阵列低环温空气源热泵外流场模拟研究

建立了无墙面阻碍和有墙面阻碍情况下低环境温度空气源热泵六列四行的阵列物理模型,对以261.15 K为名义工况下的空气源热泵外环境流场进行三维数值模拟。对比研究不同水平风速下蒸发器换热面入口空气温度和换热量,分析冷风回流现象对低环温空气源热泵传热性能的影响,指出最恶劣工况机组的位置。环境风存在阻碍风机出口冷空气的扩散,使风机出口偏转角增大,导致冷空气在风机上部堆积,阵列内部以及背风侧的机组冷风回流现象更加明显。结果表明:当机组横向间距为0.6 m时,水平风速分别从0 m/s增至5 m/s,阵列机组最低入口空气温度比环境温度低2.44~3.69 K,平均换热量下降1%~6.2%,平均入口空气温度比环境温度低0.78~1.57 K;当机组距墙间距为0.6 m时,水平风速分别从0 m/s增至5 m/s,阵列机组最低入口空气温度比环境温度低3.51~4.14 K,平均换热量下降5.9%~11.5%,平均入口空气温度比环境温度低1.29~1.98 K。在此基础上对不同横向间距、不同距墙间距下阵列空气源热泵进行模拟,结果表明:增大横向间距或距墙间距均能改善阵列低环温空气源热泵机组的换热。当横向间距增至1.2 m,阵列机组平均换热量可达原来机组换热量的96.5%以上;距墙间距增至1.2 m,阵列机组平均换热量可达原来机组换热量的91.3%以上。横向间距或距墙间距为1.2 m为较好安装间距。

低环温空气源热泵技术研究新进展

空气源热泵以其高效节能、安全环保、使用方便等特点在我国长江流域及以南地区广泛应用,但其在我国北方寒冷地区的推广应用却困难重重。主要是因为在低环境温度下,空气源热泵系统面临着制热能力和制热系数急剧下降、压缩机启动困难、排气温度过高,以及蒸发器频繁结霜等问题。针对这些问题,国内外研究人员对低温空气源热泵技术进行了大量研究。围绕低环温空气源热泵系统、蒸发器除霜技术等方面对现有的研究成果进行总结分析,分析结果对空气源热泵系统在低环温地区的进一步推广应用具有一定的指导意义。

低环温下特高压GIS设备SF6气体状态管理系统研究

特高压GIS设备中大量采用纯净SF6气体作为绝缘和灭弧介质。SF6气体的温度、湿度、纯度及其分解产物是影响特高压GIS设备可靠性重要因素之一。随着特高压工程大规模建设,出现极低温站址,此环境下SF6气体易液化和出现高概率内部放电故障,严重影响特高压电网安全稳定运行。为提高低环温下特高压GIS设备运行可靠性,文中基于不同媒介热平衡理论和一定工况下气体状态方程,并采用红外温度采集、微量气体微积分分析及电化学检测技术设计一种新型SF6气体状态管理系统。同时介绍了系统功能、硬件结构和软件控制流程。通过现场应用,数据检测可靠、系统运行稳定,应用结果表明该新型SF6气体状态管理系统可确保低环温下特高压GIS设备安全稳定运行。

工质对物性对低环温高温复叠式空气源热泵性能的影响

基于制冷工质筛选原则,对适用于低环温的高温复叠式空气源热泵工质物性参数进行比较,并为该高温空气源热泵选定了几种可用的工质对。较适合高温级的工质为:R134a、R413A、R1234ze;较适合低温级的工质为:R404A、R407C、R417A、R507、R1234yf。通过对采用上述工质组成不同工质对时高温复叠式空气源热泵性能进行热力分析,可以看出:当采用R1234ze/R404A与R1234ze/R1234yf为工质对的复叠式热泵在低温环境下较采用其他工质对时热力性能有明显优势。

