不完全湿压缩应用于转子式制冷系统的可行性研究

针对部分制冷工质排气温度较高的现象,将不完全湿压缩方法应用于转子式制冷系统,通过在不同频率下改变压缩机的吸气状态(过热至不完全湿压缩),研究了系统循环性能及核心部件的热力特性。实验结果表明:不完全湿压缩下存在一个最佳干度控制范围0x0.96,在该区间内制冷量提升5.1%～5.5%,制冷性能系数(Coefficient of Performance,COP)提升5.4%～5.8%,排气温度较过热段改善20%以上,系统性能得到了明显提升;当吸气干度范围在0x0.96时,压缩机的热力性能基本维持良好,相较于过热段的极大值处,容积效率降低仅1%～2%,电效率降低亦仅1%～2%;不完全湿压缩下,压缩机频率的变化对系统性能及压缩机热力性能影响均较大;将压缩机运行于最佳干度范围区间0x0.96的较低频或是额定频率附近将获得最优综合效率。     

转子式压缩机吸气带液时排气状态的变化

滚动转子式压缩机具有较好的抗湿压缩性能,利用少量吸气带液可有效降低压缩机排气温度,且不造成额外的系统成本.对滚动转子式压缩机少量吸气带液时,排气温度、排气比焓的变化趋势进行了实验研究,并对压缩机功耗、吸气比焓和机壳散热量等三个排气比焓的影响因子进行了分析.结果表明:少量吸气带液能有效降低排气温度,且压缩机运行性能良好;当吸气干度x为0.9x1.0时,三个影响因子均趋向定值,且机壳散热所占比例很小(低于1%).     

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。     

空气源热泵系统湿压缩与电子膨胀阀调控方式的研究

针对空气源热泵吸气带液问题,通过调节电子膨胀阀开度改变压缩机吸气口制冷剂状态,研究了四种不同调控工况对系统性能和参数的影响,分析不同调控工况下系统性能的变化。实验结果表明:较大的电子膨胀阀开度可提高蒸发压力和制冷剂质量流量,从而改善系统性能,但这不是湿压缩所产生的影响,相反后期大量的吸气带液会导致系统性能降低;吸气带液可以有效降低压缩机排气温度,同时也会使单位制热量和比功降低;在实际运行过程中,应采取定过热度控制方法,且过热度应尽量小,但要避免压缩机吸气带液。     

大型空气压缩机变工况性能试验研究

压缩空气储能系统压缩机受系统自身特性影响,长期处于变工况运行状态。对某多级压缩空气储能系统大型空气压缩机变工况条件下级间性能开展试验研究,即利用压缩机管网特性试验平台,开展排气压力6.5～9.5MPa范围试验测试,对压缩机各级吸气和排气压力、吸气和排气温度、压缩机排气量、电机电流、电压等参数进行实时采集。通过对压缩机实时变工况下各项参数分析,具体研究压缩机的容积效率、循环指示功率、等温效率、各级压比分配和各级压损随出口负荷变化而变化的规律。研究结果表明:压缩机的容积效率基本不随工况的变化而变化,平均为0.96;循环指示功率随出口负荷的增加而增加;压缩机的多变效率从74.02%上升到78.14%,多变效率随着排气压力的增加而增加;低压级压比增大速度较快,易达到额定状态,高压级压比达到额定状态较缓;一～四级的相对压力损失基本保持不变,五级出口排气到集气汇管的相对压力损失随着出口负荷的增大而减小。     

R1234yf/R134a应用于汽车空调系统的性能研究

选取R1234yf与R134a两种不同配比(56∶44与89∶11)混合而成的新型混合制冷剂对R134a汽车空调系统进行直接替代实验研究。结果表明:相同工况下,三种制冷剂压缩机排气压力相差不大;混合制冷剂循环流量均大于R134a且具有更高的压缩机容积效率;混合制冷剂制冷量与R134a相差不大,但压缩机功率较高。从性能系数上看,R134a优于两种不同配比的混合制冷剂,但差异在6.5%以内。因此,这两种低GWP混合制冷剂用于汽车空调R134a直接替换具有可行性。     

空气源热泵系统压缩机吸气带液问题的研究

以空气源热泵热水机组为实验研究对象,通过改变电子膨胀阀开度,研究压缩机吸气状态对系统性能的影响,研究结果表明:(1)在加热前期(水箱平均温度20~30℃),膨胀阀开度越大,系统COP(能效比)越大;在加热后期(水箱平均温度40~55℃),膨胀阀开度越大,系统COP越小;(2)压缩机吸气带液可以有效改善冷凝器的换热性能,提高总换热系数,但在加热后期,压缩机大量吸气带液时,制冷剂质量流量降低造成的影响更大,因此系统制热量先上升后下降;(3)以压缩机吸气过热度为控制对象调节电子膨胀阀,使压缩机处于少量吸气带液状态,可以有效提高系统COP。     

