22-04-2011, 10:18 AM
PRESENTED BY:
MS. KIRAN G. HORE
MS JYOTI S. KOTECHA
[attachment=12598]
1. ABSTRACT
It is the established fact that only about 30% of heat supplied by the fuel is converted into useful work, in case of internal combustion (I.C) engines and the rest is going waste to the atmosphere in the form of coolant losses (35%) and exhaust gas losses (35%). The conventional air conditioning system which most of the A/C vehicles use is the ‘vapour Compression refrigeration system ‘, in which the compressor needs mechanical work that is Higher-grade energy is then taken directly from the engine crankshaft. Thus it ultimately reduces the brake power (B.P.) available and increasing brake specific fuel consumption.
The ‘vapour absorption refrigeration system ‘utilizes the waste heat as it does not involve any compressor and hence not require great mechanical work instead of that it works directly on the heat energy i.e. .low grade energy.
Thus by making proper use of lost heat (about 60 –70% of total heat). The conventional air conditioning can be replaced with this system and the same effect can be experienced. The common vapour absorption refrigeration systems, which are in practice, are
1. Aqua Ammonia system and
2. Lithium Bromide water system
2.EXISITING AIR-CONDITIONING SYSTEM
The use of air conditioner for transport purpose may be a luxury in India but it is commonly used in foreign countries .In comparison to domestic air-conditioning a very large amount of air-conditioning capacity is required for a car. This is due to metal construction of the car, the flow of air around moving car and relatively large glass area in the passenger compartment. Typically, a car A/C system capacity may be between 1 to 4 tons. The system works on Vapour Compression Refrigeration System (VCRS) and the compressor consumes large amount of engine brake power (1 to 10 h.p.) as it is directly driven by the engine. This affects the fuel economy severely. A loss in economy level of the order of 1 to 1.5 km/liter can occur due to the use A/C. Maximum power is required when the car is running at maximum speed under high ambient temperature conditions. Apart far from this VCRS has got certain drawback, which limits its extensive use among common car owner.
DRAWBACKS
1. High initial cost.
2. High operating cost, since fuel economy is affected, high maintenance cost, costly refrigerant.
3. CFC’s (Chlorofluorocarbon) if leaks out of the system causes great damage to the ozone layer.
4. If the car’s reserve power is less, it can affect its acceleration.
5. Overloading and overheating of the engine takes place.
3. THE AUTOMOBILE ENGINE
The prime mover of the automobile (I.C. engine) is a heat engine, which can convert only a fraction of the total heat of fuel into the useful work.
20 to30 % for SI engines
30 to 36% for CI engines
The remaining heat is lost to the atmosphere through the coolant and exhaust. Heat balance is given in the below table: -
%AGE OF FUEL ENERGY
S.I. C.I.
To power 26 31
To coolant 30 26
To exhaust 32 30
Radiation 12 13
Also refer the fig. 1
Thus we have about 60% of heat which is going waste. So, with such a small efficiency of the heat engine. Obviously it is not worthwhile for a common man to install such an A/C in his car.
4. AN ALTERNATIVE TO THIS SYTEM
The concept is to use this otherwise going waste heat, for air-conditioning with the aid of Vapour Absorption System (VARS) which does not affect the engine power. It need no maintenance and is environment friendly.
VARS is a ‘heat operated refrigeration machine ‘ in which the compressor is replaced by the combination of absorber and generator. A solution known as the absorbent (e.g. water in case of A qua-ammonia system) which has an affinity for the ‘refrigerant’ used (i.e. ammonia) is circulated between the absorber and the generator by a pump (solution pump). I n this system, the low pressure ammonia vapour living the evaporator, enters the absorber where it is absorbed by the low temperature 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. The absorption of ammonia vapour lowers the pressure in the absorber, which in turn draws more ammonia vapour from the evaporator and thus raises the temperature of solution. Some form of cooling arrangement (usually water-cooling) is employed in the absorber to remove the heat of solution evolved there. This is necessary in order to increase the absorption capacity of water. The liquid pump pumps the strong solution thus formed in the absorber to the generator. The pump increases the pressure of the solution upto 10bar. The strong solution of ammonia in generator is heated by heat of coolant and the exhaust gases, which are waste in atmosphere without any use and the heat, wasted in cooling of engine. During the heating process, the ammonia vapour is driven of the solution at high pressure leaving behind the hot weak ammonia solution in the generator. The weak ammonia solution flows back to the absorber at low pressure after passing through the reducing valve. But then also the ammonia vapour contains some particles of water. If these unwanted water particles are not removed before entering into the condenser, they will enter into the expansion valve where they freeze and choke the pipeline. In order to remove these unwanted
particles flowing to the condenser, an analyzer is used. The analyzer may be built as an integral part of the generator or made as a separate piece of equipment. It consists of a series trays mounted above the generator. The strong solution from the absorber and the aqua from the rectifier are introduced at the top of analyzer and flow downward over the trays and into the generator. In this way, considerable liquid surface area is exposed to the vapour rising from the generator. The vapour is cooled and most of the water vapour condenses. So, that mainly ammonia vapour, leaves the top of the analyzer. Since the aqua is heated by the vapour, less the generator is condensed in the condenser to high-pressure liquid ammonia. This liquid ammonia is passed to the expansion valve through a receiver and then to the evaporator. This evaporator is made up of number of tubes, which is installed in the cabin of automobile. The function of compressor is performed by the absorbent in the absorber, and the generator performs the function of compression and discharge. The complete system is schematically represented in the fig. 2.
