## GATE ME solved Question on Convection(Heat Transfer)

Question #1

Grashof number signifies the ratio of
(A) inertia force to viscous force
(B) buoyancy force to viscous force
(C) buoyancy force to inertia force
(D) inertia force to surface tension force

[GATE 2016 Set 3, 1 mark]

Question #2

The ratio of momentum diffusivity (ν) to thermal diffusivity (α), is called

(A) Prandtl number

(B) Nusselt number

(C) Biot number

(D) Lewis number

[GATE 2015 Set 3, 1 mark]

Question #3

In the laminar flow of air (Pr = 0.7) over a heated plate, if $\delta$ and $\delta _{t}$ denote, respectively, the hydrodynamic and thermal boundary layer thicknesses, then

(A) $\delta=\delta _{t}$

(B) $\delta>\delta _{t}$

(C) $\delta<\delta _{t}$

(D)$\delta=0$ but $\delta_{t}\neq 0$

[GATE 2015 Set 2, 1 mark]

Question #4

For flow of viscous fluid over a flat plate, if the fluid temperature is the same as the plate
temperature, the thermal boundary layer is
(A) thinner than the velocity boundary layer
(B) thicker than the velocity boundary layer
(C) of the same thickness as the velocity boundary layer
(D) not formed at all

[GATE 2015 Set 1, 1 mark]

Question #5

Match Group A with Group B:

 Group A Group B P: Biot number 1: Ratio of buoyancy to viscous force Q: Grashof number 2: Ratio of inertia force to viscous force R: Prandtl number 3: Ratio of momentum to thermal diffusivities S: Reynolds number 4: Ratio of internal thermal resistance to boundary layer thermal resistance

(A) P-4, Q-1, R-3, S-2

(B) P-4, Q-3, R-1, S-2

(C) P-3, Q-2, R-1, S-4

(D) P-2, Q-1, R-3, S-4

[GATE 2014 Set 4, 1 mark]

Question #6

For laminar forced convection over a flat plate, if the free stream velocity increases by a factor of 2, the average heat transfer coefficient

(A) remains same

(B) decreases by a factor of $\sqrt 2$

(C) rises by a factor of $\sqrt 2$

(D) rises by a factor of 4

[GATE 2014 Set 2, 1 mark]

Question #7

Consider a two-dimensional laminar flow over a long cylinder as shown in the figure below. The free stream velocity is U and the free stream temperature T is lower than the cylinder surface temperature Ts. The local heat transfer coefficient is minimum at point

(A) 1

(B) 2

(C) 3

(D) 4

[GATE 2014 Set 2, 1 mark]

Question #8

A fluid (Prandtl number, Pr = 1) at 500 K flows over a flat plate of 1.5 m length, maintained at 300 K. The velocity of the fluid is 10 m/s. Assuming kinematic viscosity, ν = 30 × 10−6 m 2/s, the thermal boundary layer thickness (in mm) at 0.5 m from the leading edge is __________

[GATE 2016 Set 1, 2 marks]

Question #9

For flow through a pipe of radius R, the velocity and temperature distribution are as follows:
U(r,x)=C1 and $T(r,x)=C_{2}\left [ 1-\left ( \frac{r}{R} \right )^3\right ]$  , where $C_{1}$ and $C_{2}$ are constants. The bulk mean temperature is given by

$T_{m}=\frac{2}{U_{m}R^2}\int_{0}^{R}u(r,x)T(r,x)rdr$

with Um being the mean velocity of flow. The value of Tm is

(A) $\frac{0.5C_{2}}{U_{m}}$

(B) $0.5C_{2}$

(C) $0.6C_{2}$

(D)$\frac{0.6C_{2}}{U_{m}}$

[GATE 2015 Set 1, 1 mark]

Question #10

Water flows through a tube of diameter 25 mm at an average velocity of 1.0 m/s. The properties of water are 𝜌 = 1000 kg/m3, 𝜇 = 7.25 × 10−4 N.s/m2 , 𝑘 = 0.625 W/m.K,       Pr = 4.85. Using 𝑁u = 0.023 Re0.8 Pr0.4 , the convective heat transfer coefficient (in W/m2 .K) is ______

[GATE 2014 Set 2, 2 marks]

Question #11

The non-dimensional fluid temperature profile near the surface of a convectively cooled flat plate is given by

$\frac{T_{w}-T}{T_{w}-T_{\infty }}=a+b\frac{y}{L}+c\left ( \frac{y}{L} \right )^2$
where y is measured perpendicular to the plate, L is the plate length, and a, b and c are arbitrary constants. TW and T are wall and ambient temperatures, respectively. If the thermal conductivity of the fluid is k and the wall heat flux is q”, the Nusselt number
$N_{u}=\frac{q^{“}}{T_{w}-T_{\infty }}\frac{L}{k}$
is equal to

(A) a

(B) b

(C) 2c

(D) (b+2c)

[GATE 2014 Set 1, 2 marks]

Question #12

Consider one dimensional steady state heat conduction across a wall (as shown in figure below) of thickness 30 mm and thermal conductivity 15 W/m.K. At x = 0, a constant heat flux, q” = 1×105 W/m2 is applied. On the other side of the wall, heat is removed from the wall by convection with a fluid at 25°C and heat transfer coefficient of 250 W/m2 .K. The temperature (in °C), at x = 0 is _______

[GATE 2014 Set 1, 2 marks]

Practice other topics from Heat Transfer:

Conduction