31-07-2014, 03:23 PM
CONVENTIONAL A/C SYSTEM USED IN VEHICLES
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INTRODUCTION
The air conditioning system used usually in a vehicle is a vapor compression refrigeration system. It consists of a compressor, condenser, expansion valve, an evaporator blower set and a refrigerant which is circulated through the system. This system works by compressing the refrigerant using a compressor, which increases the pressure and temperature of the refrigerant and it vaporizes. The refrigerant is then passed through the condenser where the latent heat of the refrigerant is removed and is liquefied. This refrigerant is then passed through the expansion valve where its pressure is reduced reducing the temperature. This chilled refrigerant is then passed through the evaporator to produce the cooling effect. The blower blows the air through the evaporator to produce the required cooling inside the cabin of the vehicle. The refrigerant absorbs the heat of the air and vaporizes, which is then passed through the compressor. Hence cooling effect is produced inside the vehicle.
The main disadvantage of such a system is that the required power to run the compressor is taken from the engine main shaft, hence to maintain the same power the engine has to produce more work consuming more fuel thereby reducing the mileage of the vehicle.
VAPOUR ABSORPTION REFRIGERATION SYSTEM
The vapour absorption refrigeration is one of the oldest methods of producing refrigerating effect. The principle of vapour absorption was first discovered by Michael Faraday in 1824 while performing a set of experiments to liquefy certain gases. . The first vapour absorption refrigeration machine was developed by a French scientist Ferdinand Carre in 1860. This system may be used in both the domestic and large industrial refrigerating plants. The refrigerant, commonly used in a vapour absorption system is ammonia.
The vapour absorption system uses heat energy, instead of mechanical energy as in vapour compression systems, in order to change the conditions of the refrigerant required for the operation of the refrigeration cycle. The function of a compressor, in a vapour compression system, is to withdraw the vapour refrigerant from the evaporator. It then raises its temperature and pressure higher than the cooling agent in the condenser so that the higher pressure vapours can reject heat in the condenser. The liquid refrigerant leaving the condenser is now ready to expand to the evaporator conditions again.
STATEMENT ABOUT THE PROBLAM
The vapour compression system is used in ordinary four wheeler vehicle consume the power directly from the engine of the car which affect to the engine efficiency due to the directly consume the high grade mechanical energy from the engine. The compressor of the vapour compression system is driven by the engine shaft by using gear arrangement. The compressor work to compress the refrigerant at high temperature.
In an IC engine, fuel (usually petrol or diesel) is combusted inside the cylinder due to which the piston moves outward and rotates the crank, and hence the engine produces work. In IC engines the combustion of the fuel produces heat, which is converted to mechanical work using the piston and crank arrangement. From the heat produced from combustion of fuel only 30% (approx) of heat is converted into useful mechanical work. The remaining heat energy is wasted into the atmosphere in the form of:
METHODS OF IMPLEMENTATION IN AN AUTOMOBILE
For a road transport utilizing Vapour Absorption Refrigeration System heat energy can be supplied in two ways:-
1. Using heat of combustion of a separate fuel
By using a separate fuel for working the refrigeration system i.e. a fuel for example natural gas can be used for the working of a Vapour Absorption Refrigeration System. This can be achieved by burning the fuel in a separate combustion chamber and then supplying the Generator of a Vapour Absorption Refrigeration System with the products of its combustion to produce the required refrigerating effect. However this prospect is eliminated since it requires a separate fuel and a separate combustion chamber which makes it uneconomical and the system becomes inefficient.
TECHNOLOGIES USED
There are different types of vapour absorption systems which employ different combination of refrigerant and absorbents to produce the refrigerating effect. Some of the basic vapour absorption systems are:
1. Aqua-Ammonia Vapour Absorption System
This is the simplest of all the systems. This system employs water as the absorbent and ammonia as the refrigerant. Along with the generator it employs an analyzer and a rectifier to remove the components of water from the refrigerant, since the heat is high enough to vapourized both refrigerant and absorbent. Therefore the system employs too many components and hence the system is complicated.
2. LiBr-H2O Vapour Absorption System
The lithium-bromide absorption refrigeration system uses a solution of lithium-bromide in water. In this system water is being used as a refrigerant whereas lithium bromide, which is a highly hydroscopic salt, as an absorbent. The lithium bromide solution has a strong affinity for water vapour because of its very low vapour pressure. Since lithium bromide solution is corrosive, therefore inhibitors should be added in order to protect the metal parts of the system against corrosion. Lithium chromate is often used as a corrosion inhibitor. This system is
CONCLUSION
It is possible to install a vapour absorption refrigeration system in an automobile working using the waste heat of the vehicle engine to produce refrigerating effect inside the automobile cabin. Using a vapour absorption refrigeration system within a automobile as an air conditioner will not only reduce the fuel consumption of the vehicle while working but will also provide many other advantages.