THERMAL ENGINEERING -2

NAME :- Pamara alpesh M.

ENROLLMENT NO :- 146018319004

SUB TOPIC :- Psychrometer

GUIDANCE BY :- Arpit SIR

On Topic : :- Psychrometer

SUB :THERMAL ENGNEERIG-3

PREPARED BY

GUIDE : ARAPIT SIR Parmar Alpesh M.

146018319004

Signature of Guide: Signature of Principal: Signature of HOD:

Sling Psychrometer• consists of two thermometers

mounted together with a handle attached on a chain

• a psychrometer so designed that the wet-bulb thermometer can be ventilated, to expedite evaporation, by whirling in the air.

Sling Psychrometer

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A Sling Psychrometer A Sling Psychrometer is used to measure is used to measure relative humidity.relative humidity.

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Psychrometer Parts:Psychrometer Parts:

•Dry Bulb ThermometerDry Bulb Thermometer

•Wet Bulb ThermometerWet Bulb Thermometer

•Reservoir and StockingReservoir and Stocking WETWETDRYDRY

Uses

• The Sling Psychrometer measures the humidity of the air.

• Measures the amount of water vapor in the air• Estimates the dew point

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As the wet-bulb thermometer goes through the airAs the wet-bulb thermometer goes through the air

1. Water evaporates1. Water evaporates

2. Energy is used; water changes from liquid 2. Energy is used; water changes from liquid to vaporto vapor

3. Wet-bulb temperature goes down3. Wet-bulb temperature goes down

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What influences how What influences how much the wet-bulb much the wet-bulb temperature goes temperature goes down?down?

HumidityHumidity

TemperatureTemperature

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Using our wet- and Using our wet- and dry-bulb temperatures, dry-bulb temperatures, we can consult tables we can consult tables made by scientists…made by scientists…

……to determine to determine humidityhumidity and and saturation valuesaturation value..

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On the side of the psychrometer is On the side of the psychrometer is a sliding scale which calculates a sliding scale which calculates

relative humidity for us.relative humidity for us.

Align the dry-bulb reading with the Align the dry-bulb reading with the wet-bulb reading. The arrow will point wet-bulb reading. The arrow will point to the relative humidity reading on the to the relative humidity reading on the center scale. It’s easy!center scale. It’s easy!

Dew Point and

Relative HumidityUsing a Sling Psychrometer

Sling Psychrometer• A double thermometer

– One is ‘normal’ = dry bulb– One is covered with a wet piece

of cloth = wet bulb• When water evaporates, it

removes heat.• Therefore, the wet bulb will

always record a lower temperature than the dry bulb.

Dry Bulb

Wet Bulb

Using the psychrometer

• Wet the cloth at the end of one of the apparatus.

• Carefully (!), gently (!), etc spin the psychrometer around for a few minutes.

• Record the temperature of the dry bulb and the wet bulb in °C

Calculating Dew Point

• Subtract the wet bulb temperature from the dry bulb temperature and record this value.– You should now have 3 values recorded:

• Dry bulb ____ °C• Wet bulb ____ °C• Difference ____ °C

Calculating Dew Point, cont.

• Open your ESRT to page 12.• Locate the dry bulb temperature on the vertical

(left) axis of the Dew Point Temperature Chart.

• Locate the difference between the wet and dry bulb temperature on the horizontal (top) of the chart.

• Locate where the two values intersect: this is the dew point.

Calculating Relative Humidity (%)

• Record and calculate the same three values as you did for dew point:– Dry bulb temp ___ °C– Wet bulb temp ___ °C– Difference ___ °C

• Use the Relative Humidity chart on pg. 12 of your ESRT as you did for dew point.

• The relative humidity is at the intersection of the dry bulb temperature and the difference values.