Experimental Analysis of the Performances of Unit Refrigeration Systems Based on Parallel Compressors with Consideration of the Volumetric and Isentropic Efficiency

The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression ratio.Moreover,the following influential factors have been taken into account:evaporation temperature,condensation temperature and compressor suction-exhaust pressure ratio for different opening conditions of the compressor.The following quantities have been selected as the unit performance measurement indicators:refrigeration capacity,energy efficiency ratio(COP),compressor power consumption,and refrigerant flow rate.The experimental results indicate that the system refrigeration capacity and COP decrease with a decrease in evaporation temperature,increase of condensation temperature,and increase in pressure ratio.The refrigerant flow rate increases with the increase in evaporation temperature,decrease in condensing temperature and increase in pressure ratio.The compressor power consumption increases with the increase in condensing temperature and increase in pressure ratio,but is not significantly affected by the evaporation temperature.

Development of High Efficiency Swing Compressor for R32 Refrigerant

In the age of global warming, energy saving features and overall reduction of environmental impact are critical components that must be addressed when developing new HVAC （heating ventilation and air conditioning） units. We chose R32 refrigerant, with its lower LCCP （life cycle climate performance） as a more sustainable choice than R410A. However, R32 has its drawbacks. Due to its smaller molecular weight, internal leakage loss is higher for R32. Moreover, high discharge gas temperature decreases the reliability of the compressor, and makes a large overheating loss increase. In this study, we will describe the technologies （reducing the piston pressurizing force, heat-insulating structure, optimizing the port diameter） that were developed to overcome these drawbacks. We will also oresent the performance and reliability of the newly develoned high efficiency swing, comnressor series for R32 refrigerant.

Economy of Energy during Refrigerating Machine Operation

Idealized cycles of refrigerating machines with adiabatic and isothermal compression of refrigerant vapor were investigated. Energetic characteristics of cycles： specific mass and volume cooling capacity q0 and qv, work of compression 1, refrigerating coefficient of performance e and power N for drive of compressor were compared. These characteristics were calculated for eight refrigerants at temperature of their condensation 30 ℃ and temperatures of boiling -15℃ and -30 ℃. The calculations show that the use of isothermal compression of refrigerant vapor ensures economy of energy during refrigerating machine operation.

Improving the Reliability of a Domestic Refrigerator Compressor Subjected to Repetitive Loading

As a reliability quantitative specification, parametric accelerated life testing was used to assess the reliability of a newly designed compressor of a commercial refrigerator subjected to repetitive stresses. A generalized life-stress failure model and new sample size equation with a new load concept were derived starting with the basic refrigeration cycle. The sample size equation with the acceleration factor also enabled the parametric accelerated life testing to quickly evaluate the expected lifetime. The design of this testing should help an engineer uncover the design parameters affecting reliability during the design process of the compressor system. Consequently, it should help companies improve product reliability and avoid recalls due to the product failures in the field. A newly designed compressor in a commercial refrigerator was used as a test case.

Present status and one upgrading method with a cold compressor of the EAST sub-cooling helium cryogenic system

Since 2006, the superconducting toroidal field（TF） coils of the Experimental Advanced Superconducting Tokomak（EAST） have been successfully cooled by supercritical helium at a temperature of 4.5 K and a pressure of 4 bara in eleven experiments. To obtain higher operating currents and magnetic fields it is necessary to lower the operating temperature of the TF coils.The EAST sub-cooling helium cryogenic system, with a warm oil ring pump（ORP）, was tested twice in cool-down experiments, which made the TF coils operate at 3.8 K. However, the long term operational stability of the sub-cooling system cannot be guaranteed because of the ORP＇s poor mechanical and control performance. In this paper, the present status of the EAST subcooling helium cryogenic system is described, and then several cooling methods below 4.2 K and their merits are presented and analyzed. Finally, an upgrading method with a cold compressor for an EAST sub-cooling helium cryogenic system is proposed. The new process flow and thermodynamic calculation of the sub-cooling helium system, and the main parameters of the cold compressor, are also presented in detail. This work will provide a reference for the future upgrading of the sub-cooling helium system for higher operation parameters of the EAST device.

