The Simulation Of Ammonia-water Absorption Refrigeration System

At present energy conservation and environmental protection are two significant subjects in the world, meanwhile, energy conservation and emission reduction are the key policies to ensure the sustainable development of resource and ecological environment. With the gradual replacement of freon refrigerant, ammonia-water absorption refrigeration(AWAR) system has received more and more attention. The Ozone Depletion Potential(ODP) and Global Warming Potential(GWP) of ammonia are both 0, meaning that ammonia is a kind of environment friendly refrigerant. On the other hand, AWAR system can make use of industrial waste heat, solar energy and other low grade energy to produce refrigeration, which means AWAR system could save more energy and electric power than ammonia compression refrigeration system. Therefore, it is crucial to develop AWAR, which is of great importance to energy conservation and emission reduction.In this paper, the models of physical properties used to calculate AWAR system and equipment were introduced in detail, including Schulz's ammonia-water system equation of state to calculate thermodynamic properties, such as enthalpy, entropy, specific volume and vapor-liquid equilibrium, and other transfer properties models such as viscosity, thermal conductivity, surface tension, and diffusion coefficient. The physical properties data provided in the literature were used to verify the accuracy of the program, prepared in accordance with the above models.Based on the properties models above, using the method of piecewise numerical integration, a model of vertical tube falling-film ammonia-water absorber, as the key equipment, was proposed. Program design and calculation were carried out by using FORTRAN language, and the results matched well with process data provided by reference, showed that this model could provide reference in a certain extent for simulating and designing a falling-film ammonia-water absorber. Through the profiles analysis of absorption rate, temperature, density, and film thickness, a further explanation was given for its internal stream state.Finally, combined with the absorber mentioned above, Aspen Plus was used to simulate a 300 kW cooling capacity AWAR system. By changing working conditions, analysis of effects on Coefficient of Performance(COP) was proposed. Investigated factors included cooling-water temperature, desorption distillation feed temperature and concentration, and liquid ammonia sub-cooling degree. It shows that the COP will rise by 1.02% while cooling-water temperature drops 1?, and rise by 0.45% while liquid ammonia sub-cooling degree increases 1?. The total cost will be lower when the feed temperature reaches 110? and feed mass concentration reaches 0.2685. Meanwhile, the influence of several streams temperature, including cooling-water, barren liquor, and ammonia, on absorber were explored. It shows that ammonia temperature has few effects on mass transfer area of absorber, but the temperature of cooling-water and barren liquor is higher, the greater the mass transfer area of absorber required.