低速小负荷下提高柴油机排气温度的措施

介绍城市用重型车全球统一瞬态试验循环的背景,指出提高发动机低速小负荷时的排气温度对提高SCR系统催化剂的效率有重要意义;以某型柴油机为试验样机,通过试验对比研究带增压器发动机和自然吸气发动机在低速小负荷时对发动机排气温度及排放的影响。试验研究发现,在低速小负荷工况下相比于带增压器的柴油机,处于自然吸气状态的柴油机能够提升排气温度,转速越高负荷越大,提温能力越明显;小负荷时自然吸气有利于降低油耗率,并且自然吸气对降低NOx排放有利。     

变流量制冷系统循环性能稳定性的实验研究

针对变制冷剂流量(Variable Refrigerant Flow,VRF)空调系统中过热度、制冷量及性能系数(Coefficient of Performance,COP)等参数的不稳定现象,利用R32变流量制冷循环实验台,研究过热度振荡对系统参数稳定性的影响。结果表明:随着系统内制冷剂流量的增加,蒸发器内制冷剂流型迅速变化,引起换热方式的交替,过热度进入最小稳定过热度线(Minimal Stable Superheat,MSS)的不稳定区间,从而产生了过热度振荡;当过热度处于不同运行频率下的最小稳定点时,系统性能达到最佳,控制难度得到优化;系统定压比运行下,频率的增大对压缩机耗功有更直接的影响,因而导致COP与频率成反比。     

机械蒸汽压缩机模型及其与风力发电机耦合模拟研究

机械蒸汽压缩海水淡化是一种很有前景的消纳风能的方式,其中的压缩机是这种能源利用方式的核心部件。建立了离心式蒸汽压缩机数学模型,研究了压缩机性能参数间的关系,重点探讨了压缩机输入功率及吸气蒸汽参数与压缩机流量、压比和转速间的关系,并通过耦合风力发电机模型,研究了定压比条件下,压缩机流量和转速在风力发电机随机功率变化时的响应曲线。结果表明,风力发电机驱动的机械蒸汽压缩机需要辅助能源来保证在较小的风力发电机输入功率情况下,压缩机能稳定运行在非喘振区。对于额定功率为160 k W的压缩机,在压比2.4条件下的最小输入功率为50 k W。     

Investigation of the effects of vapour quality and oil concentration on performance of a swash plate compressor

The main objective of the present study is to experimentally investigate the effects of vapour quality and oil concentration on the performance of a swash plate compressor for automotive air conditioning systems. R‐134a is used as refrigerant. The compressor used is a typical automotive swash‐plate‐type compressor driven by a 10 hp variable‐speed electric motor and lubricated by polyalkylene glycol (PAG) oil. The variables measured during the experiment are pressure, temperature, oil concentration, total mass flow rate and vapour mass flow at the inlet and outlet of the compressor. The experiment was performed at varying compressor speeds, compression ratios and vapour quality. The results revealed some unknown aspects of the compression process in an automotive air conditioning system. The vapour quality does not affect volumetric efficiency, but influences isentropic efficiency of the compressor. In the vapour quality range of 80–90%, isentropic efficiency decreases with increasing vapour quality. During the compression process, only a portion of the liquid refrigerant evaporates. However, at the outlet of the compressor, refrigerant/oil mixture never reaches steady state. The evaporation ratio decreases with increasing compressor speed, and with increasing vapour quality as well. Copyright © 2005 John Wiley & Sons, Ltd.     

Simplified steady-state modeling for variable speed compressor

This paper presents a detailed analysis of semi-empirical methods to calculate mass flow rate, shaft power and discharge temperature for three types of variable speed compressors: reciprocating, scroll and piston rotary. The proposed methods are an integration of physical-based models for constant speed compressor and the physical characteristics of volumetric efficiency and isentropic efficiency between different speeds. The physical-based models were first validated with good agreement with experimental data from publication for the three types of constant speed compressors. The comparison between modeling results and experimental data from publication for the three types of variable speed compressors shows the RMS errors are less than 3%, 3% and 3 °C for refrigerant mass flow rate, compressor power input and discharge temperature, respectively. The model of variable speed compressor will allow the reduction of the number of experimental data required to characterize variable speed compressor behavior in the modeling of refrigeration systems because of its physical mechanisms.     

