Heat Transfer MCQ on Empirical Correlations for Free and Forced convection

This is an MCQ-based quiz on the topic of Empirical Correlations for Free and Forced convection

This includes the following:-

Correlations for Forced Convection
Laminar Flow
Turbulent Flow

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The convective heat transfer coefficient in laminar flow over a flat plate

Increases with distance Increases if a higher viscosity fluid is used Increases if a denser fluid is used Decreases with increase in free stream velocity

For laminar flow over a flat plate, the average value of a Nusselt number is prescribed by the relation Nu = 0.664 (Re) 0.5 (Pr) 0.33 Which of the following is then a false statement?

Density has to be increased four times Plate length has to be decreased four times Specific heat has to be increased four times Dynamic viscosity has to be decreased sixteen times

For turbulent flow over a flat plate, the average value of Nusselt number is prescribed by the relation Nu = 0.664 (Re) 0.5 (Pr) 0.33 Which of the following is then a false statement? The average heat transfer coefficient increases as

1/5 power of plate length 2/3 power of thermal conductivity 1/3 power of specific heat 4/5 power of a free stream velocity

A nuclear reactor with its core constructed of parallel vertical plates 2.25 m high and 1.5 m wide has been designed on free convection heating of liquid bismuth. Metallurgical considerations limit the maximum surface temperature of the plate to 975 degree Celsius and the lowest allowable temperature of bismuth is 325 degree Celsius. Estimate the maximum possible heat dissipation from both sides of each plate. The appropriate correlation for the convection coefficient is Nu = 0.13 (Gr Pr) 1/3

143 MW 153 MW 163 MW 173 MV

Consider the above problem, find the value of Grashoff number

101.3 * 10 12 102.3 * 10 12 103.3 * 10 12 104.3 * 10 12

Free correction modulus is given by

p 2 β g c P/µ p 2 β g c P/k p 2 β g c P/µ k p 2 β g c P

The free convection coefficient is given by h = C 1 d t m/l 1 – 3m The value of exponent for laminar flow is

0.5 0.6 0.7 0.8

For inclined plates we multiply Grashoff number with

Cos 2 α Sin 2 α Sin α Cos α

The free convection coefficient is given by h = C 1 d t m/l 1 – 3m The value of exponent for turbulent flow is

0.43 0.33 0.23 0.13

The oil pan of 1.6 engine approximates a flat plate 0.3 m wide by 0.45 m long and protrudes below the framework of the automobile. The engine oil is at 95 degree Celsius and the ambient air temperature is 35 degree Celsius. If the automobile runs at 36 km/hr, make calculations for the rate of heat transfer from the oil-pan surface. Assume negligible resistance to conduction through the oil pan

190.37 W 180.37 W 170.37 W 160.37 W

Air flows through a 10 cm internal diameter tube at the rate of 75 kg/hr. Measurements indicate that at a particular point in the tube, the pressure and temperature of air are 1.5 bar and 325 K whilst the tube wall temperature is 375 K. Find heat transfer rate from one meter length in the region of this point The general non-dimensional correlation for turbulent flow in the tube is Nu = 0.023 (Re) 0.8 (Pr) 0.4 Where the fluid properties are evaluated at the bulk temperature

147.35 W 157.35 W 167.35 W 177.35 W

A heat treat steel plate measures 3 m by 1 m and is initially at 30 degree Celsius. It is cooled by blowing air parallel to 1 m edge at 9 km/hr. If the air is at 10 degree Celsius. Estimate the convection heat transfer from both sides of the plate

477.7 W 547.7 W 647.7 W 747.6 W

Calculate the rate of heat loss from a human body which may be considered as a vertical cylinder 30 cm in diameter, and 175 cm high while standing in a 30 km/hr wind at 15 degree Celsius. Human has a surface temperature of 35 degree Celsius

588.86 W 688.86 W 788.86 W 888.86 W

Consider the above problem for two fold increase in the diameter of the tube, the flow velocity is maintained constant by change in the rate of liquid flow

15% 14% 13% 12%

Quiz/Test Summary

Title: Heat Transfer MCQ on Empirical Correlations for Free and Forced convection

Questions: 14

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