Numerical investigation on freeze-drying of aqueous material frozen with pre-built pores

Freeze-drying of the initially porous frozen material with pre-built pores from liquid material was found experimentally to save drying time by over 30% with an initial saturation being 0.28 compared with the conventional operation with the initial saturation being 1, using mannitol as the solid material. In order to understand the mass and heat transfer phenomena of this novel process, a two-dimensional mathematical model of coupled mass and heat transfer was derived with reference to the cylindrical coordinate system. Three adsorption–desorption equilibrium relationships between the vapour pressure and saturation value namely, power-law, Redhead's style and Kelvin's style equation, were tested. Kelvin's style in exponential form of adsorption equilibrium relation gave an excellent agreement between the model prediction and experimental measurement when the equation parameter, γ, of 5000 was applied. Analyses of temperature and ice saturation profiles show that additional heat needs to be supplied to increase the sample temperature in order to promote the desorption process. Simulation also shows that there is a threshold initial porosity after which the drying time decreased with the increase in the initial porosity. Enhanced freeze-drying is expected to be achieved by simultaneously enhancing mass and heat transfer of the process.     

A non-lithographic plasma nanoassembly technology for polymeric nanodot and silicon nanopillar fabrication

In this work, we present plasma etching alone as a directed assembly method to both create the nanodot pattern on an etched polymeric (PMMA) film and transfer it to a silicon substrate for the fabrication of silicon nanopillars or cone-like nanostructuring. By using a shield to control sputtering from inside the plasma reactor, the size and shape of the resulting nanodots can be better controlled by varying plasma parameters as the bias power. The effect of the shield on inhibitor deposition on the etched surfaces was investigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The fabrication of quasi-ordered PMMA nanodots of a diameter of 25 nm and period of 54 nm is demonstrated. Pattern transfer to the silicon substrate using the same plasma reactor was performed in two ways:(a) a mixed fluorine-fluorocarbon-oxygen nanoscale etch plasma process was employed to fabricate silicon nanopillars with a diameter of 25 nm and an aspect ratio of 5.6, which show the same periodicity as the nanodot pattern, and (b) high etch rate cryogenic plasma process was used for pattern transfer. The result is the nanostructuring of Si by high aspect ratio nanotip or nanocone-like features that show excellent antireflective properties.     

Boiling Heat Transfer Enhancement in a Vertical Annulus by Introduction of Air in Liquid Flow

In this paper, boiling heat transfer in a vertical annulus with inner side heated with and without air introduction is experimentally studied. Results show that boiling heat transfer is significantly enhanced by the introduction of air. When air is introduced into the liquid with a temperature below boiling point, the enhancement of heat transfer is also detected. It is concluded from the study that the heat transfer enhanced by introduction of inert gas is due to the liquid vaporization at the gas-liquid interface near the wall, which removes a large amount of latent heat and lowers the interfacial temperature considerably. Thus the gas-liquid interface acts as a "heat sink" and the heat transfer is augmented significantly.     

内加热垂直环隙中引入惰性气体时的沸腾传热

In this paper, boiling heat transfer in a vertical annulus with inner side heated with and without air introduction is experimentally studied. Results show that boiling heat transfer is significantly enhanced by the introduction of air. When air is introduced into the liquid with a temperature below boiling point, the enhancement of heat transfer is also detected. It is concluded from the study that the heat transfer enhanced by introduction of inert gas is due to the liquid vaporization at the gas-llquid interface near the wall, which removes a large amount of latent heat and lowers the interfacial temperature considerably. Thus the gas-liquid interface acts as a “heat sink” and the heat transfer is augmented significantly.     

