In a long cylindrical rod of radius R and a surface heat flux of q0, the uniform internal heat generation rate is
A.	\(\frac{{2{q_0}}}{R}\)
B.	2q0
C.	\(\frac{{{q_0}}}{R}\)
D.	\(\frac{{2{q_0}}}{{{R^2}}}\)
Answer» B. 2q0

Discussion

80.	In the heat flow equation \(Q = - kA\frac{{{T_1} - {T_2}}}{x},\) x/kA is known as
A.	Thermal coefficient
B.	Thermal conductivity
C.	Thermal resistance
D.	Thermal gradient
Answer» D. Thermal gradient

Discussion

81.	Assumptions made in Fourier's law is that the heat flowA. Is in steady-stateB. Through a solid medium in one dimension
A.	Only (A)
B.	Only (B)
C.	Both (A) and (B)
D.	None of these
Answer» D. None of these

Discussion

82.	Equal amounts of a liquid metal at the same temperature are poured into three moulds made of steel, copper and aluminium. The shape of the cavity is a cylinder with 15 mm diameter. The size of the moulds are such that the outside temperature of the moulds do not increase appreciably beyond the atmospheric temperature during solidification. The sequence of solidification in the mould from the fastest to slowest is(Thermal conductivities of steel, copper and aluminium are 60.5, 401 and 237 W/m-K, respectively.Specific heats of steel, copper and aluminium are 434, 385 and 903 J/kg-K, respectively.Densities of steel, copper and aluminium are 7854, 8933 and 2700 kg/m3, respectively.)
A.	Copper – Steel - Aluminium
B.	Aluminium – Steel - Copper
C.	Copper – Aluminium - Steel
D.	Steel – Copper - Aluminium
Answer» D. Steel – Copper - Aluminium

Discussion

83.	A wall of thickness 0.6 m and thermal conductivity 0.6 W / m-K has a surface area of 1 m2. If the inner and outer temperature of the wall are 1840°C and 340°C, respectively, the rate of heat transfer will be:
A.	150 W
B.	75 W
C.	750 W
D.	1500 W
Answer» E.

Discussion

84.	Consider one-dimensional steady-state heat conduction, without heat generation, in a plane wall; with boundary conditions as shown in the figure below. The conductivity of the wall is given by k = k0 + bT; where k0 and b are positive constants and T is temperature.As x increases, the temperature gradient (dT/dx) will
A.	Remain constant
B.	Be zero
C.	Increase
D.	Decrease
Answer» E.

Discussion

85.	A sphere, a cube and a disc all of the same material, quality and volume are heated to 900 K and left in air. Which of these have the lowest rate of cooling
A.	Cube
B.	Disc
C.	Sphere
D.	All will have the same rate of cooling
Answer» D. All will have the same rate of cooling

Discussion

86.	Conduction takes place due to temperature gradients
A.	in a medium which is not vacuum
B.	in a fluid medium only
C.	in solid only
D.	only in stationary medium
Answer» B. in a fluid medium only

Discussion

87.	Critical thickness of insulation yields
A.	No heat transfer rate from a pipe
B.	Minimum heat transfer rate from a pipe
C.	Maximum heat transfer rate from a pipe
D.	None of the above
Answer» D. None of the above

Discussion

88.	As the temperature increases, the thermal conductivity of a gas
A.	increases
B.	decreases
C.	remains constant
D.	increases up to a certain temperature and then decreases
Answer» B. decreases

Discussion

89.	In MLTθ system (T being time and θ temperature), what is the dimension of thermal conductivity?
A.	\(M{L^{ - 1}}{T^{ - 1}}{\theta ^{ - 3}}\)
B.	\(ML{T^{ - 1}}{\theta ^{ - 1}}\)
C.	\(ML{T^{ - 3}}{\theta ^{ - 1}}\)
D.	\(ML{T^2}{\theta ^{ - 1}}\)
Answer» D. \(ML{T^2}{\theta ^{ - 1}}\)

Discussion

90.	A metal ball of diameter 60 mm is initially at 220°C. The ball is suddenly cooled by an air jet of 20°C. The heat transfer coefficient is 200 W/m2K. The specific heat, thermal conductivity and density of the metal ball are 400 J/kg. 400 W/mK and 9000 kg/m3, respectively. The ball temperature (in °C) after 90 seconds will be approximately
A.	141
B.	163
C.	189
D.	210
Answer» B. 163

Discussion

91.	A 10 kg solid at 100°C with a specific heat, of 0.8 kJ/kg°C is immersed in 40 kg of 20°C liquid with a specific heat of 4.0 kJ/kg°C. Estimate the temperature after a long time if the container is insulated?
A.	30°C
B.	28°C
C.	26°C
D.	24°C
Answer» E.

