Heat Transfer

31. Heat transfer takes place as per –

1. zeroth law of thermodynamics
2. first law of thermodynamic
3. second law of the thermodynamics
4. Kirchoff's law
5. Stefan's law.

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32. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

1. convection
2. radiation
3. conduction
4. both convection and conduction
5. none of the above.

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33. In 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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34. In 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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35. In 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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36. In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by

1. hr (time)
2. sqm (area)
3. °C (temperature)
4. cm (thickness)
5. kcal (heat).

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37. In 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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38. Joule 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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39. LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is

1. higher
2. lower
3. same
4. depends on the area of heat exchanger
5. depends on temperature conditions.

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40. Log 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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