Experimental investigation on compressed air drying performance using pressurized liquid desiccant

As a new compressed air-drying method, the compressed air dehumidification using a pressurized liquid desiccant was proposed in our previous study. The pressurized dehumidifier is a complex and core component of the drying system. The mass transfer performance between the compressed air and LiCl aqueous solution is experimentally studied in a counter-flow pressurized dehumidifier filled with structured packing. The humidity ratio of outlet compressed air, vapor removal of processed compressed air, moisture removal rate, and dehumidification efficiency were selected as the performance indices. The results show that the minimum humidity ratio of processed compressed air could reach 0.23 g/kg under 0.71 MPa. Compressed air-drying performance could be remarkably enhanced through increasing the air pressure and liquid desiccant inlet concentration while the influence of liquid desiccant temperature is negative. Furthermore, in order to ensure high compressed air-drying performance, reduce the power consumption of the air compressor and liquid desiccant pump, and the possibility of carryover, the optimum ratio of liquid to compressed air flow rate is recommended to be around 1.5 under pressure around 0.50 MPa. Meanwhile, the energy consumption for per-gram moisture removal of a liquid-desiccant-based compressed air-drying system can reach 1.42 kJ/g lower than cooling dehumidification under 0.3 MPa, which is 16.0% lower than a compressed air-cooling dehumidification system.     

Comparative study of droplet drying models for CFD modelling

CFD simulation is used to study wall deposition and agglomeration phenomena commonly encountered in industrial spray dryers. This paper initially provides a comparison of two drying kinetics models: Characteristic Drying Curve (CDC) and Reaction Engineering Approach (REA). Comparisons are made with experimental data with application to carbohydrate droplet drying obtained from past workers. These models were then extrapolated to actual drying conditions to assess their performance. The REA model predicts the progressive reduction in drying rate better than the CDC model for the carbohydrate droplets. A modified CDC model incorporating a convex falling rate produced better agreement than the conventional linear falling rate model. Further analysis showed that the REA model can be extended to simulate the particle surface moisture which may affect the agglomeration process. The proposed concept was compared with reported simulation results from a diffusion model which showed reasonable fit with data.     

Influence of osmotic drying with an aqueous poly(ethylene glycol) liquid desiccant on alumina objects gelcast with gelatin

Gelcasting and liquid desiccant drying are novel forming and drying methods used to mitigate common issues associated with the fabrication of complex advanced ceramic objects. In this study, the molecular weight and osmotic pressure of aqueous poly(ethylene glycol) (PEG) desiccant solutions were simultaneously varied to understand their influence on the net mass loss rates of gelcast alumina samples prepared using gelatin as a gelling agent. Additionally, the amount of PEG diffusion and water diffusion to and from the ceramic samples after 150 min of immersion in the liquid desiccant was correlated to the solution properties as was the final bulk density of the sintered samples. Solutions with high molecular weight and low osmotic pressure resulted in low PEG gain and low water loss, while solutions with low molecular weight and high osmotic pressure resulted in high PEG gain and high water loss. In some cases, more than 40 wt% of the total water per sample was removed through the liquid desiccant drying process.     

Reduction of a model for single droplet drying and application to CFD of skim milk spray drying

In this work, a novel methodology for the development of a high-accuracy computational fluid dynamics (CFD) model for the spray-drying process is described. Starting point is an own spatially resolving model of droplet/particle drying, which was developed and validated on the basis of a series of single droplet drying (SDD) experiments. This sophisticated model is transformed to a much simpler version: the characteristic drying curve approach, after running the full SDD model in a wide range of operating conditions. Then, the obtained reduced model is implemented into the CFD solver. The CFD spray-drying model takes into account the hydrodynamics of the continuous phase, particle drying kinetics, changes in the particle diameter, and the heat loss from the drying chamber to the environment. Validation of the entire procedure is provided by data obtained from drying experiments performed in a co-current laboratory spray tower. High accuracy of the developed CFD model of skim milk spray drying has been found for both phases, for the mean outlet temperature of the continuous phase (air) and for the change in average particle moisture content along the spray tower (discrete phase).     

