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GATE 2019: Heat Transfer Rapid Quiz-2

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Question 1

A metal ball of diameter 60 mm is initially at 2200C. The ball is suddenly cooled by an air jet of 20o C. The heat transfer coefficient is 200 W/m2.K. The specific heat of metal, thermal conductivity and density of the metal ball are 400 J/kg.K, 400 W/m K and 9000 kg/m, respectively.

The ball temperature (in oC) after 90 seconds will be approximately

Question 2

Match the column

Question 3

Temperature profile for horizontal plate when Tplate > Tair

Question 4

Two fluids, A and B exchange heat in a counter flow heat exchanger. Fluid A enters at 4200C and has mass flow rate of 2 kg/s. fluid B enters at 200C and also has mass flow rate of 2 kg/s, effectiveness of heat exchanger is 75%. The exit temperature (0C) of fluid B is (specific heat of fluid A is 1 kJ/kg-K and that of fluid B is 4 kJ/kg-K)

Question 5

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 6

A fin has 5mm diameter and 100mm length. The thermal conductivity of fin material is 400Wm−1K−1. One end of the fin is maintained at 130 ºC and its remaining surface is exposed to ambient air at 30 ºC. if the convective heat transfer coefficient is 40Wm-2K-1, the heat loss (in W) from the fin is

Question 7

Two infinite parallel plates are placed at a certain distance apart. If the heat transfer between the plate is to be reduced by 80%, then the number of radiation shields required to be inserted between the plates is ___________.
[Assume that the emissivities of plates and radiation shield are equal]

Question 8

A thin metal plate is exposed to solar radiation. The air and the surroundings are at 30 °C. The heat transfer coefficient by free convection from the upper surface of the plate is 17.4 W/m2K. The plate has an absorptivity of 0.9 at solar wavelength and an emissivity of 0.1 at the long wavelength. Neglecting any heat loss from the lower surface, determine the incident solar radiation intensity in kW/m2, if the measured equilibrium temperature of the plate is 50 °C. Stefan Boltzmann constant is 5.67×10-8 W/m2K4.

Question 9

A tubular heat exchanger is to be design for cooling from a temperature of 800C to 300C by a large stagnant water which may be assumed to remain constant at a temperature of 200C. The heat transfer surface consist of 30 m long straight tube of 20 mm inside diameter. The oil (specific gravity =0.8) flows through cylindrical tube with an average velocity of 50 cm/s. The overall heat transfer coefficient is 298.7 W/m20C. The heat transfer through the heat exchanger is _____________ kW.

Question 10

Water at 80 °C enters a counterflow heat exchanger with a mass flow rate or 0.5 kg/s. Air enters at 30 °Cwith a mass flow rate of 2.09 kg/s. If the effectiveness of the heat exchanger is 0.8, the LMTD (in °C) is

Question 11

A solid sphere of radius r1 = 20 mm is placed concentrically inside a hollow sphere of radius r2 = 30 mm as shown in the figure.

The view factor F21 for radiation heat transfer is

Question 12

A 10 mm diameter electrical conductor is covered by an insulation of 2 mm thickness. The conductivity of the insulation surface is 0.08 W/m-K and the convection coefficient at the insulation surface is 10 W/m2-K. Addition of further insulation of the same material will
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