The thermal conductivity is minimum for
(A) Silver
(B) chrome-Nickel steel
(C) Aluminium
(D) Carbon
steel
(GATE-1989)
Answer: (B)
Evaporators are normally operated at
reduced pressure in order to
(A) Reduce the wall thickness of the
evaporator body
(B)
Enable the use of low pressure steam as
heating medium
(C)
Increase the overall heat transfer
coefficients
(D)
Prevent the thermal degradation of the
solute
(GATE-1989)
Answer: B
The rate of diffusion of momentum
relative to the rate of diffusion of heat is
(A)
Proportional to Prandtl number
(B)
Inversely proportional to Prandtl number
(C) Proportional to Colburn JH
factor
(D)
Proportional to Stanton number
(GATE-1989)
Answer: (A)
Heat transfer coefficient in a helical
coil compared to that in a straight pipe is
(A) Lower
(B) Higher
(C) Same
(D) None
(GATE-1989)
Answer: (B)
To determine the heat transfer
coefficient, Dittus-Boelter equation is valid for
(A)
Laminar flow
(B)
Liquid metals
(C)
Turbulent flow
(D)
Natural convection
GATE-1989
Answer: (C)
Grashoff number is associated with
(A)
Buoyancy effects
(B)
Free convection
(C)
Forced convection
(D)
High temperature difference
(GATE-1990)
Answer: (B)
In finned tube heat exchanger
(A)
Only heat transfer area is augmented
(B)
Only film coefficient is augmented
(C)
Both heat transfer and film coefficient
are augmented
(D)
None of these
GATE-1990
Answer: (A)
The widely used Dittus-Boelter equation is valid provided
(A)
2100<Re<10,000 and the properties
of the fluid are evaluated at the average film temperature
(B)
Re<2100 and the properties of the
fluid are evaluated at the bulk temperature
(C)
10,000<Re<120,000 and the fluid
properties are evaluated at the bulk temperature
(D)
None of the above
(GATE-1991)
Answer: (C)
The advantage of back-ward feed multiple effect evaporators over forward feed units is that
(A)
Heat sensitive materials can be handled
(B)
There is no additional cost of pumping
(C)
Most concentrated liquor is at highest
temperature
(D)
Equal heat transfer coefficients exists
in various effects
(GATE-1992)
Answer: (C)
In a heat exchanger with steam outside
the tubes, a liquid gets heated to 45⁰C when its flow
velocity in the tube is 2 m/s. If the flow velocity is reduced to 1 m/s, other
things remaining the same, the temperature of the exit liquid will be
(A)
Less than 45⁰C
(B)
Equal to 45⁰C
(C)
Greater than 45⁰C
(D)
Initially decreases and remains constant
there after
(GATE-1992)
Answer: (A)
The capacity of a multiple effect
evaporator when compared with a single-effect evaporator both operating with
significant boiling point rise at the same terminal temperatures and surface
area in each effect equal to surface area of single effect evaporator.
(A) Decreases
(B) increases
(C) remains the same
(D) none of these
(GATE-1993)
Answer: (A)
A metal wire of 0.01 m diameter and
thermal conductivity 200 W/mK is exposed to a fluid stream with a convective
heat transfer coefficient 1000 W/m2K. the Biot number is
(A) 5.6
(B) 0.0125
(C) 3.5
(D) 0.0035
GATE
1994
Answer: (B)
Prandtl number is the ratio of
(A)
Mass diffusivity to thermal diffusivity
(B)
Momentum diffusivity to thermal
diffusivity
(C)
Thermal diffusivity to mass diffusivity
(D)
Thermal diffusivity to momentum
diffusivity
(GATE-1994)
Answer: (B)
In a heat exchanger, floating head is
provided to
(A)
Facilitate cleaning of the exchanger
(B)
Increase the heat transfer area
(C)
Relieve stresses caused by thermal
expansion
(D)
Increase the logmean temperature
gradient
(GATE-1996)
Answer: (C)
In natural convection heat transfer the
correlating parameter is
(A) Graetz number
(B) Eckert number
(C) Grashoff number
(D) Bond number
(GATE-1996)
Answer: (C)
The critical radius of ‘r’ of insulation
on a pipe is given by
(A) r = 2K/h
(B) r = K/h
(C) r = K/2h
(D) r = h/K
(GATE-1996)
Answer: (B)
When the ratio of the Grashof number to
the square of the Reynolds number is one, the dominant mechanism of heat
transfer is
(A)
Free convection
(B)
Entry length problem in laminar forced
convection
(C)
Mixed convection (both free and forced)
(D)
Forced convection
(GATE-1996)
Answer: (C)
The thermal radiation flux from a
surface of emissivity 0.4 is 22.68 KW/m2. The approximate surface
temperature (K) is
(A) 1000
(B) 727
(C) 800
(D) 1200
Take
Stefan – Boltzman constant = σ = 5.67×10-8 W/m2K4
(GATE-1997)
Answer: (A)
For condensation of pure vapors, if the
heat transfer coefficients in film wise and drop wise condensation are
respectively hf and hd, then
(A) hf = hd
(B) hf > hd
(C) hf < hd
(D) hf
could be greater or smaller than hd
GATE
1997
Answer: (C)
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