Pressure swing adsorption modeling of acetone and toluene on activated carbon

A five steps pressure swing adsorption process was designed for acetone and toluene mixtures separation and recovery. Dynamic distributions of gas phase content and temperature were investigated. Based on the theory of Soret and Dufour, a non-isothermal mathematical model was developed to simulate the PSA process. Effects of heat and mass transfer coefficients were studied. The coupled Soret and Dufour effects were also evaluated. It is found that the heat transfer coefficient has little effect on mass transfer in adsorption stage. However, it has some impacts in desorption stage. The maximum value of C/C0 increases by about 25% as heat transfer coefficient decreases. The temperature variation is less than 0.05 K with the change of mass transfer coefficient, so that the effect of mass transfer coefficient on heat transfer can be ignored. It is also concluded that the Soret and Dufour coupled effects are not obvious in pressure swing adsorption compared with fixed-bed adsorption.

Effect of Adsorbent Diameter on the Performance of Adsorption Refrigeration

Adsorbents are important components in adsorption refrigeration. The diameter of an adsorbent can affect the heat and mass transfer of an adsorber. The effect of particle diameter on effective thermal conductivity was investigated. The heat transfer coefficient of the refrigerant and the void rate of the adsorbent layer can also affect the effective thermal conductivity of adsorbents. The performance of mass transfer in the adsorber is better when pressure drop decreases. Pressure drop decreases with increasing permeability. The permeability of the adsorbent layer can be improved with increasing adsorbent diameter. The effect of adsorbent diameter on refrigeration output power was experimentally studied. Output power initially increases and then decreases with increasing diameter under different cycle time conditions. Output power increases with decreasing cycle time under similar diameters.

Study on the Irreversible Thermodynamics of a Marine Engine Exhaust-powered Adsorption Refrigerating System

This study investigates the heat and mass transfer mechanism of a marine engifie exhaust-powered adsorption refrigerating system by using irreversible thermodynamics. The equations of entropy-production rate and the linear phenomenological equations of thermodynamic flux and force are established. The conventional experimental facilities of unit tube are developed and the phenomenological coefficients are obtained by fitting the experimental data. It is concluded that the thermodynamic process in the adsorbent bed is determined by the coupling effect of the heat and mass transfer; furthermore, the mass transfer is determined by the heat transfer. Taking some measures to increase heat transfer can improve the performance of the adsorption refrigerating system. The conclusions presented in this paper may be of value to the engineering applications of the system.

Effect of Adsorbent/Adsorbate Couple on the Performance of Adsorption Solar Refrigerator

This work presents a contribution to the study of the process of cold production by adsorption from solar energy. In this paper, we discuss a comparative study of the operation of a solar adsorption refrigerator using the silica gel-water couple and the zeolite-water couple through dynamic modeling and simulation. The mathematical model representing the evolution of heat and mass transfer at each component of the adsorption solar refrigerator has been developed. It appears from this study that the evolution of the temperature of the two adsorbents (zeolite and silica gel) is quasi-similar throughout the operating cycle. However, the maximum mass of water vapor adsorbed by the silicagel (0.24 kg/kg) is higher than that adsorbed by the zeolite (0.201 kg/kg). In the same way, the mass of water vapor cycled, obtained with the silicagel-water couple which is 0.14 kg/kg, is higher than that obtained with the zeolite-water couple which is 0.081 kg/kg. Therefore, the amount of cold produced 9.178 MJ and the solar coefficient of performance 0.378 obtained with the solar refrigerator using the silica gel-water couple, are better.

Preparation of composite adsorbent with high performance of heat and mass transfer

To develop a new composite adsorbent with high performance,fir sawdust and CaCl2are selected as raw materials.The mass transfer is enhanced by carbonizing and activating the sawdust and heat transfer is enhanced by adding expanded graphite into the adsorbent.The effect of the preparation temperature and the expanded graphite content on the adsorption performance is investigated.The results show that the new adsorbent exhibits a high adsorption performance due to its high porosity,uniform distribution and high content of CaCl2and high thermal conductivity.Also,the experimental results indicate that the rate of ammonia adsorption on the adsorbent depends on the expanded graphite content and the carbonization and activation temperature.The adsorbent prepared at 500°C and with the expanded graphite content of 30%has the best performance in terms of the adsorption refrigeration,which adsorbs ammonia as high as 0.37 g g 1at 10 min.

