Chem Eng Sci Research Articles

On the sensitivity analysis of the DEM oedometer experiment

The discrete element method (DEM) is frequently used to investigate the behaviour of granular media (Bravo in Simulation of soil and tillage-tool interaction by the discrete element method, 2013; Tijskens et al. in J Sound Vib 266:493–514, 2003; Langston et al. in Chem Eng Sci 50:967–987, 1995; Kohring et al. in Comput Methods Appl Mech Eng 124:273–281, 1995; Stahl et al. in Granul Matter 13:417–428, 2011). The parameter calibration is a challenging task due to the large number of input parameters and the computational effort. Sometimes, this is performed with a trial-and-error approach as mentioned in Roessler et al. (Powder Technol 343:803–812, 2019), Rackl and Hanley (Powder Technol 307:73–83, 2017) based on laboratory tests, e.g. the pile experiment, the oedometer experiment and the shear test. To achieve a more suitable calibration, a better model understanding is necessary in which the influence of the DEM parameters is analysed. Consequently, the calibration can be focused on specific parameters, which have a significant influence on thef model response. If parameters with a negligibly small influence exist, the number of calibration parameters can be reduced. On this basis, it is possible to decide whether the laboratory test is suitable for the calibration of specific parameters or not. This is demonstrated with a sensitivity analysis based on Sobol’ indices for the oedometer laboratory test. In order to reduce the computational effort, the sensitivity analysis is performed with different metamodels of the oedometer simulation. The metamodels are fitted and validated with two separate sampling point sets. It is shown that the Young’s modulus for the investigated input space is the most significant parameter. This knowledge can be used to only focus the calibration on this significant parameter which enables an easier calibration and makes clear that for calibrating of other parameters this laboratory test is inappropriate. An algorithm of a force-driven plate is developed and shown which prevents non-physical states in which the interaction force between the particles and the loadplate exceeds the applied force.

A Framework for Incorporating Transient Solute-Keratin Binding Into Dermal Absorption Models

Interpretation of experiments involving transient solute binding to isolated keratin substrates is analyzed and discussed in terms of their impact on transient permeation of topically-applied compounds through human stratum corneum. The analysis builds upon an earlier model (Nitsche and Frasch 2011 Chem Eng Sci 66:2019-41) by adding a second level of homogenization (ultrascopic-to-microscopic) prior to the microscopic-to-macroscopic conversion. Here “ultrascopic” refers to isolated keratin suspensions, “microscopic” to corneocyte interiors and “macroscopic” to tissue-averaged properties in the stratum corneum. Results are interpreted in the context of current parameterizations of the underlying ultrascopic binding parameters. The present analysis, which is limited to linear binding isotherms common in dilute solutions, reveals a maximum in the macroscopic forward binding rate constant as a function of solute lipophilicity, whereas the underlying equilibrium constant increases monotonically and the macroscopic reverse binding rate constant decreases monotonically. The size and location of the maximum depends upon the hydration state of the stratum corneum. Explicit equations expressing these findings allow both equilibrium and kinetic binding data in isolated keratins to be applied to the kinetics of transient absorption through the skin. They will enable more quantitative estimation of the long-recognized stratum corneum reservoir function.

Homogeneous and re-circulatory gas\u2013liquid flow in a bubble column: A numerical investigation using OpenFOAM

This work presents the influence of the sparger opening area, gas velocity, and bubble size on hydrodynamics and transition of the flow regime from uniform to re-circulatory in a rectangular bubble column using OpenFOAM. In the course of development of the model, the effect of several drag closures and lift on the predictability of the CFD model was studied by comparing the predictions with published experimental results. Reynolds number-based drag closure was found to be suitable for uniform sparger whereas Tsuchiya drag (Tsuchiya et al. in Chem Eng Sci 52:3053–3066, 1997. https://doi.org/10.1016/S0009-2509(97)00127-9) was used to simulate gas–liquid flow for other spargers. Simulations were performed for seven different spargers with opening area 18–100% (superficial gas velocity of 2.9–5.8 cm/s) and bubble size of 2–8 mm. The smaller opening area and higher gas velocity promote the re-circulatory flow in the bubble column. Change in bubble size affects the hydrodynamics due to change in lift and drag forces.

