制冷系统稳态运行下制冷剂分布试验研究

通过试验的方法研究制冷剂在系统中的分布规律,提出测试原理及方法。测试数据显示,热泵在稳态运行下,制冷剂主要分布在两器中,在制热工况下,气液分离器中贮存约13%的气态制冷剂。     

碳氢化合物混合工质在制冷系统中的应用研究

本文阐述了一种碳氢化合物的混合物作为制冷剂的可行性。阐明了这种物质在冰箱应用中的安全性和成份含量变化的影响,通过热力学性质和实验表明TRl2是一种热力学性质与R12极为相似。制冷效果和节能效果都优于R12的制冷制。     

复叠制冷系统低温制冷剂的替代应用综述

本文对用于替代复叠低温制冷系统中CFCs低温制冷剂的R23和R508B进行了综述,讨论了低温制冷剂的物理化学性质、系统制冷量、能效比、换热性能及其润滑油的选择等,同时也指出了HFCs低温制冷剂压缩机的选择和R23制冷剂充注量等问题.     

再循环重力供液制冷系统实验

对重力供液制冷系统形成再循环的条件和再循环时蒸发器的传热性能进行理论分析,建立相应的数学模型。将重力供液制冷系统与直接膨胀供液制冷系统进行比较,得到两种不同制冷系统工作特性上的差异。通过在焓差实验室中测定制冷系统在不同工况下的压力、风量、制冷量以及耗功等技术参数,得到重力供液制冷系统和直接膨胀供液制冷系统在室外干球温度一定的情况下传热系数、制冷量以及系统COP的变化规律。实验表明:再循环的形成可以增大制冷剂流速同时充分润湿传热表面,强化换热效果显著,在测试的工况下蒸发器的传热系数可增大近40%,COP最大提高7.6%,低温工况的增幅更大。     

自动复叠系统中非共沸混合制冷剂的组分分离

自动复叠系统利用单压缩机多元混合制冷剂来制取低于-60℃的低温。在循环过程中,混合制冷剂分离的好坏直接影响到系统的各部分性能。如何更好地分离各制冷剂组分成为一个重要的课题。本文综述自动复叠系统中选择非共沸混合制冷剂时需要考虑的问题,并讲述几种非共沸混合制冷剂组分分离的方式,提出分离程度与制冷量之间的关系。     

用于冷冻冷藏制冷系统的新型制冷剂的理论研究

综述在冷冻冷藏系统中制冷剂替代研究的现状。在此基础上,提出一种新的混合制冷剂（HFC-161/HFC-125/HFC-143a,15/45/40）用于替代HFC-404A,该新型制冷剂的ODP为零,GWP比HFC-404A和R507A要小,其基本热力学性能与HFC-404A相近。对新型混合制冷剂和HFC-404A的循环性能进行理论分析与比较。结果表明,新型混合制冷剂的性能要比HFC-404A优越,环境性能更好,是HFC-404A潜有力的替代制冷剂。     

Commercial refrigeration system using CO2 as the refrigerant

Various field-test systems using carbon dioxide as the only refrigerant have been installed since December 2001. In this paper we will analyse an ‘all-CO₂’ supermarket, which has been operating in the North of Italy since January 2003.The seasonal COP is calculated, based on prior laboratory measurements, and a comparison is made with a conventional direct expansion system using R404A.The total annual energy consumption of the installed CO₂ system is estimated to be about 10% higher than the direct expansion R404A solution. It is still possible to further improve efficiency and approach the efficiency of present R404A systems. These improvements are identified.The cost of the CO₂ installation is compared to the cost of an equivalent direct expansion R404A installation, the most economic among the various present types of commercial refrigeration systems. Because of the lack of suitable mass-produced components, the CO₂ installation is estimated to be, today, about 20% more expensive.     

环保制冷剂R290在四级自动复叠制冷系统中的应用

采用环保制冷剂R290取代R22应用于四级自动复叠制冷系统,理论模拟计算表明,R290与R22有较相似的热物理性质,并且相同温度条件下R290有更低的饱和压力;相同压力条件下具有更大的汽化潜热,与R23组成非共沸混合工质能够获得更低的蒸发温度。采用混合制冷剂R290/R23/R14/R50进行试验,获取了-142℃的理想低温,冷量达到105 W。     

Non-equilibrium two-phase refrigerant flow at subcooled temperatures in an R600a refrigeration system

A refrigeration system is typically designed such that the refrigerant reaches a subcooled state at the condenser outlet. A series of experiments are conducted to investigate the refrigerant state at the condenser outlet and the capillary tube inlet. The refrigeration system used in the present experiment is operated with R600a. The visual observations, as well as temperature and pressure measurements, demonstrate that R600a flows in a non-equilibrium two-phase state at highly subcooled temperatures. Furthermore, a set of equations is proposed for calculating the specific enthalpy of the refrigerant in a non-equilibrium two-phase state, and this calculation method is verified using experimental measurements. It is found that the thermodynamic property table does not provide an appropriate value of specific enthalpy in non-equilibrium conditions, while the enthalpy calculation method proposed in this work is in good agreement with the experimentally measured values.     

