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Humidity-Measuremente

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Aree Salah
Aree Salah

This document describes an experiment to measure humidity using a psychrometer. It includes sections on the aim, introduction, theory, instructions, calculations, discussion, and references. The introduction explains that humidity is the amount of water vapor in air and defines relative humidity. The theory section describes how vapor pressure relates to temperature and humidity. The instructions explain how to use a psychrometer to measure the dry and wet bulb temperatures and determine relative humidity from a table.

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1 Koya University Faulty of Engineering School of Chemical & Petroleum Engineering Chemical Engineering department EXPERIMENT NUMBER FIVE Thermodynamics Humidity-Measurement Instructor: Mr.Rebwar & Mr.Omer Author Name: Aree Salah Tahir Experiment Contacted on: 4/2/2013 Report Submitted on: 11/2 /2013 Group:A
2 List of content: Aim of this experiment: ………………………3 Introduction: ………………………………….4 , 5 Theory: …………………………………………..6 , 7 Instructions for use: ……………………………8 Calculation: …………………………………………9 Discussion: ………………………………..10 ,11 Reference: ………………………………………..12
3 Aim of this experiment: To determine the humidity of air (to measure the amount of water in air).
4 Introduction Air, in our normal environment, always holds humidity. The number of water molecules in the air can vary substantially, e.g. it can be as dry as in a desert or as humid as in the tropics. There is an upper limit for the amount of humidity which air can hold at a given temperature. Beyond this limit saturation occurs. If for some reason the humidity level is pushed up to this limit, condensation occurs and fog or water droplets form. Relative humidity tells you what percentage of this maximum amount of humidity is present in the air. In contrast to relative humidity, absolute humidity denotes the absolute amount of humidity in the air regardless of the saturation level expressed as the total mass of water molecules per air volume. The maximum possible amount of humidity as well as the actual present amount of humidity in the air are defined by so called water vapor pressures. According to Dalton’s law, total air pressure is the sum of the partial vapor pressures of its components and water vapor pressure is one of them:
5 The maximum amount of humidity, which air can hold, is defined by the so-called saturation water vapor pressure. This is a function of temperature. See: Figure 1 Saturation water vapor pressure. If the partial water vapor pressure is equal to the saturation water vapor pressure, condensation occurs. Mathematically, relative humidity is expressed as the ratio of the partial water vapor pressure divided by the saturation water vapor pressure as a percentage. If temperature rises or falls in a closed system, the saturation vapor pressure will increase or decrease. As a consequence, the relative humidity will drop or rise. Saturation water vapor pressure is not a function of total air pressure, but partial water vapor pressure is. If for example the total air pressure in a closed system is increased, relative humidity will increase as well, because the partial water vapor pressure increases proportionally to the overall pressure increase according to Dalton’s law and saturation vapor pressure stays the same.{1}
