 Hello, I am Ganesh B. Aglai working as an assistant professor in Department of Mechanical Engineering, Walsh University of Technology, Sulakpur. So in the session second of a psychrometry, we will study psychrometry chart. The outcomes are learning outcomes are at the end of the session, students will be able to draw psychrometric chart, locate psychrometry property lines, obtain psychrometric properties from chart. In the first session, we have studied psychrometric properties such as drywall temperature, wetwall temperature, dew point temperature, specific humidity, relative humidity, specific volume. Now these properties we can either locate or obtain from the psychrometric chart. I am going to refer carriers psychrometry chart. Remember psychrometry chart is to be used for standard atmospheric pressure of the moisture. So this chart is plotted for the atmospheric pressure 1.0123 bar for standard atmospheric pressure only and for other pressures we have to refer the steam table and the psychrometry relations. Now I will enlarge this psychrometry chart. Here along the x axis, drywall temperature scale is taken. The temperature for this carrier chart starts from minus 10 degree Celsius to plus 55 degree Celsius. Then this curve is WBT curve, wetwall temperature curve. So for DBT lines, I have to take vertical projection, parallel lines to the y axis. So these lines will be constant DBT lines. For example, this is 25 degree Celsius line. This is 20 degree Celsius line. This is 30 degree Celsius line. So we can measure the DBT temperature by using simple thermometer of moisture and those temperatures we can locate along these DBT lines. Now psychrometer will give you second property known as WBT, wetwall temperature. So on this outermost curve named as saturation curve, the WBT temperatures are located. This is 15 degree Celsius, this is 20 degree Celsius. So these temperatures are WBT temperatures. And the lines, these inclined lines passing from these temperatures are known as constant WBT lines. So as we know, easily we can obtain DBT and WBT temperatures of surrounding air. Then taking the example of DBT as 25 degree Celsius and 15 degree of WBT. So this is the 25 degree Celsius and this is the 15 degree Celsius. So the intersection of these two temperatures is this point. So this point is nothing but the state of the surrounding air or the moisture, accurately moisture. So other properties easily we can obtain by using this psychrometric chart. So third property is relative humidity. This saturation curve has 100 percent RH. Then other RH lines such as 90 percent, 80 percent, 70 percent. So all these RH lines are these curves, along these curves the RH remains constant. So that previous point was somewhere here. So we can obtain easily the RH relative humidity of that moisture. Now next property is the specific humidity. So this right hand side scale is of specific humidity in the carriers is expressed in gram per kg of dry air. Keep in mind all psychrometric properties are evaluated per kg of dry air basis. So suppose this point is the state of the surrounding air moisture, then we have to draw horizontal line parallel to the dbt scale x axis whenever it will intersect to the specific humidity will be the value of that moisture specific humidity. Then next property is the specific volume. So these inclined lines, these inclined lines are specific volume lines. So the line, this specific volume line is having 0.85 meter cube of volume per kg of dry air. If it lies in between these two constant specific volume lines by using the compass, you have to divide this distance into equal parts and proportionate value will be getting from the psychrometric chart because this is the graphical method. Now these curves are enthalpy deviation. For usual level neglecting the error in the wbt and enthalpy lines means we have to assume that if we will extend this line the error will be neglected and we can consider this line is also isenthalpic line. So for wbt and enthalpy the same line we can refer isenthalpic line of suppose 52 kilo joule per kilogram of dry air and corresponding wbt is 21 degree Celsius. So this line will be of isenthalpic and wbt line. For air washer we have to refer this line. And on this psychrometric chart on right hand side there is SHF scale. This is the sensible heat factor scale. It will start from 1 to 0.75. To draw this, to draw this scale there must be some reference point and on the carrier psychrometric chart this circle is the reference circle means we have to align the set square to this reference circle and the obtained SHF value. Then we can draw the sensible heat factor of that particular room load because room load will have sensible heat and latent heat. So any inclined line will have some value of SHF as it consists of sensible heat and latent heat. Then if we want we can get PV also PV stands for partial pressure of water vapor. In few charts the PV scale is visually given on left hand side of this one this psychrometric chart where the values will be also given. So we have to extend that line up to given PV scale we will obtain partial pressure of water vapor also. So this psychrometric chart is very important to calculate sensible heat factor, room sensible heat factor, effective sensible heat factor lines and also we can locate the process lines. Third temperature is the dew point temperature as we know the saturated air is having driable temperature equal to wearable temperature equal to dew point temperature. Now the dew point temperature lines are these horizontal lines remember horizontal line is of dew point temperature and is of specific humidity also. So the saturated air will have the 25 degree Celsius for example WBT which is also equal to 25 degree Celsius of DBT driable temperature and same is the value of dew point temperature this is the saturated curve. So this saturated psychrometric chart is the basis or the useful chart for locating actual psychrometric processes and in next sessions we will study the we will take the help of the psychrometric chart for calculating cooling and heating load calculation.