htn 2 Flashcards
Which of the following parameters of the fluid is not very
important, while deciding its route in a shell and tube heat
exchanger?
A. Corrosiveness & fouling characteristics
B. pressure
C. viscosity
D. density
D
Corrosiveness of steam condensate is due to the presence
of
A. CO2
B. dissolved O2
C. both (a) & (b)
D. neither (a) nor (b)
C
The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy.
A. Colburn
B. Reynolds
C. Prandtl
D. none of these.
A
The driving potential for the crystal growth during crystallisation
is the __________ of the solution.
A. concentration
B. viscosity
C. super-saturation
D. Density
C
It
is not recommended to use a 1-2 shell and tube heat
exchanger for a particular heat duty, whenever the LMTD
correction factor is
A. 0.75
B. < 0.75
C. < 0.50
D. < 0.25
B
Kg of liquid evaporated per hour in an evaporator is defined as
its
A. capacity
B. economy
C. steam load
D. none of these
A
Pick out the correct statement.
A. 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F.
B. In steady state heat conduction, the only property of
the substance which determines the temperature
distribution, is the thermal conductivity.
C. In unsteady state heat conduction, heat flows in the
direction of temperature rise.
D. In heat transfer by forced convection, Grashoff
number is very important.
B
Open pan evaporators are preferred to be used, when the
solution to be concentrated is
A. scaling
B. highly viscous
C. corrosive
D. salty
B
Cpu/k is termed as the __________ number.
A. Grashoff
B. Nusselt
C. Prandtl
D. Stanton
C
The maximum heat transfer co-efficient from steam heating will
be attained when the steam is
A. supersaturated
B. saturated
C. wet
D. none of these
b
Kirchoff’s law is applicable to
A. monochromatic radiation only
B. total radiation only
C. both (a) and (b)
D. only volumes and not to surfaces
C
In a forward feed multiple effect evaporator, the pressure is
A. highest in last effect
B. lowest in last effect
C. same in all effects
D. dependent on the number of effects
B
In a co-current double pipe heat exchanger used for condensing
saturated steam over the inner tube, if the entrance and exit
conditions of the coolant are interchanged, then the rate of
condensation will
A. increase
B. decrease
C. remain unchanged
D. either increase or decrease; depends on the coolant
flow rate
C
Which of the following has maximum thermal conductivity?
A. Iron
B. Coal
C. Nitrogen
D. Tar
A
Which of the following situations can be approximated to a
steady state heat transfer system ?
A. A red hot steel slab (having outside surface
temperature as 1300°C) exposed to the atmosheric
air at 35°C.
B. 10 kg of dry saturated steam at 8 kgf/cm2 flowing
through a short length of stainless steel pipe exposed
to atmospheric air at 35°C.
C. Boiling brine kept in open vessel when the bottom
surface temperature of the vessel is maintained
constant at 180°C.
D. A sub-cooled refrigerant liquid at 8°C flowing at the
rate of 6 Kg/minute through a copper pipe exposed
to atmospheric air at 35°C.
B
Sensible heat absorbed by 1 lb of water when it is heated from
32 to 212°F may be around __________ BTU.
A. 180
B. 970
C. 3.97
D. data insufficient, can’t be predicted
A
The unit of conductance in SI unit is
A. W/m
B. W/m2
C. W/°K
D. W/m°K
C
In a shell and tube heat exchanger, square pitch compared to
triangular pitch
A. gives a higher shell side pressure drop.
B. gives a lower shell side pressure drop.
C. can pack more surface area into a shell of given
diameter.
D. none of these.
B
A wall has two layers of materials A and B; each made of a
different material. Both the layers have the same thickness. The
thermal conductivity of materialA is twice that of B. Under the
equilibrium, the temperature difference across the wall is 36°C.
The temperature difference across the layer A is ________ °C.
A. 6
B. 12
C. 18
D. 24
B
The film co-efficient between condensing vapour and metal wall
increases with
A. increasing temperature of the vapour.
B. decreasing temperature of the vapour.
C. increasing viscosity of the film of condensate.
D. increasing temperature drop.
A
Critical value of the __________ number governs the transition
from laminar to turbulent flow in free convection heat transfer.
A. Grashoff
B. Reynolds
C. both ‘a’ & ‘b’
D. Prandtl & Grashoff
D
The thermal boundary layer at NPr > 1
A. is thicker than hydrodynamic boundary layer.
B. is thinner than hydrodynamic boundary layer.
C. and the hydrodynamic boundary layer are identical.
D. disappears.
D
With increase in temperature, the thermal conductivity of a gas
A. increases.
B. decreases.
C. remains same.
D. may increase / decrease depending on type of gas.
A
In the free convection regime of pool boiling, the heat flux is
proportional to
A. Δt1/2
B. Δt2
C. Δt5/4
D. Δt
C