自由活塞斯特林制冷机用直线电机性能仿真与测试

介绍了自由活塞斯特林制冷机用动磁式直线电机结构。采用Ansoft软件对直线电机进行有限元仿真,配合自由活塞制冷机整机仿真软件,研究了直线电机性能及整机制冷性能。采用三组不同外气隙参数的直线电机进行试验验证,结果表明:直线电机性能对整机性能影响较大,且直线电机的定位力会影响动子系统的固有频率,降低自由活塞制冷机的制冷效率;外气隙参数对直线电机性能影响较大,经比较:0.5 mm为外气隙优选参数,并且,在生产过程中须保证直线电机的径向加工精度。     

基于直线电机波浪能发电的制氢设计研究

波浪能是海洋中蕴含的品味最高的能源之一,捕捉波浪能进行发电是目前各国研究的重点。由于现有技术存在发电功率小、电压与电流变化大、传输困难等问题,波浪能发电难以并入陆地电网。文章提出一种系统设计,将波浪发电与海水制氢进行有机结合,可使波浪能电力就地电解海水制氢,为波浪能开发利用提供了一种新的思路。     

微型螺旋管蒸发器的沸腾换热与阻力特性实验研究

设计、制造并测试了一种微型螺旋管蒸发器。对微型螺旋管蒸发器的沸腾换热与阻力特性进行了实验研究。根据实验数据获得雷诺数在1460~10000范围内流阻系数与雷诺数的计算关系式。实验结果表明,这种微型蒸发器换热量超过300W。     

变容积量热器法测量液体比热容实验研究

基于准稳态理论,建立了一种可以实时改变工作腔体容积的非流动型量热器,并自行搭建了比热容测量系统.通过测量温度为273.15～293.15 K常压下纯水的比热容,对实验系统的测量精度及可靠性进行了检测.结果显示,该实验系统的相对偏差绝对平均值为0.35%,验证了该套实验系统设计原理的正确性及实验装置的准确性.此外,测量了4种配比下,含油制冷剂R134a在温度为273.15～293.15 K,其饱和液体的比定压热容和比定容热容.     

变频滚动转子式压缩机变工况性能的实验研究

以R32变频滚动转子式制冷系统为研究对象,通过改变电子膨胀阀开度、压缩机运转频率、蒸发温度和吸排气压比,研究压缩机在不同工况尤其是不同吸气状态下的运行性能,结果表明:在过热段,压缩机容积效率基本不随过热度的变化而变化;在两相段,容积效率随吸气干度的减小呈线性下降趋势,且各工况斜率基本相同。蒸发温度基本不影响压缩机容积效率,而压比越高,容积效率越低;压缩机电效率在过热段和两相段分别随过热度和吸气干度的减小而线性减小,且两相段斜率大于过热段斜率。在相同蒸发温度下,压比越高,电效率越小;在相同压比下,蒸发温度越高,电效率越小;在各工况下,系统COP在过热段基本不变,在两相段随干度减小而减小。吸气干度0.90处的COP比吸气饱和点的COP平均降低了5.5%;容积效率随压缩机频率的提高而增大,电效率和系统COP随压缩机频率的提高而减小。     

不同槽型对海浪发电用永磁直线同步发电机的影响研究

针对海浪发电机采用永磁直线同步发电系统会引起电机严重振动进而发生永磁体断裂的问题,基于直线电机与永磁电机理论,分析了两种槽型对海浪发电用永磁直线同步发电机的电磁力的影响,通过仿真计算确定了采用开槽结构进一步优化电机结构,使海浪发电为用永磁直线同步发电机齿槽力最小。     

护目镜式水闸结构及稳定分析

针对护目镜式水闸上部结构特殊、受力条件复杂致使对其进行结构及稳定分析难度较大的问题,以山东省某护目镜式水闸为例建立了三维有限元数值模型,采用ANSYS软件计算了闸室段各部位及基底的应力状况,得出拱形桁架及闸门槽部位承受拉应力较大,配筋及实际施工过程中应予以重点关注。同时对护目镜式水闸的安全稳定性进行了评价,指出护目镜式水闸是一种安全新颖的水闸型式。     

振动盘式粘度计工作方程的修正及R407C气相粘度的实验研究

对原有的振动盘式粘度计的测量原理进行了系统的分析，并测量了环保制冷剂R407C的气相粘度，从转动惯量，粘性力矩等角度重新分析了悬挂系统中上、中、下悬挂柱对整个测量结果的影响，进一步讨论了相位角的问题，重新确定了工业方程的修正项，用HCFC22进行了校验实验，粘度测量值与献值相比，最大偏差不大于4.5%，测量得到R407C的粘度数据32个，测量温度为295～352K，压力为0.1～2.34MPa，与献值相比，最大偏差小于4.5%，在实验数据的基础上，回归得到了其粘度随温度和密度变化的方程。     

再生式换热器的实验研究与数值模拟

为了解再生式换热器工作特性,采用Matlab软件计算简化后的模型,对换热器内流体和固体的温度分布进行了数值模拟,并进行了实验验证.研究了蓄热体长度、比表面积、速度和蓄热体材质对换热效果的影响.结果表明,面积和流速对换热效果影响明显,而改变蓄热体材质基本无影响.     