Multi-fluid Eulerian simulation of binary particles mixing and gas–solids contacting in high solids-flux downer reactor equipped with a lateral particle feeding nozzle

The performance of binary particles mixing and gas-solids contacting,which is considered qualitatively to have a significant influence on the heat transfer in internal heated circulating fluidized beds,is carefully investigated by means of a numerical approach in the newly developed high solids-flux downer lignite pyrolyzer(φ0.1 m × 6.5 m).Since binary particles are used in this system,a reasonably validated 3 D,transient,multi-fluid model,in which three heat transfer modes relating to the convection,conduction and radiation are considered,is adopted to simulate the flow behavior,temperature profiles as well as volatile contents.The simulation results showed that the solids stream impinges the left wall surface initially and turns towards the right wall in the further downward direction and then shrinks during this process resulting in that the solids concentrate a little more at the central region.In the further downward section of the downer,the particle flow disperses near the right wall and develops uniformly.Meanwhile,the coal phase is slowly heated in the downer and it is found that most of the heat absorbed by the coal is from the convection heat transfer mode.To explore the heat transfer mechanism more quantitatively,two indexes(mixing index and contacting index) are proposed,and it is found that the mixing index initially increased fast and later remained at a relatively flat state.For the contact index,it shows a trend with a first rising and then falling,finally rising continuously.Also,it is found that the convection heat transfer is closely correlated to the contacting status of gas-coal which indicates that the improving of the gas-coal contacting efficiency should be an effective way to strengthen the coal particle heating process.     

用于吸附过程开发的从分子水平级开始的多尺度模拟

This article presents a multiscale simulation approach starting at the molecular level for the adsorption process development. A grand canonical Monte Carlo method is used for the prediction of adsorption isotherms of methanol on an activated carbon at the molecular level. The adsorption isotherms obtained in the linear region （or adsorption constant） are exploited as a model parameter required for the adsorption process simulation. The adsorption process model described by a set of partial differential equations （PDEs） is solved by using the conservation element and solution element method, which produces a fast and an accurate numerical solution to PDEs. The simulation results obtained from the adsorption constant estimated at the molecular level are in good agreement with the experimental results of the pulse response. The systematical multiscale simulation approach addressed in this study may be useful to accelerate the adsorption process development by reducing the number of experiments.     

正磷酸活化木质素吸附Cr(Ⅵ)的固定床实验和模型(英文)

The advantage of using an available and abundant residual biomass,such as lignin,as a raw material for activated carbons is that it provides additional economical interest to the technical studies.In the current investigation,a more complete understanding of adsorption of Cr(VI) from aqueous systems onto H3PO4-acid activated lignin has been achieved via microcolumns,which were operated under various process conditions.The practice of using microcolumn is appropriate for defining the adsorption parameters and for screening a large number of potential adsorbents.The effects of solution pH(2-8),initial metal ion concentration(0.483-1.981 mmol·L-1),flow rate(1.0-3.1 cm3·min-1),ionic strength(0.01-0.30 mmol·L-1) and adsorbent mass(0.11-0.465 g) on Cr(VI) adsorption were studied by assessing the microcolumn breakthrough curve.The microcolumn data were fitted by the Thomas model,the modified Dose model and the BDST model.As expected,the adsorption capacity increased with initial Cr(VI) concentration.High linear flow rates,pH values and ionic strength led to early breakthrough of Cr(VI).The model constants obtained in this study can be used for the design of pilot scale adsorption process.     

Performance enhancement of water bath heater at natural gas city gate station using twisted tubes

Natural gas is transported from producing regions to consumption regions by using transmission pipelines at high pressures. At consumption regions, the pressure of natural gas is reduced in city gate stations(CGSs). Before the pressure reduction process, the temperature of natural gas is increased usually by using a water bath heater,which burns natural gas as fuel, to protect against freezing of natural gas. These types of heat exchangers have a low efficiency and consume a lot of fuel to generate the required heat. In the current study, the twisted configuration of the heating coil is proposed and investigated to enhance the heat transfer through a water bath heater with a nominal capacity of 1000 m~3·h~(-1). Firstly, the implementation procedure is validated with data collected from the CGS of Qaleh-Jiq(located in Golestan province of Iran). A very good agreement is achieved between the obtained results and the real data. Then, three different twist ratios are considered to examine the twisting effects. The proposed technique is evaluated in the terms of velocity, temperature, and pressure variations, and the results are compared with the conventional case, i.e. straight configuration. It is found that both the heat transfer rate and the pressure drop augment as the twist ratio is raised. Finally, it is concluded that the twisted tubes can reduce the length of the gas coil by about 12.5% for the model with low twist ratio, 18.75% for the model with medium twist ratio, and 25% for the model with high twist ratio as compared to the straight configuration.     