MS. KIRAN G. HORE
MS JYOTI S. KOTECHA
[attachment=12598]
1. ABSTRACT
It is the established fact that only about 30% of heat supplied by the fuel is converted into useful work, in case of internal combustion (I.C) engines and the rest is going waste to the atmosphere in the form of coolant losses (35%) and exhaust gas losses (35%). The conventional air conditioning system which most of the A/C vehicles use is the ‘vapour Compression refrigeration system ‘, in which the compressor needs mechanical work that is Higher-grade energy is then taken directly from the engine crankshaft. Thus it ultimately reduces the brake power (B.P.) available and increasing brake specific fuel consumption.
The ‘vapour absorption refrigeration system ‘utilizes the waste heat as it does not involve any compressor and hence not require great mechanical work instead of that it works directly on the heat energy i.e. .low grade energy.
Thus by making proper use of lost heat (about 60 –70% of total heat). The conventional air conditioning can be replaced with this system and the same effect can be experienced. The common vapour absorption refrigeration systems, which are in practice, are
1. Aqua Ammonia system and
2. Lithium Bromide water system
2.EXISITING AIR-CONDITIONING SYSTEM
The use of air conditioner for transport purpose may be a luxury in India but it is commonly used in foreign countries .In comparison to domestic air-conditioning a very large amount of air-conditioning capacity is required for a car. This is due to metal construction of the car, the flow of air around moving car and relatively large glass area in the passenger compartment. Typically, a car A/C system capacity may be between 1 to 4 tons. The system works on Vapour Compression Refrigeration System (VCRS) and the compressor consumes large amount of engine brake power (1 to 10 h.p.) as it is directly driven by the engine. This affects the fuel economy severely. A loss in economy level of the order of 1 to 1.5 km/liter can occur due to the use A/C. Maximum power is required when the car is running at maximum speed under high ambient temperature conditions. Apart far from this VCRS has got certain drawback, which limits its extensive use among common car owner.
DRAWBACKS
1. High initial cost.
2. High operating cost, since fuel economy is affected, high maintenance cost, costly refrigerant.
3. CFC’s (Chlorofluorocarbon) if leaks out of the system causes great damage to the ozone layer.
4. If the car’s reserve power is less, it can affect its acceleration.
5. Overloading and overheating of the engine takes place.
3. THE AUTOMOBILE ENGINE
The prime mover of the automobile (I.C. engine) is a heat engine, which can convert only a fraction of the total heat of fuel into the useful work.
20 to30 % for SI engines
30 to 36% for CI engines
The remaining heat is lost to the atmosphere through the coolant and exhaust. Heat balance is given in the below table: -
%AGE OF FUEL ENERGY
S.I. C.I.
To power 26 31
To coolant 30 26
To exhaust 32 30
Radiation 12 13
Also refer the fig. 1
Thus we have about 60% of heat which is going waste. So, with such a small efficiency of the heat engine. Obviously it is not worthwhile for a common man to install such an A/C in his car.
4. AN ALTERNATIVE TO THIS SYTEM
The concept is to use this otherwise going waste heat, for air-conditioning with the aid of Vapour Absorption System (VARS) which does not affect the engine power. It need no maintenance and is environment friendly.
VARS is a ‘heat operated refrigeration machine ‘ in which the compressor is replaced by the combination of absorber and generator. A solution known as the absorbent (e.g. water in case of A qua-ammonia system) which has an affinity for the ‘refrigerant’ used (i.e. ammonia) is circulated between the absorber and the generator by a pump (solution pump). I n this system, the low pressure ammonia vapour living the evaporator, enters the absorber where it is absorbed by the low temperature 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. The absorption of ammonia vapour lowers the pressure in the absorber, which in turn draws more ammonia vapour from the evaporator and thus raises the temperature of solution. Some form of cooling arrangement (usually water-cooling) is employed in the absorber to remove the heat of solution evolved there. This is necessary in order to increase the absorption capacity of water. The liquid pump pumps the strong solution thus formed in the absorber to the generator. The pump increases the pressure of the solution upto 10bar. The strong solution of ammonia in generator is heated by heat of coolant and the exhaust gases, which are waste in atmosphere without any use and the heat, wasted in cooling of engine. During the heating process, the ammonia vapour is driven of the solution at high pressure leaving behind the hot weak ammonia solution in the generator. The weak ammonia solution flows back to the absorber at low pressure after passing through the reducing valve. But then also the ammonia vapour contains some particles of water. If these unwanted water particles are not removed before entering into the condenser, they will enter into the expansion valve where they freeze and choke the pipeline. In order to remove these unwanted
particles flowing to the condenser, an analyzer is used. The analyzer may be built as an integral part of the generator or made as a separate piece of equipment. It consists of a series trays mounted above the generator. The strong solution from the absorber and the aqua from the rectifier are introduced at the top of analyzer and flow downward over the trays and into the generator. In this way, considerable liquid surface area is exposed to the vapour rising from the generator. The vapour is cooled and most of the water vapour condenses. So, that mainly ammonia vapour, leaves the top of the analyzer. Since the aqua is heated by the vapour, less the generator is condensed in the condenser to high-pressure liquid ammonia. This liquid ammonia is passed to the expansion valve through a receiver and then to the evaporator. This evaporator is made up of number of tubes, which is installed in the cabin of automobile. The function of compressor is performed by the absorbent in the absorber, and the generator performs the function of compression and discharge. The complete system is schematically represented in the fig. 2.
