 Hello students, myself Ganesh Beyagalave working as an assistant professor in Department of Mechanical Engineering, Valginist of Technology, Sholapur. In this session of thermodynamics, we will see steam properties first part. In this, the sub topic is temperature entropy diagram, learning outcome. At the end of the session, students will be able to describe steam properties on temperature entropy plot. So, generally the steam is studied in the refrigeration and air conditioning. In the air conditioning, psychrometry is there, where moisture is present. Also in our thermal power plant, that is in the Rankine cycle, the steam is used as a working substance, which undergoes the phase change. So, for that purpose, we require the temperature entropy plot. So, the temperature is taken on y axis and entropy on x axis. So, this is the temperature and this is the specific entropy. The unit of the temperature can be taken in either degree Celsius or in Kelvin, whereas the entropy, the unit is kilojoule per kilogram Kelvin. Now, as we know, when the water is heated, suppose one pot is taken in that pot, the water is taken and the heat is given to this water that is represented by Q s. Initial temperature of water will be equal to surrounding. This is the assumption. So, let the initial temperature of water is at a state 1, which is represented on the T s plot. As we know, by thermometer, we could measure the initial temperature, that is suppose T 1 and the heat present in that is suppose Q. So, Q by T will be the entropy. In this fashion, the point 1 is represented on the temperature entropy plot. As there is a start of heat given to the water, there will be rise in the temperature without changing the phase. Now, initially, water is in the liquid phase. So, there will be isobaric increase in the temperature. The temperature of water will go on increasing. It will go on increasing and the pressure present over the water is atmospheric pressure, which is nothing but standard atmospheric pressure, which is P 1. And as you know, the standard atmospheric pressure is 1.01325 bar and assuming the surrounding temperature as 20 degree Celsius. So, this is the point at 20 degree Celsius and corresponding entropy. As the water is heated, the pressure is constant. The pressure over the surface of this water is a standard atmospheric pressure, which will remain constant. Then the type of heat taken by the water to get it heated up to highest temperature is called as sensible heat. Up to suppose point number 2, there is no change in the phase of the water. Water is in the liquid phase and consider the maximum temperature without phase change is point number 2. Now, what happens? If we still continue heating the water behind the point number 2, then there will be start of evaporation. Such type of vapors will be generated from the water and the change in the phase from water to vapour will occur at constant temperature. So, there is a deflection. This process will get deflected and temperature remains same. Continuation of heating the water will generate will increase the rate of steam generation. It will continue till till 100 percent water gets converted into steam. Suppose this is the pot. Suppose this is the plot pot in which only now vapour is present. That is represented by the state 3. So, this type of energy or the heating process is called latent heat process. The latent heat and the sensible heat. Remember in the sensible heat there is no phase change whereas in the latent heat there is phase change. Point number 2 is called saturated vapour. State 2 is called saturated liquid point whereas state 3 is called saturated vapour state. So, can you think over the one property that will give us the range between 0 to 1? As you have studied in the EFI first year of engineering try to recall that property I will cover that in the coming points. Now, point number 2 is saturated liquid, point number 3 is saturated vapour. Now, if we further continue heating of water then the vapours are there 100 percent vapours are there. So, their temperature will continue increasing up to infinity. We can heat the vapour up to infinite temperature. It may be 1000 degree Celsius, 2000 degree Celsius. That is why water vapours are more dangerous for human beings whose exposure is to be avoided. That is why in the steam power plant the cycle is closed cycle. Now, the type of the heat which is required to suppose heat the water up to point number 4 is once again the sensible heat. Now, the formula is very simple for sensible heat it is m c p delta t and here also m c p delta t. So, you could calculate the heat required during process 1 to 2 for the for heating the water from state 1 to state 2 is mass of water into specific heat of the water in the bracket t 2 minus t 1. Keep in mind it will make the thermodynamics study of thermodynamics very simple as this was the sensible heat process. Now, heat required to convert the saturated liquid into saturated vapour is during process 2 to 3 which is nothing but latent heat process and the formula is mass flow rate of water into HFG where HFG is the latent heat to convert the fluid into the gas. Now, this process that is 1 to 2 was at constant pressure isobaric pressure. What will happen if we try increasing the pressure if we increase the pressure above the water surface suppose from 1 bar to suppose 5 bar then then I could draw the isobaric line I could draw the isobaric line at 5 bar at 5 bar pressure. So, what has happened suppose this is 1 dash 2 dash this is 3 dash and suppose this is the 4 dash we will find that this HFG HFG has decreased has decreased and if I try to join if I try to join all these points then I will be getting such type of saturated liquid vapour and saturated vapour and this point is called critical point think over the critical points latent heat yes correct. So, at critical point the HFG is equal to 0 we will continue further study in next session. For more study you can refer fundamentals of thermodynamics by Boranke and Sontek also second book fundamentals of engineering thermodynamics by Moran and Shapiro.