In natural convection heat transfer, the correlating parameter is the

The scales form in heat exchanges after a period of operation and provide additional resistance to heat transfer with some heat transfer coefficient . The reciprocal of this scale heat transfer coefficient is called .

A

scaling factor

B

forming factor

C

resisting factor

D

fouling factor

Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

A

Surrounding temperature

B

Average temperature of the fin

C

Temperature of the fin end

D

Constant temperature equal to that of the base

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

A

Convection

B

Radiation

C

Conduction

D

Both convection and conduction

A non-dimensional number generally associated with natural convection heat transfer is

A

Grashoff number

B

Nusselt number

C

Weber number

D

Prandtl number

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as

A

$${\left( {\Delta {\text{T}}} \right)^{\frac{1}{4}}}$$

B

$${\left( {\Delta {\text{T}}} \right)^{\frac{1}{2}}}$$

C

$${\left( {\Delta {\text{T}}} \right)^{\frac{5}{4}}}$$

D

$${\left( {\Delta {\text{T}}} \right)^{\frac{3}{4}}}$$

Heat transfer by natural convection is enhanced in system with

A

High viscosity

B

High co-efficient of thermal expansion

C

Low temperature gradients

D

Low density change with temperature

Heat transfer occurs by natural convection because change in temperature causes difference in

A

Viscosity

B

Density

C

Thermal conductivity

D

Heat capacity

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the

A

Existence of thermal boundary layer

B

Temperature gradient produced due to density difference

C

Buoyancy of the bubbles produced at active nucleation site

D

None of these

Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.

A

Grashoff

B

Biot

C

Stantan

D

Reynolds

For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area

A

Increases

B

Decreases

C

Remains constant

D

Passes through a maxima

In natural convection heat transfer, the correlating parameter is the

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