Suppose saturated polar air has an air temperature and dew point of -10o C, and unsaturated desert air has an air temperature of 35o C and a dew point of 10o C. The desert air contains ______ water vapour and has a _______

Consider the following statements and choose the correct answer:
1. A direct proportionality exists between vapour pressure and the concentration of water vapour in the atmosphere
2. Relative humidity is an expression of the ratio of the actual vapour pressure of the atmosphere when saturated at the same temperature
3. A rise or fall in temperature with no change in vapour pressure will cause a drop or rise, respectively, in relative humidity
4. A rise or fall in vapour pressure with no change in temperature will be accompanied by a rise or fall, respectively, in relative humidity

A

1, 2, 3 and 4 are true

B

Only 3 and 4 are true

C

Only 2 and 4 are true

D

Only 1, 2 and 3 are true

An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is

A

0.048

B

0.079

C

0.122

D

0.152

High relative humidity decreases the evaporative process and as the temperature is increased, the relative humidity decreases. The comfort range for human body is the ambient temperature of 22 to 27°C with relative humidity ranging from __________ percent.

A

5 to 10

B

15 to 25

C

45 to 50

D

75 to 80

A vessel of volume 1000 m³ contains air which is saturated with water vapour. The total pressure and temperature are 100 kPa and 20°C respectively. Assuming that the vapour pressure of water at 20°C is 2.34 kPa, the amount of water vapour (in kg) in the vessel is approximately

A

17

B

20

C

25

D

34

Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele's method, this method

A

Is more accurate in finding the number of equilibrium stages

B

Accounts for the enthalpy changes in the process

C

Facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method

D

All of the above

Suppose it is a winter night and at about 11 p.m., the air cools to the dew-point temperature and a thick radiation fog develops. If the air continues to cool during the night, in 5 hours the dew point temperature will probably:

A

Decrease as the air becomes drier

B

Decrease as the air becomes moister

C

Increase as the air becomes drier

D

Increase as the air becomes moister

With increase in absolute humidity, the dew point of an unsaturated mixture of air and water vapor (at constant pressure and temperature)

A

Increases

B

Remains unchanged

C

Decreases

D

Decreases linearly

Relative humidity is given by (where p_v = Partial pressure of water vapour, p_b = Barometric pressure, p_s = Pressure of saturated air, p_d = Pressure at dry bulb temperature, p_w = Saturation pressure corresponding to wet bulb temperature and $$\mu $$ = Degree of saturation)

A

$$\frac{{0.622{{\text{p}}_{\text{v}}}}}{{{{\text{p}}_{\text{b}}} - {{\text{p}}_{\text{V}}}}}$$

B

$$\frac{\mu }{{1 - \left( {1 - \mu } \right)\frac{{{{\text{p}}_{\text{s}}}}}{{{{\text{p}}_{\text{b}}}}}}}$$

C

$$\frac{{{{\text{p}}_{\text{v}}}\left( {{{\text{p}}_{\text{b}}} - {{\text{p}}_{\text{d}}}} \right)}}{{{{\text{p}}_{\text{d}}}\left( {{{\text{p}}_{\text{b}}} - {{\text{p}}_{\text{v}}}} \right)}}$$

D

None of these

Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?

A

Humidification only

B

Heating only

C

Both heating and humidification

D

Evaporative cooling

Saturated solution of benzene in water is in equilibrium with a mixture of air and vapours of benzene and water at room temperature and pressure. Mole fraction of benzene in liquid is x_B and the vapour pressures of benzene and water at these conditions are P_v^B and P_v^w respectively. The partial pressure of benzene in air-vapour mixture is

A

PvB

B

XB.PvB

C

(Patm - Pvw)xB

D

XB.Patm