Engineering :: Mass Transfer

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41.

For pure air at atmospheric conditions the Lewis number is

A.	<<1	B.	>>1
C.	?	D.	?

42.

For pure air at atmospheric conditions the Schmidt number is

A.	< 1	B.	1
C.	>1	D.	>>1

43.

The temperature of water cooled in a cooling tower is

A.	always less than the wet-bulb temperature of entering air	B.	always equal to the wet-bulb temperature of entering air
C.	always greater than the wet-bulb temperature of entering air	D.	always equal to the dry-bulb temperature of entering air.

44.

In the design of cooling towers the wet-bulb temperature approach is ordinarily specified to be

A.	from 5 to 10?F	B.	from 20 to 30?F
C.	from 30 to 35?F	D.	from 10 to 25?F

45.

In a cooling tower makeup fresh water must be added to replace losses from

A.	entrainment	B.	evaporation losses
C.	blowdown	D.	all of the above

46.

In an operating cooling tower the wet-bulb temperature of entering air is increased keeping all other variable constant. The outlet water temperature will

A.	remain constant	B.	decrease
C.	increase

47.

The cooling effect in a cooling tower can be increased by

A.	lowering the barometric pressure	B.	reducing the humidity of entering air
C.	increasing the air velocity over the wet surfaces	D.	all of the above

48.

When can the relative humidity of air decrease inspite of an increase in the absolute humidity?

A.	When the pressure rises	B.	When the pressure falls
C.	When the temperature rises	D.	When the temperature falls

49.

Under the same conditions

A.	1 m3 of dry air is lighter than 1 m3 of humid air	B.	1 m3 of humid air is lighter than 1 m3 of dry air
C.	both 1 m3 of dry air and 1 m3 of humid air have the same weight

50.

The percentage saturation and relative saturation of a vapour-gas mixture approach equality when the vapour concentration approaches

A.	0	B.	1
C.	0.5	D.	0.6