GATE
2018
Answer: 27.27%
Vapour bubbles are found in the nucleate boiling regime
at a frequency of 10 bubbles per second per nucleation site. There are 100
nucleation sites per m2 of heating area. The latent heat of
vaporization and the density of vapour under the operating condition are 1000
kJ/kg and 1 kg/m3 respectively. The diameter of each bubble is 10-3
m. Assume that the entire heat supplied is used for vapour generation. The heat
flux (in Watt per m2 of heating area) is _______ (rounded off to
third decimal place).
GATE 2018
Answer: 0.523 W/m2
Economy of evaporators
used for concentrating sugarcane juice is
GATE
2018
Answer: (C)
The wall of a pipe of radius 1 m is at a uniform
temperature of 200°C, and is covered by insulation of thickness 0.1 m. The
ambient air outside the insulated pipe is at 20°C and has heat transfer
coefficient of 10 Wm-2 K-1. The thermal conductivity of
the insulation material is 0.05 W m-1 K-1. If the heat
transfer occurs at steady state, the temperature (in °C) of the outer surface
of insulation is _______ (rounded off to second decimal place).
GATE
2018
Answer: 28.193°C
An insulated storage tank contains 1000 kg liquid of
specific heat 10 kJ kg-1K-1. The liquid is heated by
saturated steam, condensing in a helical coil at a temperature of 180°C. The
heat transfer area of the coil is 0.1 m2. If the overall heat
transfer coefficient is constant at 1000 W m-2 K-1, then
the time (in hours) required to raise the temperature of the liquid in the tank
from 20°C to 80°C is _________ (rounded off to second decimal place).
GATE
2018
Answer: 13.05 hr
Segmental
baffles in a 2 - 4 shell and tube heat exchanger
(A) Change the flow pattern of the tube side fluid
and increase the overall heat transfer coefficient
(B) Increase the heat transfer coefficient in the
shell side and support the tubes
(C) Help
to reduce the thermal expansion of the tubes and increase the heat transfer
coefficient in the tube side
(D) Increase
the number of passes in the shell side and increase the heat transfer
coefficient in the tube side
GATE
2018
Answer: (B)
Prandtl
number signifies the ratio of
(A)
Momentum diffusivity/thermal diffusivity
(B)
Mass diffusivity/thermal diffusivity
(C)
Thermal diffusivity/momentum diffusivity
(D)
Thermal diffusivity/mass diffusivity
GATE
2019
Answer: (A)
Consider the two
countercurrent heat exchanger designs for heating a cold stream from tin
to tout as shown in figure. The hot process stream is available at Tin.
The inlet stream conditions and overall heat transfer coefficients are
identical in both the designs. The heat transfer area in design I and design II
are respectively
If
heat losses are neglected, and if both the designs are feasible, which of the
following statements holds true:
GATE-2019
Answer: (D)
A 20 cm
diameter cylindrical solid pellet of a nuclear fuel with density 6000 kg/m3
and conductivity of 300 W/(m K) generates heat by nuclear fission at a
spatially uniform rate of 104 W/kg. The heat from the fuel pellet is
transferred to the surrounding coolant by convection such that the pellet wall
temperature remains constant at 300 °C. Neglecting the axial and azimuthal
dependence, the maximum temperature (in °C) in the pellet at steady state
is_________________ (rounded off to the nearest integer).
GATE
2019
Answer: 800
A solid sphere of radius 1 cm and
initial temperature of 25⁰C is exposed to a gas stream at 100⁰C. For the solid sphere, the density is 104 kg/m3
and the specific heat capacity is 500 J/(kg K). The density of the gas is 0.6
kg/m3 and its specific heat capacity is 103 J/(kg K). The
solid sphere is approximated as a lumped system (Biot number << 1) and
all specific heats are constants. If the heat transfer coefficient between the
solid and gas is 50 W/(m2K), the time (in seconds) needed for the
sphere to reach 95⁰C is _________ (rounded off to the
nearest integer)
GATE
2019
Answer: 902.68
Steam A with specific heat capacity
CPA = 2000 J/(kg K) is cooled from 90⁰C to 45⁰C in concentric double pipe counter current heat exchanger
having a heat transfer area of 8 m2. The cold stream B of specific
heat capacity CPB = 1000 J/(kg K) enters the exchanger at a flow
rate 1 kg/s and 40⁰C. The overall heat transfer
coefficient U = 250 W/(m2K). Assume that the mean driving force is
based on the arithmetic mean temperature difference, that is
Where, Ti,in and Ti,out
refer to the temperature of the ith stream (i = A, B) at the inlet
and exit, respectively. The mass flow rate of stream A (in kg/s), is
_____________ (rounded off to two decimal places).
GATE
2019
Answer: 0.305
Ratio of
momentum diffusivity to thermal diffusivity is
(A) Reynolds
number
(B) Prandtl
number
(C) Nusselt
number
(D) Peclet
number
GATE
2020
Answer: (B)
Leidenfrost
phenomena refers to
(A) The
condensation of vapour on a cold surface
(B) The
exchange of heat between two solids
(C) The
melting of frost
(D) Film
boiling and evaporation of liquid droplets falling on a very hot surface
GATE
2020
Answer: (D)
An aqueous
suspension at 60ºC is fed to the first effect of a double effect forward feed
evaporator with a mass flow rate of 1.25 kg s-1. The sum of the
rates of water evaporated from the first and second effects is 1.0 kg s-1.
Temperatures of the exit streams from the first and the second effects are
100ºC, 60ºC, respectively. Consider the specific heat of the aqueous suspension,
and the latent heat of phase change for water to be 4 kJ kg-1 K-1
and 2200 kJkg-1, respectively, over this temperature range. The
steam economy (in kg per kg) is _______ (round off to 2 decimal places).
GATE
2020
Answer: 1.779
A hollow
cylinder of equal length and inner diameter (i.e., L = D) is sealed at both
ends with flat plate, as shown in the figure. Its inner surfaces, A1,
A2, and A3 radiate energy.
Fij
denotes the fraction of radiation energy leaving the surface Ai
which reaches the surface Aj. It is also known that
Which
one of the following is correct?
GATE Chemical Engineering Questions and Answers-Thermodynamics
No comments:
Post a Comment