MCQOPTIONS
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MCQOPTIONS
This section includes 75 Mcqs, each offering curated multiple-choice questions to sharpen your Heat Transfer knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
The value of correction length for equilateral fin is |
| A. | L C = 2 L + a/4(3)^1/2 |
| B. | L C = L + a/4(3)^1/2 |
| C. | L C = 3 L + a/4(3)^1/2 |
| D. | L C = 6 L + a/4(3)^1/2 |
| Answer» C. L C = 3 L + a/4(3)^1/2 | |
| 52. |
The parameter m = (h P/k A C)^1/2 has been stated to increase in a long fin. If all other parameters are constant, then |
| A. | Profile of temperature will remain the same |
| B. | Along the length temperature drop will be less |
| C. | The parameter influences the heat flow only |
| D. | The temperature drop along the length will be steeper |
| Answer» E. | |
| 53. |
A rod of 10 mm square section and 160 mm length with thermal conductivity of 50W/m K protrudes from a furnace wall at 200 degree Celsius with convective coefficient 20 W/ square m K. Make calculations for the heat convective up to 80 mm length |
| A. | 6.84W |
| B. | 7.34W |
| C. | 4.54W |
| D. | 5.47W |
| Answer» B. 7.34W | |
| 54. |
A fin protrudes from a surface which is held at a temperature higher than that of its environment. The heat transferred away from the fin is |
| A. | Heat escaping from the tip of the fin |
| B. | Heat conducted along the fin length |
| C. | Convective heat transfer from the fin surface |
| D. | Sum of heat conducted along the fin length and that convected from the surface |
| Answer» D. Sum of heat conducted along the fin length and that convected from the surface | |
| 55. |
The relevant boundary conditions in case of heat dissipation from a fin insulated at the tip are |
| A. | t = t₀ at x = 0 and d t/d x = 0 at x = 0 |
| B. | t = t₀ at x = 0 and d t/d x = 0 at x = 1 |
| C. | t = t₀ at x = 1 and d t/d x = 0 at x = 1 |
| D. | t = t₀ at x = infinity and d t/d x = 0 at x = infinity |
| Answer» C. t = t₀ at x = 1 and d t/d x = 0 at x = 1 | |
| 56. |
An electronic semiconductor device generates 0.16 k J/hr of heat. To keep the surface temperature at the upper safe limit of 75 degree Celsius, it is desired that the heat generated should be dissipated to the surrounding environment which is at 30 degree Celsius. The task is accomplished by attaching aluminum fins, 0.5 square mm and 10 mm to the surface. Work out the number of fins if thermal conductivity of fin material is 690W/m K and the heat transfer coefficient is 45k J/square m hr K. Neglect the heat loss from the tip of the fin |
| A. | 4 |
| B. | 3 |
| C. | 2 |
| D. | 1 |
| Answer» B. 3 | |
| 57. |
The temperature distribution in case of fin insulated at the tip is given by |
| A. | t – t₀/t₀ – t a = cos h m (3 – x)/cos ml |
| B. | t – t₀/t₀ – t a = cos h m (2 – x)/sin h ml |
| C. | t – t₀/t₀ – t a = cos h m (l – x)/cos h ml |
| D. | t – t₀/t₀ – t a = cos m (l – x)/sin ml |
| Answer» D. t – t₀/t₀ – t a = cos m (l – x)/sin ml | |
| 58. |
“Fin is insulated at the tip”. What does that mean? |
| A. | Less heat is transferred from the tip |
| B. | Heat will transferred from tip only |
| C. | More heat is transferred from the tip |
| D. | No heat is transferred from the tip |
| Answer» E. | |
| 59. |
Find the heat transfer rate from a hot surface for 6 fins of 10 cm length? The base temperature of the fin is maintained at 200 degree Celsius and the film is exposed to a convection environment at 15 degree Celsius with convective coefficient 25W/square m K. Each fin has cross-sectional area 2.5 square centimeter and is made of a material having thermal conductivity 250W/m K |
| A. | 120.34W |
| B. | 130.18W |
| C. | 145.46W |
| D. | 165.43W |
| Answer» C. 145.46W | |
| 60. |
The rate of heat transfer from the fin in case of fin insulated at the tip is |
| A. | (h P k A)^1/2 (t₀ – t a) tan h ml |
| B. | (h k A)^1/2 (t₀ – t a) tan h ml |
| C. | (h P A)^1/2 (t₀ – t a) tan h ml |
| D. | (h P k)^1/2 (t₀ – t a) tan h ml |
| Answer» B. (h k A)^1/2 (t₀ – t a) tan h ml | |
| 61. |
Two long rods A and B of the same diameter have thermal conductivities k and 4k and have one of their end inserted into a furnace at 400 K. At 9.5 m away section from the furnace, the temperature of rod B is120 degree Celsius. So find out at what end from the furnace end, the same temperature would be reached in the rod A? |
