CENG 231 Heat and Mass Transfer
Tutorial Example 11
Q1. Air flows through a cylindrical tube made of naphthalene at a velocity of 5 m/s. the diameter of the
tube is 0.1 m and the temperature of the air is 20 oC. Calculate the mass transfer coefficient using
Reynolds analogy and j factor analogy. Explain the difference in the mass transfer coefficients
estimated using different models.
(Ans. 0.0146, 6.326 x10-3 m/s)
Q2. If the temperature rise per meter length along a pipe carrying air at 12.2 m/s is 66 K, what will be
the corresponding pressure drop for a pipe temperature of 420 K and an air temperature of 310 K? The
density of air is 1.14 kg/m3 and assumed to be constant. Using Reynolds analogy.
(Ans. 155.47 Pa/m)
Q3. Water at 25oC enters a 5 m long 30 mm ID smooth tube which is used to cool a nuclear reactor.
The water flow rate is 2x10-3 m3/s. The tube wall temperature is kept constant at 145oC. Determine the
exiting water temperature and total heat transfer using both the Reynolds and Colburn analogy (i.e. j
factor) . Use the Moody diagram to estimate Cf.
Density
Viscosity
Thermal conductivity
Specific heat capacity
: 982 kg/m3
: 4.2 cP
: 0.66 W/m K
: 2.187 kJ/kg K
(Ans. 131.25oC, 873.72 kW; 50.87oC, 212.74 kW)
Q4. In a gas cooled nuclear reactor, coolant flows in a channel of diameter 8 cm and length of 2.6 m
with a rate of 0.0052 kg/s. The inlet and outlet pressures are 5.08 MPa and 5 MPa respectively.
Calculate the heat transfer coefficient using Reynolds analogy. The properties of coolants are :
 = 0.65 kg/m3
 = 32.9 x 10-6 kg/ms
k = 0.268 W/m K
Cp = 5.2 kJ/kg K
(Ans. 2 x 106 W/m2 K)
Q5. It is required to warm a quantity of air form 289 K to 313 K by passing it through a number of
parallel metal tubes of inner diameter 50 mm maintained at 373 K. The pressure drop must not exceed
250 Pa. How long should the individual tubes be? The density of air at 301 K is 1.19 kg/m 3 and the
coefficients of heat transfer by convection from the tube to air are 45, 62 and 77 W/m2 K for velocities
of 20, 24 and 30 m /s at 301 K respectively.
(Ans. 1.955)
Q.6 Calculate rise in temperature of water which is passed at 3.5 m/s through a smooth 25 mm
diameter pipe, 6 m long by using Reynolds analogy. The water enters at 300 K and tube wall may be
assumed constant at 330 K.
Properties of water :
 = 1000 kg/m3
k = 0.65 W/m K
(Ans. 326.01 K)
 = 0.7 x 10-3 kg/ms
Cp = 4.18 kJ/kg K