共查询到18条相似文献,搜索用时 140 毫秒
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运用分布参数法建立采用CO2的翅片管式蒸发器的数学模型,分析制冷剂侧和空气侧温度、压力和换热的变化情况。同时讨论迎面风速和制冷剂质量流量对蒸发器换热和流动性能的影响,结果表明提高迎面风速可以增加换热效果,但增加的趋势趋于平缓。制冷剂侧压降则成近似线性增大;随着管内工质流量的增大,蒸发器总换热量和制冷荆侧压降都成近似线性增大。这些工作有助于进一步了解CO2在翅片管式蒸发器中的换热和流动特性,并为换热器的优化设计和系统的匹配提供理论依据。 相似文献
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针对微通道蒸发器制冷剂流量分配不均匀造成的换热性能恶化和干蒸现象,本文搭建了双流程微通道蒸发器性能测试实验台,研究导气装置对蒸发器换热性能及扁管中制冷剂分配均匀性的影响,并与常规的双流程微通道蒸发器进行对比。结果表明:由于入口制冷剂流量不变,液相制冷剂蒸发为气体的最大相变潜热不变,导致二者换热量和传热系数差值较小,最大值仅相差0.5%和6.9%。但加导气装置后流动阻力降低,两相段长度较常规结构增幅为87.3%,过热度显著降低,风速为3 m/s时两种结构的过热度降幅为44.4%。各扁管间制冷剂分布趋于一致,均匀性得到提升,干蒸现象得到缓解。 相似文献
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《制冷》2020,(1)
针对微通道蒸发器结霜问题,设计了具有相同换热面积的单层和双层微通道蒸发器。基于制冷剂分布平定参数(RDP)分析了不同结构微通道蒸发器制冷剂分布对结霜的影响,并对比分析了单、双层微通道蒸发器在结霜工况下的换热性能。研究表明:单层蒸发器RDP高于双层蒸发器,结霜30min时,双层蒸发器结霜量高于单层蒸发器1.1倍,随着结霜时间的增长,蒸发器制冷剂压损逐渐降低,空气侧阻力逐渐升高。单层蒸发器和双层蒸发器的换热量分别减少56.4%、72%,制冷剂压损分别下降26.5%、53.05%,空气阻力分别增大30.08%、51.55%,结霜对双层蒸发器出风温度均匀性影响更大。单层结构的微通道蒸发器比双层结构更适用于结霜工况。 相似文献
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微通道蒸发器内制冷剂流量分配均匀性对换热器性能有着较大影响。本文在理想工况运行情况前提下,以水为流动工质,数值模拟了微通道蒸发器内流量分配特性,探讨了4种集流管形式(A型、B型、C型、D型)、不同入口速度(0.08 m/s~0.42 m/s)对换热器各扁管流量分配的影响。研究结果表明,集流管入口流速对换热器内各扁管流量分配具有较大影响,当速度从0.08 m/s增大到0.42 m/s时,换热器内流量分布从两侧高,中间低的分布转变为入口侧低,出口侧高的分布特性,且流量分配不均匀度随流速增加而显著增大;通过改变集流管结构能够在一定程度上改善流量分配特性。各扁管进口静压力分布与各扁管内流量分配具有相关性,可通过改进集流管结构保证静压力分布一致,使各扁管流量分配均匀,从而获得较好的换热性能。 相似文献
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《制冷与空调(北京)》2018,(12)
在相同的芯体尺寸下,试验研究微通道平行流蒸发器流程结构和扁管改变对制冷剂流动及换热性能的影响。当蒸发器芯体由2流程改为4流程时,试验结果表明制冷能力降低2.1%~4.1%,制冷剂压力损失增加7.8%,空气侧阻力减小2.9%~3.8%,芯体出风侧温度均匀性有明显改善。此外,在4流程基础上,当扁管高度由1.4 mm改为1.8 mm时,芯体每流程的流通面积增大65.1%,制冷能力提高6.9%~11.3%,制冷剂压力损失降低27.8%,空气侧阻力增大8.4%~10.1%,芯体出风侧温度均匀性与之前相当。 相似文献
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为研究迎面风速对不同流路数CO2翅片管蒸发器性能的影响,本文建立分布参数模型对蒸发温度为-25℃,风速为0.5~4 m/s条件下5种流路数CO2翅片管蒸发器的制冷剂压降、换热量、温度分布及传热系数的变化进行分析,并通过实验验证了蒸发器模型的可靠性。蒸发器模型的换热量、制冷剂压降和风侧压降等参数模拟值与相同工况下实验值的误差均在±4%以内。结果表明:同一流路数蒸发器的换热量、制冷剂压降及传热系数均随风速的增大而增大,而其涨幅随风速增大而减小,综合考虑换热效果和能耗可得最佳风速范围为2.5~3.5 m/s;在一定风速条件下,蒸发器设计时在合理范围内选择较多流路数可有效提升蒸发器换热性能并增强换热均匀性,本次实验中24流路蒸发器为最佳设计方案。 相似文献
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Effect of refrigerant flow direction and throttle opening in RAC unit using micro-channel evaporator
Experimental comparisons are made on the performance of a room air conditioner using micro-channel evaporator with the refrigerant flowing in the Upward Flow mode (UF mode, meaning refrigerant flowing upward from the bottom) and Downward Flow mode (DF mode, meaning refrigerant flowing downward from the top). Test results show that UF mode develops a superior refrigerant distribution in the micro-channels to what DF mode does. This is then illustrated by the infrared thermographs at the nominal operating condition. Subsequently, the effect of the width of throttle opening on the sample unit performance is investigated experimentally in the micro-channel evaporator adopting the UF mode. Measurement and calculation results of pressure difference between evaporator inlet and outlet, mean temperature of the evaporator surface, cooling capacity, input power and EER show that the tested unit operates with the best performance with the refrigerant pressure of 993.61 kPa at the inlet of micro-channel evaporator. Infrared thermographs of the working evaporator verify this conclusion. 相似文献
