484 ENGINEERING THERMODYNAMICS
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\M-therm\Th10-2.pm5- Relative humidity, φ = ppv
vs - A ‘Psychrometer’ is a device which is used for measuring dry bulb and wet-bulb temperatures simultaneously.
- The processes which affect the psychrometric properties of air are called ‘psychrometric processes’.
Important psychrometric processes are :
(i) Mixing of air streams (ii) Sensible heating
(iii) Sensible cooling (iv) Cooling and dehumidification
(v) Cooling and humidification (vi) Heating and dehumidification
(vii) Heating and humidification.
Objective Type Questions
Choose the Correct Answer :
- In an unsaturated air the state of a vapour is
(a) wet (b) superheated
(c) saturated (d) unsaturated. - 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. - 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. - During sensible heating of moist air, enthalpy
(a) increases (b) decreases
(c) remains constant (d) none of the above. - During sensible cooling, wet bulb temperature
(a) decreases (b) increases
(c) remains constant (d) can decrease or increase. - 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. - An air washer can work as a
(a) filter only (b) humidifier only
(c) dehumidifier only (d) all of the above. - The relative humidity, during sensible heating,
(a) can increase or decrease (b) increases
(c) decreases (d) remains constant. - The vapour pressure, during sensible heating of moist air,
(a) increases (b) decreases
(c) can increase or decrease (d) remains constant.