R245fa传热性能实验

蒸发器和冷凝器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素,为了提高中低温余热在热泵机组和地热双工质发电系统中的利用效率,本文选用R245fa循环工质,对满液式蒸发器和冷凝器进行实验研究,分别讨论热水温度进口温度对蒸发器和冷凝器的传热系数、蒸发压力和冷凝压力的影响。研究结果表明,在工质流量和冷却水流量保持不变的条件下,蒸发器传热系数随着热水进口温度和温差的增大而减小,冷凝器的传热系数随着热水进口温度的增加先增大后减小,蒸发器传热系数可以达到2500 W/(m2?℃);蒸发器压力和汽轮机前后的压差随着热水出口温度的增加而增加,热水流量对蒸发压力和冷凝压力的变化浮动较小。     

HFC-245fa体系聚氨酯硬泡导热系数的改善

介绍了在冰箱、冰柜制冷行业中作为下一代有很大发展前景的HFC 2 4 5fa体系 ,以及如何改善HFC 2 4 5fa体系聚氨酯硬泡导热系数偏高的问题     

霍尼韦尔Enovate-245fa发泡剂的性能与应用

随着蒙特利尔条约在相关国家的实施，CFC化合物已经逐步被淘汰．HCFC化合物也己在欧洲、美国、日本等一些国家实行了禁止和淘汰.我国是HCFC化合物生产和使用的大国，其逐步淘汰也已经提上了议程。霍尼韦尔公司很早就致力于HCFC-141b的替代工作，并为其OODP发泡剂产品HFC-245fa在不同的领域的应用都作了相应的研究。本文介绍了该公司HFC-245fa的一些基本性能及其在冰箱，喷涂和板材的应用情况。     

采用HFC245fa新制冷剂的离心式冷水机组

日本荏原（Ebara）公司近期开发成一种采用新型低压制冷剂HFC-245fa的离心式冷水机组。首台样机已经售予日本东北部的一家工厂。     

新型环保发泡剂HFC-245fa的现状及发展趋势

介绍了HFC-245fa发泡剂的各种性质、在聚氨酯硬泡中的应用及发展趋势。指出HFC-245fa体系将是未来普遍采用的体系。     

R245ca—R11潜在的远期替代工质

初步试验证明，Ｒ２４５ｃａ将是最终取代Ｒ１１或Ｒ１２３工质的最理想的候选制冷剂。     

发泡剂替代物HFC 245fa介电系数的实验研究

我国制冷产品随着在国际市场上的份额不断扩大，需要满足严格的环境保护要求，其中一项就是采用对臭氧层无破坏作用的制冷剂与发泡剂，HFC-245fa不仅介电性能好而且温室气体排放量小，是非常好的发泡剂。主要对新型发泡剂HFC-245fa的介电系数进行了实验研究。通过对大量实验数据的拟合处理，得出了介电系数与温度、压力和温度、密度的关联式，为产品设计提供基本参考数据。     

小功率变频空调器采用电子膨胀阀与毛细管节流的性能对比分析

应用经试验验证的电子膨胀阀的数学模型及制冷系统稳态模型,分析了在小功率变频空调器制冷系统中分别采用电子膨胀阀与毛细管节流时,在不同运行频率下制冷系统性能的变化情况。分析表明,在２０Ｈｚ－１２０Ｈｚ运行频率下,采用电子膨胀阀均具有较大的优越性,但在常用频率范围（４０Ｈｚ－８０Ｈｚ）内毛细管亦具有令人接受的性能,因而小功率变频空调器采用毛细管节流是可行的。     

电子膨胀阀的优势和发展趋势

从制冷系统节流机构的流量调节稳定性、过热度控制原理、系统节能、瞬态反应特性、部分负荷调节特性方面,比较分析了几种节流机构应用于制冷装置中的特点。提出了电子膨胀阀在容量调节和过热度稳定控制方面的优点,并对电子膨胀阀的发展趋势和在各方面的应用进行了分析。     

R245fa高温蒸气热泵理论与实验研究

工业领域中高温蒸气的需求较大,由于小型锅炉的禁用、电锅炉的低能效及余热资源的浪费,因此高温热泵作为制取水蒸气的装置,有广阔的发展前景。本文设计了一种采用R245fa为工质的高温热泵系统与水蒸气制备装置,建立数学模型对系统及各部件进行模拟和性能预测,并搭建实验台研究其性能和运行参数随工况等的变化规律。结果表明:随着蒸发温度的上升,系统COP快速上升,相对值为0.55~1.3,上升速度逐渐减缓,制热量近似线性升高,排气过热度下降,换热温差显著上升;换热系数随着水流率的增加而增加,变化范围为1.7~2.8 k W/(m2·K)。     

两种双侧强化管管外R245fa降膜蒸发的实验对比

本文搭建了水平单管降膜蒸发实验台,以R245fa为工质实验研究两种三维翅双侧强化管降膜蒸发的换热特性。提出了新型Wilson-Gnielinski图解法,用于从实验的总传热系数中获得管内外表面传热系数。分析强化管表面结构对换热性能的影响,拟合出管内外换热关联式并提出强化换热方案。结果表明,与光滑管理论表面传热系数相比,Y型管的管内、管外换热强化倍率分别为2.12～2.94和2.27～5.54,T型管的管内、管外强化倍率分别为2.48～2.98和2.58～3.00。Y型管管外换热性能较好,T型管管内换热性能较好。Y型管的最佳喷淋密度(0.14～0.18 kg/(m·s))比T型管的最佳喷淋密度(约0.10 kg/(m·s))大;两种强化管表面传热系数均随热流密度的增加先上升后下降,但Y型管表面传热系数的变化速率较快;两种管子的换热效果均随蒸发温度的升高而增强。     

