Viscous dissipation effect on solidification of a liquid onto a tube wall

The effect of viscous dissipation on solidification onto the inner surface of a straight circular tube of a liquid flowing laminarly with a specified volumetric rate is analytically determined. Steady conditions and a constant tube wall temperature below the solidification temperature of the liquid are assumed. Solutions for the thickness of the solidified shell and for the pressure drop are obtained. The pressure gradient versus volumetric flow rate curve exhibits a minimum, suggesting that it might be possible to design runners for injection molding machines to have a minimum pressure drop if the volumetric flow rate is specified.     

测定二元互溶系恒沸点的新方法

本文在配制组成为x_((?)0)的二元互溶溶液置于平衡釜或沸点计中,恒压下运行至稳定后测出平衡室温度T,由此得出T—x_((?)0)曲线.本文证明了:最高(低)恒沸点存在的充分必要条件是0(<0),i=1,2;且它与T～x_((?)0)的极大(小)点一致.对恒温时的p～x_((?)0)曲线结论类似.     

Globally optimal design of Minimal WHEN systems using enumeration

The process synthesis problem referred to as work and heat exchange networks (WHENs) asks to determine the optimal heat exchanger network intertwined with compressors, expanders, and valves, all integrated into one single network, such that streams with certain initial temperature and pressure attain their temperature and pressure targets at minimum cost. This article presents a procedure that obtains the globally optimal solution of Minimal WHEN systems using an enumeration scheme, using only a few subproblems, each one solved using mathematical programming to global optimality. Minimal structures feature one compression/decompression task and one heat exchange task per stream. In addition, we depart from the ideal gas assumption and use a cubic equation of state for stream properties. Finally, the approach allows for the use of turboexpanders. Four examples are presented to show the effectiveness and accuracy of the proposed method.     

A four parameter cubic equation of state with temperature dependent covolume parameter

A four-parameter, Ghoderao–Dalvi–Narayan 2 cubic equation of state(GDN2 CEOS), is presented which incorporates the following: 1. The experimental value of the critical compressibility factor has been used as a fixed input parameter for calculations; 2. All the parameters(a, b, c, d) of CEOS are temperature dependent functions in the subcritical region and are temperature independent functions in the supercritical region and; 3. A new α function is introduced with two compound specific parameters which are estimated by matching saturated vapor pressure at two fixed temperature points T_r= 0.5, 0.7. Our formalism enables us to cast three of the four parameters of the CEOS as a function of the remaining parameter. The proposed CEOS is used to predict properties of 334 pure compounds, including saturated vapor pressure and liquid density, compressed liquid density, heat capacities at the constant pressure and volume, enthalpy of vaporization, sound velocity. To calculate thermodynamic properties of a pure compound, the present CEOS require the critical temperature, the critical pressure, the Pitzer's acentric factor, the critical compressibility factor, and two parameters of the alpha function. The saturated liquid density predictions for pure fluids are very accurate when compared with GDN1(Ghoderao–Dalvi–Narayan 1),MPR(Modified Peng–Robinson), and PT(Patel–Teja) equations of state. Unlike MPR EOS, the proposed temperature dependent covolume parameter b in the present work satisfies all the constraints mentioned in the literature to avoid thermodynamic inconsistencies at the extreme temperature and pressure. Using van der Waals one-fluid mixing rule, the present CEOS is further used to predict bubble pressure and the vapor mole fraction of binary mixtures.     

Vacuum membrane distillation simulation of desalination using polypropylene hydrophobic microporous membrane

Numerical simulation is an effective method to get the optimal operating parameters in the chemical engineering process. In this work, the transport mechanism of vacuum membrane distillation (VMD) process was simulated and predicted by mathematical model, which was established based on the convective heat transfer coefficient, and 0.5M aqueous NaCl solution was concentrated with isotactic polypropylene (iPP) hydrophobic microporous membrane prepared via thermally induced phase separation (TIPS) in the VMD process. The as‐presented mathematical model simulated the effects of different operating parameters on the VMD performances for aqueous NaCl solution, such as feed temperature, feed flow rate, absolute pressure of membrane permeate side, temperature coefficient, membrane thickness, and porosity. A comparison between experimental data and simulated data was also considered to verify the proposed mathematical model. Additionally, the salt rejection of aqueous NaCl solution production water in VMD was higher than 99.9%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41632.     

