毛细管的进出口状态参数对制冷剂流量的影响

本文建立了绝热毛细管的分布参数仿真模型,分析了毛细管内制冷剂的流动特性,得出了毛细管进口压力、进口过冷度和出口压力对制冷剂流量的影响情况.     

采用R134a和R600a制冷剂系统毛细管特性分析

建立毛细管模型并通过实验数据验证了模型,给出制冷剂的干度x、温度t、速度W、压力P沿毛细管长度的变化关系,研究了毛细管的内直径、长度、冷凝温度、过冷度等因素对毛细管内R134a、R600a两种制冷剂的质量流量的影响.     

采用R22、R134a两种制冷剂的毛细管特性对比研究

建立单相区和两相区毛细管模型,模型计算的毛细管质量流量与实验测量的质量流量差别小于(10%.研究了R134a代替R22后毛细管的质量流量随冷凝温度、过冷度、毛细管内直径和毛细管长度的变化规律,结果表明,两种制冷剂有相同的变化规律,但是在相同的条件下,R22的质量流量比R134a大,比如冷凝温度为45℃时,R22的质量流量比R134a高31.1%.     

相关技术用于毛细管内制冷剂流量的测量

提出一种采用相关技术测量毛细管内制冷剂流量的方法。制冷剂在毛细管内流动存在流动噪声，利用电容传感器测出反映流动噪声的两路随机相关信号，经相关分析，便可求出毛细管内制冷剂的流量。介绍测量原理、流动噪声的提取方法和电容检测电路，并且还建立了相关的理论计算模型。这一方法的实现将解决制冷装置中毛细管内流量测量的技术难题，为制冷系统中制冷量等有关参数的准确测量和系统的最佳匹配提供了可靠的依据。     

制冷装置毛细管数值计算方法研究

对毛细管模型进行简化,避免计算制冷剂物性,提出由制冷剂流量确定毛细管长度和已知毛细管长度确定制冷剂流量的数值方法,并用这2种方法分析影响毛细管特性的主要因素。将模拟结果与试验结果进行比较,发现模拟值高于试验值,相对误差在10％以内。该简化计算方法可应用于工程计算。     

相关技术有于毛细管内制冷剂流量的测量

提出一种采用相关技术测量毛细管内制冷剂流量的方法，制冷剂在毛细管内流动存在流动噪声，利用电容传感器测出反映流动噪声的两路随机相关信号，经相关分析，便可求出毛细管内制冷剂的流量。介绍测量原理，流动噪声的提取方法和电容检测电路，并且还建立了相关的理论计算模型。这一方法的实现将解决制冷装置中毛细管内流量测量的技术难题，为制冷系统中制冷量等有关参数的准确测量和系统的最佳匹配提供了可靠的依据。     

非绝热毛细管的数值计算和特性分析

针对非绝热毛细管内制冷剂的流动特性,建立了采用两相流动的漂移流动模型,并开发了非绝热毛细管数值计算程序.利用该模型和程序对非绝热毛细管内制冷剂的流动特性进行了数值计算和特性分析,得到了毛细管内制冷剂干度、空隙率和相对漂移流速3者在毛细管内流动特性上的关系.     

含油制冷剂流过毛细管的流动特性理论模型

本文提出了一个预测含油制冷剂流过绝热毛细管的流动特性的理论模型,将纯制冷剂流过毛细管时压力和温度分布的理论预测结果与实验数据进行了比较。并用该模型预测了含油制冷剂流过毛细管的性能。     

绝热毛细管两相流特性与实验研究

在对绝热毛细管内制冷剂的流动特性进行研究的过程中,运用两相流漂移模型,并考虑制冷剂在实际流动中存在的亚稳态,开发了绝热毛细管内制冷剂两相流的数值计算程序,对毛细管内制冷剂的流动特性进行了分析;搭建了毛细管两相流实验装置,并将计算结果与实验数据进行比较,结果吻合的较好。     

考虑亚稳态的绝热毛细管模型与计算

制冷剂在通过毛细管过程中,存在一个不稳定的亚稳态流动阶段.在考虑亚稳态现象的基础上,基于两相流动的漂移流模型,建立了绝热毛细管内制冷剂流动特性的数学模型.针对工质为R134a的制冷系统开发了绝热毛细管数值模拟程序,并对漂移流模型中的3个重要参数:空隙率、漂移速度和干度进行了计算和分析.该程序在制冷系统毛细管的匹配中具有一定实用价值.     

