A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m2K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?

Adding the insulation will increase the heat loss.

The outer radius of the pipe is equal to the critical radius.

The outer radius of the pipe is less than the critical radius.

Adding the insulation will reduce the heat loss.

Adding the insulation will increase the heat loss.

48 + Mcqs in Heat Transfer Miscellaneous in Heat Transfer Page 1 McqOptions

1.	A fluid (Prandt/number, Pr = 1) at 500 K flows over a flat plate of 1.5 m length, maintained at 300 K. The velocity of the fluid is 10 m/s. Assuming kinematic viscosity. = 30 10⁶ m /s, the thermal boundary layer thickness (in mm) at 0.5 m from the leading edge is ______.
A.	m = 6.1237 mm
B.	m = 5.002 mm
C.	m = 7.135 mm
D.	m = 6.958mm
Answer» B. m = 5.002 mm

Discussion

2.	A solid cylinder (surface 2) is located at the centre of a hollow sphere (surface 1). The diameter of the sphere is 1 m, while the cylinder has a diameter and length of 0.5 m each.'The radiation configuration factor F₁₁ is
A.	0.375
B.	0.625
C.	0.75
D.	1
Answer» C. 0.75

Discussion

3.	The properties of mercury at 300 K are: Density = 13529 kg/m , cp = 0.1393 kJ/kgK, dynamic viscosity = 0.1523 10² Ns/m and thermal conductivity = 8.540 W/mK. The Prandtl number of the mercury at 300 K is
A.	0.0248
B.	2.48
C.	24.8
D.	248
Answer» B. 2.48

Discussion

4.	Heat is generated uniformly in a long solid cylindrical rod (diameter =10 mm) at the rate of 4 10⁷ W/m³. The thermal conductivity of the rod material is 25 W/mK. Under steady state conditions, the temperature ditference between the centre and the surface of the rod is 1 C.
A.	-10 C
B.	10 C
C.	-11 C
D.	-9 C
Answer» B. 10 C

Discussion

5.	A plane wall has a thermal conductivity of 1.15 W/mK. If the inner surface is at 1100 C and the outer surface is at 350 C, then the design thickness (in meter) of the wall to maintain a steady heat flux of 2500 W/m² should be
A.	0.345 m.
B.	0.245 m.
C.	1.145 m.
D.	1.345 m.
Answer» B. 0.245 m.

Discussion

6.	A cylindrical uranium fuel rod of radius 5 mm in a nuclear is generating heat at the rate of 4 107 W/m³. The rod is cooled by a liquid (convective heat transfer coefficient 1000 W/ m²K) at 25 C. At steady state, the surface temperature (in K) of the rod is
A.	308
B.	398
C.	418
D.	448
Answer» C. 418

Discussion

7.	A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m²K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?
A.	The outer radius of the pipe is equal to the critical radius.
B.	The outer radius of the pipe is less than the critical radius.
C.	Adding the insulation will reduce the heat loss.
D.	Adding the insulation will increase the heat loss.
Answer» D. Adding the insulation will increase the heat loss.

Discussion

8.	The ratios of the laminar hydrodynamic boundary layer thickness to thermal boundary layer thickness of flows of two fluids P and Q on a flat plate are 1/2 and 2 respectively. The Reynolds number based on the plate length for both the flows is 10⁴. The Prandtl and Nusselt numbers for P are 1/8 and 35 respectively. The Prandlt and Nusselt numbers for Q are respectively
A.	8 and 140
B.	8 and 70.
C.	4 and 70
D.	4 and 35
Answer» B. 8 and 70.

Discussion

9.	The total e-missive power of a surface is 500 W/ m² at temperature T₁ and 1200 W/m² at temperature T₂, where the temperature are in Kelvin. Assuming the e-missivity of the surface to be constant, the ratio of the temperature T₁ /T₂ is
A.	0.0308
B.	0.416
C.	0.803
D.	0.874
Answer» D. 0.874

Discussion

10.	If q"w = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m²K, the temperature in C at the inner surface of the pipe at the outlet is
A.	71
B.	76
C.	79
D.	81
Answer» E.