并联低温多效海水淡化系统优化与分析

建立了并联流程下的低温多效蒸发海水淡化系统优化数学模型。该模型以整个系统的单位产量淡水成本最小为优化目标,以加热蒸汽温度及各效二次蒸汽温度为决策变量,并应用MATLAB及其优化工具箱对其进行了求解,同时与非优化设计情况进行了比较。结果表明:当淡水产量不变,随着效数的增加,淡水成本先减小后增大,最优效数为7效,优化淡水成本为5.51元/t;与非优化设计相比,在达到6效之前,优化设计的加热蒸汽量减小,蒸发器传热面积增大,优化设计的淡水成本小于非优化设计的淡水成本。在6效之后,二者相差不大。     

超临界CO2中异丁醇的相平衡研究

Vapor-liquid phase equilibrium data including composition, densities, molar volume and equilibrium constant of isobutanol in supercritical carbon dioxide from 313.2 K to 353.2 K were measured in a variable-volume visual cell. The properties of critical point were obtained by extrapolation. The results showed that critical temperature, critical pressure and critical compressibility factor of CO2-isobutanol system decreased with the increase of critical CO2 content. The phase equilibrium model was established by Peng-Robinson equation of state and van der Waals-2 mixing regulation, and model parameters were determined by optimization calculation of nonlinear least square method. The correlation between calculated values and the experimental data showed good agreement.     

Start-up pressure transients in a capillary rheometer

The “rise time” required to achieve a steady pressure reading in a capillary rheometer operated at constant piston speed can be very long, up to several hours under certain circumstances. This phenomenon can pose a serious problem in the measurement of melt viscosity, and it would be useful to be able to estimate the rise time in the planning of experiments. Based on experiments involving several types of polyethylene, we found that the rise time increases with L/D and the amount of polymer initially in the reservoir and decreases with diameter and piston speed. When the rise time is short, melt viscoelasticity contributes to the rise time, but when it is long, melt compressibility is the dominant factor. A model was developed for the latter case, and this was found to give an accurate prediction of the rise time, given the viscosity and compressibility. The model can also be used to determine the power-law parameters from the start-up pressure trace, P(t), for a single experiment. Alternatively, if the viscosity is known, the compressibility can be inferred from a single pressure trace.     

内部热耦合精馏塔基于非理想物系的最优评价

Internal thermally coupled distillation column(ITCDIC) is a frontier in energy saving distillation research. In this paper, the optimal assessment on the energy saving and the operating cost for ITCDIC of nonideal mixture is explored. An evaluating method is proposed, and the pertinent optimization model is then derived. The ethanol-water system is studied as an illustrative example. The optimization results show that the maximum energy saving in ITCDIC process is about 35% and the maximum operating cost saving in ITCDIC process is about 30%,as compared with a conventional distillation column(CDIC) under the minimum reflux ratio operating; the optimal operating pressure of the rectifying section is found to be around 0.25 MPa; the effects of the feed composition,operating pressure and the heat transfer rate on operation are also found and analyzed. It is revealed that ITCDIC process possesses high energy saving potential and promising economical prospect.     

Investigations of heat transfer and pressure drop between parallel channels with pseudoplastic and dilatant fluids

Central to the problem of heat exchangers design is the prediction of pressure drop and heat transfer in the noncircular exchanger duct passages such as parallel channels. Numerical solutions for laminar fully developed flow are presented for the pressure drop (friction factor times Reynolds number) and heat transfer (Nusselt numbers) with thermal boundary conditions [constant heat flux (CHF) and constant wall temperature (CWT) ] for a pseudoplastic and dilatant non‐Newtonian fluid flowing between infinite parallel channels. A shear rate parameter could be used for the prediction of the shear rate range for a specified set of operating conditions that has Newtonian behavior at low shear rates, power law behavior at high shear rates, and a transition region in between. Numerical results of the Nusselt number [constant heat flux (CHF) and constant wall temperature (CWT) ] and the product of the friction factor and Reynolds number for the Newtonian region were compared with the literature values showing agreement within 0.36% in the Newtonian region. For pseudoplastic and dilatant non‐Newtonian fluids, the modified power law model is recommended to use because the fluid properties have big discrepancies between the power law model and the actual values in low and medium range of shear rates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3601–3608, 2003     

Effect of transfer in the vapour phase on the extraction by pervaporation through organophilic membranes: experimental analysis on model solutions and theoretical extrapolation

Mass transfer in pervaporation is usually regarded as limited by the solution-diffusion step inside the dense selective polymer layer. In the case of pervaporation for the extraction of volatile organic compounds through organophilic membranes, especially at low feed temperature (about 300 K), the influence of the downstream pressure cannot be neglected. A contribution to the study of the operating parameters on the vapour side in a pilot plant — from the membrane to the condenser — to the overall mass transfer is presented.

