冷库氨制冷系统的应用研究

发布时间：2019-04-01 06:36

【摘要】：氨是一种具有良好热力性能的自然工质,并且ODP和GWP都为零,特别是在冷库制冷系统中取得了广泛的应用。但是由于其具有毒性且可燃,氨泄漏造成的冷库安全事故频繁发生。因此,减少氨的使用量是保证系统安全的有效途径之一。在此背景下,本文提出一种氨泵定量供液系统,在保证传热性能的同时降低氨的循环倍率,并进而降低蒸发排管及整个制冷系统中的氨的充注量。首先,对氨泵定量供液系统和现有氨泵供液系统与氨直接膨胀供液系统进行了对比,表明氨泵定量供液系统避免了储液器出口至蒸发器入口高压液体管路的存在,降低了泄漏的危害程度;且其中供液量为实际需求量,减少了蒸发器内、蒸发器出口至低压循环桶之间长管路的存液量,增强了系统的安全性。其次,采用理论分析的方法研究了不同循环倍率下蒸发排管内的氨充注量。采用在制冷系统制冷剂充注量计算中较为广泛使用的Tom界面含气率模型、Zivi滑动比修正模型和Smith滑动比修正模型来计算整个蒸发排管内的氨平均密度,并进而计算整个蒸发排管内的氨充注量。两种模型的计算结果吻合的较好,并且结果表明,循环倍率从4降到1,蒸发排管内的氨充注量降低60%左右。上述结果说明,采用氨泵定量供液系统降低循环倍率可以大幅度降低蒸发排管内的氨充注量,并进而降低制冷系统中高/低压循环桶内的氨充注量。再次,采用理论分析的方法分析了不同循环倍率下蒸发排管的换热系数。建立了基于管内强制对流换热经验公式的蒸发排管数学模型,通过仿真计算分析了质量流速、循环倍率、霜层厚度等对系统换热性能的影响,计算结果表明,循环倍率从4降到1,蒸发排管总传热系数仅降低7.1%。最后,搭建了氨泵定量供液系统实验台,进一步对循环倍率与充注量和换热性能的关系进行了实验研究,实验结果同样表明,降低循环倍率可大幅减少供液管、蒸发排管和回程管内的氨充注量;并且循环倍率从4.7降到1.4,蒸发排管总传热系数仅降低6.6%,说明循环倍率对换热性能的影响较小。进而,对北京二商集团有限责任公司西郊食品冷冻厂的氨制冷系统进行改造,改造之后的氨泵定量供液系统运行良好。综上所述,氨泵定量供液系统在保证换热性能的情况下显著降低了蒸发排管内的存氨量,本文的研究成果对现有氨制冷系统改造以及新建氨制冷系统中提高氨系统安全性具有重要的理论意义和实用价值。
[Abstract]:Ammonia is a natural refrigerant with good thermal performance, and both ODP and GWP are zero. Especially, ammonia has been widely used in refrigeration system of cold storage. However, because of its toxicity and flammability, the safety accidents of cold storage caused by ammonia leakage occur frequently. Therefore, reducing the use of ammonia is one of the effective ways to ensure the safety of the system. Under this background, a quantitative liquid supply system of ammonia pump is proposed in this paper, which can not only guarantee the heat transfer performance but also reduce the cycle ratio of ammonia, and then reduce the charge of ammonia in the evaporating pipe and the whole refrigeration system. First of all, the quantitative liquid supply system of ammonia pump and the existing ammonia pump supply system are compared with the ammonia direct expansion liquid supply system. The results show that the ammonia pump quantitative liquid supply system avoids the existence of high pressure liquid pipeline from the outlet of the storage device to the inlet of the evaporator. The harm degree of leakage is reduced; The liquid supply is the actual demand, which reduces the amount of liquid stored in the evaporator and the long pipeline between the evaporator outlet and the low pressure circulation barrel, and enhances the safety of the system. Secondly, the ammonia charge in the evaporator with different cycle rate was studied by theoretical analysis. The Tom interface void ratio model, the modified Zivi slip ratio model and the Smith slip ratio correction model, which are widely used in the calculation of refrigerant charge in refrigeration system, are used to calculate the average ammonia density in the entire evaporating row. And then the ammonia charge in the whole evaporating tube is calculated. The calculated results of the two models are in good agreement, and the results show that the circulation ratio decreases from 4 to 1, and the ammonia charge in the evaporating row decreases by about 60%. The above results indicate that the ammonia charge in evaporating tube can be greatly reduced by using ammonia pump quantitative liquid supply system, and then the ammonia charge in high / low pressure cycle barrel in refrigeration system can be reduced. Thirdly, the heat transfer coefficient of evaporating tube with different cycle rate is analyzed by theoretical analysis. A mathematical model of evaporating tube based on empirical formula of forced convection heat transfer in a tube is established. The effects of mass flow rate, circulation ratio and frost thickness on the heat transfer performance of the system are analyzed by simulation calculation. The results show that the heat transfer performance of the system is affected by mass flow rate, circulation ratio and frost layer thickness. The total heat transfer coefficient of evaporating tube is reduced by 7.1% when the cycle rate is reduced from 4 to 1. Finally, the quantitative liquid supply system of ammonia pump is set up, and the relationship between circulation ratio and charge and heat transfer performance is further studied. The experimental results also show that the reduction of circulation ratio can greatly reduce the supply pipe. The amount of ammonia charge in the evaporating pipe and the return pipe; The circulation ratio decreased from 4.7 to 1.4, and the total heat transfer coefficient of evaporating tube decreased only 6.6%, which indicated that the circulation rate had little effect on the heat transfer performance. Furthermore, the ammonia refrigeration system of the Xipao Food Refrigeration Plant of Beijing Erzhang Group Co., Ltd has been reformed, and the ammonia pump quantitative liquid supply system has been running well after the revamping. To sum up, the ammonia pump quantitative liquid supply system significantly reduces the amount of ammonia stored in the evaporating drain under the condition of ensuring the heat transfer performance. The research results of this paper have important theoretical significance and practical value to the revamping of the existing ammonia refrigeration system and the improvement of the safety of the ammonia refrigeration system in the new ammonia refrigeration system.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657.1

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