 Hello, I welcome you to this series of lectures on an introduction to turbomachines. I assume that all of you would have undergone either a first level course in thermodynamics or both a first and a second level course in thermodynamics and would be familiar with all the concepts and ideas associated with these courses. You might have encountered the following examples in your thermodynamics courses, such as air flows through, steadily flows through a compressor at the rate of 2 kg per second, where it is compressed from such and such a temperature and pressure to such and such a temperature and pressure, determine the power that is required to run the compressor. Or you might have encountered an example like steam flows steadily through a turbine where it expands from such and such a pressure and temperature to such and such a pressure and temperature. If the mass flow rate is such and such, what is the power that is produced by the turbine? Now, a thermodynamic analysis of these devices does not require you to know what is actually inside the device or how the state changes are accomplished. So, you simply apply the steady flow energy equation and knowing the inlet and exit state, you can calculate the power that is required to run the compressor or the power that is produced by the turbine. Now, the objective of this series of lectures is to actually look inside the device and understand the working, the design and workings of the device. In other words, how does this device accomplish the change in the thermodynamic state that it accomplishes using the given input power or how does it generate the power that it does based on the change in the thermodynamic state of the flow. That is the objective of the course. So, we will look at many such devices and try to understand their design and working. What we will not try to do is to answer questions like, I have such and such an application, which compressor or turbine is best suited for this purpose. So, a question like this falls within the purview of a full course on turbo-missions. So, the outline of the lecture is like this. We start with an introduction and classification of turbo-missions, then we look at the basic theory of turbo-missions, then we look at hydro-turbo-missions where we see both the pumps and turbines, then we have positive displacement machines, which actually are not turbo-missions, but the positive displacement machines are quite extensively used in mechanical engineering applications. So, it would be good to know how these devices work and also how they compare with turbo-missions. So, to that end, we will look at positive displacement machines also. And the last module in the sense of lecture would be on turbo-turbo-missions. Turbo-missions are rotating machinery used either for generating power through an enthalpy drop, in which case it will be a turbine, or for raising the enthalpy of a fluid using input power, in which case it could be a compressor or a pump by means of rotodynamics. What exactly do we mean by rotodynamics? Appropriately shaped blades are mounted on a hub or disc, usually called the rotor, and the rotor in turn is mounted on a rotating shaft. Now, the shape of the blade is such that as the fluid flows into the device and is forced to flow through the passage between the blades, its enthalpy changes depending on whether the machine is power producing or power absorbing. In other words, the fluid that flows through the passage whose shape is determined by the shape of the blade itself, and depending on whether the power is supplied or absorbed, the enthalpy of the fluid increases or decreases. So, in the case of a power producing machine, the enthalpy of the fluid decreases and is realized as work, and in the case of a power absorbing machine, the enthalpy of the fluid increases and as a result of the power that is supplied to the machine. Now, you may recall from your course in turbo-animics that the specific enthalpy h is some of the specific internal energy plus the term p over rho, and for most substances, especially p over compressible substance, the specific enthalpy is a function of temperature and pressure, and the specific internal energy is also a function of temperature and pressure. Now, in case the working fluid in the turbo machine is compressible, such as air or steam or refrigerant, any change in enthalpy can be due to a change in internal energy of the working substance as well as a change in pressure. Since the fluid is compressible, changes in pressure and temperature are related through the equation of state, and it usually results in a change in the density as well. So, for a compressible fluid, the change in enthalpy can possibly be due to change in internal energy and changes in pressure. Whereas, in the case of an incompressible working substance, such as water, any liquid which is incompressible, such as water, for which density is constant, any change in enthalpy is due only to a change in pressure. Of course, it is possible that there can be a change in internal energy. It may be recalled that the specific internal energy of liquids depends only on temperature. And in the case of turbo machines that handle liquids, there is very little change in the temperature of the fluid as it goes through the machine. So, the flow is practically isothermal, which means there is no change in the specific internal energy of the fluid. So, in the case of liquids, any change in specific enthalpy is due entirely to a change in pressure. So, consequently, we can actually interpret this statement, enthalpy drop in the case of a liquid as a pressure drop and increase in enthalpy of the fluid in the case of liquid as increase in pressure. So, when power is extracted, that means there is a pressure decrease in the case of a liquid and when power is supplied, such as in a pump, the pressure of a liquid increases. Turbo machines may be classified in several different ways and we will actually look at classification of turbo machines in these two ways. The first one classifies the machine according to the type of fluid that it handles. So, if the machine handles a compressible fluid such as air, steam or refrigerant, then it is referred to as a turbo turbo machine because there is a change both in pressure and temperature of the fluid. In case the turbo machine handles liquids such as water, oil or any other liquid, then it is referred to as hydro turbo machines this only change in pressure. The term hydro refers to water, but it is used in general to classify or denote any turbo machine that handles liquids. Now, we can also classify turbo machines based on whether they are power producing, namely turbines or power absorbing. If it is power producing, it can be a steam turbine, a gas turbine or a hydraulic turbine which of course uses water