 So, welcome back. Now, in order to study properties of fluids, we are focusing mainly on two engineering fluids that are air and water, because these are the two fluids that we always deal with in practice in mechanical engineering. For example, we use air compressors, air condenser and similarly, what we have is water for various cooling purposes for various heating purposes in heat exchangers. So, these two fluids are predominantly used in most of the applications in mechanical engineering. So, if I want to study properties of fluids, I would normally like to use such a fluid that is predominantly used in mechanical engineering. And therefore, what we had studied earlier are the air and water properties. So, if I want to go ahead and compare air and water again, just bringing some salient features of these two fluids, let us just see those things. So, if I see air, I can assume it to be a siminal component, though it is a mixture of various gases, which is a plus point. It remains completely in the gaseous form near ambient conditions, because my studies are not going to be at very low temperatures or at very high pressures. I am going to talk about near ambient conditions, wherein we use these fluids mostly. I would like to use such fluids, air and water, which are normally used in atmospheric conditions at around ambient temperatures. And if I compare those properties, that it remains completely in gaseous form near ambient conditions. Similarly, air which is a siminal component, though a mixture, I can still assume to be it an ideal gas for analysis purposes and therefore, I can apply ideal gas law to get various properties of the air at different pressures and temperatures. So, these are the advantages of what we have as air, but then I will be able to study only gaseous air, because at ambient temperature what we have is only gaseous air and therefore, I will not be able to understand the liquid properties of the fluids in liquid form if I use air as a fluid. Because against that, if I see water now, if I were to use water as a fluid, I can observe water in all the three phases at near ambient condition. So, when I say ambient condition, it is around room temperature up to let us say 100 degree centigrade and 0 degree centigrade and for atmospheric pressure, I can see that water exists in all the three forms and I normally use all these three phases for various engineering applications too. So, I can use liquid and gaseous in a predominantly more forms than solid form, but still I can get solid ice, liquid water and gas vapor in the form of steam. All these three phases or the mixture of these phases, all these which constitute water as substance, they exist in near ambient condition. As far as air is considered, I got only gaseous air near ambient condition. The boiling point of air is much below room temperature and therefore, out of these two fluids, two engineering fluids, if I were to study water or air for fluid, I will always prefer water because water exists as a pure substance even if we got two phase mixture of water while air is not and I can study the gaseous as fluids and liquids as fluid also as far as water is considered. So, I am very happy with water if I want to study fluids because I can study gaseous and liquid both. So, water in 0 to 100 degree centigrade easily attainable temperature range, two or three phases mixture of water is a pure substance and therefore, these phases together also constitute as a pure substance. The phase transition from water at one atmosphere are near ambient conditions and are distinctly visible. So, I can study the phase transitions also and each phase of water has significant application in various fields. So, liquid, vapours, solids have got significant applications in various engineering fields also. These are the different advantages of using water as a fluid. So, if I were to study properties of fluid, if I go for water, the fluids which I want to study in the form of gaseous and liquid, water exists in all these forms, water can be studied in gaseous form, water can be studied in liquid form. So, my properties of fluids therefore, can be kept limited to water only. So, here afterwards now therefore, if I want to study properties of fluids, I will study the properties of fluid through water where I can have the gaseous phase, I can have liquid phase also and I can have a combined gaseous plus liquid phase which is also a pure fluid and therefore, I conclude that my study of fluids, properties of fluid can be understood from study the properties of water henceforth. So, my further discussion now will revolve around water vapour, water in gaseous phase, water in liquid phase and water may be gas plus liquid also together. So, various properties of water as far as we know that we got a liquid and we have earlier seen that there is no simple equation of state available for water which is true for liquids, liquid also. The properties of fluids therefore, can be understood and obtained by two methods here and therefore, we can use graphical methodology to get various properties of the for water, we can have a molier chart which gives you some conceptual understanding. We cannot get actual accurate values because it is a graphical method but what normally we refer to get the properties of water is a tabular method where we use steam tables which is basically collection of all the experimental data that they have done and with some property relations they have acquired the data for other points. So, what we have is therefore, steam tables which is what we will refer in the lectures to come, it is essential for calculation because what you get from here are some accurate properties of water at different pressures and temperatures. So, we got steam tables which is what we will refer in future studies. So, summarizing what we have learnt, we have learnt what is a pure fluid, what is the impure fluid, the difference between the two then we concentrate on two basic engineering fluids that we normally use in engineering practice which is air and water and ultimately we concluded that we would like to study water in order to study fluids and we will then go to study the properties of water in the discussions to come.