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1.
比较了CAVALLINI的纯质和混合工质水平内螺纹管中流动沸腾换热系数的关联式,结果显示在内螺纹管中,对近共沸混合工质R404A的沸腾换热系数进行工程计算时,R404A被看作纯质和混合工质计算所得的沸腾换热系数值差别最大不到10%,因此可将其以纯质对待;对CAVALLINI的纯质和混合工质、KOYAMA及THOME等四个水平内螺纹管流动沸腾换热系数的影响因素进行对比分析,结果表明R404A的沸腾换热中对流沸腾换热占主导地位,且随干度增加而增加.对关联式的理论预测和实验结果进行对比,表明CAVALLINI和THOME关联式的预测误差小于21%,因此它们对R404A适用性较好,这对R404A蒸发器的工程设计及优化具有一定参考意义.  相似文献   

2.
刘易斯因子是反映湿工况下空气侧热质传递特性的重要参数。在此提出了可计算湿工况下翅片侧刘易斯因子的数值模型和适用于工程应用的关联式,通过建立相间传质数值模型、潜热传递数值模型,利用CFD分别计算出空气侧的热质传递系数,从而求得刘易斯因子的数值解。利用数值仿真方法分析了翅片管换热器结构和运行工况对刘易斯因子的影响和已有热质传递类比关系的适用性;同时采用刘易斯因子的数值计算结果拟合得到关联式。传热和传质数值计算结果和实验的相对误差分别为6.93%和12.1%;关联式与数值模型之间的相对误差为5.52%。该数值模型有足够的精度与适用面,所得关联式可代替数值模型。  相似文献   

3.
参照IEC 61267-2005《医用诊断X射线测量特性使用的辐射条件》关于辐射质测量与计算的方法,通过实际测量与计算确定符合JJF 1621-2017 《诊断水平剂量计校准规范》对参考辐射质要求的纯铝过滤片厚度,制作了所需的纯铝过滤片并用半值层测量装置验证了辐射质,建立了校准诊断水平剂量计的X参考辐射质。  相似文献   

4.
食品冻干中的热质传递特性与最佳升华压力   总被引:10,自引:3,他引:7  
通常情况下,食品冷冻干燥中的升华速率受物料已干层内的热量传递过程控制,冻干室压力可较大程度地影响通过物料已干层的传热速率。本文建立了辐射给热条件下食品冷冻干燥过程的数学模型,并在物料热质传递特性随压力变化关系的基础上,用数值法计算出了物料的最佳升华压力,实验证明、计算值与实验值相吻合。  相似文献   

5.
基于现有理论循环性能分析方法,采用工质状态方程结合实验所得出工质的P-V-T关联式进行有机工质热力学性质的联合计算,同时结合热力学一般关系式计算出该工质的导出热力学参数。应用改进的理论循环性能计算方法,以HFC134a纯工质,在冷凝温度20~50℃、循环温升45~70℃的设计运行工况范围内进行热泵循环的循环效率和循环参数间关系以及循环参数选择和系统回热循环性能的特性研究。对该型工质的低温热泵系统,当循环有合理温升时,其有更高COP和较小的压比,得到了在各种应用条件下热泵的最优参数和最优循环。计算结果表明纯质HFC134a具有作为超低温热泵工质的潜力。  相似文献   

6.
船用主汽轮机汽缸冲击响应的计算与实验研究   总被引:1,自引:0,他引:1       下载免费PDF全文
目前船用大型设备的抗冲击性能研究主要采用数值手段进行仿真,而相关实验研究较少,数值计算的精度能达到多少还不确定。为此以船用主汽轮机汽缸为研究对象,建立有限元模型,采用时域模拟法计算汽缸模型在冲击载荷作用下的响应;以计算结果为指导,在大型冲击振动台上进行扫频、冲击实验。将计算值与实验值对比验证,证明计算模型和方法的正确性,分析误差产生原因,评估结构的强度。研究表明:时域模拟法计算的结果比实验值有30%左右的误差;实验与数值计算相结合才能合理的对设备进行抗冲击分析。  相似文献   

