 11183 Jaya Chhama Rajendra College Mysore I think yesterday you had a question for Professor Purani Are you ready with that question again? Over to you So my question is, what the use of shock waves present in the system Means, please clarify the shock waves, what are the benefits in turbines Means energy-producing devices and compressive energy-absorbing devices And also transmitting this process What is the function of these shock waves in these types of devices And why we need to study about these shock waves Okay, so the question is on shock waves And if they occur in energy-producing or energy-absorbing devices What is the use of these shock waves? I will actually say that these shock waves are totally undesirable When it comes to either energy-producing or energy I should say power-producing or power-absorbing devices So in general, the objective would be not to have these shock waves in situations like these Because as we have seen, shock waves are associated with irreversibilities And irreversibilities will degrade the performance of the system So the short answer is that there is no use of shock waves in these devices There are some situations in which you just cannot avoid the shock waves being present And in that situation, you should be able to at least figure out what the effect of these shock waves is And therefore we perform the analysis The only situations where shock waves are probably going to be useful Is something of a futuristic application Where people are thinking about what are called as supersonic ramjet type engines Where the combustion efficiency can probably be increased By artificially creating shock waves within the combustion chamber Because there is a phenomenon associated with shock-induced mixing And the idea is that perhaps such a phenomenon will enhance the mixing between the oxidizer and the fuel in those kinds of applications However, these applications are not at all developed fully They are under development And may be in the next 15-20 years you may see such things in practice But as of now, I will say that if you are dealing with power-producing or power-absorbing machines That we normally use, shock waves would be totally undesirable for you Thank you So, these shock waves are attached to the surface or above the surface in the fluid flow problems So, the question is on whether the shock waves are attached to the surfaces or detached from the surfaces See, the attached or detached type of a shock wave will come only when you are talking about a multi-dimensional steady type flow We have analyzed in this part of the course only a simple normal shock wave However, to answer your question, depending on the shape of the object The shock can be attached to the surface or it can be detached So, for example, if you imagine something like a sharp pointed nose type object Like a wedge or a cone which is flying supersonicly Then the shock is going to be attached at the nose But if you think about a blunt nose type body Like let's for example say a bullet or a missile which is flying supersonicly Then the shock for such objects is going to be detached from the surface Thank you So, flow measuring devices like 20 meter, nozzle meter and alipase meter They are having an ISO standard value, sir Okay See, we have the standard value, sir For analysis purposes, further studying purposes through CFD See, I think you are referring to flow measuring devices Which are routinely used for such purpose And there is some standardization involved However, we haven't really talked about the nozzles, etc. That we discussed in this class Being used for any flow measurement type purpose And therefore, I don't think really that there is any standardization Associated with the kind of devices that we have talked about Thank you Sir, that is not the question, sir Actually, to study the convergent-divergent nozzle We need one model or a specification Where you get this specification of CD nozzle, sir? Oh, I mean the shape of the nozzle I assume perhaps that you are talking about the profile Or the shape of the nozzle as some sort of a specification Or a standardization And the answer is that we don't really consider Any specific or standardized shape for the CD nozzle, etc. As long as any shape which is reasonably conforming To our quasi-one-dimensional approximation Which simply means that the cross-sectional area Of the nozzle is slowly changing Along the flow direction Is sufficient for the purpose of our simple analysis There are some specific applications Where nozzle profiles are defined for specific end applications But those are definitely out of the scope of this class For which you will have to refer to Specialized compressible flow textbooks As of now, what you can keep in mind That as long as we are dealing with a quasi-one-dimensional situation As far as cross-sectional area changing very slowly In the flow direction The shape of the nozzle or the profile of the nozzle Really doesn't play any part Thank you Okay, thank you, sir Why can't I, sir? Yeah, please go Sir, in a real gas PV is equal to Hello Yes, go ahead In a real gas PV is equal to ZRT Sir, actually what that Z is Means, sir What does it mean? That is compressibility factor Okay Don't write it as PV equals ZRT Because that gives a totally odd picture For an ideal gas we know PV equals RT Or PV by RT is one Okay So for a real gas PV by RT PV by RT is not one And for some reason it is given the symbol Z And called a compressibility factor In fact Z is simply a ratio of PV, R and T There is no compressibility of any kind involved Compressibility means you are increasing the pressure And studying the change in volume There is nothing of that sort It's unfortunate that it is called a compressibility factor And it is used as a dimensionless number To plot properties of various fluids As a function of dimensionless temperature And dimensionless pressure So that chart is known as the compressibility chart Over It's a last one thing, sir Actually in this course I learnt a lot from your centre, sir That's why from this centre we tell to Thank you for this one, sir Over and out Thank you Over and out 1148 Krishna Institute, Ghaziabad Over to you What is the difference between a reversible adiabatic and adiabatic process? See and what is the question is What is the difference between a process Which is reversible adiabatic And a process which is only adiabatic We have defined an adiabatic process As work transfer only So this means there is no heat transfer DQ is 0 A reversible process We have defined it in detail At something which can go forward and reverse By retracing the path in the complete detail Reproaching all the interactions in complete detail In such a way that when it is executed In the forward direction And in the other direction Bringing the systems involved back to their original state No trace of the processes having taken place Is ever left, is ever available That is the reversibility And after developing second law of thermodynamics This comes to a situation that For a reversible process DQ should be not 0 DQ should be equal Ds should be equal to DQ by T This is for a reversible process So if DQ is 0 It is adiabatic If DQ by T equals Ds Then it is reversible So if you have reversible and adiabatic That means not only is this equation applicable But this equation is applicable So if you have adiabatic And reversible That means since both these equations are applicable This also means Ds equals 0 So adiabatic and reversible means isentropic Adiabatic by itself does not mean isentropic It only means DQ equals 0 Over to you Thank you Thank you 1 0 4 0 College of Engineering Pune Over to you Good