Experimental study on drop breakup time and breakup rate with drop swarms in a stirred tank

AbstractThe direct experimental data for breakup parameters of drop breakup time, multiple breakage, and breakup rate are urgently required to understand drop breakup phenomena. In this regard, drop breakup experiments were carried out in a stirred tank using a high‐speed online camera. The influences of the rotating speed, interfacial tension, and drop viscosity on the above breakup parameters were then quantitatively investigated. An mechanism correlation for the breakup time is proposed and is further verified by comparing with the results of Solsvik and Jakobsen (Chem Eng Sci, 2015;131:219‐234). The percentage of multiple breakage comparing to binary breakup was statistically counted. The results indicated that the dimensionless drop diameter η = d/dmax can be adopted to characterize the proportion of binary breakup. Finally, the breakup rate was experimentally measured and the breakup probability was calculated using the inverse method.

Modelling and Experimental Characterization of Unsaturated Flow in Absorbent and Swelling Porous Media: Material Characterization

A comprehensive experimental protocol is presented for the characterization of physico-chemical and morphological properties of absorbent hygiene products (AHPs), composite materials, mainly made of super absorbent polymer (SAP) granules blended with cellulose fibres (fluff). The protocol is based on a combination of experimental methods for the characterization of the material properties varying SAP/fluff ratio (SFR): absorption rate, porosity, hydraulic conductivity, retention model and swelling. Major findings were that: (1) liquid absorption rate by the SAP particles was nonlinear; (2) the hydraulic conductivity could be expressed as a function of the porosity of the composite medium for any sample and liquid uptake; and (3) the retention model showed moderate variability with SFR, in the range investigated. Experimental results have been used to determine the constitutive equations for the multiphase flow model developed in the literature (Diersch et al. in Theory Transp Porous Media 83:437–464, 2010. https://doi.org/10.1007/s11242-009-9454-6 ) for the prediction of the performance of AHPs during cycles of imbibition and drainage (Chem Eng Sci 224:115765, 2020. https://doi.org/10.1016/j.ces.2020.115765 ).

Heat transfer to supercritical hydrocarbon fuel in horizontal tube: Effects of near-wall pyrolysis at high heat flux

Understanding heat transfer to endothermic hydrocarbon fuels (EHFs) with pyrolysis at high heat flux is a challenging issue for the design of regenerative cooling panels in the fuel-cooled thermal management technology of advanced aircrafts. In this work, the convective heat transfer of supercritical EHFs in presence of pyrolysis reactions was experimentally investigated in horizontal tubes at the heat flux up to 1.836 MW/m2 under 3.5 MPa. A CFD model with an improved kinetics (Chem Eng Sci 2019, 207, 202-214) has been developed and extensively validated to get detailed information on the coupling mechanism of heat transfer and pyrolysis. The heat transfer rate can be enhanced by pyrolysis reactions at relative low heat flux (below 400 kW/m2). With increasing heat flux, the rapid and high-degreed pyrolysis near-wall considerably changes the local composition and thus the thermophysical properties, resulting in the significant heat absorption differences in the cross section and local heat transfer deterioration. Typically, Nub decreases from 108.8 to 73.4 (about 30%) when the heat flux increases from 426 to 758 kW/m2. The possible reasons may be attributed to the weakened near-wall turbulence by the increased fluid viscosity in presence of secondary products, as well as the increased thermal boundary layer effect attributed to the high near-wall heat absorption and huge radial property gradient at high heat flux.