Discussion

92.	Metals are good conductor of heat because
A.	Their atoms collide frequently
B.	Their atoms are relatively far apart
C.	They contain free electron
D.	They have high density
Answer» D. They have high density

Discussion

93.	Heat flow in unsteady-state heat conduction may be expressed in terms of which of the following two dimensionless numbers?
A.	Nusselt and Fourier numbers
B.	Prandtl and Schmidt numbers
C.	Grashof and Graetz numbers
D.	Biot and Fourier numbers
Answer» E.

Discussion

94.	It is proposed to coat a 1mm diameter wire with enamel paint ( k = 0.1 W/mK) to increase heat transfer with air. If the air side heat transfer co-efficient is 100 W/m2K, the optimal thickness of the enamel paint should be
A.	0.25 mm
B.	0.5 mm
C.	1 mm
D.	2 mm
Answer» C. 1 mm

Discussion

95.	A plastic sleeve of outer radius r0 = 1 mm covers a wire (radius r = 0.5 mm) carrying electric current. Thermal conductivity of the plastic is 0.15 W/m-K. The heat transfer coefficient on the outer surface of the sleeve exposed to air is 25 W/m2-K. Due to the addition of the plastic cover, the heat transfer from the wire to the ambient will
A.	increase
B.	remain the same
C.	decrease
D.	be zero
Answer» B. remain the same

Discussion

96.	A furnace wall is constructed as shown in the figure. The interface temperature T1 will be
A.	560°C
B.	200°C
C.	920°C
D.	1120°C
Answer» D. 1120°C

Discussion

97.	A composite hollow sphere with steady internal heating is made of 2 layers of materials of equal thickness with thermal conductivities in the ratio of 1 : 2 for inner to outer layers. Ratio of inside to outside diameter is 0.8 What is ratio of temperature drop across the inner and outer layers?
A.	0.4
B.	1.6
C.	2 In 0.8
D.	2.5
Answer» E.

Discussion

98.	A thin copper wire at 300° is suddenly immersed in water at 30°C. It cools down to 150°C in 70 seconds. It is then reheated to the initial temperature of 300°C and suddenly exposed to air at 30°C where it cools down to 150°C in 200 seconds. This difference in cooling time is due to
A.	Larger specific heat of water
B.	Larger heat transfer coefficient of water
C.	Smaller heat transfer coefficient of water
D.	None of the above
Answer» C. Smaller heat transfer coefficient of water

Discussion

99.	A hot liquid is kept in a big room. Its temperature (θ) is plotted as a function of time (t), which of the following curve may represent the plot?
A.	Curve d
B.	Curve b
C.	Curve c
D.	Curve a
Answer» E.

Discussion

100.	A building has to be maintained at 21°C (dry bulb) and 14.5°C (wet bulb). The dew point temperature under these conditions is 10.17°C. The outside temperature is -23°C (dry bulb) and the internal and external surface heat transfer coefficients are 8 and 23 W/m2K respectively. If the building wall has a thermal conductivity of 1.2 W/mK, the minimum thickness (in m) of the wall required to prevent condensation is
A.	0.471
B.	0.407
C.	0.321
D.	0.125
Answer» C. 0.321

Discussion

Explore topic-wise MCQs in Heat Transfer.

Lumped heat transfer analysis of a solid object suddenly exposed to a fluid medium at a different temperature is valid when

In a furnace the heat loss through the 150 mm thick refractory wall lining is estimated to be 50 W/m2. If the average thermal conductivity of the refractory material is 0.05 W/mK, the temperature drop across the wall will be:

A solid copper ball of mass 500 gm when quenched in a water bath at 30°C, cools from 530°C to 430°C in 10 sec. What will be the temperature of the ball after the next 10 seconds?

