 Hello everyone, I am happy to invite you to this series of lectures on the second level thermodynamics course namely applied thermodynamics. In the first level course, we discussed primarily the concepts relating to thermodynamics in a concepts like system control volume, state of a system, properties, pure substances, how to evaluate changes in properties of pure substances and then first law of thermodynamics for a system, first law of thermodynamics for a control volume. And then we developed concepts relating to second law of thermodynamics namely Clausius inequality, the Kelvin-Planck statement of the second law, Clausius statement of the second law. Then we introduced the property called entropy and we looked at methods by which we could calculate entropy change of a system undergoing a process. Then we looked at some other fundamental concepts like isentropic efficiency and importantly principle of increase of entropy. And we concluded those lectures by looking at systems executing cyclic processes in particular system executing a Rankine cycle, Brayton cycle and which are both power producing cycles. And then we also looked at system executing a vapor compression refrigeration cycle which was a power absorbing cycle. So, the primary learning objective of that course was to understand, learn and understand all the all these fundamental concepts relating to engineering thermodynamics and apply them to certain examples, illustrative examples which bring out certain aspects of these ideas of these concepts and ideas and so on. That was the learning objective of that course. What we will pursue in this course is the following. The learning objectives in this course or to apply the concepts that we discussed in the first level course to practical devices mostly in mechanical engineering. Although some of these applications that we look at can be said to span different branches of engineering, but primarily in mechanical engineering. So, basically we will look at practical devices or applications and apply first law and second law to these applications and calculate quantities that are of interest, maybe exit properties from the device or efficiency of the device and so on and so forth. For instance, in the previous course, we had defined efficiency which was basically defined from the energy perspective. What we will do now in this course is to define an efficiency which is even more general than this and is based on a second law perspective. So, these are important things that we will develop in this course. So, the applications that we will look at in this course are wide ranging. For instance, we will look at steam turbine, gas turbine power plant, vapor compression, refrigeration device. We have already seen these three in the simplest form in the previous course or the end of the previous course, but what we will see here are applications which are much more detailed than the simple cycles that we saw in the previous course. So, the steam turbine itself, we will just look at not only the steam turbine, but also variations of the Rankine cycle. Then again in the case of the gas turbine, we will look at not only the basic gas turbine cycle. We will also look at advanced versions of the gas turbine cycle. For example, it will not be just the Brayton cycle. We would do Brayton cycle with intercooling, Brayton cycle with reheat, Brayton cycle with regeneration and so on. Similarly, for steam power plant. So, it is not going to be just basic Rankine cycle, but Rankine cycle with superheat, Rankine cycle with regeneration, reheat and so on and so forth. We will also look at vapor compression refrigeration devices. Again the cycle that we saw in the previous course was the basic cycle. So, here we will allow for additional complexities in the cycle. So, we will look at more realistic cycle and then analyze the performance of the cycle using things, metrics that we have already developed and additional metrics that we will develop now. For example, one important metric that we will develop is the so-called exergy, which we did not discuss in the previous course at all. So, we will develop the notion of exergy from second law in this course and then define efficiency, which is the so-called second law efficiency. So, in addition to efficiency calculated on an energy basis, we will also calculate efficiency from a second law perspective, which is much more useful. No doubt, the efficiency based on energy is quite useful, but the efficiency based on second law allows us to make very good engineering decisions, comparative engineering decisions for different applications, which are executing the same thing. We will then move on to look at applications like spark ignition, compression ignition, IC engines. These are actually very complicated in real life. So, what we will do is, we will sort of consider an idealized version of these devices, the so-called air standard cycles and then we will do an analysis using methods that we have developed so far and then we move on to psychrometry. Psychrometry is a very important application in mechanical engineering. So, basically, if you look at many heating, ventilation and air conditioning application today, HVAC, it is used in automobiles to maintain the cabin at a comfortable temperature. It is used in large buildings to maintain the building at comfortable temperatures. Some part of the buildings may require heating, some people may require heating, some may require a slightly colder temperature, slightly warmer temperature and so on. So, different parts of the building have to be maintained at different conditions, temperature as well as humidity and HVAC is the part of mechanical engineering that deals with that. HVAC itself is founded on psychrometry