Transition from laminar to turbulent zone in free convection heat transfer is governed by the critical value of ?

Related Mcqs:

1. Nusselt number is related to Grashoff number (Gr) in turbulent & laminar flow respectively, in respect of free convection over a vertical flat plate as_________________?

   A. Gr0.25, Gr
   B. Gr0.25, Gr0.33
   C. Gr, Gr0.25
   D. Gr0.33, Gr0.25

2. Transition from laminar flow to turbulent flow in fluid flow through a pipe does not depend upon the___________________?

   A. Length of the pipe
   B. Diameter of the pipe
   C. Density of the fluid
   D. Velocity of the fluid

3. _______________ number determines whether the fluid flow in an open channel is super-critical, critical or sub-critical ?

   A. Mach
   B. Reynolds
   C. Froude
   D. Weber

4. Nusselt number is related to the Reynolds number (Re) in turbulent & laminar flow respectively as______________________?

   A. Re0.5, Re0.8
   B. Re0.8, Re-0.5
   C. Re0.8, Re0.5
   D. Re-0.8, Re0.5

5. The laminar boundary layer thickness in zero pressure gradient flow over a flat plate along the x-direction varies as x0.5 while the thickness of turbulent boundary layer varies as (where, x = distance from the leading edge) ?

   A. x1.5
   B. x0.8
   C. x-1.5
   D. x-0.8

6. What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively ?

   A. 2
   B. 8
   C. 10
   D. 40

7. The transition temperature at which all the ferromagnetic materials become paramagnetic materials is termed as the ‘Curie temperature’. Its value for cobalt is ______________ °C?

   A. 768
   B. 1127
   C. 1359
   D. 1480

8. Cold cracking in the heat affected zone of a high strength steel weld can take place because of the___________________?

   A. Retained austenite
   B. Martensite formation
   C. Relatively high sulphur content in the base metal
   D. Sufficient hydrogen present in the welding arc

9. The critical pressure at which the latent heat of vaporization of steam becomes zero is _____________ Kg/cm2 ?

   A. 273.15
   B. 225.65
   C. 100.03
   D. 373.15

10. A reduction in thermal resistance during heat transfer does not occur in the___________________?

    A. Convection heat transfer by stirring the fluid and cleaning the heating surface
    B. Conduction heat transfer by reduction in the material thickness and increase in the thermal
    conductivity
    C. Radiation heat transfer by increasing the temperature and reducing the emissivity
    D. None of these