Experimentation and modeling of refrigerant flow through coiled capillary tubes

Air-conditioners use spirally coiled capillary tubes as an expansion device to enhance compactness of the unit. However, most empirical correlations for predicting refrigerant flow rate through capillary tubes were developed for straight capillary tubes without consideration of coiled effects. The objectives of this study are to investigate the flow characteristics of the coiled capillary tubes and to develop a generalized correlation for the mass flow rate through the coiled capillary tubes. The mass flow rate of R22 through the coiled capillary tubes and straight capillary tubes was measured for various operating conditions and tube geometries. The mass flow rates of the coiled capillary tubes decreased by 5–16% more than those of the straight capillary tubes at the same operating conditions. A generalized correlation for predicting refrigerant mass flow rate through coiled capillary tubes was developed by introducing the parameter of capillary equivalent length. The present correlation showed good predictions with the present database for R22, R407C and R410A in the straight and coiled capillary tubes, yielding average and standard deviations of 0.24% and 4.4%, respectively.     

Experimental investigation of the performance of R22, R407C and R410A in several capillary tubes for air-conditioners

The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.     

A generalized dimensionless local power-law correlation for refrigerant flow through adiabatic capillary tubes and short tube orifices

This paper presents a new method to obtain generalized dimensionless correlation of refrigerant mass flow rates through adiabatic capillary tubes and short tube orifices. The dimensionless Pi groups were derived from the homogeneous equilibrium model, which is available for different refrigerants entering adiabatic capillary tubes or short tube orifices as the subcooled liquid, two-phase mixture, or supercritical fluid. To mitigate the potential over-fitting risk in neural network, a new “local” power-law correlation reformed from the homogeneous equilibrium model was proposed and compared with the conventional “global” power-law correlation and recently developed neural network model. About 2000 sets of experimental mass flow rate data of R12, R22, R134a, R404A, R407C, R410A, R600a and CO₂ (R744) in the open literature covering capillary and short tube geometries, subcritical and supercritical inlet conditions were collected for the model development. The comparison between the recommended six-coefficient correlation and experimental data reports 0.80% average and 8.98% standard deviations, which is comparable with the previously developed neural network and much better than the “global” power-law correlation.     

Model-based neural network correlation for refrigerant mass flow rates through adiabatic capillary tubes

A capillary tube is a common expansion device widely used in small-scale refrigeration and air-conditioning systems. A generalized correlation of refrigerant mass flow rate through adiabatic capillary tubes covering both subcooled and two-phase inlet conditions is expected for multiple purposes. Based on the homogeneous equilibrium flow model, a new group of dimensionless parameters has been proposed. To express the nonlinear relationship between the mass flow rate and the associated parameters, the multi-layer perceptron neural network is employed as a universal function approximator. Simulated data from a validated homogeneous equilibrium model are used for the neural network training and testing. A 5-6-1 network trained with the simulated data of R600a and R407C shows good generality in predicting the simulated data of R12, R22, R134a, R290, R410A, and R404A. Also, the deviations between the trained neural network and the experimental data from the open literature fall into ±10%.     

绝热毛细管流量数值计算

根据两相流动的均相流假设 ,建立了绝热毛细管分布参数的稳态数学模型 ,结合制冷工质HFC 134a基于MH状态方程的热力学性质计算模型 ,采用新的基团贡献法计算粘度 ,用熵增判据考虑壅塞流动的影响 ,对绝热毛细管流量进行数值模拟计算。对理论计算结果与相关文献的实验数据进行了比较。针对以HFC 134a为工质的制冷系统 ,编制了一套较为实用的绝热毛细管流量计算软件     

A generalized correlation for the characteristics of adiabatic capillary tubes

The capillary tube is often served as an expansion device in small refrigeration and air-conditioning systems. In this paper, a generalized correlation for predicting the refrigerant mass flow rate through the adiabatic capillary tube is developed with approximate analytic solutions based on the extensive data for R12, R22, R134a, R290, R600a, R410A, R407C, and R404A, in which a homogeneous equilibrium model for two-phase flow is employed, and there is a subcooled liquid or saturated two-phase mixture at the inlet of the capillary tubes. The collected database about capillary tubes covers the inner diameter from 0.5 mm to 2 mm, the tube length from 0.5 m to 5 m, the condensing temperature from 20 °C to 60 °C, the subcooling from 0 °C to 20 °C, and the quality from 0 to 0.3 at the inlet. Assessments for the correlation are made with some experimental data for R12, R22, R134a, R290, R407C, R410A, and R404A obtained from the open literature and some existing correlations based on the experimental database also. The present correlation yields an average deviation of −0.83% and a standard deviation of 9.02% from the database.     

