【作者】 韩妮；

【导师】 赵建会；

【作者基本信息】 西安科技大学 ， 安全技术及工程， 2009， 硕士

【摘要】 近年来,现代化建筑中空调用电量巨大,占建筑物总用电量的50%。空调不仅耗电巨大,而且其冷负荷高峰时间与城市用电尖峰期相吻合,加剧了峰谷供电的不平衡和供电不足的矛盾,而蓄冷式空调系统能较好的解决这一问题。为了满足家用蓄冷空调的要求,因此小型冰蓄冷空调系统应运而生,然而国内外对小型冰蓄冷蓄、融冰的研究处于正在成熟阶段,因此,本文利用数学模型来进一步研究小型冰蓄冷空调系统的蓄冰特性。蓄冰过程中,管子内外存在复杂的相变过程,即管内汽化相变过程和管外凝固相变过程,本文仅考虑管外的凝固相变过程。文中以蓄冰槽内的某一直管段和管段截面作为研究对象,建立了直接蒸发式盘管结冰过程的数学模型,运用FLUENT模拟软件对六组不同蒸发温度和不同初始水温的工况进行二维数值模拟。针对研究对象的具体特点,经过反复试算确定出网格划分的步长为1mm,对存在冰水两相状态的直管段及管段截面进行模拟,采用多相流中的VOF模型及界面追踪法进行模拟计算。在建成数理模型之后便开始进行数值模拟,在此数值模型的指导下设计完成蓄冰周期为3h的蓄冰过程,模拟出蒸发温度分别为-5℃,-10℃,-15℃和初始温度分别为10℃和15℃的六种工况下的蓄冰过程,并且模拟计算出蓄冰槽内温度分布、管外冰层厚度、蓄冰率以及蓄冰量随蓄冰时间的变化规律。通过对模拟结果分析研究,得出盘管外融冰系统的蓄冰特性规律,即蓄冰过程可以大体分为显热快速蓄冷阶段、潜热快速蓄冷阶段及潜热慢速蓄冷阶段。蓄冷量代表显热蓄冷和潜热蓄冷的总和,得出整个蓄冰过程的变化规律。蓄冷量呈现出在前约1/5时期内阶段增长速度最快,后期增长逐渐减慢的趋势;制冷剂的蒸发温度影响蓄冰的全过程,蓄冷量随时间变化曲率随蒸发温度的不同而不同;初始水温对蓄冰量的影响较小,主要存在于蓄冰过程中的显热蓄冷阶段。最后将数值模拟结果与实验结果进行对比分析,表明数值模拟结果能较好的反应实验情况,进一步验证了数值模拟的可靠性,并且本文选择出最佳蓄冰工况。更多还原

【Abstract】 In recent years, a huge consumption of electricity of air-conditioned in modern building account for the total electricity consumption in buildings by 50%. Air conditioning is not only a great power, and the peak hours of cooling load match the peak period of electricity in the city, which exacerbated the imbalance of peak power shortage and the contradictions of the lack of electricity, so thermal storage air conditioning systems can better solve this problem. In order to meet domestic requirements on storage air-conditioning, so small-scale ice-storage air conditioning system came into being, but ice charging and discharging of the small-scale ice-storage air conditioning system is in the research stage at home and abroad, therefore, this paper will use the mathematical model to further study on characteristics of the thermal storage of small-scale ice-storage air-conditioning system.In ice storage process, the inside and outside of ice-on-coil exist complex phase-change process, namely, the phase-change process of vaporization and the phase-change process of solidification, this paper only consider the phase change process of solidification on the tube outside.This paper will reserch a tube sections and section of pipe sections in a storage tank, and set up the mathematical model of direct evaporation coil freezing process, and use FLUENT simulation software to simulate the six groups working conditions of different evaporation temperature and different initial fluild temperature with two-dimensional numerical simulation. For the specific characteristics of the study objects, I determine the step size of grid for the 1mm after repeated accounting,then simulate straight pipe sections and the cross-section of pipe sections which exist ice water two-phase states,which use the VOF model of multiphase flow model and interface tracking method.The numerical simulation begins after the mathematical model builted , under the guidance of this numerical model, the simulation compltetes the storage process which has the design cycle of ice storage for 3h, and simulates the six conditions of the storage process ,which is the evaporation temperature of -5℃, -10℃, -15℃and initial temperature of 10℃and 15℃, and simulates the temperature distribution inside the ice storage tank, ice thickness outside the ice-on-coil, the rate of ice storage and the quantity of ice storage with the changes of ice storage time .Through the analysis of simulation results, we know the ice-melting characteristics of the outside of ice-on-coil ice storage system, namely, the thermal storage process can be roughly divided into three phase which is sensible heat express ice storage phase, latent heat express ice storage stage and the latent heat slow ice storage phase.The ice storage capacity is on behalf of the sum of sensible heat ice storage and latent heat ice storage, which can know the variation characteristics of the entire ice storage process.It shows that the ice storage capacity has the fastest-growing stage about the former 1/5 period and the latter growth trend has gradually slowed down; evaporation temperature of refrigerant influence the entire process of ice storage and the curvature which change with time of ice storage capacity is different with the different of the evaporation temperature; the initial fluild temperature has less influence to ice storage capacity, which mainly exist in the process of sensible heat ice storage stage.Finally, the results of numerical simulation compare with the results of experimental, which shows that numerical simulation have the better response to the experimental situation, and further verifys the reliability of numerical simulation, and this paper select the best ice storage parameter.更多还原