运用液体声学理论研究超临界二氧化碳的声特性

利用液体声学模型，根据美国国家标准局提供的二氧化碳声速、密度、摩尔体积和绝热压缩系数数据，计算了气态、液态和超临界态二氧化碳在不同温度和压力条件下的摩尔声速、摩尔压缩系数及Van der Waals 常数. 分析发现，在较宽的温度和压力范围内，液体中的声学模型能够很好地运用于超临界态二氧化碳的研究. 并在液体声学模型适用范围内，计算了超临界二氧化碳在不同温度及压力状态下的表面张力、粘度、自扩散系数，为超临界流体技术提供了参考数据，并分析了这些参量的变化规律.     

超临界点附近二氧化碳流体的声速

使用压缩蒸气模型,推导了超临界流体在超临界点附近区间的声速表达式,表达式揭示了声速和密度波动指数、等温压缩系数、定体摩尔热容量等参量的联系.在超临界点附近,二氧化碳流体的声速和密度波动指数呈减函数关系,密度波动指数越大,声速越小,在密度波动指数最小处,声速最大,此时,较小的密度波动会引起较大的声速波动.当压强逐渐增大并接近临界点时,定体热摩尔容量的迅速增大导致声速减小,当压强增大而远离临界点时,定体摩尔热容量的迅速减小导致声速增大.由表达式得到的计算值与由美国国家标准局提供的参考值符合较好. 关键词： 超临界二氧化碳 声速 密度波动 定体摩尔热容量     

超临界二氧化碳萃取磷脂的工艺研究

建立了用超临界二氧化碳萃取法从粗磷脂中萃取纯化磷脂的方法。考察了影响油脂萃取率的因素,采用正交实验确定了最佳萃取条件:萃取压力为30MPa,萃取温度为55℃,萃取时间为2h。大豆、葵花和胡麻三种磷脂得率分别为:88.5%、76.5%及79.2%,含磷量分别为:3.83%、2.62%及2.90%。     

超临界二氧化碳布雷顿循环夹点问题研究

针对超临界二氧化碳布雷顿循环存在的夹点问题,从循环设计角度进行了深入细致的分析,并在换热器效能公式的基础上提出了不同初、终参数下夹点问题是否出现的判定方法。分析了不同边界条件下回热型超临界布雷顿循环出现夹点问题的临界条件,得到了判定是否出现夹点问题的公式,可用于指导循环的设计。     

二氧化碳超临界流体的管内对流换热研究

随着自然工质ＣＯ２研究的进一步发展，系统中气体冷却器的换热问题越来越受到人们的重视，这是因为高的换热效率是提高系统ＣＯＰ的重要因素．本文首先阐明了超临界流体换热研究的处理原则和分类方法，并重新定义了ＣＯ２临界区范围．利用修改的 ＢＷＲ方程计算得出了 ＣＯ２临界区的物性变化规律，并分析了获得超临界换热关联式的理论求解方法．最后，建立了超临界ＣＯ２管内冷却过程的数学模型，为求解其换热规律提供了方法和依据．     

流动方向对超临界二氧化碳流动传热特性的影响

本文基于拟沸腾理论研究了超临界二氧化碳(sCO₂)在水平和垂直向上管中的流动和传热特性差异.比较了不同质量流量、热流密度和压力下水平管与垂直向上管的流动和换热特性差异.与以往超临界流体的经典单相流体假设不同,本文引入拟沸腾理论来处理sCO₂在两管中的流动和传热,将超临界流体视为多相结构,包括近壁区的类气层和管芯中的类液流体.结果发现,传热方面,在正常传热模式下垂直向上管内壁温和水平管底母线内壁温基本一致.当垂直向上管发生传热恶化时,垂直向上管的壁温峰值会随着超临界沸腾数(SBO)的增大超过对应焓值位置的水平管顶母线内壁温.垂直向上管中SBO区分了正常传热和传热恶化.而在水平管中,当弗劳得数小于100时,SBO主导顶底壁面最大壁温差.相比于垂直向上管,相同压力下的超临界流体在水平管内发生传热恶化需要更高的热流密度和质量流量的比值.流动方面,引起垂直向上管压降斜率增高的机理是孔口收缩效应.主导水平管压降变化的机理是分层效应,并用弗劳得数在水平管中顶底壁温差异与压降之间建立联系.     