| A. | 0.25 m |
| B. | 0.75 m |
| C. | 0.15 m |
| D. | 0.50 m |
| Answer» B. 0.75 m | |
| 62. |
Three fins of equal length and diameter but made of aluminum, brass and cast iron is heated to 200 degree Celsius at one end. If the fins dissipate heat to the surrounding air at 25 degree Celsius, the temperature at the free end will be least in |
| A. | 1/ml |
| B. | 2/ml |
| C. | Aluminum fin |
| D. | 4/ml |
| Answer» D. 4/ml | |
| 63. |
The following factors need consideration for the optimum design of fins(i) Cost(ii) Space considerations(iii) Weight considerationsChoose the correct option |
| A. | 1 only |
| B. | 1 and 2 only |
| C. | 1, 2 and 3 |
| D. | 2 only |
| Answer» D. 2 only | |
| 64. |
A heating unit is made in the form of a vertical tube of 50 mm outside diameter and 1.2 m height. The tube is fitted with 20 steel fins of rectangular section with height 40 mm and thickness 2.5 mm. The temperature at the base of fin is 75 degree Celsius, the surrounding air temperature is 20 degree Celsius and the heat transfer coefficient between the fin as well as the tube surface and the surrounding air is 9.5 W/m² K. If thermal conductivity of the fin material is 55 W/m K, find the amount of heat transferred from the tube with fin |
| A. | 1234 .98 W |
| B. | 1004.84 W |
| C. | 6539.83 W |
| D. | 3829.46 W |
| Answer» C. 6539.83 W | |
| 65. |
The fins would be effective for heat conduction if the ratio P k/h A C is |
| A. | Greater than 5 |
| B. | Less than 5 |
| C. | Equal to 5 |
| D. | Varies between 2 to 9 |
| Answer» B. Less than 5 | |
| 66. |
For a straight rectangular fin of thickness δ and width b, choose the correct option |
| A. | P/A C = 1/ δ |
| B. | P/A C = 2/ δ |
| C. | P/A C = 3/ δ |
| D. | P/A C = 4/ δ |
| Answer» C. P/A C = 3/ δ | |
| 67. |
“Effectiveness of fin is the ratio of the fin heat dissipation with fin to that of no fin”. Choose the correct answer |
| A. | True |
| B. | False |
| C. | May be |
| D. | Can't say |
| Answer» B. False | |
| 68. |
For a fin of finite length with an insulated end, the fin efficiency is given as |
| A. | tan h (ml) |
| B. | tan (ml)/ml |
| C. | tan h (m)/ml |
| D. | tan h (ml)/ml |
| Answer» E. | |
| 69. |
For an infinitely long fin, the effectiveness of fin is given as |
| A. | (P k/h AC) |
| B. | (P k/h AC)^3/2 |
| C. | (P k/h AC)^1/2 |
| D. | (P k/h AC)^2 |
| Answer» D. (P k/h AC)^2 | |
| 70. |
For an infinitely long fin, the efficiency of fin is given by |
| A. | 1/ml |
| B. | 2/ml |
| C. | 3/ml |
| D. | 4/ml |
| Answer» B. 2/ml | |
| 71. |
It is said that fins can take a variety of forms(i) Longitudinal fins of rectangular cross section attached to a wall(ii) Cylindrical tubes with radial fins(iii) Conical rod protruding from a wallIdentify the correct statement |
| A. | 1 only |
| B. | 1 and 2 |
| C. | 2 and 3 |
| D. | 1, 2 and 3 |
| Answer» E. | |
| 72. |
The extended surface used for the enhancement of heat dissipation is |
| A. | Convective coefficient |
| B. | Fourier number |
| C. | Fin |
| D. | No finned surface |
| Answer» D. No finned surface | |
| 73. |
A very long copper rod 20 mm in diameter extends horizontally from a plane heated wall maintained at 100 degree Celsius. The surface of the rod is exposed to an air environment at 20 degree Celsius with convective heat transfer coefficient of 8.5 W/m² degree. Workout the heat loss if the thermal conductivity of copper is 400 W/m degree |
| A. | 10.71 W |
| B. | 20.71 W |
| C. | 30.71 W |
| D. | 40.71 W |
| Answer» C. 30.71 W | |
| 74. |
Common applications of finned surfaces are with(i) Electrical motors(ii) Economizers for steam power plant(iii) Convectors for steam and cold water heating systems(iv) Cooling coilsIdentify the correct option |
| A. | 1, 2 and 4 |
| B. | 1, 2 and 3 |
| C. | 1, 2, 3 and 4 |
| D. | 1 and 2 |
| Answer» B. 1, 2 and 3 | |
| 75. |
A steel rod (k = 30 W/m degree) 1 cm in diameter and 5 cm long protrudes from a wall which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an environment with h = 50 W/m² degree and t a = 30 degree Celsius. Calculate the fin efficiency |
| A. | 56.57% |
| B. | 66.57% |
| C. | 76.57% |
| D. | 86.57% |
| Answer» C. 76.57% | |