基于蒙特卡罗法的平行流冷凝器的翅片参数优化

运用蒙特卡洛法,在家用空调运行工况下,对平行流冷凝器空气侧的传热和流动性能进行了优化计算,分析了翅片的各种几何参数组合对换热系数和压力损失的影响.得出了影响换热系数的主要因素是翅片高度和百叶窗长度,同时增大两者既可以快速增大换热系数又可以降低压力损失;影响压力损失的主要因素是翅片宽度,因为翅片宽度的微减能带来压力损失的大大将低,但换热系数不受翅片宽度的影响;并同时得出影响换热系数和压力损失的次要影响因素是翅片间距和百叶窗角度.翅片间距减少、百叶窗角度增大均会引起换热系数与压力损失的增大.用这种优化方法得出的结论进行翅片参数组合的平行流冷凝器,可以在满足压力损失需要的情况下大大提高其换热性能.     

平行流冷凝器百叶窗翅片结构优化

建立平行流冷凝器百叶窗翅片的三维流动和换热模型,并对不同迎面风速下百叶窗翅片的流动和换热性能进行数值模拟,计算结果与试验结果具有较好的一致性,验证计算模型和方法的正确性。在此基础上,建立8种结构形式的百叶窗翅片模型,并对其空气侧的换热和流动过程进行仿真,分析结构形式和排列方式对百叶窗翅片换热量和空气阻力的影响,结果表明:增加开窗区域数能够有效提高翅片的换热性能,增加百叶窗的转向区数目能够有效降低进出口的压降。     

空气侧结构对多元微通道平行流冷凝器传热流动性能的影响

建立了多元微通道平行流冷凝器的稳态分布参数模型,与实验对比验证了模型的正确性。利用所建立的模型,研究了翅片高度、翅片间距、百叶窗开窗间距、百叶窗开窗角度变化对多元微通道平行流冷凝器传热和流动性能的影响。结果表明,随着翅片高度的增大,换热量逐渐增大,空气侧压降逐渐减小;随着翅片间距或者百叶窗开窗间距的增大,换热量和空气侧压降都是逐渐减小;随着百叶窗开窗角度的增大,换热量和空气侧压降都是逐渐增大。     

翅片结构参数显著性影响分析及最优化

建立百叶窗式热交换器空气侧三维稳态对流换热数学模型,对不同几何特征参数的百叶窗式翅片进行了流动和换热数值模拟,采用j因子、f因子和JF因子分别对传热效率、流动性能以及综合性能进行评价。研究发现,百叶窗翅片的几何特征参数中百叶窗角度θ、百叶窗间距Lp、翅片间距Fp、翅片厚度δ、对流动换热性能影响程度较大,选取这四个因素进行正交试验,得出翅片的最优结构参数。最优模型与基础模型相比,f因子降低了7.7%,j因子的值增幅为11.3%,JF综合评价因子的值增幅达到14.1%,表明优化后的翅片结构可以在压损增加较小的前提下有效的提升换热性能。     

平行流蒸发器冷凝水排除问题研究

平行流换热器因其结构紧凑、换热效率高,被当作冷凝器广泛地应用于汽车空调系统。近年来,又作为蒸发器被应用于家用空调器。但是,平行流蒸发器的冷凝水排除问题限制了其在家用空调器的应用发展和普及。本文针对家用空调器用的平行流蒸发器的冷凝水排除问题进行综合性评述,系统讨论蒸发器材料表面特性、蒸发器布置及导流、蒸发器内通道均流等因素对冷凝水排除的影响。     

翅片管式蒸发器的计算机辅助设计

拟合了制冷剂(R22、R134a和R407C)热力性质的公式,并以这三种制冷剂为工质,选择平直翅片、波纹翅片、开缝翅片和百叶窗翅片,采用稳态集中参数模型,用VB语言编制翅片管式蒸发器的计算机设计程序。在程序的编制过程中,还采用了模块化开发技术,避免公式的反复使用和繁琐的迭代计算而造成的错误,以提高计算效率和准确性。软件主要的计算结果包括热流密度、换热系数、压降等基本量,还包括蒸发器尺寸以及蒸发器的耗材。本软件的界面可视化较好,功能比较齐全,精确度满足空冷式蒸发器工程设计的要求。最后算例验证了程序的可靠性。     