DEM–LBM numerical modeling of submerged cohesive granular discharges

Empirical predictions of discharge rates for dry non-cohesive grains are commonly based on the Beverloo law (Chem Eng Sci 15:260–269, 1961). The present work extends this practical configuration to submerged and cohesive cases to investigate the flow behavior of granular media with applications in the geophysical process of sinkhole formation. The analysis of the hydrostatic collapse of soil in the presence of underground conduits is performed with a 2D GPU-parallelized simulation coupling the lattice Boltzmann method and the discrete element method to describe the fluid and the solid phases, respectively. The discharge rate of a large submerged granular sample is analyzed by varying orifice sizes and inter-particle cohesion strengths. For the submerged cohesionless case, we first study the revisited Beverloo relationship that includes the terminal velocity of a single falling particle in the fluid, proposed in the experimental work of Wilson et al. (Pap Phys 1307: 2812, 2014). We consistently take into account the interstitial fluid with an effective orifice size smaller than in the dry case. Then, the additional contribution of grain cohesion is examined. Our main finding is that the empirical prediction remains valid provided that the orifice cutoff increases with cohesion. Finally, the evolution of fluid pressure during the discharge, at the vicinity of the orifice, is studied and favorably compared with the recent experimental study of Guo et al. (Granul Matter 19(3): 1–8, 2017). By considering the pressure drop around the orifice as a driven-term, we succeed in predicting the solid flow rate with a similar Beverloo approach.

Determination of dynamic interfacial tension in a pulsed column under mass transfer condition

AbstractInterfacial tension is an essential physical property in two‐phase flow, and it changes due to the mass transfer. The measurement of dynamic interfacial tension (DIFT) in such a condition is a difficult problem. In the previous study (Zhou et al., Chem Eng Sci. 2019; 197:172–183), we presented the quantitative relation between the droplet breakup frequency function (DBFF) and interfacial tension. It is found that the DBFF is highly depended on interfacial tension. Therefore, the DBFF is a suitable parameter to quantitatively characterize the interfacial tension. Based on this concept, the DIFT in the column is determined by regression method after the DBFF under mass transfer condition is measured. It is found that the DIFT is smaller than the static interfacial tension. This result indicates that interphase mass transfer leads to decreasing of the interfacial tension. The decreasing extent of the DIFT has a positive correlation with the mass transfer flux.

CFD Research on the Influence of 45° Disk Turbine Agitator Blade Diameter on the Solid–Liquid Mixing Characteristics of the Cone-Bottom Stirred Tank

A numerical simulation of a solid–liquid mixture concentration field in a cone-bottom stirred tank (diameter D = 150 mm) was conducted using computational fluid dynamics (CFD). The influence of the 45° disk turbine impeller diameter on the mixing time number of solid–liquid mixture, mixing energy per unit volume, concentration standard deviation, turbulence energy and turbulent dissipation rate as well as solid just-suspended impeller speed was analyzed. The Eulerian two-fluid model was employed along with the standard k–e turbulence model to simulate the turbulent solid–liquid flow in the cone-bottom stirred tank. A multiple reference frame approach was used to simulate the impeller rotation in a fully baffled reactor. The Fluent® 14.5 commercial CFD software was employed for the transient simulation. The radial and tangential velocities at the outer edge of the impeller along the blade width were compared with the experimental data of Wu and Patterson (Chem Eng Sci 44:2207–2221, 1989), Mahouast et al. (Entropy 133:7–17, 1987) and Kemoun et al. (IChemE Symp Ser 136:399–406, 1994). The further extended computational model could well predict the influence of impeller diameter on the solid–liquid mixing characteristics.

