The transient response of an evaporator fed through an electronic expansion valve

The primary task of an expansion valve in a refrigerating machine is to control the mass flowrate into the evaporator to obtain optimal operation without ‘hunting’ under given conditions. A stepper-motor-controlled expansion valve and an evaporator have been studied. The tests were carried out on a fixed refrigerating machine of cooling capacity less than 6 kW, with constant condensation conditions and variable evaporating temperature (−20 to +10°C) and compressor speed (1000 to 3000 r.p.m). Two control algorithms (proportional/derivative and qualitative optimal regulation) have been developed for opening and closing the valve with the stepper motor. The control parameters depend on both the expansion valve and the evaporator transfer functions. In steady-state conditions, the system is stable with a superheat equal to the set value. Under transient conditions, with step excitations of 300 and 1000 r.p.m as well as for cold-start of the machine, the control algorithms are adequate for regulating the refrigerant flowrate into the evaporator. © 1997 John Wiley & Sons, Ltd.     

蒸发器电子膨胀阀过热度模糊控制仿真及分析

建立了蒸发器一电子膨胀阀过热度模糊控制仿真系统，通过仿真分析了量化因子、比例因子及不同的采样时间，对控制效果及参数设置的影响、模糊控制与PID的控制效果比较：同时将带自修正因子参数自调整模糊控制应用到对电子膨胀阀的控制当中。对蒸发器过热度电子膨胀阀模糊控制系统的设计及调试有一定的指导意义。     

电子膨胀阀对变频压缩机排气温度控制的实验研究

排气温度的有效控制对压缩机长期正常工作有重要影响。传统的办法是采用喷液冷却,但其装置复杂、控制难度大;而以过热度和排气温度作为电子膨胀阀——干式蒸发器调节回路的双反馈信号,弥补了仅仅以过热度作为反馈信号的不足,能够同时实现对蒸发器效率、压缩机吸/排气安全的综合控制,使得制冷系统简单、易用。     

The choice of a thermostatic expansion valve for a CFC12 refrigeration system retrofitted with HFC134a

There is a need to develop a suitably charged thermostatic expansion valve to work with systems charged with HFC134a. The conventional CFC12 cross-charged valve does work, but with a slight loss of superheat sensitivity. A pure HFC134a charged valve lacks a constant superheat over a range of evaporator temperatures, and may require a smaller orifice size than the conventional cross-charged valve.     

The control of a refrigeration system using a compact plate heat exchanger as an evaporator

This paper will show some of the problems that may be encountered when using a compact plate exchanger as an evaporator in a refrigeration system which utilizes a thermostatic expansion valve as its controlling device.     

Off‐design performance and operation strategy of expansion process in compressed air energy systems

Compressed air energy storage (CAES) systems usually operate under off‐design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. In order to optimize design and operation of CAES systems, it is significant to study off‐design performance. The expansion process plays an important role in the whole system. The main objective of this study is to explore the off‐design characteristics and optimization strategy of the multistage expansion process of CAES systems with thermal storage. Two kinds of off‐design operating modes, which are equal‐power‐ratio (EPR) operation and optimizing variable stator vane rotation angle (OVRA) operation, are proposed and compared for the first time. Correlation between key parameters such as total output power ratio, exergy efficiency, outlet air/water temperature versus mass flow rate ratio, and inlet pressure are revealed. Furthermore, optimal operation principles are obtained. The primary optimizing operation principle is to optimize the isentropic efficiencies of low‐pressure stages to improve the whole efficiency of expansion process. Lastly, the optimized regulating law for variable stator vane is expressed in a polynomial form.     

天然气发动机废气控制阀控制及性能匹配

基于天然气发动机废气控制阀控制机理,试验研究不同结构原理下的废气控制阀的性能指标,通过综合对比分析发现:废气控制阀样件A与增压器性能匹配最佳,增压高效区为R PWM=15%~75%,为优化标定发动机的低速性能及增压器的瞬态响应提供了理论依据。     

平衡阀在供热系统中的应用

在阐述平衡阀发展及工作原理的基础上,给出各种常用平衡阀的选择方法,探讨平衡阀的应用场所及安装注意问题。简要介绍电动动态平衡阀的应用系统调节过程,并推导调节传递函数,对平衡阀在工程中经济、科学选用具有指导意义。     

辐照强度对直膨式太阳能热泵性能影响的研究

文章搭建了直膨式太阳能热泵热水系统实验装置,研究了辐照强度对直膨式太阳能热泵性能的影响。结果表明,在环境温度及冷凝温度不变的情况下,蒸发温度及性能系数(COP)值随着辐照强度的增大而升高,且辐照强度增加200 W/m2,蒸发温度升高3~5℃,COP值升高0.8~1.2;得热效率随着辐照强度的增大而降低,其降低速率随着辐照强度的增大而逐渐减小。     

Constraints of using thermostatic expansion valves to operate air-cooled chillers at lower condensing temperatures

Thermostatic expansion valves (TXVs) have long been used in air-cooled chillers to implement head pressure control under which the condensing temperature is kept high at around 50 °C by staging condenser fans as few as possible. This paper considers how TXVs prevent the chillers from operating with an increased COP at lower condensing temperatures when the chiller load or outdoor temperature drops. An analysis on an existing air-cooled reciprocating chiller showed that the range of differential pressures across TXVs restricts the maximum heat rejection airflow required to increase the chiller COP, though the set point of condensing temperature is reduced to 22 °C from a high level of 45 °C. It is possible to use electronic expansion valves to meet the differential pressure requirements for maximum chiller COP. There is a maximum of 28.7% increase in the chiller COP when the heat rejection airflow is able to be maximized in various operating conditions. The results of this paper emphasize criteria for lowering the condensing temperature to enhance the performance of air-cooled chillers.     