Measurement of refrigerant mass distribution within a R290 split air conditioner

R-290 (propane) has been chosen as one of the most potential next generation working fluids of RACs because of its favourable environmental and thermo-physical properties. However, its use is hindered by its flammability and resulting concerns on safety. In addition, the charge mass is limited strictly by the standards which would impact RAC's heating performance. In this paper, refrigerant mass distributions within a R290 split type air conditioner were experimentally investigated at both static and dynamic state, in which the liquid nitrogen method (LNM) was used to determine the refrigerant mass inside the components of the circuit. The distribution of refrigerant that changes with temperatures and compressor speed were also measured and discussed. The results can assist with improving the design of the products (performance improvement, safety measures, etc.) and providing data for further theoretical study and simulation analyses.     

充注量对小型CO2制冷系统影响的实验研究

为了研究充注量对小型二氧化碳制冷系统的影响,利用一套展示柜二氧化碳制冷系统,进行了不同充注量的实验。讨论了充注量对二氧化碳制冷系统吸排气压力、运行功率、吸排气温度的影响。同时,结合本系统,对假临界现象进行了分析,结果表明:充注量不足,蒸发、冷凝压力低,压缩机吸、排气温度高,系统COP较低;充注量过多,系统运行功率高,系统制冷系数降低;系统运行一段时间后,回热器热侧出口达到假临界温度,吸、排气温度产生突降;随着充注量的增加,吸、排气温度突降点前移。本研究可为跨临界二氧化碳制冷系统最佳充注量的确定及如何维持系统高效运行提供理论指导。     

Optimizing the magnetic system parameters inside a measuring coil

Conclusions The magnetic core inside the coil of a magnetic measuring system has an optimal diameter to height ratio d_m/h_m for which the torque is maximal. The magnet diameter and height depend on the coil perimeter P, and their optimal ratio K_F is practically independent of the coil perimeter but depends on the alloy of which the magnet is made. Implementing optimal magnet dimensions makes possible fuller utilization of the energy of a permanent magnetic core inside the magnetic system coil. If the optimal ratio of magnet diameter to its height is known, calculation of the magnetic system parameters and the design of the entire measuring instrument becomes quite simple.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 32–34, April, 1991.     

低温冷库制冷领域使用CO2作为制冷剂的应用概述

对天然制冷工质CO2(R744)应用于低温大容量制冷工况下的循环形式进行了叙述,在给定工况下进行了循环性能计算,并与传统工质进行了比较.指出CO2跨临界循环与传统制冷剂循环相比有明显优势,适合应用于低温冷库工况.     

CO_2载冷剂氨双级压缩制冷系统及其性能分析

针对氨制冷系统在实际应用中存在安全隐患的问题,总结提高系统安全性的方法和途径,介绍以CO2为载冷剂的半封闭式氨制冷系统的组成及其应用。对以CO2为载冷剂的氨双级压缩制冷系统性能进行理论计算与对比分析,结果表明：在蒸发温度为-50~-30℃范围内,与NH3/CO2复叠式制冷系统相比,CO2载冷剂氨双级压缩制冷系统的EER约高5.7%~10.8%。     

Practical test methods for measuring the zero shear viscosity of bituminous binders

When the zero shear ciscosity (ZSV) is derived from a creep test, the creep time should be sufficiently long to obtain a steady state with a constant shear rate. The creep test works well for most conventional binders. Unfortunately, for polymer modified binders (PmBs), the long waiting times required to obtain a steady state are not always acceptable from a practical point of view and three are problems concerning the repeatability. This paper compares the steady state creep test to alternative test methods for the determination of the ZSV. One method is a short time creep/recovery test, with a short creep period and a longer recovery period, where the ZSV is derived from the recovery part. The other method is an oscillation test at low frequencies, where the complex viscosity is extrapolated to zero frequency to obtain the ZSV. Measurements are presented on a pure 70/100 binder and on a highly SBS-modified binder. While all methods give comparable and repeatable results for the case of the pure binder, complications occur for the highly modified binder. The oscillation method seems to be the most promising, method.

