9 + Interview Questions in GENERAL QA IN PSYCHROMETRICS Page 1 InterviewSolution

1.	During sensible heating of moist air, enthalpy (a) increases (b) decreases (c) remains constant (d) none of the above
Answer» (a) increases

Discussion

2.	An air washer can work as a (a) filter only (b) humidifier only (c) dehumidifier only (d) all of the above.
Answer» (d) all of the above.

Discussion

3.	Which one of the following statements is correct ? (a) Evaporative cooling and sensible cooling is the same (b) Evaporative cooling is a cooling and humidification process (c) Evaporative cooling is a cooling and dehumidification process (d) Evaporative cooling is not effective for hot and dry climates
Answer» (b) Evaporative cooling is a cooling and humidification process

Discussion

4.	Which one of the following statements is correct ? (a) Dew point temperature can be measured with the help of thermometer (b) Dew point temperature is the saturation temperature corresponding to the partial pressure of the water vapour in moist air. (c) Dew point temperature is the same as the thermodynamic wet bulb temperature. (d) For saturated air, dew point temperature is less than the wet bulb temperature.
Answer» (b) Dew point temperature is the saturation temperature corresponding to the partial pressure of the water vapour in moist air.

Discussion

5.	The air supplied to a room of a building in winter is to be at 17°C and have a relative humidity of 60%. If the barometric pressure is 1.01325 bar, find : (i) The specific humidity ; (ii) The dew point under these conditions.
Answer» Dry bulb temperature, t_db = 17ºC Relative humidity, φ = 60% Barometric or total pressure, p_t = 1.01325 bar Specific humidity, W : Corresponding to 17ºC, from steam tables, p_vs = 0.0194 bar φ = \(\cfrac{p_v}{p_{vs}}\) 0.6 = \(\cfrac{p_v}{0.0194}\) p_v = 0.6 × 0.0194 = 0.01164 bar. Specific humidity, W = \(\cfrac{0.622\,p_v}{p_i-p_v}\) = \(\cfrac{0.622\times0.01164}{1.01325-0.01164}\) = 0.00723 kg/kg of dry air. Dew point temperature, t_dp : If the air is cooled at constant pressure the vapour will begin to condense at the saturation temperature corresponding to 0.01164 bar. By interpolation from steam tables, the dew point temperature, t_dp is then t_dp = 9 + (10 – 9) × \(\cfrac{0.011642-0.01150}{10.01230-0.01150}\) = 9.18°C.

5.

The air supplied to a room of a building in winter is to be at 17°C and have a relative humidity of 60%. If the barometric pressure is 1.01325 bar, find : (i) The specific humidity ; (ii) The dew point under these conditions.

Answer»

Dry bulb temperature, t_db = 17ºC

Relative humidity, φ = 60%

Barometric or total pressure, p_t = 1.01325 bar

Specific humidity, W :

Corresponding to 17ºC, from steam tables,

p_vs = 0.0194 bar

φ = \(\cfrac{p_v}{p_{vs}}\)

0.6 = \(\cfrac{p_v}{0.0194}\)

p_v = 0.6 × 0.0194 = 0.01164 bar.

Specific humidity,

W = \(\cfrac{0.622\,p_v}{p_i-p_v}\) = \(\cfrac{0.622\times0.01164}{1.01325-0.01164}\)

= 0.00723 kg/kg of dry air.

Dew point temperature, t_dp :

If the air is cooled at constant pressure the vapour will begin to condense at the saturation temperature corresponding to 0.01164 bar. By interpolation from steam tables, the dew point temperature, t_dp is then

t_dp = 9 + (10 – 9) × \(\cfrac{0.011642-0.01150}{10.01230-0.01150}\)

= 9.18°C.

Discussion

6.	For saturated air (a) Wet bulb depression is zero (b) Wet bulb depression is positive (c) Wet bulb depression is negative (d) Wet bulb depression can be either positive or negative
Answer» (a) Wet bulb depression is zero

Discussion

7.	During sensible cooling, wet bulb temperature (a) decreases (b) increases (c) remains constant (d) can decrease or increase.
Answer» (a) decreases

Discussion

8.	In an unsaturated air the state of a vapour is (a) wet (b) superheated (c) saturated (d) unsaturated.
Answer» (b) superheated

Discussion

9.	The relative humidity, during heating and humidification, (a) increases (b) decreases (c) may increase or decrease (d) remains constant.
Answer» (a) increases

Discussion

Explore topic-wise InterviewSolutions in .

During sensible heating of moist air, enthalpy (a) increases (b) decreases (c) remains constant (d) none of the above

An air washer can work as a (a) filter only (b) humidifier only (c) dehumidifier only (d) all of the above.

The air supplied to a room of a building in winter is to be at 17°C and have a relative humidity of 60%. If the barometric pressure is 1.01325 bar, find : (i) The specific humidity ; (ii) The dew point under these conditions.

For saturated air (a) Wet bulb depression is zero (b) Wet bulb depression is positive (c) Wet bulb depression is negative (d) Wet bulb depression can be either positive or negative

During sensible cooling, wet bulb temperature (a) decreases (b) increases (c) remains constant (d) can decrease or increase.

In an unsaturated air the state of a vapour is (a) wet (b) superheated (c) saturated (d) unsaturated.

The relative humidity, during heating and humidification, (a) increases (b) decreases (c) may increase or decrease (d) remains constant.