Nusselt number is a function of Prandtl number and ______________ number of fluid in natural convection heat transfer?

Related Mcqs:

1. Nusselt number (for forced convection heat transfer) is a function of the _____________ number?

   A. Prandtl
   B. Reynolds
   C. Both A. & B.
   D. Neither A. nor B.

2. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the_________________?

   A. Existence of thermal boundary layer
   B. Temperature gradient produced due to density difference
   C. Buoyancy of the bubbles produced at active nucleation site
   D. None of these

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. 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

6. In forced convection, the Nusselt number is a function of ____________________?

   A. Re and Pr
   B. Re and Gr
   C. Pr and Gr
   D. Re and Sc

7. 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

8. Heat transfer occurs by natural convection because change in temperature causes difference in__________________?

   A. Viscosity
   B. Density
   C. Thermal conductivity
   D. Heat capacity

9. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________?

   A. (ΔT)1/4
   B. (ΔT)1/2
   C. (ΔT)5/4
   D. (ΔT)3/4

10. Heat transfer by natural convection is enhanced in system with__________________?

    A. High viscosity
    B. High co-efficient of thermal expansion
    C. Low temperature gradients
    D. Low density change with temperature