Heat exchangers operating, when the asymptotic range is reached, ?

Related Mcqs:

1. Indirect contact heat exchangers are preferred over direct contact heat exchangers, because_________________?

   A. Heat transfer co-efficient are high
   B. There is no risk of contamination
   C. There is no mist formation
   D. Cost of equipment is lower

2. Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is________________?

   A. Finned tube heat exchanger with air inside and steam outside
   B. Finned tube heat exchanger with air outside and steam inside
   C. Shell and tube heat exchanger with air inside tubes and steam on shell side
   D. Shell and tube heat exchanger with air on shell side and steam inside tubes

3. Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube___________________?

   A. Exit-fluid temperature > wall temperature
   B. Exit fluid temperature < wall temperature
   C. Exit fluid temperature = wall temperature
   D. Graetz number > 100

4. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?

   A. (COP)R = (COP)HP = 0.6
   B. (COP)R = 2.5; (COP)HP = 1.5
   C. (COP)R = 1.5; (COP)HP = 2.5
   D. (COP)R = (COP)HP = 2.5

5. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?

   A. Greater than that for un-insulated steam pipe
   B. Less than that of the un-insulated steam pipe
   C. Equal to that of the un-insulated steam pipe
   D. Less than the steam pipe with 5 cms insulation

6. Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the________________?

   A. Surrounding temperature
   B. Average temperature of the fin
   C. Temperature of the fin end
   D. Constant temperature equal to that of the base

7. LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the ______________ flow?

   A. Parallel
   B. Mixed
   C. Counter flow
   D. Same in either A , B. or C.

8. Multipass heat exchangers are used______________________?

   A. Because of simplicity of fabrication
   B. For low heat load
   C. To obtain higher heat transfer co-efficient and shorter tube
   D. To reduce the pressure drop

9. Double pipe heat exchangers are preferably useful, when____________________?

   A. High viscosity liquid is to be cooled
   B. Requirement of heat transfer area is low
   C. Overall heat transfer co-efficient is very high
   D. A corrosive liquid is to be heated

10. Baffles are provided in heat exchangers to____________?

    A. Remove dirt
    B. Increase heat transfer rate
    C. Reduce vibrations
    D. Reduce heat transfer rate

    Submitted by: Faheem Zaman Dhaunroo