硅胶干燥剂涂层等温除湿传质特性的数值模拟研究

吸附除湿循环存在复杂的热质耦合传递现象,其中吸附阶段干燥剂释放的吸附热会导致除湿性能下降,而理想等温除湿可有效消除吸附热影响。为研究硅胶干燥剂涂层等温除湿传质特性,本文将热质传递解耦,依托实验验证的二维共轭传热传质数值模型,模拟研究决定气固侧传质阻力的两个关键因素——空气流速和干燥剂层厚度对传质特性的影响规律。结果表明:空气流速的增加能够强化气侧传质,因而固侧传质阻力对总传质制约作用增强,吸/脱附过程Sh和Bi_(m)均增大,而干燥剂层厚度增加时,固侧传质阻力增大,吸/脱附过程Sh减小、Bi_(m)增加。特别指出,干燥剂涂层除湿过程数值建模通常需要同时考虑气固侧传质阻力影响。

纳米流体强化气体水合物生成研究进展

水合物的高效快速生成对水合物技术的工业化应用具有重要的意义。对当前纳米流体促进水合物生成过程进行了分析和总结。结果表明,纳米流体能够极大地强化水合物反应体系的传热过程。纳米粒子的浓度、纳米颗粒本身的物性、纳米颗粒的尺寸大小、纳米流体中固体颗粒的分散稳定性、纳米流体在管道中的流动速度及湍动程度是影响体系传热的主要因素。此外,纳米颗粒能够极大地强化水合物反应体系的传质过程,运输作用、防气泡聚合机理、边界层混合机理、渗透机理被用来解释这一现象。但其具体的促进机理仍不清楚,基础理论的建立是未来研究方向。

两组分有机气体等温吸附模拟与传热传质分析

理论与实验研究了丙酮和甲苯气体在活性炭中的吸附性能与温度变化,根据吸附规律,建立了丙酮和甲苯的线性推动力模型(linear driving force,LDF)等温数学模型,并应用有限差分方法求解模型。讨论了传热与传质系数对吸附床层温度和流出浓度曲线的影响,并与实验进行了对比分析。结果发现吸附相传质系数ki变小,轴向导热系数KL、内换热系数hi和轴向质扩散系数DLi变大时,丙酮和甲苯的吸附饱和时间延长,床层温度波动变小,有利于吸附净化丙酮和甲苯的混合气体;反之,结果相反,但有利于变压吸附分离甲苯和丙酮。同时通过模拟计算得到与实际情况相符的各组分传质传热参数:KL=0.00319W/(m·K)-1,hi=0.01542W/(m2·K)-1,丙酮DL1=0.05692m2/s,k1=0.0605s-1,甲苯DL2=0.6556m2/s,k2=0.00756_s-1。

吸附式制冷中吸附剂传热传质的强化

对吸附式制冷系统中吸附剂的两种关键性能有效吸附量及导热系数进行了实验及理论研究。测量了几种吸附剂的上述性能并进行了数据拟合，分析了吸附剂吸附性能及导热系数对吸附制冷系统效率的影响，提出了以吸附制冷最佳经济效率为目标函数的吸附剂性能强化手段，并进行了一些实验研究，取得了较好的效果。

非饱和土壤中重金属污染物迁移机理分析

视土壤为非饱和多孔介质,将描述非饱和多孔介质中多种迁移场量耦合的热质传递模型,结合土壤中溶质迁移的对流-弥散规律,并考虑土壤固体骨架对重金属污染物的吸附特性,建立非饱和土壤中重金属污染物迁移的数学模型.数值分析了非饱和土壤不同深度处和土壤含湿量不同时,污染物在土壤中的迁移状况.随着土壤深度的增加,污染物在土壤中的迁移呈现滞后性;湿含量较高的土壤,在迁移状况趋于稳定时,污染物沿土壤深度的增加其浓度梯度相对较小,数值分析所得污染物在土壤中的迁移规律与文献已有试验结果相一致.因此,所建立的数学模型和数值分析结果,可为分析重金属污染物在土壤中的迁移状况和修复重金属污染的土壤提供一定的理论指导.

新型吸附床的研究进展

吸附床是吸附式制冷装置的核心部件,其性能的优劣直接关系到吸附式制冷装置的制冷效果。通过吸附床的热阻分析,得出强化吸附床传热的措施。文中重点介绍了提高吸附剂与换热壁面的换热系数和吸附剂间的导热系数来强化吸附床传热的方法,详细介绍了填充式吸附床、涂抹式吸附床以及固化式吸附床的结构特点,比较分析3种吸附床的传热传质特点,并阐述了涂抹式吸附床和固化式吸附床的最新研究进展,最后阐述了吸附床的发展方向。

分子筛氧浓缩器非等温吸附模型

介绍了机载分子筛产氧系统OBMSOGS(OnBoardMolecularSieveOx ygenGeneratingsystem)的工作原理和变压吸附PSA(PressureSwingAdsorption)的基本理论 ,建立了分子筛氧浓缩器MSOC(MolecularSieveOxygenConcentrator)的数学模型 .模型考虑了筛床的传热传质、压力变化和吸附热引起的吸附等温梯度的变化等因素对吸附性能的影响 .动力方程采用线性推动力方程 ,采用混合Langmuir吸附等温理论计算吸附量 .

