吸附式制冷装置中吸附床传热传质的研究

本文根据吸附式制冷装置中吸附床的操作特性,建立了吸附床在受热解吸过程中的传热传质数学模型.在这个模型中,假设吸附床是均质的,吸附床的导热系数可用一个当量寻热系数表示,并考虑吸附床中吸附剂与传热片之间的接触热阻.以本文作者所建立的吸附式制冰机为例,对此数学模型进行了计算,计算值与实验结果吻合得较好.     

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。     

不同板翅式涂层吸附床的性能研究

涂层吸附床能够降低吸附剂间的热阻提高吸附床传热性能,是一种高效吸附床。文中采用COMSOL Multiphysics软件建立了局部非热平衡的二维板翅式吸附床模型,开展板翅式吸附床性能数值模拟;采用制冷性能(COP)和单位质量吸附剂制冷能力(SCP)分别对不同翅片形状吸附床(三角形翅片吸附床、梯形翅片吸附床与六边形翅片吸附床)的性能进行分析和评价。研究发现:驱动热源为333—363 K时,随着热源温度的升高,3种不同结构的板翅式涂层吸附床的COP和SCP都随之增大;在相同的条件下,3种不同翅片结构的板翅式吸附床中,六边形翅片吸附床的COP最大,其值为0.514;而梯形翅片吸附床的SCP最高,其值为848.61 W/kg。     

余热制冷吸附床的一个新传热传质模型

在既考虑吸附剂颗粒内部的传质阻力,又考虑吸附剂颗粒之间的外部传质阻力的前提下,建立了余热吸附制冷系统中吸附床的三维非平衡传热传质数学模型,它包括加热/冷却流体传热模型、换热管传热模型、肋片传热模型、吸附剂颗粒床传热传质模型4部分;通过对模型的数值求解,获得了吸附床内部的温度演变曲线和性能指标,与实验结果基本吻合。     

硅胶粒径对太阳能吸附制冷系统性能的影响

针对以硅胶-水为工质对的太阳能吸附式制冷系统,实验研究了不同粒径的硅胶材料对吸附床传热传质特性及系统制冷能力的影响。三组对比实验的硅胶材料平均粒径分别为1mm、3mm和5mm,在太阳辐射接近的条件下完成实验测试,结果表明粒径中等的硅胶材料表现最优,其制冷系数COP和按照循环周期定义的比制冷功率SCP2均最高。小粒径材料虽然使吸附剂填充量有所增加,但是会导致吸附床轴向传质阻力增加,影响其末端吸附能力的发挥。而材料的粒径过大,则会降低吸附床的吸附剂填充量及其传热性能,从而导致预热脱附和冷却过程的时间延长,不利于系统的制冷性能改善。实验结果表明,吸附剂粒径是影响太阳能吸附式制冷系统工作性能的一个重要因素,在系统设计中需要给予重视。     

一种能同时提高固体吸附制冷吸附剂传热传质性能的方法

通过在沸石分子筛中添加膨胀石墨和发泡剂并固结成型进行处理,使吸附剂的导热系数和渗透性有了显著提高,并测定了几种吸附剂的导热系数,采用SEM观察了发泡前后的沸石分子筛的晶体结构和微观形貌的变化,分析了膨胀石墨所具有的特性是使其成为合适的添加剂的原因。通过TGA测试表明吸附剂的传质性能有提高。     

新型旋转填料床的气相传质特性

以CO2-NaOH体系化学吸收测定不同超重力因子、液量和气液比(体积流量比)条件下的有效传质比表面积a,在相同操作条件下,以氨-空气-水体系进行空气吹脱含氨富液测定不同超重力因子、液量和气液比条件下的气相体积传质系数kya,从而得到气相传质系数ky,对其气相传质特性进行了研究. 结果表明,a随超重力因子、液量和气液比增大而增大,kya和ky均随超重力因子和气液比增大而增大,随液量增大而减小. 通过对比可知,在相近操作条件下新型旋转填料床的气相体积传质系数比文献折流旋转填料床的提高36%. 对实验数据进行回归,拟合出a, kya和ky分别与气相雷诺数ReG、液相韦伯数WeL和伽利略数Ga之间的关联式.     