Discussion

11.	Two large parallel plates having a gap of 10 mm in between them are maintained at temperatures T₁, = 1000 K and T₂ = 400 K. Given emissivity values, ₁ = 0.5, ₂ = 0.25 and Stefan-Boltzmann constant = 5.67 10^-8 W/ m²K⁴, the heat transfer between the plates (in kW/m²) is ______
A.	11.049
B.	11.041
C.	11.042
D.	11.0
Answer» B. 11.041

Discussion

12.	A slender rod of length L, diameter d (L >> d) and thermal conductivity k₁ i s joined with another rod of identical dimensions, but of thermal conductivity k 2, to form a composite cylindrical rod of length 2L. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is
A.	K
B.	K
C.	K
D.	+ K
Answer» B. K

Discussion

13.	A balanced counter flow heat exchanger has a surface area of 20 m² and overall heat transfer coefficient of 20 W/m2K. Air (c_p = 1000 J/kgK) entering at 0.4 kg/s and 280 K is to be preheated by the air leaving the system at 0.4 kg/s and 300 K. The temperature (in K) of the preheated air is
A.	290
B.	300
C.	320
D.	350
Answer» B. 300

Discussion

14.	Consider a parallel-flow heat exchanger with area A_p and a counter-flow heat exchanger with area A_c. In both the heat exchangers, the hot stream flowing at 1 kg/s cools from 80 C to 50 C. For the cold stream in both the heat exchangers, the flow rate and the inlet temperature are 2 kg/s and 10 C, respectively. The hot and cold streams in both the heat exchangers are of the same fluid. Also, both the heat exchangers have the same overall heat transfer coefficient. The ratio A_c /A_p is _____.
A.	0.927
B.	0.244
C.	0.945
D.	0.955
Answer» B. 0.244

Discussion

15.	In a counter-flow heat exchanger, water is heated at the rate of 1.5 kg/s from 40 C to 80 C by an oil entering at 120 C and leaving at 60 C. The specific heats of water and oil are 4.2 kJ/ kgK and 2 kJ/kgK, respectively. The overall heat transfer coefficient is 400 W/m²K. The required heat transfer surface area (in m²) is
A.	0.104
B.	0.022
C.	10.4
D.	21.84
Answer» E.

Discussion

16.	Steam in the condenser of a thermal power plant is to be condensed at a temperature of 30 C with cooling water which enters the tubes of the condenser at 14 C and exits at 22 C. The total surface area of the tubes is 50 m², and the overall heat transfer coefficient is 2000 W/ m². The heat transfer (in MW) to the condenser is ______(correct to two decimal places).
A.	1.154
B.	1.150
C.	1.159
D.	1.15
Answer» B. 1.150

Discussion

17.	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 0.12 W/mK. The heat transfer coefficient on the outer surface of the sleeve exposed to air is 25 W/m²K. 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

18.	A brick wall (k = 0.9 W/mK) of thickness 0.18 m separates the warm air in a room from the cold ambient air. On a particular Winter day, the outside air temperature is - 5 C and the room needs to be maintained at 27 C. The heat transfer coefficient associated with outside air is 20 W/m²K. Neglecting the convective resistance of the air inside the room, the heat loss, in (W/m²), is
A.	88
B.	110
C.	128
D.	160
Answer» D. 160

Discussion

19.	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/kgK, 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

20.	A spherical thermocouple junction of diameter 0.706 mm is to be used for the measurement of temperature of a gas stream. The convective heat transfer coefficient on bead surface is 400 W/m²K, Thermophysical properties of thermocouple material are k = 20 W/mK, c = 400 J/kgK and = 8500 kg/m³. If the thermocouple initially at 30 C is placed in a hot stream of 300 C, the time taken by the bead to reach 298 C, is
A.	2.35 s
B.	4.9 s
C.	14.7 s
D.	29.4 s
Answer» C. 14.7 s

