Author Topic: Analysis of Ammonia-Water (NH3-H2O) Vapor Absorption Refrigeration System based  (Read 10872 times)

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Author : Satish Raghuvanshi, Govind Maheshwari
International Journal of Scientific & Engineering Research Volume 2, Issue 9, September-2011
ISSN 2229-5518
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Abstractó The continuous increase in the cost and demand for energy has led to more research and development to utilize available energy resources efficiently by minimizing waste energy. Absorption refrigeration systems increasingly attract research interests. Absorption cooling offers the possibility of using heat to provide cooling. For this purpose heat from conventional boiler can be used or waste heat and solar energy. Absorption system falls into two categories depending upon the working fluid. These are the LiBr-H2O and NH3-H2O Absorption Refrigeration system. In LiBr-H2O system water is used as a refrigerant and LiBr is used as an absorbent, while in NH3-H2O system ammonia used as an refrigerant and water is used as an absorbent, which served as standard for comparison in studying and developing new cycles and new absorbent/refrigerant pairs. The objective of this paper is to present empirical relations for evaluating the characteristics and performance of a single stage Ammonia water (NH3-H2O) vapour absorption system. The necessary heat and mass transfer equations and appropriate equations describing the thermodynamic properties of the working fluid at all thermodynamic states are evaluated. An energy analysis of each component has been carried out and numerical results for the cycle are tabulated. Finally the variations of various thermodynamic parameters are simulated and examined.
         Index Termsó Energy, Energy Rate, Coefficient of Performance

1   INTRODUCTION                                                                      
In view of shortage of energy production and fast increas-ing energy consumption, there is a need to minimize the use of energy and conserve it in all possible ways. Energy conservation (i.e., energy saved is more desirable than energy produced) is becoming a slogan of the present decade and new methods to save energy, otherwise being wasted, are being explored. Recovering energy from waste heat and/or utilizing it for system efficiency improvement is fast becoming a common scientific temper and industrial practice now days. The present energy crisis has forced the scientists and engineers all over the world to adopt energy conservation measures in various industries. Reduction of the electric power and thermal energy consumption are not only desirable but unavoidable in view of fast and competitive industrial growth throughout the world. Refrigeration systems form a vital component for the industrial growth and affect the energy problems of the country at large. Therefore, it is desirable to provide a base for energy conservation and energy recovery from Vapour Absorption System. Although, the investigations undertaken in this work are of applied research nature but certainly can create a base for further R & D activities in the direction of energy conservation and heat recovery options for refrigera-tion systems and the analysis can be extended further to other Refrigeration and Air Conditioning Systems. In recent years, research has been devoted to improvement of Absorption Refrigeration Systems (ARSs). Mechanical Vapour Compression Refrigeration requires high grade energy for their operation. Apart from this, recent studies have shown that the conventional working fluids of vapour compression system are causing ozone layer depletion and green house effects.

   However, ARSís harmless inexpensive waste heat, solar, biomass or geothermal energy sources for which the cost of supply is negligible in many cases. Moreover, the working fluids of these systems are envoi mentally friendly [1-3]. The overall performance of the absorption cycle in terms of refrigerating effect per unit of energy input generally poor, however, waste heat such as that rejected from a power can be used to achieve better overall energy utilization. Ammonia/water (NH3/H20) systems are widely used where lower temperature is required. However, water/lithium bromide (H20/LiBr) system are also widely used where moderate temperatures are required (e.g. air conditioning), and the latter system is more efficient than the former [4-6].
   The objective of this paper is to evaluate thermody-namic properties and tabulated also energy transfer rate in each components are calculated and tabulated with the help of empirical relation. Mass flow rate and heat rate in each components of the system are evaluated and tabulated. The coefficient of performance of the system is determining for various temperatures ranges. The result of this study can be used either for sizing a new refrigeration cycle or rating an existing system.

SYSTEM DESCRIPTION

   Figure 1 shows the schematic block diagram of a simple absorption refrigeration system it consist of an absor-ber, a pump, a generator and a pressure reducing valve to replace the compressor in vapour compression refrigeration system. The other component of the system is same (condenser, evaporator and expansion valve). In this system the NH3 is used as a refrigerant and the water is used as an absorbent. In this system the low pressure ammonia vapour refrigerant leaving the evaporator enters the absorber, where itís absorbed by the cold water in the absorber. The water has an ability to absorb a very large quantity of ammonia vapour, and the solution thus formed is known as aqua ammonia solution. The absorption of ammonia vapour in water lowers the pressure in the absorber which turn draw the more ammonia vapour from the evaporator and thus raise the temperature of the solution. Some form of cooling arrangement (usually water cooling) is employed in the absorber to remove the heat of solution evolved here, this is necessary in order to increase the absorption capacity of water, because of higher temperature water absorb less am-monia vapour, the strong solution thus formed in absorber is pumped to the generator by the liquid pump. The pump increases the pressure of solution up to the 10 bar. The strong solution of ammonia in the generator is heated by some external source such as gas, steam, solar energy. During the heating process ammonia vapour is driven off from the solution at higher pressure and leaving behind the hot week solution in the generator. The weak ammonia solu-tion flows back to the absorber at low pressure after passing through the pressure reducing valve. The high pressure am-monia vapour from the generator is condensed in the con-denser to high pressure liquid ammonia thus liquid ammonia is passed to the expansion valve through the receiver and then to the evaporator. This is the complete working of simple vapour absorption refrigeration cycle. 

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