Previous Years GATE Questions on Psychrometrics

Solved Gate Questions on Psychrometrics

Question 1. For air at a given temperature, as the relative humidity is increased isothermally,

(A) The wet bulb temperature and specific enthalpy increases

(B) The wet bulb temperature and specific enthalpy decreases

(D) The wet bulb temperature decreases and specific enthalpy increases

GATE-ME-2001

Hint 1. (Ans D)

Question 2. For air with a relative humidity of 80 %

(A) The dry bulb temperature is less than the wet bulb temperature

(B) The dew point temperature is less than wet bulb temperature

(D) The dry bulb and dew point temperatures are equal

GATE-ME-2003

Hint 2. (Ans B)

Question 3. Dew point temperature of air at one atmospheric pressure (1.013 bar) is 18 . The air dry bulb temperature is 30. The saturation pressure of water at 18 and 30 are 0.02062 bar and 0.04241 bar respectively. The specific heat of air and water vapour respectively are 1.005 and 1.00 kJ/kg K and the latent heat of vapourization of water at is 2500 kJ/kg. The specific humidity (kJ/kg of dry air) and enthalpy (kJ/kg of dry air) of this moist air respectively, are

(A) 0.01051, 52.64

(B) 0.01291, 63.15

(D) 0.01532, 81.40

GATE-ME-2004

Hint 3. (Ans B)

Given p=1.013 bar,

Specific humidity

=63.15 kJ/kg of dry air

Alternative method

Saturation pressure0.02062 bar

Partial pressure of air 0.04241 bar

Dry bulb temperature

Wet bulb temperature

Specific humidity,

Total enthalpy,

Question 4. During chemical dehumidification process of air

(A) Dry bulb temperature and specific humidity decreases

(B) Dry bulb temperature increases and specific humidity increases

(D) Dry bulb temperature and specific humidity increases

GATE-ME-2004

Hint 4. (Ans B)

Question 5. Various psychrometric processes are shown in the figure below.

Process in Figure	Name of the process
P. 0-1	1. Chemical dehumidification
Q. 0-2	2. Sensible heating
R. 0-3	3. Cooling and dehumidification
S. 0-4	4. Humidification and steam injection
T. 0-5	5. Humidification with water injection

The matching pairs are

(A) P-1, Q-2, R-3, S-4, T-5

(B) P-2, Q-1, R-3, S-5, T-4

(D) P-3, Q-4, R-5, S-1, T-2

GATE-ME-2005

Hint 5. (Ans B)

Question 6. Water at 42 is sprayed into a steam of air at atmospheric pressure, dry bulb temperature of 40 and wet bulb temperature of 20. The air leaving the spray humidifier is not saturated. Which of the following statement is true?

(A) Air gets cooled and humidified

(B) Air gets heated and humidified

(D) Air gets cooled and dehumidified

GATE-ME-2005

Hint 6 (Ans B)

Here,

Water sprayed at temperature

Since,

Question 7. For a typical sample of ambient air (35, 75% relative humidity and standard atmospheric pressure) the amount of moisture in kg per kg of dry air will be approximately

(A) 0.002

(2) 0.027

(D) 0.75

GATE-ME-2005

Hint 7. (Ans B)

Question 8. The statement concern psychrometric chart.

1. Constant relative humidity lines are uphill straight lines to the right

2. Constant wet bulb temperature lines are downhill straight lines to the right.

3. Constant specific volume lines are downhill straight lines to the right.

4. Constant enthalpy lines are coincident with constant wet bulb temperature lines.

Which of the statement are correct?

(A) 2 and 3

(B) 1 and 2

(3) 1 and 3

(D) 2 and 4

GATE-ME-2006

Hint 8. (Ans A)

Question 9. Dew point temperature is the temperature at which condensation begins when the air is cooled at constant

(A) Volume

(B) Entropy

(D) Enthalpy

GATE-ME-2006

Hint 9. (Ans C)

Air is cooled at constant pressure to make unsaturated air to saturated one

Question 10. Atmospheric air at a flow rate of 3 kg/s (on dry basis) enters a cooling and dehumidifying coil with an enthalpy of 85 kJ/kg of dry air and humidity ratio of 19 grams/kg of dry air. The air leaves the coil with an enthalpy of 43 kJ/kg of dry air and a humidity ratio of 8 grams/kg of dry air. If the condensate water leaves the coil with an enthalpy of 67 kJ/kg, the required cooling capacity of the coil in KW is

(A) 75.0

(B) 123.8

(D) 159.0

GATE-ME-2007

Hint 10. (Ans C)

Question 11. Air (at atmospheric pressure) at a dry bulb temperature of 40 and wet bulb temperature of 20 is humidified in an air washer operating with continuous water recirculation. The wet bulb depression (i.e., the difference between the dry bulb and the wet bulb temperature) at the exit is 25 % of that at the inlet. The dry bulb temperature at the exit of the air washer is closest to

(A) 10

(B) 20

(D) 30

GATE-ME-2008

Hint 11. (Ans C)

Wet bulb depression at the exit

Question 12. Moist air at a pressure of 100 kPa is compressed to 500 kPa and then cooled to 35 in an aftercooler . the air at the entry to the after cooler is unsaturated at the exit of the aftercooler. The saturation pressure of water at 35 is 5.628 kPa. The partial pressure of the water vapour (in kPa) in the moist air entering the compressor is closest to

(A) 0.57

(B) 1.13

(D) 4.52

GATE-ME-2008

Hint 12. (Ans B)

Assuming that compression is isentropic in air compressor, the process can be described on the T-s diagram. The process in the intercooler is at constant pressure.