Discussion

21.	A cylindrical steel rod, 0.01 m in diameter and 0.2 m in length is first heated to 750 C and then immersed in a water bath at 100 C. The heat transfer coefficient is 250 W/m²K. The density, specific heat and thermal conductivity of steel are = 7801 kg/m³, c = 473 J/kgK, and k = 43 W/mK, respectively. The time required for the rod to reach 300 C is ______ seconds.
A.	413.49
B.	34.49
C.	43.49
D.	None of these
Answer» D. None of these

Discussion

22.	A small copper ball of 5 mm diameter at 500 K is dropped into an oil bath whose temperature is 300 K. The thermal conductivity of copper is 400 W/mK, its density 9000 kg/m³ and its specific heat 385 J/kgK. If the heat transfer coefficient is 250 W/m²K and lumped analysis is assumed to be valid, the rate of fall of the temperature of the ball at the beginning of cooling will be, in K/s,
A.	8.7
B.	13.9
C.	17.3
D.	27.7
Answer» D. 27.7

Discussion

23.

Two cylindrical shafts A and B at the same initial temperature are simultaneously placed in a furnace. The surfaces of the shafts remain at the furnace gas temperature at all times after they are introduced into the furnace. The temperature variation in the axial direction of the shafts can be assumed to be negligible. The data related to shafts A and B is given in the following Table.
Quantity Shaft A Shaft B
Diameter (m) 0.4 0.1
Thermal Conductivity (W/mK) 40 20
Volumetric heat capacity (J/m³K) 2 10⁶ 2 10⁷

The temperature at the centerline of the shaft A reaches 400 C after two hours. The time required (in hours) for the centerline of the shaft B to attain the temperature of 400 C is ____.

A.

12.5 hrs

B.

2.5 hrs

C.

1.5 hrs

D.

3 hrs

Answer» C. 1.5 hrs

Discussion

24.	The average heat transfer coefficient on a thin hot vertical -plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assume the plate temperature to be uniform at any instant of time and radiation heat exchange with the surroundings negligible. The ambient temperature is 25 C, the plate has a total surface area of 0.1 m² and a mass of 4 kg. The specific heat of the plate material is 2.5 kJ/kgK. The convective heat transfer coefficient in W/m²K, at the instant when the plate temperature is 225 C and the change in plate temperature with time dT/dt = 0.02 K/s, is
A.	200
B.	20
C.	15
D.	10
Answer» B. 20

Discussion

25.	A steel ball of 10 mm diameter at 1000 K is required to be cooled to 350 K by immersing it in a water environment at 300 K. The convective heat transfer coefficient is 1000 W/m²K. Thermal conductivity of steel is 40 W/m K. The time constant for the cooling process is 16 s. The time required (in s) to reach the final temperature is
A.	42.2249 sec
B.	412.2249 sec
C.	142.2249 sec
D.	None of the above
Answer» B. 412.2249 sec

Discussion

26.

Saturated vapor is condensed to saturated liquid in a condenser. The heat capacity ratio
is C_r = C_min . The effectiveness ( ) of the condenser is
C_max

A.

1 - exp[ -NTU ]

Answer» E.

Discussion

27.	A stainless steel tube (k_s = 19 W/mK) of 2 cm ID and 5 cm OD is insulated with 3 cm thick asbestos (k_a = 0.2 W/mK). If the temperature difference between the inner most and outermost surfaces is 600 C, the heat transfer rate per unit length is
A.	0.94 W/m
B.	9.44 W/m
C.	944.72 W/m
D.	9447.21 W/m
Answer» D. 9447.21 W/m

Discussion

28.	In a parallel flow heat exchanger operating under steady state, the heat capacity rates (product of specific heat at constant pressure and mass flow rate) of the hot and cold fluid are equal. The hot fluid, flowing at 1 kg/s with cp = 4 kJ/kgK, enters the heat exchanger at 102 C while the cold fluid has an inlet temperature of 15 C. The overall heat transfer coefficient for the heat exchanger is estimated to be 1 kW/m²K and the corresponding heat transfer surface area is 5 m². Neglect heat transfer between the heat exchanger and the ambient. The heat exchanger is characterized by the following relation: 2 = 1 expt( 2NTU). The exit temperature (in C) for the cold fluid is
A.	45
B.	55
C.	65
D.	75
Answer» C. 65

