UNIVERSITY OF THE EAST
COLLEGE OF ENGINEERING
MECHANICAL ENGINEERING DEPARTMENT
Experiment No. 5
SLING PSYCHROMETER
DIZON, DYLLAN C.
20130134155
NME 412 – ME 1
Engr. Joselito H. Recio
Instructor
Date performed: September 20, 2017
Date submitted: October 14, 2017
I.
OBJECTIVES





II.
To determine the dry bulb and wet bulb tours and various location inside the
campus using the different types of instrument.
To determine the relative humidity using (a) direct reading from the sling
psychrometer; (b) computation/chart method using the determine values of dry
bulb and wet bulb.
To determine the % relative humidity using two methods.
To determine who/then/there is significant difference in the dry bulb, wet bulb and
RH for every location.
To determine whether there is significant in error in RH using two methods.
THEORETICAL BACKGROUND
Relative humidity is the ratio of the current absolute humidity to the highest
possible absolute humidity (which depends on the current air temperature). A reading of
100 percent relative humidity means that the air is totally saturated with water vapor and
cannot hold any more, creating the possibility of rain. This doesn't mean that the relative
humidity must be 100 percent in order for it to rain -- it must be 100 percent where the
clouds are forming, but the relative humidity near the ground could be much less.
A hygrometer is a device used for measuring the humidity of air. The humidity of
an air-water vapor mixture is determined through the use of psychrometric charts if both
the dry bulb temperature (T) and the wet bulb temperature (Tw) of the mixture are
known. These quantities are readily estimated by using a sling psychrometer.
Humidity is simply water vapor in the air, which is needed to form rain.
Additionally, water vapor holds heat in the air. It is a greenhouse gas, which means it is
a can absorbs heat and warms the atmosphere. This is why humid air feels warmer.
III.
APPARATUS
1. Sling psychrometer - a sling psychrometer - consists of two thermometers
mounted together with a handle attached on a chain. One thermometer is ordinary.
The other has a cloth wick over its bulb and is called a wet-bulb thermometer. When
a reading is to be taken, the wick is first dipped in water and then the instrument is
whirled around. During the whirling, the water evaporates from the wick, cooling the
wet-bulb thermometer. Then the temperatures of both thermometers are read. If the
surrounding air is dry, more moisture evaporates from the wick, cooling the wet-bulb
thermometer more so there is a greater difference between the temperatures of the
two thermometers.
Fig. 1 Sling Psychrometer
2. Portable hygrometer - A hygrometer is an instrument used for measuring the water
vapor in the atmosphere. Humidity measurement instruments usually rely on
measurements of some other quantity such as temperature, pressure, mass or a
mechanical or electrical change in a substance as moisture is absorbed.
Fig. 2 Portable Hygrometer
3. Timer - A timer which counts upwards from zero for measuring elapsed time is often
called a stopwatch.
Fig. 3 Timer
IV. PROCEDURE
1. Locate the areas
would be conducted.
where
the
experiment
2.
Fig. 4 – Dr. Lucio Tan Bldg
Fig. 5 ME Lab
Calibrate the thermometers to be achieve an accurate result.
3. with a use of a piece of cloth, saturate it with a small amount of water, and wrapped it
to the bulb of one thermometer attached in the hygrometer, and again with a use of
piece of cloth, saturate it with a small amount of water, and wrapped it to the bulb of
sling psychrometer.
4. Using timer, set 3 minutes for each area, and apply a centrifugal force on the sling
psychrometer to determine the wet and dry bulb reading of the area. For the
hygrometer, set also 3 minutes to determine the wet and dry bulb temperature.
Fig. 5 Applying Centrifugal Force
5. After 3 minutes, record the reading in the sling psychrometer, and hygrometer.
6. The same procedure is done for the remaining areas.
7. After gathering all the data, determine the relative humidity using (a) direct reading
from the sling psychrometer; (b) computation/chart method using the determine values
of dry bulb and wet bulb.
V. DATA
A.
DATA TABLE
Area
TYK Blg.
ENG Blg.
L. Tan
Blg.
A. Office
GYM
Wet
Bulb
Dry
Bulb
81
85
80
83
79
82
79
79
79
81
Sling Psychrometer
Wet
Wet
Wet
Bulb
Bulb
Bulb
Dry
Dry
Dry
Bulb
Bulb
Bulb
82
83
82
87
88
85
78
80
78
84
84
83
79
80
80
81
82
82
79
79
79
79
79
79
80
80
79
82
82
80
Wet
Bulb
Dry
Bulb
80
83
80
84
80
83
78
80
80
80
Wet
Bulb
Dry
Bulb
27
30
27
28
27
29
27
28
27
28
Portable Hygrometer
Wet
Wet
Wet
Bulb
Bulb
Bulb
Dry
Dry
Dry
Bulb
Bulb
Bulb
27
27
27
30
30
30
27
27
27
28
28.5
39
27
27
27
29
29
29
27
27
27
28
28
28
27
27
27
28
28
28
Wet
Bulb
Dry
Bulb
27
30
26
28
27
29
27
28
26
29
Table 1 – Data
As you can see from the table 1, all the data is recorded and tabulate to visualize the
final result of the experiment. As you can see, from the area of TYK blg. up to the GYM,
the data in the wet bulb temperature in the portable hygrometer are a bit higher than the
recorded data in the wet bulb temperature in the sling psychrometer. The same thing
happens in the data from the dry bulb temperature. As you can see, the data in the dry
bulb temperature in the portable hygrometer are a bit higher than the recorded data in
the dry bulb temperature in the sling psychrometer.
