GRASHOFF NUMBER CODES
5. Grashoff Number
Codes: A
B
C
D
A
B
C
D
(a)
5
1
2
3
(b)
2
1
5
4
(c)
4
2
1
3
(d)
2
3
5
4
IES-18. In free convection heat transfer transition from laminar to turbulent
flow is governed by the critical value of the
[IES-1992]
(a) Reynolds number
(b) Grashoff's number
(c) Reynolds number, Grashoff number (d) Prandtl number, Grashoff number
IES-19. Nusselt number for fully developed turbulent flow in a pipe is given by
a
b
.
N
=
CR P
The values of a and b are:
[IES-2001]
u
e
r
(a)
a = 0.5 and b = 0.33 for heating and cooling both
(b)
a = 0.5 and b = 0.4 for heating and b = 0.3 for cooling
(c)
a = 0.8 and b = 0.4 for heating and b = 0.3 for cooling
(d)
a = 0.8 and b = 0.3 for heating and b = 0.4 for cooling
IES-20. For natural convective flow over a
vertical flat plate as shown in the given
figure, the governing differential
equation for momentum is:
2
∂
∂
∂
⎛
+
⎞
=
−
+
u
u
u
u
v
g T T
y
⎜
∂
∂
⎟
∂
(
)
2
x
y
β
∞
y
⎝
⎠
If equation is non-dimensionalized by
T T
U
u
=
−
θ
∞
=
,
X
x
T
T
−
=
L
and
=
L
,
Y
y
U
∞
s
∞
then the term
g T T
β
(
−
∞
)
, is equal to:
[IES-2001]
(a) Grashof number
(b) Prandtl number
Grashof number
(c)
Rayleigh
number
(d)
(
)
2
Reynolds number
IES-21. Which one of the following numbers represents the ratio of kinematic
viscosity to the thermal diffusivity?
[IES-2005]
(a) Grashoff number
(b) Prandtl number
(c) Mach number
(d) Nusselt number
IES-22. Nusselt number for a pipe flow heat transfer coefficient is given by the
equation
Nu
D
= 4.36. Which one of the following combinations of
conditions does exactly apply for use of this equation?
[IES-2004]
(a) Laminar flow and constant wall temperature
(b) Turbulent flow and constant wall heat flux
(c) Turbulent flow and constant wall temperature
(d) Laminar flow and constant wall heat flux
Page 45 of 97
IES-23. For steady, uniform flow through pipes with constant heat flux
supplied to the wall, what is the value of Nusselt number?
[IES-2007]
(a) 48/11
(b) 11/48
(c) 24/11
(d) 11/24
IES-24. A fluid of thermal conductivity 1.0 W/m-K flows in fully developed flow
with Reynolds number of 1500 through a pipe of diameter 10 cm. The
heat transfer coefficient for uniform heat flux and uniform wall
temperature boundary conditions are, respectively.
[IES-2002]
(a)
36.57 and 43.64
W
2
m K
(b)
43.64 and 36.57
W
2
m K
(c)
43.64
W
2
for both the cases
m K
(d)
36.57
W
2
for both the cases
IES-25. Which one of the following statements is correct?
[IES-2004]
The non-dimensional parameter known as Stanton number (St) is
used in
(a) Forced convection heat transfer in flow over flat plate
(b) Condensation heat transfer with laminar film layer
(c) Natural convection heat transfer over flat plate
(d) Unsteady heat transfer from bodies in which internal temperature gradients
cannot be neglected
IES-26. A 320 cm high vertical pipe at 150°C wall temperature is in a room with
still air at 10°C. This pipe supplies heat at the rate of 8 kW into the
room air by natural convection. Assuming laminar flow, the height of
the pipe needed to supply 1 kW only is:
[IES-2002]
(a) 10 cm
(b) 20 cm
(c) 40 cm
(d) 80 cm
IES-27. Natural convection heat transfer coefficients over surface of a vertical
pipe and vertical flat plate for same height and fluid are equal. What
is/are the possible reasons for this?
[IES-2008]