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VEHICLE AIR CONDITIONING BY EXHAUST GASES
INTRODUCTION
1.1 CONVENTIONAL A/C SYSTEM USED IN VEHICLES
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 2.1 INTRODUCTION 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 tempreture. 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: (i) heat carried away by the cooling water, (ii) heat taken away by the exhaust gases, (iii) heat carried away by the lubricating oil, (iv) and, heat lost by radiation. The cooling water and exhaust gases carry away the maximum amount of heat from the engine, ie around 60% (approx). This heat is called the low grade energy of the engine. The vapour absorption system is driven directly by using the low grade energy which in the form of heat energy of i.c. engine. This
Why the particular topic choosen
• Vapour compression system has some disadvantages in car air conditioning system so to redress these dvantages we use vapour absorption system in vehicle. The disadvantages are given below.
• A vapour compression system has more, tear and noise due to moving parts of the compressor.
• The amount of work required to compress the gas in the compressor is very high.
• Vapour compression system take the mechanical power directly from the engine i.e. why the engine are less efficient
• The capacity of vapour compression system drops rapidly with lowered evaporator pressure.
• The performance of a vapour compression system at partial loads is poor.
Objectives and scope of the project
It is well known that an IC engine has an efficiency of about 35-50%, which means that only one-third of the energy in the fuel is converted into useful work and about 50-55% is wasted to environment. In which about 28-30% is lost by cooling water and lubrication losses, around 30-32% is lost in the form of exhaust gases and remainder by radiation, etc. In a Vapour Absorption Refrigeration System, a physicochemical process replaces the mechanical process of the Vapour Compression Refrigeration System by using energy in the form of heat rather than mechanical work. The heat required for running of a Vapour Absorption Refrigeration System can be obtained from the exhaust of any vehicle working with an IC engine, which would otherwise be exhausted into the atmosphere.
Hence using a Vapour Absorption Refrigeration System will not only prevent the loss of power from the vehicles engine but will also produce refrigeration using the low grade energy (i,e. exhaust) from the engine. The use of a Vapour Absorption Refrigeration System will also reduce pollution by reducing the amount of fuel burned while working the conventional vapour compression refrigerating unit.
Summary
This refrigeration system consists of a condenser, an expansion valve and an evaporator similar to a Vapour Compression Refrigeration System. But the compressor of the Vapour Compression Refrigeration System is replaced by a generator, an absorber and a small pump. A Vapour Absorption Refrigeration System utilizes two or more than two fluids which has high affinity towards each other, in which one is the refrigerant and the other is the absorbent. The process of working of this refrigeration system is that a mixture of refrigerant and an absorber (i,e. strong solution) is pumped from the absorber using a small pump to the generator. The generator is the main unit of the whole refrigeration system. This is the place where heat is supplied to the strong solution. Due to the supplied heat to the mixture in the generator the refrigerant is separated from the strong solution and forms vapour. The remaining weak solution flows back through a restrictor in to the absorber. The refrigerant is then allowed to pass through a
condenser where the heat of the vapour is extracted and the refrigerant temperature is brought to the room temperature. This cooled refrigerant is then passed through an expansion device where during expansion the temperature of the refrigerant falls below the atmospheric temperature. This cold refrigerant is then passed through an evaporator from where the refrigerant absorbs heat and produces refrigerating effect. The refrigerant coming from the evaporator is hot and it is passed to the absorber. The weak solution coming from the generator mixes with the refrigerant coming from the evaporator in the absorber due to high affinity towards each other for the two fluids, hence forming a strong solution. The formed strong solution is again pumped into the generator and the cycle repeats itself.
4.2 METHODS OF IMPLEMENTATION IN AN AUTOMOBILE
For a road transport utilizing Vapour Absorption Refrigeration System heat energy can be supplied in two ways:
4.2.1 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.
4.2.2 Using waste heat of the IC engine Another method is by utilizing the heat of combustion which is wasted into the atmosphere. By designing a generator capable of extracting the waste heat of an IC engine without any decrease in engine efficiency, a Vapour Absorption Refrigeration System can be brought to work. Since this arrangement does not require any extra work expect a small amount of work required for the pump, which can be derived from the battery, this system can be used in automobiles where engine efficiency is the primary consideration
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:
2.2.1 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 vapourize both refrigerant and absorbent. Therefore the system employs too many components and hence the system is complicated.
2.2.2 LiBr-E^O 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 hyroscopic 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 very popular for air conditioning in which low temperatures not below 0°C are required.
2.2.3 Domestic Electrolux (Ammonia Hydrogen) Refrigerator. This type of refrigerator is also called three fluids absorption system. The main purpose of this system is to eliminate the pump so that in the absence of moving parts, the machine becomes noise-less. The three fluids used in this system are ammonia, hydrogen and water. The ammonia is used as a refrigerant because it possesses most of the desirable properties. It is toxic, but due to absence of moving parts, there is very little chance for leakage and the total amount of refrigeration used is small. The hydrogen being the lightest gas is used to increase the rate of evaporation of the liquid ammonia passing through the evaporator. The hydrogen is also non-corrosive and insoluble in water. This is used in the low pressure side of the system. The water is used as a solvent because it has the ability to absorb ammonia readily.
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.
9.2 ADVANTAGES OF USING VAPOUR ABSORPTION SYSTEM IN AUTOMOBILES
The use of a Vapour Absorption Refrigeration System in road transport vehicles has the following advantages: • No dedicated IC engine is required for the working of the refrigerating unit. • No refrigerant compressor is required. • No extra work is required for the working of the refrigerating unit. • Reduction in weight of unit. • Reduction in capital cost. • Reduction in fuel cost. • Reduced atmospheric pollution. • Reduced maintenance. • Reduced noise pollution.
(BY ANUJ GARG ABHISHEK SARASWAT AKSHAT RAJ SINGH DHEERAJ VERMA RAHIMUDDIN KHAN)