空调循环中HCs/阻燃剂混合工质的泄漏特性

结合空调循环分析了非共沸HCs/阻燃剂混合工质的泄漏特性,包括一定泄漏率下引起最大组成变化的泄漏点和工质相态、泄漏率-总组成变化关系、泄漏引起的组成变化对HCs/阻燃剂混合工质安全性与循环性能的影响分析。     

混合工质HFC134a/HCs替代R502的性能分析

针对目前R502主流替代工质R507和R404A存在的温室效应指数高、与矿物油互溶性差等缺点,提出了环保性能更好的三组近共沸混合工质R134a/R290、R134a/R1270和R134a/R290/R1270作为R502新型替代工质；并对其热物性、循环性能、安全性能和溶油性进行了计算分析。结果表明：除了压缩机排气温度偏高,这三组R134a/HCs混合工质的其它主要循环性能参数如压缩机压力比、容积制冷量和系统性能系数COP都优于R507和R404A,并且从理论上讲不存在可燃可爆的危险,同时可以与矿物油互溶,在替代R502方面更具有优势,其中R134a/R290/R1270在高热负荷下的综合性能最优良。     

二元环保型混合工质一次分凝循环性能优化

应用定循环运行压比优化方法,对采用环保型二元混合工质的单级压缩一次分凝循环,进行了-60℃温度位的循环性能数值优化。计算结果表明,影响循环COP的因素有混合工质成分(工质组元、工质浓度)和循环压力位(循环低压和循环压比),必须综合考虑进行优化。不可燃混合工质R23/R134a、R23/R227ea和R23/R236ea中,R23摩尔浓度为0.55和0.6的R23/R236ea循环在压比为7和10时,分别有最大的COP;自然混合工质R170/R290、R170/R600a和R170/R600中,R170摩尔浓度为0.65和0.7的R170/R600循环在压比为7和10时,分别有最大的COP。     

R1234yf/HCs混合工质热泵系统循环性能分析

在名义工况下建立热泵热水器系统的热力学循环模型,利用EES分别计算三种HCs纯工质及其与HFO1234yf混合工质的热泵性能。结果显示:R1234yf/R600(Z_1)和R1234yf/R600a(Z_2)均在质量分数(10/90)处出现最大制热COP值,分别为3.413和3.305,R1234yf/R290(Z_3)则出现单调递减的趋势。在最优配比(10/90)情况下,混合工质Z_1系统排气温度为76.26℃,冷凝压力为0.681 MPa,压比为6.284,制热量为193.6 J/g,■效率为0. 212;系统Z_2、Z_3及纯工质R600、R600a、R290的制热性能系数COP分别较Z_1降低3.06%、3.09%、13.94%、5.10%、5.66%。Z_1具有较好的热力学性能,有望成为替代工质。     

喷射增效自复叠制冷循环工质选择

为选择适合喷射增效自复叠制冷循环的工质,选取R32/R1234ze、R23/R134a、R170/R290和R23/R227ea四组混合工质,计算分析在给定工况下不同工质对喷射增效自复叠制冷循环性能的影响,并与传统自复叠制冷循环进行对比。结果表明,在喷射增效自复叠制冷循环中,R170/R290制冷量最大,R23/R227e压缩机压比最小,R23/R227e具有最佳性能,其性能系数较传统自复叠制冷循环提高了13.8%—28.4%;各组混合工质均存在最优组分配比使循环COP最大。     

压缩/喷射制冷循环中喷射器引射室的最优压降

建立了蒸气压缩/喷射制冷循环稳定运行时两相喷射器的热力学模型,以常压沸点相差较大的制冷剂为工质,比较了两相喷射器引射室压降最优范围的差异,并在同一工况下,研究了不同工质压缩/喷射制冷循环的性能。结果表明:喷射器引射室压降存在最佳范围使压缩/喷射制冷循环性能接近最优值;在相同工况下不同制冷工质这个最佳范围不相同;在同一工况下,当采用压缩/喷射制冷循环时,不同工质的循环性能系数和单位容积制冷能力相比基本循环均增强了。研究结果为压缩/喷射制冷循环制冷工质的选择及两相喷射器结构的优化设计提供理论参考。     