which deals with moist air. So, basically, what we need to understand is that the level of comfort that a person feels is related or dependent not only on just the temperature of the atmosphere, but also the level of humidity in the atmosphere. So, we need to develop thermodynamic models which can handle moist air or humid air and then look at applications and see how the temperature and the moisture are interrelated and how they play a role in determining the final conditions in an application. That is what we will look at in psychrometry. Then we move on to combustion of fuels. In combustion of fuels, basically, we look at many different types of fuels and the thermodynamics and thermochemistry associated with the combustion of fuels. So, we look at their composition and their combustion, we write down the chemical equation, then we do things like that. And this is an application of concepts that we have already studied. So, it could be a, for example, an IC engine where fuel undergoes combustion. If that is the case, then we will treat the device as a thermodynamic system and then analyze it appropriately. Now, in case it is a gas turbine combustor, then we will treat it as a study flow combustor and again apply our study flow energy equation and other concepts and then carry out an analysis. So, basically this will be an analysis, this course will deal with analysis of different applications, wide range of applications, mostly using concepts that we have developed earlier. And in addition, concepts that will be developed in the early part of this course. The last part of this course, we look at compressible flow through nozzles. Now, flow through nozzles is a very, very important application for mechanical engineers. It may be obvious that it is a very important application for aerospace engineers, but actually, it is a very important application for mechanical engineers. And for mechanical engineers, the application is even broader than what aerospace engineers see. Because aerospace engineers typically work only with air as the working substance, whereas mechanical engineers have to deal with flow through nozzles, not only involving air, but also involving steam and also refrigerant. All these three types of nozzles are used in many practical applications involving mechanical engineers. For example, in turbo machines, steam turbines and so on, the nozzles work with steam as the working substance. And in other refrigeration applications, again nozzles work with refrigerant as the working substance. So, what we will look at is compressible flow through nozzles involving not only air, but also steam. We really do not look at any particular example involving refrigerants, but the extension to doing calculations with refrigerants is not very difficult to do. From steam going to refrigerants is not very difficult to do. Now, what are the students expected to be able to do at the end of this course? So, basically, given any device that you have not encountered. For example, when we look at all these applications, we are looking at a wide range of applications. So, you will become familiar with many conventional devices in mechanical engineering, but you may encounter a new device. So, what this course should equip you is to take any new device, carry out a thermodynamic analysis of the device, evaluate first law and second law efficiencies of such a device and any other thermodynamic property of interest. For example, what is the exit pressure, exit temperature or work power required, work required and so on. Now, in case we are looking at compressible flow through nozzles, then students should be able to calculate thermodynamic properties of interest at the exit of the nozzle with air or steam as the working substance. Primarily, with air or steam as the working substance, extension to refrigerant is not really very difficult. It is relatively straightforward. But in this course, we will look primarily at air or steam as the working substance in the nozzle. So, these are the learning outcomes of the course. Let us go through the outline of the course. The outline given here is relatively detailed, but I will just discuss the highlights, then we will go through the details as we go through the lecture. So, we start by developing expressions for calculating entropy change of a control volume. In the first level course, we looked at calculating entropy change of a system that is undergoing a process. Here, we start by developing expressions for calculating entropy change of a control volume. So, basically, we will derive what is called an entropy balance equation. So, this entropy balance equation will allow us, if applied to the control volume or when applied to the control volume, it will allow us to evaluate, for example, the rate of entropy generation due to internal irreversibilities within the control volume. That is one of the most important quantities that we are interested in. Rate of entropy generation, remember, as we discussed in the previous course, entropy generation can be due to internal irreversibilities or external irreversibilities or both. So, we will derive an entropy balance equation similar to the steady flow energy equation. And the most important quantity that will come out of this equation would be the ability to calculate the rate of entropy generation due to internal irreversibility in a control volume. We will follow it up by applying the entropy balance equation to the control volume, then we will also take into account the entropy change of the surroundings or rate of change of entropy of the surroundings. And by putting the two together, we should be able to calculate rate of entropy generation in the universe, which is perhaps an even more important metric as