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A micro-channel separate heat pipe (MCSHP) as a cooling device for telecommunication stations (TSs) was experimentally investigated in this work. A steady-state mathematical model was built and validated with experimental data. The cooling capacity, inlet and outlet of refrigerant temperatures and refrigerant pressure of evaporator section were measured in an enthalpy difference laboratory (EDL). The average relative errors between simulation and experiment were less than 10%. The effects of geometrical design and environment conditions on thermal performance were analyzed using the validated model. As a result of the simulations, the refrigerant side pressure drop decreased by 96.61% at the flat tube height 3.0 mm compared to 1.4 mm. And the air side pressure drop decreased by 94.49%, when fin height ranged from 4 mm to 20 mm. The cooling capacity increased by 50.65% at the fin pitch 3.0 mm compared to 1.0 mm. These factors were of practical engineering importance in optimum design of MCSHP. 相似文献
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In this paper, a distributed parameter (DP) numerical model with the new proposed flow boiling heat transfer correlation was established for parallel flow minichannel (PFMC) evaporator. DP model validation was made by comparing the measured values obtained on experimental studies, which were conducted under refrigerant mass flow rate range of 34.6–245.6 kg h−1 and evaporation pressure of 200–500 kPa. The effects of four different flow boiling heat transfer correlations on DP model performance were investigated. Results showed that the new correlation predicted 99% of experimental data in ± 30% error bands. Moreover, the DP model with the new correlation yielded the mean absolute error (MAE) of 1.5%, 9.1%, 18.8%, 14.2% and 19.8% in prediction of cooling capacity, outlet air temperature, refrigerant superheat, air side and refrigerant side pressure drop, respectively. The presented DP model can be implemented to evaluate the performance of PFMC evaporator, and therefore can save efforts on component and system design and optimization. 相似文献
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本文建立了CO_2微通道气冷器集流管和微通道扁管两部分的物理模型并进行网格划分,模拟研究了扁管插入集流管深度f分别为4、5、6 mm和入口管在集流管1/6、1/2位置处对质量流量分配的影响,实验验证了CO_2微通道气冷器扁管壁面温度分布。结果表明:当f为4 mm、入口管位于集流管1/6处时,质量流量分配最均匀,此时不均匀度为0.4×10~(-3);模拟扁管内CO_2换热特性发现随着CO_2质量流量的增加,扁管换热量增加,流量由2.3 kg/h增至2.5 kg/h,换热量提高了21.4%;当质量流量一定时,CO_2的出口温度随着CO_2入口温度的升高而升高,在不同CO_2入口温度条件下,微通道扁管壁面温度实验值与模拟值误差在10%以内,验证了模拟的准确性。 相似文献
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Deniz Seker Hakan Karatas Nilufer Egrican 《International Journal of Refrigeration》2004,27(4):367-374
In this study, the heat and mass transfer characteristics of heat exchangers during frost formation process are analyzed numerically. Unsteady heat and mass transfer coefficients of the air side, heat transfer coefficient of the refrigerant side, air-frost layer interface temperature, the surface efficiency of the heat exchanger and the mass flow rate of the frost accumulated on the heat exchanger surface are calculated. The total conductivity (UA) and pressure drop of the heat exchanger are reported for different air inlet temperature, relative humidity, air mass flow rate and the refrigerant temperature. 相似文献
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Simulation analyses for a vapour compression heat pump cycle using nonazeotropic refrigerant mixtures (NARMs) of R22 and R114 are conducted under the condition that the heat pump thermal output and the flow rate and inlet temperatures of the heat sink and source water are given. The heat transfer coefficients of the condensation and evaporation are calculated with empirical correlations proposed by the authors. The validity of the evaluation method and the correlations is demonstrated by comparison with experimental data. The relations between the coefficient of performance (COP) and composition are shown under two conditions: (1) the constant heat transfer length of the condenser and evaporator; and (2) the constant temperature of refrigerant at the heat exchanger inlet. The COP of the NARMs is higher than that of pure refrigerant when the heat transfer lengths of the condenser and evaporator are sufficiently long. 相似文献