Performance analysis of a supersonic ejector cycle working with R245fa

A supersonic ejector chiller for industrial use is currently being developed and tested as part of a project cooperation between Frigel s.p.a and DIEF (Department of Industrial Engineering, University of Florence). The refrigerator was built following a “ready to market” setup criterion and is intended for applications on the industrial refrigeration market or in air conditioning. The plant has a nominal cooling power of 40 kW and is powered by low temperature heat (from 90 up to 100 °C). The ejector is equipped with a movable primary nozzle and 9 static pressure probes along the mixing chamber/diffuser duct. The working fluid is R245fa. An extensive numerical campaign was performed to analyze the internal dynamics of the ejector. All the simulations were carried out by accounting for the real gas properties of the refrigerant. Comparison with experimental data resulted in close agreement both in terms of global and local parameters. Analyses showed that in order to achieve an accurate matching with the experimental data, it is necessary to correctly account for the surface roughness of the ejector. This is especially true for off-design operating conditions.     

Experimental investigation of startup characteristics of R290 rotary compressor under low ambient temperature heating condition

The cold and warm startup characteristics of an R290 heat pump system and its rotary compressor were experimentally investigated under a low ambient temperature heating condition. These startup characteristics included the temperatures in the compressor shell and system and the pressures in the cylinder and system. The results showed that the minimum suction gauge pressure (−48 kPa) during a cold startup was lower than that during a warm startup (155 kPa) under a low ambient temperature heating condition. In addition, the time required for the R290 heat pump system to reach a steady pressure was much longer than that of a system using R410A as the refrigerant. Compared with that of the cooling condition, smaller amounts of liquid were generated in the cylinder at the beginnings of both the cold and warm startup processes under the low ambient temperature heating condition.     

Experimental and theoretical study on a novel double evaporating temperature chiller applied in THICS using R32/R236fa

A novel chiller with double evaporating temperatures is proposed in this paper, which can be applied in temperature and humidity independent control system (THICS). A zeotropic mixture R32/R236fa is selected as the refrigerant, and chilled water with two different temperatures is produced. The experimental coefficient of performance (COP_exp), theoretical coefficient of performance (COP_th), and second law efficiency (η) of the chiller are studied. The performance of the chiller is studied by varying the mass fraction of R32 in the R32/R236fa (W(R32)), chilled water temperature, and the flow rates of the heat transfer media (chilled water and cooling water). The results show that the high temperature chilled water (T_H,out) can be at 15–18 °C, and the low temperature chilled water (T_L,out) can be at 6–8 °C. When T_H,out is 17 °C and T_L,out is 7 °C, the maximum COP_th and COP_exp are 4.73 and 3.97, respectively. Second law efficiency, η, increases to 31% as W(R32) increases from 0.3 to 0.6.     

Experimental investigation on heating performance of gas-injected scroll compressor using R32, R1234yf and their 20wt%/80wt% mixture under low ambient temperature

In this paper, an integrated gas-injected scroll compressor heat pump system using R1234yf, R32 and its binary mixtures as working fluid was developed and their heating performances under low ambient temperature were quantitatively evaluated. A composite test system consisting of second-refrigerant calorimeter and water-cooled condenser was used to test the system working performance. The condensing temperature, evaporating temperature, compressor power input and other variables were analyzed to evaluate the system heating capability and energy efficiency. Test results showed that the R1234yf system can run at an evaporating temperature of −25 °C. R1234yf/R32 mixture can run at an evaporating temperature of −20 °C and it has the highest heating COP value among other refrigerants; R1234yf/R32 gas injection system provided very significant performance improvements for heating performance, compared with no gas injection, the heating capacity and heating COP can improve 16%~20% and 13%~16%, respectively.     

Experimental investigation on the compression behaviors of epoxy with carbon nanotube under high strain rates

The compressive properties of epoxy with different carbon nanotubes (CNTs) contents at quasi-static and high strain rates loading had been investigated via experiment to evaluate the compressive failure behaviors and modes at different CNTs contents and different strain rates. The results indicated that the stress train curves were strain rate sensitive, and the compressive stiffness, compressive failure stress of composites with various CNTs contents was increased with the strain rates and CNTs contents. The compressive failure stress and the compressive failure modes of the composites were apparently different as the change of CNTs contents.     

Experimental investigation on the bond of reinforcing bars in high performance concrete under cyclic loading

The bond performance between reinforcing bars and concrete under cyclic loads were experimentally investigated in this paper. In particular, the effects of steel fibers and hybrid fibers (including steel fibers and carbon fibers) on␣the bond performance were analyzed. Based on the experimental results, the deterioration laws of the peak bond stress, the stiffness of the unloading branch, frictional bond resistance and remnant ultimate bond stress under cyclic loads were summarized. Meanwhile, the increasing law of the remnant slip and the effect of the loading order on the deterioration of the bond performance were studied. Then, two damage factors d _u and D _u were introduced, where d _u is a factor that reflects the damage of the peak bond stress under constant controlling displacement and D _u is also a factor that reflects the damage of the remnant ultimate bond stress under changeable controlling displacement. Making use of the two damage factors and other key variables, the bond constitutive relationships between reinforcing bars and concrete under cyclic loads could be expressed by formulas. The computed τ–s relationships agreed well with those obtained by experiments.