morning sir Good morning So the query is regarding Thermal power plant K study of a thermal power plant of small size Okay In this power plant The flow through the turbine Same flow through the turbine is almost double Than the rated quantity Now in this There can be two reasons One is that in general Which is saying that Sailing through, internal sailing through the turbine And Flow through the model Keeping these two things apart What could be any other reason Which to be seen specified Difficult to say But what does this have to do with thermodynamics You have a small power plant And you say that the turbine flow rate Is double the design flow rate In principle I cannot say that there is anything against it But generally this does not happen And what does it have to do with our thermodynamics course That is something which I do not understand now Over to you Sir means His question sir is related to thermal power plant Basically Through the thermal power plant The question required more than electricity One minute So we want to Run this plant As per Means the unit rate As compared to electricity See you can Extract some more power from a turbine But you I do not think you will be able to ever Double the flow rate through that turbine You are far away from the normal Design and operating condition And Even at off design conditions What happens to the turbine and how it behaves Depends significantly On the internal details of the turbine Which we are not looking at During our course in thermodynamics Remember our turbine was us For us was simply a black box All that we said is The inlet enthalpy is this Exit enthalpy is this Flow rate is this This is the power output you should get That is it We stop there Over to you We want to study this So give the guidelines No You attend the course in energy conversion Or steam turbines And then you will get more than guidelines For this 1002 Amal Jyoti Kottayam Over to you Yes go ahead Sir we have come to understand now that Adiabatic constant volume process Or adiabatic constant pressure process Or adiabatic isothermal process Can also take place Yes But these type of examples are not Worked out in conventional text books Right Can there be a source for materials For our students on this matter Yes see I have noticed And it has been brought to my notice That students have And many teachers also have a mental set Which means adiabatic Quite often when I ask What is adiabatic The answer is pv raise to gamma is constant We have seen during our exercise That adiabatic is just dw only Or dq equals 0 And for If for you to reach from adiabatic To pv raise to gamma is constant There are a number of assumptions Which you have to make Pv raise to gamma constant Is a very special case And as you said It is very nice that you have appreciated That an adiabatic process Can also have Can also be a constant volume process Or a constant pressure process Or an isothermal process Unfortunately The so called standard text books Do not have Many examples Or hardly have any examples Of this kind I think I have been able to Put some examples Of these kind in the exercise sheet But since we are teachers of Thermodynamics It is for us to set up Examples of this kind For our students And give them additional exercises Along with whatever are there in the books That is how we have created These exercises And I think you should also create your own It is not very difficult In fact one lacuna Which I find in these exercises Is there is hardly any exercise In which Data e is significantly different From data u And I have noticed that And I will try to include now Some exercises in which Along with data u You have even data ek Or data ep which is significant I think the only exercise Or one of the few exercises In which data u Apart some component other than Data u is significant Is the air gun and bullet problem I think somewhere in the first law 1.7 And also the Last problem in combined first and second law CL6 That is somebody throwing a sack of Sack of sand on to a professor That one Over to you I have got one more question in psychrometrics The question itself See at a particular temperature Dry air can hold Maximum certain saturation level of water What is the property Why the air has got certain affinity to water And what limits the maximum quantity Saturation level of this water At a particular temperature So the question is regarding What kind of Or what What is the affinity Of putting Water vapor into air There is no such thing You can put any vapor into Or any vapor into air The only thing is What you have to worry about is There is a saturation pressure corresponding To the existing temperature And as long as you reach that saturation Pressure you cannot put in anything More if you want to put in anything More you have to raise the temperature So if you want to have One atmospheric Or a pressure of one atmosphere You will need to raise the temperature to 100 degrees So similarly Instead of water vapor If you want to put in any other vapor Of any other fluid Then corresponding To that vapor pressure You can put in as much of vapor of that fluid So let us say it is 30 degrees C And instead of water There is some other refrigerant You want to put in Just check the vapor pressure of that fluid At 30 degrees C And that is the maximum amount you can put in So what you can put in depends on the saturation Pressure corresponding to the existing temperature Thank you My question is to Professor Gayithande Sir you have mentioned Adiabatic process can happen At constant temperature Sir in that case Will it be a quasi static process Can we consider the equation PV raise to gamma is a constant Again you are confusing PV raise to gamma Process means dq equals 0 Constant temperature process It self means At least along an isotherm All states are defined So moment you say constant temperature To a significant extent You have already made an assumption That it is quasi static Because at every stage Temperature is defined So an adiabatic process Only means no heat interaction Of any kind It can be quasi static It can be non quasi static Keep in mind As your colleague has earlier said That adiabatic means dq is 0 Throughout the process The process may follow any route While maintaining that Constraint So it can be constant volume Constant pressure Constant temperature It can be PV raise to gamma is constant It can be PV raise to gamma Into V equals constant Provided you arrange the other interactions accordingly Some of these things will be possible Because remember Some of these will be impossible Because for an adiabatic process The second law says that The process can take place Only in a direction In which the entropy increases So long as you select a direction In which the entropy increases Or at most does not change You can execute that process But an adiabatic process In which you Expect that the entropy decreases That will not be allowed By the second law of thermodynamics And this will be An impossible process An unrealistic process So although we say For example You take a fluid In a rigid container You take I can stir it That is a work interaction The Suppose it is a gas Temperature will rise It is an adiabatic constant volume process And we have solved an exercise Based on that But you say It is an adiabatic constant volume process In which temperature should reduce By some means That will not be possible Because the temperature reduces That is the simple entropy Relation And hence For an adiabatic constant volume process A process in which we expect the temperature to reduce Will not be allowed Because that is an unrealistic process So we will close this session now