Numerical Modelling of Performance of R22 and R290 in Adiabatic Capillary Tubes Considering Metastable Two-Phase Region ——Theoretical Model Description and Validation

A homogeneous theoretical model is developed to predict the performance of R22 and R290 in adiabatic capillary tubes. The model is based on conservation equations of mass, momentum and energy. Metastable both liquid and two-phase flow regions are considered in the model. In metastable two-phase region, superheated liquid is introduced into the metastable mixture viscosity and two methods are presented to evaluate it. The model is validated by comparing the predicted pressure and temperature profile and mass flow rate with several investigators′ experimental data of R22 and one of its alternatives R290 reported in literature. All of the predicted mass flow rates are within ±800 of measured values. Comparisons are also made between the present model and other investigators′ models or sizing correlation. The model can be used for design or simulation calculation of adiabatic capillary tubes.

Numerical Modeling of the Performance of R22 and R290 in Adiabatic Capillary Tubes Considering Metastable Two-Phase Region——Flow Characteristics and Parametric Analysis of R22 and R290

Characteristics of R22 and its new alternative refrigerant R200 flowing through adiabatic capillary tubes are investigated based on the homogeneous model. Extensive flow variables along tube length such as pressure, temperature, viscosity, velocity. Reynolds number, friction factor and vapor quality etc are compared between the two fluids under the same operating condition. Two cases are considered, namely, either the same tube length or the same mass flow rate as inlet condition. The results show that the mass flow rate in the capillary tube of R290 is 40% lower than that of R22 due to the differences of physical properties between the two fluids. Further. a parametric analysis is performed and it appears that effects of geometric and thermodynamic parameters on mass flow rate of R290 are weaker than that of R22. When the condensing temperature is increased from 40℃ to 50℃ C. the mass flow rate for R22 is increased by 16%. while the increasing rate for R290 is 13%.

Performance Investigation of Capillary Tubes for Machine Tool Coolers Retrofitted with HFC-407C Refrigerant

The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC （hydro-chloro-floro-carbon） refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC （hydro-floro-carbon） refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.

Fractal model of spontaneous imbibition in low-permeability reservoirs coupled with heterogeneity of pore seepage channels and threshold pressure

Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability reservoirs is extremely challenging.Commonly,traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure(TP)on imbibition.Therefore,in this work,based on capillary model and fractal theory,a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established.On this basis,the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil.The proposed new SI model was verified by imbibition experimental data.The study shows that for weakly heterogeneous cores with permeability of 0-1 m D,the traditional SI model can characterize the imbibition process relatively accurately,and the new imbibition model can increase the coefficient of determination by 1.05 times.However,traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10-50 m D.The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem,and the determination coefficient is increased from 0.344 to 0.922,which is increased by2.68 times.For low-permeability reservoirs,the production of the oil in transitional pores(0.01-0.1μm)and mesopores(0.1-1μm)significantly affects the imbibition recovery,as the research shows that when the heterogeneity of pore seepage channels is ignored,the oil recovery in transitional pores and mesopores decreases by 7.54%and 4.26%,respectively.Sensitivity analysis shows that increasing interfacial tension,decreasing contact angle,oil-water viscosity ratio and threshold pressure will increase imbibition recovery.In addition,there are critical values for the influence of these factors on the imbibition recovery,which provides theoretical support for surfactant optimization.

An approximate analytic model for flow through capillary tubes

An analytic model for working fluids flowing through capillary tubes has been established with the approximate integral method. All the possible flow regimes in the capillary tubes,including subcooled, two-phase and superheated regimes, are covered in the model, and different analytic solutions are given respectively for each flow regime. As examples, the mass flow rates of refrigerants R12, R134a and R600a through capillary tubes are predicted by the model,and compared with those evaluated by a general distributed-parameter model. The mean bias falls into 1% and the maximum bias is 2.2%, while the computation speed of the new model is more than one order of magnitude higher than that of the distributed-parameter one.

冰箱系统用铝毛细管加工工艺及性能研究

从铝毛细管的加工工艺、产品性能和应用的难点与措施三方面,探讨了在冰箱制冷系统中铝毛细管替代铜毛细管的可行性。试验结果表明,铝毛细管在成型加工方面具有可行性,力学性能、耐压性能、防腐性能和弯曲性能均能满足回气管组件的使用需求。相比于铜毛细管,使用铝毛细管的圆管铝回气管组件的冰箱日平均耗电量升高10.20%;使用铝毛细管的凹槽铝回气管组件的冰箱日平均耗电量升高1.113%。

Theoretical model for removal of volatile organic compound (VOC) air pollutant in trickling biofilter