DEM simulation of the packing of cylindrical particles

Discrete element method is used to study the effect of particle aspect ratio on the packing structure of cylinders in this work. Two contact scenarios are complemented to detect particle contacts, following the work of Kodam et al. (Chem Eng Sci 65:5852–5862, 2010) and Guo et al. (Powder Technol 228:193–198, 2012). The results show that the packing density-aspect ratio curve has two small peaks at aspect ratio of 0.625 and 1.25, and a small cusp at aspect ratio of 1.0. Excluded volume is used to explain the variation of packing density with aspect ratio for cylinders, spherocylinders and ellipsoids. The lowest ensemble-averaged coordination number is found at aspect ratio of around 0.75. For platy cylinders, the dominant contact scenario is the face–edge contacts, followed by band–edge contacts. For elongated cylinders, the major contact scenarios are band–edge and band–band contacts. The existence of the planar faces of a platy cylinder makes the radial distribution functions of disks quite different from that of smooth-curved oblates. Most platy cylinders have their principal axis of pointing to and almost paralleling to the vertical direction, while the principal axis of elongated cylinders tends to point to the horizontal plane. The platy particles tend to form stacks composed of 2–4 particles for different aspect ratios. The force gradient increases and force magnitude becomes less uniform when L/D deviates from 1.0.

An improved subgrid scale model for front‐tracking based simulations of mass transfer from bubbles

AbstractGas–liquid bubble column reactors are often used in industry because of their favorable mass transfer characteristics. The bubble mass boundary layer in these systems is generally one order of magnitude thinner than the momentum boundary. To resolve it in simulations, a subgrid scale model will account for the sharp concentration variation in the vicinity of the interface. In this work, the subgrid scale model of Aboulhasanzadeh et al., Chem Eng Sci, 2012, 75:456–467 embedded in our in‐house front tracking framework, has been improved to prevent numerical mass transfer due to remeshing operations. Furthermore, two different approximations of the mass distribution in the boundary layer have been tested. The local and global predicted Sherwood number has been verified for mass transfer from bubbles in the creeping and potential flow regimes. In addition, the correct Sherwood number has been predicted for free rising bubbles at several Eötvös and Morton numbers with industrial relevant Schmidt numbers (103–105).

Dynamics of obstructed droplet breakup in microfluidic T-junction based on diffuse interface method

Gas-liquid two phases flow is common in microfluidics but still needs more study. Precise but efficient controlling the droplets volumes is important for subsequent reaction or processing. In this paper, the diffuse interface method and boundary condition equations are introduced at the beginning. Then, to validate the present phase-field model, three kinds of simulation results are shown and fitted well with the experiments. It indicates that this method can be used to simulate the droplet deformation process in the T-junction. Afterwards, the details about the three kinds of droplet behaviors are presented and due to the instability of droplet breakup with tunnels, we mainly focus on the droplet with t obstruction for the steady breakup process. By analyzing the sensitivity about capillary number and static contact angle, we find that they both have great influence on the breakup process. The fitted curve under a 45 degree contact angle agree well with the experiment of Fu et al. Chem Eng Sci 66(18) 4184-4195, [9] which verifies the accuracy of simulation again. Next, we fit the relation between scaled critical droplet length and the Ca number and the static contact angle. At last, the critical neck width observed in the experiment is discussed based on the minimum surface energy principle as supplementary to improve this two-dimensional formula.

Analysis Through an Analytical Solution of the Mathematical Model for Solid Catalyzed Reactive HiGee Stripping

In this study, we investigated the effects of nonlinear behavior of the dimensionless concentrations of ester, ether, acid, alcohol and water in HiGee stripping under the three phases of reaction viz. catalyzed phase, liquid phase and gas phase. The mathematical model has been developed based on the nonlinear reaction diffusion equations (Rangaiah et al. Chem Eng Sci 80:242–252, 2012). The developed second order governing differential equations represents catalyzed phase is solved analytically and numerically using modified Adomain decomposition method and Finite element method using MATLAB program respectively. We have observed the good accuracy of the present results by comparing with the numerical solution and with published work (Rangaiah et al. Chem Eng Sci 80:242–252, 2012) in literature. Also, we have derived the analytical solutions for liquid and gas phases using Homotopy perturbation method. In addition, we have presented the analytical expression for effectiveness factor for all the concentration under the diffusion restrictions. The analytical expressions derived. There are good enough to predict the behavior of the system. The influence of dimensionless governing parameters is discussed and presented in graphically.

