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GATE 2020: Heat Transfer Quiz 1

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Question 1

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 2

A composite wall is formed of a 5 cm copper plate, a 3.5 mm layer of asbestos, and a 4 cm layer of fiberglass. The wall is subjected to an overall temperature difference of 510 °C. Calculate the heat flow per unit area through the composite structure. Thermal conductivity of copper, asbestos and fiber glass are 370, 0.4 and 1.5 W/m °C respectively.

Question 3

A plane wall 0.30 m thick generates heat uniformly at the rate of 5 × 104 W/m3. The convective heat transfer coefficient between each face of the wall and the ambient air is 50 W/m2K. Assume the ambient air temperature to be 25 , the walls have same temperature on both the sides & the thermal conductivity of the wall material to be 25 W/m K. The maximum temperature () in the wall is

Question 4

A sphere of mass 5.5 kg and initially at a temperature of 290 K is suddenly emerged in a liquid of 15 K and convective heat transfer coefficient is 58 W/m2K. Estimate the time(in minutes) required to cool the sphere to 95K and the given properties are
ρ = 2700kg/m3, C= 900J/kg and k=205W/m K r=4.5 mm

Question 5

A cylindrical uranium fuel rod of radius 5 mm in a nuclear reactor is generating heat at the rate of 4 × 107 W/m3 the rod is cooled by a liquid (convective heat transfer coefficient 1000 W/m2-K) at 25 °C. At steady state, the surface temperature (in K) of the rod is

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
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