新学科“制冷系统热动力学”初探

本文论述了新学科“制冷系统热动力学”形成的必要性及基本内容,它是基于动态、分布参数及参数间定量耦合的观点,综合制冷原理、计算传热学与流体力学、自控原理及计算方法而形成的边缘新学科。作者应用“微元法”建立起一套基本分析方法,导出了制冷系统各参数的动态分布参数模型,在该基础上进行系统匹配与仿真研究。该学科的成熟将导致制冷设备及系统设计方法的更新,它对制冷系统优化设计、新型制冷自控元件研制,计算机控制深入制冷循环将产生巨大的影响。本文以压缩式制冷系统为例给出了系统各设备的动态分布参数数学模型。理论计算与试验数据十分吻合,得到了一系列令人感兴趣的新结果,证实了模型的可信性。     

机器学习方法的CO2并行压缩系统最优控制

为了研究一种高效的跨临界CO2并行压缩系统的控制方法,本文借助GT-SUITE仿真软件,建立了跨临界CO2并行压缩系统的动态仿真模型,基于仿真得到的系统性能数据集,建立并对比了二阶多项式模型和神经网络模型的系统性能预测模型,并基于神经网络模型开发了跨临界CO2并行压缩系统的模型预测控制器,研究控制器对系统控制稳定性、高效性、实时控制的性能。结果表明：在模型预测控制器作用下,不同制冷工况在150 s内系统能达到稳定运行状态;对比定值控制,采用模型预测控制的系统性能最大提升13.3%;仿真验证了提出的模型预测控制策略对于CO2并行压缩系统实时控制性能优化的可行性,在给定工况下相比对定值控制整体提升性能7.3%。     

机载准双级压缩蒸发制冷系统动态仿真

基于MATLAB Simulink使用移动界面法建立了蒸发器、冷凝器分区集总参数动态模型,采用补气-压缩模型和闪发器模型结合迭代计算时间步长内系统的中间补气压力和流量,建立了准双级压缩机模型,将蒸发循环制冷系统各个部件整合形成准双级压缩蒸发循环制冷系统,用以研究机载准双级蒸发循环制冷系统动态特性。研究表明在单一参数或者多参数改变时系统能较好的提供动态特性参数并提供动态特性仿真曲线,对进一步研究机载蒸发循环制冷系统故障诊断、机载蒸发循环控制方法等有参考意义。     

CO2低温制冷循环热力学分析

通过对CO2单级压缩和双级压缩制冷循环的热力学分析得出,在一定的蒸发温度和冷凝温度下,CO2单级压缩制冷循环的COP比CO2双级压缩制冷循环的COP低、压差大、压比高.因此,CO2低温制冷循环系统应采用双级压缩制冷循环,为提高CO2双级压缩制冷循环的循环效率,应尽可能升高蒸发温度、降低冷凝温度,可以看出自然工质CO2双级压缩制冷循环有很好的发展前景.     

小孔型脉管制冷机动态特性的实验研究

本文建立了小孔型脉管制冷机实验台，通过测量制冷机中动态的压力、示功图、制冷温度和制冷量，研究了阀门开度对制冷过程的影响。多路旁通方案比常规小孔和双向进气方案获得更低的制冷温度，达到２３．８Ｋ，且Ｐ－Ｖ功最小。随着小孔开度增大，压缩腔和脉管中压力的相位差增大，压缩腔中压比增大，而脉管中压比减小，Ｐ－Ｖ功增大。双向进气阀和多路旁通阀开度的影响恰好与小孔的影响相反，有利于制冷过程。     

半导体制冷在氡室温度调节系统中的应用

对蒸汽压缩式制冷法和半导体制冷法进行了比较,简述了适用于氡室温度控制的半导体制冷法的原理,并用实验结果对半导体制冷法的制冷和加热效果进行了直观的阐述。     

飞机空调系统制冷技术现状及展望

从飞机空调系统制冷技术角度,分别介绍了传统和新型空气制冷循环。在比较空气制冷循环和蒸汽压缩制冷循环的基础上对当前飞机空调用蒸汽压缩制冷循环的关键技术研究和发展方向进行了展望,指出:空气制冷循环仍将在较长时间内占据主导地位:蒸汽压缩制冷循环是飞机空调制冷技术的发展趋势。     

基于20-sim的减振器试验台液压系统键合图建模与动态仿真分析

研究了液压系统键合图建模方法.使用20-sim软件,建立了减振器试验台压缩时液压系统的键合图模型,并进行动态仿真,得到系统输出速度和输出压力的动态响应曲线,仿真结果证明了建模方法的可行性与正确性;通过建立系统的Simulink模型进行对比仿真分析,进一步验证仿真结果的可靠性.研究工作为液压系统的动态建模及仿真提供新的思路.     

