Controlling heat transfer film co-efficient is the one, which offers ______________ resistance to heat transfer?

Related Mcqs:

1. 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

2. If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer co-efficient is________________?

   A. Always less than h1
   B. Always between h1 and h2
   C. Always higher than h2
   D. Dependent on metal resistance

3. 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

4. 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

5. 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

6. For a laminar flow of fluid in a circular tube, ‘h1’ is the convective heat transfer co-efficient at velocity ‘V1’. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is________________?

   A. 1.26 h1
   B. 0.794 h1
   C. 0.574 h1
   D. 1.741 h1

7. For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus- Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of________________?

   A. 1
   B. 1.74
   C. 6.1
   D. 37

8. The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is___________________?

   A. More
   B. Less
   C. Some
   D. Either more or less; depends on the nature of vapor

9. The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter D. as _________________?

   A. D-1.8
   B. D-0.2
   C. D0.2
   D. D1.8

10. If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?

    A. ha = hl
    B. ha = 2hl
    C. ha = 0.5 hl
    D. ha = 0.75 hl