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Résumé Lorsque la viscosité à taux de cisaillement nul (VTCN) est dérivée d'un essai de fluage, le temps de fluage doit être suffisamment long pour obtenir un état stable où la vitesse de cisaillement est constante. L'essai de fluage convient pour les liants conventionnels. Malheureusement, pour les bitumes modifiés (BmP), les longs temps d'attente nécessaires pour atteindre cet état stable ne sont pas toujours acceptables d'un point de vue pratique et il existe des problèmes concernant la répétabilité. Cet article compare l'essai de fluage avec attente de l'état stable à des méthodes d'essai alternatives pour déterminer la VTCN. Une des méthodes consiste en un essai fluage/recouvrance, avec une période de fluage courte et une période de recouvrance plus longue. La VTCN est alors dérivée de la partie recouvrance. L'autre méthode consiste en un, essai d'oscillation à basse fréquence. La viscosité complexe est extrapolée à la fréquence zéro pour obtenir la VTCN. Des résultats de mesure sont présentés pour un liant conventionnel (70/100) et pour un BmP à teneur élevée en SBS. Tandis que toutes la méthodes donnent des résultats comparables et répétables pour le liant conventionnel, beaucoup de complications apparaissent pour le bitume modifié à teneur élevée en SBS. La méthode d'oscillation semble la méthode la plus prometteuse.

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Editorial Note Presented at the 6^th International RILEM Symposium on Performance Testing and Evaluation of Bituminous Materials (PTEBM'03), held on 14^th–16^th April 2003, in Zurich, Switzerland, this paper was selected as an outstanding communication and peer-reviewed by the Scientific Committee of the JournalMaterials and Structures.     

中国制冷空调行业制冷剂替代策略的思考

中国制冷空调行业淘汰HCFCs面临国际上的巨大压力和挑战。为此,从直接排放和间接排放2个方面对制冷剂应用对环境影响以及从制冷剂管理方面进行分析与阐述,提出制冷空调行业应负责任地使用制冷剂:提高制冷空调设备效率,降低制冷剂间接排放,减少制冷剂充注量,加强控制制冷剂泄漏,提高制冷剂回收、再生利用率来减少制冷剂的直接排放;应进行可燃制冷剂应用的基础研究和制定产品及应用安全标准,寻找对环境影响最小、经济可行、替代成本市场可接受、安全的替代制冷剂。同时建议行业协会配合国家有关部门制定适合中国国情的HFCs制冷剂的减排基准线和减排时间表。     

工质泄漏对HCs商用制冷系统性能影响的理论分析

建立混合工质R290／R600a在系统中发生泄漏的模型，对系统存在泄漏点时系统内工质组分配比随不同泄漏情况发生时的变化进行分析，其后对相应的系统性能的变化进行了研究。     

A year-round dynamic simulation of a solar-driven ejector refrigeration system with iso-butane as a refrigerant

In this paper, the performance of the solar-driven ejector refrigeration system with iso-butane (R600a) as the refrigerant is studied. The effects that both the operating conditions and the solar collector types have on the system's performance are also examined by dynamic simulation. The TRNSYS and EES simulation tools are used to model and analyze the performance of a solar-driven ejector refrigeration system. The whole system is modelled under the TRNSYS environment, but the model of the ejector refrigeration subsystem is developed in the Engineering Equations Solver (EES) program. A solar fraction of 75% is obtained when using the evacuated tube solar collector. In the very hot environment, the system requires relatively high generator temperature, thus a flat plate solar collector is not economically competitive because the high amount of auxiliary heat needed to boost up the generator temperature. The results from the simulation indicate that an efficient ejector system can only work in a region with decent solar radiation and where a sufficiently low condenser temperature can be kept. The average yearly system thermal ratio (STR) is about 0.22, the COP of the cooling subsystem is about 0.48, and the solar collector efficiency is about 0.47 at T_e 15 °C, T_c 5 °C above the ambient temperature, evacuated collector area 50 m² and hot storage tank volume 2 m³.     

制冷剂充注量对冷藏车用制冷机组性能的影响

为了研究制冷剂充注量对冷藏车用制冷机组性能的影响,在数值模拟得到的制冷剂标准充注量的基础上,试验研究制冷剂充注量对压缩机吸/排气压力、吸/排气温度、蒸发器出口过热度、冷凝器出口过冷度及制冷能力的影响。研究表明,数值模拟方法得到的制冷剂标准充注量适用于实际制冷机组。     

混合制冷工质充注装置设计与分析计算

设计了一套混合制冷工质充注装置,该装置采用定容积储气罐,通过测量其温度和压力变化,根据工程热力学原理可以得到所充制冷工质的质量。针对充注过程进行了分析,对装置的结构和原理进行了讨论。运用两种方法计算本装置在环境温度下充注制冷工质的质量,并对两种计算结果进行了对比分析。