螺旋压缩膨胀制冷机制冷循环热力性能分析

螺旋压缩膨胀制冷机是一种近似布雷顿循环的新型制冷机,与布雷顿制冷循环相比,其压缩过程更接近于等温压缩过程.首先提出了螺旋压缩膨胀制冷机制冷循环,其次采用数学理论计算方法就特定工况下螺旋压缩膨胀制冷机制冷循环过程的热力性能和制冷系数与布雷顿循环进行比较研究.研究发现:一定条件下,得到相同制冷量时,螺旋压缩膨胀制冷机制冷循...     

自然冷却/蒸气压缩复合制冷系统研究

本文研发了一种由蒸气压缩制冷和分离式热管集成的自然冷却/蒸气压缩复合制冷空调系统,分别采用第一工质和由液泵驱动的第二工质进行循环。该系统具有蒸汽压缩制冷、复合制冷和自然冷却3种运行模式,高温季节压缩制冷提供全部冷量,过渡季节压缩制冷补充自然冷却不足的制冷量,低温季节自然冷却提供全部冷量。同时,研制了复合制冷系统样机HKF-200FH,其压缩制冷回路由3个独立的制冷单元并联,并与热管环路通过壳管式蒸发冷凝器相连。蒸发冷凝器的管程作为压缩制冷回路的蒸发器,在压缩制冷模式和复合制冷模式下为通过壳程的第二工质提供冷量。对样机性能进行了实验测试,结果显示：随着室外温度降低,复合系统的制冷量变化较小,能效比EER逐渐升高;压缩制冷模式（环境温度35 ℃）和自然冷却模式（环境温度10 ℃）下机组的制冷量分别为197.38 kW和196.89 kW,EER分别为3.5和15.3。2台系统样机自2014年5月在北京某“EB级云存储实验室”空调示范工程安全可靠的运行至今,监测结果显示,相比传统压缩制冷系统年节能率约为45%,节能优势显著。     

Unsteady state analysis of the compression cycle of a hermetic reciprocating compressor

In this work, an unsteady state analysis of the compression cycle of a small hermetic reciprocating compressor for domestic refrigeration was carried out. A specific one-dimensional model of the valves was developed and the mass and energy balances were applied to the refrigerant inside the cylinder to determine the mass, pressure and temperature behaviour and the heat and work transfer through the compression process. This analysis was inserted into a traditional steady state model of the compressor to evaluate the efficiency of the compression cycle and the performance of the compressor unit. The whole simulation code was validated against the experimental measurements carried out on a R134a commercial unit in a wide range of operative conditions: a fair agreement was found between predicted and measured performances. The simulation code can be a useful tool for the analysis, the design and the development of small hermetic reciprocating compressors for domestic refrigeration.     

适用于制冷系统动态仿真的全封闭式压缩机准动态模型

制冷系统动态仿真中要求压缩机模型能够适用于吸入制冷剂状态从两相到气相的宽变化范围,并且能够快速地反映其关键的动态特性,为了解决这个问题,提出了可覆盖进口状态从气相到两相制冷剂的准动态压缩机模型。此模型按其热力过程分解为吸入气相或两相制冷剂与腔内制冷剂混合过程的动态模型、壳体换热过程的动态模型和气缸内制冷剂压缩过程的稳态模型。此压缩机模型克服了通常压缩机模型中忽略腔内制冷剂混合过程所导致预测的流量大于实际流量的缺点,以及全部采用动态模型导致计算复杂的问题。通过某压缩机厂生产的全封闭式压缩机的稳态实验数据和模型预测值的比较,结果表明:模型预测的稳定工况时的质量流量和输入功率与实验数据误差小于5%;开机过程质量流量和输入功率与实验测量值趋势一致,误差小于10%。     

基本型脉管内气体振荡制冷机理的分子动力学模拟

脉管制冷机在当今社会应用广泛,但目前对脉管内部气体流动的热力动态过程缺乏微观机理研究。本文采用分子动力学模拟方法,建立微通道模型,并对微通道内进行充气和放气,模拟脉管的压缩和膨胀过程,研究脉管轴向压力、密度、速度和温度随时间的变化。结果表明:随着过程进行,气体轴向的压力与密度梯度逐渐减小,直至达到平衡,但会出现微小的逆向梯度。膨胀和压缩过程在64 ps时,在微通道出口附近出现最大速度,分别为775 m/s和864 m/s,且随着反应的进行,最大速度处逐渐向压力低的方向移动。微通道内各点压力波与速度波的相位随位置而变。在压缩过程中,微通道内靠近封闭端温度较高,可高达500 K;远离封闭端温度较低,可降至223 K,膨胀过程则相反。一次循环温度场叠加时,在热端处,时间积分的平均值为375 K;在冷端处,时间积分的平均值为244 K,有利于热端向环境散热和冷端制冷。     