Characterization of a superabsorbent polymer

We studied an amorphous polymer superabsorbent, able to absorb until 1000 times its weight of water. It is consisted of macromolecular chains, dependent between them by chemical bonds. The swelling of the product in the presence of water gives rise to a polyelectrolytic gel. The chemical analysis of polymer by energy dispersive spectrometry and photoelectrons spectroscopy with a microsounder X showed that the product is homogeneous. It contains carbon, oxygen, and sodium. The measurements of specific surface of the product show that the polymer is nonporous and present a weak surface of about 2.1 m²/g. The thermal study of polymer showed that, under the effect of the temperature and with atmospheric pressure, the polymer is degraded only at temperatures higher than 200°C and becomes porous. When the material is heated at higher temperature of 200°C, its surface becomes increasingly porous with also an increase in the size of the pores. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 782–786, 2007     

CFD Modeling of Microwave-Assisted Fluidized Bed Drying of Moist Particles Using Two-Fluid Model

The drying behavior of moist spherical particles in a microwave-assisted fluidized bed dryer was simulated. The two-fluid Eulerian model incorporating the kinetic theory of granular flow was applied to simulate the gas–solid flow. The simulations were carried out using the commercial computational fluid dynamics (CFD) package Fluent 6.3.26. The effects of different levels of microwave power densities as well as initial gas temperature on the prediction of solids moisture content, gas temperature, and gas absolute humidity were investigated. The effect of microwaves was incorporated into calculations using a concatenated user-defined function (UDF). The simulation results were compared with experimental data obtained from drying of soybeans in a pilot-scale microwave-assisted fluidized bed dryer and reasonable agreement was found. The mean relative deviation for prediction of solids moisture content, gas temperature, and gas absolute humidity were less than 3, 10, and 5%, respectively. Further work is needed to validate the proposed model for large-scale plants.     

Absorption and desorption of liquid water by a superabsorbent polymer: Effect of polymer in the drying of the soil and the quality of certain plants

In this work, we were interested in the study of the kinetic behavior of the reaction of drying soil representing the Marrakesh region (south of Morocco) in the presence of an superabsorbent polymer. The presence of a polymer in the soil diminished the kinetic drying of the soil, which will have as an application a reduction in water loss in the process of irrigation. The presence of a polymer in the soil enables a complete modification of the kinetic regimes controlling the soil‐drying kinetic. We also realized the first study of the behavior of certain selected plants in the melange of a soil and a polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 234–243, 2002     

CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

A steady-state, three-dimensional, multiphase computational fluid dynamics (CFD) modeling of a pilot-plant countercurrent spray drying tower is carried out to study the drying behavior of detergent slurry droplets. The software package ANSYS Fluent is employed to solve the heat, mass, and momentum transfer between the hot gas and the polydispersed droplets/particles using the Eulerian–Lagrangian approach. The continuous-phase turbulence is modeled using the differential Reynolds stress model. The drying kinetics is modeled using a single-droplet drying model, which is incorporated into the CFD code using user-defined functions (UDFs). Heat loss from the insulated tower wall to the surrounding is modeled by considering thermal resistances due to deposits on the inside surface, wall, insulation, and outside convective film. For the particle–wall interaction, the restitution coefficient is specified as a constant value as well as a function of particle moisture content. It is found that the variation in the value of restitution coefficient with moisture causes significant changes in the velocity, temperature, and moisture profiles of the gas as well as the particles. Overall, a reasonably good agreement is obtained between the measured and predicted powder temperature, moisture content, and gas temperature at the bottom and top outlets of the tower; considering the complexity of the spray drying process, simplifying assumptions made in both the CFD and droplet drying models and the errors associated with the measurements.     

粉煤灰高吸水复合材料的表征及其释钾性能

采用溶液聚合法首次合成的粉煤灰/聚丙烯酸-丙烯酰胺高吸水复合材料,吸蒸馏水、自来水、生理盐水倍率达到并超过了国家"863"项目技术指标,成本比纯高分子吸水树脂低。粉煤灰复合到高吸水材料之后,其中的钾离子释放8.70%,使得此复合材料同时具有释钾的功能。释钾机理即是粉煤灰中的K2O与体系中的丙烯酸发生了中和反应。X-衍射分析说明复合材料中粉煤灰的主要晶体结构没有变化;红外光谱分析较深入地研究了此材料的结构和成分;扫描电镜分析表明粉煤灰与高分子基体没有开裂,复合效果良好。     