Discussion

29.	Heat is being transferred conductivity from a cylindrical nuclear reactor fuel rod of 50 mm diameter to water at 75 C, under steady state condition, the rate of heat generation within the fuel element is 106 W/m³ and the convective heat transfer coefficient is 1 kW/m²K, the outer surface temperature of the fuel element would be
A.	700 K
B.	625 K
C.	360 K
D.	400 K
Answer» D. 400 K

Discussion

30.	Hot and cold fluids enter a parallel flow double t ube heat exchanger at 100 C and 15 C, respectively. The heat capacity rates of hot and cold fluids are C_h = 2000 W/K and C_c = 1200 W/ K, respectively. If the outlet temperature of the cold fluid is 45 C, the log mean temperature difference (LMTD) of the heat exchanger is _____ K (round off to two decimal places).
A.	5.771 C or K
B.	517.71 C or K
C.	157.71 C or K
D.	57.71 C or K
Answer» E.

Discussion

31.	A double pipe counter flow heat exchanger transfers heat between two water streams. Tube side water at 19 litre/s is heated frim 10 C to 38 C. Shell side water at 25 litre/s is entering at 46 C Assume constant properties of water, density is 1000 kg/m³ and specific heat is 4186 J/kgK. The LMTD (in C) is ____.
A.	11.0206 C
B.	11.06 C
C.	11.0 C
D.	None of these
Answer» B. 11.06 C

Discussion

32.	Sphere 1 with a diameter of 0.1 m is completely enclosed by another sphere 2 of diameter 0.4 m. The view factor F₁₂ is
A.	0.0625
B.	0.25
C.	0.5
D.	1.0
Answer» E.

Discussion

33.	A plate having 10 cm² area each side is hanging in the middle of a room of 100 m² total surface area. The plate temperature and emissivity are respectively 800 K and 0.6. The temperature and emissivity value for the surfaces of the room are 300 K and 0.3 respectively. Boltzmann's constant = 5.67 10^-8 W/m²K⁴. The total heat loss from the two surfaces of the plate is
A.	13.66 W
B.	27.32 W
C.	27.87 W
D.	13.66 MW
Answer» C. 27.87 W

Discussion

34.	Consider the radiation heat exchange inside an annulus between two very long concentric cylinders. The radius of the outer cylinder is R₀ and that of the inner cylinder is R_i. The radiation view factor of the outer cylinder onto itself is
A.	1 -
B.
Answer» E.

Discussion

35.	The irradiation (in kW/m²) for the plate (plate 1) is
A.	2.5
B.	3.6
C.	17.0
D.	19.5
Answer» E.

Discussion

36.	If plate 1 is also a diffuse and Gray surface with an emissivity value of 0.8, the net radiatibn heat exchange (in kW/m²) between plate 1 and plate 2 is
A.	17.0
B.	19.5
C.	23.0
D.	31.7
Answer» E.

Discussion

37.	Two large diffuse Gray parallel plates, separated by a small distance, have surface temperature of 400 K and 300 K. If the emissivities of the surfaces are 0.8 and the Stefan-Boltzmann constant is 5.67 10^-8W/m²K⁴, the net radiation heat exchange rate in kW/m² between the two plates is
A.	0.66
B.	0.79
C.	0.99
D.	3.96
Answer» B. 0.79

Discussion

38.	A hemispherical furnace of 1 m radius has the inner surface (emissivity, = 1) of its roof maintained at 800 K, while its floor ( = 0.5) is kept at 600 K. Stefan-Boltzmann constant is 5.668 110^-8W/m²K⁴. The net radiative heat transfer (in kW) from the roof to the floor is _______.
A.	22 kW.
B.	25 kW.
C.	24.9 kW.
D.	24. kW.
Answer» D. 24. kW.