An innovative trigeneration system using biogas as renewable energy

One of the ways to decrease the global primary energy consumption and the corresponding greenhouse gas emissions is the application of the combined cooling, heating and power generation technologies, known as trigeneration system. In this research an innovative trigeneration system, composed by an absorption heat pump, a mechanical compression heat pump, a steam plant, and a heat recovery plant is developed. The low temperature heat produced by absorption chiller is sent to a mechanical compression heat pump, that receives process water at low temperature from the heat recovery plant and bring it to higher temperatures. The trigeneration system is fed by biogas, a renewable energy. A design and a simulation of the system are developed by Chem Cad 6.3? software. The plant produces 925 kW of electrical energy, 2523 kW of thermal energy and 473 kW of cooling energy, by the combustion of 3280 kW of biogas. Primary energy rate(P.E.R.) is equal 1.04 and a sensitivity analysis is carried out to evaluate the effect of cooling capacity, produced electrical energy and process water temperature. The first has a negative effect, while other parameters have a positive effect on P.E.R. Compared to a cogeneration system, the trigeneration plant produces the 28% higher of power and the 40%lower of carbon dioxide emissions. An economic analysis shows that the plant is economically feasible only considering economic incentives obtained by the use of heat pumps and steam plant at high efficiency. Saving 6431 t·a~(-1) corresponding to 658000 EUR·a~(-1) of incentives, the plant has a net present value(N.P.V.) and a pay back period(P.B.P.) respectively equal to 371000 EUR and 4 year. Future works should optimize the process considering cost and energetic efficiency as the two objective functions.     

Fabrication of chitosan microspheres for efficient adsorption of methyl orange

In this article, morphology, structure and size controllable chitosan microspheres with high mechanical strength were synthesized by microfluidic technology combining chemical crosslinking and used as an adsorbent for methyl orange. The synthesized adsorbents were characterized using scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR), and an Energy Dispersive Spectrometer(EDS). The effect of pH revealed that the adsorption process depended on pH and the pH variation of methyl orange solution after adsorption indicated that adsorption capacity was affected through the associated role of chitosan nature and pH variation. Experimental results suggested that the as-prepared chitosan microspheres were controlled within a narrow size distribution(coefficients of variation is 1.81%), whose adsorption capacity reached to 207 mg·g~(-1) and mechanical strength was suitable to resist forces. In addition, the adsorption isotherm was well fitted with the Langmuir model, and the adsorption kinetic was best described by the pseudo-second-order kinetic model.The high performance microfluidic-synthesized chitosan microspheres have promising potentials in the applications of removing dyes from wastewater.     

Dynamics of pressurization and blowdown of an adiabatic adsorption bed: 4. Intraparticle diffusion/convection models

The importance of intraparticle mass transfer during pressurization and blowdown steps of PSA processes in an adiabatic adsorption bed was assessed by comparing intraparticle diffusion/ convection and intraparticle diffusion models. Film mass/heat transfer resistances are also considered in the model. The film heat transfer resistance is more important than the heat transfer resistance inside the particle; it can be assumed to be negligible in PSA processes when the temperature variation is not very large, otherwise it leads to serious errors when the adsorption capacity of adsorbents is high and the heat capacity of the system is not high. Intraparticle convection improves the mass transfer inside the particle and leads to faster heat releases into and out of the adsorbents.     

水热合成MnO2及其染料吸附性能的构效关系

以MnSO₄和(NH₄)₂S₂O₈为反应原料,采用水热法制备廉价低毒的MnO₂吸附剂。借助X射线粉末衍射（XRD）、扫描电镜（SEM）和静态吸附实验,探究材料的结构、形貌、吸附性能以及构效关系。结果表明,通过改变水热温度、反应时间,可以得到毛刺球状α、β、γ三种晶型MnO₂以及类球状和针状β-MnO₂。其中水热温度80℃、反应12h时得到的毛刺球状γ-MnO₂吸附亚甲基蓝（MB）效果最好,达到19.33mg/g。当水热温度在50～110℃反应12h以及水热温度为80℃反应4h、8h、24h,所得到的产品的形貌均为毛刺球状。晶型和形貌对MnO₂吸附MB能力均有影响。不同晶型的MnO₂毛刺球对MB吸附性能的影响为β＜α＜γ;不同形貌的β-MnO₂却对吸附效果影响较大,为针状＜类球状＜毛刺球形。随着MB溶液的pH从10.00减少到1.00时,毛刺球状γ-MnO₂对MB的吸附量呈上升趋势,吸附过程还伴随着化学反应,且吸附的过程符合Langmuir等温模型。本文将为MnO₂吸附染料的机制和构效关系研究提供依据。     

