 Myself P. Vikhande, working as assistant professor in Department of Mechanical Engineering at Walsh Institute of Technology, Soolapur. Today we will discuss regarding introduction to vapor compression refrigeration system which is popularly known as VCRS. At the end of this session, students will be able to discuss the working of vapor compression refrigeration cycle or vapor compression refrigeration system that is VCRS. In VCRS, there are mainly four elements which are called as evaporator, compressor, condenser and expansion valve or the expansion device which may be of different type. This VCRS works on the principle of one of the statements of second law of thermodynamics which states that there is no engine or the system which while working in a cycle can transfer the heat from low temperature region to high temperature region on its own. But this is possible with the help of external work which is to be given to the system and this statement is called as Claus's statement because we know that as a normal course heat transfer takes place from high temperature region to low temperature region. But against this, as an adverse part of this, the heat transfer from low temperature region to high temperature region is not possible on its own but it is possible by adding some mechanical work to the refrigeration system and based on this only there is a refrigeration system or the air conditioning system and for working of these there is one of the popular system which is called as a VCRS or Vapor Compression Refrigeration System. Another system is also there which is known as Vapor Absorption Refrigeration System, VARS. But nowadays VARS has become obsolete, nowadays there is almost 90% coverage by the VCRS in most of the area or in most of the fields where the cooling of the area is needed. Now in this we will have the discussion related to the VCRS by considering this figure. This figure which is over here is shown with the four main parts, apart from these four main parts there are other parts also needed but those are ancillary parts or the ancillary units which are needed over there. When we consider any refrigeration system whether it is required for the refrigerator or the cold storage or the any cooling device or it may be for the air conditioning system we require these four elements. First there is a compressor, the compressor is the part where we will be incurring some amount of the mechanical energy, some amount of the mechanical work. Here the mechanical work is obtained by inputting electrical energy from the electrical source. So this electrical energy will provide us reciprocating motion in the compressor or it may be a rotary motion in the compressor depending upon the compressor type. As per the clauses statement at this location at the compressor we will be having the input as a mechanical energy and we will get the output as a refrigeration effect from the VCRS that is the vapor compression refrigeration system. Second part is a heat exchanger which is called as a condenser. So this is the second part which comes after the compressor. After condenser there is an expansion device which can be a capillary tube or it can be a throttle valve and after this expansion device the last part is the evaporator or this is one more heat exchanger where we will be having the space or the region which is to be cooled and maintained at lower temperature as compared to the outside temperature. Now if we consider this whole figure that has been divided into two sections one is the high pressure side and other is the low pressure side. So low pressure exists in this half area whereas in the remaining half area there is a existence of the high pressure. If we start with the compressor in the compressor there will be entry of gaseous state of the refrigerant from the evaporator. From the evaporator the refrigerant comes in the gaseous state or in the superheated condition and this superheated vapor stage of the refrigerant enters in the compressor where the compression of that takes place and the pressure of that refrigerant increases to the high pressure. After the entry point should have the gaseous state it should not contain any liquid particles that's why when the liquid is passing through the vaporator it should come out in the vapor phase or the gaseous state. Otherwise what will happen over here in this suppose liquid particles are coming liquid is entering in that case there will not be the compression to that refrigerant rather it will be sort of pushing that to the further part. So this is the starting point if we are considering where the compression of the refrigerant takes place from low pressure to the high pressure and during this certain rise in the temperature will be there so this high pressure high temperature gaseous state of the refrigerant then goes to the condenser. Now the condenser as we know that is one of the heat exchanger where the exchange of the heat takes place from one working substance to other working substance. Here the working substance in the system is the refrigerant which is in the gaseous state over here that passes to the condenser and the heat will be rejected from the refrigerant to the atmospheric air with the help of the air which will pass over the condenser. In the condenser at the entry point there will be there will be a gaseous state of the refrigerant entering and as it proceeds in the forward direction it will have the conversion from gaseous state to the liquid state. So that is the main purpose of the condenser and the name itself indicates that the condensation of the refrigerant takes place in this device so that is the condenser and for condensation purpose either we can have the force convection or the natural convection system where the air can be blown with the help of the blower over here or it can be a natural convection system as that is the case for the domestic refrigerator. After passing through this condenser the refrigerant gets converted into liquid and that liquid goes to the expansion device which is a either throttle valve or the capillary tube. Now in the capillary tube when it passes there will be sudden drop of the pressure from high temperature high pressure to the low pressure and during the drop of the pressure there will be sudden drop of the temperature and that is why the temperature of the refrigerant which is suppose approximately at 40-50 degree centigrade which is entering in the expansion device will have the sudden drop which may be in the range of minus 10-20 degree centigrade. So this is a device where the cooling of the refrigerant takes place so it will have the sudden drop in the temperature along with the sudden drop of the pressure. Now when the refrigerant comes out from the expansion device it is at minus 15-20 degree centigrade that passes to the evaporator so evaporator is the space or the heat exchanger where the heat is absorbed or heat is extracted from the substance or the area which is to be cooled. So it passes through the tubings of the evaporator and then because of the absorption of the heat over here this liquid which is passing in the evaporator will get converted into vapor form and that is the main function of the evaporator as the name itself implies. So that is the evaporation of the refrigerant takes place from liquid to vapor state. So after passing through this evaporator the vapor form of the refrigerant is again sent to the compressor where the compression of the refrigerant takes place again it goes to the condenser it passes to the throttle valve it goes to the evaporator where the evaporation takes place and this evaporation takes place because of transfer of the heat again between two working substances. So here the working substance passing through the tubing is a refrigerant at minus 10 to minus 20 degree centigrade and it is surrounded by the area which is in the range of 10 to 20 degree centigrade and because of this temperature difference the absorption of the heat energy will be there and the evaporation takes place. So like this there is a cycle which is performed continuously without crossing the boundary of the system by the matter or that is the refrigerant and that is why it is also known as a closed system because the refrigerant is circulated again and again through this vapor compression refrigeration system for almost more than 20 years which is the case for the domestic refrigerator or at the other places it may be few years. So this is the working of vapor compression refrigeration system. Thank you.