6 Theory: Air is a mix of different gases. Under regular ambient conditions these gases behave quasi "ideal". That means that each gas molecule can act totally independent. This leads to the Dalton's law: p = p1 + p2 + p3 + ... The total pressure of an ideal mixture of gases is the sum of the single pressures (partial pressure) of its components. Vapour pressure mostly behaves like an ideal gas too and appears as an additional element in the Dalton's law: p = p1 + p2 + p3 + ...+pW = pda + pW pD: Partial water vapour pressure, pda: Partial pressure of dry air Vapour pressure over water In a self-contained box which is partly filled with water an equilibrium will be reached between the process of evaporation and condensation. A low concentration of water molecules in the vapour leads to an increased evaporation that will increase the vapour pressure. A higher concentration on the other side lowers the vapour pressure by condensation. This molecule movement depends on the kinetic energy of the molecules in water. Hereby the temperature of the medium plays an important role. The molecules in the water vapour phase behave similar. The equilibrium between the evaporation and condensation leads to a vapour pressure which is dependant on the temperature in the box. At the thermal equilibrium the partial water vapour pressure pW is the maximum value at the temperature t which is reached in the box at this temperature and is called: Saturation vapour pressure pS over water at the temperature t.
7 Relative humidity rh (%) The relative humidity rh is defined as the ratio between the actual water vapour pressure pW and the saturation vapour pressure pS over water rh = pW / pS * 100 [%] Since the partial water vapour pressure pW can never exceed the saturation perssure pS the maximum posible value of rh = 100% {2}
8 Instructions for use: This wet bulb psychrometer is used to measure The humidity of air with using the table Above. The percentage values are valid for still Temperatures are measured in 'C. • The tubular glass tank in the middle is to be filled with -dean water. The wick attached to the thermometer should dip into the water approx. 2 cm. • To determine the humidity read of the temperatures at the dry and the wet thermometer shortly after-each other and determine the difference. • Search the values in the table and you can determine the relative humidity of the air, {3}
9 Calculation: 19=0 cdT = 160 cwT 3=0 cT∆ Relative Humidity = %
11 Discussion: We use distilled water because...1. . we have to use NEUTRAL(according to PH factor) water in someA reactions.other wise reaction goes wrong. water always contain some type of mineral impurity like some.regularB salts and in some reactions we have to avoid the effect of those impurities .if we are doing experiment with regular water ,some time resultsC the water.changes slightly according to impurity which is in .though if there is no impurity in regular filtered water(rare case) weD can't say that it is NEUTRAL and don't contain any impurity by only seeing it with naked eye so it is best way to use distilled water. 2.What does humidity measures? humidity measures the amount of water vapor in the air. Water concentration in air or water vapour.The amount of water vapor in the air. water vapor moisture 3.What is relative humidity measured in? Relative humidity is measured in %. 4.Can relative humidity be measured with an instrument? Yes, you can check the whether with an instrument. this instrument is called a thermometer. this is how it works... when it's freezing cold it should be below 0. when it's hot it should be at least above 10 degrees. These thermometers should be kept outside so the thermometer is absolutely right or it's close to the right answer. However, a hygrometer can be used to use relative humidity. Or it is how much water vapor is in the air.
11 5.Relative humidity can be measured with a? Hygrometer We used wet cloth on a humid day there is moisture in the air. On a dry6. day the moisture in the clothes more easily evaporates. 7.There are many reasons to change the temperature and makes the temperature be unstable like condition in the room and being close to the thermometer
12 Reference: 1/ http://www.elektronika.rs.ba/files_bin/projekti/TermoHigrometar/Introduction_to_Relative _Humidity_E.pdf 2/ -air-dp-http://www.novasina.com/wEnglisch/Knowledge_Center/Theorie/Theorie Luftfeuchte_und_Temperatur.php-aw/Theorie 3/ d_561.html-measurement-http://www.engineeringtoolbox.com/humidity 4/ http://wiki.answers.com/Q/What_is_the_Bernoulli_theory#slide=2

