A thorough investigation of the optimal operating temperatures is necessary to ensure effective operation of the system. By means of this simulation, the system response to varying absorber, generator and condenser temperatures was analyzed. Received in October , accepted in March This paper was with the authors 1 month for 1 revision. This leads to higher power demands from power stations which in turn lead to more CO2 emissions. Absorption systems use a low grade form of energy in order to provide a cooling effect.
This means that the source of input energy need not necessarily come from electric power but rather from any other heat source which is at a sufficiently high temperature. Apart from being advantageous from this perspective of energy use, such systems also provide other advantages over vapour compression refrigeration units employing compressors.
For example, their silent operation is unmatched when compared to the latter systems. As absorption units become more popular not only in industry but also on a domestic level, their simulation becomes more important.
This enables better understanding of the complex thermodynamic behaviour which such systems exhibit. Various mathematical models have been created in the past []. Much of the focus of these studies was put on systems using water-lithium Bromide LiBr-H2O refrigerant-absorbent pair.
Analysis of these systems has also been extended to multi effect units. Although the latter systems are in principle the same, they require additional devices which in themselves require thermodynamic modelling. In this work, a simulation of single-effect absorption was performed.
The developed mathematical model, being linear, can be easily extended to model double or multi-effect systems. This however will be done in future work. By means of certain user inputs, the model calculates output parameters which are of fundamental importance for the analysis of these systems. Relationships between input and output parameters may be plotted automatically for better visualization of the system behaviour.
A secondary aim of the simulation was to be able to aid DOI : In particular, it is possible to find in a relatively crude manner the solar panel area required for a certain refrigeration effect given the relevant system temperatures.
Similar work was performed by V. Mital et al. The most basic components of a vapour absorption cycle are the evaporator, absorber, pump s , generator or desorber , a condenser and throttle valves [].
The compressor is replaced by the absorber, pump, generator and an optional heat exchanger which is generally known as the solution heat exchanger SHX.
Another difference from vapour compression cycles is that this system, apart from the refrigerant, makes use of an absorbent fluid. The evaporator-condenser part of the system is not different from that of vapour compression systems.
The absorber-generator part however consists of the above mentioned units. In the absorber, the absorbent fluid absorbs within it the refrigerant in the vapour phase, with the consequence of heat release.
The refrigerant- absorbent mixture is then transferred to the generator via a pump. In this unit, heat is transferred to the mixture in order to drive off the refrigerant from the mixture, leaving behind a weak mixture low percentage of refrigerant which is transferred back to the absorber via a throttle valve.
As the refrigerant-absorbent mixture is pumped to the generator some heat may be gained from the weak mixture leaving the generator through a solution heat exchanger. The pumps required in this system consume a minute amount of power compared to compressors and this is usually ignored in most engineering analysis, including the mathematical model proposed in this work. In vapour compression the energy input is of a high quality shaft power , in vapour absorption on the other hand the energy input is in the form of heat from a source at a suitable temperature.
It is therefore possible to use any source provided the temperature is high enough. These sources of heat may come from the burning of natural gas, waste heat from a particular process or say from solar heating of a secondary fluid. Water may instead be used as the absorbent and ammonia as the refrigerant. Such systems tend to be more complex primarily due to the volatility of the absorbent which requires the use of a rectifier column which separates the absorbent from the refrigerant.
One major advantage is that ammonia can reach sub-zero temperatures [4]. In general, if system 3 is to be solved as a whole the problem would be non-linear.
However since energy and mass conservation equations are uncoupled the problem is reduced to linear form. P Coefficient of Performance.
It has low C. A possibility of leakage of refrigerant is more. A possibility of leakage of refrigerant is less. Performance is adversely affected by part loads. Reduced loads have no effect on its performance. It can not be located outside without shelter. Liquid traces in the suction line may damage the compressor.
Liquid traces in the refrigerant at the exit of the evaporator is not harmful to any component. It has a compressor and a motor.
Therefore, It is more noise in operation. It has a pump only a moving part. The Vapour absorption refrigeration system uses heat energy for refrigeration, while the vapor compression system uses work energy for refrigeration which is much more expensive to produce.
The Vapour absorption refrigeration systems are best for locations where heat energy is readily available at a low cost. This process is best for steams power plants. Steams power plants can easily run this refrigeration system using the waste heat produced in the power plant.