多元混合工质筛选及配比原则的研究

1前言目前，混合工质组元的筛选及配比的优化问题一直困绕着人们。对于如何通过筛选合理的组元及配比，国内外学者对此问题进行了初步的研究。这些文献大都从物性着手，把注意力集中在物性、循环特性的理论和简单匹配上，往往忽略系统设备和实际应用中存在的问题对混合工质组元的筛选及配比的影响。本文从循环本身出发，探讨混合工质组元的筛选及配比的优化问题。2混合工质组元筛选的分析从理论上讲，几种优势互补的纯工质经合理配比，总可望得到与被替代物性能相当的混合物。但如何通过筛选合理的组元以保证因泄漏而再补充新混合工质后系统…     

HFC32/HFO1234ze二元混合工质的热物性模型

在实验数据基础上,建立了适用于HFC32/HFO1234ze二元混合工质的PR方程模型,并对实验数据、模型计算结果和Refprop 9.0计算结果进行了比较分析;作出了定温度下泡、露点压力随混合比的变化关系图以及定压力下饱和温度随混合比的变化关系图,分析得出HFC32/HFO1234ze二元混合工质属于非共沸工质,存在温度滑移,500 kPa压力下混合物在0.27/0.75处温度滑移达到最大为12.7℃;选取状态参考点后,作出了不同混合比下的混合工质的logP-h图,得出了随混合比变化混合工质的热力学性质的变化趋势,为系统的设计提供基本的热力学数据;最后,以R410A循环性能为基准,对不同混合比下混合工质的"相对循环性能"(COP_(mix)/COP_(R410A))进行了分析,为家用空调制冷剂的替代和系统的优化提供方向。     

基于不同自然工质的斯特林循环特性研究

本文主要针对一台自主设计的100 W级的声型斯特林发动机,研究三种自然工质气体(氦气、氮气和二氧化碳)的斯特林循环特性与斯特林发动机的运行性能,包括不同转速、压强和工质气体对斯特林循环的膨胀腔和压缩腔工质气体温度、指示功、循环输出功率和循环效率等的影响。实验发现,低转速下,三种工质气体的循环功率和循环效率比较接近,而二氧化碳同时具有更好的密封性能;高转速下,氦气小分子工质气体具有更大的做功潜力。     

自复叠制冷循环中混合工质泄漏性能的研究

尽管自复叠制冷循环越来越广泛的用于深冷及普冷领域,对于循环中工质泄漏特性的研究却较少。以非共沸混合工质两相区的等温泄漏为基础,分析了在自复叠循环装置中各部件的泄漏对工质组成的影响,其中发生在冷凝器出口处、气液分离器和蒸发器出口处的泄漏对工质组成影响较大。以采用非共沸混合工质R600 a/CO2的自复叠低温冷冻箱为例,研究了不同泄漏点不同泄漏率的泄漏特性。结果说明当工质泄漏时混合工质组成和循环性能发生变化,在蒸发器出口处的泄漏对循环性能影响最大;当泄漏引起循环工质组成发生较大变化时,压缩机变容量和变压力比调节能力明显降低,此时系统不能满足设计工况的要求,工作性能变差。     

空调冷凝热热回收技术研究现状及发展趋势

界定了空调冷凝热热回收系统的分类,总结了国内外空调冷凝热热回收技术的研究现状,提出了空调冷凝热热回收技术的发展趋势。     

Spiral MRSI and tissue segmentation of normal-appearing white matter and white matter lesions in relapsing remitting multiple sclerosis patients☆

