Hot
liquid is flowing at a velocity of 2 m/s through a metallic pipe having an
inner diameter of 3.5 cm and length 20 m. The temperature at the inlet of the
pipe is 90⁰C.
Following data is given for liquid at 90⁰C
Density = 950 kg/m3; Specific heat = 4.23 kJ/kg ⁰C;
Viscosity = 2.55×10-4
kg/m.s; Thermal conductivity = 0.685 W/m ⁰C
The heat transfer coefficient (in W/m2 ⁰C) inside the tube is
(A) 222.22
(B) 111.11
(C) 22.22
(D) 11.11
GATE 2008
Answer: (D)
A metallic ball (ρ = 2700 kg/m3 and Cp = 0.9 kJ/kg ⁰C) of diameter 7.5 cm is allowed to cool in air at 25⁰C. When the temperature of the ball is 125⁰C, it is found to cool at the rate of 4⁰C per minute. If the thermal gradients inside the ball are neglected, the heat transfer coefficient (in W/m2 ⁰C) is
(A) 2.034
(B) 20.34
(C) 81.36
(D) 203.4
GATE
2008
Answer: (B)
Two
plates of equal thickness (t) and cross-sectional area, are joined together to
form a composite as shown in the figure. If the thermal conductivities of the
plates are k and 2k then, the effective thermal conductivity of the composite
is
(A) 3k/2
(B) 4k/3
(C) 3k/4
(D) 2k/3
GATE
2008
Answer: (B)
Transient
three-dimensional heat conduction is governed by one of the following
differential equations (α – thermal diffusivity, k – thermal conductivity and Ψ
– volumetric rate of heat generation)
GATE 2008
Answer: (D)
Common
statement for next two questions
A
slab of thickness L with one side (x = 0) insulated and the other side (x = L)
maintained at a constant temperature T0 is shown below.
A uniformly distributed internal heat source produces heat in the slab at the rate of S W/m3. Assume the heat conduction to be steady and 1-D along the x-direction.
The
maximum temperature in the slab occurs at x equal to
(A) 0
(B) L/4
(C) L/2
(D) L
GATE
2009
Answer: (A)
The heat flux at x = L is
(A) 0
(B) SL/4
(C) SL/2
(D) SL
GATE
2009
Answer: (D)
For
the composite wall shown below (Case 1), the steady state interface temperature
is 180⁰C.
If the thickness of layer P is doubled (Case 2), then the rate of heat transfer
(assuming 1-D conduction) is reduced by
(A) 20%
(B) 40%
(C) 50%
(D) 70%
GATE 2009
Answer: (B)
A double-pipe
heat exchanger is to be designed to heat 4 kg/s of a cold feed from 20 to 40⁰C using a hot stream
available at 160⁰C
and a flow rate of 1 kg/s. The two streams have equal specific heat capacities
and the overall heat transfer coefficient of the heat exchanger is 640 W/m2.K.
Then the ratio of the heat transfer areas required for the co-current to
counter-current modes of operation is
(A) 0.73
(B) 0.92
(C) 1.085
(D) 1.25
GATE
2009
Answer: (C)
A
well-insulated hemispherical furnace (radius = 1 m) is shown below:
The self-view factor of radiation for the curved surface 2 is
(A) ¼
(B) ½
(C) 2/3
(D) ¾
GATE 2009
Answer: (B)
The
Prandtl number of a fluid is the ratio of
(A) Thermal
diffusivity to momentum diffusivity
(B) Momentum
diffusivity to thermal diffusivity
(C) Conductive
resistance to convective resistance
(D) Thermal
diffusivity to kinematic viscosity
GATE 2009
Answer: (B)
During
the transient convective cooling of a solid object, Biot number → 0 indicates
(A) Uniform
temperature throughout the object
(B) Negligible
convection at the surface of the object
(C) Significant
thermal resistance within the object
(D) Significant
temperature gradient within the object
GATE
2009
Answer: (A)
Common statement for next two
questions
Hot oil at 150⁰C is used to preheat a cold fluid at 30⁰C in a 1 - 1 shell and
tube heat exchanger. The exit temperature of the hot oil is 110⁰C. Heat capacities
(product of mass flow rate and specific heat capacity) of both the streams are
equal. The heat duty is 2 kW
Under
co-current flow conditions, the overall heat transfer resistance (I/UA) is
(A) 0.4 ⁰C/W
(B) 0.04 ⁰C/W
(C) 0.36 ⁰C/W
(D) 0.036
⁰C/W
GATE
2010
Answer: (D)
Under
counter-current flow conditions the overall heat transfer resistance (I/UA) is
(A) 0.4 ⁰C/W
(B) 0.04⁰C/W
(C) 0.36 ⁰C/W
(D) 0.036 ⁰C/W
GATE
2010
Answer: (B)
The
view factor matrix for two infinitely long co-axial cylinders, shown in the
figure below, is
Answer: (A)
The figure below
shows steady state temperature profiles for one dimensional heat transfer
within a solid slab for the following cases:
P:
uniform heat generation with left surface perfectly insulated
Q: uniform heat generation with right surface
perfectly insulated
R: uniform heat consumption with left surface
perfectly insulated
S: uniform heat consumption with right surface
perfectly insulated
Match the profiles with appropriate cases.
(A) P-I, Q-III, R-II, S-IV
(B) P-II, Q-III, R-I, S-IV
(C) P-I, Q-IV, R-II, S-III
(D) P-II, Q-IV, R-I, S-III
GATE
2010
Answer: (A)
Which
one of the following statements about baffles in a shell and tube heat
exchanger is FALSE? Baffles
(A) Act
as a support to the tube bundle
(B) Reduce
the pressure drop on the shell-side
(C) Alter
the shell-side flow pattern
(D) Help
in increasing the shell-side heat transfer coefficient
GATE 2010
Answer: (B)
The ratio of the thermal boundary layer
thickness to the concentration boundary layer thickness is proportional to
(A) Nu
(B) Le
(C) Sh
(D) Pr
GATE 2010
Answer: (B)
The
ratio of Nusselt number to Biot number is
(A) Conductive
resistance of fluid/conductive resistance of solid
(B) Conductive
resistance of fluid/convective resistance of fluid
(C) Conductive
resistance of solid/conductive resistance of fluid
(D) Unity
GATE
2010
Answer: (A)
Heat is generated uniformly within a solid slab. The slab separates fluid 1 from fluid 2. The heat transfer coefficients between the solid slab and the fluids are h1 and h2 (h2 > h1) respectively. The steady state temperature profile (T vs, x) for one-dimensional heat transfer is CORRECTLY shown by
GATE 2011
Answer: (A)
An
aqueous sodium chloride solution (10 wt%) is fed into a single effect
evaporator at a rate of 10000 kg/hr. It is concentrated to a 20 wt% sodium
chloride solution. The rate of consumption of steam in the evaporator is 8000
kg/hr. the evaporator capacity (kg/hr) and economy are
(A) 5000, 0.625
(B) 10000, 0.625
(C) 5000, 1.6
(D) 10000, 1.6
GATE
2011
Answer: (A)
No comments:
Post a Comment