棉花杆废弃物制备高吸水树脂的研究

利用棉花杆作为基准材料,以过硫酸钾(APS)为引发剂引发单体丙烯酰胺(AM)和丙烯酸(AA)接枝共聚制备高吸水树脂的最优合成条件为:引发剂APS用量为棉杆的5%,单体AM与AA的质量比为7∶3,棉杆∶单体质量比为1∶5,AA中和度80%,反应时间3 m in,交联剂N,N-亚甲基双丙烯酰胺用量为5%,树脂吸生理盐水率135 g/g。     

纤维状纤维素高吸附材料制备工艺的研究

本文研究对水和生理液有很好吸附和保持能力的纤维状高吸附材料的制备工艺。该材料是将纤维素纤维（棉短绒、外科用纱布）经由一种处理液进行醚化、交联等反应得到，使纤维的表面形成一层交联聚电解质，而芯层保持原有的天然结构。文中讨论了影响水吸附保持值（WRV）和生理盐水吸附保持值（SRV）的工艺因素，检测了聚电解质层中纳和铜可迁移金属平衡离子对血浆吸附性能的影响。结果表明，采用本工艺使改性棉短绒的WRV和SRV分别为未变性时的12倍和6倍，变性纱布则分别为未改性时的6倍和4．7倍。     

Modeling and simulation of the drying of thin sheets in a continuous infrared dryer

The model gives the temperature and moisture distributions of the air, and of the moist sheet, as a function of time and distance in the dryer. The influence of the sheet's velocity and that of the radiant energy on the dryer performance as well as the effect of the moisture content of the entering sheet have been studied. A set of 27 experiments was carried out using the infrared dryer in order to calibrate the model. In these, the following three variables each had three operational levels: web velocity, initial web moisture and heating power. The model predictions agreed very well with the experimental data. Model predictions using arithmetic averages for the parameters, and parameters correlated with operational variables, are also presented and discussed.     

微波干燥玉米籽粒的试验研究

针对玉米热风干燥中存在的问题。运用自制的微波干燥试验设备。采用不同的质量比功率和加热时间及配套的工艺流程。研究了玉米微波干燥特性及干燥条件对干燥品质、能耗的影响；分析了微渡干燥玉米过程中单位质量功耗、温度、平均失水速率与玉米籽粒发芽率、爆腰率和淀粉得率的关系；确定了影响微波干燥玉米的工艺参数和玉米微波干燥的合理工艺流程。研究结果表明：玉米微波干燥主要处于恒率干燥阶段，应用微波技术既能快速而经济地对玉米籽粒进行干燥，又能保持其种用价值，且有利于改善其品质。     

Adsorption of anionic dyes on a reversibly swelling cationic superabsorbent polymer

A cationic monomer [2‐(methacryloyloxy)ethyl]trimethylammonium chloride was polymerized using N,N′‐methylenebisacrylamide as the crosslinker to obtain a cationic superabsorbent polymer (SAP). This SAP was characterized by Fourier transform‐infrared spectroscopy, and the equilibrium swelling capacity was determined by swelling in water. The SAP was subjected to cyclic swelling/deswelling in water and NaCl solution. The conductivity of the swelling medium was monitored during the swelling/deswelling and was related to the swelling/deswelling characteristics of the SAP. The adsorption of five anionic dyes of different classes on the SAP was carried out and was found to follow the first‐order kinetics. The Langmuir adsorption isotherms were found to fit the equilibrium adsorption data. The dye adsorption capacity of the SAP synthesized in this study was higher than that obtained for other hydrogels reported in the literature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Modeling and simulation of the drying process of natural gas pipeline using vacuum drying method

Abstract

Vacuum drying is one of the most effective methods to protect submarine natural gas pipes from blockage caused by hydrate and internal corrosion. This article presents a model for analyzing the mass, momentum, and energy transfer processes in pipeline drying with vacuum drying method. Model of the evaporation rate of liquid water is derived from Hertz–Knudsen–Schrage equation. Finite volume method is employed to discretize the governing equations with an upwind implicit scheme in present work, and 2nd order upwind scheme for energy equation is adopted to weaken numerical dissipation. Non-linear algebraic equations after discretization are solved by Newton-Raphson method. Reliability and accuracy of this model are validated via three experimental cases. Numerical results coincide well with the experimental data, and the relative errors of the calculated drying time are 1.7% in Case 1, 1.2% in Case 2, and 5.5% in Case 3. Finally, the dynamic characteristics of the vacuum drying process are analyzed such as dynamic distributions of pressure, temperature, mass flow rate, and liquid holdup. Mathematical model and algorithm developed in present work provide understanding and insights of the vacuum drying process, which aids in determining cost-effective pipeline drying scheme.     