变径毛细管在R410A冷暖空调器中的流量特性

为减少变径毛细管在R410A冷暖空调器应用中的匹配实验工作量,利用节流元件制冷剂流量测试台对多个结构尺寸规格的变径毛细管进行了R410A制冷剂流量测试,建立了基于阻抗计算方法的流量特性经验模型。利用该模型计算出KFR-32GW冷暖空调器所需变径毛细管的初步结构尺寸,并在该冷暖型空调器上进行精确匹配实验,确定最佳变径毛细管结构尺寸。实验结果表明:采用变径毛细管节流的空调器相对采用毛细管组件节流的空调器,制冷量减少0.3%,制冷能效比不变,制热量增加0.5%,制热能效比减少0.3%,两者的性能指标基本相同。因此变径毛细管可以代替毛细管组件应用于R410A冷暖空调器,且通过实验方法建立的变径毛细管R410A制冷剂流量特性经验模型精度较高,可以满足实际工程应用。     

A study of transcritical carbon dioxide flow through adiabatic capillary tubes

This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO₂) through adiabatic capillary tubes. The influence of both operating conditions (inlet and exit pressures, inlet temperature) and tube geometry (capillary diameter and tube length) on the CO₂ mass flow rate was experimentally evaluated using a purpose-built testing facility with a strict control of the measured variables. A dimensionless correlation to predict the refrigerant mass flow rate as a function of tube geometry and operating conditions was developed. In addition, a theoretical model was put forward based on the mass, energy and momentum conservation principles. The model results were compared with experimental data, when it was found that the model predicts 95% of the measured refrigerant mass flow rate within an error band of ±10%. The model was also employed to advance the knowledge about the transcritical carbon dioxide flow through adiabatic capillary tubes.     

Generalized correlation of refrigerant mass flow rate through adiabatic capillary tubes using artificial neural network

A capillary tube is a common expansion device widely used in small-scale refrigeration and air-conditioning systems. Generalized correlation method for refrigerant flow rate through adiabatic capillary tubes is developed by combining dimensional analysis and artificial neural network (ANN). Dimensional analysis is utilized to provide the generalized dimensionless parameters and reduce the number of input parameters, while a three-layer feedforward ANN is served as a universal approximator of the nonlinear multi-input and single-output function. For ANN training and test, measured data for R12, R134a, R22, R290, R407C, R410A, and R600a in the open literature are employed. The trained ANN with just one hidden neuron is good enough for the training data with average and standard deviations of 0.4 and 6.6%, respectively. By comparison, for two test data sets, the trained ANN gives two different results. It is well interpreted by evaluating the outlier with a homogeneous equilibrium model.     

A generalized correlation for refrigerant mass flow rate through adiabatic capillary tubes

A capillary tube is a common expansion device used in small sized refrigeration and air-conditioning systems. A generalized correlation for refrigerant flow rate in adiabatic capillary tubes is developed by implementing dimensionless parameters based on extensive experimental data for R-22, R-290, and R-407C measured in this study. Dimensionless parameters are derived from the Buckingham Pi theorem, considering the effects of tube inlet conditions, capillary tube geometry, and refrigerant properties on mass flow rate. The generalized correlation yields good agreement with the present data for R-22, R-290, and R-407C with average and standard deviations of 0.9 and 5.0%, respectively. Approximately 97% of the present data are correlated within a relative deviation of ±10%. Further assessments of the correlation are made by comparing the predictions with measured data for R-12, R-134a, R-152a, R-410A, and R-600a in the open literature. The correlation predicts the data for those five refrigerants with average and standard deviations of −0.73 and 6.16%, respectively.