微细管内超临界二氧化碳冷却换热研究

本文对超临界二氧化碳在微细管内冷却对流换热进行数值模拟研究,分析不同流动方向和管径大小对超临界二氧化碳对流换热的影响,考察管内局部流体温度、管壁温度以及无量纲温度分布的变化。湍流模型采用低雷诺数YS模型。研究表明,在LPV范围比较大的截面,超临界二氧化碳局部换热系数达到最大值,同时管内传热受流动方向和管径的影响均较大。     

超临界流体二氧化碳——溶剂绿色化

 早在1879年,J.B.Hannay.就已发现金属卤化物在高压乙醇或乙醚中溶解度异常增加的现象。到20世纪60年代已有不少研究者从各方面研究这一特殊现象。人们惊奇地发现处于临界压力和临界温度以上的流体对有机化合物溶解度一般都能增加几个数量级。然而应用这一特性却是近20年的事。1978年联邦德国建成从咖啡豆脱除咖啡因(Coffein咖啡碱)的超临界CO₂萃取工业化装置(处理量达到27Kt/a)。分离过程采用二氧化碳作为萃取剂,由于超临界CO₂流体兼具气体和液体的特性,溶解能力强,传质性能好,而且无色无味无毒、化学惰性、不燃烧、无残留等一系列优点.     

竖直管内超临界二氧化碳传热研究

本文对超临界压力下二氧化碳在竖直管内的对流换热进行了模拟研究,分析了超临界二氧化碳在临界点附近的物性变化,以及不同进口温度对换热系数的影响和换热系数与(火积)的关系。结果表明,在临界点附近,物性变化非常剧烈,尤其是比热容的变化最为明显;在较大雷诺数下,二氧化碳进口温度对微细管道换热系数的影响较小;不同截面处换热系数和(火积)的变化趋势一致。     

超临界二氧化碳在突扩管中对流换热的流动特性研究

对流动分岔后的超临界二氧化碳在平面对称突扩管中进行强迫对流换热进行了数值模拟,研究了热流密度在流体发生流动分岔现象后流动特性的影响。计算结果表明:随着热流密度的增加,临界雷诺数和转换雷诺数减小,流动稳定性遭到削弱;对应于相同的雷诺数,由于流动分岔引起的不对称压力分布随着热流密度的增加对应于突扩管上、下半部有不同变化规律,这使得对应回流区的大小分别减小和增大。     

超声场强化超临界CO2萃取除虫菊酯的初步研究

本文以除虫菊花中的除虫菊酯萃取为对象,研究用超临界CO2对其萃取时,施加超声场对萃取物降解及萃取速率的影响.结果表明,在实验范围内施加超声场(200kHz,200W电功率)没有引起超临界CO2流体"空化",从而没有使易分解组分除虫菊酯降解;施加超声场可以提高除虫菊酯的萃取速率,且对萃取速率的影响比用水为共溶剂强,在实验范围内,萃取优化工艺条件为萃取压力(20MPa);施加超声场(200kHz,200W电功率);萃取温度(40℃);添加共溶剂水(0.5ml水/g干花);CO2流量(2.0L·min-1).     

超临界二氧化碳和模型共聚物的相平衡和成核性质研究

在Weeks-Chandler-Andersen （WCA）微扰理论的基础上,建立了一个状态方程,研究了温度和压力以及模型共聚物分子链长对体系相平衡和临界胶束浓度的影响. 关键词： 超临界二氧化碳 模型共聚物 相平衡 临界胶束浓度     

Study on solubility and solubilisation of drying agent in supercritical carbon dioxide for improving local permeability of tight gas reservoir

The AC component of drying agent described in literature 6 can be injected into tight gas reservoir formation to reduce original and residual water saturation caused by completion and stimulation. However, the pore and throat of formation in tight gas reservoir are so small that AC particles are difficult to be injected into them directly. Through experiments, we discovered that a certain amount of AC could dissolve in supercritical carbon dioxide (SCCO₂) and it could separate out from SCCO₂ when pressure decreased. Therefore, SCCO₂ can be used as transport agent and bring it into tight gas reservoir for drying formation. We further study the solubility of AC in SCCO₂ under different temperature and pressure, and also screen solubilizer to enhance the solubility in this paper. The results show that the solubility of AC in SCCO₂ is 0.0005?mol/mol at 40°C and 8?MPa. When temperature is constant, the solubility of AC in SCCO₂ increases with the increase of pressure, but the impact of temperature on the solubility shows different variation principle with pressure increasing. In addition, ethyl alcohol is the best solubilizer for increasing the solubility of AC in SCCO₂, and the optimal concentration of solubilizer in SCCO₂ is 10%.     

基于拟沸腾理论的超临界CO2管内传热恶化量纲分析

超临界流体广泛应用于工程技术领域,其流动传热特性对工程设计具有重要意义,但是,由于超临界流体的物理微观和宏观行为的机理尚不清晰,所以其异常的流动传热特性并未得到很好的解决.普遍认为超临界流体在分子尺度上可分为类气和类液两种不同的特性,直到最近通过实验在宏观上监测到超临界水类液和类气之间的转变,且这一过程与拟沸腾理论一致...     

