Heat Transfer

51. n counter flow heat exchangers

1. both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
2. both the fluids at inlet are in their hottest state
3. both the fluids .at exit are in their hottest state
4. one fluid is in hottest state and other in coldest state at inlet
5. any combination is possible depending on design of heat exchanger.

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52. n free con-vection heat transfer, Nusselt number is function of

1. Grashoff no. and Reynold no.
2. Grashoff no. and Prandtl no.
3. Prandtl no. and Reynold no.
4. Grashoff no., Prandtl no. and Reynold no.
5. none of the above.

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53. n heat exchangers, degree of approach is defined as the difference between temperatures of

1. cold water inlet and outlet
2. hot medium inlet and outlet
3. hot medium outlet and cold water inlet
4. hot medium outlet and cold water outlet
5. none of the above.

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54. n regenerator type heat exchanger, heat transfer takes place by

1. direct mixing of hot and cold fluids
2. a complete separation between hot and cold fluids
3. flow of hot and cold fluids alternately over a surface
4. generation of heat again and again
5. indirect transfer.

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55. og mean temperature difference in case of counter flow compared to parallel flow will be

1. same
2. more
3. less
4. depends on other factors
5. none of the above.

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56. otal emissivity of polished silver compared to black body is

1. same
2. higher
3. more or less same
4. very much lower
5. very much higher.

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57. oule sec is the unit of

1. universal gas constant
2. kinematic viscosity
3. thermal conductivity
4. Planck's constant
5. none of the above.

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58. ourier's law of heat conduction is valid for

1. one dimensional cases only
2. two dimensional cases only
3. three dimensional cases only
4. regular surfaces having non-uniform temperature gradients
5. irregular surfaces.

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59. Pick up the wrong case. Heat flowing from one side to other depends directly on

1. face area
2. time
3. thickness
4. temperature difference
5. thermal conductivity.

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60. Planck's law holds good for

1. black bodies
2. polished bodies
3. all coloured bodies
4. all of the above
5. none of the above.

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