This paper presents an analytical model for predicting VOC waste gas degradation in a trickling biofilter. To facilitate the analysis, the packed bed is simplified into a series of straight capillary tubes covered by the biofilm. The gas-liquid flow field through the tube is divided into the liquid film flow on the biofilm and the gas core flow in the center. The biofilm consists of a reaction free zone close to solid wall and a reaction zone beneath the liquid film. The capillary tube model accounts for the effect of mass transport resistance in the liquid film and the biofilm, the gas-liquid interfacial mass transport resistance, the biochemical reaction, and the limitation of oxygen to biochemical reaction. The liquid film thickness in the capillary tube is obtained by simultaneously solving a set of hydrodynamic equations representing the momentum transport behaviors of the gas-liquid two-phase flow. The mass transport equations are established for gas core, liquid film, and biofilm combined with biochemical kinetics equations. An iterative computation process is employed to solve the discrete equations. The predicted purification efficiencies of VOC waste gas in trickling biofilter are found to be in good agreement with the experimental data. It has been revealed that for a fixed inlet concentration of toluene, the purification efficiency of trickling biofilter decreases with the increase in gas flow rate and liquid flow rate. The purification efficiency of VOC waste gas is dominated by mass transport resistance in liquid film and biofilm. The highest biodegradation rate occurs at the inlet of waste gas in trickling biofilter.

混合式制冷制热系统控制方法研究

混合式制冷制热系统的控制难点在于如何合理切换冷热源。采用改进的DBN网络进行短期、中期和长期冷热负荷预测,并通过实测数据验证了模型的准确性。在负荷预测的基础上采用健康评估技术,对地源热泵的短期、中期和长期健康状态进行评估,并根据评估结果进行相应控制,从而实现长期稳定高效运行。最后,对比了两种不同控制方法的运行情况,采用新控制方法后,主机性能系数提高8.5%。结论验证,基于健康评估技术的控制方法有利于混合式系统的高效运行。

绝热毛细管性能模拟的平均参数模型

根据分区集中和参数平均的思想，建立了一种简单、精度和通用性良好的绝热毛细管流动模型．出于系统动态仿真的需要，模型中考虑了过热流动和壅塞流动．基于Ｒ１２的分布参数模型计算结果，提出了不同流动区域内参数平均的一个关联式．该关联式对制冷剂Ｒ１３４ａ和Ｒ６００ａ也取得了与Ｒ１２相仿的效果，表明该关联式具有良好的通用性．对Ｒ１２、Ｒ１３４ａ和Ｒ６００ａ在毛细管内的流动特性进行了模拟计算．结果表明。

毛细管的通用积分模型

It is necessary to establish a simple and accurate mathematical model of capillary tubesfor the study of the system performance of refrigeration appliances equipped with the capillary tube. In this work, a new general integral model of capillajry tubes has been presented. It covers subcooled, two--phase and superheated flow regions which may occur inthe capillary tube. In the different flow region, special approximate integral equation is developed. This model is used in prediction of mass flow rate of the refrigerants, R12, R134aand R600a flowing through the capillary tube. The results are compared with those of thedistribut ed-- p aramet er mo del. The average devtat ion is 1. 3 0 % and t he maximum deviationis +4.58/-6.39%. The computation speed of the recommended model is more than one orderof magnitude higher than that of the distributed-parameter one.

空调器毛细管与充液量匹配的理论与试验研究

用理论分析的方法计算了空调器毛细管长度，并进行了试验研究，理论计算与试验结果比较吻合，表明其计算方法是可行的。同时，为了研究毛细管与制冷剂充注量的相互影响，又对不同毛细管长度及制冷剂充注量的匹配进行了试验研究。试验结果表明：毛细管长度及系统氟里昂充注量对空调器的制冷量、性能系数（αＣＯＰ）均有较大的影响，且二者存在最佳匹配，使得空调器的制冷量及αＣＯＰ均达到最大；制冷剂充注量过多时空调器性能下降较多，说明充注量过多更具危害性。试验结果已用于生产实际。

毛细管内制冷剂的综合成核理论与模型

对毛细管内制冷剂的闪蒸机理提出“综合成核”理论 ,从该理论出发 ,建立了毛细管内制冷剂流动的数学模型 ,包括气泡密度模型、气泡成长模型和毛细管内制冷剂闪蒸流动数学模型 .计算出管内制冷剂闪蒸流动过程中的压力、温度、气泡密度、干度和空泡份额的分布 ,并对计算结果进行了理论分析 .结果表明 :在实际闪蒸的流动过程中 ,由于液体的过热度较小 ,壁面成核是气泡产生的最主要原因 .

