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Test: Correlations For Free Convection


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10 Questions MCQ Test Mass Transfer | Test: Correlations For Free Convection

Test: Correlations For Free Convection for Chemical Engineering 2022 is part of Mass Transfer preparation. The Test: Correlations For Free Convection questions and answers have been prepared according to the Chemical Engineering exam syllabus.The Test: Correlations For Free Convection MCQs are made for Chemical Engineering 2022 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Correlations For Free Convection below.
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Test: Correlations For Free Convection - Question 1

In respect to free convection over a vertical flat plate, the Nusselt number for laminar and turbulent flows varies respectively with Grashoff number G r as 

Detailed Solution for Test: Correlations For Free Convection - Question 1

Explanation: It varies as G r1/4 and G r1/3.

Test: Correlations For Free Convection - Question 2

Experimental results indicate that the local heat transfer coefficient h g for flow over a flat plate with an extremely rough surface is approximated by the relation
x = a x -0.12
Where a is a constant coefficient and x is distance from the leading edge of the plate. What is the relation between this local heat transfer coefficient and the average heat transfer coefficient for a plate of length x? 

Detailed Solution for Test: Correlations For Free Convection - Question 2

Explanation: h = 1.136 a x -0.12 = 1.136 h x.

Test: Correlations For Free Convection - Question 3

 For the free convection circumstances, the following dimensionless numbers apply
(i) Grashof number
(ii) Prandtl number
(iii) Nusselt number
Identify the correct answer

Detailed Solution for Test: Correlations For Free Convection - Question 3

Explanation: All these numbers are useful in free convection.

Test: Correlations For Free Convection - Question 4

 Two horizontal steam mains with diameters 5 cm and 15 cm are to be laid in a boiler house that any mutual heat effect is precluded. The mains are at the same surface temperature of 500 degree Celsius whilst the ambient air is at 50 degree Celsius. Workout the ratios of the heat transfer coefficients

Detailed Solution for Test: Correlations For Free Convection - Question 4

Explanation: h 1/h 2 = (d 2/d 1) 0.25 = 1.136.

Test: Correlations For Free Convection - Question 5

Consider the above problem, workout the heat losses from one meter length of the mains

Detailed Solution for Test: Correlations For Free Convection - Question 5

Explanation: Q 1/Q 2 = h l/h 2 l = 0.438.

Test: Correlations For Free Convection - Question 6

A spherical heater of 20 cm diameter and at 60 degree Celsius is immersed in a tank of water at 20 degree Celsius. Determine the value of convective heat transfer coefficient 

Detailed Solution for Test: Correlations For Free Convection - Question 6

Explanation: h = Nusselt number (k/d) = 458.32 W/mK.

Test: Correlations For Free Convection - Question 7

 A steam pipe 50 mm diameter and 2.5 m long has been placed horizontally and exposed to still air at 25 degree Celsius. If the pipe wall temperature is 295 degree Celsius, determine the rate of heat loss. At the mean temperature difference of 160 degree Celsius, the thermo-physical properties of air are
k =3.64 * 10 -2 W/m K
v =30.09 * 10 -6 m2/s
r =0.682
Β =1/160 + 273 = 2.31 * 10 -3 per K

Detailed Solution for Test: Correlations For Free Convection - Question 7

Explanation: Q = h A d t, where h = 14.60 k/D.

Test: Correlations For Free Convection - Question 8

 Consider the above problem, find out the Grashof number 

Detailed Solution for Test: Correlations For Free Convection - Question 8

Explanation: Grashoff number = D 3 P 2 (β g d t)/µ 2.

Test: Correlations For Free Convection - Question 9

Estimate the heat transfer from a 40 W incandescent bulb at 125 degree Celsius to 25 degree Celsius in quiescent air. Approximate the bulb as a 50 mm diameter sphere. The approximate correlation for the convection coefficient is
Nu = 0.60 (Gr Pr) 0.25
Where the different parameters are evaluated at the mean film temperature, and characteristics length is the diameter of the sphere

Detailed Solution for Test: Correlations For Free Convection - Question 9

Explanation: Q = h A d t = 7.71 W.

Test: Correlations For Free Convection - Question 10

Consider the above problem, find what percent of power is lost by free convection?

Detailed Solution for Test: Correlations For Free Convection - Question 10

Explanation: Percentage of power lost by free convection = 7.71 * 100/40 = 19.278%.

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