翻斗式雨量计翻斗翻转特性的试验和仿真模拟研究

翻斗式雨量计作为水文气象领域最为基础的降水采集设备,具有实用和稳定好等特点,但对翻斗翻转特性机理及翻斗式雨量计机械误差的产因的研究存在不足。为此,利用高速摄像机的室内试验和数值模拟相结合的方法从机理上探究了翻斗式雨量计翻斗的翻转过程。研究结果表明,翻斗在翻转过程中,从启动到停止的用时约为0.35～0.40 s,翻斗从启动到水平的耗时t₁占比较高,约为80%～85%左右,从水平到停止t₂仅约为0.05 s,且存在翻斗触及调节螺帽后的轻微回弹现象。在t₁时间段内水会持续注入翻斗内,是造成附加水量及雨量计机械误差随雨强变化的根本原因。翻斗在极短时间内(约0.40 s)将水倾倒出,且由于翻斗在触碰停止螺栓时会造成轻微回弹现象,由此造成雨量计翻斗在翻出水时产生翻出流量的“双峰”现象,且随着翻斗左右安装倾角变小,而增大的现象。研究结果可为未来翻斗式雨量计的改进提供基础理论支撑。     

Performance of a scroll compressor with R134a at medium temperature heat pump conditions

The isentropic and volumetric efficiency of a scroll hermetic compressor is measured using R134a under medium temperature heat pump conditions. The evaporating temperature ranges from 3 to 36°C and the condensing temperature from 34 to 78°C. The efficiency parameters are fitted to functions of the suction and discharge pressures. At the same port pressures, there are only small differences between the isentropic and volumetric efficiency parameters for R134a and those for R22, the latter determined from the manufacturer's data. The efficiency parameters for R134a are used to compare the performance of the compressor with R12, R134a and R152a in a medium temperature heat pump cycle. The COP and heating capacity exhibit trends similar to those in previous experimental data for a reciprocating compressor.     

小型离心式压气机的湿压缩特性研究

从工程热力学和传热传质学基本原理出发,给出了理想湿压缩的定义,研究了湿压缩对压气机性能的影响,并把计算结果与实验进行对比,得出可以通过湿压缩来减少压缩功以改善燃气轮机的性能,为湿压缩技术的可实现性提供了依据。     

An economic and technical case for a compressor/expander unit for heat pumps

Despite their obvious environmental benefit, heat pumps in general have difficulties in penetrating the heating market because of the high initial capital cost. However, given the fact that in the U.K. space heating alone accounts for nearly 50 per cent of all the primary energy used, the universal adoption of heat pump subsidies similar to those offered by certain German utilities for example would be an effective contributor to the reduction of greenhouse gas emission. However, it would be improper for subsidies alone to be the only mechanism by which heat pumps could gain the scale of market acceptance necessary in order to make the required greenhouse gas emission cuts. Therefore, a new generation of heat pumps must have a superior performance than existing units operating with HCFC R22 or R407c. The use of R410a can aid heat pump market penetration by having heat pumps of a superior performance and a smaller size. However, to make full use of R410a, the difficulties of the relatively low critical point must be overcome and the use of a novel compressor/expander unit is illustrated. Copyright © 2000 John Wiley & Sons, Ltd.     

Simulation and design of a three-stage metal hydride hydrogen compressor based on experimental thermodynamic data

A semi-empirical method was developed to design a three stage Metal Hydride Hydrogen Compressor (MHHC) through the determination of thermodynamic properties of several hydrides. As a first step, three AB₂-type alloys that satisfy operation conditions were selected from published thermodynamic data entailing over 200 single plateau hydrides. These alloys were synthetized by arc melting and characterized by X-Ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM) and Energy Dispersion X-ray spectroscopy (EDX). Absorption and desorption Pressure-composition-Isotherms (P-c-I) were determined between 23 and 80 °C to characterize their thermodynamic properties. Subsequently, an algorithm that uses these experimental data and a real equation of state for gaseous H₂ was implemented to simulate the volume, alloy mass, pressure and temperature of operation for each compressor stage, while optimizing the compression ratio and total number of compressed H₂ moles. Optimal desorption temperatures for the three stages were identified within the range of 110–132 °C. A system compression ratio (CR) of 92 was achieved. The number of H₂ moles compressed, the alloy mass and volume of each stage depend linearly on the volume of the external tank in which the hydrogen is delivered.     

