25-01-2013, 02:54 PM
vapour absorption refrigeration system
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The vapour absorption refrigeration system 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 machine was based on Vapour Absorption Refrigeration machine was developed by a French scientist, Ferdinand Carry, in 1860. This system may be used in both the domestic and large industrial refrigerating plants. The refrigerant commonly used in vapour absorption system is Ammonia.
This system uses Heat energy instead of mechanical energy as in vapour compression system, in order to change the condition of refrigerant required for the operation of the refrigeration cycle.
This idea of refrigeration system is being utilized in our project for the purpose of air conditioning. Like other air conditioner systems, the automobile air conditioner must provide adequate comfort cooling to the passenger in the conditioned space under a wide variety of ambient conditions. In automobile air conditioning load factors are constantly and rapidly changing as the automobile moves over highways at different speeds and through different kind of surroundings. As the car moves faster there is greater amount of infiltration into the car and the heat transfer between the outdoor air and the car surface is increased. The sun baking down on a black top road will raise its temperature to 350C – 450C approximately and thus increases the amount of heat transmitted into car. When driving through a grassy terrain, much less radiant heat is experienced than when passing through sandy flats or rocky hills. Therefore, the car is subjected to varying amounts of heat load when its orientation changes during the journey.
An automobile engine utilizes only about 35% of available energy and rests are lost in the form of heat and mechanical losses to cooling and exhaust system. If one is adding conventional air conditioning system to automobile, it further utilizes about 4-5% of the total energy. Therefore automobile becomes costlier, uneconomical and less efficient. The conventional air conditioning system in car decreases the life of engine and increases the fuel consumption, further for small cars compressor needs 3 to 4 bhp i.e. a significant ratio of the power output. Keeping these problems in mind, a car air conditioning system is proposed which is using exhaust heat. The advantages of this system over conventional air-conditioning system are that it does not affect designed efficiency life and fuel consumption of engine.
NEED
An automobile engine utilizes only about 35% of available energy and rests are lost to cooling and exhaust system. If one is adding conventional air conditioning system to automobile, it further utilizes about 5% of the total energy. Therefore automobile becomes costlier, uneconomical and less efficient. Additional of conventional air conditioner in car also decreases the life of engine and increases the fuel consumption. For very small cars compressor needs 3 to 4 bhp, a significant ratio of the power output. Keeping these problems in mind, a car air conditioning system is proposed using exhaust gases. The advantages of this system over conventional air-conditioning system are that it does not affect designed efficiency life and fuel consumption of engine. And hence makes the running of the engine efficient and economical.
Thus to have the more economical air conditioning and more efficient engine in the automobile the need of this system arises.
Mechanism Details
Working Principle
Operational Stages
WORKING PRINCIPLE
The underlying principle is the “Practical Vapour Absorption System” that uses a Generator, instead of compressor (i.e. used in vapour compression system). This Generator requires a Heat Source to generate Ammonia vapours from Aqueous Ammonia Solution received from Absorber. The above heat requirement is served by the exhaust heat of the engine.
Some power is also required to run the Pump, which is used to raise the pressure of Aqueous Ammonia Solution as well as to transmit it from Absorber to Generator. As the pump consumes very less amount of power in comparison to Compressor, it is quite comfortable to drive it from battery power or directly from crank-shaft.
Using the above setup, we can relieve the crank-shaft from excess load of compressor; this will help in decreasing the fuel requirement of engine. Thus, increases the fuel efficiency.
So, without using any other equipment or source of energy besides the vehicle itself, it is possible to introduce this air-conditioning system in existing automobiles/vehicles. Also it uses Ammonia as refrigerant, which do not affect the ozone layer as well as it does not contribute to the greenhouse effect, and it’s LCCP (Life-Cycle Climate Performance) is also highly favorable.
-The low pressure ammonia vapour leaving the evaporator enters the absorber where it is absorbed by the cold water in the absorber.
-The water has the ability to absorb very large quantity of ammonia vapour and the solution thus formed, is known as aqua-ammonia.
Stage 2-3:
-The strong solution thus formed in the absorber is pumped to the generator by the liquid pump to increase the pressure of the solution up to 10 bar.
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Stage 3-4:
-The strong solution of ammonia is heated by some external source, in our system by the exhaust heat of automobile.
-During the heating process the ammonia vapour is driven off the solution at high pressure leaving behind the hot weak ammonia solution in the generator.
Stage 4-5:
-The weak ammonia solution flows back to the absorber at low pressure after passing through the pressure reducing valve.
Stage 6-7:
-The high pressure vapour from the generator is condensed in the condenser to high pressure liquid ammonia.
Stage 7-8:
-The condensed liquid ammonia from the condenser is stored in a vessel known as receiver valve, from where it is supplied to the evaporator through the expansion valve.
Stage 8-9:
-The liquid ammonia is passed to the expansion valve in which its high pressure and temperature is reduced at a controlled rate after passing through it.