| The development of the world economy and the growth of the world population increases the need for freshwater.On the other hand,the problem of Ozone depletion and global warming is one of the worst global issues due to the great harm to the environment.Meanwhile,the rise of global temperatures renders refrigeration and air-conditioning demands to increase.The production process of cooling and freshwater consumes an enormous amount of energy,leading to increase the greenhouse gas emissions.Therefore,the lack in freshwater sources and the high demand and need for refrigerating are life-threatening problems all over the world,which makes freshwater and refrigeration among the essential products that are required simultaneously,especially in hot regions such as Middle Eastern countries and tropical areas,where there are not sufficient sources of freshwater.Integrated systems,which simultaneously produce more than one product,are more energy-efficient than those that generate the same products separately.Therefore,the combined refrigeration and boosted multi-effect desalination(B-MED)systems are advantageous and energy-efficient for water and cold cogeneration.This research explores the most efficient ways of improving these combined systems.An original system of a combined transcritical CO2 refrigeration system and B-MED system is studied and analyzed;then,the original system is optimized by adding another booster module,so,the original system has only one booster module B-MED while the optimized system has two booster modules 2B-MED.A mathematical model of the two systems is developed to evaluate the impact of the design parameters on the system performance.The model is based on the energy balance,mass balance,and the salinity balance of the desalination system components.The heat transfer equations of the refrigeration and the desalination systems and the physical properties of saline water will also be included in the mathematical model.All parameters will be included in the mathematical model to analyze and evaluate the effect of each one.The two systems will be studied and analyzed in two different cases(scenarios).In the first case,these systems are analyzed at different inlet heat source temperatures with a different number of effects;in other words,the two systems will be studied at 85?-110?inlet heat source temperatures with six to eleven effects.While in the second case,the two systems are studied at different inlet heat source temperatures with a fixed number of effects(six effects).These systems will be analyzed and assessed thermodynamically to understand and highlight the strengths and weaknesses of the two systems in order to choose the effective conditions of each system,then,some comparisons between the two systems will be carried out to identify the more efficient system.The freshwater production rate of the original system(B-MED)reaches 446 m3 per day at 110? and 11 effects(the first case),while it reaches 429 m3 per day at the same temperature with six effects(the second case).In comparison,the freshwater production rate of the optimized system(2B-MED)reaches 550 m3 per day at 110? and 11 effects(the first case),while it is about 491 m3 per day at the same temperature with six effects(the second scenario),which means that by increasing the number of effects at various temperatures of the inlet heat source,the two systems are thermodynamically more effective than the second case with a fixed number of effects(six effects).Optimizing the original system by adding another booster module can improve the system in many sides,the results of the optimized system show that the freshwater production rate increases by about 65,74,82,87,97 and 104 m3per day at 85,90,95,100,105,and 110? respectively,with an increasing rate ranging between 22%-23%in comparison with that of the 1 B-MED system.On the other hand and due to the decreasing in the temperature of the inlet heat source to the gas cooler by adding another booster module,the heat transfer rate of the gas cooler in the optimized system(2B-MED)is decreasing by about 47%,55%,60%,64%,67%and 70%at 85,90,95,100,105,110? respectively,which leads to decrease the heat transfer area(HTA)of the gas cooler,and all that will reduce the total annual cost(TAC)of the refrigeration cycle.The two systems are studied at different inlet heat source temperatures and different top brine temperatures(TBT)as well.The TBTs in our simulation are ranging from 56.5?-70?,the results show that at high inlet heat source temperatures,the optimum values of the TBTs in the two systems are ranging between 65-68?.In contrast,other temperatures out of this range will not be thermodynamically feasible.A thermodynamic analysis was carried out for the first effect and the first booster module in the two systems;the investigation focused on three parameters;the freshwater production rate,the heat transfer rate,and the heat loss of the inlet heat source temperature.The results show that the produced freshwater in the first booster module is more than the first effect.Besides,the heat transfer rate and temperature loss in the first booster is less than the first effect,all that proves the priority of the first booster module in the MED system.On the other hand,the results show that the freshwater production rate in the second booster module is more than the first booster module and the first effect utilizing the same energy;in addition,the heat transfer rate and the temperature loss have the lowest values in the second booster module.The first effect consumes heat transfer rate and loses heat source temperature more than the two booster modules.All that proves that the first booster module is more efficient than the first effect,while the second booster is more efficient than the first one.In conclusion,the results demonstrated that the optimized system with two booster modules is thermodynamically better than the original one.The optimized system can increase the freshwater production rate in the desalination system and decrease the heat transfer rate of the gas cooler in the refrigeration system simultaneously. |
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