Preparation and properties of a salt‐resistant superabsorbent polymer

Crosslinked sodium polyacrylate was prepared by solution polymerization with N,N‐methylene‐bisacrylamide (bisAM) as crosslinking agent; it was subsequently surface‐crosslinked by ethylene glycol diglycidyl ether (EGDE) and then was modified with inorganic salt to obtain a superabsorbent with water absorbency in 0.9 wt % NaCl aqueous solution at atmosphere and applied pressure (P ≈ 2 × 10³ Pa) of 55 and 20 g.g^?1, respectively. Moreover, it also had excellent hydrogel strength. The effects of reaction temperature, reaction time, neutralization degree (ND) of acrylic acid, amount of initiator, crosslinking agent, and surface‐crosslinking agent, mass ratio of inorganic salt to initial superabsorbent, molar ratio of sodium aluminate (NaAlO₂) to potassium dihydrogen hyphosphate (KH₂PO₄) on water absorbency (WA) in 0.9 wt % NaCl aqueous, and the hydrogel modulus were investigated and optimized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2532–2541, 2004     

On the simulation of hydrocyclones using CFD

This study reports on the development of a complete solution methodology for the simulation of a hydrocyclone. A commercial software package, Ansys 12 Fluid Dynamics, is used to solve the governing conservation equations. Turbulence is modelled using the large eddy simulation, and the discrete particle model was used to predict the particle separation. Two hydrocyclones of differing geometries are explored, and the results compared with experimental values. It is shown that there are two key factors for obtaining a reliable result. The first is the domain discretisation, and the second is the generation of a consistent initial value, including the establishment of a stable air core. Using the methodology developed, superior agreement was obtained for predicted and experimental values of pressure, velocity distribution, air core profile and separation efficiency. © 2012 Canadian Society for Chemical Engineering     

Conditions for Accurate CFD Modeling of Spray-Drying Process

The paper presents concluding results of extensive experimental and theoretical research on confident CFD modeling of spray drying. An earlier developed experimental method to determine spray-drying kinetics in a lab scale allowed us to find a critical material moisture content and to determine generalized spray-drying curves. The generalized drying curves, identical in shape in the laboratory and pilot plant units, were used in the CFD model of spray drying process. Extensive simulations for spray drying of 10, 30, and 50% of initial solid content of maltodextrin proved high accuracy of the predictions of discrete (particle size distribution, particle moisture content, particle velocity, spray temperature) and continuous-phase parameters (gas temperature and humidity). Maximum error of the predictions of discrete-phase parameters was on the level of 20%, which is probably close to the current capacity of the CFD technique for modeling of spray-drying process. Comparison of experimental measurements and theoretical results shows that incorporation of realistic spray-drying kinetics into the CFD model and correct definition of initial drying and atomization parameters enable reliable simulations of spray-drying process.     

压缩空气溶液除湿中不同除湿剂除湿性能比较

在压缩空气溶液除湿实验平台上,分别以LiBr和LiCl水溶液作为除湿剂,实验研究了两种溶液在压缩空气溶液除湿系统中的除湿性能。以溶液表面水蒸气分压力作为比较基准,压缩空气出口含湿量和除湿量作为除湿性能的评价指标,对二者的除湿能力进行比较分析。同时基于压缩空气溶液除湿器传热传质模型,结合实验数据,研究了LiBr、LiCl溶液与压缩空气间的传质系数大小以及变化规律。结果表明：在相同的处理工况下,采用LiCl溶液对压缩空气进行除湿能得到更低的空气出口含湿量和更高的除湿量,LiCl溶液除湿过程的传质系数也高于LiBr溶液,即在压缩空气溶液除湿系统中LiCl溶液具有更优的除湿能力和传质性能。