as a working substance. In the case of a power absorbing machine, we could have a compressor, fan or blower, all of which handle air or we could have a pump which handles any liquid including water. Here we have an application of a turbo machine, namely the centrifugal pump. As mentioned earlier, there is a shaft and the hub plate is mounted on the shaft. The blades are fixed to the hub plate and as the shaft rotates in this direction, the water is drawn in through this part of the pump called the eye in an axial direction. So the water flows in an axial direction then because of the power supplied to the impeller, the water is forced to turn direction and flow in a radial direction through the blade passage as you can see here through the blade passage and then it leaves through the casing or the passage that is located here. So this assembly, the hub plate together with the blade is called the impeller and the passage between the casing and the impeller is actually a wallude shape. It is a wallude shape because as more and more fluid comes from the impeller onto the casing, the area of the casing increases to accommodate the increasing amount of fluid in order to maintain almost a constant velocity in the casing for the fluid to be sent out. You may also notice that in this case that the direction of rotation of the impeller is clockwise whereas the blades actually curve in this direction which is in the opposite direction to the direction of rotation. Such blades are usually called backward curved blades because the direction of curvature is in an opposite direction to the direction of rotation. The next example or next application that we have is an automotive turbocharger. You are probably familiar with the turbocharger in the context of diesel engines. These are used in the intakes of diesel engines to compress the incoming air so that a higher mass of air may be admitted into the cylinder which increases the volumetric efficiency of the engine. Here we see a centrifugal compressor located on the right and just like the centrifugal pump, its counterpart the centrifugal pump air in this case enters axially and then because of the supplied power it flows out radially and exits through the wallude casing. You may recall that the cross-sectional area of the wallude casing increases in the direction of the rotation for a pump or a compressor so we can judge by the increasing cross-sectional area here that the centrifugal pump spins in a clockwise direction when viewed from this end. Now here we have a centrifugal turbine which does the exact opposite. So here fluid enters from the casing radially inverts into the impeller and then leaves axially. So as the fluid goes through the impeller it expands and the expansion process causes an enthalpy drop increases the produces work which is used to drive the compressor. Now since the flow is radially inward we can imagine that the area of the skull casing decreases in the direction of rotation and judging by the cross-sectional area here it is easy to see that the direction of rotation of the impeller is in the anti-clockwise direction when viewed from this side same direction. So this is anti-clockwise when viewed from here clockwise when viewed from here so it is easy to see that the turbine drives the compressor. So the work that the turbine produces is used entirely to drive the compressor and compress incoming air. So this machine would be classified as a thermal turbo machine because it handles air or the working substance is air this would be classified as a hydro turbo machine because it handles water and it's also a pump because it absorbs work. Here because it absorbs work we refer to this as a compressor. Now some of the questions that we will try to answer in this course are questions such as why does the fluid enter a centrifugal compressor or a centrifugal pump axially and then move radially? Why not the other way around? Is it possible for a compressor to have a flow going this way? So we will try to answer questions like this because we are taking it for granted now but we will establish these things in a much more precise manner based on the theory of turbo machines in the next module. So the next device that we look at is the so-called gas turbine. This particular device is used for is a land based and used for generation of power. So here as you can see the blades are visible clearly and they are mounted on a shaft. What is that in contrast to this machine and this machine where the flow through the blade is actually in the radial direction. What is that the flow may enter axially but when it goes in the passage between the blades the flow is predominantly in the radial direction there is no axial motion. Similarly here also the flow is in the radial direction as it goes through the passage between the blade whereas in this case when the fluid flows through the passage between the blades the flow is in the axial direction or along the direction of the shaft. So you can see that these blades are usually mounted on a disc which in turn is mounted on the hub and as the air which is the working substance here flows through this blade it is progressively compressed and you can also see that from the height of the blade you can see that the height of the blades keeps decreasing in the direction of flow as the fluid is working substance of fluid is compressed. Then of course we have a combustor where fuel is burnt and heat is supplied to the working substance and the working substance then undergoes expansion in a turbine here. So we can infer that the process in the turbine or this is the turbine or the process in the turbine is expansion by looking at the size of the blade. So you can see that as the fluid expands it requires more and more volume or cross sectional area to go through and consequently the size of the blade also keeps increasing as the fluid keeps expanding. So this is the turbine section of the blade this is the compressor section contrary to the centrifugal compressor here the turbine produces power not only to run the compressor it also produces power to run a generator which in turn is used to generate electricity. This is also a gas turbine but unlike the previous one this one is actually used in aircraft engines for propulsion purposes. So here we see similar types of components we see a fan here and the compressor blades compressor blades can be identified here like this. So here is the combustor and here is the turbine section and we can infer that this is the turbine section based on the fact that the diameter increases the cross sectional area increases. Here in contrast to the previous one we see multiple sets of compressors. So we see a fan distantly and we see one set of blades here which is usually called the intermediate pressure compressor. We see