5. Discuss properties of ideal and real refrigerant-absorbent mixtures (Section. ). 6. Describe a single stage vapour absorption refrigeration system with. Introduce ammonia-water systems (Section ). 2. Explain the working principle of vapour absorption refrigeration systems based on ammonia-water ( Section. PDF | Most of the energies are utilized by the industries due to depletion of " Design and Fabrication of Vapour Absorption Refrigeration System [Libr-H20]".
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The vapour absorption refrigeration system consists of: • Absorber: Absorption of refrigerant vapour by a suitable absorbent or adsorbent, forming a strong or rich. PROJECT REPORT On VAPOUR ABSORPTION REFRIGERATION SYSTEM BY SOLAR ENERGY SUBMITTED BY: 1. GEVARIYA AKSHAY C. (). system is that it requires large volume of refrigerant vapour In the absorption system, the compressor is replaced by an absorber, generator.
In the evaporator the refrigerant enters at very low pressure and temperature after passing through the expansion valve.
This refrigerant absorbs the heat from the substance that is to be cooled so the refrigerant gets heated while the substance gets cooled. Even after cooling the substance the temperature of the refrigerant leaving the evaporator is less the than the substance.
The refrigerant leaves the evaporator in vapor state. The most common medium consists of parallel tubes but others have plates or coils typically made from copper or aluminum. The concentrating and separating section removes the vapor being produced from the solution. Thus the absorber consists of the weak solution of the refrigerant ammonia in this case and absorbent water in this case.
When ammonia from the evaporator enters the absorber, it is absorbed by the absorbent due to which the pressure inside the absorber reduces further leading to more flow of the refrigerant from the evaporator to the absorber. At high temperature water absorbs lesser ammonia, hence it is cooled by the external coolant to increase it ammonia absorption capacity.
Here, solar panel is used for the heating purpose. Separates the dissolved ammonia from the water-ammonia solution. The refrigerant ammonia solution in the generator is heated by the external source of heat.
This is can be steam, hot water or any other suitable source. Due to heating the temperature of the solution increases. The refrigerant in the solution gets vaporized and it leaves the solution at high pressure. The high pressure and the high temperature refrigerant then enters the condenser, where it is cooled by the coolant, and it then enters the expansion valve and then finally into the evaporator where it produces the cooling effect.
This refrigerant is then again absorbed by the weak solution in the absorber.
Vapour Absorption Refrigeration System
This solution enters the pressure reducing valve and then back to the absorber, where it is ready to absorb fresh refrigerant. In this way, the refrigerant keeps on repeating the cycle.
The pressure of the refrigerant is increased in the generator, hence it is considered to be equivalent to the compression part of the compressor. There are two types under this category a Natural convection and b forced-air type. As air comes in contact with the warm-condenser tubes, it absorbs heat from the refrigerant and thus the temperature of the air increases. Warm air being lighter, rises up and in its place cooler air from below rises to take away the heat from the condenser. This cycle goes on.
Since air moves very slowly by natural convection, the rate of flow of heat from the refrigerant to air will be small. Thus a natural convection condenser is not capable of rejecting heat rapidly. Therefore a relatively large surface area of the condenser is required.
Hence the use of this type of condenser is limited to very small units such as domestic refrigerators. It, however, requires very little maintenance. In the small units, the condenser is fixed at the rear of the refrigerator cabinets. Generally, steel tubes are used, steel being cheaper than copper. To increase the heat-transfer area, wires are welded to the condenser tubes.
These wires provide mechanical strength to the coil as well. In certain designs, widely-spaced fins are used. It is necessary to space the fins quite widely to avoid resistance to free natural convection air movement over the condenser. The condenser coil is of the finned type.
Fins in such coils are closely spaced ranging between 8 and 17 fins per inch. The space between the fins gets choked with dirt and lint.
Therefore to obtain optimum capacity, the fins should be kept clean. For bigger- capacity plants a separate motor is used to drive the fan or blower as also for hermetic- compressor units 25 7.
Pumps operate via many energy sources, including manual operation, electricity, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial pumps. When the absorbent absorbs the refrigerant strong solution of refrigerant absorbent ammonia water is formed. This solution is pumped by the pump at high pressure to the generator. Thus pump increases the pressure of the solution.
Absorption Refrigeration System, Cycle, unit, how does it Work?
This refrigerant ammonia in this case then enters the evaporator. Controls the amount of refrigerant flow into the evaporator. Cause a pressure drop Isenthalpic of the working fluid. Causes sudden drop in temperature. If the solute itself has some vapour pressure i. If the solute is non-volatile e.
In the simplest absorption refrigeration system, refrigeration is obtained by connecting two vessels, with one vessel containing pure solvent and the other containing a solution. Since the pressure is almost equal in both the vessels at equilibrium, the temperature of the solution will be higher than that of the pure solvent. This means that if the solution is at ambient temperature, then the pure solvent will be at a temperature lower than the ambient.
Absorption Refrigeration System
Hence refrigeration effect is produced at the vessel containing pure solvent due to this temperature difference.
The solvent evaporates due to heat transfer from the surroundings, flows to the vessel containing solution and is absorbed by the solution. This process is continued as long as the composition and temperature of the solution are maintained and liquid solvent is available in the container.
As shown in the figure, low temperature and low pressure refrigerant vapour from evaporator at state 1 enters the absorber and is absorbed by solution weak in refrigerant state 8. The heat of absorption Qa is rejected to an external heat sink at To. The solution, rich in refrigerant state 2 is pumped to the generator pressure Pg by the solution pump state 3.