太阳能真空管吸附集热器集热与制冷性能研究及其经济分析

以分子筛 -水为吸附工质对对真空管型太阳能吸附集热器的集热性能进行了详细的分析计算 ,其中包括真空管内、外玻璃间非均匀温度表面的辐射换热 ,两相邻管之间的辐射换热 ,真空管与背板间的辐射换热以及背板的反光等 .同时以制冷量、成本和集热器面积三要素构成新的评判指标 ,对吸附器的结构参数 (管径、管距和吸附剂厚度 )进行了分析 .计算结果表明 ,以大直径的真空管作吸附集热器时 ,可获得较好的综合性能 ;从评判指标来看 ,应用大管径吸附器且两相邻管的中心距离等于 2 .5倍的管径 ,吸附剂的最佳厚度大约为 10mm时经济效果最佳     

活性炭纤维填充床内多组分竞争吸附

建立了活性炭纤维填充床内多组分竞争吸附传质动力学模型 ,采用正交配置方法求解数学模型以预测突破曲线 ,从理论上探讨了竞争吸附平衡及吸附质在填充床内的轴向弥散、纤维内扩散和纤维外对流传质等因素对强、弱吸附组分突破曲线的影响。在间歇和填充床吸附器内进行了脱除水溶液中酚类化合物的实验 ,测定了活性炭纤维吸附水溶液中苯酚和氯代苯酚的吸附等温线 (间歇吸附 )以及苯酚和氯代苯酚在活性炭纤维填充床内竞争吸附时的突破曲线 ,并与模型计算值进行了比较。结果表明 ,吸附质在活性炭纤维内扩散和纤维外对流传质阻力不是填充床内吸附过程的控制步骤 ,而轴向弥散影响显著 ,不可忽略     

新型旋转填料床强化气膜控制传质过程

转子结构为相互嵌套填料环的新型旋转填料床是基于强化气膜控制传质过程的新型高效传质设备,可适用于受气膜控制的吸收、精馏和低浓度工业气体的净化等过程。分别以化学吸收体系CO2-NaOH和物理吸收体系NH3-H2O测定了不同气量、液气比和超重力因子条件下的有效比表面积a和气相体积传质系数kya,并由此得到气相传质系数ky,对其传质性能进行研究。实验结果表明：a、kya和ky均随着气量、液气比和超重力因子的增大而增大。通过对比可知,新型旋转填料床的气相体积传质系数在相近操作条件下是文献逆流旋转填料床的2倍。并对实验数据进行了回归,拟合出了a、kya和ky分别与气相雷诺数ReG、液相韦伯数WeL和伽利略数Ga之间的关联式。     

一种高效吸附床的设计及二维传热数值模拟分析

设计了一种特殊的高效换热的板翅式吸附床,用于硅胶-水连续循环的吸附式制冷系统中。建立了吸附床的二维数学模型。因硅胶-水吸附式制冷系统具有很快的吸附和解吸过程,热量的及时传递成为极其关键的因素。因此在该模型中,只考虑了快速加热和冷却的传热过程,以寻求提高传热速度的途径。对于吸附床的各关键尺寸对换热性能的影响进行了对比和分析,并对实验结果也进行了对比分析。理论研究表明,吸附床的各参数的最优尺寸为：翅片间距为3～6 mm,翅片高度为6～12 mm,翅片厚度为0.03～0.15 mm。实验结果表明,使用这种吸附床结构,系统的循环时间可短至420 s。在硅胶的热导率仅为0.175 W·(m²·℃)^-1的情况下,吸附床的总传热系数可提高至相似文献   

Fixed-Bed adsorber dynamics in binary physisorption-diffusion

Reactions carried out under conditions close to the equilibrium vapour pressure of the participating species involve physisorption on the catalyst surface. Such conditions are encountered for propene metathesis over rhenium oxide/γ-alumina catalyst at room temperature. The sorption-diffusion effects were tested by excluding effects due to reaction. Single-component sorption characteristics were determined by steady-state experiments. The model equations comprising several differential and nonlinear algebraic equations were solved by orthogonal collocation within the method of lines. The model predictions were tested against transient experiments performed in a gradientless, internal recirculation reactor.     

Numerical simulation of the effect of maldistribution in a fixed bed adsorber

The paper deals with the modeling of the effect of maldistribution in pollutant abatementtrichloroethylene(TCE)concerning low concentration(10~(-5)-10~(-8)kg·m~(-3))adsorption in an adsorber.Such a concentration range is rather typical in many an environmental application.Isotherms andbreakthrough curves for TCE adsorption are obtained both for a commercial activated carbonSorbonorit 4 and a laboratory adsorber of d_B/d_P=11.Two two-dimensional nonequilibrium isothermalmodels are developed to describe the mass transfer in the fixed bed taking into account the effect ofmaldistribution.It is found the simulation results with maldistribution are in very good agreementwith the experimental findings.Low concentration TCE adsorption in a fixed bed of activated carbonis found to be strongly influenced by maldistribution.The non-uniform distributions of concentrationand loading of the pollutant in the adsorber are predicted by the model.Maldistribution and its ef-fect on the initial breakthrough of TCE in the     

