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GATE 2019: Heat Transfer Rapid Revision Quiz

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Question 1

Solar radiation of 1000 W/m2 falls perpendicularly on a grey surface of emissivity 0.6. if the surface temperature is 40 °C and surface emissive power is 500 W/m2 the radiosity of that will be

Question 2

A water at 15˚C is used to cool methyl glycol from 100˚C to 60˚C. Both the fluids pass through a concentric tube heat exchanger with a mass flow rate of 0.5 kg/s. Which mode of operation is preferred. The following are the properties of fluids :
Cc = 4187 J/kgK ; Ch = 2650 J/kgK
kc = 0.63 W/mK ; kh = 0.33 W/mK

Question 3

A steam container with thick walled hemispherical end of inner diameter 324 mm and geometric mean radius of 170 mm. The container is to be thermally insulated with a material having thermal conductivity k W/m and it is placed in surrounding having 10 W/m2 K heat transfer coefficient. So what should be value of k to reduce heat transfer from end ?

Question 4

Nusselt number signifies the ratio of

Question 5

If the temperatures at the inlet of a hot and cold fluid are 150℃ and 30℃ and outlet are 90℃ and 60℃, determine the overall heat transfer coefficient for the above HE which is much efficient. If the HE have area 8 m2. Take heat transfer is equal to 74 kW.

Question 6

The properties of mercury at 300 K are: Density = 13529 kg/m3, Cp = 0.1393 kJ/kg-K, Dynamic viscosity = 0.1523 × 10–2 N-s/m2 and Thermal conductivity = 8.540 W/m-K. The Prandtl number of the mercury at 300 K is

Question 7

A hollow cylinder of a material that has a thermal conductivity of 3.46 W/m-K 0C has an inner radius of 7.5 cm and an outer radius of 15 cm. The temperature of the inner surface is 1500C and the temperature profile is given by
Description: Description: E:\Gate\SSC JE Mechanical Part 1\Made Easy Questions\08_Heat-Transfer_BLok_files\image066.png    
 where r is in cm & log is Natural logarithmic function. then the heat transfer rate per unit length is _________ kW.

Question 8

Heat transfer through a composite wall is shown in figure. Both the sections of the wall have equal thickness (l). The conductivity of one section is k and that of the other is 2k. The left face of the wall is at 600 K and the right face is at 300 K.

The interface temperature Ti (in K) of the composite wall is

Question 9

A iron bar 0.4 m long is connected to the walls of two heated reservoirs each at 150 °C. The ambient air temperature is 35 °C and convective heat transfer coefficient is 17.4 W/m2-K. The thermal conductivity of iron is 52 W/m-K. What is the rate of heat loss from the bar?

Question 10

Water (specific heat, cp = 4.18 kJ/kg-K) enters a pipe of diameter 100 mm and length 2m at a rate of 0.02 kg/s and temperature of 25 °C. The pipe is subjected to a wall heat flux qw = 2000 W/m2, where is in meter and in the direction of flow ( = 0 at the inlet), the bulk mean temperature of the water leaving the pipe in °C is

Question 11

Heat is being transferred by convection from water at 48 °C to a glass plate whose surface that is exposed to the water is at 40 °C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of glass is 1.2 W/mK. The spatial gradient of temperature in the water at the water-glass interface is dT/dy = 1×104 K/m.
Description: D:\GradeStack Courses\GATE Tests (Sent by Ravi)\GATE ME-28-Mar\GATE-ME-2003_files\image432.jpg
The value of the temperature gradient in the glass at the water-glass interface is K/m is

Question 12

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 W/m2.K. The ambient temperature is 30 °C. Heat is uniformly generated inside the object at the rate of 100 W/m3. Assuming the face PQRS to be at uniform temperature, its steady state temperature is

Question 13

A cylindrical body of 30 cm diameter, 170 cm long having a uniform temperature of 75 °C and thermal conductivity k is 6.08 W/m-K is placed in a surrounding of 20 °C with a heat transfer coefficient to of 8 W/m2-K. The Biot number is ____________.

Question 14

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 = 0.023Re0.8Pr0.4, the convective heat transfer coefficient (in W/m2.K) is ________.

Question 15

A long laddle is used to fry potatoes in hot oil kept at a temperature of 200 as shown in the figure. The section of the handle of the ladle is 6mm×18mm. The surroundings are at 27. The conductivity of the material is 195W/m. If the temperature at a distance of 350mm from the oil should not reach 45, determine the convective heat transfer coefficient.
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