Q.1.Loss of heat from unlagged steam pipe to the ambient air is by
conduction
convection
radiation
all (a), (b) & (c)
Q.2.Fourier's law applies to the heat transfer by
convection
radiation
conduction
all (a), (b) & (c)
Q.3.Fourier's law of heat conduction applies to .......... surfaces.
isothermal
non-isothermal
both (a) and (b)
neither (a) and (b)
Q. 4.Unsteady state heat conduction occurs, when
temperature distribution is independent of time
temperature distribution is dependent on time
heat flows in one direction only
three dimensional heat flow is concerned
Q.5.What is the unit of thermal conductivity ?
Kcal/hr.m2 0C
Kcal/hr.m. 0C
Kcal/hr.m
Kcal/hr.0C
Q.6.The unit of heat transfer co-efficient is
BTU/hr.ft2 0F
BTU/hr.0F.ft.
BTU/hr.0F
BTU/hr.ft
Q.7.Which of the following is correct ?
Rate = Driving force * Resistance
Driving force = Rate * Resistance
Resistance = Driving force * Rate
Rate = Resistance/Driving force
Q.8.An insulator should have
low thermal conductivity
high thermal conductivity
less resistance to heat flow
a porous structure
Q.9.Heat flux through several resistance in series in analogous to the current flowing through several
resistances in parallel
capacitors in series
resistances in series
none of these
Q.10.The overall resistance for heat transfer through a series of flat resistance, is the ..... of the resistances.
average
geometric mean
product
sum
Q.11.Which of the following has the highest thermal conductivity ?
Brick
Air
Water
Silver
Q.12.Which area is used in case of heat flow by conduction through a cylinder ?
Logarithmic mean area
Arithmetic mean area
Geometric mean area
None of these
Q.13.For heat flow through very thick walled cylinder, use ............ mean radius.
arithmetic
logarithmic
geometric
either (a) or (c)
Q.14.What is the logarithmic mean of r1 and r2 ?
r1 - r2/ln r1/r2
r1 - r2/ln r2/r1
r2 - r1/ln r1/r2
r1 - r2/ - ln r1/r2
Q.15.What is Nusselt number ?
Cp.μ/k
hD/k
h.Cp/μ
Cp.μ/h
Q.16.Prandtl number is given by
Cp.μ/a
hD/k
Cp.μ/k
μ/h.Cp
Q.17.Thermal diffusivity is given by
k/r.Cp
r.Cp/k
Cp.μ/a
μ/hCp
Q.18.Grashhoff number is given by
g D3. β .∆ tr2/μ2
g D2β∆tr/μ2
g D2β∆tr2μ
g D3β∆tr2/μ
Q.19.If h1=inner film co-efficient & h2=outer film co-efficient, then the overall heat transfer co-efficient is
always less than h1
always between h1 and h2
always higher than h2
dependent on metal resistance
Q.20.Gratez number is give by
mCp/kL
kL/mCp
mCp/kμ
kL/mCp
Q.21.In the equation Q= UA ∆t ; ∆t is
geometric mean temperature difference.
arithmetic mean temperature difference.
logarithmic mean temperature difference.
the difference of average bulk temperatures of hot and cold fluids.
Q.22.Peclet number (Pe) is given by
Pe = Re.Pr
Pe = Re/Pr
Pe = Pr/Re
Pe = Nu.Re
Q.23.Prandtl number is the reciprocal of
Thermal diffusivity/ Momentum diffusivity
Thermal diffusivity x Momentum
Thermal diffusivity x Mass diffusivity
Mass diffusivity x Momentum diffusivity
Q.24.Maximum heat transfer rate is obtained in .......... flow.
laminar
turbulent
creeping
transition region
Q.25.Heat flux is the time rate of heat transfer per unit
length
area
volume
none of these
Q.26.Nusselt number is the ratio of the
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.27.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.28.Viscosity of gases ....... with increase in temperature.
increase very rapidly
increase slowly
decrease slowly
remain unaffected
Q.29.Heat transfer co-efficient (h1) for liquids increases with
increasing temperature
decreasing temperature
decreasing Reynolds number
none of these
Q.30.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.31.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.32.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.33.Natural convection is characterized by
Grashhoff number
Peclet number
Reynolds number
Prandtl number
Q.34.Which of the following is unimportant in forced convection ?
Reynolds number
Prandtl number
Grashhoff number
none of these
Q.35.In fored convection, the heat transfer depends on
Re, Pr
Re, Gr
mainly Gr
Re only
Q.36.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.37.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.38.Reynold's analogy states that
St = f/2
St = f/4
St = 4f
St = f1/2
Q.39.For what value of Prandtl number, St = f/2 ?
1.5
1
> 1
< 1
Q.40.Which has the lowest Prandtl number ?
Liquid metal
Aqueous solution
Water
Lube oil
Q.41.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.42.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.43.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.44.Choose the correct equation.
Nu = (Re) (Pr) (Gz)
Nu = (Re) (Pr) (St)
Nu = (Re) (Pr)
Nu = (Pr) (St)
Q.45.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.46.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.47.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.48.The heat transfer co-efficient in film type condensation is ....... that for dropwise condensation.
greater than
lower than
is same as
half
Q.49.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.50.All analogy equations connecting friction factor and heat transfer co-efficient apply only to
wall or skin friction
form friction
both (a) and (b)
turbulent flow
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