Objective

To determine the relative humidity of a location using whirling hygrometer and compare the result using psychrometric chart.

Apparatus used:

Whirling Hygrometer, Psychrometric Chart, Distilled Water, Stopwatch etc.

Description Whirling Hygrometers: have a pair of thermometers, one of them having its bulb covered with wet muslin cloth. Here dry and wet bulb thermometer are mounted side by side on bass frame fitted with a handle for whirling purpose.

STEP  1 

Wet the muslin cloth present at the nose of wet bulb thermometer.

Place 1:Near the working face of a gallery.

Dry bulb
thermometer

Wet bulb
thermometer

STEP  2 

Attach rod to the hygrometer to rotate the whirling hygrometer at the speed of 200rpm for atleast 2 minutes and start the stopwatch simultaneously.

Time=_____s

Note:

1.Keep the instrument away from the body while rotation before whirling.

   

STEP  3 

Take the reading of wet bulb and dry bulb temperature just after stopping the stopwatch.

Dry bulb
thermometer

Wet bulb
thermometer

Wet bulb temperature=______ ℃

Dry bulb temperature=______ ℃

Observations:

Place 1

Place	Wet bulb temperature(Tw),(℃)	Dry bulb temperature(Td),(℃)
1

Barometric pressure(P)=1.01325*10⁵ Pa

Saturated vapour pressure at wet bulb temperature (e_sw)=      Check

✔

✘

Moisture content of unsaturated air(X_s)=      Check

✔

✘

Latent heat of evaporation(L_w)=      Check

✔

✘

Sigma heat(S)=      Check

✔

✘

Moisture content of saturated air(X)=      Check

✔

✘

Actual vapour pressure(e)=      Check

✔

✘

Saturated vapour pressure at any bulb temperature(e_sd)=      Check

✔

✘

Relative humidity = % Check

✔

✘

STEP  5 

Wet the muslin cloth present at the nose of wet bulb thermometer.

Place 2:In the middle of the gallery.

Dry bulb
thermometer

Wet bulb
thermometer

Note:

1.Wait atleast for 2 minutes before starting the next observation of the instrument.

   

STEP  6 

Attach rod to the hygrometer to rotate the whirling hygrometer at the speed of 200rpm for atleast 2 minutes and start the stopwatch simultaneously.

Time=_____s

STEP  7 

Take the reading of wet bulb and dry bulb temperature just after stopping the stopwatch.

Dry bulb
thermometer

Wet bulb
thermometer

Note:

1.Wait atleast for 2 minutes before starting the next observation of the instrument.

   

Wet bulb temperature=______ ℃

Dry bulb temperature=______ ℃

Observations:

Place	Wet bulb temperature(Tw),(℃)	Dry bulb temperature(Td),(℃)
1

Barometric pressure(P)=1.01325*10⁵ Pa

Place 2 Saturated vapour pressure at wet bulb temperature (e_sw)=      Check

✔

✘

Place 1 Moisture content of unsaturated air(X_s)=      Check

✔

✘

Latent heat of evaporation(L_w)=      Check

✔

✘

Sigma heat(S)=      Check

✔

✘

Moisture content of saturated air(X)=      Check

✔

✘

Actual vapour pressure(e)=      Check

✔

✘

Saturated vapour pressure at any bulb temperature(e_sd)=      Check

✔

✘

Relative humidity = % Check

✔

✘