孔径对平行流蒸发器内气液两相流均匀分布的影响

发布时间：2018-03-25 08:21

  本文选题：平行流蒸发器　切入点：孔径　出处：《天津商业大学》2014年硕士论文

【摘要】：平行流蒸发器由于具有很好的换热物性，所以受到广泛的关注。但目前用在低温下的平行流蒸发器较少，且流场温度均匀性较差。本文采用数值模拟的方法，研究了在相同R134a制冷剂充注量下，8根与10根管内径为0.4cm的平行蒸发管内制冷剂温度场均匀时的孔径大小；同时研究了在孔径大小不变时，调整进口制冷剂流量和平行蒸发管的管间距后温度场的变化情况，调整平行蒸发管的管间距后温度场的变化情况；同时与蒸发面积、管间距、制冷剂充注量相等的蛇形管蒸发器温度场进行对比研究。在实验方面，加工平行流蒸发器，对模拟得出的孔径大小进行验证。通过研究发现： 1.当平行流蒸发器进口速度为V=0.01m/s时，靠近平行流蒸发器进口越近的蒸发管制冷剂量越大；当蒸发器进口速度为V=0.1m/s时，靠近平行流蒸发器进口越近的蒸发管内制冷剂量越小。 2.当平行流蒸发器的管根数为8根、进口速度为V=0.04m/s时，在降温阶段，平行蒸发管的管间距在5cm时的降温曲线较分散；平行蒸发管的管间距在3cm时的温度变化较小，8根蒸发管间的降温曲线较集中。 3.当进口速度V=0.04m/s时，蛇形管蒸发器和平行流蒸发器的降温速率相近，当系统稳定后，，由于压降的作用，蛇形管蒸发器蒸发管之间的温度相差较大，且蛇形管蒸发器的温度随着制冷剂的流向越来越低。 4.根据模拟孔径大小，并根据实验数据适当的调整孔径大小后，在三组实验中均未发现10根蒸发管的平行流蒸发器具有较均匀的温度场，根据10根蒸发管的测量数据分析并调整8根蒸发管的模拟孔径大小，实验结果测得8根蒸发管的温度场较均匀。 5.平行流蒸发器集管与蒸发管处的孔径较小，使得孔径处制冷剂产生节流，并且制冷剂液体在平行蒸发管内的节流降温与气体吸热升温的差值相差不大，使得蒸发器的蒸发温度维持在稳定状态，温度场较好。 6.在相同的工况下，平行流蒸发器模拟值的降温速率高于实验值的降温速率，在初始降温阶段，两曲线降温的吻合度较好，都呈现出竖直下降的趋势，在下降到6℃左右时，实验温度曲线下降速度放缓，模拟温度曲线的降温速率不变，并且模拟温度值在100s后达到稳定状态。由于制冷系统和外界因素的影响，实验温度值的整体下降趋势较缓慢，在800s后稳定并和模拟温度值吻合。
[Abstract]:The parallel flow evaporator has attracted wide attention because of its good heat transfer properties. However, there are few parallel evaporators used at low temperature, and the temperature uniformity of the flow field is poor. In this paper, the numerical simulation method is used. The pore size of 8 parallel evaporative tubes with 0.4cm inner diameter of 10 tubes under the same charge of R134a refrigerant has been studied, and the pore size of the refrigerant in parallel evaporative tubes with constant pore size has been studied. The change of temperature field after adjusting the inlet refrigerant flow rate and the tube spacing of the parallel evaporator tube, and the change of the temperature field after adjusting the tube spacing of the parallel evaporative tube, at the same time, The temperature field of the serpentine tube evaporator with equal refrigerant charge was compared. In the experiment, the size of the pore diameter obtained by the simulation was verified by processing the parallel flow evaporator. 1. When the inlet velocity of parallel evaporator is V=0.01m/s, the quantity of refrigerant in the evaporator near the inlet of parallel evaporator is larger, and when the inlet velocity of evaporator is V=0.1m/s, the refrigerant quantity in the evaporator pipe which is closer to the inlet of parallel evaporator is smaller. 2. When the number of tubes in parallel evaporator is 8, and the inlet velocity is V=0.04m/s, the cooling curve of parallel evaporator in 5cm is scattered in the cooling stage. The temperature change of the parallel evaporator tube at 3cm is smaller than that between the eight evaporator tubes. 3. When the inlet velocity is V=0.04m/s, the cooling rate of the serpentine tube evaporator and the parallel flow evaporator is similar. When the system is stabilized, the temperature difference between the serpentine tube evaporator and the parallel flow evaporator is larger because of the effect of pressure drop. The temperature of serpentine tube evaporator is lower and lower with the flow of refrigerant. 4. According to the size of simulated aperture and the appropriate adjustment of aperture size according to experimental data, the temperature field of parallel flow evaporator of 10 evaporators has not been found in three groups of experiments. According to the measured data of 10 evaporative tubes, the simulated aperture of 8 evaporators is analyzed and adjusted. The experimental results show that the temperature field of 8 evaporators is uniform. 5. The aperture of the collector tube and the evaporation tube of parallel flow evaporator is small, which makes the refrigerant throttling at the aperture, and the difference between the throttling cooling of refrigerant liquid in parallel evaporator tube and gas endothermic heating is not obvious. The evaporation temperature of evaporator is maintained in a stable state, and the temperature field is better. 6. Under the same working condition, the cooling rate of the simulated value of parallel flow evaporator is higher than that of the experimental value. In the initial cooling stage, the coincidence between the two curves is good, and both curves show a vertical downward trend, and when the temperature drops to about 6 鈩

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