喷雾干燥法制备氧化镁材料及其吸附性能

采用喷雾干燥结合热处理法制备花瓣状的MgO,通过对热处理温度的调整,实现MgO表面形貌的调控。研究了所制备MgO粉末作为吸附剂对刚果红的吸附性能,当热处理温度为400℃,得到花瓣状的MgO纳米结构,比表面积达到140.5 m²·g^-1,且对刚果红溶液的饱和吸附量约为1480 mg·g^-1。它们对刚果红的吸附能力比报道的其他花瓣状结构的金属氧化物要高。此外,对其吸附模型、吸附动力学以及吸附机制进行探究,表明吸附过程符合Langmuir吸附模型,所制备样品对刚果红溶液的吸附过程可以由准二级动力学来描述。所制备的花瓣状MgO其高效的吸附性能,使其成为非常有前景的吸附剂用于去除污水中的刚果红染料。     

吸附过程强化对提升高温热泵蒸汽生成性能的影响

在基于直接接触换热法的开式吸附热泵系统中,引入预吸附过程或预设传质通道,考察其对蒸汽生成和系统性能的影响。实验结果表明,预吸附蒸汽压力为0.0680 MPa(饱和温度=89.2℃),系统生成高温蒸汽的平均温度为203℃,系统整体温升为98.4℃,相对于无预吸附系统,生成蒸汽的时间和质量分别增加52.2%和27.0%,系统制热系数和制热功率分别提升28.2%和27.2%。预置树枝状传质通道后,生成蒸汽的时间和质量分别增加了17.8%和8.75%,系统制热系数和制热功率分别提升8.16%和9.05%。预吸附过程使吸附床较快达到整体吸附和热力平衡,缩短蒸汽到达床层出口的时间。预吸附压力越高,系统到达整体吸附平衡的用时越短,蒸汽生成时间越早。传质通道促进吸附床局部平衡的达成,减小局部传质阻力,使部分蒸汽可迅速到达出口。整体和局部吸附平衡的快速达成,均强化了蒸汽的动态生成过程,提升系统整体性能。     

Non-isothermal adsorption in a bidisperse adsorbent pellet

The kinetics of adsorption in bidisperse pellets has been largely studied under isothermal condition. But due to large heat of adsorption, the isothermal models may lead to erroneous results. The present paper proposes a non-isothermal bidisperse model, taking into account two scale mass diffusion (macro—micropore diffusion) and one scale heat diffusion (the temperature within the microparticles is assumed uniform). This model is solved numerically, yielding the sorption uptake and temperature evolution. It turns out that considering the simultaneous macro—micropore diffusion is only necessary for 10⁻⁶ < α < 10⁻¹ (α is the ratio of macropore and micropore diffusional resistances). The macropore diffusion should be rate limiting if the parameter α > 10⁻¹ and the micropore diffusion become rate limiting if α < 10⁻⁶. On the other hand, heat effect may make the isothermal assumption quite erroneous when the diffusion in the macropores and micropores is rapid and the heat transfer between the adsorbent and the ambient sorbate is small.     

Enhanced adsorption of malachite green onto carbon nanotube/polyaniline composites

To enhance adsorption of organic dyes like malachite green (MG) onto polymeric absorbents, we prepared carbon nanotube (CNT) filled polyaniline (PANI) composites with large surface areas by simply using entangled CNTs as porous frameworks during PANI polymerization. Adsorption behavior of the CNT/PANI composites in MG solutions was experimentally investigated and theoretically analyzed. The CNT/PANI composites exhibit much higher equilibrium adsorption capacity of 13.95 mg g^?1 at an initial MG concentration of 16 mg L^?1, increasing by 15% than the neat PANI, which is mainly attributed to large surface areas and strong CNT‐PANI interactions of the composites. In addition, theoretical analyses indicate that the adsorption kinetics and the isothermal process of the composites can be well explained by using the Ho pseudosecond‐order model and the Langmuir model, respectively. In light of their high MG adsorption and easy operation, the CNT/PANI composites have great potential as high‐efficiency adsorbents for removal of dyes from wastewater. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

