A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

A steam pipe is intended to be insulated with two layers of insulating materials of different thermal conductivities. For minimum heat transfer to take place

A

The better insulation material should be put just next to pipe (i.e., inside)

B

The better insulating material should be put outside

C

Either of the insulating material could be put on either side

D

Steam temperature is considered before deciding as to which insulating material is to be put inside (i.e., just next to the pipe)

A steam carraying pipeline is insulated with two layers of insulating materials with the inferior insulation material forming the inner part. If the two insulating layers are interchanged, the heat conducted will

A

Increase

B

Decrease

C

Remain unaffected

D

May increase or decrease; depends on the thickness of each layer

A tank is filled by three pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The second pipe fills the tank 5 hours faster than the first pipe and 4 hours slower than the third pipe. The time required by the first pipe is:

A

6 hours

B

10 hours

C

15 hours

D

30 hours

An insulating refractory brick should have high porosity and low thermal conductivity. Which of the following is not used for inducing porosity in the insulating refractory bricks during its manufacture?

A

Cork

B

Saw dust

C

Sand

D

Chemically prepared foam

A steam pipe is to be insulated by two insulating materials put over each other. For best results

A

Better insulation should be put over pipe and better one over it

B

Inferior insulation should be put over pipe and better one over it

C

Both may be put in any order

D

Whether to put inferior OIL over pipe or the better one would depend on steam temperature

A pipe fills a tank in P minuties and another pipe fills the tank in Q minutes. A different pipe makes the tank empty in R minutes. If all these three pipe are opened then in how many minutes the tank will be full?

A

p+q-qpqr

B

pq+pr-pqpqr

C

pq+qr-prpqr

D

pqrqr+pr-pq

Low thermal conductivity of heat insulating materials is due to its

A

Dense structure

B

High proportion of air space

C

High specific heat

D

None of these

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

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

A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

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