热风阀阀板的节能探讨

我国国内的热风阀阀板同国外阀板相比,存在着热损失大的缺点,原因是耐火材料衬热阻较小。文中以有限元模拟技术为手段,以增大热阻为目的,进行了耐火材料组合衬设计。设计结果表明,组合衬的热损失可以降到单一衬的43％～56％左右,节能效果十分显著。     

进口压力对燃气轮机气体燃料阀调节性能的影响及其修正补偿方法研究

燃料调节阀是精确控制燃气轮机燃料流量和机组负荷的基本组件。本文基于调节阀的位移-流量特性及其液压伺服机构组成,建立了燃料阀位置伺服系统的数学模型,分析了燃料阀组及其控制系统的动态响应特性,研究了进口压力对调节阀性能的影响,并提出了一种燃料进口压力修正补偿控制方法。仿真结果表明：经过压力修正后,系统响应频宽提高0.5 Hz,幅值裕量增大20°。     

Choking phenomenon and pressure drop mechanism in electronic expansion valves

A quasi one-dimensional model in which oblique evaporation wave theory and shock wave theory are employed is developed to investigate the choking phenomenon and the pressure drop mechanism in electronic expansion valves (EEV). The data predicted by the model are validated by the experimental data presented by Zhang. The results show that the choking mass flow rate of EEVs calculated by Abuaf’s model, which was developed with water, agrees well with the tested data when R22 is used as the working fluid. The relative deviation between the predicted data and Zhang’s test results is in the range from −5% to 6%. Compared with the test data, the choking mass flow rate of EEVs with the mixture R407c is over predicted by Abuaf’s model. The back pressure at the EEV exit when choking just occurs is decreased as the flow area (opening pulse number) is decreased. The trend is consistent with Zhang’s test results.     

直膨式太阳能热泵运行特性的实验研究

对直接膨胀式太阳能热泵热水系统进行了实验研究,实验期间,太阳能辐照度变化范围为143.12~664.6 W/m2,分别采用三种不同结构的集热器和蒸发器,得出系统COP为2.49~3.47,表明该系统在各种天气情况下均能够可靠地生产45℃的生活热水,热性能稳定,可以全天候地提供生活热水且具有节能效果;同时选取双集热器的两组数据,分析了太阳辐照度对热泵系统运行的影响。     

涡轮增压器排气旁通阀对柴油机性能的影响

通过计算和试验提出了旁通阀开启面积、预紧压力等参数对增压器和柴油机在功率、油耗及排温等性能参数的影响。     

倒装式自封阀设计

该自封阀是根据某游艇机配套倒装式机油滤清器的功能要求设计的产品,安装于倒装式机油滤清器旋装滤内腔,与滤芯进口止回阀相结合,在维护机油滤清器需拆下旋装滤时可快速将滤芯进、出口封断,防止油液从滤芯进出口流出,减少维护时对环境的污染。     

球型调节阀流动引起阀体关键点压力脉动试验研究

以汽轮机常用的球型调节阀为研究对象，通过在阀座喉部、阀碟头部等阀体内各关键部位设置测点，利用微小型高频动态压力传感器及其采集系统，进行了多种工况和多个方位的试验研究，探讨了由于阀内气体流动引发的阀门工作不稳定性。试验研究表明，原型阀的气体压力脉动强度微弱，不稳定工况范围小，稳定性比较良好。     

凝水压力控制阀的设计与数值研究

在船用凝汽式汽轮机凝水系统的设计与调试中,为防止凝水泵出现汽蚀,通常需要对凝水系统压力进行调整。为实现凝水系统压力的在线便捷调节,稳定凝水泵出口扬程及流量,设计了凝水压力控制阀。该阀采用二级节流的结构形式,可通过调整阀开度改变节流效果。通过公式计算得到了不同开度下凝水压力控制阀的调节性能,根据计算结果,控制阀满足设计要求。采用CFD流体计算软件对凝水压力控制阀进行三维数值模拟,验证计算的准确性。     

焊接波纹管式温控阀的设计和试验研究

针对风电机组润滑油冷却系统中传统橡胶囊式温控阀使用寿命短、综合运营成本居高不下等问题,设计、制造了焊接波纹管式温控阀,实验研究了其动作特性并进行了实际应用。风机齿轮箱润滑油冷却系统中,温控阀的调节行程长、稳定性要求高、使用环境恶劣,焊接波纹管结构的引入,既满足了温控阀的实际功能需求,又克服了传统囊式温控阀使用寿命低、性能不稳定等缺点。通过试验,合理设计了温控阀的调节弹簧参数,将其与焊接波纹管配合使用,满足了温控阀的复位调节需求。通过填充蜂窝铝材料强化了储蜡腔的内部导热能力,有效提高了焊接波纹管式温控阀的响应速度。实际挂机试验表明,焊接波纹管式温控阀能有效代替传统囊式温控阀,有效降低风机综合运营成本,可作为风机齿轮箱润滑油冷却系统技术改造方案推广使用。     

全液压制动系统控制阀变参数仿真分析

控制阀决定了全液压制动系统的充液压力。从物理运动及结构两方面介绍全液压制动控制阀的工作原理,分析影响充液压力上限的因素。建立控制阀三维数学模型,应用Fluent软件对不同进口速度u、阀芯套筒锥角β以及钢球直径D的控制阀进行模拟研究,对比分析其内部流场的变化。搭建全液压制动系统试验台进行充液压力上限测试试验,验证理论分析及仿真结果的有效性,得出各参数对充液压力上限的影响规律。结果表明,控制阀的进口速度、阀芯套筒锥角与充液压力上限呈正相关,钢球直径与充液压力上限呈负相关。