 Today we are going to continue from previous lecture properties of pure substance. At the end of this session, student will be able to apply knowledge of basic thermodynamic concepts such as specific heat, sensible heat, latent heat and dryness fraction. Students will be able to calculate the heat required for wet, dry as well as saturated steam. These are the contents we are going to discuss in this session. First, we will define what do you mean by specific heat, sensible heat and latent heat. Then we will move towards the quality of steam that is wet, saturated, superheated steam. Then what do you mean by degree of superheat and dryness fraction. Then we will go into the module diagram and references. Definitions before moving towards the definitions. In previous lecture we have studied the steam generation at a constant pressure which takes place at 1 bar. Here that 1, 2, 3, 4, 1, 2, 3, 4, 5 line represents the steam generation at a constant pressure. 2 is the saturated liquid point, 4 is the saturated vapor point and 4 to 5 is the superheating. First one that is specific heat that is denoted by Cp. How you are going to define the Cp that is nothing but let us take one example. If you are having in a container 1 kg of water which is at 20 degree Celsius and suppose if I supply Q amount of heat whatever it may be Q amount of heat if there is a change in 1 degree Celsius temperature of that water means the temperature of the water starts means change from 20 to 21 that quantity of heat is called as specific heat. Now specific heat of water is 4.187 kilo joule per kg Kelvin means for unit mass and for unit degree Celsius if you supply 4.187 kilo joule amount of heat to water then there is 1 degree Celsius or 1 degree Kelvin change in temperature of that water that is called as specific heat of water moving towards the next definition, sensible heat. Now if you consider this 1 to 2 line if you consider this 1 to 2 line that is called as sensible heat. Sensible heat is simply defined as when you are going to supply the amount of heat if there is a change in temperature but there is no change in the phase that type of heat is called as sensible heat means what if you are going to heat the water from 0 degree Celsius to 100 degree Celsius which is at 1 bar whatever the quantity of heat we have supplied that type of heat or that quantity of heat is called as sensible heat because there is change in temperature but the water will remain in a liquid phase itself means there is no change in the phase that type of heat is called as sensible heat and the sensible heat is denoted by Hf. Moving towards the next definition that is latent heat now if consider at 0.2 all the what you can say in previous lecture I have studied all the points are at a saturated level and all the molecules are in liquid state and whatever the heat you are going to supply to convert that heat from liquid to vapor that type of heat is called as latent heat and the unit of the latent heat is joule per kg and that is denoted by Hf in latent heat there is a change in phase but the temperature remains constant means that is a exactly reverse in sensible there is change in temperature but no change in phase in latent heat there is change in phase but the temperature remain constant means this 2 to 4 line it will takes place at the constant temperature of 100 for normal atmospheric pressure that is of 1 bar dryness fraction dryness fraction it is nothing but it is denoted by x which is equal to the ratio of if you consider given quantity of mixture in it suppose for example out of 100 molecules 40 molecules are in steam and 60 molecules are in water then you can define the dryness fraction it is a ratio of amount of steam molecules divided by total molecules contained in a mixture means as I have given example out of 100 40 molecules are steam means 40 divided by 40 plus 60 you will get the dryness fraction x equal to 0.4 considering this example at 0.2 dryness fraction x is 0 and at 0.4 the dryness fraction is 1 because all the molecules are in vapor state and in between 2 to 3 at 0.3 dryness fraction is greater than 0 and less than 1 now quality of steam the quality of steam can be bifurcated or classified as weight steam superheated steam and saturated steam now total heat contained by the weight steam is given by h f plus x h f g at 0.3 weight steam is there h f is the sensible heat contained by the water plus x is the dryness fraction and h f g is the latent heat if let us say suppose for example x is 0.5 means that is absorbed half of this latent heat therefore h f g multiplied by 0.5 that will give you the quantity of the latent heat and whereas h f is the sensible heat contained by the water at a given temperature at a given pressure now pause this video for a moment and try to write the equation for total heat contained by the saturated steam now the total heat contained by the saturated steam is given by the equation h f plus h f g and whereas for dry saturated steam the value of x becomes 1 means at 0.4 and the value of x becomes at 0.3 the value of x is in between 0 to 1 similarly if you want to write the total heat contained by the superheated steam the equation is given by h f plus h f g plus m c p delta t whereas m c p delta t is the heat contained by the superheated whereas that delta t is called as the degree of superheated how you are going to find out the delta t that is temperature of the superheated steam minus temperature of saturation temperature at a given pressure now we will move we will take one simple example so that you will get the brief idea how to calculate the total heat required now here the question is determine the amount of heat which should be supplied to supplied to 2 kg of water which is at 25 degree Celsius to convert it into steam at 5 bar and 0.9 percent dry now what will the first we are going to write down the given things and as the pressure is given as 5 bar we will use the steam table and we are going to find the value of h f and h f g at 5 bar by using the steam table we will get at 5 bar h f equal to 640.1 kilo joule per kg and h f g is the equal to 2107.4 now I want to calculate the total heat required which is at a superheated let us see at 5 bar now you know the equation as the 0.9 percent dry means that is weight steam the equation to calculate the total heat required by the weight steam is given by h f plus x h f g now you know the values now this equation is given by h f plus h f is applicable for 1 kg of weight steam which is given by h f plus x h f g we are putting we will put the values and we will get the total heat required for 1 kg of steam and whereas as the temperature whatever this h f is there that will give you the total heat required from 0 to 100 degree Celsius or from 0 to saturation temperature but already that water is at 25 degree Celsius we are going to subtract the total heat or sensible heat contained by the water which is calculated by which is given by m c p delta t then this equation is for unit mass and the net quantity of heat to be supplied per kg of water is total heat minus sensible heat therefore this will come as 2432.26 and this is for per kg now as the total mass is given as 2 kg we are going to multiply by this by 2 and we will get 4864.52 kilo joule amount of it means what if you want to convert the 2 kg of water which is at 25 degree Celsius into 5 bar and 0.9 dry we will we have to supply 4864.52 kilo joule amount of heat these are the references thank you.