7.
王佐民  蔺磊  俞悟周 《声学技术》2007,26(5):904-906
根据声波导管理论,探讨计算高频条件下均匀直管和矩形弯头四端网络参量的方法,以及应用传递矩阵方法分析通风隔声窗高频声学性能的基本思路;实例计算某种通风隔声窗高频隔声量的频响特性,数值计算的结果与实验测量值吻合很好。  相似文献   

8.
开展了全氟甲烷(R14)纯质池内核态沸腾换热特性的实验研究,测量了不同热流密度和不同系统压力下的R14纯质池内核态沸腾换热数据,分析了热流密度和压力对沸腾换热特性的影响。实验结果同现有的经验关联式的计算结果进行了比较,对不同压力下R14沸腾换热提出了不同的关联式,为混合工质节流制冷等相关领域提供基础数据。  相似文献   

9.
王佐民  俞悟周  蔺磊 《声学技术》2007,26(2):277-281
根据平面波理论,提出一种计算矩形消声弯头传递矩阵参量的近似方法;详细介绍应用传递矩阵方法分析通风隔声窗声学性能的基本思路和相关公式;实例计算某种通风隔声窗隔声量的频响特性,数值计算的结果与实验测量值吻合甚好。  相似文献   

10.
多孔介质质扩散系数的参数估计方法及测定方法   总被引:1,自引:0,他引:1  
提出一种在第三类边界条件下,通过使数值计算的湿分蒸发与规律实测值之间的最佳逼近,以瞬态确定计算多孔介质质扩散系数的参数估计方法。设计并制造了对流蒸发实验装置。在假设质扩散系数为含湿量线性函数的情况下,对石膏板和水泥板的质扩散系数进行了测量和计算。测试及计算方法简单可行,测定时间较稳态方法大大缩短,因此比较实用。  相似文献   

11.
A coaxial cylinder viscosimeter has been used to determine the pressure-viscosity coefficient of a pure refrigeration oil and of a mixture of refrigerant and oil at gauge pressures up to 15 MPa. The test fluid, Gargoyle Arctic oil 300, is a naphthenic-base oil. The refrigerant was R22, chlorodifluoromethane, which is a commercially important refrigerant. In a gap apparatus the refrigerant-oil mixture has been visually inspected at different pressures. Two different mechanisms are involved in the refrigerant-oil mixture: the change in solubility with pressure and the change in viscosity with refrigerant concentration. If the mixture is pressurized with excess refrigerant available then the concentration of refrigerant will increase with increasing pressure and therefore the viscosity will decrease. If the concentration is kept at a constant level then the viscosity will increase with pressure. The results from the cylinder viscosimeter showed that the viscosity increase with pressure for the mixture was almost the same as for the pure oil.  相似文献   

12.
The paper reports the results of condensation heat transfer and pressure drop from tests with pure and oil-contaminated refrigerant HFC134a in a horizontal tube (10 m in length, 6 mm ID). The experimental results are compared with prediction from correlation. The heat transfer coefficient in the case of oil-contaminated refrigerant is shown to depend strongly on the definition of the saturation temperature. Using the pure refrigerant saturation temperature (hence disregarding the influence of oil on the vapour pressure), the results for average heat transfer coefficient show only minor effect of the oil contents. If the saturation temperature of the refrigerant—oil mixture is used, there is thus a significant degradation of the heat transfer coefficient (as expected) with increasing oil concentrations.  相似文献   

13.
Refrigeration oil having good miscibility with refrigerant is generally used in refrigeration units. Precise measurement of the mixing ratio of refrigerant to refrigeration oil is required for a sufficient understanding of the refrigeration cycle. In this paper, refractive index is chosen as a property which indicates the mixing concentration of the refrigerant/oil mixture. A laser displacement sensor is used to detect a change of optical path which changes according to the refractive index of test medium. The refractive indices of pure refrigerant, pure refrigeration oil and refrigerant/refrigeration oil mixture are measured with several combination of refrigerant/oil. It is found that the difference of refractive index between the refrigerant and the oil is sufficient for the measurement of the mixing concentration of refrigerant/oil mixture, and that the refractive index of the refrigerant/oil mixture changes almost linearly according to the mixing concentration. These data will be utilized for development of an in situ sensor in refrigerant compressors.  相似文献   