Non-thermal pasteurization of lipid emulsions by combined supercritical carbon dioxide and high-power ultrasound treatment

Supercritical carbon dioxide (SC-CO₂) is a novel method for food pasteurization, but there is still room for improvement in terms of the process shortening and its use in products with high oil content. This study addressed the effect of high power ultrasound (HPU) on the intensification of the SC-CO₂ inactivation of E. coli and B. diminuta in soybean oil-in-water emulsions. Inactivation kinetics were obtained at different pressures (100 and 350 bar), temperatures (35 and 50 °C) and oil contents (0, 10, 20 and 30%) and were satisfactorily described using the Weibull model. The experimental results showed that for SC-CO₂ treatments, the higher the pressure or the temperature, the higher the level of inactivation. Ultrasound greatly intensified the inactivation capacity of SC-CO₂, shortening the process time by approximately 1 order of magnitude (from 50 to 90 min to 5–10 min depending on the microorganism and process conditions). Pressure and temperature also had a significant (p < 0.05) effect on SC-CO₂ + HPU inactivation for both bacteria, although the effect was less intense than in the SC-CO₂ treatments. E. coli was found to be more resistant than B. diminuta in SC-CO₂ treatments, while no differences were found when HPU was applied. HPU decreased the protective effect of oil in the inactivation and similar microbial reductions were obtained regardless of the oil content in the emulsion. Therefore, HPU intensification of SC-CO₂ treatments is a promising alternative to the thermal pasteurization of lipid emulsions with heat sensitive compounds.     

Ultrasound-assisted of alkali chloride separation using bulk ionic liquid membrane

An ultrasonic-assisted separation of alkali chloride (LiCl, NaCl, and KCl) salts have been carried out using of an hydrophobic ionic liquid membrane (ILM). The ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and tributyl phosphate mixture have been used as ILM. An ultrasonic probe with different frequencies (25, 100, and 250) kHz have been applied as source of ultrasound generator with different times of sonication (2, 5, and 10) min in three phases system containing feed, ILM, and receiver in osmotic U-shaped tube. Also, 250, 500, and 1000 ppm of the feed (alkali chloride) concentration have been used to separate. The frequency of 250 kHz with higher sonication time provides optimum condition for separation of LiCl with lower feed concentration. The thermodynamic properties such as density and speed of sound and the related thermodynamic properties have been calculated to optimize ILM composition (x_IL = 0.45) for ultrasound-separation.     

Ultrasound coupled with supercritical carbon dioxide for exfoliation of graphene: Simulation and experiment

Ultrasound coupled with supercritical CO₂ has become an important method for exfoliation of graphene, but behind which a peeling mechanism is unclear. In this work, CFD simulation and experiment were both investigated to elucidate the mechanism and the effects of the process parameters on the exfoliation yield. The experiments and the CFD simulation were conducted under pressure ranging from 8 MPa to 16 MPa, the ultrasonic power ranging from 12 W to 240 W and the frequency of 20 kHz. The numerical analysis of fluid flow patterns and pressure distributions revealed that the fluid shear stress and the periodical pressure fluctuation generated by ultrasound were primary factors in exfoliating graphene. The distribution of the fluid shear stress decided the effective exfoliation area, which, in turn, affected the yield. The effective area increased from 5.339 cm³ to 8.074 cm³ with increasing ultrasonic power from 12 W to 240 W, corresponding to the yield increasing from 5.2% to 21.5%. The pressure fluctuation would cause the expansion of the interlayers of graphite. The degree of the expansion increased with the increase of the operating pressure but decreased beyond 12 MPa. Thus, the maximum yield was obtained at 12 MPa. The cavitation might be generated by ultrasound in supercritical CO₂. But it is too weak to exfoliate graphite into graphene. These results provide a strategy in optimizing and scaling up the ultrasound-assisted supercritical CO₂ technique for producing graphene.     

利用溶液理论计算饱和甲烷中二氧化碳溶解度

求取二氧化碳在饱和液态甲烷中的溶解度,对于在较高温度下实现液化天然气至关重要。文中在理想溶液基础上,采用正规溶液关系式和改进的Scatchard-H ildebrand关系式进行二氧化碳的溶解度计算,并且在临界点附近采用经验公式对其进行修正。将上述计算结果与Davis实验数据进行比较后表明,改进的正规溶液理论计算方法在低于140K温区时可推荐用于此项溶解度计算,经验公式可用于接近临界温度区域的溶解度计算。