250+ TOP MCQs on HT Equipment – Pipe Wall Temperature and Flow in Pipe Profiles

Heat Transfer Operations Questions and Answers for Aptitude test on “HT Equipment – Pipe Wall Temperature and Flow in Pipe Profiles”.

1. Velocity profile in a pipe is independent of axial position whereas Temperature Profile is not.
a) True
b) False

Answer: a
Clarification: When a fluid flows through a pipe, the wall effect acts on it and eventually after some time the velocity profile gets fully developed, which is independent of axial position and depends only on radial position. Though this is not the case with Temperature profile in a fluid flowing through a constantly heated pipe, it depends on both axial and radial positions.

2. A liquid is heated by passing it through a circular pipe (k_pipe = 15W/mK, viscosity = 2.5×10^-5 Pa-s, C_p = 1000 J/Kg-K, k_liquid = 0.035 W/mK) of ID = 25mm and OD = 30mm with length L = 15 m. If the Reynolds No. is 79000. What is the outer surface average heat transfer coefficient?
a) 773KW/m²K
b) 83KW/m²K
c) 104KW/m²K
d) 43KW/m²K

Answer: b
Clarification: Nusselt number = 0.023×(Re)^0.8(Pr)^0.4
here Pr = Cpxμ/k, density=1Kg/m³ Hence Pr = 0.7
Nu = h×OD/k_pipe = 165, h = 83KW/m²K.

3. Given a fluid enters at a temperature of 22℃into a pipe of length 1m. On fully developed thermal flow, the wall temperature is 92℃, determine the temperature of the bulk of the liquid at exit. (Given λ = 0.5)
a) 50℃
b) 100℃
c) 104℃
d) 150℃

Answer: a
Clarification: The temperature profile for a fully developed thermal flow is,
T_bulk – T_wall = (T_inlet – T_wall)exp(-λL)
Where we have T_inlet = 22 ℃ and T_wall = 92 ℃, putting values we get T_bulk = 50 ℃.

4. The temperature profile of a fully developed Thermal flow in a pipe of length L can be defined by the formula. T_bulk – T_wall = (T_inlet – T_wall)e^λL
a) True
b) False

Answer: a
Clarification: The correct formula is T_bulk – T_wall = (T_inlet – T_wall)e^-λL where λ is constant = P.x.h_L /m.Cp.

5. Given the convective heat transfer Coefficient of the inner surface to be 15W/m²K, OD = 30mm and ID = 25mm. Find the outer surface heat transfer coefficient.
a) 15 W/m²K
b) 12 W/m²K
c) 12.5 W/m²K
d) 13.5 W/m²K

Answer: c
Clarification: The formula for heat transfer coefficients in a thick Pipe is,
h_inner ×ID = h_outer × OD
Hence, h_outer = 15×25/30 = 12.5W/m²K.

6. A non-conducting liquid is passed inside a metal tube carrying electricity (Voltage=220V, current=0.5A), what is the final temperature of the bulk of liquid if it enters at 10℃. (h =100 W/m²K, Area =0.2m²)
a) 25.5℃
b) 15.0℃
c) 15.5℃
d) 14.5℃

Answer: c
Clarification: The heat energy supplied by the metal at unit time = V×I = 220×0.5 = 110J
Hence final temperature, 110 = hA(To-Ti)
To = 110/(100×0.2) + 10 = 15.5 ℃.