Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is__________________?

Related Mcqs:

1. 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

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. 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

4. 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

5. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be__________________?

   A. 15 min
   B. 22 min
   C. 44 min
   D. 51 min

6. In case of heat transfer by conduction in a hollow cylinder, ______________ mean area is used to calculate the heat transfer rate?

   A. Geometric
   B. Arithmetic
   C. Logarithmic
   D. Either A., B. or C.

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

   A. No
   B. The least
   C. The largest
   D. Lower

8. 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

9. Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is ____________________?

   A. Thin walled having the value of Ao Ai/< 2
   B. Thick walled
   C. Having the value of Ao/Ai > 2
   D. Both B. and C.

10. 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