another set of blades here which is usually called the high pressure compressor. Now as the fluid goes past the combustor you can see rings of turbine blades. So we see one ring of turbine blades here which is the high pressure turbine. Notice that the high pressure turbine is used to drive the high pressure compressor they are connected on the same shaft unlike the previous device which had one shaft here we have multiple shafts. You know the next set of blades which are these two are actually called the intermediate turbine blades and these all run on the same shaft and this turbine is then used to drive the intermediate pressure compressor. So the intermediate turbine drives the intermediate pressure compressor then the last few stages are actually the LP turbine stages all of these are mounted on the same shaft and that shaft drives the fan. So you can see three sets of blades or three sets of compressor turbines and each set is driven on its own shaft by the corresponding turbine which means that the shafts in this engine are actually hollow. So the outermost shaft is actually the high pressure turbine compressor set shaft. The next inner one is the actually the shaft corresponding to the intermediate pressure compressor and turbine and the innermost shaft is the one which runs the fan in this case. Now contrary to the previous example here the turbine generates enough power to run the compressor and the remaining enthalpy of fluid is actually taken to generate thrust through a nozzle. This video actually is quite nice it's available in YouTube it's an overview on the GNE MX engine which is a turbofan engine similar to this one. I recommend this video very highly it is put together very nicely and easily understandable and they describe a lot of interesting details or especially relating to turbo-missionary aspects of the aircraft engine. So I encourage you to watch this video. So these machines that we looked at so far as I mentioned earlier the gas turbine the aircraft engine all these would be classified as axial machines and that too axial thermal turbo-machine because here is the working substance in these turbo-missions. The next one is also a turbo-turbo-machine and it is also an axial machine but it is an axial steam turbine. So this is the GEE supercritical steam turbine which is used for generating power in in steam power plant. Once again you see multiple sets of blades here this one is the high pressure turbine and we can integrate this high pressure turbine judging by the increase in size of the blades from inlet to outlet. You can see that the increase in size is not very much so normally the first stage of a turbine does not allow the fluid to expand a whole lot because we are operating at supercritical pressure that should expand a whole lot. So this is the initial expansion then we see double flow turbine blades countered on the same shaft here. So steam enters through the middle here then flows this way towards the right for this rotor and towards the left for this rotor. So this is steam which is taken from a reheat boiler. So the steam after expansion from here is taken to a reheat boiler and the reheated steam is then brought back here for further expansion. So this would be the second stage expansion in in the supercritical ranken cycle. Now we see here another set of turbine rotors again mounted on the same shaft so and it can be informed from here that this is the third stage turbine because now you can really see that the steam is beginning to expand considerably in contrast to this the expansion here is more and in contrast to this expansion here is even more. So it's quite possible that the turbine here is expanded almost up to the condenser pressure and once again you see entry through the middle and then expansion to the right here and expansion to the right here. So the steam that enters here actually comes from this steam turbine which is then taken to a reheat boiler and then supplied to the third stage turbine. So normally this would be the high pressure turbine this would be like the intermediate pressure turbine this would be the low pressure turbine it is possible also to have additional expansion stages if required. The last turbo machine that we look at is the so-called Pelton wheel or the water wheel the water wheel perhaps is the oldest known turbo machinery to man time this has been used for almost for centuries by Chinese for not for generating power but for generating but for running other things for example for drawing up water from a well and so on and so forth. So here we see a runner which is actually drum on which these cup shaped buckets are mounted and the runner itself is key to the shaft which is rotated as the runner turns. Now water is taken from a reservoir at a higher elevation then it comes through this pipe which is called the pen start and this water impinges on the buckets turning the wheel in this way and again if this wheel were to be connected to a generator there is sufficient head for the water here then this could be connected to a generator to generate power okay and the flow through the through the nozzle is regulated by means of this sphere which is pushed in or pulled back and that allows the flow rate to be controlled if it is pushed in then the flow rate obviously decreases if it is pulled back the flow rate increases. Now one interesting aspect of this Pelton wheel is that it does not fit into the definition of a turbo machine that we gave in the beginning it was said that a turbo machine is a rotary machine in which there is an enthalpy drop or enthalpy rise now just being a turbine there should be an enthalpy drop which should be converted into power but in this case there is no change in enthalpy of the fluid the buckets are shaped in such a way that you know the fluid impinges on the bucket and there is a change in the direction of the water flow and the change in direction causes a change in momentum which is then converted into a force on the rotor which is then converted into power so this actually does not fit into the classification that we mentioned earlier because the enthalpy remains constant but the Pelton wheel is a widely used turbine so we will have a detailed look at the runner how it generates power and we will also look at the design and working aspects of the Pelton wheel later on when we talk about hydro turbo machines now this machine would be classified as a hydro turbo machine because the working fluid is water and the flow in the rotor strictly speaking is neither axial nor radial so this is a very interesting device in contrast to all the other devices that we looked at earlier now this concludes our discussion on introduction and classification of turbo machines and in the next lecture we will take up the basic theory of turbo machines