A “convection-diffusion” model has been established to calculate the partial pressure gradients in the vapour phase up to the downstream face of the membrane. This equation has been combined with a relation for the mass transfer inside the membrane with a driving force expressed as a difference in fugacities.

The partial permeate pressures and the pervaporate fluxes obtained first with a pure compound (water) and secondly with binary mixtures (water-ethanol) pervaporated through membranes of polydimethylsiloxane (PDMS) on a pilot plant scale are well predicted by the model. Moreover, on the permeate side, the effects of unavoidable non-condensable gases, of the condenser temperature and of the distance between the module and the condenser on the flux and on the selectivity have been established for different total permeate pressures (300–3000 Pa). At high pressure, the pervaporation selectivity towards ethanol exhibits a minimum value as a function of the permeate circuit design.     

天然气流量计量中确定压缩因子的方法

以天然气流量计量为背景,对天然气压缩因子的修正进行了分析,并基于数理统计方法对压缩因子与拟对比温度、压力建立曲面函数模型,用于快速、准确地确定压缩因子,修正天然气流量,提高流量计量的准确度。     

Energetics of gas sorption in glassy polymers

The molar enthalpy for gas sorption in glassy polymers at a fixed concentration, often called the isosteric enthalpy of sorption, exhibits a clearly discernable minimum when plotted as a function of penetrant concentration. This unexpected behaviour has been observed in several glassy polymer systems including poly(ethylene terephthalate), polyacrylonitrile and polycarbonate. The behaviour can be modelled by analysing the temperature dependence of the various equilibrium parameters comprising the so-called dual mode sorption model for gas sorption in glassy polymers. The fundamental significance of the various enthalpies describing the temperature dependence of the Henry's law solubility constant, the Langmuir affinity constant and the Langmuir capacity constant are included in the discussion. Provision is made for non-ideal vapours and gases by introduction of the compressibility factor in the expression for the isosteric enthalpy. Application of relationships for calculating both the isosteric and the isothermal enthalpies of sorption is made to the case of CO₂ in poly(ethylene terephthalate) in the temperature range 35° to 115°C. These results and analyses complement the wealth of equilibrium and transport data which are consistent with the dual mode sorption model for penetrant sorption in glassy polymers.     

Thermoacoustic properties of methyl esters ofn-alkanoic acids

A number of thermoacoustic parameters, including the Sharma constant S₀, the isochoric temperature coefficient of volume expansivity (d Inα/d InT)_V, the isochoric temperature coefficient of internal pressure (d InP _i/d InT)_V, reduced volume V, reduced compressibility β and the Huggins parameter F, are estimated by using only the volume expansivity α from the density temperature data for a number of methyl esters ofn-alkanoic acids. The methyl esters give excellent separation of saturated fatty acid mixtures. The Sharma constant, which relates the molecular constantn and other thermoacoustic parameters, is a constant with a characteristic value of 1.11+0.01 for all these esters.     

A novel mathematical method for prediction of rapid expansion of supercritical solution (RESS) processed ibuprofen powder size distribution

A fundamental understanding of the interplay among the variables involved in a rapid expansion of supercritical solution (RESS) process is necessary in order to achieve control of product within the desired specifications. A model is proposed where the experimental data are fitted to a 2-D Sp-line equation that results in a mathematical pattern matching function that can easily be processed analytically to yield a continuous motion estimate. This model presents a novel promising method to interpolate between any two experimental results. Comparison of the mean particles size values which are calculated as a function of nozzle temperature (T _N ) and pre-expansion pressure (P _{pre-expansion} ) with the experimental data, results in a ±8% accuracy. The optimum operational point that leads to the minimum mean particles diameter (40 nm) is determined through mathematical optimization of this equation and confirmed experimentally. Furthermore, 600 more values of mean particle size are predicted by varying the nozzle temperature and dissolution pressure and the results are presented in the form of a 3-dimesional curve.     

