Heat Transfer

431. Use of transverse baffles in a shell and tube heat exchanger is done to increase the

1. Rate of heat transfer
2. Flow velocity
3. Turbulence of shell side fluid
4. All (A), (B) and (C)

432. Vacuum is generally maintained in the vapour space of an evaporator mainly to

1. Get economical temperature difference by using moderate pressure steam
2. Facilitate forward feeding in multiple effect evaporation
3. Concentrate heat sensitive materials
4. Achieve very high concentration of the final product

433. Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is

1. 0.5
2. 2
3. 10
4. 100

434. Value of Prandtl number for water ranges from

1. 1 to 2
2. 5 to 10
3. 100 to 500
4. 1000 to 2000

435. Vent pipes are provided in a condenser to

1. Remove non-condensable gases
2. Purge the condenser
3. Facilitate easy cleaning of tubes
4. None of these

436. Vibrations in the tubes of a shell and tube heat exchanger is induced due to the

1. Flow of fluid on the tube and shell sides
2. Oscillations in the flow of shell/tube sides fluid
3. Vibrations transmitted through piping and/or supports due to external reasons
4. All (A), (B) and (C)

437. View factor is important in heat transfer by

1. Steady state conduction
2. Natural convection
3. Forced convection
4. Radiation

438. Viscosity of gases _________ with increase in temperature.

1. Increase very rapidly
2. Increase slowly
3. Decrease slowly
4. Remain unaffected

439. Viscous & heat sensitive liquids are concentrated in _________ evaporators.

1. Open pan
2. Long tube
3. Agitated film
4. None of these

440. Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?

1. 35.5
2. 43.75
3. 81.25
4. 48.25