Graph for Table 1
GRAPH 2 - PORTABLE HYGROMETER
200
150
100
50
0
1
2
3
4
5
Portable Hyrgrometer Area
Portable Hyrgrometer Wet Bulb Dry Bulb
Portable Hyrgrometer Wet Bulb Dry Bulb
Portable Hyrgrometer Wet Bulb Dry Bulb
Portable Hyrgrometer Wet Bulb Dry Bulb
Portable Hyrgrometer Wet Bulb Dry Bulb
As you can see from graph 2 shows the resulting data of wet bulb and dry bulb
temperature in the portable hygrometer. This graph shows how the measured data from
wet bulb and dry bulb in the portable hygrometer changes over a period of time. As you
can see almost all the measured temperature in the wet and dry bulb are the same in
each area where the experiment conducted.
B.
Area
TYK Blg.
Relative
Humidity
71.5
Using Sling Psychrometer
Relative
Relative
Relative
Relative
Humidity
Humidity
Humidity
Humidity
71
71.5
79
70
Average
RH
72.6
ENG Blg.
L. Tan
A. Blg.
Office
79
79
79
86
84
81.4
70
66
68
64
70
67.7
65
66
66
73
67
67.4
GYM
77
64
64
62
63
66
Table 2 – Relative humidity in sling psychrometer
In the table 2 shows the relative humidity using sling psychrometer. As you can see the
in the data above the average relative humidity in all areas from the TYK Blg. up to the
GYM all the data is not the same this is because the temperature in all areas is not the
same that causes in changes in relative humidity.
GRAPH 2 - RELATIVE HUMIDITY USING SLING PSYCHROMETER
GYM
A. Office
L. Tan Blg.
ENG Blg.
TYK Blg.
0
10
20
30
40
Using Sling Psychrometer Relative Humidity
Using Sling Psychrometer Relative Humidity
Using Sling Psychrometer Relative Humidity
Area
TYK
Blg.
ENG
L.Blg.
Tan
Blg.
A.
Office
GYM
Relative
Humidit
80
79
68.5
69
71.6
50
60
70
80
90
100
Using Sling Psychrometer Relative Humidity
Using Sling Psychrometer Relative Humidity
Using Sling Psychrometer Average RH
Using Portable Hygrometer
Relative Relative Relative
Humidity
Humidit
Humidit
80
80
80
81.4
85
82
66
69
68
64
63
66
71.6
69
71
Relative
Humidit
77
82
66
68
71.6
Average
RH
79.4
81.88
67.5
66
71
In
the
graph 2
shows
how the
relative
humidity
in
different
areas changes when the temperature changes over a period of time. In the ENG
building the relative humidity is high because the temperature is low resulting in high
humidity, and some areas like GYM the temperature is high resulting in low humidity.
Table 3 – Relative humidity using hygrometer
In the table 3 shows the relative humidity using portable hygrometer, as you can see the
average humidity in all areas is not the same, this is because the temperature in each
area is not the same resulting in different relative humidity. As you can see the ENG
building have highest relative humidity and the lowest is the A. office. In the ENG
building the temperature is low and in the A. office the temperature is high.
GRAPH 3 - RELATIVE HUMIDITY USING HYGROMETER
TYK Blg.
8079
6971.6
68.5
ENG Blg.
8081.4
71.6
6664
L. Tan Blg.
85
80
69 69
63
A. Office
8082
686671
GYM
82
81.88
79.4
77
71.6
68
67.56671
66
In the graph 3 shows the changes of the relative humidity over a period of time and also
it shows when the changes in the temperatures occurs it will result in change in relative
humidity too.
VI. CONCLUSION AND RECOMMENDATION
A sling psychrometer can be used to find relative humidity, which is expressed
as a percentage. It is computed by multiplying the amount of moisture in the air at a
given temperature, dividing by the maximum amount of moisture the air could contain at
that same temperature, and then multiplying the quotient by 100. The dew-point
temperature is always lower than the dry-bulb temperature, unless the air is saturated,
in which case they are identical. Also, the wet-bulb temperature is higher than the dewpoint temperature, except when the air is saturated; in that case, the two are equal. Dew
point is the temperature at which water vapor starts to condense out of air that is
cooling, whereas wet-bulb temperature represents how much moisture the air can
evaporate.
A sling psychrometer consists of two thermometers. One is a wet bulb and the
other is a dry bulb. To make a wet-bulb thermometer, wrap a piece of white, porous
cloth which has been soaked in water around the bulb of one of the thermometers and
secure it with a rubber b and or twine. Use a screw to attach the thermometers to the
wooden dowel, with the spacer between the thermometers and the washers between
the screw head and top thermometer and the bottom thermometer and dowel, in order
that they can be circulated around a point, allowing air movement across each bulb.
Safety glasses should be worn while twirling the sling psychrometer. Whirling the wetbulb thermometer causes the water on the wet cotton to evaporate. This evaporation
cools the bulb of the wet-bulb thermometer. The drier the ambient air, the more
evaporation can take place. This is why you feel more comfortable on a day with lower
humidity. If the humidity is lower, more evaporation of perspiration from your skin can
occur. Thus, you’ll feel cooler even though the dry-bulb temperature may be exactly the
same as that on a more humid day.
The hygrometer is also a temperature reading instrument this instrument used
to get both wet and dry bulb temperature. The hygrometer looks like a thermometer with
mercury inside of it.
VII. REFERENCE
Helmenstine, P. A. (n.d.). This Is How to Calculate Percent Error. Retrieved October 12,
2017, from https://www.thoughtco.com/how-to-calculate-percent-error-609584
Maxwell Science. (n.d.). Retrieved October 12, 2017, from http://maxwellsci.com/
www.google.com.ph