Psychrometric Chart and Processes MCQ Quiz in தமிழ் - Objective Question with Answer for Psychrometric Chart and Processes - இலவச PDF ஐப் பதிவிறக்கவும்

Explanation:

Concept:

T_sp = Temperature of water sprayed = 42°C, DBT = Dry bulb temperature of air = 40°C

WBT = Dry bulb temperature of air = 20°C

Now,

Here we see that T_sp > DBT, Hence air gets heated. 

Also, water is added to it, so air gets humidified.

Concept:

A psychometric chart is represented as shown in the figure.

Dry Bulb Temperature: Actual temperature of gas or mixture of gases

Wet Bulb temperature: Temperature obtained by an accurate thermometer having a wick moistened with distilled water

Dew point temperature: Temperature at which the liquid droplets just appear when the moist air is cooled continuously.

Relative humidity along the saturation line is 100%.

The wet-bulb depression is the difference between the dry-bulb temperature and the wet-bulb temperature. If there is 100% humidity, dry-bulb and wet-bulb temperatures are identical, making the wet-bulb depression equal to zero.

In such conditions as the air becomes dry, this difference will increase. Because as the moisture content will decrease we will move away from the saturation line and hence the difference will increase between the dry bulb temperature and wet bulb temperature.

• The process in which the moisture or water vapour or water spray or humidity is added to the air without changing its dry bulb (DB) temperature is called a humidification process.
• So the given process of humidification. As the temperature of the water spray is higher than the temperature of the entering air so the process will be heating and humidification.

• In heating and humidification psychrometric process of the air, the dry bulb temperature as well as the humidity of the air increases.
• The heating and humidification process is carried out by passing the air overspray of water, which is maintained at a temperature higher than the dry bulb temperature of the air or by mixing air and steam. During winter it is essential to heat and humidify the room air for comfort.

Concept:

Every psychometric chart includes

• vertical lines that represent the constant dry bulb temperatures,
• The diagonal lines that represent wet bulb temperature and enthalpy
• curved lines that represent relative humidity.
• Horizontal lines represent constant Humidity ratio

Dry Bulb Temperature: Actual temperature of gas or mixture of gases.

Wet Bulb temperature: Temperature obtained by an accurate thermometer having a wick moistened with distilled water

Dew point temperature: Temperature at which the liquid droplets just appear when the moist air is cooled continuously.

Relative humidity along the saturation line is 100%.

Concept:

RSHF (Room Sensible Heat Factor): It is defined as sensible heat load divided by total heat load in a room.

RTH = Room Total Heat, RSH = Room Sensible Heat, RLH = Room Latent Heat.

RTH = RSH + RLH ……….(I)

\({\bf{RSHF}} = \frac{{{\bf{RSH}}}}{{{\bf{RTH}}}} \) ..... (II)

RLH = 50 × cmm × (ω₁ – ω₂) .....(III) 

where, cmm is cubic meter per minute i.e., air changes per minute.

ω₁, ω₂ = specific humidity of the room and supplied air.

Calculation:

Given:

RSHF = 0.75, RTH = 100 kW, Air changes per minute = 100 m³/min ⇒ 100 × 10⁶ cm³/min.

By using equation (II)

\({{RSHF}} = \frac{{{{RSH}}}}{{{{RTH}}}} \)

RSH = 0.75 × 100 kW = 75 kW.

By using equation (I)

RTH = RSH + RLH

RLH = 100 – 75 = 25 kW.     

By using equation (III)

RLH = 50 × cm; × (ω1 – ω2)

25 = 50 × 100 × (ω₁ - ω₂)

(ω1 - ω2) = 0.005

0.01 - ω2 = 0.005

ω₂ = 0.005 kg/kg of dry air.

Concept:

Every psychometric chart includes

• vertical uniformly spaced lines that represent the constant dry bulb temperatures,
• The diagonal lines that represent wet bulb temperature and enthalpy
• curved lines that represent relative humidity.
• Horizontal lines represent constant Humidity ratio

Dry Bulb Temperature: Actual temperature of gas or mixture of gases.

Wet Bulb temperature: Temperature obtained by an accurate thermometer having a wick moistened with distilled water

Dew point temperature: Temperature at which the liquid droplets just appear when the moist air is cooled continuously.

Relative humidity along the saturation line is 100%.

Explanation:

When relative humidity of the air is 100%, i.e the air is saturated, the dew point temperature (DPT) equals the wet bulb temperature (WBT), which is also equal to the dry bulb temperature.

So, DBT = WBT = DPT

For unsaturated air:

DBT > WBT > DPT

Concept:

In the figure, it shows that,

OA → Sensible heating

OB → Sensible cooling

OC → Humidification

OD → Dehumidification

OE → Heating + humidification

OF → Cooling + dehumidification

OG → Cooling + humidification

OH → Heating + dehumidification

In heat exchangers, the humid air is cooled, and (partial condensation) dehumidification is taking place. So the OF will be the process which is diagonal to the left side in a downward direction.

Concept:

• The process in which the moisture or water vapour or humidity is added to the air without changing its dry bulb (DB) temperature is called a humidification process.
• This process is represented by a straight vertical line on the psychometric chart starting from the initial value of specific humidity, extending upwards and ending at the final value of the specific humidity.
• The various types of processes on the psychometric chart are:

In the above process, we can say that whenever the humidification is involved in any process the humidity ratio increases or we can say that specific humidity increases.