Recovery of vinyl chloride from by-streams of polyvinyl chloride production by TPSA in a multitubular adsorber

This work aims at developing an efficient and feasible adsorption-based separation process for the separation of vinyl chloride and nitrogen, on activated carbon, by employing a multitubular packed bed geometry, with adsorbent material inside the tubes. Using this geometry, a 2-dimensional mathematical model of a temperature pressure swing adsorption process was used to developed a 6-step three multitubular adsorbers system capable of separating and purifying an industrial scale gas stream of a 40:60% (v/v) vinyl chloride/nitrogen mixture into a 95% (v/v) vinyl chloride stream and a nitrogen stream with a vinyl chloride limit concentration of 8 ppm (w/w). The process reported energy consumption of 4.88 × 10⁶ J/kg_VCM and recovery capacity of 24.35 kg_VCM/(m³_unit h). The multitubular geometry enabled the use of lower adsorbent loads, shorter cycle times, and lower regeneration temperatures. An equivalent 1-dimensional model has also shown to satisfactorily estimate the performance of the current equipment.     

Effect of Adsorbent Diameter on the Performance of Adsorption Refrigeration

Adsorbents are important components in adsorption refrigeration. The diameter of an adsorbent can af-fect 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.     

穿透曲线法获取固定床吸附器的传质扩散系数

研究了煤质活性炭对不同浓度苯酚溶液的吸附，应用固定床吸附动力学模型、非线性回归固定床吸附流出曲线数据，获得了酚类在活性炭上的扩散传质系数。结果发现，酚类的表面扩散系数ＤＳ强烈地依赖于入口酚的浓度，随着酚浓度的升高，表面扩散系数增大。采用上述扩散系数理论预测了其他操作条件下的流出曲线，结果表明实验曲线与预测曲线相符甚好，穿透曲线法能可靠地获取液固吸附过程的吸附扩散系数，为吸附工程设计提供有益的帮助     

Modeling separation of proteins by inert core adsorbent in a batch adsorber

Adsorption/desorption kinetics of protein on the binding ligand of inert core adsorbent in a batch adsorber is analyzed theoretically for Langmuir isotherm coupled with the intraparticle diffusion and film mass transfer resistances. For the two limiting cases of Langmuir isotherm, there are analytical solutions. New analytical solutions are derived for Henry isotherm, and the analytical solution of shrinking core model is recommended for rectangular isotherm. The effects of the inert core radius, equilibrium constant, intraparticle diffusion and film mass transfer resistances on the time evolution of bulk concentration and particle radial profiles were investigated. The applicable range of the analytical solution with rectangular isotherm is given. A new method to estimate both film mass transfer coefficient, k_f, and effective pore diffusivity, D_pe, from a single bulk concentration-time curve in batch adsorber is given and tested with literature data for the adsorption of BSA on CB-6AS inert core adsorbent.     

变压吸附制氧机吸附器结构研究进展

介绍了变压吸附制氧机中吸附器的内部结构、分流板、分子筛布局与装填方式、压料部件与装配等内容,对影响制氧机性能的因素进行了剖析和论述,探讨了变压吸附制氧机设计中关键影响因素和技巧。     

一种回热回质循环吸附式制冷系统的仿真

吸附式制冷常采用回热回质循环来提升系统性能。研究了一种采用串联回热和类回质方式的回热回质循环吸附式制冷系统,并对其进行仿真。系统的主要部件（含作为储液器的蒸发器）采用3层换热法建立数学模型。仿真结果表明,随着制冷时间的延长,系统性能系数（COP）单调增大,单位质量制冷量（SCP）单调减小。随着回热时间的延长,COP和SCP是先增大后减小,最佳的回热时间为10 s。随着回质时间的延长,COP和SCP波动性下降,回质过程未提高系统性能。COP和SCP随着热水、冷冻水温度的升高以及冷却水温度的下降而增大。热水温度对SCP以及冷冻水、冷却水温度对COP和SCP的影响,呈现线性变化,而热水温度对COP的影响呈现二次变化。     

A study of a simulated moving bed adsorber based on the axial dispersion model

On the basis of the axial dispersion model, the concentration profiles for a simulated moving bed adsorber were theoretically predicted. Experimentally, an apparatus consisting of four sections was employed. Glucose and sorbitol were separated from the liquid dissolved with these components both co-currently and counter-currently. The experimental results seemed to support the predicted curves.