Enhanced cancer cell invasion caused by fibroblasts when fluid flow is present.

It has been demonstrated that interstitial fluid (IF) flow can play a crucial role in tumor cell progression. Swartz and collaborators (Cancer Cell 11: 526-538, Shields et al. 2007) demonstrated that cells that secrete the lymphoid homing chemokines CCL21/CCL19 and express their receptor CCR7 could use flow to bias the secreted chemokine, causing pericellular gradients that stimulate cells to migrate in the direction of the flow. In a further work by Shieh et al. (Cancer Res 71: 790-800, 2011), a synergetic enhancement of tumor cell invasion caused by interaction between tumor cells and fibroblasts in the presence of fluid flow was reported. In the present work, we extend a previous proposed cell-fluid mathematical model for autologous chemotaxis (Chem Eng Sci 191: 268-287, Waldeland and Evje 2018) to also include fibroblasts. This results in a cell-fibroblast-fluid model. Motivated by the experimental findings by Shieh et al, the momentum balance equation for the fibroblasts involves (1) a stress term that accounts for chemotaxis in the direction of positive gradients in secreted growth factor TGF-[Formula: see text]; (2) a fibroblast-ECM interaction term; (3) a cancer cell-fibroblast interaction term. Imposing reasonable simplifying assumptions, we derive an explicit expression for the cancer cell velocity [Formula: see text] that reveals a balance between a fluid-generated stress term, a chemotactic-driven migration term (autologous chemotaxis), and a new term that accounts for the possible mechanical interaction between fibroblasts and cancer cells. Similarly, the model provides an expression for the fibroblast velocity [Formula: see text] as well as the IF velocity [Formula: see text]. The three-phase model is then used for comparison of the simulated output with experimental results to elucidate some of the possible mechanism(s) behind the reported fibroblast-enhanced tumor cell invasion.

From dynamic response surface models to the identification of the reaction stoichiometry in a complex pharmaceutical case study

The dynamic response surface methodology (DRSM) (Klebanov and Georgakis, Ind Eng Chem Res. 2016;55(14):4022–4034) was proposed as a generalization of the classical response surface methodology (RSM). The power of DRSM is evaluated here in a blind test against a complex pharmaceutical process containing 10 observed species involved in eight reactions. The obtained DRSM models, one for each species, accurately represented the time‐varying concentrations of 8 of the 10 species. The DRSMs for two intermediate species suffered a bit from oscillatory behavior toward the end of the batch, due to their small concentration values and the polynomial‐based model. These DRSM models greatly facilitated the application of target factor analysis (Bonvin and Rippin, Chem Eng Sci. 1990; 45(12): 3417–3426) correctly identifying six of the eight true reaction stoichiometries, whereas all six false reactions were rejected. In addition, the ability to distinguish true and false reaction stoichiometries was not affected by a less informative design of experiments (DoEs) than the original center composite design (CCD). © 2018 American Institute of Chemical Engineers AIChE J, 65: 1173–1185, 2019