PurposeTo evaluate the performance of novel spiral MRSI and tissue segmentation pipeline of the brain, to investigate neurometabolic changes in normal-appearing white matter (NAWM) and white matter lesions (WML) of stable relapsing remitting multiple sclerosis (RRMS) compared to healthy controls (HCs).MethodsSpiral 3D MRSI using LASER-GOIA-W [16,4] was undertaken on 16 RRMS patients and 9 HCs, to acquire MRSI data from a large volume of interest (VOI) 320 cm³ and analyzed using LCModel. MRSI data and voxel tissue segmentation were compared between the two cohorts using t-tests. Support vector machine (SVM) was used to classify tissue types and assessed by accuracy, sensitivity and specificity.ResultsCompared to HCs, RRMS demonstrated a statistically significant reduction in all mean brain tissues and increase in CSF volume. Within VOI, WM decreased (−10%) and CSF increased (41%) in RRMS compared to HCs (p < 0.001). MRSI revealed that total creatine (tCr) ratios of N-acetylaspartate and glutamate+glutamine in WML were significantly lower than NAWM-MS (−9%, −8%) and HCs (−14%, −10%), respectively. Myo-inositol/tCr in WML was significantly higher than NAWM-MS (14%) and HCs (10%). SVM of MRSI yielded accuracy, sensitivity and specificity of 86%, 95%, and 70%, respectively for HCs vs WML, which were higher than HC vs NAWM and WML vs NAWM models.ConclusionThis study demonstrates the benefit of MRSI in evaluating MS neurometabolic changes in NAWM. SVM of MRSI data in the MS brain may be suited for clinical monitoring and progression of MS patients. Longitudinal MRSI studies are warranted.     

Complex tone processing in primary auditory cortex of the awake monkey. II. Pitch versus critical band representation

Noninvasive neurophysiological studies in humans support the existence of an orthogonal spatial representation of pure tone frequency and complex tone pitch in auditory cortex [Langner et al., J. Comp. Physiol. A 181, 665-676 (1997)]. However, since this topographic organization is based on neuromagnetic responses evoked by wideband harmonic complexes (HCs) of variable fundamental frequency (f0), and thus interharmonic frequency separation (deltaF), critical band filtering effects due to differential resolvability of harmonics may have contributed to shaping these responses. To test this hypothesis, the present study examined responses evoked by three-component HCs of variable f0 in primary auditory cortex (A1) of the awake monkey. The center frequency of the HCs was fixed at the best frequency (BF) of the cortical site. Auditory evoked potential (AEP), multiunit activity, and current source density techniques were used to evaluate A1 responses as a function of f0 (=deltaF). Generally, amplitudes of nearly all response components increased with f0, such that maximal responses were evoked by HCs comprised of low-order resolved harmonics. Statistically significant increases in response amplitude typically occurred at deltaFs between 10% and 20% of center frequency, suggestive of critical bandlike behavior. Complex tone response amplitudes also reflected nonlinear summation in that they could not be predicted by the pure tone frequency sensitivity curves of the cortical sites. A mechanism accounting for the observed results is proposed which involves mutual lateral inhibitory interactions between responses evoked by stimulus components lying within the same critical band. As intracortical AEP components likely to be propagated to the scalp were also strongly modulated by deltaF, these findings indicate that noninvasive recordings of responses to complex sounds may require a consideration of critical band effects in their interpretation.     

基于PLC 的中央空调制冷系统变频控制研究

针对现有中央空调系统能源消耗严重的现状,基于可编程逻辑控制器(Programmable Logic Controller,PLC)对中央空调系统进行变流量节能改造。分析改造后中央空调系统的结构组成和变频运行原理,并提出适用于冷冻水泵和冷却水泵的分段速温差控制和PID温差控制设计方案。控制硬件选用三菱FX3U系列PLC和台达VFD-EL变频器,软件选用GX Work2编程软件及力控组态软件。将控制方案进行实验验证,实验结果表明,所设计的两种控制策略不仅跟随系统末端负荷变化快速达到稳定运行状态,提高运行能效比,而且节能效果显著,节能率分别为40.2%和48.7%。     

