Eldin D. Murillo AGENG 424BSAE-4 Engr. A. Maristaza

PSYCHROMETERLaboratory Exercise 1

I. Introduction

Humidity is a term that everyone uses, but technically speaking, not always

accurately. We sometimes assume air is at high humidity when we are uncomfortably

warm.

Relative humidity is expressed as a measure of the amount of water vapor the air

contains as a percentage of the total amount it could contain at a specific temperature. If

you think of air as a paper towel for a moment, it can only hold a specific amount of water

at a specific temperature. However, unlike a paper towel, the total amount of moisture the

air can hold changes as the temperature changes. As the air becomes warmer, it can hold

a greater mass of moisture.

To find out the relative humidity or moisture content of the air, one may use a

psychrometer, a kind of hygrometer. A psychrometer is an instrument that computes both

the wet bulb and dry bulb temperatures. Two thermometers are required to compute these

constraints. From the values obtained, the relative humidity can be known.

II. Objectives

At the end of this laboratory exercise, I will be able to:

a. Familiarize myself with the science behind the sling psychrometer;b. Learn how to use the sling psychrometer;c. Gain knowledge of the use of a psychrometric chart, andd. Find the useful applications of a psychrometer.

III. Materials

a. Bacharach Sling Psychrometerb. Improvised Sling Psychrometer

- 2 pcs. Thermometer- Cotton

- Water- Stopwatch & Fan

IV. Procedure

Go to the ff. location:(classroom, aggies consultation room, 2nd floor lobby of aggies bldg., aggies elevator, 6th

floor lobby of aggies bldg., CR men of SC bldg.) Get the temperatures of each location using Bacharach Sling Psychrometer and

Improvised Sling Psychrometer. Do the temperature reading in Two (2) trials. Do the temperature readings at aggies consultation room with and without air-condition. Record each temperature reading.

V. Data

Bacharach Sling PsychrometerTrial 1 Trial 2

Location Dry bulb Wet bulb Dry bulb Wet bulbClassroom 28.33 °C 26.67 °C 27.77 °C 26.67 °C

Consultation room (no aircon)

26.67 °C 23.3 °C 27.22 °C 23.89 °C

Lobby 27.77 °C 26.11 °C 27.22 °C 26.11 °CElevator 30 °C 27.78 °C 30 °C 27.78 °C6th floor 27.78 °C 26.11 °C 27.78 °C 26.11 °C

Cr men (SC) 28.33 °C 26.11 °C 27.78 °C 26.67 °CConsultation room (w/

aircon)22.22 °C 17.78 °C 22.22 °C 16.67 °C

Improvised Sling PsychrometerTrial 1 Trial 2

Location Dry bulb Wet bulb Dry bulb Wet bulbClassroom 28 °C 26 °C 28 °C 26 °C

Consultation room (no aircon)

28 °C 22 °C 28 °C 22 °C

Lobby 27 °C 25 °C 27 °C 25 °CElevator 30 °C 27 °C 30 °C 28 °C6th floor 28 °C 26 °C 27 °C 25 °C

Cr men (SC) 28 °C 25 °C 29 °C 26 °CConsultation room (w/

aircon)21 °C 16 °C 21 °C 15 °C

VI. Discussion

a. The Science Behind The Sling Psychrometer

A psychrometer is a device used to measure relative humidity of a certain area. A

psychrometer has two bulbs: one wet and one dry. Both bulbs are

traditional thermometers, though one is covered with a wet towel. After a period of time,

the water on the wet bulb evaporates and at that time, the temperature is measured on

each bulb. The difference between the temperatures is noted. Then each is used on a

chart to find the relative humidity of that temperature and area. A small difference between

the temperatures of the bulbs shows a high relative humidity coming from a low

evaporation rate. In dry air, evaporation happens faster showing a large difference in

temperature thus giving you a low relative humidity.

b. How to Use the Sling Psychrometer .

A sling psychrometer is an instrument that measures relative humidity (a

hygrometer). The sling has two thermometers, a dry bulb and a wet bulb thermometer,

mounted together on a chain. The wet bulb thermometer is wrapped in muslin that is

moistened with distilled water. The user then swings the sling until the temperatures

stabilize, then quickly notes the two temperatures.

Hence, to use a sling psychrometer, you have to swing the contraption (some have a

little fan instead to blow across the bulbs). The air flowing over the one with gauze/alcohol

will have evaporation going on around the bulb. The temperature that results on the bulb

with the evaporation is called the wet-bulb temperature. The wet-bulb temp is in between

the dewpoint (the point at which water vapor in the atmosphere can start condensing) and

the regular air temperature. The reason that it is not the dewpoint is because as water

evaporates, it gives off heat. So the result is that it shows a temperature higher than the

actual dewpoint.

c. How to Use the Psychrometric Chart

To interpret the readings and determine the humidity, a chart is then used for the

specific altitude at which the reading was taken. This chart is called the psychrometric

chart. Basically, the drier the air is, the more moisture evaporates from the moistened

muslin-covered thermometer, and the greater the difference between the two

thermometers. If the relative humidity is 100%, then the two temperatures will be the

same.

VII. Conclusion

Using a psychrometer determines the humidity of a certain area by relating it to the

temperature reading of a psychrometric chart. A psychrometer is composed of dry and wet

bulbs. The reading from these dry and wet bulbs is projected to get the relative humidity.

After the activity and as provided in the above data, I came to know about the

science behind psychrometer. That humidity can be identified because of such device.

Moreover, as seen from the data gathered and discussions above, I was able to

successfully use a sling psychrometer in determining the humidity of some specified areas

inside the campus. This I did with the use of a psychrometric chart that shows, by graphs,

the parameters relating to water moisture in air.

Lastly, I found out that psychrometers are used wherever the humidity and

precipitation is an issue. Meteorology depends on psychrometers to forecast weather.

Also, museums possessing valuable ancient works make use of the psychrometers.

Greenhouses, humidors and saunas may also use psychrometers and within houses and

in a lot of industrial applications, engineers use psychrometers for air conditioning

maintenance and determine appropriate humidity levels for manufacturing.

References

Florida Solar Energy Center (FSEC). “Humidity”. University of Central Florida. Retrieved on 4 March 2013 from website: http://www.fsec.ucf.edu/en/consumer/buildings/ basics/humidity.htm

Innovation and Information for Sustainable Living. “What is a Psychrometer?” ©2006-2011 InnovateUs Inc. Retrieved on 4 March 2013 from website: http://www.innovateus.net /science/what-psychrometer

Walker, Ken. “What is a Sling Psychrometer?” Kestrel 4000 Pocket Weather Meter. Published on 12 August 2008. Retrieved on 4 March 2013 from website: http://www.kestrel4000.com.au/kestrel4000/what-is-a-sling-psychrometer-.html