we saw in the previous course. Entropy generation in the universe is a very important performance metric. Devices should operate in such a manner as to minimize entropy generation in the universe. So, rate of entropy generation in the universe is a very important quantity. And in fact, we will use that to define the second law efficiency in this particular course. Then we also develop expressions for work interaction of internally reversible steady flow processes. You may recall from the previous course that we had explicitly stated that two processes are of fundamental importance in thermodynamics. One is the reversible isothermal process, the other one is the reversible adiabatic process. You may recall that the Carnot cycle is composed entirely of reversible isothermal and reversible adiabatic processes. And we also showed that any reversible cycle may be written as or any reversible process may be actually written or replaced by a sequence of reversible isothermal and reversible adiabatic processes. And we extended that to demonstrate that any reversible cycle itself may be replaced by set of infinite number of Carnot cycle, infinitesimally small Carnot cycles. So, we had done that. So, what we do here of course, all that was done for a thermodynamic system, here we will develop expressions for work interaction of. So, we will develop expressions for work interaction for an internally reversible process, for an internally reversible isothermal and internally reversible adiabatic process. The next module that we will take up is exergy. Now, exergy is fundamental importance in thermodynamics because it actually allows us to calculate lost work. Exergy basically is availability. So, we have a thermodynamic system. Any thermodynamic system which is not at the same condition as the ambient condition. So, if a system or thermodynamic system is at the ambient condition, then there is no scope for developing any work from the system. Anything that is not at the ambient system, for example, a vessel containing air at a higher pressure or a block of metal which is at a higher temperature than the ambient temperature or a block which is at a higher elevation than the data. So, all these systems are at a state, thermodynamic state which is different from the ambient state. So, the ambient state is a so called dead state. So, if a system is in the ambient state, there is no scope for developing work. So, any system that is at a state which is different from the ambient state. When I say different, it is not just air at a higher pressure than ambient pressure. We may have a vessel where we have air at a lower pressure than ambient pressure. Even that can be used for developing work. We may have a block of metal which is at a temperature less than the ambient temperature. There is scope for developing work there also. So, any system that is at a state different from the ambient state may be, I am sorry, has the potential to develop work and that is what XSG quantifies. So, when the system actually executes a process, whether it is a system executing a process or steady flow process, it does not matter. We can actually see or compare how much of the work that is developed during this process is, let me put it differently. So, we can actually see how the work that is developed during this process compares with the amount of work that we could have developed using the system based on XSG. So, basically we have a system, we start out with a system and the system then undergoes a process. Let us say we get a certain amount of work. Now, based on the definition of XSG, we also know how much work could have been developed by the system. So, basically we can compare the work that is actually developed with the work that could have been developed. And this gives us an idea of how good the process is. And this is tied to the amount of entropy that the process generates in the universe. And based on the notion of XSG, we will develop the so-called second law efficiency. So, this takes into account, as I said, irreversibility is both internal and external and is a very, very important performance metric in many practical applications in mechanical engineering. The next module involves thermodynamic cycles. And as I mentioned earlier, we basically will look at Rankine cycle here, but not just the basic Rankine cycle, but additional variations of the Rankine cycle. Then we look at the so-called air standard cycle, where air is the working substance. And again remember, we gave the definition of heat engine in the previous lecture. So, we actually treat each one of this as a heat engine and with air as the working substance and carry out an analysis. So, we start with the air standard Brayden cycle. And then we move on to air standard Otto cycle, Diesel cycle and Dole cycle. Then the last cycle that we look at in this module would be the vapor compression refrigeration cycle. Again, we look at the basic cycle and then modifications to the cycle that are usually seen in practical applications. So, we look at real cycles also. So, the next module deals with psychrometry. And as I said, this has to do with calculations involving moist air. So, we start with definition of moist air, thermodynamic state and so on. And then application of first law to psychrometric processes. Basically, this is application of first law, but to moist air. New concept that is introduced here is the so-called wet bulb temperature. Then we discuss psychrometric chart and many other applications. All these applications will relate to the so-called HVAC type of application, heating venting, heating ventilation and air conditioning. How to maintain temperature and humidity level in a particular environment is what we will be looking at. There are