19-02-2013, 04:40 PM
Theoretical and Experimental Evaluation of Vapour Absorption Refrigeration System
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ABSTRACT
The vapour absorption system uses heat energy, instead of mechanical energy as in vapour compression system, in order to change the condition of the refrigerant required for the operation of the refrigeration cycle. In this system, the compressor is replaced by an absorber, a pump, a generator, and a pressure reducing valve.
This complete papers discuss about the theoretical calculations are made of different components of the systems like evaporator, absorber, condenser and pump of vapour absorption system for a capacity of 0.25TR and experimentally developed and run system to validated for reducing the temperature for the free of cost of operation.
INTRODUCTION
In the vapour absorption refrigeration (VAR) system, a physicochemical process replaces the mechanical pro-cess of the vapour compression refrigeration (VCR) sys-tem by using energy in the form of heat rather than mechanical work. The main advantage of this system lies in the possibility of utilizing waste heat energy from industrial plants or other sources and solar energy as the energy input.
The VAR systems have many favourable characteristics. Typically a much smaller electrical input is required to drive the solution pump, compared to the power requirements of the compressor in the VCR systems, also, fewer moving parts means lower noise levels, higher reliability, and improved durability in the VAR systems [1–5].
METHODOLOGY
Fig.1 shows the schematic diagram of a vapour absorption system. Ammonia vapour is produced in the generator at high pressure from the strong solution of NH3 by an external heating source. A solar cooker will produce the heat and generate ammonia gas. Ammonia gas then enters into the condenser. High pressure NH3 vapour is condensed in the condenser. The cooled NH3 solution is passed through a throttle valve and the pressure and temperature of the refrigerant are reduced below the temperature to be maintained in the evaporator. The low temperature refrigerant enters the evaporator and absorbs the required heat from the evaporator and leaves the evaporator as saturated vapour. Slightly superheated, low pressure NH3 vapour is absorbed by the weak solution of NH3 which is sprayed in the absorber.
CONCLUSIONS
After designing, manufacturing and run the system the achieved temperature drop of 3.5oC below ambient temperature with the time period of 32.5s as shown in Fig.3. Although the system was designed for a capacity of 0.25TR the desired capacity was not completely achieved. This was due to fact that certain parameters could not be achieved during the practical design as compared to the theoretical design as stated below.
1 Less number of turns of condenser& tube length resulted in inefficient heat rejection. This caused the hot vapour from the generator to enter the evaporator coil without changing its phase completely and thus reduced the cooling effect.
2 The system couldn’t sustain desired pressure range. The pressure capacity of the flexible hoses used in the system limited the system pressure and thus the design pressure could not be achieved due to fear of failure.
3 Concentration of ammonia in the system design was for 50% concentration of ammonia but in the ammonia commercially available is of 25% concentration. This was also a limitation.