| 26. | Logarithmic mean area of the cylindrical tube is given as |
| a. | 2πrm |
| b. | πrml |
| c. | 2πrml |
| d. | 2rml |
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Answer: (c).2πrml
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| 27. | A hot fluid is being conveyed 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 further covering with same insulation. Calculate the additional thickness of insulation |
| a. | 11 cm |
| b. | 12 cm |
| c. | 13 cm |
| d. | 14 cm |
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Answer: (b).12 cm
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| 28. | The heat flow equation through a cylinder of inner radius r1 and outer radius r2 is desired to be written in the same form as that for heat flow through a plane wall. For wall thickness (r₂-r₁) the area will be |
| a. | A1 + A2/2 |
| b. | A1 + A2 |
| c. | A2 – A1/ log e (A2/A1) |
| d. | A1 + A2/2 log e (A2/A1) |
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Answer: (a).A1 + A2/2
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| 29. | A cylinder of radius r and made of material of thermal conductivity k 1 is surrounded by a cylindrical shell of inner radius r and outer radius 2r. This outer shell is made of a material of thermal conductivity k 2. Net conductivity would be |
| a. | k 1 + 3 k 2/4 |
| b. | k 1 + k 2/4 |
| c. | k 1 + 3k 2 |
| d. | k 1 + k 2 |
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Answer: (a).k 1 + 3 k 2/4
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| 30. | For steady state and constant value of thermal conductivity, the temperature distribution associated with radial convection through a cylinder is |
| a. | Linear |
| b. | Parabolic |
| c. | Logarithmic |
| d. | Exponential |
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Answer: (c).Logarithmic
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