## Refrigeration and Air-conditioning Miscellaneous

#### Refrigeration and Air-conditioning

1. If a mass of moist air contained in a closed metallic vessel is heated, then its

1. ##### Correct Option: A

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

1. NA

##### Correct Option: C

NA

1. 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 a 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

1. Mass flow rate of condensate,
w = ṁa (w1 - w2) 3 × (.019 - .008) = .033kg/s
By applying energy balance equation we get
a h1 = ṁa h2 + ṁa hfg + Q
3 × 85 = 3 × 43 + 0.033 × 67 + Q
Q = 123.8 kW

##### Correct Option: B

Mass flow rate of condensate,
w = ṁa (w1 - w2) 3 × (.019 - .008) = .033kg/s
By applying energy balance equation we get
a h1 = ṁa h2 + ṁa hfg + Q
3 × 85 = 3 × 43 + 0.033 × 67 + Q
Q = 123.8 kW

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

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

##### Correct Option: C

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

1. Various psychrometric processes are shown in the figure below.
process in FigureName of the Process
P. 0-1(i) Chemical dehumidification
Q. 0-2(ii) Sensible heating
R. 0-3(iii) Cooling and dehumidification
S. 0-4 (iv) Humidification with steam injection
T. 0-5(v) Humidification with water injection

The matching pair are

1. Process 0 - 1 : DBT ↑ ,w C; sensibleheating
Process 0 - 2 : DBT ↑ ,w ↓ ;heating & dehumidification
Process 0 – 3; Cooling and dehumidification
Process 0 – 4 ; Humidification with water injection (DBT↓, w ↑)
Process 0 – 5; DBT ↑, w ↑ : Humidification with steam injection.

##### Correct Option: B

Process 0 - 1 : DBT ↑ ,w C; sensibleheating
Process 0 - 2 : DBT ↑ ,w ↓ ;heating & dehumidification
Process 0 – 3; Cooling and dehumidification
Process 0 – 4 ; Humidification with water injection (DBT↓, w ↑)
Process 0 – 5; DBT ↑, w ↑ : Humidification with steam injection.