Thermal diffusivity is the most important in heat transfer by__________________?

Related Mcqs:

1. 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

2. 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

3. The ratio of momentum diffusivity to thermal diffusivity is the ______________ number?

   A. Prandtl
   B. Nusselt
   C. Stanton
   D. Grashoff

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. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place____________________?

   A. Between two bodies in physical contact with each other
   B. Between two bodies not in physical contact with each other
   C. From one part of a body to the another part of the same body
   D. Both B & C

6. Thermal diffusivity is given by__________________?

   A. k/ρCp
   B. ρCp/k
   C. μCp/a
   D. μ/hCp

7. Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) ?

   A. U1 – U2
   B. 1/U1 – 1/U2
   C. 1/U2 – 1/U1
   D. U2 – U1

8. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m2.K. The overall heat transfer co-efficient at this time is _____________________?

   A. 1200 W/m2.K
   B. 894 W/m2.K
   C. 333 W/m2.K
   D. 287 W/m2.K

9. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area___________________?

   A. Increases
   B. Decreases
   C. Remain constant
   D. Passes through a maxima

10. 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