Heat transfer quiz 2015

HEAT TRANSFER QUIZ

Q. 1 For a pure liquid the rate of change of vapour pressure with temperature os 0.1 bar/K in the temperature range of 300 to 350K. If the boiling point of the liquid at 2 bar is 320K, the temperature(in K) at which it will boil at 1 bar (up to one decimal place) is......

Q. 2.Two infinitely large parallel plates (I and II) are held at temperatures T₁ and T_II (T_I > T_II) 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:

0.5
0.75
0.25
0

Q. 3 In the figure below, the temperature profiles of cold and hot fluids in counter-current double pipe heat exchanges ( in different modes of operation) are shown on the left. For each case, match the heat exchange process for the fluid represented by the bold curve with the options given on the right.

I-P,II-Q,III-R,IV-S
I-P,II-Q,III-S,IV-R.
I-P,II-Q,III-S,IV-R
I-Q,II-S,III-P,IV-R.

Q. 4 Consider a solid block of unit thickness for which the thermal conductivity decreases with an increase in temperatures: T(x = 0)>T(x = 1). Heat transfer is by steady state conduction in x-direction only. there is no source or sink of heat inside the block. In the figure below, Identify the correct temperature profile in the block.

I
II
III
IV

Q. 5 Air is flowing at a velocity of 3m/s perpendicular to a long pipe as shown in the figure below. The outer diameter of the pipe is d = 6cm and temperature at the outside surface of the pipe is maintained at 100 ⁰C. The temperature of the air far from the tube is 30 ⁰C.
Data for air : Kinematic viscosity, V=18×10^-6 m²/s; Thermal conductivity, k=0.03W/(m.k) using the Nusselt number correlation: Nu = hd/k = 0.024 * 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. 6 A heated solid copper sphere (of surface area A and volume v) is immersed in a large of cold fluid. Assume the resistance to heat transfer inside the sphere to be negligible and heat transfer coefficient (h), density (p), heat capacity (C), and thermal conductivity (k) to be constant then, at time t, the temperature difference between the sphere and the fluid is proportional to: