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QUESTION: 1

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

Solution:

It mostly increasers if a denser fluid is used.

QUESTION: 2

For laminar 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?

Solution:

The dynamic viscosity has an inverse relation to 1/6 power. To double the convective heat transfer coefficient, the dynamic viscosity has to be decreased 64 times.

QUESTION: 3

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

Solution:

The average heat transfer coefficient reduces with length as 1/5th power of the length.

QUESTION: 4

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}

Solution:

Q = 2 h A d t = 153 MW.

QUESTION: 5

Consider the above problem, find the value of Grashoff number

Solution:

Grashof number = l ^{3 }p ^{2 }β g d t/µ ^{2}.

QUESTION: 6

A thin walled duct of 0.5 m diameter has been laid in an atmosphere of quiescent air at 15 degree Celsius and conveys a particular gas at 205 degree Celsius. Base your calculations on one meter length of the duct, estimate the convective coefficient of heat transfer

Solution:

h = 1.37 (d t/l) ^{0.25} = 5.086 W/m^{2} K.

QUESTION: 7

Free correction modulus is given by

Solution:

It contains only fluid properties and is called the free convection modulus.

QUESTION: 8

The free convection coefficient is given by

h = C _{1} d t ^{m}/l ^{1 – 3m}

The value of exponent for laminar flow is

Solution:

For laminar flow h = C _{1} (d t/l) ^{0.25}.

QUESTION: 9

For inclined plates we multiply Grashoff number with

Solution:

It should be multiplied with cos α, as α is angle with the horizontal.

QUESTION: 10

The free convection coefficient is given by

h = C _{1} d t ^{m}/l ^{1 – 3m}

The value of exponent for turbulent flow is

Solution:

For turbulent flow h = C (d t).

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