Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is

A

In the central core of the fluid

B

Uniformly distributed throughout the fluid

C

Mainly confined to a thin film of fluid near the surface

D

None of these

Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

A

Finned tube heat exchanger with air inside and steam outside

B

Finned tube heat exchanger with air outside and steam inside

C

Shell and tube heat exchanger with air inside tubes and steam on shell side

D

Shell and tube heat exchanger with air on shell side and steam inside tubes

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

In a shell and tube heat exchanger for a given heat transfer surface area, smaller diameter tubes are favoured as compared to larger diameter ones ; because the smaller diameter tubes

A

Are easier to clean

B

Are less prone to fouling

C

Can be fitted into a smaller shell diameter hence the cost of the heat exchanger would be less

D

None of these

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

For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of

A

1

B

1.74

C

6.1

D

37

In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is

A

Infinity

B

Zero

C

Same as average heat transfer co-efficient for tube side

D

None of these

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

A

Decreases the pressure drop

B

Decreases the outlet temperature of cooling medium

C

Increases the overall heat transfer coefficient

D

None of these

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

Tube side heat transfer co-efficient for turbulent flow of liquid through tubes is proportional to

A

G^0.2

B

G^0.5

C

G^0.8

D

G^1.5

Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.

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