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Humidity-Measuremente

  • 1. 1 Koya University Faulty of Engineering School of Chemical & Petroleum Engineering Chemical Engineering department EXPERIMENT NUMBER FIVE Thermodynamics Humidity-Measurement Instructor: Mr.Rebwar & Mr.Omer Author Name: Aree Salah Tahir Experiment Contacted on: 4/2/2013 Report Submitted on: 11/2 /2013 Group:A
  • 2. 2 List of content: Aim of this experiment: ………………………3 Introduction: ………………………………….4 , 5 Theory: …………………………………………..6 , 7 Instructions for use: ……………………………8 Calculation: …………………………………………9 Discussion: ………………………………..10 ,11 Reference: ………………………………………..12
  • 3. 3 Aim of this experiment: To determine the humidity of air (to measure the amount of water in air).
  • 4. 4 Introduction Air, in our normal environment, always holds humidity. The number of water molecules in the air can vary substantially, e.g. it can be as dry as in a desert or as humid as in the tropics. There is an upper limit for the amount of humidity which air can hold at a given temperature. Beyond this limit saturation occurs. If for some reason the humidity level is pushed up to this limit, condensation occurs and fog or water droplets form. Relative humidity tells you what percentage of this maximum amount of humidity is present in the air. In contrast to relative humidity, absolute humidity denotes the absolute amount of humidity in the air regardless of the saturation level expressed as the total mass of water molecules per air volume. The maximum possible amount of humidity as well as the actual present amount of humidity in the air are defined by so called water vapor pressures. According to Dalton’s law, total air pressure is the sum of the partial vapor pressures of its components and water vapor pressure is one of them:
  • 5. 5 The maximum amount of humidity, which air can hold, is defined by the so-called saturation water vapor pressure. This is a function of temperature. See: Figure 1 Saturation water vapor pressure. If the partial water vapor pressure is equal to the saturation water vapor pressure, condensation occurs. Mathematically, relative humidity is expressed as the ratio of the partial water vapor pressure divided by the saturation water vapor pressure as a percentage. If temperature rises or falls in a closed system, the saturation vapor pressure will increase or decrease. As a consequence, the relative humidity will drop or rise. Saturation water vapor pressure is not a function of total air pressure, but partial water vapor pressure is. If for example the total air pressure in a closed system is increased, relative humidity will increase as well, because the partial water vapor pressure increases proportionally to the overall pressure increase according to Dalton’s law and saturation vapor pressure stays the same.{1}
  • 6. 6 Theory: Air is a mix of different gases. Under regular ambient conditions these gases behave quasi "ideal". That means that each gas molecule can act totally independent. This leads to the Dalton's law: p = p1 + p2 + p3 + ... The total pressure of an ideal mixture of gases is the sum of the single pressures (partial pressure) of its components. Vapour pressure mostly behaves like an ideal gas too and appears as an additional element in the Dalton's law: p = p1 + p2 + p3 + ...+pW = pda + pW pD: Partial water vapour pressure, pda: Partial pressure of dry air Vapour pressure over water In a self-contained box which is partly filled with water an equilibrium will be reached between the process of evaporation and condensation. A low concentration of water molecules in the vapour leads to an increased evaporation that will increase the vapour pressure. A higher concentration on the other side lowers the vapour pressure by condensation. This molecule movement depends on the kinetic energy of the molecules in water. Hereby the temperature of the medium plays an important role. The molecules in the water vapour phase behave similar. The equilibrium between the evaporation and condensation leads to a vapour pressure which is dependant on the temperature in the box. At the thermal equilibrium the partial water vapour pressure pW is the maximum value at the temperature t which is reached in the box at this temperature and is called: Saturation vapour pressure pS over water at the temperature t.
  • 7. 7 Relative humidity rh (%) The relative humidity rh is defined as the ratio between the actual water vapour pressure pW and the saturation vapour pressure pS over water rh = pW / pS * 100 [%] Since the partial water vapour pressure pW can never exceed the saturation perssure pS the maximum posible value of rh = 100% {2}
  • 8. 8 Instructions for use: This wet bulb psychrometer is used to measure The humidity of air with using the table Above. The percentage values are valid for still Temperatures are measured in 'C. • The tubular glass tank in the middle is to be filled with -dean water. The wick attached to the thermometer should dip into the water approx. 2 cm. • To determine the humidity read of the temperatures at the dry and the wet thermometer shortly after-each other and determine the difference. • Search the values in the table and you can determine the relative humidity of the air, {3}
  • 10. 11 Discussion: We use distilled water because...1. . we have to use NEUTRAL(according to PH factor) water in someA reactions.other wise reaction goes wrong. water always contain some type of mineral impurity like some.regularB salts and in some reactions we have to avoid the effect of those impurities .if we are doing experiment with regular water ,some time resultsC the water.changes slightly according to impurity which is in .though if there is no impurity in regular filtered water(rare case) weD can't say that it is NEUTRAL and don't contain any impurity by only seeing it with naked eye so it is best way to use distilled water. 2.What does humidity measures? humidity measures the amount of water vapor in the air. Water concentration in air or water vapour.The amount of water vapor in the air. water vapor moisture 3.What is relative humidity measured in? Relative humidity is measured in %. 4.Can relative humidity be measured with an instrument? Yes, you can check the whether with an instrument. this instrument is called a thermometer. this is how it works... when it's freezing cold it should be below 0. when it's hot it should be at least above 10 degrees. These thermometers should be kept outside so the thermometer is absolutely right or it's close to the right answer. However, a hygrometer can be used to use relative humidity. Or it is how much water vapor is in the air.
  • 11. 11 5.Relative humidity can be measured with a? Hygrometer We used wet cloth on a humid day there is moisture in the air. On a dry6. day the moisture in the clothes more easily evaporates. 7.There are many reasons to change the temperature and makes the temperature be unstable like condition in the room and being close to the thermometer