低环温空气源热泵外流场模拟及换热性能影响分析

空气源热泵作为一种高效、节能装置,具有广泛的应用前景和市场价值。建立了低环境温度空气源热泵物理模型,对1×1机组、3×4阵列以及4×6阵列低环温空气源热泵外流场进行三维数值模拟,分析水平风速、机组布置、墙面阻碍等因素对机组平均入口空气温度和机组换热性能的影响。结果表明,水平风速越大,机组布置数目越多,有墙面阻碍下的低环温空气源热泵机组平均入口空气温度越低。当水平风速增大到5m/s,无墙面阻碍下1×1机组、3×4阵列以及4×6阵列平均入口空气温度与环境温差分别为0.92℃、1.16℃和1.57℃;有墙面阻碍下温差分别为0.92℃、1.4℃和1.98℃。对于单一机组热泵,水平风速越大,机组换热量越大。对于阵列机组,水平风速越大,机组平均换热量出现先增大后下降的趋势。特别的当水平风速大于2.5m/s后,背风侧阵列机组入口空气温度降低,阵列机组平均换热量开始下降,有墙面阻碍下24台机组平均换热量为原来机组换热量的91.9%。阵列机组布置时,应增大机组距墙间距,减小墙面对风机出口冷空气扩散的阻碍。进行具体定量分析对实际工程和系统研究具有重要意义。

两种低环温空气源热泵系统供暖的经济性分析

通过对比补气增焓及采用电子膨胀阀控制排气过热度的低环温空气源热泵应用在室外环境温度-15℃以上的性能对比以及在-15℃下运行的经济性分析,确定了电子膨胀阀控制排气过热度低环温空气源热泵机组的辅助电加热使用时间节点,为设计选型、工程应用提供参考。

低环温空气源热泵供暖系统的技术应用及案例分析

本文以山西省A市县综合办公楼为例,阐述了低环温空气源热泵的产品性能及供暖系统构成,介绍了在项目中如何对低环温空气源热泵供暖系统进行制热设备选型设计、定压系统设计、循环水泵的选型设计、末端供暖系统设计以及工程中施工注意事项。

基于低环温空气源热泵机组的制冷剂替代实验研究

本文介绍了R32制冷剂在低环温空气源热泵机组上替代R410A制冷剂的实验研究,通过不同实验工况对比测试,结果表明:采用R32替代R410A后,机组的名义制冷能效提升9.7 %,名义制热能效提升3 %,低温制热能效提升4.6 %,整机IPLV(H)提升4.8 %。各工况下的机组性能系数得到全面提升,表现出较好的性能优势,可推广至小型商用机组。

低环温空气源热泵机组低温静置后启动制热失效分析

本文主要针对低环温空气源多联热泵机组在低温-30℃以下经过长时间静置后,由于冷媒大量迁移,液态冷媒集中堆积在外机系统,机组启动后为了防止机组大量回液,机组自带压缩机降频等保护措施限制冷媒循环流量,从而一引起制热启动后长时间出现制热功能失效,严重时长期吹冷风的问题,本文针对此通过理论分析,并结合实验过程数据做过程实践分析,并最终找出冷媒量、环境温度、连接管长度等是影响静置启动后制热功能恢复所需时间的重要影响因素,最后为低温机组静置启动后缩短失效时间提供解决方法。

二次过冷系统在低环温热泵的应用研究

针对冬冷夏热地区的空气源热泵产品应用,目前低环温热泵在制热性能已取得较好的成效,本文研究低环温热泵产品兼顾制冷性能的设计改进,通过设计二次过冷系统提升制冷运行性能,实际测试不同工况、不同过冷度对于系统制冷运行参数的影响,寻找最优的制冷性能。结果表明,相对于常规低环温热泵系统,二次过冷的低环温热泵系统可明显提升制冷性能,在标况下可以提升2%制热量和2.66%能效,可为低环温热泵在制冷性能的提升设计提供应用参考。

分离式氨热管低环温空气加热器多目标优化

本文提出了一种以低温余热热水为热源的分离式氨热管低环温空气加热器设计方案,可提高能源利用率,同时消除低环温时的结冰风险。基于分布参数模型和改进的NSGA-Ⅱ多目标优化算法,以功耗和质量为目标,优化了该空气加热器设计。结果表明,与常规工程经验设计相比,优化设计的功耗降低了28.9%,质量降低了31.9%。此外,该优化算法的收敛速度比热管设计时常用的随机组合算法更快,可显著节省寻优时间。对比三种热管工质(氨、甲醇和乙醇)的性能后发现,氨热管空气加热器性能最佳。