百叶窗波纹翅片换热器的积灰试验研究

对百叶窗波纹翅片换热器在有灰尘的环境中加速积灰过程进行试验研究,对比5种结构参数的百叶窗波纹翅片的积灰层对风速和换热能力等参数的影响。研究结果表明,翅片密度越大,风速和换热量衰减越快。     

电动汽车热泵空调冷凝器空气侧性能模拟与结构优化

电动汽车热泵空调是用于解决电动汽车冬季无法制热的问题,本文设计一种用于电动汽车热泵空调的新型平行流换热器。通过对换热器的冷凝工况进行数值模拟,得到不同入口速度条件下的换热及阻力特性,并与经验公式进行比较,验证数值模拟的正确性。分析不同的翅片倾斜角度及翅片间距下换热及阻力特性变化,得到优化的结构参数,为电动汽车热泵空调换热器设计提供依据。     

家用空调器中平行流冷凝器翅片参数对空气侧传热流动性能的影响

为了推广平行流冷凝器在家用空调器中的应用,根据经验传热及压降关联式,采用数值模拟的方法,研究家用空调器中平行流冷凝器翅片参数对其空气侧传热流动性能的影响规律.结果表明:适当减小平行流冷凝器的翅片高度和翅片间距,可提高其换热系数、增加压降,保证其换热性能变化较小.     

管带式水冷散热器的换热性能研究

本文对管带式水冷散热器的换热性能进行数值模拟研究并通过实验进行验证,以求提高换热器换热性能。建立模型分别从管带式百叶窗、扁管翅片单元进行全面的性能分析。其中对管带式散热器百叶窗的开窗角度进行了分析,结果表明:管带式散热器的百叶窗开角在23°~27°之间的散热效果最佳,提出并通过数值模拟验证了一种优化翅片结构的方案,与传统结构对比,散热效果有明显提高。搭建实验台并设计正交试验,研究了不同因素对散热器整体散热效果的影响程度。在本实验研究的范围下,通过多组实验数据分析得出,进口水温、循环水流量、风扇转速3种因素对散热器散热量的影响程度为:进口水温>循环水流量>风扇转速。     

多联式空调换热器自动清洁功能研究

为研究空调的除尘和杀菌能力,使空调提供品质优良的空气,本文设计了基于变制冷剂流量型多联式空调系统换热器的自动清洁功能。首先通过换热器产生凝结水实现室内机除尘清洗,然后通过换热器产生高温实现室内机杀菌。通过选用空调中常见的翅片管式换热器,以室内机的凝结水量和盘管表面温度为指标,实验分析了室内风机转速、压缩机频率、室外温度、运行时长等对换热器除尘和杀菌能力的影响。结果表明:在除尘阶段,随着室内风机转速的增加,凝结水量先增加后降低,在相同的条件下运行20 min,室内风机转速为350 r/min时凝结水量达到最优值186 g,可以达到最优的清洁效果,增加运行时长、提高压缩机运行频率可提高凝结水量;在杀菌阶段,降低室内风机转速可提高换热器的盘管温度,转速为200 r/min时盘管温度达58.6℃,提高室外温度有利于提升杀菌阶段的盘管温度,但会降低除尘阶段的凝结水量。     

分流板开孔面积对微通道平行流蒸发器性能的影响

采用数值模拟与实验研究相结合的方法,以R134a为工质,研究了微通道平行流蒸发器内入口处分流板的开孔面积变化时,对蒸发器的流动和换热性能的影响。结果表明:随着分流板上的开孔孔径增大,蒸发器内的流动阻力会降低,制冷剂流量分配的均匀性变差,而制冷量却先增加后减小。分流板的开孔孔径存在一个最佳值,此时蒸发器内的阻力损失低,制冷剂的流量分配均匀性好,两者的匹配性最好,使得蒸发器的制冷量达到最大。此蒸发器中入口分流板的最佳开孔面积约为150.7 mm2。     

Quick and empirical correlations for refrigerant pressure drop in mobile air conditioning system evaporators

In heat exchanger design and simulation, a precise refrigerant pressure drop prediction is difficult because of limited correlation's accuracy. In the present paper, several quick and accurate empirical correlations for refrigerant pressure drop of the typical evaporators (laminated plate evaporator and minichannel parallel flow (MCPF) evaporator) used in mobile air conditioning (MAC) system were proposed. A factor which was related with the refrigerant mass flow rate, thermodynamic properties and refrigerant status was introduced. The types of evaporator and refrigerant were considered in the correlations which were available under typical MAC evaporator application conditions. The analysis results showed the refrigerant pressure drops were implied in a linear relationship with the proposed factor. The predicted data agreed with the experimental data very well. For laminated palate evaporators, the average deviations were 1.8% and 0.7% for R134a and R1234yf, respectively. For MCPF evaporator, the average deviations were 4.5% and 0.6% for R134a and R1234yf, respectively.     

