冷库用翅片蒸发器流程优化的理论分析和实验研究

发布时间：2018-02-17 07:38

本文关键词： 翅片蒸发器流程布置有向图换热效率　出处：《天津商业大学》2016年硕士论文　论文类型：学位论文

【摘要】：冷库用翅片蒸发器是冷冻冷藏设备中的重要组成部分,近年来如何通过合理的技术手段提高冷库用翅片蒸发器的性能成为研究热点。在现有技术中,可以通过提高传热系数、增大换热面积以及提高换热温差等方式来改善翅片蒸发器的传热性能。在提高换热系数的方法中增强翅片侧气流扰动、采用强化管和改变翅片结构都能提高传热系数,但会增加制造成本和翅片蒸发器耗功;增大换热面积可以通过采用内螺纹管和改变翅片蒸发器结构来实现,但金属消耗量和设备成本显著提高,且在空间受限制区域无法应用;改变翅片蒸发器的流程布置可有效提高传热温差,通过流程优化不仅可以避免翅片蒸发器成本和功耗的增加,还可以实现翅片蒸发器的高效运行。因此,本文以翅片蒸发器为研究对象,开展流程优化对翅片蒸发器传热性能影响的理论分析和实验研究。翅片蒸发器流程布置优化原则通常以制冷量最大化作为优化目标,根据逆流布置优于叉流布置、叉流布置优于顺流布置,建议采用“U”字形连接方式和依靠重力使制冷剂由高向低流动等原则,分别设计8种三排管翅片蒸发器流程布置方式和8种四排管翅片蒸发器流程布置方式,其中流程数从一流程增加到三流程,以R404A为制冷剂工质,采用NIST公司设计的EVAP-COND软件对16种设计的翅片蒸发器流程进行理论分析,从设计的16种布置方式中筛选出传热效果最优的4种流程布置方案,并开展相应的实验研究。利用现有的冷风机性能测试实验台,以两台设计面积相同的三排和四排管翅片蒸发器为实验对象进行实验研究。在实验数据的基础上,对四种流程型式的翅片蒸发器进行仿真模拟,采用传统翅片蒸发器设计方法、软件EVAP-COND法和利用有向图的集中参数法进行理论分析。寻求最优的翅片蒸发器流程设计方法。模拟值与实验值比较表明:利用有向图的集中参数模拟方法与实验结果最为吻合,最大误差为±7.94%,其次为传统翅片蒸发器设计方法和软件EVAP-COND计算方法,最大误差分别为±54.92%和±34.38%。通过对翅片蒸发器的实验研究和理论分析,结论如下:1、由制冷量、传热温差、传热系数和压降的变化规律可知,当流程分布均匀时,流程数的增加会使蒸发温度降低,传热温差增大,传热系数随着环境温度的降低先减小后增大,制冷剂压降降低,最终制冷量增大。当流程分布不均匀时,流程数的增加会使蒸发温度降低,传热温差增大,但由于制冷剂流量分布不均匀,压降增大,传热系数减小,传热系数的减小量远远大于传热温差的增加量,最终制冷量减小。增加翅片蒸发器的流程数可以通过增大换热温差而提高制冷量,但是管路中制冷剂的分液不均最终导致每条流程中制冷剂的流量不均匀,进而影响翅片蒸发器的传热效果,制冷剂分液不均对制冷量的影响远远大于增加管路流程数对制冷量的影响。2、对于两流程翅片蒸发器,空气侧入口和出口的平均温差约为0.5℃,中间纵面约为1.3℃,中间纵面的换热温差最终影响了空气侧换热效果。对于三流程翅片蒸发器,空气侧入口的平均温差约为2.3℃,中间纵面的平均温差约为0.8℃,出口纵面约为0.08℃,空气入口迎风面处在空气侧换热部分起到关键作用,且随着纵面数的增加,换热温差下降,传热效果减弱。3、从空气侧各纵面温度测点均方差可知,当翅片蒸发器流程分布均匀时,两流程变为三流程,空气入口与出口的温度均方差分别减小1.3℃和0.15℃,增加流程数可以使空气入口和出口处的纵面温度更加均匀,制冷量得到提高;当翅片蒸发器每条流程长度不相同时,增加流程数对纵面温度均匀性没有影响。4、对于同一个翅片蒸发器的不同流程间的温度分布是不相同的,且相互影响较大,制冷剂入口处温差和出口处温差较大,处于翅片蒸发器中间部分的制冷剂温差较小,主要原因是由于入口制冷剂重力势能和空气流量不同导致。
[Abstract]:Cold storage with fin evaporator is an important part of refrigeration equipment, in recent years, how to improve through reasonable means has become a research hotspot with the performance of finned evaporator refrigerator. In the existing technology, can improve the heat transfer coefficient, increase the heat transfer area and high heat transfer temperature and other ways to improve the heat transfer performance of the fin evaporator. Enhanced fin side airflow disturbance in improving the method of heat transfer coefficient, using enhanced tube and fin structure change can increase the heat transfer coefficient, but will increase the manufacturing cost and power consumption of fin evaporator; increase the heat transfer area can be achieved by changing the screw tube and fin evaporator structure is used, but the metal consumption and the equipment cost increased significantly, and the restricted area can not be applied in space; change the layout of the fin evaporator can effectively improve the heat transfer temperature difference, not only through process optimization In order to avoid increasing the fin evaporator cost and power consumption, can also realize the efficient operation of the fin evaporator. Therefore, the fin evaporator as the research object, carry out theoretical analysis and Experimental Research on the influence of process optimization on heat transfer performance of the fin evaporator. The fin evaporator layout optimization principle usually with cooling capacity maximization as the optimization goal, according to the current arrangement better than cross flow layout, cross flow layout is better than the parallel layout, recommend the use of "U" shaped connection mode and rely on gravity to make the refrigerant flow from high to low were designed 8 principles, three row tube fin evaporator process arrangement and 8 kinds of four row tube fin evaporator process arrangement, which flow from a number of flow increase to the three process, with R404A as the refrigerant flow, fin evaporator of 16 kinds of design were analyzed by NIST EVAP-COND software design company 4, screening process layout scheme of the best heat transfer efficiency from 16 kinds of layout design, and carry out corresponding experimental research. By using the cooling fan performance test bench of the existing