Solvation of Perfluorsulfonate Ion Exchange Membrane in Non-Aqueous Solvents

As a typical single ion conductor, the perfluorsulfonate (PFSA) ion exchange membrane performance predominantly relies on the interactions amongst cation, sulfonate group and solvent. Such solvation information is crucial to the performance of electrochemical devices. The well-studied interaction between water and proton exchange membranes paved the way for the development of fuel cells and redox flow batteries (1–3). The emerging non-aqueous redox flow battery (NARFB) features alkyl or organic cations. Given the overall inferior performance of NARFBs to aqueous systems, it is important to try to find paths to improve the conductance of the membrane. Despite this and its importance in determining conductivity, the understanding of PFSA cation solvation in non-aqueous solvent is limited so far. We previously reported the surprisingly high ionic conductivity of bulky tetraalkylammonium cations in organic solvents compared to conventional alkyl cations(4). To further investigate the fundamental aspects of cation solvation, we applied different characterization techniques to build connections between ionic conductivity and cation-solvent interaction. Ion mobility data will be discussed in light of solvent uptake. As an example, Figure. 1 shows the relationship between the degree of solvation and relative quantity of deuterated acetonitrile solvating tetrabutylammonium (TBA) form 825EW 3M PFSA. The degree of solvation was derived from solvation signal picked up from carbon-13 NMR on cyanide carbon of deuterated acetonitrile. The degree of solvation increased accordingly with the amount of solvent until it reaches saturation when excess solvent molecules would not participate in the solvation. The respective diffusion coefficients from NMR pulsed gradient diffusion experiments on cations were also presented. A clear signal corresponding to solvent molecules involved in solvation is captured by FTIR and this will also be analyzed as a function of composition and ion type. Acknowledgement We gratefully acknowledge the support of this work by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability (Dr. Imre Gyuk). We also thank 3M for providing membranes. References Vishnyakov A, Neimark AV. Molecular Simulation Study of Nafion Membrane Solvation in Water and Methanol. J Phys Chem B. 2000;104(18):4471–8.Bontha JR, Pintauro PN. Water orientation and ion solvation effects during multicomponent salt partitioning in a Nafion cation exchange membrane. Chem Eng Sci. 1994;49(23):3835–51.Zawodzinski TA, Derouin C, Radzinski S, Sherman RJ, Smith VT, Springer TE, et al. Water Uptake by and Transport Through Nafion® 117 Membranes. J Electrochem Soc. 1993;140(4):1041–7.Lou K, Peng J, Tang Z, Fujimoto C, Zawodzinski TA. Investigation of Ionic Conductivity, Uptake and Cation Diffusion of Perfluorsulfonate and Sulfonated Block Copolymer Ion Exchange Membrane in Non-Aqueous Solvents. Meet Abstr. 2017;MA2017-01(2):166–166. Figure 1. Degree of solvated CN vs relative acetonitrile quantity of TBA+ form 825EW 3M membrane in deuterated Acetonitrile. Figure 1

Fluid dynamic characterization of a fluidized‐bed perfusion bioreactor with CFD–DEM simulation

AbstractBACKGROUNDIn the recent development of regenerative medicine, the low yields of progenitor cells have limited the large‐scale clinical applications. To overcome the limitation, a novel fluidized bed bioreactor has emerged. However, a detailed understanding of its fluid dynamics is still lacking.RESULTSA 3D modeling approach that couples computational fluid dynamics (CFD) and a discrete element method (DEM) was used to simulate the liquid and solid flows in a bioreactor being designed for stem cells expansion. The model was validated by comparing the simulation results with literature experimental data [Chem Eng Sci 60:1889–1900 (2005)], which showed a good agreement. Using the validated model, the effects of the superficial liquid velocity, particle size and particle density on the solids volume fraction, shear stress on the particles and liquid–solid mass transfer coefficient of dissolved oxygen and glucose were analyzed.CONCLUSIONSSimulation results show that particle size and density have an important impact on the shear stress distribution, and that the liquid velocity affects the shear stress distribution rather modestly when its value is beyond the minimum fluidization velocity. The liquid–particle mass transfer coefficient of dissolved oxygen and glucose can be improved by raising the liquid velocity, and the adoption of a high‐density material allows the reactor to operate with higher liquid velocities before reaching shear stress heterogeneities. Furthermore, the two objectives, (i) maintaining lower and homogeneously distributed shear stress and (ii) improving mass transfer, pose conflicting requirements on certain design parameters which need to be carefully considered in the reactor design. © 2018 Society of Chemical Industry