跨临界制冷循环中二氧化碳在毛细管内的流动仿真

根据跨临界制冷循环中二氧化碳在毛细管内流动过程中的状态变化,毛细管划分为超临界气体区、液体区和两相区。针对各分区建立均相数学模型并进行模拟计算。研究结果表明:毛细管内的流动主要是超临界气体区和液体区的流动,两相区的长度短,而且两相区中制冷剂的干度增加快;随着入口温度的升高,超临界气相区长度逐渐增加,而液相区长度缩短,直至接近于0 m,而两相区的长度虽然有一个先增加后缩短的变化过程,但变化幅度小,几乎不变;当其他参数固定时,毛细管总长度随入口压力成比例增长,而与入口温度成反比例增长;此外,当内径或质量流量改变时,毛细管长度变化明显。

制冷剂充注量与毛细管长度对家用空调性能的影响

通过试验的方法研究了空调器制冷剂充注量与毛细管长度对制冷系统的影响,得出了相应的试验曲线,找出最佳匹配结果,并根据试验结果分析毛细管长度与制冷剂充注量影响空调性能的规律。

毛细管内两相流的通用积分模型

毛细管是制冷空调装置中常用的节流元件之一.毛细管的流动特性对装置的系统性能影响显著,因此,建立一个好的毛细管模型对于装置的设计和优化都是必要的.尤其是近年来,CFCs环保问题的影响,推动了毛细管研究从理论和实验两方面向着工质替代的方向发展.从文献中的毛细管模型来看,早期的模型受计算工具等条件的限制,大都比较简单,精度也不高;近年来,这些限制不再存在,研究者趋向于采用分布参数模型以提高预测精度.但是,分布参数模型在计算速度和计算的健壮性方面尚有欠缺,不适用于实用型的系统仿真和优化.因此,建立简单、准确、通用的毛细管模型,具有重要的理论和应用价值.

混合工质在制冷机节流元件毛细管中的流动特性

可用于天然气液化的深冷多元混合工质节流制冷技术由于其固有的优点以及其制冷温区跨度大的特点 ,近年来得到了前所未有的重视和发展。随着这项技术的不断成熟 ,对混合工质在深冷制冷机节流元件内的流动特性的研究也显得日益重要。纵观现有的众多节流毛细管的研究文献 ,内容主要涉及普冷工质的流动特性 ,而且其中大多采用的是均相模型。而深冷多元混合工质由于其本身的特点 ,与普冷工质有着很大的不同。为此 ,文章旨在研究混合工质在毛细管内的流量特性 ,尝试使用了分相流动模型来计算深冷多元混合工质在绝热毛细管中的流量特性 ,建立了深冷混合制冷剂在毛细管中流动的控制方程 ,并依此编制了计算程序 ;同时搭建了深冷混合工质在绝热毛细管中流动特性实验台 ,进行了深冷多元混合工质在绝热毛细管中的流动特性实验研究。理论计算结果与实验结果符合度较好 ,其偏差均在 10 %以内 ,基本满足了工程上的需要 ;

基于模型和神经网络的绝热毛细管快速仿真方法

为简化毛细管模型，采用分相集中参数方法，将平均比容的权重因子作为两相区简化的特征参数，用人工神经网络方法建立特征参数与其影响参数之间的非线性映射。神经网络的学习样本采用工质Ｒ１２，检验样本包括Ｒ１２、Ｒ２２、Ｒ１３４ａ和Ｒ６００ａ等多种工质。在常用制冷空调工况范围内，该简化模型与分布参数模型相比，平均偏差０３％，计算速度提高１个数量级。

制冷空调系统毛细管和压缩机流量匹配研究

对小型制冷系统毛细管和压缩机的匹配进行理论实验研究，分别建立毛细管和压缩机的流量模型，然后用实验值对压缩机模型进行修正，对Ｒ１２ ，Ｒ１３４ａ ，Ｒ１５２ａ 分别进行了计算和实验。

漂移流模型用于毛细管两相流数值计算

毛细管作为家用空调器、电冰箱的节流元件,因为不能随制冷系统负荷变化而调节流量,所以设计毛细管合理参数至关重要。今将整个毛细管内的流动分为过冷液体区和气液两相区两个过程,建立了毛细管内制冷剂两相流动的漂移流模型;这一模型考虑了各相平均速度之间的差异,克服了以往均相流动模型的缺点。进一步考虑两相间相对运动和空隙率及流速沿截面的分布规律,对毛细管长度进行了数值计算。编制了毛细管长度计算的应用程序,并将数值计算结果与文献中的实验数据进行了分析比较,其误差在工程设计的允许范围之内。

制冷热泵装置毛细管组件及其应用特性研究

研究一种新型结构的毛细管组件,可克服传统毛细管流量变化单一的缺点,并通过优化设计其结构,使其具有较灵活的流量变化特性.采用均相流模型,对普通毛细管与毛细管组件在变工况、变工作模式下的流量变化规律进行了对比计算.计算表明,毛细管组件可较好地满足制冷热泵装置流量变化的需求.建立R22制冷热泵实验装置,对毛细管组件的应用特性进行了实验研究.结果表明,在典型工况下,当制冷负荷和制热负荷不同时,毛细管组件能提供不同的制冷剂流量,与相应的冷热负荷相匹配.