Comparison of processes for the supercritical carbon dioxide extraction of oil from soybean seeds

Three different process alternatives for the production of soybean oil by supercritical carbon dioxide extraction were analyzed. The first two processes were organized according to the classical scheme, based on high-pressure extraction followed by separation induced by pressure reduction. Different techniques were used to recover the solvent in these two schemes, in the liquid and in the gas phases, respectively. The third alternative was based on an isobaric scheme—the oil, extracted at high pressure, was separated by chainging the temperature in the separator. In a further improvement, a technique for the heat transfer network integration was added to all the process schemes. The different schemes were used to establish the process configuration that can produce a lower operating cost for soybean oil extraction. Operating costs were considered on an industrial scale to carry out a screening of the different alternatives. The operating cost of these plants were then compared with the hexane extraction process. A substantial reduction in the specific costs was obtained in the case of heat transfer integration, and the operating costs fell in the same range as conventional extraction plants.     

Advanced oxidation processes for the degradation of p‐hydroxybenzoic acid 1: Photo‐assisted ozonation

The oxidation of p‐hydroxybenzoic acid in aqueous solution by UV radiation and by photo‐assisted ozonation (UV+O₃) has been studied. The effects of temperature (10, 20, 30 and 40 °C), pH (2, 5, 7 and 9) and ozone partial pressure (0.10–0.38 kPa) on the conversion of p‐hydroxybenzoic acid were established. Experimental results indicated that the kinetics for both oxidation processes fit pseudo‐first‐order kinetics well. In the combined process, the overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH·) generated in the system. The importance of these two reaction paths for each specific value of ozone partial pressure, temperature and pH was quantified. Lastly, a general expression is proposed for the reaction rate which takes into account the two reaction pathways and is a function of known operating variables. © 2001 Society of Chemical Industry     

Capital and total cost targets for mass exchange networks: Part 1: Simple capital cost models

This paper presents a method for targeting the capital and total cost of a mass exchange network. This part of the paper considers stagewise systems and uses a simplified capital cost correlation in order to convey the fundamentals. The method starts by determining the number of stages required, using the y−x composite curve plot presented previously, and then converts this to a capital cost. This target is combined with utility targets to give a target for the total annual cost. Simple design guidelines are presented, which allow these targets to be approached to within a few percent. The method is applied to a coke-oven gas sweetening example, which is a case involving two mass separating agents (MSAs) which do not overlap. It is also applied to an example involving phenol removal, in which there are overlapping MSAs. A final example deals with multicomponent transfer by extending the coke-oven gas problem. The paper introduces a new graphical tool, the y−y* composite curve plot, for handling systems with overlapping MSAs. The paper demonstrates that, contrary to previous belief, using the minimum number of units does not necessarily lead to a minimum cost design.     

Minimum end time policies for batchwise radical chain polymerization. Part VI: The initiator addition policies for copolymerization with constant copolymer composition control

For batchwise radical chain solution copolymerization, the minimum end time problem with constant copolymer composition control is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. During copolymerization, the more rapidly depleting monomer is continuously fed to the reactor to maintain the comonomer ratio constant. The volume variation due to contraction during copolymerization, in addition to monomer and solvent feeding, is also considered. It is found that the optimal initiator addition policy is to make the rate of initiation (2fk_dIV) constant. The volume factor V is for taking account of volume variation. For the isothermal case, the number of moles of initiator in the reactor should remain constant. Experimental verification for acrylonitrile and styrene isothermal copolymerization with the proposed stepwise feeding of the more rapidly depleting monomer to simulate the optimal continuous monomer feeding policy shows that the present method is applicable.     

Air Separation through Modified Ethyl Cellulose Thin Film Supported on Porous Polyethersulfone

Abstract

Composite membranes for air separation were prepared from a liquid crystal DYC-modified ethyl cellulose (EC) thin film ranging in thickness from 1 to 7 μm and a porous polyethersulfone support with a thickness of 120 μm. The effects of DYC/EC (9/91) solution concentration, water, and operating parameters such as temperature, pressure, and time on the air-separation properties of the composite membranes were examined by a constant pressure—variable volume method. The permeate flux and oxygen concentration of the oxygen-enriched air (OEA) through the membranes increase significantly with increasing operating pressure difference. With decreasing casting solution concentration, or with increasing humidity around the membranes or operating temperature, the OEA flux increases greatly while the oxygen concentration sometimes decrease slightly. An increase in the operating time leads to an OEA flux decline, but the oxygen concentration rose when the operating time was varied for 70 hours. However, a further increase of the operating time from 70 to 500 hours does not lead to further changes of the OEA flux and oxygen concentrations. A thin-film composite membrane exhibits a slightly lower oxygen concentration accompanied by a very significant enhancement in the OEA flux and membrane stability compared to a homogeneous dense membrane of the same materials.