Visualisation of gas-liquid mass transfer around a rising bubble in a quiescent liquid using an oxygen sensitive dye

An approach for visualizing and measuring the mass transfer around a single bubble rising in a quiescent liquid is reported. A colorimetric technique, developed by (Dietrich et al. Chem Eng Sci 100:172–182, 2013) using an oxygen sensitive redox dye was implemented. It was based on the reduction of the colorimetric indicator in presence of oxygen, this reduction being catalysed by sodium hydroxide and glucose. In this study, resazurin was selected because it offered various reduced forms with colours ranging from transparent (without oxygen) to pink (in presence of oxygen). These advantages made it possible to visualize the spatio-temporal oxygen mass transfer around rising bubbles. Images were recorded by a CCD camera and, after post-processing, the shape, size, and velocity of the bubbles were measured and the colours around the bubbles mapped. A calibration, linking the level of colour with the dissolved oxygen concentration, enabled colour maps to be converted into oxygen concentration fields. A rheoscopic fluid was used to visualize the wake of the bubbles. A calculation method was also developed to determine the transferred oxygen fluxes around bubbles of two sizes (d = 0.82 mm and d = 2.12 mm) and the associated liquid-side mass transfer coefficients. The results compared satisfactorily with classical global measurements made by oxygen micro-sensors or from the classical models. This study thus constitutes a striking example of how this new colorimetric method could become a remarkable tool for exploring gas-liquid mass transfer in fluids.

Cost-effective downstream processing of recombinantly produced pexiganan peptide and its antimicrobial activity

Antimicrobial peptides (AMPs) have significant potential as alternatives to classical antibiotics. However, AMPs are currently prepared using processes which are often laborious, expensive and of low-yield, thus hindering their research and application. Large-scale methods for production of AMPs using a cost-effective approach is urgently required. In this study, we report a scalable, chromatography-free downstream processing method for producing an antimicrobial peptide, pexiganan, using recombinant Escherichia coli (E. coli). The four helix bundle structure of the unique carrier protein DAMP4 was used to facilitate a simple and cheap purification process based on a selective thermochemical precipitation. Highly pure fusion protein DAMP4var-pexiganan was obtained at high yield (around 24 mg per 800 mL cell culture with a final cultivation OD600 ~ 2). The purification yield of DAMP4var-pexiganan protein is increased twofold with a 72.9% of the protein recovery in this study as compared to the previous purification processes (Dwyer in Chem Eng Sci 105:12–21, 2014). The antimicrobial peptide pexiganan was released and activated from the fusion protein by a simple acid-cleavage. Isoelectric precipitation was then applied to separate the pexiganan peptide from the DAMP4var protein carrier. The final yield of pure bio-produced pexiganan was 1.6 mg from 800 mL of bacterial cell culture (final cultivation OD600 ~ 2). The minimum bactericidal concentration (MBC) test demonstrated that the bio-produced pexiganan has the same antimicrobial activity as chemically synthesized counterpart. This novel downstream process provides a new strategy for simple and probable economic production of antimicrobial peptides.

Heat transfer intensification for retrofitting heat exchanger networks with considering exchanger detailed performances

The challenging of this work is to present a thorough study of implementing heat transfer intensification in heat exchanger network (HEN) retrofitting, including all details of exchanger geometry, stream bypassing and splitting, temperature‐variation of properties, LMTD and its correction, and pressure drops. This leads to very complex mixed integer nonlinear programming (MINLP) problems rarely reported before. By adopting the MILP‐based iterative approach proposed in the earlier work (Pan et al., Chem Eng Sci. 2013;104:498–524.), temperature‐variation of properties, LMTD and its correction are initialized to parameters at first, and the rest nonlinear terms are then linearized and expressed as first‐order Taylor series expansions. Finally, two iteration loops are executed to find optimal solutions. A small‐scale motivating problem and an industrial scale problem are presented to demonstrate the validity and efficiency of the proposed methods. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2052–2077, 2018