Discussion

39.	A fin has 5 mm diameter and 100 mm length. The thermal conductivity of fin material is 400 Wm¹K¹. One end of the fin is maintained at 130 C and its remaining surface is exposed to ambient air at 30 C. If the convective heat transfer coefficient is 40 Wm²K¹, the heat loss (in W) from the fin is
A.	0.08
B.	5.0
C.	7.0
D.	7.8
Answer» C. 7.0

Discussion

40.	In a heat exchanger, it is observed that T₁ = T₂ where T₁ is the temperature difference between the two single phase fluid streams at one end and T₂ is the temperature difference at the other end. This heat exchanger is
A.	a condenser
B.	an evaporator
C.	a counter flow heat exchanger
D.	a parallel flow heat exchanger
Answer» D. a parallel flow heat exchanger

Discussion

41.	Cold water flowing at 0.1 kg/s is heated from 20 C to 70 C in a counter flow type heat exchange by a hot water stream flowing at 0.1 kg/s and entering at 90 C. The specific heat of water is 4200 J/(kgK) and density is 1000 kg/m³ . If the overall heat transfer coefficient U for the heat exchange is 2000 W/(m² K), the required heat exchange area (in m² ) is
A.	0.052
B.	0.525
C.	0.151
D.	0.202
Answer» C. 0.151

Discussion

42.

Match List-I with List-ll and select the correct answer using the code given below the lists:
List-I List-II
A. Grashof number 1. Mass diffusion
B. Schmidt number 2. Transient heat conduction
C. Weber number 3. Free convection
D. Fourier number 4. Forced convection
5. Surface tension
6. Radiation

A.

A - 4 , B - 2 , C - 3 , D - 5

B.

A - 3 , B - 1 , C - 5 , D - 2

C.

A - 5 , B - 1 , C - 2 , D - 4

D.

A - 1 , B - 2 , C - 5 , D - 4

Answer» C. A - 5 , B - 1 , C - 2 , D - 4

Discussion

43.	The radiative heat transfer rate per unit area (W/m²) between two plane parallel gray surfaces (emissivity = 0.9) maintained at 400 K and 300 K is ( = Stefan Boltzmann constant = 5.67 10⁸ W/m²K⁴)
A.	992
B.	812
C.	464
D.	567
Answer» C. 464

Discussion

44.	The heat transfer coefficient h in w/m²K is
A.	0.0
B.	4.8
C.	6
D.	750
Answer» E.

Discussion

45.

Match Group with Group B:
Group A Group B
A: Biot number 1: Ratio of buoyancy to viscous force
B: Grashoff number 2: Ratio of inertia force to viscous force
C: Prandtl number 3: Ratio of momentum to thermal diffusivities
D: Reynolds number 4: Ratio of internal thermal resistance to boundary layer thermal resistance

A.

A - 4 , B - 1 , C - 3 , D - 2

B.

A - 4 , B - 3 , C - 1 , D - 2

C.

A - 3 , B - 2 , C - 1 , D - 4

D.

A - 2 , B - 1 , C - 3 , D - 4

Answer» B. A - 4 , B - 3 , C - 1 , D - 2

Discussion

46.

Match the property with their units
Property Units
A. Bulk modulus 1. W/s
B. Thermal conductivity 2. N/m²
C. Heat transfer coefficient 3. N/m³
D. Heat flow rate 4. W
5. W/mK
6. W/m²K

A.

A - 1 , B - 2 , C - 6 , D - 5

B.

A - 2 , B - 5 , C - 6 , D - 1

C.

A - 2 , B - 6 , C - 4 , D - 1

D.

A - 1 , B - 5 , C - 3 , D - 2

Answer» C. A - 2 , B - 6 , C - 4 , D - 1

Discussion

47.	A fluid flowing over a flat plate has the following properties: dynamic viscosity = 25 10⁶ kg/ ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be
A.	0.1 mm
B.	0.5 mm
C.	1.0 mm
D.	None of these
Answer» C. 1.0 mm

Discussion

48.	Water flows through a tube of diameter 25 mm at an average velocity of 1.0 m/s. The properties of water are = 1000 kg/m³, = 7.25 104 Ns/m , k = 0.625 W/mK, Pr = 4.85. Using Nu = 0.023 Re^0.8 Pr^0.4, the convective heat transfer coefficient (inW/m K) is _______
A.	None of the above
Answer» B.

