Previous Years GATE Questions on Convection

Solved GATE Questions on Convection

Question 1. Water (Prandtl) flows over a flat plate which is heated over the entire length. Which one of the following relationship between the hydrodynamic boundary layer thickness () and the thermal boundary layer thickness () is true?

(A) 

(B) 

(C) 

(D) Cannot be predicted

GATE-ME-2001

Hint

Question 2. The properties of mercury at 300 K are : density=13529 , specific heat at constant pressure =0.1393 kJ/kg-K, dynamic viscosity=0.1523 and thermal conductivity=8.540 . The Prandtlnumber of the mercury at 300 K is

(A) 0.0248

(B) 2.48

(C) 24.8

(D) 248

GATE-ME-2002

Hint

Data for Question 3-4 are given below. Solve the problems and choose correct answers.

Heat is being transferred by convection from water at 48  to a glass plate whose surface that is exposed to the water is 40. The thermal conductivity of water is 0.6 W/m K and the thermal conductivity of glass is 1.2 W/m K. The spatial gradient of temperature in the water –glass is 1.2 W/mK. The spatial gradient of temperature in the water –glass interface  is 

Question 3. The value of the temperature gradient in the glass at the water –glass interface in K/m is

(A) 

(B) 0.0

(C) 

(D) 

GATE-ME-2003

Hint

Question 4. The heat transfer coefficient h in  is

(A) 0.0

(B) 4.8

(C) 6

(D) 750

GATE-ME-2003

Hint

Question 5. In a condenser, water enters at 30 and flows at the rate 1500 kg/hr. The condensing steam is at a temperature of 120 and cooling water leaves the condenser at 80. Specific heat of water is 4.187 kJ/kg K. If the overall heat transfer coefficient is 2000 , then heat transfer area is

(A) 0.707 

(B) 7.07 

(C) 70.7 

(D) 141.7 

GATE-ME-2004

Hint

Statement for Linked Answer Questions 6 and 7:

An un-insulated air conditioning duct of rectangular cross section 1m0.5 m, carrying air at 20 with a velocity of 10 m/s, is exposed to an ambient air of 30. Neglect the effect of duct construction material. For air in the range of 20-30, data are as follows: thermal conductivity =0.025 W/m K ; velocity 18 ; Prandtl number=0.73 ; density=1.2 .the laminar flow Nusselt number is 3.4 for constant wall temperature conditions and, for turbulent flow, Nu=0.023

Question 6. The Reynolds number for the flow is

(A) 444

(B) 890

(C) 4.44

(D) 5.33

GATE-ME-2005

Hint

Question 7. The heat transfer per metre length of the duct, in watts, is

(A) 3.8

(B) 5.3

(C) 89

(D) 769

GATE-ME-2005

Hint

Question 8. The average heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assume the plate temperature is uniform at any instant of time and radiation heat exchange with the surroundings is negligible. The ambient temperature is 25, the plate has a total surface area of 0.1 and a mass of 4 kg. The specific heat of the plate material is 2.5 KJ/kg K. The convective heat transfer coefficient in , at the instant when the plate temperature is 225 and the change in plate temperature with time , is

(A) 200

(B) 20

(C) 15

(D) 10

GATE-ME-2007

Hint

Question 9. The temperature distribution within the thermal boundary layer over a heated isothermal flat plate is given by , where  are the temperatures of free stream and plate respectively, and y is the normal distance measured from the plate. The local Nusselt stream based on the thermal boundary layer thickness  is given by

(A) 1.33

(B) 1.50

(C) 2.0

(D) 4.64

GATE-ME-2007

Hint

Question 10. For the three-dimensional object shown in the figure below, five faces are insulated. The sixth face (PQRS), which is not insulated, interacts thermally with the ambient, with a convective heat transfer coefficient of 10 . The ambient temperature is 30. Heat is uniformly generated inside the object at the rate of 100 . Assuming the face PQRS to be at uniform temperature, its steady state temperature is

(A) 10

(B) 20

(C) 30

(D) 40

GATE-ME-2008

Hint

Question 11. For flow of fluid over a heated plate, the following fluid properties are known

Viscosity=0.01 Pa.s ; specific heat at constant pressure =1 kJ/kg K;

Thermal conductivity=1 W/m K.

The hydrodynamic boundary layer thickness at specified location on the plate is 1 mm. the thermal boundary layer thickness at the same location is

(A) 0.001 mm

(B) 0.01 mm

(C) 1 mm

(D) 1000 mm

GATE-ME-2008

Hint

Question 12. A coolant fluid at 30 flows over a heated flat plate maintained at a constant temperature of 100. The boundary layer temperature distribution at a given location on the plate may be approximated as  where (y) (in m) is the distance normal to the plate and T is in . If thermal conductivity of the is 1.0 mK, the local convective heat transfer coefficient () at that location will be

(A) 0.2

(B) 1

(C) 5

(D) 10

GATE-ME-2009

Hint

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