Optimal synthesis of compression refrigeration system using a novel MINLP approach

The optimal design of a compression refrigeration system(CRS) with multiple temperature levels is very important to chemical process industries and also represents considerable challenges in process systems engineering. In this paper, a general methodology for the optimal synthesis of the CRS, which simultaneously integrates CRS and Heat Exchanger Networks(HEN) to minimize the total compressor shaft work consumption based on an MINLP model, has been proposed. The major contribution of this method is in addressing the optimal design of refrigeration cycle with variable refrigeration temperature levels. The method can be used to make major decisions in the CRS design, such as the number of levels, temperature levels, and heat transfer duties. The performance of the developed methodology has been illustrated with a case study of an ethylene CRS in an industrial ethylene plant, and the optimal solution has been examined by rigorous simulations in Aspen Plus to verify its feasibility and consistency.

Reducing the Gas Pressure Drop in Suction Mufflers of Hermetic Reciprocating Compressors

The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.

Estimation of Vapor Quality at Compressor Suction of Air Conditioner

To evaluate performance and reliability of an air conditioner, the states of its refrigerant in the refrigeration cycle need to be understood. Since the isentropic exponent of the next-generation refrigerant R32 is larger than that of conventional refrigerant R410A, the compressor discharge temperature of R32 is higher than that of R410A. When a wet refrigerant is entered into a compressor suction line to decrease the discharge temperature, it is generally difficult to estimate the vapor quality at the suction. This paper describes a method that estimates a vapor quality at the compressor suction by applying energy balances on the compressor with the values of suction pressure, discharge pressure, discharge temperature, etc. In the air conditioner test, the vapor qualities at the compressor suction estimated with this method agreed well with those estimated with the conventional method by measuring liquid and vapor flow-rates. Moreover, this paper derived a relational expression for estimating a compressor suction state from a discharge state and discusses the characteristics of the coefficients in the expression calculated from the test results.

涡轮压缩膨胀机的设计与性能分析

随着人们环境保护意识的加强,天然工质制冷剂重新受到研究人员的关注。空气是一种安全且对环境绝对友好的天然制冷剂,未来,压缩空气制冷循环有望成为传统蒸气压缩制冷循环的潜在替代品。压缩膨胀机作为压缩空气制冷的核心部件,其工作效率对机组性能有直接影响。为了设计出能够配合膨胀机高效工作的离心压缩机,需要对传统的设计方法进行一些修正。本文将质量、动量、能量守恒与射流尾迹区理论相结合,并将传统的离心压缩机相关参数推广到较低压力的范围中,提出了一种与现有的涡轮膨胀机相匹配的离心压缩机几何参数的设计方法。使用该方法为现有的膨胀机设计了对应的离心压缩机,并利用其他学者分析过的离心压缩机模型对该方法进行验证,利用计算流体力学方法(CFD)对压缩膨胀机变工况下的工作性能及对膨胀功的利用率进行模拟分析。按本方法设计的离心压缩机在设计工况下能够以高于92%的效率利用膨胀机的输出功。在变工况条件下能够以高于88%的效率利用膨胀机的输出功,并且在设计质量流量附近能够顺利运行。

嵌入式冰箱压缩机仓散热优化研究

针对嵌入式冰箱压缩机仓散热效果不佳的问题,采用数值模拟与试验结合的方法对其散热进行研究。模拟了嵌入式冰箱压缩机仓的散热过程,结果显示冰箱背部气流未经过充分散热再次进入到压缩机仓形成短路气流,且由于橱柜的影响进入压缩机仓内的总气流相较于自由状态下减少了51.78%;针对散热效果差的原因提出了3种不同适用场景的优化方案,并对各方案在通风量、能耗、制冷性能方面进行对比研究。结果表明,3种优化方案均能改善散热效果,但各有优劣,优化方案的总风量比原嵌入方案分别提高了3.9%,75.3%,55.3%;在32℃和16℃的环境温度下,3种优化方案的能耗相较于原嵌入方案分别降低了6.50%和3.90%,23.03%和25.07%,17.70%和17.50%。研究结果为不同适用场景下的嵌入式冰箱压缩机仓散热优化提供了解决思路和参考。

