太阳能喷射制冷系统冷凝器的特性研究及优化

发布时间：2018-10-16 11:51

【摘要】：空调制冷技术的应用给人类带来了舒适的工作生活环境,同时也消耗了大量能源。太阳能喷射制冷系统凭借其具有节约能源、结构简单、使用寿命长以及系统运行可靠、稳定性高等优势而备受瞩目。然而,现阶段太阳能喷射制冷系统的效率较低,因此,提高系统效率对实现其广泛应用具有重要意义。现有文献中针对系统性能的提高进行了制冷剂、喷射制冷系统结构形式以及喷射器优化等方面的研究,但缺乏通过优化系统重要部件冷凝器来提高系统整体性能的研究。本文在研究冷凝器综合性能的基础上,运用数值模拟的方法,通过合理设计冷凝器结构以实现提高系统制冷量,优化系统性能的目的。选取冷凝器壳程对流传热系数与压降三分之一次方的比值与太阳能喷射制冷系统制冷量、性能系数COP作为冷凝器综合性能与系统整体性能的评价指标,主要研究内容及结论如下:1.根据系统数学模型及FORTRAN编制的喷射器结构设计程序,在TRNSYS软件中建立太阳能喷射制冷系统,计算某气象日运行工况下,制冷系统各参数随太阳辐射强度的变化情况。由TRNSYS软件模拟结果可知,从11:00至18:00点,喷射器结构不变时,系统的一次流量随时间变化的规律是先增大后减小,喷射系数随时间则先减小后增大,这是由于在蒸发温度和喷射器结构参数一定时,发生温度越高,临界冷凝温度越高,喷射系数越小。2.冷凝流量由一次流量与二次流量之和决定,系统运行开始和结束时冷凝流量较小,15:00左右达到最大值,约为0.1801 skg/。计算得出的冷凝器换热量30kW,运用HTRI换热器软件设计管壳式冷凝器,并在FLUENT中建立冷凝器模型。3.将FLUENT模拟与TRNSYS软件相结合进行模拟,计算结果表明:当冷凝器折流板间距取260mm,换热管间距取32mm,折流板圆缺高度在0.2D-0.4D之间变化时,折流板圆缺高度增大,冷凝器壳程的对流传热系数与压降的整体趋势均减小。当折流板圆缺高度取0.2D时,冷凝器的综合性能与系统性能相对较好。4.当冷凝器折流板圆缺高度取0.2D,换热管间距取32mm,折流板间距取值在180mm-260mm之间变化时,折流板间距越小,冷凝器壳程的对流传热系数和压降越大,当折流板间距取180mm时,冷凝器的综合性能与系统性能的表现均最佳。5.当冷凝器圆缺高度为0.2D,折流板间距为180mm,换热管中心距在30mm-34mm之间变化时,换热管间距存在最优值。当取32mm或34 mm时,冷凝器的综合性能较好,当管间距取32mm时,系统性能最好。
[Abstract]:The application of air conditioning and refrigeration technology brings people a comfortable working and living environment, but also consumes a lot of energy. Solar ejector refrigeration system has attracted much attention because of its advantages of saving energy, simple structure, long service life, reliable operation and high stability. However, the efficiency of solar ejector refrigeration system is low at present, so it is very important to improve the efficiency of solar energy ejector refrigeration system to realize its wide application. In the existing literature, the refrigerant, the structure of the ejector refrigeration system and the optimization of the ejector are studied, but there is no research on how to improve the overall performance of the system by optimizing the condenser, an important part of the system. Based on the study of the comprehensive performance of the condenser, the purpose of improving the cooling capacity of the system and optimizing the performance of the system is achieved by using the method of numerical simulation and the reasonable design of the condenser structure. The ratio of convection heat transfer coefficient to the pressure drop of the condenser shell to the 1/3 power and the cooling capacity of the solar ejector refrigeration system are selected. The performance coefficient COP is used as the evaluation index of the condenser's comprehensive performance and the overall performance of the system. The main contents and conclusions are as follows: 1. According to the mathematical model of the system and the structural design program of the ejector compiled by FORTRAN, the solar ejector refrigeration system is established in the TRNSYS software, and the variation of the refrigeration system parameters with the solar radiation intensity is calculated under a meteorological daily operating condition. From the simulation results of TRNSYS software, it can be seen that from 11:00 to 18:00, when the ejector structure is invariant, the primary flow rate of the system increases first and then decreases, and the ejection coefficient decreases first and then increases with time. This is because the higher the evaporation temperature and the ejector structure parameter, the higher the critical condensation temperature and the smaller the ejection coefficient. The condensing flow is determined by the sum of primary flow and secondary flow. At the beginning and end of system operation, the condensing flow is small, reaching the maximum value about 15:00, about 0.1801 skg/.. The calculated heat transfer of condenser is 30kW, and the shell and tube condenser is designed by using HTRI heat exchanger software, and the model of condenser is established in FLUENT. By combining FLUENT simulation with TRNSYS software, the results show that when the condenser baffle spacing is 260mm and the heat transfer tube spacing is 32mm, the baffle circular gap height increases with the change of 0.2D-0.4D height. The overall trend of convection heat transfer coefficient and pressure drop in the condenser shell is decreased. When the height of baffle plate is 0.2D, the condenser's comprehensive performance and system performance are relatively good. 4. 4. When the circular gap height of condenser baffle plate is 0.2D, the distance of heat transfer tube is 32mm, and the distance of baffle plate is changed between 180mm-260mm, the smaller the baffle spacing is, the greater the convective heat transfer coefficient and pressure drop of condenser shell are. When the baffle spacing is taken as 180mm, the convection heat transfer coefficient and pressure drop of the condenser shell are increased. The comprehensive performance and system performance of condenser are the best. 5. 5. When the height of the condenser is 0.2D, the baffle spacing is 180mm, and the center distance of the heat transfer tube varies between 30mm-34mm, there is an optimum value of the heat transfer tube spacing. When 32mm or 34 mm is used, the condenser has better comprehensive performance, and when the tube spacing is 32mm, the system performance is the best.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU831

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