Final Me Lab Report

TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES COLLEGE OF ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING

EXPERIMENT IN

ME 5L MECHANICAL ENGINEERING LABORATORY 1

SUBMITTED BY: MARBELLA, AMADOR II A. BSME 4A

SUBMITTED TO: ENGR. MANUEL EUROPEO

Experiment No. 1

The Psychrometer and the Psychrometric Chart Course Code: ME 5L Course Title: Mechanical Engineering Laboratory 1 Section: BSME 4A Members: 1. Armidilla, John Carlo H. 2. Magdala, Marco T. 3. Marbella, Amador II A. 4. Recato, Glenn Haxelon B. 5.Santos, Ray Carl M. 1. OBJECTIVES:

Program: Date Performed: July 29, 2015 Date Submitted: August 10, 2015 Instructor: Engr. Manuel L. Europeo

1.1 Determine and meet quantitative and qualitative data such as air properties, air humidity, air temperature using Psychrometer 1.2 Plot different air properties on the Psychrometric chart and to distinguish the relationships between them 2. INTENDED LEARNING OUTCOMES (ILOs): The students shall be able to: 2.1 Understand and familiarize the use and function of Psychrometer and Psychometric Chart and be able to apply it in the field of work 2.2 Be able to identify different air properties in certain areas and enumerate factors why did it arrive in such analysis 2.3 Apply math, science, and engineering knowledge to solve openended problems 2.4 Make engineering decisions using engineering analysis tools 2.5 Set up and perform experiments to help make final decisions 2.6 Effectively function in a multi-disciplinary environment 3. DISCUSSION: AIR and its PROPERTIES Earth's atmosphere is composed of air. Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components. We usually model air as a uniform (no variation or fluctuation) gas with properties that are averaged from all the individual components. Any gas has certain properties that we can detect with our senses. The values and relations of the properties define the state of the gas. PROPERTIES  WEIGHT Air is a mixture of gases and has weight like any other material. Standard Air is the condition of air that is mainly used for many calculations and comparisons. Standard air is dry air at 70°F and a barometric pressure of

29.92 Hg (mercury) at sea level. It weighs about 0.075 pounds per cubic foot, or 1.2kilograms per cubic meter. Dry air contains no moisture. 

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DENSITY and SPECIFIC VOLUME For a given pressure and temperature, the volume depends directly on the amount of gas. Since the mass and volume are directly related, we can express both the mass and volume by a single variable. When a gas is moving, it is convenient to use the density of a gas, which is the mass divided by the volume the gas occupies. The sea level standard value of air density r: r = 1.229 kilograms/cubic meters = .00237 slug/cubic feet When working with a static or unmoving gas, it is more convenient to use specific volume, which is the volume divided by the mass. The sea level standard value of specific volume v is v = .814 cubic meters/kilogram = 422 cubic feet/slug PRESSURE The pressure of a gas equals the perpendicular force exerted by the gas divided by the surface area on which the force is exerted. The sea level standard value of air pressure p is p = 101.3 kilo Newtons/square meter = 14.7 pounds/square inch TEMPERATURE The temperature of a gas is a measure of the kinetic energy of the molecules of the gas. The sea level standard value of air temperature T is T = 15 degrees C = 59 degrees Fahrenheit VISCOSCITY A gas can exert a tangential (shearing) force on a surface, which acts like friction between solid surfaces. This "sticky" property of the gas is called the viscosity and it plays a large role in aerodynamic drag. The sea level standard value of air viscosity mu is mu = 1.73 x 10^-5 Newton-second/square meters = 3.62 x 10^-7 poundsecond/square feet DRY-BULB TEMPERATURE Dry bulb temperature is what is usually meant by "air temperature". It is measured with a normal thermometer. DEW POINT Dew point is the temperature at which water vapor begins to condense out of the air. Dew points can be defined and specified for ambient air or for compressed air. WET-BULB TEMPERATURE Wet bulb temperature is never higher than dry bulb temperature. They are equal when air is at its dew point or saturation temperature. The difference

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between the dry bulb and wet bulb temperatures is an indicator of the humidity level. Wet-bulb temperature is the lowest temperature that water will reach by evaporative cooling, and that temperature is almost always lower than dry bulb. Wet bulb temperature is a critical parameter for sizing, and measuring the performance of evaporative-cooled cooling water systems. RELATIVE HUMIDITY Relative humidity at dew point conditions is 100%. Otherwise, relative humidity isthe percentage of the amount of water vapor actually present in the air, to the maximum amount that the air could hold under those temperature and pressure conditions. This measurement is highly correlated with human comfort - with about 50% being most comfortable ABSOLUTE HUMIDITY With the aid of a psychrometric chart, or its computerized equivalent, absolute values for water content such as weight fraction of ambient air, or weight-per-unit-volume of ambient air can be determined for any combination of dry bulb and wet bulb temperatures, or combination of dry bulb temperature and relative humidity. This measurement is required to design various types of moisture removal or humidification systems.

