摘要
本论文的主要目的是从宏观可见的角度研究了流体运动对相平衡的影响,重点分析研究了流体运动对二氧化碳-水体系吸收-解吸平衡的影响和流体振荡对纯液体汽液相平衡压力的影响。
在温度和压强相同时,两相的化学势相同(相平衡)。相平衡原理对传统的化工传质单元操作有非常重要的实际意义,然而传统的相平衡极限是两相在静态下达到的传质极限,实际生产中物质处于不断的运动状态,因而达到的相对稳定相平衡状态可能与静态时存在不同。
本文首先以二氧化碳—水体系为研究对象,使饱和二氧化碳溶液在管路中流动,观察液相流动时二氧化碳溶解度的变化,探索流动状态对二氧化碳—水体系吸收—解吸平衡的影响规律；接着以纯物质乙醇、异丙醇和水为研究对象,通过恒温水浴振荡器使达到热力学汽液相平衡的纯液体产生回旋运动,观察运动状态下纯液体的汽液相平衡压力变化情况,探索运动液体的汽液相平衡压力的变化规律,从而使宏观的实验现象可以指导实践。
本论文得到的实验结果如下：
1.流体的运动使得二氧化碳-水体系的吸收-解吸平衡发生明显的偏移,使二氧化碳从其饱和溶液中解吸出来并且达到一个新的吸收-解吸平衡状态。不同雷诺数下解吸程度与时间成指数关系,液相湍动得越剧烈二氧化碳从其饱和溶液中吸出的越多,到达新的吸收-解吸平衡状态所需要的时间越短,温度为16±0.5℃,原有溶解在水中的二氧化碳最大约有18%解吸出来,二氧化碳在液相中的溶解度减小为34.77mol·m-3；雷诺数为4.5×104体系达到动态吸收-解吸平衡时,11±0.5℃时二氧化碳的溶解度减小为41.23mol·m-3,最大解吸度是13%,然而14±0.5℃时二氧化碳的溶解度是37.01mol·m-3,最大解吸度是17%,符合高温有利于解吸,低温有利于吸收的特性；雷诺数为3.8×104和温度为16±0.5℃下体系达到动态平衡时,反转时二氧化碳的溶解度是35.65mol·m-3,最大解吸度是15%,正转时二氧化碳的溶解度为35.07mol·m-3,最大解吸度是16%,说明了管路的解析能力大于泵。
2.流体的振荡使纯物质乙醇、异丙醇和水的汽液相平衡压力发生明显偏移,使封闭体系液相上方的压力变大,在3min左右达到一个新的平衡状态,不同振荡频率下偏移程度与时间成指数关系,实验条件下物系的最大偏移程度可达14.5%；同种物质在不同温度下偏移程度不同,温度越高,偏移程度越大,振荡频率130min-1,乙醇在30℃时最大偏移程度是3.9%,35℃时最大偏移程度是6.3%,符合高温有利于蒸发的特性；不同物质在相同对比温度下偏移程度不同,对比温度0.59和振荡频率130min-1时,乙醇的最大偏移程度是6.3%,而异丙醇的最大偏移程度为5.1%；振荡后乙醇达到动态汽液相平衡时终压的对数与温度的倒数具有非常好的线性关系。
3.流体的运动无论对二氧化碳-水体系吸收-解吸平衡还是纯液体汽液相平衡压力都有明显的影响,当液体处于运动的状态下,无论进行工程计算或设计时都应当考虑流体流动的影响。
The main purpose of the present dissertation is to study the influences ofliquid motion on phase equilibrium in macroscopic, especially the absorption-desorption equilibrium and the gas–liquid equilibrium.
Principle of phase equilibrium is very significant to unit operation.Thelimit of traditional phase equilibrium is that the rate of mass transfer reachszero on static state. In actual production, the substances are incessantmovement, so the contrary stable condition which the substances may achievemay be different from static phase equilibrium.
In the dissertation, the absorption-desorption equilibrium of carbondioxide-water system has been firstly studied. When the saturated solution ofcarbon dioxide flows in the pipeline, solubility of carbon dioxide has beenobserved.Then the gas-liquid equilibrium pressure of ethanol, isopropanoland water have been studied.When liquid is forced to wave with certainfrequency by an oscillator, the pressures have been observed. So the macroexperiment phenomenon may direct the practice.
The main experimental results are as follows:
1The liquid motion can make the carbon dioxide escape from the saturated solution of carbon dioxide, and achieve a new absorption-desorptionequilibrium. Under different Reynolds number, the desorption degree andtime accord with exponential function. The more carbon dioxide escape fromthe liquid and the less time is needed with higher intensity of turbulence whenachieving the dynamic equilibrium. At16±0.5, about18%dissolved carbondioxide escapes from the system and the solubility of carbon dioxidedecreases to37.40mol·m-3. Under Reynolds number4.5×104, the dynamicsolubility of carbon dioxide decreases to41.23mol·m-3and the maximumdesorption degree is13%at11±0.5, but at14±0.5the dynamic solubilityof carbon dioxide decreases to37.01mol·m-3and the maximum desorptiondegree is17%. The dynamic absorption-desorption equilibrium of carbondioxide-water system still accord with that low temperature is helpful toabsorption.Under Reynolds number3.8×104, the dynamic solubility of carbondioxide decreases to35.65mol·m-3and the maximum desorption degree is15%by reverse at16±0.5, but the solubility of carbon dioxide decreases to35.07mol·m-3and the maximum desorption degree is16%by corotation at thesame temperature. The result shows that the desorption ability of pipeline ishigher than that of pump.
2The oscillation of liquid can make gas-liquid equilibrium pressures ofethanol, isopropanol and water away from saturation pressures. The pressuresabove liquid level increase and stop rising within about3minutes. Underdifferent oscillation frequency, the deviation degree and time accord with exponential function. Under210min-1, the differential pressure of ethanol is1996Pa and the maximum deviation degree is14.5%at35. At differenttemperature, the deviation degree of material is different under the sameoscillation frequency. The deviation degree would be bigger with highertemperature. Under130min-1, the deviation degree of ethanol is3.9%at30and is6.3%at35. The dynamic gas-liquid equilibrium still accord with thathigh temperature is helpful to evaporation. At the same reduced temperature,different materials have different the deviation degree. Under130min-1, thedeviation degree of ethanol is6.3%and the deviation degree of isopropanol is5.1%at the reduced temperature0.59. The logarithm of a dynamic gas-liquidpressure and the reciprocal of temperature have a very good linearrelationship.
3Flow rate can make either the absorption-desorption equilibrium ofcarbon dioxide-water system or the gas-liquid equilibrium away fromprimitively static equilibrium. On the condition of liquid motion, engineeringcalculation or designing should consider the influence of flow rate.
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