14.
Pressure-enthalpy charts are presented for refrigerant R 12-oil mixtures, for a range of oil concentrations. The effect that the existence of this mixture has on evaporator performance and COP of a refrigeration/heat pump system is discussed and some results are compared with the pure refrigerant cycle normally considered.  相似文献   

15.
The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.

Résumé

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility in keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.  相似文献   


16.
Non-azeotropic refrigerant mixtures (NARMs) are investigated for a two-temperature level heat exchange process found in a domestic refrigerator-freezer. Ideal (constant air temperature) heat exchange processes are assumed. The results allow the effects of intercooling between the evaporator refrigerant stream and the condenser outlet stream to be examined in a systematic manner. For the conditions studied, an idealized NARM system will have a limiting coefficient of performance (COP) that is less than that of the best performing pure refrigerant component. However, for non-ideal heat exchange processes (gliding air temperature), the NARM-based system can have a higher limiting COP than a system running on either pure NARM component. Intercooling significantly affects the COP of NARM-based systems; however, depending on the location of ‘pinch points’ in the heat exchangers, only one intercooling heat exchanger may be needed to obtain a NARM's maximum refrigerator COP. The results are presented for mixtures of R22–R142b, R22–R123 and R32–R142b.  相似文献   

17.
The wettability of micro/nanostructured surface is a key property for its application in enhancing the boiling heat transfer of refrigerant–oil mixture. The objective of this research is to experimentally investigate the wetting behavior of refrigerant–oil mixture on micro/nanostructured surface. Three types of surfaces including plain copper surface (PS), micro/nanostructured surface (MNS) and micro/nanostructured surface with fluorinated self-assembled monolayer (MNFS) were fabricated; and the wetting behavior of pure R141b as well as R141b-NM56 mixtures with different oil concentrations on three types of surfaces was measured. The experimental results show that the protuberant liquid film is formed during the wetting of refrigerant–oil mixture on MNS or PS, but does not exist on MNFS; the presence of F-SAM or micro/nanostructure modified by F-SAM reduces the surface wettability, while the presence of micro/nanostructure increases the surface wettability; oil increases the wettability of refrigerant on MNS, while it reduces the wettability of refrigerant on MNFS.  相似文献   

18.
A recently developed scheme, based on considerations of hard-sphere theory, is used for the simultaneous prediction of the thermal conductivity and the viscosity of binary and ternary HFC refrigerant mixtures, consisting of HFC-32, HFC-125, and HFC-134a. In this prediction scheme, the hypothetical molecular parameters of HFC refrigerant mixtures were assumed to be the molar average of the pure component values. The close agreement between the predicted values and the experimental results of thermal conductivity and viscosity demonstrate the predictive power of this scheme.  相似文献   

19.
This paper presents a comparative study of the condensation heat transfer coefficients in a smooth tube when operating with pure refrigerant R134a and its mixture with lubricant Castrol “icematic sw”. The lubricant is synthetic polyol ester based oil commonly used in lubricating the compressors. Two concentrations of R134a-oil mixtures of 2% and 5% oil (by mass) were analysed for a range of saturation temperatures of refrigerant R134a between 35 °C and 45 °C. The mass flow rate of the refrigerant and the mixtures was carefully maintained at 1 g/s, with a vapour quality varying between 1.0 and 0. The effects of vapour quality, flow rate, saturation temperature and temperature difference between saturation and tube wall on the heat transfer coefficient are investigated by analysing the experimental data. The experimental results were then compared with predictions from earlier models [Int J Heat Mass Transfer (1979), 185; 6th Int Heat Transfer Congress 3 (1974) 309; Int J Refrig 18 (1995) 524; Trans ASME 120 (1998) 193]. Finally two new empirical models were developed to predict the two-phase condensation heat transfer coefficient for pure refrigerant R134a and a mixture of refrigerant R134a with Castrol “icematic sw”.  相似文献   

20.
混合工质在脉管制冷机中的可能应用   总被引:3,自引:3,他引:0  
提出了采用合适的混合工质代替纯质氦以提高脉管制冷机在80K温区制冷量的新构思。概述了国外在制冷循环,天然气液化及J-T节流制冷中应用混合制冷剂从而提高了系统热力学效率的研究成果,及国内对混合物低温制冷物质的研究进展情况,进一步论证了混合工质应用于脉管制冷机的可行性。  相似文献   

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