PHYSICAL PROPERTIES INVOLVED IN AIR CONDITIONING In order to achieve air conditioning, the physical process like air purification, temperature control, humidity control and air circulation have to be carried out and hence in the equipment’s of air conditioning plants, the units performing these duties are incorporated. 1. Air purification: The air taken from the atmosphere carries dust, bacteria and odors which are harmful for human health. In order to safeguard the health of occupants, it is necessary to remove all possible harmful ingredients from the air before admitting into the air conditioning systems. 2. Temperature control: Temperature control is a major process in air conditioning system. It is intended to regulate the dry bulb temperature by various Psychrometric processes. This is attained by simple heating or cooling, which may be associated with humidification process. Cooling of air means lowering its dry bulb temperature. It can be attained by passing the air over evaporator coils of a refrigerating system. In a small room air conditioner the intake air is forced to flow over the evaporator coil directly. In such case the relative humidity aspect is neglected or is of such order that it gets adjusted by itself. In most cases, an indirect evaporator system is used for cooling the air. In such cases chilled water is used to cool the air. The chilled water after absorbing heat from the air rejects heat to the refrigerant in the

evaporator. Psychrometry The properties of moist air are called Psychrometric properties and the subject the subject that deals with the behavior of moist air is known as psychrometry. It is the foundation on which most of the air conditioning calculations are based. Several special terms used in the study of psychrometry are defined below: 1. Dry air: Dry air is a mixture of oxygen, nitrogen, carbon-dioxide, hydrogen, argon, neon, helium etc. with oxygen and nitrogen as its major constituents. 2. Moist air: It is ordinary atmospheric air which is a mixture of dry air and water vapour. 3. Relative humidity: It is the ratio of mass of water vapour in a given volume of moist air at a given temperature to the mass of water vapour contained in the same volume of moist air at the same temperature when the air is saturated. 4. Dry bulb temperature: It is temperature of air measured by an ordinary thermometer. 5. Sensible heat of air: It is the enthalpy of dry air which can be calculated by measuring its dry bulb temperature. 6. Total heat: The total heat of moist air is the sum of sensible heat of dry air and sensible plus latent heat of water vapour present in it. 7.

INSTRUMENTS/

APPARATUSES

USED

IN

MEASURING

AIR

PROPERTIES THERMOMETER measures the air temperature. Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and moves up the tube. A scale then shows what the actual temperature is. BAROMETER measures air pressure. It tells you whether or not the pressure is rising or falling. A rising barometer means sunny and dry conditions,

while a falling barometer means stormy and wet conditions. An Italian scientist named Torricelli built the first barometer in 1643.

SLING

PSYCHROMETER

measures

relative

humidity,

using the cooling effect of evaporation. Two thermometers are used in a sling psychrometer. Wet the cloth of one of the thermometers and swing the psychrometer around a few times. Water evaporates from the cloth, causing the temperatures on that thermometer to be lower the the other.

AEROMETERS are relatively uncomplicated instruments that are designed to measure the density and weight of a gas especially air. Using a weight and a scale that is included within the body of the aerometer, it is possible to place the device directly into the element to be measured and receive an accurate reading.

ATMOMETER

is

used

for

measuring

evaporating

capacity of air.

APPLICATION OF SLING PSYCHROMETER

1.

It is used for checking humidity level in air-conditioned rooms and installations.

2.

It is used to set and check hair hygrometer.

3.

It is used in the measurement range of 0 to 100% RH.

4.

It is used for measuring wet bulb temperature between 0’C to 180’C.

LIMITATION OF SLING PSYCHROMETER

1.

The measured medium is disturbed due to the act of measurement. The evaporation process at the wet bulb will add moisture to the air.

2.

It cannot be used in automation requirement situations.

3.

It cannot be used for continuous recording purpose.

4.

If the wick is covered with dirt, the wick will become stiff and its water absorbing capacity will reduce, however, a stiff/dirty wick will resume normalcy when boiled in hot water.

