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BARC 2019: Heat Transfer Nuclear Quiz-2
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Question 1
A 100 m long electrical wire of 10 mm diameter with thermal conductivity 30 W/m
is carrying voltage 200 V. Temperature of wire at half of radius of wire is found to be 103 
. if the heated wire is in air having heat transfer coefficient of 15 W/m2 
. What is the electrical conductivity of wire?
is carrying voltage 200 V. Temperature of wire at half of radius of wire is found to be 103 . if the heated wire is in air having heat transfer coefficient of 15 W/m2 . What is the electrical conductivity of wire? Question 2
Hot air at atmospheric pressure and 80 °C enters an 8 m long uninsulated rectangular duct of cross section 0.3 m 
0.2 m that passes through the top of a house at a rate of 0.15 m3/s. The duct is observed to be nearly isothermal at 60 °C. Determine the LMTD of air.
0.9994 kg/m3, Cp =1008 J/kg °C, k = 0.02953 W/m °C, Pr = 0.7154 
m2/s
0.2 m that passes through the top of a house at a rate of 0.15 m3/s. The duct is observed to be nearly isothermal at 60 °C. Determine the LMTD of air. 0.9994 kg/m3, Cp =1008 J/kg °C, k = 0.02953 W/m °C, Pr = 0.7154 m2/s Question 3
Heat engine oil available at 1500C flowing through the shell side is used to heat 2.4 kg/s of water from 200C to 800C in a shell and tube heat exchanger. Water flows through eight tubes of 25 mm diameter.The exit oil temperature is 900C. Take oil side heat transfer coefficient as 400 W/m2-K.The overall heat transfer coefficient is _______ W/m2-K. Take Pr= 3.55
Question 4
Water flows through a pipe of diameter 30 mm at an average velocity of 2 m/s. The properties of water:
= 9× 
Ns/m2, 
= 1000 kg/m3, h= 4500 W/m2K, K =0.725 W/mK
For turbulent flow, Nu = 0.037 Re4/5Pr1/3
For laminar flow, Nu = 0.664 Re1/2Pr1/3
The correct relationship between velocity boundary layer thickness (
and thermal boundary layer thickness (
is
= 9× Ns/m2, = 1000 kg/m3, h= 4500 W/m2K, K =0.725 W/mK For turbulent flow, Nu = 0.037 Re4/5Pr1/3
For laminar flow, Nu = 0.664 Re1/2Pr1/3
The correct relationship between velocity boundary layer thickness (
and thermal boundary layer thickness ( is Question 5
A hollow sphere shape liquid chemical mixer having 150 mm internal diameter and 300 mm outer diameter and made of a material of thermal conductivity 75 W/mK. The inner and outer surface temperatures are 400
and 200
respectively. Assume the steady state conditions and temperature varies in radial direction only. The temperature (in 
) at the mid of the way between the inner and outer surfaces is
and 200 respectively. Assume the steady state conditions and temperature varies in radial direction only. The temperature (in ) at the mid of the way between the inner and outer surfaces is Question 6
A plane wall 0.30 m thick generates heat uniformly at the rate of 5 × 104 W/m3. The convective heat transfer coefficient between each face of the wall and the ambient air is 50 W/m2K. Assume the ambient air temperature to be 25
, the walls have same temperature on both the sides & the thermal conductivity of the wall material to be 25 W/m K. The maximum temperature (
) in the wall is
, the walls have same temperature on both the sides & the thermal conductivity of the wall material to be 25 W/m K. The maximum temperature () in the wall is Question 7
A spherical shaped orange (k= 0.3W/m℃) 80mm in diameter undergoes ripening process and generates 5000W/m3 of energy. If external temperature of orange is 10℃ and it is surrounded by air having heat transfer coefficient 20W/m2-k then the maximum temperature (℃) in at the centre of orange will be
Question 8
A counter flow heat exchanger using steam as hot fluid is used to heat water at flow rate of 2.917kg/sec. The inlet and exit temperature of hot fluid is 175 °C and 135 °C and for cold fluid is 30 °C and 75 °C respectively. If the heat transfer coefficient is 350W/
, find percentage change in heat transfer area if flow changes from counter flow to parallel flow.
, find percentage change in heat transfer area if flow changes from counter flow to parallel flow. Question 9
An uninsulated air conditioning duct of rectangular cross section 1 m x 0.5 m, carrying air at 20 ° C with velocity of 10 m/s. is exposed to an ambient of 30C. Neglect the effect of duct construction material. Fo rair in the range of 20-30 °C, data are as follow: thermal conductivity = 0.025 W/m, K Viscosity = 18 µPa. s, Prandlt number = 0.73, density = 1.2 kg/m3.the laminar flow nusselt number is 3.4 for constant wall temperature conditions and, for turbulent flow, Nu = 0.023 Re0.8 Pr0.33. Find out the Reynold number for the flow.
Question 10
A heat exchanger is used to cool down hot water for a process plant. The hot water of mass flow rate 0.035 kg/s enters at 370 ℃ and leaves at 300 ℃ while the cooling water of mass flowrate 0.027 kg/s enters at 270 ℃and 218 ℃. Take specific heat of both the fluids as 4087 J/kg℃.The fraction of heat loss through Heat exchanger is
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