固定床吸附过程传热传质耦合影响数值模拟

To explore the coupled effect of heat and mass transfer,the coupled model of heat and mass transfer for a fixed bed adsorption process was established according to the Soret effect and the Dufour effect theory.Numerical analysis methods were adopted to discuss the influences of heat transfer coefficients,mass transfer coefficients,and the coupled effect of heat and mass transfer on the fixed bed adsorption process respectively.Results have shown that heat transfer coefficients have little effect on mass transfer.To the degree of influence on the temperature field,the greatest is the heat transfer coefficient,followed by the axial thermal conductivity,the smallest is the external heat transfer coefficient.The mass transfer coefficients have some impact on the heat transfer and the mass transfer effect caused by the temperature gradient is more obvious than the heat transfer effect caused by the concentration gradient.

一种新型太阳能吸附式制冷系统的设计及性能模拟

为了解决传统的双床连续吸附制冷系统中因在制冷剂环路使用真空挡板阀而存在的制冷剂压降的问题,使吸附式制冷系统更适合于应用太阳能,提出了利用硅胶-水作为吸附工质对的新型太阳能制冷系统.系统热源由40 m2的热管式真空管集热器提供,制冷机为特殊设计的吸附制冷系统,在上海典型日照条件下该系统可以较为稳定地提供5～8 kW的制冷量,系统COP达0.2以上.通过对系统的动态模拟和理论分析,证实了以硅胶-水为工质对的吸附式系统更适合利用太阳能,研究结果为进一步实验和改进系统性能提供理论指导.

吸附式制冷系统传热传质过程的数值模拟

建立了沸石水吸附式制冷系统吸附床在非第一类边界条件时的二维传热传质模型。考虑了工质对的吸附特性对脱附过程的影响，讨论了肋片数量、肋片物性参数、吸附床的有效导热系数、接触热阻等参数对脱附时间的影响。结果表明，增加肋片可以改善吸附床的性能，其中肋片的数量和接触热阻的影响较大，肋片的物性参数影响不大。

吸附式制冷系统传热传质的简化分析及吸附床的设计

近年来，围绕解决阻碍吸附式制冷系统走向市场的技术问题展开了许多研究，研究结果表明，采用经济实用又能改善传热传质的吸附床比较关键。本文对吸附床的传热传质做了简化分析；并对各种吸附床进行比较，在此基础上设计了一种新型的吸附床。

吸附制冷系统中吸附床的传热传质分析及结构设计

对化学吸附制冷系统中吸附剂颗粒之间以及整个吸附床的传热传质特性进行了分析,并总结了目前国内外强化吸附床传热传质性能的主要措施和方法.分析比较了两种用于化学吸附制冷的典型吸附床结构,在此基础上设计了一种新型的吸附床.

颗粒分布对吸附热变换器内传热传质的影响

采用直接接触法提高吸附热变换器内的传热传质速率,回收热水直接生成过热蒸汽。对蒸汽生成过程进行数值建模,耦合质量、能量和动量方程。气液固的三相计算被合理简化成两个由一个移动水-气界面连接的两相区域计算。模拟研究填充床内的沸石颗粒分布如松散-密集型和密集-松散型对蒸汽生成的影响。两种填充床生成蒸汽的总质量相同。密集-松散型生成蒸汽的时间短,但生成速率快。密集-松散型生成蒸汽与入水的时间比值为58.8%,生成的蒸汽均保持在峰值,最高温度达249℃,系统整体温升达139℃,而松散-密集型生成的蒸汽仅有1/3保持在峰值。密集-松散型出口处与水-气液面产生蒸汽的质量比值大,表明该床层的颗粒分布更有利于蒸汽的快速通过。

内冷却紧凑式叉流除湿器性能数值模拟与分析

该文提出了一种内冷却紧凑式叉流除湿器,对的该除湿器的除湿以及再生过程建立了热质交换的二维动态数学模型,并运用全隐式差分格式获得了该模型的数值解,对影响该类除湿器工作性能的多种因素及其作用结果进行了分析和对比,为除湿器结构的设计、工作状态点的选择提供了必要的理论依据。结果表明,本文提出的内冷却紧凑式叉流除湿器的性能较普通固定床式除湿器的性能有显著提高。

固定床气体吸附过程温升的计算模型

本文采用等温模型、非等温绝热模型和非等温定壁温模型对二氧化碳占10%的二氧化碳氮气双组分气体在吸附剂沸石13X上吸附过程进行了数值模拟,并对结果进行了分析。结果表明三种模型计算的结果差别很大,非等温非绝热模型的分离效果,温升幅度均处于另两种模型之间,温度对吸附过程有着巨大的影响,必须考虑边界条件和吸附剂热物性的影响。采用非等温非平衡模型进行吸附过程模拟是最合理的。