 So, welcome back. Now, till now we have seen the state of a substance, the state of water substance can be traced on the phase diagram. So, here I would just give a summary of locating the state of the substance, water substance on the phase diagram, but there is still something missing. And let us find out from this slide what is that is missing till now. I have given the states at every possible places, but when I want to trace properties, when I want to get properties, there is something still missing. And let us see what is that part which is missing related to the state of the water substance as far as the steam table is concerned as far as the phase diagram of water is considered. So, let us look at this slide and in general now I will just summarize the state of a substance can be found out from various places and it can lie on various regions. So, depending on the T set or P set values. So, I know that this substance where it should lie, I can compute and compare its temperature and pressure and we had seen about that. We have seen the tutorial also related to that. Depending on the T set or P set value, I can locate where exactly this substance lies. And what form it lies? Is it a vapor, liquid on the on the line, elevator, whatever, I can trace all those things from based on the T set and P set value. I may use a steam table for this. So, there are three, four, five possibilities. The first possibility could be it could be a sub cooled or compressed liquid region, is not it? If the temperature is less than T set value, if the pressure is more than P set value, you could be in sub cooled or compressed liquid region. Or if the temperature is more than T set value, if the pressure is less than P set value, you could be in super heated vapor region. Or if the temperature and pressures are beyond the critical limits, then we could be in super critical fluid region which is what we have seen earlier. Or if temperature is T set, pressure is P set, we could be on a saturated liquid or saturated vapor region. So, I know I am on the LV line here. So, I could be saturated liquid or saturated vapor region. And I can get all these properties for a given pressure P and T condition using steam tables. What is not known to me right now? There is one more possibility is two phase mixture when I got liquid plus vapor region. The properties of these is going to be a question mark right now for you. So, if I want to get the properties of all these 1, 2, 3, 4 regions, I will go to the steam table, I may have to do some interpolation of properties and I can use table 3 and I may use even for these properties I can use table 1 and 2 also. So, I can use this steam tables and I can directly get the properties for these different regions directly from the steam tables. The problem is two phase region, wherever I got liquid and vapor existing together and if I want to get properties for liquid and vapor together, I do not know where to go as of now. And therefore, this is right now a question mark for me, how to get properties of a mixture where the substance has got some vapor and some liquid together. They are together they are existing at the same pressure and same temperature alright. So, properties of two phase mixture how to get from steam table is now a question. So, the answer to this is in a very important term called quality. The quality of a mixture is going to give the answer to get properties of a two phase mixture of liquid and vapor mixture and let us now see more about this quality in the forthcoming lectures. So, introduction to quality is what we are going to talk about. Again, what region I am going to confine myself to now alright. So, again I have got a P T diagram and a P V diagram. This is my L and V regions I think most of you are now used to this habituated with these slides and if I draw take any condition which lies on a L V line saturated liquid vapor line I will be somewhere here if I can draw a horizontal at the same pressure I will be here and now if I just look at saturated liquid line and saturated vapor line alright. In this diagram I will look at only this point while in this diagram P V diagram I can see on the left side of this dome and the right side of this dome. The left side is saturated liquid the right side is saturated vapor and if you recollect the properties associated with liquid are U F V F H F S F alright saturated liquid everything is liquid over here on this line is 100% vapor line properties associated with that are for the dry saturated vapor is U G V G H G and H G alright. So, got two regions saturated liquid saturated vapor and the properties for these two I can directly get from the steam table alright. This can be obtained from stable three as well as from table one and table two my question is now two phase mixture which lies in between this and if you remember that the difference between this two is delta U delta V H F G and S F G the question is if I want to get properties of the mixture which lie anywhere between the saturated liquid line and saturated vapor line or inside the dome from this end to this end anywhere you know that the mixture will be there liquid and vapor in the varying proportion I have just shown a representative figure here vapor could be more liquid could be less whatever depending on where it is how do I get the properties of a mixture which is in between saturated liquid line and saturated vapor line or under the dome inside the dome here I have to introduce one more parameter quality unless I know the quality now I will not be able to calculate properties of any mixture liquid and vapor mixture which lies inside this dome and therefore I should know quality and this quality of the mixture actually would determine what are the properties of a two phase mixture inside the dome. So, I will just introduce this term quality to you and then we will use this quality further to calculate the properties at various two phase mixtures that lie inside the dome. What we have learnt properties of subcooled or compressed liquid we have understood what kind of approximation which we have to do for subcooled or compressed liquid how do I get the properties of S U V for the compressed liquid and we also understood the part related to enthalpy in summary I have shown the slide we show the state of a substance could be obtained and we lastly I just introduce you to term called quality and this quality will determine actually the properties of the two phase mixtures. Thank you very much.