过冷器改善低环温热泵机组化霜底部结冰研究

针对常规翅片换热器在低环温运行时换热器的底部容易结冰、融冰困难问题,设计了经济器机组的过冷装置。在基本不增加换热器材料的基础上,通过改变换热器底部的制冷剂管路增加了过冷器。理论分析和测试结果表明:制冷制热性能与原系统基本相同,化霜时翅片换热器底部无结冰现象,最低压力在411k Pa以上,化霜干净彻底。过冷器可以用于新型的低环温经济器热泵机组设计。

R32经济器系统涡旋压缩机中间补气参数的分析与优化

为了优化带经济器的R32空气源热泵系统的制热性能,结合涡旋压缩机的结构以及实际运行特点,本文利用MATLAB建立了系统的数学模型,并通过实验数据验证了仿真结果,研究了在不同环境温度下系统的补气压力、准一级压缩内容积比对相对喷气量的影响。研究结果表明:经济器系统较普通热泵系统,更适宜在环境温度低于-10℃的工况下运行;R32经济器热泵系统制热模式的最佳结构和运行参数为:系统的准一级压缩内容积比为1.1时,压缩机的相对喷气量值最大;当环境温度低于-10℃时,最佳相对喷气量宜取为0.22~0.33;当环境温度为-10~-5℃时,最佳相对喷气量宜取0.20~0.22;当环境温度高于-5℃时,则宜为0.18~0.20。相应的最佳相对喷气压力在0.85~1.31之间,处在最佳补气参数范围内,经济器热泵系统的优势越明显。

Photochemical Efficiency of PSⅡ and Membrane Lipid Peroxidation in Leaves of indica and japonica Rice (Oryza sativa) Under Chilling Temperature and Strong Light Stress Conditions

Relationships between fluorescence parameters and membrane lipid peroxidation in leaves of indica and japonica rice (Oryza sativa L.) during later growth stage were studied under chilling temperature and strong light stress conditions. Results showed that D1 protein contents of PSⅡ in photosynthetic apparatus dropped, the generation of antheraxanthin (A) and zeaxanthin (Z) of xanthophyll cycle were inhibited partly, PSⅡ photochemical efficiency (F v/F m)and non-photochemical quenching (q N) were also decreased obviously. In addition, endogenous active oxygen scavenger—superoxide dismutase (SOD) reduced, superoxide anion radical (O -· 2) and malondialdehyde (MDA) accumulated, as a result, photooxidation of leaves occurred under chilling temperature and strong light stress conditions. Obvious differences in the changes of the above mentioned physiological parameters between indica and japonica rice were observed. Experiments in leaves treated with inhibitors under chilling temperature and strong light conditions showed that indica rice was more sensitive to chilling temperature with strong light and subjected to photooxidation more than japonica rice. Notable positive correlation between D1 protein contents and F v/F m or (A+Z)/(A+Z+V), and a marked negative correlation between F v/F m and MDA contents were obtained by regression analysis in indica and japonica rice during chilling temperature and strong light conditions. According to the facts mentioned above, it was inferred that PSⅡ photochemical efficiency(F v/F m) was the key index to forecast for the prediction of photooxidation under stress circumstances and the physiological basis were the synthetic capacity of D1 protein and the protection of xanthophyll cycle.

Changes in Violaxanthin Deepoxidase Activity and Unsaturation of Thylakoid Membrane Lipids in Indica and Japonica Rice Under Chilling Condition and Strong Light

To explore the differences of sensitivities to chilling and strong light in indica and japonica rice (Oryza sativa L), the changes in unsaturation of thylakoid membrane lipids and xanthophyll cycle were studied under chilling condition and strong light. The contents of unsaturated fatty acids of thylakoid membrane lipids decreased and that of the saturated ones increased with the time of chilling and strong light treatment, resulting in the reduction of the index of unsaturation of fatty acids (IUFA). The activity of violaxanthin deepoxidase (VDE), a key enzyme of xanthophyll cycle, also reduced. The content of violaxanthin (V) increased, and the contents of antheraxanthin (A) and zeaxanthin M decreased, the ratio of (A+Z)/ (A+Z+V) decreased correspondingly. Arrhenius analysis showed that VDE was sensitive to both chilling and unsaturation level of thylakoid membrane lipids. Correlation analysis showed that there was distinctly positive relationships between IUFA of thylakoid membrane lipids and the activity of VDE, Fv/Fm, and D, protein content. Lower IUFA values, less fluidity and stability of thylakoid membrane lipids, lower VDE activity and (A+Z)/(A+Z+V) ratio were found in indica rice cv. Shanyou 63 than in japonica rice cv. 9516 under chilling and strong light.