结构化5A分子筛吸附床结构及工艺参数对N2/H2吸附性能的影响

利用吸附等温线获得动力学参数,建立了CFD模型,模拟了氢气/氮气在结构化5A分子筛吸附床中的吸附过程,研究了吸附剂层片间距、吸附剂厚度等结构参数和吸附压力、进气流量等工艺参数对混合气吸附效果的影响。结果表明：减小层片间距和吸附剂厚度可显著提高传质系数和床层利用率。增大吸附压力可提高床层利用率,但会减小传质系数。进气流量对传质系数的影响不明显,但当流量较大时,吸附容量和床层利用率均呈减小趋势。结构化5A分子筛吸附剂吸附性能良好。     

基于多功能热管的高效吸附式制冰机组回质回热实验研究

设计了一种基于多功能热管的高效吸附式制冰机组,采用氯化钙/活性炭复合吸附剂和氨作为吸附工质对。吸附床的加热解吸、冷却吸附及回热过程均由热管工作完成,对该新型吸附制冰机组进行了回质回热研究,结果表明,回质回热型循环可使机组的制冷性能系数COP提高25.5 %,加热量减小约13 %,同时冷却器负荷降低约21 %;采用先回质后回热方式,在回质过程中继续加热解吸床可进一步增加机组制冰量。与传统回质相比,系统COP和单位质量吸附剂制冷功率SCP提高幅度均在15 %以上,且机组SCP的提高幅度高于COP的幅度;吸附制冰机组性能随冷却水温度的升高而下降,但系统的SCP始终维持在较高的水平。当冷却水温度为27℃、蒸发温度为-18.9℃时,系统的SCP仍然高达356.5 W·kg-1。     

壳聚糖印迹聚合物对Zn2+的吸附动力学

以Zn²⁺作为模板,加入分散剂石蜡、预交联剂甲醛、交联剂环氧氯丙烷,制得特性壳聚糖印迹聚合物,用X射线衍射仪表征了聚合物的结构,考察了聚合物用量、温度等对吸附Zn²⁺的影响,研究了印迹聚合物对Zn²⁺的吸附动力学、等温吸附特性。结果表明,印迹聚合物合成过程中打破了壳聚糖原有晶体的规整性,增加了大量的配位基团,使聚合物的吸附容量大大增加,同时聚合物对Zn²⁺有很好的选择吸附性,对Zn²⁺、Cd²⁺、Mg²⁺、Mn²⁺溶液的分离因子均大于1.5;印迹聚合物能快速吸附溶液中Zn²⁺,整个吸附过程符合拟二级动力学模型：t/Q_t=8.1744+2.0186t,相关系数为0.998,吸附平衡容量模型计算值与实验值较为吻合;印迹聚合物对Zn²⁺的等温吸附过程符合Langmuir吸附等温吸附模型：C_e/Q_e=1.3297+0.02701C_e,最大吸附容量为37.023 mmol/g,吸附过程主要以单分子层的吸附形式进行。     

矿物基化学吸附储热技术的研究进展

化学吸附储热技术近年来在太阳能利用和中低温余热领域得到了广泛关注,与传统的显热储热和相变储热技术相比具有储热密度高、储热损失小、可实现冷热双储等优点,然而其传质传热问题和液解问题导致的吸附性能和循环稳定性能的降低限制了其规模化应用。本文综述了利用矿物基多孔结构材料对化学吸附材料进行封装的方法以解决上述问题,总结了近年来石墨、蛭石等不同矿物基化学吸附储热材料的特点及其在化学吸附系统中的应用,主要介绍了矿物基化学吸附材料的两种体系（无机盐-水体系和氯盐-氨体系）的传质传热、化学吸附热等性能,并进一步指出了矿物基化学吸附储热技术未来的发展趋势,提出开发新型矿物基复合材料和优化化学吸附系统是未来的研究热点。