The pressurized solution gets heated up sensibly as it flows through the solution heat exchanger by extracting heat from hot solution coming from generator state 4. Heat is supplied to this solution from an external heat source in the generator Qg at Tg , as a result refrigerant vapour is generated absorbent may also boil to give off vapour in case of ammonia-water systems at state 5.
This high pressure refrigerant liquid is throttled in the expansion device to evaporator pressure Pe state 10 from where it enters the evaporator, extracts heat from low temperature heat source Qe at Te and leaves the evaporator as vapour at state 1, completing a cycle. The hot solution that is weak in refrigerant state 6 leaves the generator at high temperature and is cooled sensibly by rejecting heat to the solution going to the generator in the solution heat exchanger state 7.
Then it is throttled to the evaporator pressure in the throttle valve state 8 , from where it enters the absorber to complete the cycle. It can be seen that though not an essential component, the solution heat exchanger is used in practical systems to improve the COP by reducing the heat input in the generator.
As a result of this heat exchange, less heat input is required in the generator and less heat is rejected in the absorber, thus improving the system performance significantly. The refrigerant should exhibit high solubility with solution in the absorber. There should be large difference in the boiling points of refrigerant and absorbent greater o than C , so that only refrigerant is boiled-off in the generator.
This ensures that only pure refrigerant circulates through refrigerant circuit condenser-expansion valve- evaporator leading to isothermal heat transfer in evaporator and condenser. It should exhibit small heat of mixing so that a high COP can be achieved.
The refrigerant-absorbent mixture should have high thermal conductivity and low viscosity for high performance. It should not undergo crystallization or solidification inside the system. The mixture should be safe, chemically stable, non-corrosive, inexpensive and should be available easily. Air is used as cooling medium.
Draw and explain simple vapour absorption refrigeration system
In case of the vapor absorption refrigeration system, the pump requires very small amount of power and it remains almost the same or may increase slightly even for higher capacities of refrigeration. Thus the power consumed by the vapor absorption refrigeration system is much more than that required by the vapor compression system.
The vapor absorption refrigeration system comprises of all the processes in the vapor compression refrigeration system like compression, condensation, expansion and evaporation.
In the vapor absorption system the refrigerant used is ammonia, water or lithium bromide. The refrigerant gets condensed in the condenser and it gets evaporated in the evaporator. The refrigerant produces cooling effect in the evaporator and releases the heat to the atmosphere via the condenser. The major difference between the two systems is the method of the suction and compression of the refrigerant in the refrigeration cycle. In the vapor compression system, the compressor sucks the refrigerant from evaporator and compresses it to the high pressure.
The compressor also enables the flow of the refrigerant through the whole refrigeration cycle. In the vapor absorption cycle, the process of suction and compression are carried out by two different devices called as the absorber and the generator. Thus the absorber and the generator replace the compressor in the vapor absorption cycle.
The absorbent enables the flow of the refrigerant from the absorber to the generator by absorbing it. Another major difference between the vapor compression and vapor absorption cycle is the method in which the energy input is given to the system.
In the vapor compression system the energy input is given in the form of the mechanical work from the electric motor run by the electricity. In the vapor absorption system the energy input is given in the form of the heat.
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Actions Shares. Embeds 0 No embeds. No notes for slide. Simple Vapor Absorption Refrigeration System 1. Simple Vapor- Absorption Refrigeration System 2. Simple Vapor Absorption Refrigeration System Point 1 -low temperature and low pressure refrigerant vapour from evaporator at state 1 enters the absorber and is absorbed by solution weak in refrigerant state 8.
Simple Vapor Absorption Refrigeration System Point 2 -The solution, rich in refrigerant is pumped to the generator pressure Pg by the solution pump state 3. The pressurized solution gets heated up sensibly as it flows through the solution heat exchanger by extracting heat from hot solution coming from generator state 4. Point 5 -Heat is supplied to this solution from an external heat source in the generator Qg at Tg , as a result refrigerant vapour is generated absorbent may also boil to give off vapour in case of ammonia-water systems at state 5.
Simple Vapor Absorption Refrigeration System 5. Point 10 - the high pressure refrigerant liquid is throttled in the expansion device to evaporator pressure Pe from where it enters the evaporator, extracts heat from low temperature heat source Qe at Te and leaves the evaporator as vapour at state 1, completing a cycle. Simple Vapor Absorption Refrigeration System 6.
Point 6 - The hot solution that is weak in refrigerant state 6 leaves the generator at high temperature and is cooled sensibly by rejecting heat to the solution going to the generator in the solution heat exchanger state 7.
Then it is throttled to the evaporator pressure in the throttle valve state 8 , from where it enters the absorber to complete the cycle. Simple Vapor Absorption Refrigeration System 7.The mixture of ammonia vapour and hydrogen is passed to the absorber where ammonia is absorbed in water while the hydrogen rises to the top and flows hack to the evaporator.
Hence, in practice a trade-off is required between solubility and heat of mixing. It is seen that the second law or exergetic efficiency of absorption system is of the same order as that of a compression system.
It is necessary to space the fins quite widely to avoid resistance to free natural convection air movement over the condenser. Since there are number of moving parts of the compressor that move at very fast speed some or the other failure occurs regularly. CREO parametric Solid model Therefore, in response to global concerns over greenhouse resorts are being made to produce refrigerator-freezers with low energy consumption. Refrigerant-absorbent combinations for VARS The refrigerant should exhibit high solubility with solution in the absorber.
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