4. MATERIALS: Psychrometer A sling psychrometer, or wet-and-dry-bulb thermometer, consists of two thermometers, one that is dry and one that is kept moist with distilled water on a sock or wick. The two thermometers are thus called the dry-bulb and the wet-bulb. At temperatures above the freezing point of water, evaporation of water from the wick lowers the temperature, so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer. When the air temperature is below freezing, however, the wet-bulb is covered with a thin coating of ice and may be warmer than the dry bulb. Relative humidity is computed from the ambient temperature as shown by the drybulb thermometer and the difference in temperatures as shown by the wet-bulb and dry-bulb thermometers. Relative humidity can also be determined by locating the intersection of the wet and dry-bulb temperatures on a psychrometric chart. The two thermometers coincide when the air is fully saturated, and the greater the difference the drier the air. Psychrometers are commonly used in meteorology, and in the HVAC industry for proper refrigerant charging of residential and commercial

air conditioning systems.

Psychrometric Chart

A psychrometric chart is a graph of the thermodynamic parameters of moist air at a constant pressure, often equated to an elevation relative to sea level. The ASHRAE-style psychrometric chart, shown here, was pioneered by Willis Carrier in 1904.[9] It depicts these parameters and is thus a graphical equation of state. The parameters are: 

Dry-bulb temperature (DBT) is that of an air sample, as determined by an ordinary thermometer. It is typically plotted as the abscissa (horizontal axis) of the graph. The SI units for temperature are kelvins or degrees Celsius; other units are degrees Fahrenheit and degrees Rankine.

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Wet-bulb temperature (WBT) is that of an air sample after it has passed through a constantpressure, ideal, adiabatic saturation process, that is, after the air has passed over a large surface of liquid water in an insulated channel. In practice this is the reading of a thermometer whose sensing bulb is covered with a wet sock evaporating into a rapid stream of the sample air (see Hygrometer). When the air sample is saturated with water, the WBT will read the same as the DBT. The slope of the line of constant WBT reflects the heat of vaporization of the water required to saturate the air of a given relative

humidity. 

Dew point temperature (DPT) is the temperature at which a moist air sample at the same pressure would reach water vapor "saturation." At this point further removal of heat would result in water vapor condensing into liquid water fog or, if below freezing point, solid hoarfrost. The dew point temperature is measured easily and provides useful information, but is normally not considered an independent property of the air sample as it duplicates information available via other humidity properties and the saturation curve.

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Relative humidity (RH) is the ratio of the mole fraction of water vapor to the mole fraction of saturated moist air at the same temperature and pressure. RH is dimensionless, and is usually expressed as a percentage. Lines of constant RH reflect the physics of air and water: they are determined via experimental measurement. The concept that air "holds" moisture, or that moisture "dissolves" in dry air and saturates the solution at some proportion, is erroneous (albeit widespread); see relative humidity for further details.

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Humidity ratio is the proportion of mass of water vapor per unit mass of dry air at the given conditions (DBT, WBT, DPT, RH, etc.). It is also known as the moisture content or mixing ratio. It is typically plotted as the ordinate (vertical axis) of the graph. For a given DBT there will be a particular humidity ratio for which the air sample is at 100% relative humidity: the relationship reflects the physics of water and air and must be determined by measurement. The dimensionless humidity ratio is typically expressed as grams of water per kilogram of dry air, or grains of water per pound of air (7000 grains equal 1 pound).

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Specific enthalpy, symbolized by h, is the sum of the internal (heat) energy of the moist air in question, including the heat of the air and water vapor within. Also called heat content per unit mass. In the approximation of ideal gases, lines of constant enthalpy are parallel to lines of constant WBT. Enthalpy is given in (SI) joules per kilogram of air, or BTU per pound of dry air.

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Specific volume is the volume of the mixture (dry air plus the water vapor) containing one unit of mass of "dry air". The SI units are cubic meters per kilogram of dry air; other units are cubic feet per pound of dry air. The inverse of specific volume is usually confused as the density of the mixture (see "Applying the Psychrometric Relationships" CIBSE, August 2009). However, to obtain the actual mixture density one must multiply the inverse of the specific volume by unity plus the humidity ratio value at the point of interest (see ASHRAE Fundamentals 1989 6.6, equation 9).

The psychrometric chart allows all the parameters of some moist air to be determined from any three independent parameters, one of which must be the pressure. Changes instate, such as when two air streams mix, can be modeled easily and somewhat graphically using the correct psychrometric chart for the location's air pressure or elevation relative to sea level. For locations at not more than 2000 ft (600 m) of altitude it is common practice to use the sea-level psychrometric chart.