Theoretical study on the ideal open cycle of the liquid nitrogen engine

This article described the characteristics of the liquid nitrogen engine's ideal open cycle.Using two interconnecting strokes to achieve the power output can mitigate the trade-off between high efficiency and the potential mechanical complexity of multiple-cylinder engines. The total specific energy of the binary media (methane-nitrogen) cycle system could be much higher than the unitary medium (liquid nitrogen) cycle system. By theoretical analysis, the reasonably acceptable driving range proved the feasibility of the liquid nitrogen engine used for supplying power for a lightweight car.

Low temperature induces oocytes p34^(cdc2) synthesis and accumulation-the acquisition of competence to resume meiosis in toad oocytes

Full grown oocytes derived from Bufo Bufo gargarizans rearing at high temperature environment (24℃),never underwent GVBD after progesterone treatment. No p34cdc2, H1 kinase activity was detected in the oocytes after progesterone stimulation or OA microinjection; Western blotting analysis showed that the level of p3cdc2, and p33 in the oocytes are significantly lower than those in the oocytes derived from the hibernating toads (below 10 ℃). 25S-Met incorporation analysis showed that when the oocytes were incubated at 6℃, synthesis of about thirty defferent polypeptides was promoted or induced, including p34cdc2 and some other p13suc1-binding proteins. All these results indicated that a low temperature environment is essential for the oocytes of Bufo Bufo gargarizans to express and store some cell cycle drivers and its regulators, and to gain the maturation competence. These results will also provide a new clue for explaining the molecular mechanisms why gametogenesis of some organisms depends on a relative low temperature and how to maintain the geographical distribution of some animals.

Exploring the Low-Temperature Oxidation Chemistry of Cyclohexane in a Jet-Stirred Reactor:an Experimental and Kinetic Modeling Study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry （SVUV-PIMS） was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window （-80 K） was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 （2013）], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the de- composition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-l-al and OH radical.

Electrodeposition Behavior of Nickel from a Low Temperature Urea-molten Salt

The electrodeposition behavior of nickel at glassy carbon(GC)and stainless steel(SS)electrodes in low temperature urea-acetamide-NaBr-KBr melt was investigated using cyclic voltammetry,chrono-amperometric current-time transients and scanning electron microscopy.Cyclic voltammograms and dimensionless chronoamperometric current-time transients analysis show that the electrodeposition of nickel is an irreversible process and proceeds via three-dimensional progressive nucleation with diffusion-controlled growth on both GC and SS substrates.Scanning electron microscopic analysis indicates the nickel deposits obtained on SS electrode are generally uniform,dense,and adherent to the substrate with rounded crystallites in the nanometer size regime.It is also found that the crystal structure of the electrodeposited nickel is independent on the deposition potential.The nickel deposits produced from the melt at higher cathodic potential exhibit larger grain size.

The Influence of Paraffinic Base Oil on Low-temperature Viscosity of Naphthenic Base Oil

Low-temperature viscosity of lube oils mixed with paraffinic base oil and naphthenic base oil at different mass ratios has been tested by experiments. The influence of paraffinic base oil on the performance of naphthenic base oil was investigated by studying the low-temperature viscosity of tested oils. The viscosity of lube oils increased with an increasing content of high-viscosity paraffinic base oil in the oil mixture. And the low-temperature viscosity was less influenced when the content of paraffinic base oil in the mixture was insignificant. In order to reduce the cost for formulating lubricating oil, a small fraction of paraffinic base oil can be added into naphthenic base oil as far as the property of lubricating oil can meet the specification. According to the study on low-temperature viscosity of the oil mixed with paraffinic base oil and naphthenic base oil, a basic rule was worked out for the preparation of qualified lubricating oils.