two units in the same design area of the three and four row finned tube evaporator experimental research was performed based on the experimental data. On the fin evaporator of four kinds of process types are simulated, using the traditional fin evaporator design method, EVAP-COND method and software using the theoretical analysis to the lumped parameter method. The graph design method of optimum fin evaporator process. The simulation value and the experimental value comparison shows that use the lumped parameter graph simulation method the most consistent with the experimental results, the maximum error is about 7.94%, the calculation method for the traditional fin evaporator design method and the software EVAP-COND, the maximum error is + 54.92% and + 34.38%. respectively. Through experimental study and theoretical analysis, the conclusions are as follows: 1 fin evaporator, the refrigeration, heat transfer temperature difference, the variation of heat transfer coefficient and pressure drop, when the flow distribution, the number of processes will increase the evaporation temperature decreased, the increase of temperature difference, heat transfer coefficient decreases with the ambient temperature decreased first and then increased. Finally, the refrigerant pressure drop decreases, cooling capacity increases. When the flow distribution is not uniform, the number of processes will increase the evaporation temperature decreased, the temperature difference of heat transfer increases, but due to the uneven distribution of the refrigerant flow, the pressure drop increases, reducing the heat transfer coefficient, heat transfer coefficient reduction is far greater than the temperature increase, the final cooling capacity decreases. Can increase the cooling capacity by increasing the heat transfer temperature increase process of fin evaporator, liquid refrigerant in the pipeline but not all refrigerant flow in each resulting in uneven flow, Then the influence on heat transfer fin evaporator, refrigerant liquid uneven influence on cooling capacity is far greater than the increase in pipeline flow number influence on cooling capacity of.2, for the two flow fin evaporator, air side entrance and outlet average temperature is about 0.5 DEG C, the middle vertical plane is about 1.3 degrees Celsius, the middle longitudinal heat transfer temperature the ultimate impact of the air side heat transfer effect. For the three flow fin evaporator, air side entrance of the average temperature is about 2.3 degrees Celsius, the middle vertical surface mean temperature difference is about 0.8 degrees Celsius, the export profile is about 0.08 degrees Celsius, air entrance in the windward side of the air side heat exchange part plays a key role, and with the increase of vertical surface the number, the heat transfer temperature decreased, the heat transfer effect weakened.3 from the air side of the vertical temperature measuring point variance shows that when the fin evaporator process distribution, two process into three processes, air entrance and exit temperature variance respectively. Reduced to 1.3 degrees and 0.15 degrees, increasing the number of processes can make the vertical air temperature at the entrance and exit of more uniform cooling capacity is improved; when the length of each fin evaporator process phase at the same time, increase the flow number on the vertical temperature uniformity had no effect on.4, is not the same for different processes with a fin evaporator the temperature distribution, and the mutual influence, entrance and exit temperature of the refrigerant in the refrigerant temperature difference, the smaller temperature difference between the middle part of the fin evaporator, the main reason is because the entrance of refrigerant and air flow volume of different gravitational potential cause.

【学位授予单位】：天津商业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB65

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