复叠制冷系统:理论分析篇

从什么是复叠制冷系统着手,分析复叠制冷系统的流程、仿真计算方法、容积比对COP值的影响,并比较双级压缩系统与复叠制冷系统的优劣。最后,提出几种提高复叠制冷系统COP值的方法。     

Computationally efficient model for refrigeration compressor gas dynamics

In this paper a computationally efficient steady state model for a typical refrigeration reciprocating compressor is proposed. The plenum cavity is modelled using the acoustic plane wave theory, while the compression process is modelled as a one-dimensional gas dynamics equation. Valve dynamic models, based on a single vibration mode approximation, are coupled with the gas dynamics equation and acoustic plenum models. The steady-state solution of the resultant coupled non-linear equations are posed as a boundary value problem and solved using Warner's algorithm. The Warner's algorithm applied to compressor simulation is shown to be computationally more efficient as compared to conventional techniques such as shooting methods. Comparisons are based on the number of iterations and time taken for convergence. Effect of operating conditions on the overall compressor performance is also investigated.     

A state-space dynamic model for vapor compression refrigeration system based on moving-boundary formulation

A transient response model for vapor compression refrigeration system has been developed in the paper. The system model contains four sub-models representing condenser, evaporator, compressor and electronic expansion valve (EEV). The condenser and the evaporator are developed based on the moving-boundary formulation. Through linearization, these dynamic models are transformed into state-space representation which is expressed in the form of matrix. The compressor and EEV adopt steady models because their thermal inertia is much smaller compared with the heat exchangers (i.e., condenser and the evaporator). The system model has been validated by experiment in terms of step change of EEV opening degree and heat load as well as ramp increase of inlet temperature of coolant oil of condenser. The results show that the model simulations have a good agreement with the experimental data. The simulation errors compared with the experimental data are mostly less than 10%. Since the model proposed in this study is expressed in the form of state-space matrix, they are featured by strong portability and high computation efficiency. It allows us to investigate the thermal dynamic characteristics of a refrigeration system under any complicated conditions and develop excellent control schemes.     

Development and performance analysis of a multi-temperature combined compression/ejection refrigeration cycle using environment friendly refrigerants

A combined compression/ejection refrigeration cycle intended for the simultaneous production of cold for refrigeration and freezing, and operating based on environment friendly refrigerants is proposed and analyzed in this study. This makes it possible to valorize the low-temperature heat sources in the ejector cycle, thereby reducing the share of mechanical energy otherwise required to operate the conventional two-stage vapor compression system.A selection of eight candidates' fluids was performed. The developed simulation model helped to establish the strong dependence between system performances and the ratio of the cooling capacities of refrigeration and freezing. In addition to the effect of the temperature level of cold production, the influence of the ambient temperature on system performance was also analyzed when using refrigerants R290, R152a and R134a.     

Dynamic simulation and optimal matching of a small-scale refrigeration system

This paper describes a principle and method of optimal matching to reduce energy consumption in small-scale refrigeration systems, based on systems analysis. A knowledge of the dynamic characteristics of a refrigeration system is important for predicting the performance of the system. A simulation model of a refrigeration system consisting of a compressor, an evaporator, a condenser and a capillary tube has been established to illustrate optimal matching. For each component a mathematical model has been developed, in which the concept of transient and distributive is introduced. On the basis of dynamic simulation, a method of optimal matching to minimize power consumption is recommended. To test the reliability of the theoretical models, an experiment was carried out on a small-scale refrigeration system. The experimental data were compared with the theoretical results and it is shown that the theory is valid.     

制冷工质引射式减压原理及其技术应用

分析常规蒸气压缩制冷系统存在的不足,介绍引射式减压原理,并将其技术应用于制冷(热泵)循环系统,提出新型压缩/喷射制冷循环系统。对改进后的新型制冷系统进行热力学分析,结合制冷工质R134a的制冷工况特性,得出改进后新型制冷系统的优越性能,即提高制冷系统的能量利用效率。对制冷和空调系统节能研究具有一定的指导意义。     

结霜工况下热泵空调器性能的数值模拟

本文对热泵空调器在结霜工况下的运行性能进行了理论模拟,建立了热泵空调器制冷系统稳态分布参数模型和结霜过程的动态分布参数模型.在系统模型建立中把结霜过程视为准稳态过程.计算结果表明在霜刚开始形成时,有助于增大管壁和空气之间的换热系数,当霜层达到一定厚度时热泵的制热能力,性能系数等讯速下降.经与其他已发表的文献比较计算结果合理.