 Hello, I am Ganesh B. Aglawe working as an assistant professor in Department of Mechanical Engineering, Walsh University of Technology, Solopur. In this session, we will see the heat exchangers introduction, learning outcome. At the end of this session, students will be able to classify types of heat exchangers, select heat exchanger for the particular application. One of heat exchanger, the heat exchangers are those devices in which the heat exchange takes place between two fluids. Obviously, the fluids will be at different temperatures and these will be separated by a solid wall. Now, to study the heat exchangers, usually we take this as a this diagram as a typical one in which this is known as inner tube, this is the outer tube. So, this is the tube-in-tube type of the heat exchanger, in detail we will see later. The hot fluid generally is flowing through the inner tube, hot fluid inlet temperature will be T H I, hot fluid outlet temperature will be T H O, through the annular space, this is known as annular space, the space between inner tube outer surface, outer tube inner surface. So, through this annular surface, the cold fluid will be flowing having temperature T C I, outlet temperature T C O. Now, the classification of heat exchanger, types of the heat exchanger. First one is concentric tube is subclassified as parallel flow, counter flow. Second one cross flow in which finned with both fluids unmixed, second unfinned with one fluid mixed and another unmixed. In third type, shell and tube type of heat exchanger is there, in which one shell pass, one tube pass, second one shell pass and two tube pass, third one, two shell pass and four tube passes are there, fourth one is the compact heat exchanger. Now, in the first type of the heat exchanger, the two tubes will be concentric, in which if the fluid flow direction is in the same, then this is known as parallel flow heat exchanger. If the hot fluid is flowing in the right hand direction and cold fluid is flowing in the opposite direction, then this is known as counter flow heat exchanger. In the cross flow heat exchanger, the tubes will be finned and through the tubes, hot fluid will be flowing and through these gaps, we may throw the cold fluid, now the direction is cross 90 degree to each other, so this type of the heat exchanger is known as finned with both fluids unmixed. While in the second type, we can take one plate on that plate, we can place the tubes, so through these tubes, hot fluid will be flowing and over the hot fluid, over these tubes, the cold fluid is free to flow. Now, here this cold fluid may get mixed with itself, that's why this is known as unfilmed with one fluid mixed and other fluid is unmixed. Here now you think over the fluid, this type of heat exchanger, find the this type of the heat exchanger in day to day life. Next in the shell and tube type of the heat exchanger, there is shell, so this outer enclosure is known as shell, in which number of tubes are inserted. We can pass the cold fluid from the shell side and the hot fluid from these tubes. In this shell and tube type of the heat exchanger, for increasing the heat transfer area, the baffles are inserted. Baffles helps to increase the time required by the cold fluid to remain in the more time. So the heat transfer rate depends upon the number of passes of this cold fluid. In the shell and tube type of the heat exchanger, there will be four openings will be there. This is tube side opening inlet and tube side outlet opening. This is the shell side inlet opening and shell side outlet opening. Depending upon the type of the passes, the shell and heat exchanger is further subclassified. Remember, there is limited use of this type of heat exchanger in automotive and aircraft as the size occupied by this heat exchanger and the weight is comparatively more. For other processing industries, it is preferred as the effectiveness of this heat exchanger is more in tube pass. Second type of the shell and tube type of the heat exchanger, here this is one shell and two tube passes are there. So this is the one shell and the hot fluid will be flowing through this one pass then it is redirected and is kept inside the shell itself. So second pass is also in the same shell that is why this is one shell and two tube passes and the cold fluid will be given the number of passes by using the baffles. But remember shell is one. We can increase the number of shells. So this is the first shell, this is the second shell and the cold fluid passes will be first tube pass, second tube pass, third tube pass and fourth tube pass that is why this is known as two shell pass and four tube passes type of the heat exchanger. So if the space availability is more then instead of a single shell we can adopt this two shell type of the heat exchanger. Last type of the heat exchanger which is known as compact type of the heat exchanger, if the surface area to the volume ratio is greater than 700 these heat exchangers are known as compact type of the heat exchangers. And if it is less then the traditional heat exchangers will be there that is concentric tube or shell and tube type of the heat exchangers etcetera. Now here we can give the geometry to the tubes like rectangular or circular. Then these fins will be of a flat nature or the disc also we can adopt for the fins. Now actually the compact heat exchangers will be like this nature. So here the cold fluid will be flowing through this fins while the hot fluid may be flowing through this inner space. So here the surface area is very very large in comparison with traditional heat exchangers. Now the passes also is possible like cold fluid is flowing from this direction will get moved from the above then from the last row. So in this fashion we can also increase the time duration of the cold fluid for the heat for the hot fluid also this will be first pass second pass and third pass. So in this way the compact type of the heat exchangers are giving largest heat exchange within that size limit. Other references you can have fundamentals of heat and mass transfer by Frank and David the Willi publication.