Discussion

Explore topic-wise MCQs in Heat Transfer.

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Heat is generated uniformly in a long solid cylindrical rod (diameter =10 mm) at the rate of 4 107 W/m3. The thermal conductivity of the rod material is 25 W/mK. Under steady state conditions, the temperature ditference between the centre and the surface of the rod is 1 C.

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A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m2K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?

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Saturated vapor is condensed to saturated liquid in a condenser. The heat capacity ratio is Cr = Cmin . The effectiveness ( ) of the condenser isCmax

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Sphere 1 with a diameter of 0.1 m is completely enclosed by another sphere 2 of diameter 0.4 m. The view factor F12 is

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The irradiation (in kW/m2) for the plate (plate 1) is

If plate 1 is also a diffuse and Gray surface with an emissivity value of 0.8, the net radiatibn heat exchange (in kW/m2) between plate 1 and plate 2 is

Two large diffuse Gray parallel plates, separated by a small distance, have surface temperature of 400 K and 300 K. If the emissivities of the surfaces are 0.8 and the Stefan-Boltzmann constant is 5.67 10-8W/m2K4, the net radiation heat exchange rate in kW/m2 between the two plates is

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The radiative heat transfer rate per unit area (W/m2) between two plane parallel gray surfaces (emissivity = 0.9) maintained at 400 K and 300 K is ( = Stefan Boltzmann constant = 5.67 10 8 W/m2K4)

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A fluid flowing over a flat plate has the following properties: dynamic viscosity = 25 10 6 kg/ ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be

Water flows through a tube of diameter 25 mm at an average velocity of 1.0 m/s. The properties of water are = 1000 kg/m3, = 7.25 104 Ns/m , k = 0.625 W/mK, Pr = 4.85. Using Nu = 0.023 Re0.8 Pr0.4, the convective heat transfer coefficient (inW/m K) is _______

A fluid (Prandt/number, Pr = 1) at 500 K flows over a flat plate of 1.5 m length, maintained at 300 K. The velocity of the fluid is 10 m/s. Assuming kinematic viscosity. = 30 10⁶ m /s, the thermal boundary layer thickness (in mm) at 0.5 m from the leading edge is ______.

A solid cylinder (surface 2) is located at the centre of a hollow sphere (surface 1). The diameter of the sphere is 1 m, while the cylinder has a diameter and length of 0.5 m each.'The radiation configuration factor F₁₁ is

The properties of mercury at 300 K are: Density = 13529 kg/m , cp = 0.1393 kJ/kgK, dynamic viscosity = 0.1523 10² Ns/m and thermal conductivity = 8.540 W/mK. The Prandtl number of the mercury at 300 K is

Heat is generated uniformly in a long solid cylindrical rod (diameter =10 mm) at the rate of 4 10⁷ W/m³. The thermal conductivity of the rod material is 25 W/mK. Under steady state conditions, the temperature ditference between the centre and the surface of the rod is 1 C.

A plane wall has a thermal conductivity of 1.15 W/mK. If the inner surface is at 1100 C and the outer surface is at 350 C, then the design thickness (in meter) of the wall to maintain a steady heat flux of 2500 W/m² should be

A cylindrical uranium fuel rod of radius 5 mm in a nuclear is generating heat at the rate of 4 107 W/m³. The rod is cooled by a liquid (convective heat transfer coefficient 1000 W/ m²K) at 25 C. At steady state, the surface temperature (in K) of the rod is

A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m²K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?