以R407C为工质的翅片式蒸发器结霜过程模拟

翅片式蒸发器的结霜特性对于空气热源热泵的冬季运行十分关键。随着 对HCFCs替代的展开,一些非共沸制冷剂被建议为替代品。同现在使用的纯工质相比,这些非共沸制冷剂的温度滑移使和沿流动方向制冷剂的温度分布更加不均匀。在本文中,作者建立了翅片式蒸发器的分布参数模型,用以模拟结霜过程。传热与流动被认为是准稳态的。文中探讨了数值算法,并以某蒸发器为例进行了模拟。计算表明,结霜过程中空气量的改变明显,整个结霜过程存在一转折点,经过这点后流量急剧下降。R407C在蒸发过程中的温度滑移对霜层在蒸发器上的分布有重要影响。     

风速对不同流程数CO2蒸发器性能的影响

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。     

A hybrid method for refrigerant flow balancing in multi-circuit evaporators: Upstream versus downstream flow control

A hybrid method for optimizing refrigerant distribution in evaporators is presented that involves the use of small balancing valves in each circuit along with a primary expansion device to control the overall superheat from the evaporator. The flow balancing valves could be located upstream or downstream of the evaporator. This paper presents the results of a study to investigate the benefits of this hybrid scheme for both upstream and downstream flow balancing for the case of air flow mal-distribution. In order to perform this investigation, a simulation model was developed to consider evaporator flow mal-distributions for a 10.55 kW residential R410A heat pump and then validated through comparisons of predicted results with measurements. Simulation results show that there are significant benefits in controlling the superheat of each circuit of evaporators through the hybrid–individual superheat control method. Furthermore, the upstream refrigerant flow control consistently outperforms the downstream refrigerant flow control, and recovers most of the loss in cooling capacity and COP due to non-uniform air flow distribution.     

New approach to improve performance by venting periodic reverse vapor flow in microchannel evaporator

This paper presents a proposal for a venting reverse vapor in flash gas removal A/C system in order to improve refrigerant distribution and reduce pressure drop in microchannel evaporator and thus increase system efficiency. Introduction to the reverse vapor flow observed in parallel flow microchannel evaporator was presented in earlier IJR paper by the authors. An experimental comparison of the A/C system with new approach to an FGB system revealed that vapor venting provided a 5% increase of cooling capacity and 3% of COP when operated at identical test conditions, while the maximum COP improvement was approximately 10%–12% when capacity is matched by reduction of compressor speed. The improvement compared to direct expansion system was significantly higher.     

Modeling and experimental evaluation of an automotive air conditioning system with a variable capacity compressor

A steady state computer simulation model has been developed for refrigeration circuits of automobile air conditioning systems. The simulation model includes a variable capacity compressor and a thermostatic expansion valve in addition to the evaporator and micro channel parallel flow condenser. An experimental bench made up of original components from the air conditioning system of a compact passenger vehicle has been developed in order to check results from the model. The refrigeration circuit was equipped with a variable capacity compressor run by an electric motor controlled by a frequency converter. Effects on system performance of such operational parameters as compressor speed, return air in the evaporator and condensing air temperatures have been experimentally evaluated and simulated by means of developed model. Model results deviate from the experimentally obtained within a 20% range though most of them are within a 10% range. Effects of the refrigerant inventory have also been experimentally evaluated with results showing no effects on system performance over a wide range of refrigerant charges.     

气体导流装置对微通道蒸发器性能的影响

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。     

R290微通道冷凝器性能优化及其充注量分析

采用仿真方法,以R290家用空调器用微通道冷凝器为研究对象,比较不同流路布置方案对冷凝器性能的影响,并对外形尺寸相同的微通道冷凝器与翅片管冷凝器充注比进行对比。结果表明：流程布置及各流程扁管分配对微通道冷凝器性能有较大影响,存在较优的流程数及流程扁管数;R290微通道冷凝器充注比与Ф5mm单排冷凝器充注比水平相当,经进一步结构优化后,微通道冷凝器将比小管径换热器在降低冷凝器充注比和材料成本方面具有更大的潜力和优势。