三元乙丙橡胶共混改性聚丙烯

分别用茂金属催化聚合所得的三元乙丙橡胶(mEPDM)和传统Ziegler-Natta催化剂聚合所得的三元乙丙橡胶(EPDM)对PP进行共混改性。考察了增韧剂质量分数对共混物冲击强度、拉伸强度和热变形温度等力学性能的影响,以及共混物结构形态和结晶行为。结果表明,与PP／EPDM共混物相比,PP／mEPDM共混物的脆韧转变增韧剂临界质量分数小,扯断伸长率高。PP／mEPDM共混物的脆韧转变区间远小于PP／EPDM共混物。随增韧剂质量分数的增加,PP／mEPDM和PP／EPDM共混物的拉伸强度、弹性模量和维卡软化点均单调下降,但后者的下降幅度更大。电镜分析和结晶行为研究表明,PP与mEPDM的相容性优于PP与EPDM的。     

Flow pattern, mass flow rate, pressure distribution, and temperature distribution of two-phase flow of HFC-134a inside short-tube orifices

New experimental data on the influence of short-tube orifice configuration, including diameter, length, length-to-diameter ratio (L/D), and orientation on the flow pattern, mass flow rate, and pressure distribution of HFC-134a inside the short-tube orifice are presented. Short-tube orifice diameters ranging between 0.605 and 1.2 mm with L/D ranging between 1.87 and 33 are used in the experiments. Three different forms of the metastable liquid flow, which are metastable liquid core flow, conical metastable liquid core flow, and full metastable liquid flow are visually observed. The short-tube orifice diameter has a significant effect on the increase in the flow rate. Conversely, the change in the orientation of the test section has no significant effect on the flow rate. The choke flow phenomenon disappears inside the short-tube orifice when L/D is less than 2.91. Based on the present data, a correlation for predicting the mass flow rate through short-tube orifices is proposed.     

焦油沥青净化和浸渍剂沥青的生产

介绍了我国浸渍剂沥青开发情况和几种浸渍剂沥青的生产工艺和特点。根据国内浸渍剂沥青的生产和使用情况,提出了加快浸渍剂沥青工业化生产的建议。     

Study of capillary tubes in a transcritical CO2 refrigeration system

Capillary tubes have been used in refrigeration systems for many years, but not with a transcritical CO₂ system. In this article, the effects of capillary tubes in a transcritical CO₂ refrigeration system have been investigated experimentally and theoretically. Different types of capillary tubes with different lengths (0.5–4 m) and diameters (1–2 mm) have been tested. The result of this work is a static model, which is used in the further work to make a simulation model (static) of a complete refrigeration system. The model is based on Friedel's and Colebrook's pressure drop correlations.

The behaviour of an adiabatic capillary tube in a refrigeration cycle has been investigated theoretically. The conclusion is that the COP of a system with capillary tubes generally is better than when a fixed high pressure is used, but not as good as when variable optimal high pressure is used. Capillary tubes are especially interesting in applications where the evaporation pressure is constant and the temperature out of the gas cooler varies no more than ±10 K from the design condition. The reduction in COP is more significant at low temperatures out of the gas cooler.     

Nucleate boiling heat transfer coefficients of flammable refrigerants on various enhanced tubes

In this study, nucleate boiling heat transfer coefficients (HTCs) of five flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), and dimethylether (RE170) were measured at the liquid temperature of 7 °C on a low fin tube of 1023 fins per meter, Turbo-B, and Thermoexcel-E tubes. All data were taken from 80 to 10 kW m⁻² with an interval of 10 kW m⁻² in the decreasing order of heat flux. Flammable refrigerants' data showed a typical trend that nucleate boiling HTCs obtained on enhanced tubes also increase with the vapor pressure. Fluids with lower reduced pressure such as DME, isobutene, and butane took more advantage of the heat transfer enhancement mechanism of enhanced tubes than those with higher reduced pressure such as propylene and propane. Finally, Thermoexcel-E showed the highest heat transfer enhancement ratios of 2.3–9.4 among the tubes tested due to its sub-channels and re-entrant cavities.     

Numerical investigation of a diffusion absorption refrigeration cycle

A thermodynamic model was developed for an ammonia–water diffusion absorption refrigeration (DAR) cycle with hydrogen or helium as the auxiliary inert gas, manufactured by Electrolux Sweden (currently known as Dometic). The performance of the system was examined parametrically by computer simulation. Mass and energy conservation equations were developed for each component of the cycle and solved numerically. The model was validated by comparison with previously published experimental data for DAR systems. Investigation of cycle performance under different conditions indicated that the best performance was obtained for a concentration range of the rich solution of 0.2–0.3 ammonia mass fraction and that the recommended concentration of the weak solution was 0.1. It was also found that as the degree of rectification decreased, the performance of the DAR cycle decreased. Finally, the study showed that helium was superior to hydrogen as the inert gas: the coefficient of performance of a DAR unit working with helium was higher by up to 40% than a cycle working with hydrogen.     

Condensation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficients were measured for the condensation of R410A and R22 inside internally grooved horizontal tubes. The experiment was performed for five different kinds of internally grooved tubes of about 8.00 mm o.d. the shapes of which were conventional helical grooved and herring-bone grooved ones. To measure the local heat transfer coefficients, the test section was subdivided into 10 small sections having 1 m working length. The ranges tested are as follows: the refrigerant mass velocity was from 130 to 400 kg/(m²/s) for R410A and R22, and the vapour pressure was 2.4l MPa for R410A and 1.53 MPa for R22. The obtained heat transfer data of R410A and R22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of helical one. All measured local heat transfer coefficients of condensation were compared with the predicted values from previous correlations proposed by other researchers, and were well correlated with the empirical equation using the frictional coefficients for each tube proposed by the author.     

Liquid dynamic viscosity: A general prediction method with application to refrigerants and refrigerant mixtures

This paper discusses prediction methods which are able to provide the dynamic viscosity, μ, of liquids along the saturation line. The best empirical or semi-empirical correlations existing in the literature are critically presented and checked to outline the usefulness of the new prediction method presented in this paper. Fifty substances (organic compounds, inorganic compounds and pure elements) are examined to show the reliability of the new simple equation which contains three factors (A, B and C) related to the molecular structure and the most important physical properties. The general scheme of prediction is then applied to the particular case of refrigerant fluids belonging to the methane and ethane families and to their binary mixtures. The accuracy of the proposed prediction method is checked using the most recent and reliable experimental dynamic viscosity data available in literature, and the mean and the maximum deviations between predicted and experimental μ values are shown to be less than 3 and 8%, respectively.     

Optimum control of the gas overheat in the evaporator of a vapour compression refrigeration system when the refrigerant is polluted

Results concerning the response of a refrigeration system simulation software to an increase in the amount of oil flowing with the refrigerant are presented. It is shown that there are optima of the apparent overheat value, for which either the exchanged power or the refrigeration coefficient of performance (COP) is maximised: consequently, it is not possible to optimise both the refrigeration COP and the evaporator power. However, in most of the cases (i.e. contents of circulating lubricant), the optimal values of the apparent overheat are below the values that the expansion valves usually impose.