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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
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
where r is in cm & log is Natural logarithmic function. then the heat transfer rate per unit length is _________ kW.
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
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.
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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