Energy and exergy analyses of a two‐stage vapour compression refrigeration system

In this paper exergy analysis of two‐stage vapour compression refrigeration (VCR) system has been carried out with an objective to evaluate optimum inter‐stage temperature (pressure) for refrigerants HCFC22, R410A and R717. A thermodynamic model based on the principles of mass, energy and exergy balances is developed for this purpose. The computed results illustrate the effects of evaporation and condensation temperatures, isentropic efficiencies of compressors, sub‐cooling of refrigerant and superheating of suction vapour on optimum inter‐stage saturation temperature (pressure). The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are proximate to arithmetic mean of evaporation and condensation temperatures (AMT) when assuming superheating of suction vapour and non‐isentropic compression processes in low‐pressure and high‐pressure compressors. The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are near to geometric mean of evaporation and condensation temperatures (GMT) when it is assumed that cycle involves the effects of sub‐cooling, superheating of suction vapour and non‐isentropic compression of the suction vapour. The optimum inter‐stage saturation temperature (pressure) for R717 is close to GMT irrespective of sub‐cooling, superheating of suction vapour and non‐isentropic compression in the cycle. The efficiency defects, computed corresponding to optimum inter‐stage temperature in condenser is higher in comparison to the other components. Finally, it is deduced that R717 is a better alternative refrigerant to HCFC22 than R410A in two‐stage VCR system. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical analysis on the effects of refrigerant injection on the scroll compressor

Refrigerant injection is an effective method to improve the performance of the scroll compressor and its system under high compression ratio working conditions. This paper intends to find the exhaustive relationship between the injection parameters and the compressor’s performance. Based on a thermodynamic model, the effects of various parameters of refrigerant injection on general performance and inner compression process of scroll compressor have been investigated. As a result, it is found that the injected scroll compressor will get the maximum indicated efficiency when the ratio of inner compression ratio and outer compression ratio is a right value. The right value is 1 for the isentropic compression process, and smaller than 1 for a real compression process. Finally, the effects of all the injection factors on the compression work, refrigerant mass flow rate, p–h diagram, volumetric efficiency, and indicated efficiency are investigated detailedly.     

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.     

两级填充床蓄热器式绝热压缩空气储能系统变工况特性研究

利用压缩机和透平的变工况模型及填充床蓄热器的非稳态模型,对两级填充床蓄热器式绝热压缩空气储能系统一次完整的充放电循环过程进行模拟,分析系统的热力学性能和各个部件的变工况特性.结果表明,系统的充放电效率可达62.4％.储能时,受洞穴内压力变化影响,两级压缩机压比、效率不断改变,从而引起下游填充床蓄热器进口温度变化;释能时...     

Study on performance of a heat pump water heater using suction stream liquid injection

Liquid refrigerant injection into a suction line is an effective and practical method to reduce the discharge temperature when a scroll compressor operates at high compression ratios. In the present study, correlations among the compressor suction temperature, discharge temperature, heat pump heating capacity, power consumption, coefficient of performance (COP) and the quantity of suction liquid injection are established. The paper presents experimental analysis and a comparison with calculated results of the heat pump water heater (HPWH) performance with suction liquid injection in different conditions. It is found that the suction liquid injection explicitly lowers the discharge temperature of the compressor and the heating capacity of the unit, but the power consumption increases with COP decreasing. In addition, the highest injection ratio must be controlled fewer than 5%. The suction liquid injection has a better effect on the HPWH at the temperature ranging from ?15 °C to 20 °C. Within this temperature range, the 5% ratio suction liquid injection decreases the discharge temperature of the compressor by 10 °C, while the heating capacity of the HPWH decreases by less than 5%, power consumption increases by less than 1.5%, and COP decreases by less than 7%.     

Exergy analysis of a compression–absorption system for heating and cooling applications

An exergy analysis of a single‐stage compression–absorption system with R22‐E181 as the working fluid pair is carried out. Theoretical results obtained have been compared with those obtained from the experiment. Results show that the heat of mixing of the refrigerant vapour and solution at absorber and desorber contributes a significant amount to the internal entropy generation rates. A significant part of internal entropy generation rate is also due to non‐isentropic compression of refrigerant vapour at higher absorber pressure. The exergetic efficiency of the system increases with the increase in absorber pressure due to reduction in internal irreversibilities. Higher value of weak solution concentration along with the increase in solution concentration difference results in higher exergetic efficiency of the system. Thus, a compression–absorption system performs better when operated at higher absorber pressure, and an improved system performance can also be achieved with higher value of weak solution concentration with higher possible solution concentration difference. Copyright © 2008 John Wiley & Sons, Ltd.