Experimental research of surface roughness effects on highly-loaded compressor cascade aerodynamics

Aircraft engines deteriorate during continuous operation under the action of external factors including fouling, corrosion, and abrasion. The increased surface roughness of compressor passage walls limits airflow and leads to flow loss. However, the partial increase of roughness may also restrain flow separation and reduce flow loss. It is necessary to explore methods that will lower compressor deterioration, thereby improving the overall performance. The experimental research on the effects of surface roughness on highly loaded compressor cascade aerodynamics has been conducted in a low-speed linear cascade wind tunnel. The different levels of roughness are arranged on the suction surface and pressure surface, respectively. Ink-trace flow visualization has been used to measure the flow field on the walls of cascades, and a five-hole probe has been traversed across one pitch at the outlet. By comparing the total pressure loss coefficient, the distributions of the secondary-flow speed vector, and flow fields of various cases, the effects of surface roughness on the aerodynamics of a highly loaded compressor cascade are analyzed and discussed. The results show that adding surface roughness on the suction surface and pressure surface make the loss decrease in most cases. Increasing the surface roughness on the suction surface causes reduced flow speed near the blade, which helps to decrease mixing loss at the cascades outlet. Meanwhile, adding surface roughness on the suction surface restrains flow separation, leading to less flow loss. Various levels of surface roughness mostly weaken the flow turning capacity to various degrees, except in specific cases.     

Elastoplastic frictional contact problem study on interference fits of compressor

The FE parametric quadratic programming (PQP) method developed from the parametric variational principle (PVP) was used for the analysis of the stress distribution of the 3D elastoplastic frictional contact of an impeller-shaft sleeve-shaft. A locomotive-type turbocharger compressor with 24 blades under combined centrifugal and interference-fit loading was considered in the numerical analysis. The solution of elastoplastic frictional contact problems belongs to unspecified boundary problems where the interaction between two kinds of nonlinearities should occur. To save time in the numerical computation, a multi-substructure technique was adopted in the structural modeling. The effect of fit tolerance, wall thickness of the shaft sleeve, and rotational speed on the contact stress was discussed in detail in the numerical computation. To decrease the difficulty of the assembly process and ensure the safety of the working state, the amount of interference between the shaft sleeve and shaft by press-fitting should be controlled strictly to avoid the rapid increase of contact stress. The numerical results show that the algorithm has high accuracy and good convergence. The study can be referred to in deciding the proper fit tolerance and improving the design and manufacturing technology of compressor impellers. __________ Translated from Engineering Mechanics, 2007, 24(1): 186–192, 177 [译自: 工程力学]     

Transcritical CO2 refrigerator and sub‐critical R134a refrigerator: A comparison of the experimental results

This paper describes experiments comparing a commercial available R134a refrigeration plant subjected to a cold store and a prototype R744 (carbon dioxide) system working as a classical ‘split‐systems’ to cool air in residential applications in a transcritical cycle. Both plants are able to develope a refrigeration power equal to 3000 W. The R744 system utilizes aluminium heat exchangers, a semi‐hermetic compressor, a back‐pressure valve and a thermostatic expansion valve. The R134a refrigeration plant operates using a semi‐hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a manifold with two expansion valves, a thermostatic one and a manual one mounted in parallel, and an air cooling evaporator inside the cold store. System performances are compared for two evaporation temperatures varying the temperature of the external air running over the gas‐cooler and over the condenser. The refrigeration load in the cold store is simulated by means of some electrical resistances, whereas the air evaporator of the R744 plant is placed in a very large ambient. The results of the comparison are discussed in terms of temperature of the refrigerants at the compressor discharge line, of refrigerants mass flow rate and of coefficient of performance (COP). The performances measured in terms of COPs show a decrease with respect to the R134a plant working at the same external and internal conditions. Further improvements regarding the components of the cycle are necessary to use in a large‐scale ‘split‐systems’ working with the carbon dioxide. Copyright © 2009 John Wiley & Sons, Ltd.     

往复式压缩机空冷器加装保温棉提高外输气温度的实践

介绍往复式压缩机的参数和工作概况,针对冬季3台往复式压缩机组频繁停机问题,分析造成压缩机出口排气温度过低的原因;提出通过加装保温棉、控制空冷器的风量来进行改进,以达到提升压缩机的排气温度,保证机组正常运行。     

An experimental analysis of a thermodynamic model of a vapour compression refrigeration plant on varying the compressor speed

The principal aim of this paper is the study of a thermodynamic model that simulates the working of a vapour compression refrigeration plant. The model allows the evaluation of plant performances when the compressor capacity is regulated varying its velocity by means of an inverter inserted into the compressor electric motor feeder. This type of control allows to match continuously the compressor refrigeration capacity to the load, determining an energy saving in comparison with the classical thermostatic control. In particular, in this paper the outputs of the model are compared with the experimental results. The vapour compression experimental refrigeration plant, whose evaporator is located in a commercially available cold store, presents a semi‐hermetic reciprocating compressor able to work with the R22 and some its substitutes, and designed for a revolution speed corresponding to a 50 Hz frequency of a compressor electric motor supply current. The comparison of model and experimental results is realized by varying the supply current frequency of the compressor in the range 30–50 Hz using the R407C (R32/R125/R134a 23/25/52% in mass) that represents the most suitable working fluid for the R22 substitution. The model‐experimental comparison results reported in terms of condensation temperature, compression ratio, condensation power and Coefficient Of Performance are completely acceptable. Moreover, an exergetic analysis is realized to explain the performances of the plant components when the compressor speed is varied. Copyright © 2004 John Wiley & Sons, Ltd.