If thermal conductivity of a material of wall varies as k0(1 - αT), the temperature at the center of the wall will be (α is +ve)

For given combined radiative and convective heat transfer coefficient ‘ht’ and given thermal conductivity k, Critical thickness of insulation for cylinder and sphere is given as

A refrigerator with COP of 5 is used in a room at 300 K. What will be the heat intake through a section of refrigerator wall of area 100 cm × 100 cm with a thickness of 10 cm, assuming only conduction? Value of thermal conductivity of the wall can be taken as 1 W/cm.K

Heat pipe is widely used now a days because

A 40 mm diameter electric cable of an Aluminium conductor of thermal conductivity 240 W/mK is to be insulated with rubber of thermal conductivity 0.15 W/mK. The cable is to be located in the air with a heat transfer coefficient of 6 W/m2K. The critical thickness of insulation will be

A dimensionless number associated with transient conduction heat transfer is

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A beaker filled with hot water in a room cools from 70°C to 65°C in t1 minutes, 65°C to 60°C in t2 minutes and from 60°C to 55°C in t3 minutes, then

A 1000 kg vehicle travelling at 80 m/s impacts a plunger attached to a piston-cylinder arrangement. If all of the energy of the vehicle is absorbed by the 20 kg of liquid contained in the cylinder, what is the maximum temperature rise of the liquid? (The specific heat of the liquid is 4.0 kJ/kg°C)

For the same heat transfer, the temperature profile between two metal walls joined together is shown in the figure. if l1 = l2, from the figure it can be concluded that

For a current-carrying wire of 20 mm diameter exposed to air (h = 20 W/m2K), maximum heat distribution occurs when the thickness of insulation (k = 0.5 W/mK) is

An insulated pipe of 50 mm outside diameter with e = 0.8 is laid in a room at 30°C. If the surface temperature is 250°C and the convective heat transfer coefficient is 10 W/m2K, the total heat loss per unit length of the pipe will be

For conduction through a spherical wall with constant thermal conductivity and with inner side temperature greater than outer wall temperature (one-dimensional heat transfer), what is the type of temperature distribution?

A furnace is made of red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. What is the thickness if it is replaced by a layer of diatomite earth of conductivity 0.14 W/mK under the same heat loss per unit area and same temperature drop?

Heat conduction in a semiconductor takes place

Heat is lost steadily through a 0.5 cm thick 2 m × 3 m window glass whose thermal conductivity is 0.7 W/m°C. The inner and outer surface temperatures of the glass are measured to be 12°C to 9°C. The rate of heat loss by conduction through the glass is:

A hot steel spherical ball is suddenly dipped into a low temperature oil bath.Which of the following dimensionless parameters are required to determine instantaneous center temperature of the ball using a Heisler chart?

A metal plate has a surface area of 2 m2, thickness 10 mm and a thermal conductivity of 200 W/m-K. What is the thermal resistance of the plate ?

In a long cylindrical rod of radius R and a surface heat flux of q0, the uniform internal heat generation rate is

In the heat flow equation \(Q = - kA\frac{{{T_1} - {T_2}}}{x},\) x/kA is known as

Assumptions made in Fourier's law is that the heat flowA. Is in steady-stateB. Through a solid medium in one dimension

A wall of thickness 0.6 m and thermal conductivity 0.6 W / m-K has a surface area of 1 m2. If the inner and outer temperature of the wall are 1840°C and 340°C, respectively, the rate of heat transfer will be:

A sphere, a cube and a disc all of the same material, quality and volume are heated to 900 K and left in air. Which of these have the lowest rate of cooling

Conduction takes place due to temperature gradients

Critical thickness of insulation yields

As the temperature increases, the thermal conductivity of a gas

In MLTθ system (T being time and θ temperature), what is the dimension of thermal conductivity?

A 10 kg solid at 100°C with a specific heat, of 0.8 kJ/kg°C is immersed in 40 kg of 20°C liquid with a specific heat of 4.0 kJ/kg°C. Estimate the temperature after a long time if the container is insulated?

Metals are good conductor of heat because

Heat flow in unsteady-state heat conduction may be expressed in terms of which of the following two dimensionless numbers?

It is proposed to coat a 1mm diameter wire with enamel paint ( k = 0.1 W/mK) to increase heat transfer with air. If the air side heat transfer co-efficient is 100 W/m2K, the optimal thickness of the enamel paint should be

A furnace wall is constructed as shown in the figure. The interface temperature T1 will be

A composite hollow sphere with steady internal heating is made of 2 layers of materials of equal thickness with thermal conductivities in the ratio of 1 : 2 for inner to outer layers. Ratio of inside to outside diameter is 0.8 What is ratio of temperature drop across the inner and outer layers?

A thin copper wire at 300° is suddenly immersed in water at 30°C. It cools down to 150°C in 70 seconds. It is then reheated to the initial temperature of 300°C and suddenly exposed to air at 30°C where it cools down to 150°C in 200 seconds. This difference in cooling time is due to

A hot liquid is kept in a big room. Its temperature (θ) is plotted as a function of time (t), which of the following curve may represent the plot?