采用免疫算法的离心压缩机叶轮 多目标优化及性能分析

为进一步探索高性能离心压缩机的优化设计方法,以某气浮轴承离心制冷压缩机叶轮为研究对象,结合多层前向神经网络,发展了基于非支配近邻免疫算法的叶轮多目标优化策略。首先,采用免疫算法优化神经网络的隐含层结构,以提升其作为代理模型的非线性逼近能力;其次,以近喘振点、设计点、近堵塞点的多变效率最大为优化目标,采用免疫算法进行叶轮全工况性能寻优,并通过数值仿真对优化前、后叶轮的气动性能及流动特性进行了对比分析。仿真结果表明:采用免疫算法进行优化后,叶轮在近喘振点、设计点、近堵塞点的多变效率分别提高了1.8%、1.9%、4%,稳定运行工况范围明显拓宽;对比流场后发现,在90%叶高处,主叶片和分流叶片载荷从前缘至尾缘均明显增加,叶片做功能力增大;分流叶片进口倾角减小使得叶片进口冲击损失降低,流道内泄漏流与主流掺混现象明显减弱,叶轮内部流动更加均匀。研究结果验证了所提多目标优化策略的有效性。

双向旋转斜盘压缩机润滑油循环性能工程试验研究

为了解决双向旋转斜盘式活塞压缩机在汽车空调温控系统中因润滑油充注量不当而导致的制冷效率降低和潜在故障问题,对润滑油充注策略进行优化,以提高系统运行的效率和稳定性。分析了润滑油充注量不足或过量可能导致的各种问题,探究了在不同压缩机转速条件下,不同润滑油充注量对制冷性能的具体影响。通过对比试验发现,当润滑油充注量被精确控制在390±20~535±20 mL的范围内,空调系统能够在变化的工作状态下保持最优性能,并显著降低由润滑油不足带来的风险;最佳的润滑油与制冷剂的配比约为12%,并提出了一系列技术措施,这些措施旨在提高斜盘式活塞压缩机的可靠性,为斜盘式活塞压缩机在广泛的工程应用中的润滑策略提供了理论依据和实践指导。

气悬浮制冷压缩机的研究进展

气悬浮制冷压缩机采用气体轴承,相较于传统压缩机的滑动轴承,气体轴承制冷压缩机具有速度快、无油、小型化、低成本等优点。本文综述了气悬浮制冷压缩机轴承承载力、稳定性和制冷系统性能方面的研究新进展,介绍了气悬浮制冷压缩机在制冷空调行业的应用,总结了气悬浮制冷压缩机关键技术的改进措施,为高效制冷压缩机的开发奠定理论基础。

无霜冰箱压缩机与风机运行特性研究

为了提高制冷系统的能源效率,通过优化压缩机与风机的匹配运行,建立了冰箱动态运行仿真模型,分析了压缩机转速和风机风量对冰箱运行特性的影响,包括冷却换热量、结霜换热量、功率。同时,研究了压缩机与风机的匹配方案对系统性能的影响。结果表明,在满足降温需求的前提下,提升压缩机运行率有助于降低能耗;在1 200~2 100 r/min转速范围内,增加压缩机转速可以显著提升换热量,当转速超过2 100 r/min时,压缩机的运行率随压缩机转速增加而下降,系统功率随压缩机转速增加而升高;增加风机风量可提高冷却换热量占总换热量的比重,与0.013 kg/s风量相比,0.023 kg/s风量下冷却换热量的比重提升了2.73%,然而,风机风量的增加也导致了系统运行功率的增加;在特定降温需求下,存在最佳的压缩机转速与风机风量的匹配方案,使得系统功率取得最小值,在68 W的降温需求下,冰箱功率最低的匹配方案为风机风量0.017 kg/s,压缩机的转速2 111 r/min,此时系统运行功率为54.28 W。研究揭示了结霜换热量、冷却换热量及功率的变化规律,并提出了风机风量与压缩机转速的低能耗匹配策略,为制冷系统中压缩机与风机的运行参数优化、能效提升提供了理论依据。

