temperature gradient of the wall to that across the entire pipe.
temperature difference to the temperature gradient at the wall.
heat flux at the wall to that across the entire pipe.
none of these
Q.2.Fouling factor
is a dimensionless quantity.
does not provide a safety factor for design.
accounts for additional resistances to heat flow.
none of these.
Q.3.Viscosity of gases ....... with increase in temperature.
increase very rapidly
increase slowly
decrease slowly
remain unaffected
Q.4.Heat transfer co-efficient (h1) for liquids increases with
increasing temperature
decreasing temperature
decreasing Reynolds number
none of these
Q.5.At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe ?
0.5
< 0.5
> 0.6
< 0.1
Q.6.At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the
buffer zone
turbulent core
both (a) and (b)
viscous sub-layer
Q.7.Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is
0.1
> 1
< 1
1
Q.8.Natural convection is characterized by
Grashhoff number
Peclet number
Reynolds number
Prandtl number
Q.9.Which of the following is unimportant in forced convection ?
Reynolds number
Prandtl number
Grashhoff number
none of these
Q.10.In fored convection, the heat transfer depends on
Re, Pr
Re, Gr
mainly Gr
Re only
Q.11.The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
Re. Gz
Nu, Pr
Nu, Pr, Re
Nu, Gz
Q.12.At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?
1
< 1
> 1
none of these
Q.13.Reynold's analogy states that
St = f/2
St = f/4
St = 4f
St = f1/2
Q.14.For what value of Prandtl number, St = f/2 ?
1.5
1
> 1
< 1
Q.15.Which has the lowest Prandtl number ?
Liquid metal
Aqueous solution
Water
Lube oil
Q.16.Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid
for fluids in laminar flow
for fluids in tubulent flow
when Grashhoff number is very important
for liquid metals
Q.17.For what value of Prandtl number, the Colburn analogy is valid ?
0.06 to 120
0.6 to 120
1 to 103
1 to 50
Q.18.Pick out the correct equation.
jH = (St) (Pr)2/3 = f/2
jH = (St) (Pr)1/3 = f/2
jH = (St)2/3 (Pr) = f/2
jH = (St)1/3 (Pr) = f/2
Q.19.Choose the correct equation.
Nu = (Re) (Pr) (Gz)
Nu = (Re) (Pr) (St)
Nu = (Re) (Pr)
Nu = (Pr) (St)
Q.20.For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
Nu = 0.023 Re0.8 . Pr0.4
Nu = p/2 Gz
Nu = 2/p Gz
Nu = 2Gz0.5
Q.21.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
ha = hl
ha = 2 hl
ha = 0.5 hl
ha = 0.75 hl
Q.22.When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids ?
At high fluid velocity
At low velocity
When fluid flows past a smooth surface
None of these
Q.23.The heat transfer co-efficient in film type condensation is ....... that for drop wise condensation.
greater than
lower than
is same as
half
Q.24.Prandtl number is the ratio of
momentum diffusivity to mass diffusivity
momentum diffusivity to thermal diffusivity
thermal diffusivity to mass diffusivity
thermal diffusivity to momentum diffusivity
Q.25.All analogy equations connecting friction factor and heat transfer co-efficient apply only to
wall or skin friction
form friction
both above
turbulent flow
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