The total e-missive power of a surface is 500 W/ m² at temperature T₁ and 1200 W/m² at temperature T₂, where the temperature are in Kelvin. Assuming the e-missivity of the surface to be constant, the ratio of the temperature T₁ /T₂ is

If q"w = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m²K, the temperature in C at the inner surface of the pipe at the outlet is

Two large parallel plates having a gap of 10 mm in between them are maintained at temperatures T₁, = 1000 K and T₂ = 400 K. Given emissivity values, ₁ = 0.5, ₂ = 0.25 and Stefan-Boltzmann constant = 5.67 10^-8 W/ m²K⁴, the heat transfer between the plates (in kW/m²) is ______

A balanced counter flow heat exchanger has a surface area of 20 m² and overall heat transfer coefficient of 20 W/m2K. Air (c_p = 1000 J/kgK) entering at 0.4 kg/s and 280 K is to be preheated by the air leaving the system at 0.4 kg/s and 300 K. The temperature (in K) of the preheated air is

Saturated vapor is condensed to saturated liquid in a condenser. The heat capacity ratio
is C_r = C_min . The effectiveness ( ) of the condenser is
C_max

A stainless steel tube (k_s = 19 W/mK) of 2 cm ID and 5 cm OD is insulated with 3 cm thick asbestos (k_a = 0.2 W/mK). If the temperature difference between the inner most and outermost surfaces is 600 C, the heat transfer rate per unit length is

Sphere 1 with a diameter of 0.1 m is completely enclosed by another sphere 2 of diameter 0.4 m. The view factor F₁₂ is

Consider the radiation heat exchange inside an annulus between two very long concentric cylinders. The radius of the outer cylinder is R₀ and that of the inner cylinder is R_i. The radiation view factor of the outer cylinder onto itself is

The irradiation (in kW/m²) for the plate (plate 1) is

If plate 1 is also a diffuse and Gray surface with an emissivity value of 0.8, the net radiatibn heat exchange (in kW/m²) between plate 1 and plate 2 is

Two large diffuse Gray parallel plates, separated by a small distance, have surface temperature of 400 K and 300 K. If the emissivities of the surfaces are 0.8 and the Stefan-Boltzmann constant is 5.67 10^-8W/m²K⁴, the net radiation heat exchange rate in kW/m² between the two plates is

A hemispherical furnace of 1 m radius has the inner surface (emissivity, = 1) of its roof maintained at 800 K, while its floor ( = 0.5) is kept at 600 K. Stefan-Boltzmann constant is 5.668 110^-8W/m²K⁴. The net radiative heat transfer (in kW) from the roof to the floor is _______.

A fin has 5 mm diameter and 100 mm length. The thermal conductivity of fin material is 400 Wm¹K¹. One end of the fin is maintained at 130 C and its remaining surface is exposed to ambient air at 30 C. If the convective heat transfer coefficient is 40 Wm²K¹, the heat loss (in W) from the fin is

In a heat exchanger, it is observed that T₁ = T₂ where T₁ is the temperature difference between the two single phase fluid streams at one end and T₂ is the temperature difference at the other end. This heat exchanger is

Match List-I with List-ll and select the correct answer using the code given below the lists:
List-I List-II
A. Grashof number 1. Mass diffusion
B. Schmidt number 2. Transient heat conduction
C. Weber number 3. Free convection
D. Fourier number 4. Forced convection
5. Surface tension
6. Radiation

The radiative heat transfer rate per unit area (W/m²) between two plane parallel gray surfaces (emissivity = 0.9) maintained at 400 K and 300 K is ( = Stefan Boltzmann constant = 5.67 10⁸ W/m²K⁴)

The heat transfer coefficient h in w/m²K is

Match the property with their units
Property Units
A. Bulk modulus 1. W/s
B. Thermal conductivity 2. N/m²
C. Heat transfer coefficient 3. N/m³
D. Heat flow rate 4. W
5. W/mK
6. W/m²K

A fluid flowing over a flat plate has the following properties: dynamic viscosity = 25 10⁶ kg/ ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be

Water flows through a tube of diameter 25 mm at an average velocity of 1.0 m/s. The properties of water are = 1000 kg/m³, = 7.25 104 Ns/m , k = 0.625 W/mK, Pr = 4.85. Using Nu = 0.023 Re^0.8 Pr^0.4, the convective heat transfer coefficient (inW/m K) is _______