HCFC22及其HC/阻燃剂替代物的变工况空调循环性能

分析了二元交互作用系数kij不确定度对工质热力学性质与循环性能计算的影响;对HCFC22及其HC/阻燃剂混合工质替代物进行了变工况空调循环性能对比分析。结果表明,kij取值误差对汽液平衡计算结果影响明显,对循环分析的影响则相对较弱;各种工质主要循环性能指标的相对优序随工况变化不明显。     

A wall sub-model in KIVA3 for the prediction of transient exhaust HC concentrations

Unburned fuel is one of three main pollutants from spark ignition internal combustion engines. The mechanisms of escape of this fuel from the main combustion event have been well studied. However, while up to 10% of the main chamber fuel may escape the initial combustion phase, 80–90% of this is oxidized during the postflame period. Modelling of this oxidation requires a detailed understanding of heat and mass transfer in the boundary layer on the surfaces of the combustion chamber. The resolution of the temperature and concentration gradients requires cell sizes less than 0.1 mm. This means that the processes may not be directly estimated with standard computational fluid dynamics (CFD) representations of combustion. In addition, combustion in the vicinity of the wall is usually quite different from that in the main chamber. A one-dimensional (1D) wall model for the oxidation of HCs was implemented into the wall cells of a KIVA3 computational model. The wall layer was used to follow the postfame oxidation of HCs during the expansion stroke. The CFD model was retained to predict combustion, quench and boundary conditions for the wall model, and to follow the entrainment, mixing and oxidation of HCs throughout the exhaust stroke. This paper describes the model. It presents some of the results of the model in the prediction of various features of interest within the processes of postflame oxidation. Most importantly it allows the prediction of mixing and entrainment of HCs from the exhaust gases in the exhaust stream. A comparison of the predictive capabilities of the model with some experimental HC traces is also presented.     

基于LNG冷能利用的公交车空调制冷系统优化

公交车的LNG燃料蕴含大量冷量,目前尚未得到利用。文中就LNG冷能用于公交车空调系统低温送风和空调系统的过冷循环分别进行了优化分析。应用Cleland公式和VB编程计算,结果表明:LNG冷能用于12m公交车低温送风,空调制冷系统COP可提高6.8%～8.6%;将LNG冷能用于12m公交车空调系统的过冷循环,空调制冷系统COP可提高18.2%。     

Distribution of light alkanes in the reaction of graphite hydrogenation at pressure of 0.1–7.8 GPa and temperatures of 1000–1350°C

ABSTRACT

We studied the effect of pressure and temperature on the hydrocarbon (HC) chain length distribution and total amount of HCs in the reaction of direct graphite hydrogenation at pressures of 0.1–7.8?GPa and temperatures of 1000–1350°C. An increase in pressure was found to lead both to an increase in the absolute yield of HCs due to direct graphite hydrogenation and to chain elongation of HC products. Light alkanes predominate among HCs in the entire studied range of P–T parameters. However, their concentration in quenched fluids increases as pressure is elevated, from less than 10?rel.% at 0.1?GPa to more than 40–50?rel.% at P?≥?3.8?GPa. Methane is actually the only light alkane among reaction products at 0.1?GPa and 1000°C, while it is a minor component at 7.8?GPa and 1350°C. The most stable alkane at pressures above 3.8?GPa is ethane (C₂H₆).     

理论制冷循环绝热压缩过程的改进计算

基于对工质在压缩机中经历的实际过程的分析,提出了一种在理论制冷循环中与之相应的过程模型-由定压加热子过程、绝热压缩子过程、定压放热子过程组成的复合过程;给出了包含余隙容积影响的过程计算式和计算方法,计算简单易行.较之现有的单一绝热压缩过程模型,新的过程模型及相应的过程和循环性能计算结果更加接近实际.