In the ω-t chart, the dry bulb temperature (t) appears as the abscissa (horizontal axis) and the humidity ratio (ω) appear as the ordinate (vertical axis). A chart is valid for a given air pressure (or elevation above sea level). From any two independent ones of the six parameters dry bulb temperature, wet bulb temperature, relative humidity, humidity ratio, specific enthalpy, and specific volume, all the others can be determined.

5. PROCEDURE:

1. Inspect the cotton wick on the sling psychrometer and make sure that it is in good condition and firmly in contact with the thermometer bulb. A psychrometer with a yellowed or frayed wick will not give an accurate reading, and the wick should be replaced. Do not touch the wick with your fingers, because contaminants will affect the accuracy. Also, check for a separated mercury column. 2. Thoroughly saturate the wick with distilled water. If the water beads up and does not easily soak in, the wick should be replaced.

3. Face into the wind (if any) and begin swinging the psychrometer at a steady, comfortable pace (about 2 turns per second is good). Be extremely careful that you don’t strike the psychrometer on a nearby table, railing, or other obstruction! Also, keep it far enough from your body that you don’t pick up your own body heat. 4. After about 1 minute, stop and check the wet-bulb temperature, quickly reading it to the nearest 1/10 degree (if you stop too long, the temperature will start to change). Then continue swinging the psychrometer for another minute or so. Check the wet-bulb temperature again and see whether it has changed from your previous reading. If it has, continue swinging for another minute and check again. Repeat as necessary. Your goal is to get the lowest possible reading out of the wet bulb thermometer (assuming that it started out near the dry air temperature). Important note: make sure that the wick does

not become too dry. If it does, you will need to add another drop or two of distilled water and start over.

5. Carefully but quickly read and record the final wet bulb and dry bulb temperatures to the nearest 0.1 degree, interpolating between tick marks as necessary.

6. Use whatever method is available (psychrometric computer, Skew-T diagram, or table) to compute the dewpoint and relative humidity.

Note: If the Psychrometer is rotated for a short period, then the wet bulb temperature recorded will not be proper. Note: If the Psychrometer is rotated for a longer period, the wick will get dried soon and the wet bulb temperature will not be at its minimum value

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Measuring Temperature using Psychrometer

Area Conditions:     

Area Conditions:     

Near Court TIME : 12: 26 pm Weather Condition: Cloudy Ventilation: Open area No of persons –many

Front of Bahay Kalinga TIME : 12: 56 pm Weather Condition: Sunny/Windy Ventilation: Open area, direct sunlight No of persons – n/a

Area Conditions:     

Technical Education department Lobby TIME : 12:21pm Weather Condition: Sunnyand windy Ventilation: Open areaand Indirect sunlight No of persons – 4

Area Conditions:     

COE 13 Corridor TIME : 12:06 pm Weather Condition: Sunny Ventilation: Open area No of persons – 7

8. ANALYSIS AND DATA INTERPRETATION: The experiment was done near the covered court at 12:26 pm. The weather was cloudy and the surrounding was well ventilated being an open area. Because of these factors, the reading of the wet-bulb and dry-bulb temperatures

are 24 and 34 degrees Celsius respectively. The sling psychrometer was made to spin for about 2 minutes to achieve a more accurate reading.

9. CONCLUSION AND RECOMMENDATION:

A sling psychrometer measures the relative humidity of air in a given environment. The reading of the dry-bulb and wet-bulb thermometers changes depending on the type of surrounding where the experiment was done. The dry bulb thermometer measures the air temperature. The wet bulb thermometer measures the lowest temperature the air could reach through evaporation. Based on the experiment, we can conclude that the measurement taken by the sling psychrometer depends on the humidity, air pressure and temperature of the given surrounding. The reading on the dry-bulb thermometer increases as the weather changes from a cloudy to sunny weather. Also, the dry-bulb reading increases as the number of person in the given surrounding increases. The reading in the wet-bulb thermometer greatly increases in a less ventilated room which has low humidity. We can also conclude that when the temperatures are nearly the same, the air in the area is almost saturated and the relative humidity is almost 100%. We recommend that the sling psychrometer used in the experiment should be regularly maintained to produce a more accurate reading of wet-bulb and drybulb temperatures. The data also should be listed carefully to be able to determine the properties of the surrounding air properly. during the experiment, the sling psychrometer must be spun in a clear area to avoid bumping and breakage of the psychrometer.