Heat Transfer GATE-2015
Q 1. Two infinitely large parallel plates (I and II) are held at temperatures T1 and TII (TI > TII) respectively, and placed at a distance 2d apart in vacuum. An infinitely large flat radiation shield (III) is placed in parallel in between I and II. The emissivities of all the plates are equal. The ratio of the steady state radiative heat fluxes with and without the shield is:
Q 2. In the figure given below, the temperature profiles of cold and hot fluids in counter-current double-pipe heat exchangers (in different modes of operation) are shown on the left. For each case, match the heat exchanger process for the fluid represented by bold curve with the options given on the right.
 | (P) Heating of sub-cooled feed to super-heated vapor |
 | (Q) Condensation of super-heated vapor |
 | (R) Boiling of sub-cooled liquid |
 | (S) Condensation of saturated vapor followed by sub-cooling |
Q 3. A heated solid copper sphere (of surface area A and volume V) is immersed in a large body of cold fluid. Assume the resistance to heat transfer inside the sphere to be negligible and heat transfer coefficient (h), Density (ρ), heat capacity (C), and the thermal Conductivity (k) to be constant. Then, at time t, the temperature difference between the sphere and the fluid is proportional to:
Q 4. Air is flowing at a velocity of 3 m/s perpendicular to a long pipe as shown in the figure given below. The outer diameter of the pipe is d = 6 cm and temperature at the outside surface of the pipe is maintained at 100o C. The temperature of the air far from the tube is 30o C.
Data for air: Kinematic viscosity, ν = 18×10-6 m2/s; Thermal conductivity, k =0.03 W/(m.K). Using the Nusselt number correlation: Nu=\frac{hd}k=0.024\times{Re}^{0.8} , the rate of heat loss per unit length (W/m) from the pipe to air (up to one decimal place) is __________________.
Q 5. Consider a solid block of unit thickness for which the thermal conductivity decreases with an increase in temperature. The opposite faces of the block are maintained at constant but different temperatures: T (x = 0) > T (x = 1). Heat transfer is by steady-state conduction in the x-direction only. There is no source or sink of heat inside the block. In the figure given below, identify the correct temperature profile of the block.