some other applications in psychrometry that we will also look at. For example, drying and cooling tower or sort of different from all the other HVAC applications. Psychrometry is mostly HVAC, but there are also other applications like this, which are not HVAC, but which are also quite extensively encountered in mechanical engineering. The next module deals with combustion thermodynamics. And we first start with combustion stoichiometry, where we write down chemical equation describing the combustion of a fuel, hydrocarbon fuel or a non-hydrocarbon fuel. And then we develop notions of excess air, equivalence ratio and so on. Then we apply first law, mostly steady flow energy equation to a combustion system. So, we have a certain amount of fuel coming into a steady flow reactor. We have a certain amount of air coming in. We have combustion products which are exiting the reactor and we will apply energy balance to calculate perhaps the maximum temperature in the reactor or maximum temperature of the product stream or the heat that is released from the reactor and so on and so forth. So, this will basically be steady flow energy analysis of the reactor where combustion is taking place. One new concept that we will develop in this module is the so called that we will develop is the so called enthalpy of formation and sensible enthalpy. So, in the first level thermodynamics course, we have used the term enthalpy and we have done calculations using the enthalpy. We basically said you know for ideal gases it is just H is equal to Cp times T and for steam and refrigerant we looked up enthalpy values from the tables. So, here we will actually make a very important distinction which is enthalpy of formation and sensible enthalpy. It turns out that most of the calculations that we have done so far actually utilize the sensible enthalpy. But now because we have chemical reactions we need to take enthalpy of formation also into account. So, as I said we will do first law calculations and calculate enthalpy of combustion, calorific value of a fuel, then adiabatic flame temperature. Then we will also do a second law analysis of combustion systems. Basically the idea is to calculate rate at which entropy is generated as a result of this combustion process. So, that is a very important quantity. So, we will do both the first law and second law analysis of combustion systems. The last module involves compressible flow through nozzles. We start by discussing compressibility of fluids. What is compressibility of fluid? Then we make a distinction between compressible flow and incompressible flow. So, basically you can have a compressible fluid and an incompressible fluid, compressible flow and incompressible flow. So, we make these distinctions very, very carefully. Then we do we look at one-dimensional flows. We develop basic ideas in one-dimensional flows. For example, things like static temperatures, stagnation temperatures and so on, which were not required so far. But now, when you deal with compressible flow, we need to distinguish these types of concepts. Then we look at normal shock waves, calculations involving normal shock waves. Then we go to quasi-1-dimensional flow, basically flow through nozzles. We will look at both flow through a convergent nozzle as well as convergent-divergent nozzle. And then we will develop a theory for flow of steam through nozzles. So, concept so far developed so far will be very general. Then we see how we modify this to look at flow of steam through nozzles. We will not be look I mean sorry we will not be looking at normal shock waves involving steam. That is a much more advanced material involves a lot of non-equilibrium effects. So, we will not be looking at normal shock waves in steam. We will only be looking at flow of steam through nozzles. Mostly isentropic flow of steam through nozzles, equilibrium flows or isentropic flow through nozzles. Like what I did for the first level course, I will be teaching out of my book titled Fundaments of Engineering Thermodynamics, second edition. The work examples, illustrations have all been taken from this book. Of course, the work examples that I will be presenting here is a limited subset of what is available in the book. There are far more work examples in the book. So, I urge you to consult this book or whichever textbook you are comfortable with. And again, this is the first level thermodynamics course that is now available in NPTEL and also YouTube. In fact, most of the examples that we will do in this course will be carried over from the first level course. And that is done deliberately with the objective of demonstrating how for a particular example, we can do first law analysis and evaluate certain type of quantities and how for the same example, we build on whatever we have done so far and do a second law analysis and calculate even more quantities which are of importance in mechanical engineering. So, it is done with the specific objective of demonstrating what a first law analysis can yield for a particular application and what a second law analysis can yield for a particular application. So, many of the examples, work examples that we will discuss here have been carried over from the previous set of lectures. So, I urge you to just go through these lectures at your leisure and make sure that you are able to sort of go back and locate titles, concepts and examples from the previous lecture. So, what we will do in the next lecture is start our discussion of entropy change of a control volume. We will develop an as I said an entropy balance equation which will allow us to calculate rate of generation of entropy due to internal irreversibilities as well as external as well as rate of entropy generation in the universe.