Fluid Mechanics and Thermal Sciences - Online Test
Q1. If a mass of moist air contained in a closed metallic vessel is heated, then its
Answer : Option A
Explaination / Solution:
Given that mass of moist air contained in a closed metallic vessel is heated, means its specific
humidity (𝜔) is constant.
So, from the psychometric chart, 
We can say that at constant specific humidity, as temperature increases relative humidity
decreases i.e.,(Φ2<Φ1)
Q2. In a counter-flow heat exchanger, water is heated at the rate of 1.5kg/s from 40°C to 80°C by
an oil entering at 120°C and leaving at 60°C. The specific heats of water and oil are
4.2kJ/kg.K and 2kJ/kg.K respectively. The overall heat transfer coefficient is 400 W/m2.K.
The required heat transfer surface area (in m2) is
Answer : Option D
Explaination / Solution:
Given counter flow Heat Exchanger
Q3. The volume and temperature of air (assumed to be an ideal gas) in a closed vessel is 2.87 m3 and 300K, respectively. The gauge pressure indicated by a manometer fitted to the wall of the
vessel is 0.5bar. If the gas constant of air is R = 287 J/kg. K and the atmospheric pressure is 1
bar, the mass of air (in kg) in the vessel is
Answer : Option C
Explaination / Solution:
Q4. A calorically perfect gas (specific heat at constant pressure 1000 J/kg.K) enters and leaves a gas
turbine with the same velocity. The temperatures of the gas at turbine entry and exit are 1100 K
and 400 K. respectively. The power produced is 4.6 MW and heat escapes at the rate of 300 kJ/s
through the turbine casing. The mass flow rate of the gas (in kg/s) through the turbine is.
Answer : Option B
Explaination / Solution:
Q5. A metal ball of diameter 60mm is initially at 220 °C. The ball is suddenly cooled by an air jet
of 20°C. The heat transfer coefficient is 200 W/m2. K and 9000kg/m3, respectively. The ball
temperature (in °C) after 90 seconds will be approximately.
Answer : Option A
Explaination / Solution:
Q6. During the turning of a 20mm-diameter steel bar at a spindle speed of 400 rpm, a tool life of
20 minute is obtained. When the same bar is turned at 200 rpm, the tool life becomes 60
minute. Assume that Taylor's tool life equation is valid. When the bar is turned at 300 rpm, the
tool life (in minute) is approximately.
Answer : Option B
Explaination / Solution:
Taylors Tool life equation,
Q7. The instantaneous stream-wise velocity of a turbulent flow is
given as follows:
The time-average of the fluctuating velocity u’(x, y, z, t) is
Answer : Option C
Explaination / Solution:
No Explaination.
Q8. For a floating body, buoyant force acts at the
Answer : Option D
Explaination / Solution:
Buoyancy force is the force due to displaced volume of water. Hence,
buoyancy force always act on the centroid of displaced volume.
Q9. A plastic sleeve of outer radius r0 = 1 mm covers a wire (radius
r = 0.5 mm) carrying electric current. Thermal conductivity of the
plastic is 0.15 W/m-k. The heat transfer coefficient on the outer
surface of the sleeve exposed to air is 25 W/m2-K. Due to the
addition of the plastic cover, the heat transfer from the wire to the
ambient will
Answer : Option A
Explaination / Solution:
r = 0.5 mm, r0 = 1 mm.
Given, the wire is like a cylinder. Hence, critical radius of insulation is
Now if we add insulation (plastic cover), the heat transfer will
increase.
Q10. The INCORRECT statement about regeneration in vapor power
cycle is that
Answer : Option C
Explaination / Solution:
No Explaination.