双螺杆制冷压缩机排气压力脉动特性的实验研究

为研究一台冷水机组用双螺杆制冷压缩机的压力脉动特性,本文测录了压缩机压缩及排气过程的瞬态压力变化,解析其压力脉动频域特性,研究了运行转速和冷凝温度对压力脉动特性的影响,对比了压缩机采用变频与变滑阀两种容量调节方式在相同制冷量下的压力脉动、噪声和热力性能。研究结果表明:压缩腔压力脉动来源于转子工作容积内压力周期性升高,并受齿间多通道泄漏过程的影响;排气腔压力脉动来源于工作容积与排气腔的周期性连通与脱开,受排气压力及气体质量流量等因素影响。随着转速的升高,排气腔压力脉动从转速为1380 r/min时的58.6 kPa升至4200 r/min时的141.0 kPa。随着冷凝温度的升高,压力脉动幅值从34℃时的132.0 kPa升至57℃时的314.0 kPa。在相同制冷量下与容调滑阀相比,双螺杆制冷压缩机采用变频的容量调节方式在压力脉动、噪声和热力性能方面均具有显著优势,压力脉动降低54.6%以上,噪声值下降2.9 dB(A)以上,COP提升5.5%以上。

冰箱压缩机活塞轻量化优化分析

在对冰箱压缩机活塞参数进行计算,对活塞材料特性进行分析的基础上,对活塞进行轻量化优化。通过建模,对优化前后的冰箱压缩机活塞进行仿真分析,得到活塞受到的侧向力和曲轴受到的作用力。对装配优化后活塞的冰箱压缩机进行寿命试验,并对优化前后的活塞进行冰箱压缩机装机测试,确认活塞轻量化优化效果良好,可以为提高冰箱压缩机效率及降低成本提供参考。

基于虚拟仿真的“制冷压缩机”课程教学与实践训练改革——以“滚动转子式压缩机”教学为例

基于“卓越工程师培养计划”的课堂教学要求,结合“制冷压缩机”课程大纲及教学内容,提出了基于虚拟仿真平台的“制冷压缩机”课程教学与实践训练改革。在教学内容方面,通过归纳教学内容,加强学生对于知识内容的掌握,并使教学内容与前沿技术和工程应用紧密联系,拓宽学生的眼界;在教学方法方面,通过引入模拟软件和虚拟实验,丰富授课方法,激发学生的学习兴趣;在实践训练方面,着重强调理论知识的应用,开发多层次、多模块的实验实践训练体系,培养学生的理论知识应用能力、动手能力、解决实际工程问题的能力、创新思维、团队协作能力等综合素质。

冰箱压缩机高频噪声识别及优化

当前冰箱压缩机高频噪声问题突出,高频噪声听感差易引发用户投诉,识别冰箱压缩机的高频噪声问题,并进行相关优化已迫在眉睫。针对当前的冰箱压缩机易出现的高频噪声问题,以某款定速机型为例,从噪声源和传递路径进行研究,针对某款定速机型的2500 Hz、4000 Hz、5000 Hz等高频噪声问题进行了深度分析并优化。测试结果显示,采用此优化方案能够明显改善其高频噪声问题,为冰箱压缩机高频噪声问题改善提供了相关思路和理论依据,对后续的产品设计具有一定的指导意义。

高温工况下两相补气对空调压缩机热力性能的影响研究

在夏季超高温条件下,室外局部环境温度可达到50℃以上。过高的冷凝温度意味着压缩机排气压力较高、压比较大,同时压缩机散热困难,导致压缩机的排气温度超过120℃,压缩机内润滑油面临碳化风险,严重地影响了压缩机的可靠性。此外,在夏季超高温条件下,空调的制冷量快速衰减,制冷效果不尽人意。对于上述问题,在现有补气增焓技术的基础上提出两相补气,以解决夏季超高温工况下压缩机排气温度过高、制冷量衰减较大的问题。

往复式压缩机动平衡分析

低频噪声问题是冰箱市场噪声客诉案例中非常常见的一类问题,这类问题的大部分原因是压缩机与冰箱底板的共振,而产生共振的激励源大部分为压缩机运转时的不平衡惯性力,对往复式压缩机进行动平衡优化设计,可以显著降低其运转时的不平衡惯性力,进而改善冰箱系统的低频噪声。基于某种定频往复式压缩机,将其曲轴-连杆-活塞系统简化成曲柄连杆机构,对机构进行动力学分析,推导了不平衡惯性力的理论公式并对往复方向与铭板方向的惯性力特征进行说明。依据不平衡惯性力的理论公式,开发了专用的往复式压缩机动平衡设计软件,该软件可以实现计算不同配平方案的往复惯性力曲线以及计算最优配平质量的功能;针对这一软件,提出了无量纲因数法对软件计算值与试验值进行对比,结果表明两者的误差水平满足工程应用的要求。