The next component and analyzer send water particles back to the generator through this pipe for further processing. With this generator, the diluted solution of water and ammonia residues deposited here will be sent back to the absorber again.
The very cold liquid will exit the ammonia expansion valve that enters the evaporator coil through the connected pipe. The main cooling is always in the evaporator. When liquid ammonia enters the evaporator coil, it will absorb all the heat present on the surface of the evaporator coil by absorbing all the heat from the area around the evaporative coil.
The cooled liquid ammonia will convert to ammonia vapor inside these coils, and the surrounding surface of the evaporator will be cooled by losing heat to the liquid; thus, a cooling effect or refrigeration effect has occurred insides the evaporator.
It will then release the low-pressure ammonia vapor evaporator and enter the absorber through the connecting pipe. The absorber already has a weak solution of ammonia and the water inside it, and when it enters the low-pressure ammonia vapor absorber, the water present in the weak solution of this absorber will start absorbing this ammonia vapor, and A weak solution will gradually transform into a strong one—Ammonia-water solution.
The more ammonia Vapour from the evaporator is absorbed by the water of this weaker solution, the stronger the solution will form, but when the water absorbs the ammonia Vapour, it also releases it from heat. To keep the slurry temperature at an optimum level, cold water is supplied through this pipe so that this cold water keeps the heat away from the slurry, and thus the water gains the ability to absorb the incoming ammonia Vapour continuously.
There is a pump next to the absorber; now that power is provided, this pump starts working. An Auxiliary generator or external heat is provided to this generator using steam or hot water or any heater, gas burner. So when the ammonia and water solution reaches the generator and heat is applied to the slurry from an external source, the water from the ammonia-water solution both turn into vapor inside this generator. In fact, ammonia turns into Vapour faster than water, and water completely turns into vapor.
Now here we also have analyzers on top of the generator. Only ammonia is allowed to pass when ammonia and water Vapour try to pass through this analyzer. This is because if waters Vapour enters the system, it may reduce the efficiency of the refrigeration system, or if a large amount of water vapor enters the system, the system may be damaged; Thus, the analyte separates the water particles from the ammonia Vapour and only allows the ammonia to pass through the pressure reducing valve.
Therefore the high pressure, high-temperature pure ammonia vapor coming out of the generator will now enter the condenser through this connected pipe. We have a condenser; When high pressure, high-temperature ammonia Vapour enters the cold condenser, the condenser absorbs heat from the ammonia vapor and converts it completely into a liquid. This condenser can be either water-coolers or air-cooled. This will release the latent heat of the Vapour coming into the condenser, and thus condensation continues.
Now we have an expansion valve. After condensation, the liquid ammonia will release the condenser and pass-through this expansion valve. Now inside this expansion valve, the high-pressure liquid ammonia coming from the condenser will be expanded. We know that when the expansion occurs, the pressure between the molecules decreases significantly.
Thus as the temperature falls, this high-pressure liquid ammonia will be expanded into low-pressure, low-temperature liquid ammonia; Thus, we exit the very cold low-temperature liquid ammonia expansion valve. After that, thises liquid ammonia will be passed through the connection pipe to the evaporator, absorbing all the heat from the area around the evaporator coil, the cooled cold liquid ammonia will again turn into low-pressure ammonia Vapour inside the coil, And the area around the evaporator will be cooled by losing heat to this liquid.
This low-pressure ammonia Vapour will then release the evaporator and enter the absorber through this connecting pipe. This entire cycle will be repeated again and again. Therefore, refrigeration will occur continuously in the evaporation zone. The main function of the evaporators is to provide cooling to the area with which it is in contact. The cooled liquid will enter inside this evaporator and receive heat from the evaporator, and be converted into vapor.
This Vapour will be at low pressure. With this evaporator, the ammonia Vapour comes out under low pressure and will go towards the absorber. Absorbers are used to absorb refrigerants. In the absorber, there will be a weak solution of water and ammonia. When the ammonia Vapour from the evaporator reaches the absorber, the water present in the absorber will absorb it.
As the water absorbs the ammonia, a strong ammonia solution and water will begin to form. When the water absorbs ammonia, the water will liberate from the heat, and the absorptive capacity of the water will be reduced.
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