•We propose a model for direct contact membrane distillation that accounts for fouling.•We design an adaptive observer for descriptor systems.•We use the adaptive observer for the estimation of the ...thermal resistance of the fouling.•Simulations are presented to show the effectiveness of the approach.
This paper develops a lumped parameter model-based method for membrane fouling detection in Direct Contact Membrane Distillation (DCMD) process. First, a previously published mathematical model of DCMD is extended to account for the thermal resistance of the fouling layer. Then, an adaptive nonlinear descriptor observer is developed. The adaptive observer estimates the thermal resistance of the fouling layer in addition to the temporal and spatial temperature distribution of the bulk feed and permeate solutions and at membrane interface layers. Simulation results are presented to illustrate the performance of the proposed method.
Membrane distillation (MD) is an emerging technology that has a great potential for sustainable water desalination. In order to pave the way for successful commercialization of MD-based water ...desalination techniques, adequate and accurate dynamical models of the process are essential. This paper presents the predictive capabilities of a lumped-parameter dynamic model for direct contact membrane distillation (DCMD) and discusses the results under wide range of steady-state and dynamic conditions. Unlike previous studies, the proposed model captures the time response of the spacial temperature distribution along the flow direction. It also directly solves for the local temperatures at the membrane interfaces, which allows to accurately model and calculate local flux values along with other intrinsic variables of great influence on the process, like the temperature polarization coefficient (TPC). The proposed model is based on energy and mass conservation principles and analogy between thermal and electrical systems. Experimental data was collected to validated the steady-state and dynamic responses of the model. The obtained results shows great agreement with the experimental data. The paper discusses the results of several simulations under various conditions to optimize the DCMD process efficiency and analyze its response. This demonstrates some potential applications of the proposed model to carry out scale up and design studies.
•We present a reduced order dynamic predictive model for direct contact membrane distillation process.•Both time varying and steady-state responses are well captured and have been validated with experimental data.•Analysis shows the response of several intrinsic variables under various conditions.
•We propose a novel dynamic model for direct contact membrane distillation process.•The model is a reduced version of a distributed system.•It is based on the analogy between electrical and thermal ...systems.•The model has been validated with experimental data.•The model is written in the form of differential algebraic system.
Membrane distillation (MD) is an emerging water desalination technology that offers several advantages compared to conventional desalination methods. Although progress has been made to model the physics of the process, there are two common limitations of existing models. Firstly, many of the models are based on the steady-state analysis of the process and secondly, some of the models are based on partial differential equations, which when discretized introduce many states which are not accessible in practice. This paper presents the derivation of a novel dynamic model, based on the analogy between electrical and thermal systems, for direct contact membrane distillation (DCMD). An analogous electrical thermal network is constructed and its elements are parameterized such that the response of the network models the DCMD process. The proposed model captures the spatial and temporal responses of the temperature distribution along the flow direction and is able to accurately predict the distilled water flux output. To demonstrate the adequacy of the proposed model, validation with time varying and steady-state experimental data is presented.
In order to understand the chelation process and investigate the intermediate species as a step towards verifying the exact functional groups that are involved in bonding with transition metals, ...specifically Cu(II) and Zn(II), pH-oscillotitrimetric (pHOT) and volumetric-oscillographic (VOG) methods have been profoundly used. Alizarin Red S (ARS) - as one of the chameleon compounds (chromogenic) - confirms its different approach of bonding with copper and zinc in different mediums. These two methods thoroughly confirm the adequate conditions for each metal to chelate with ARS. pH is responsible for the ambience in which the formation energy in its less value for the salt or complex to be formed, confirming that pH = 5 is the value that allows Cu(II) to bond with ARS, whereas Zn(II) bonds at pH = 6. A new approach has been also suggested as to how to discuss the titrimetric curves in both methods, taking into account the importance of ‘volumetric-oscillographs’ that give more information when analysed appropriately. Volumetric-oscillographs have been shown and utilized as fingerprint spectrums to track any change in the solutions and firmly expect the compounds that can be step-by-step formed during titration operation. The resulting-in rules have been suggested during reading the graphs. Moreover, the competition between these two metals to chelate with ARS has been extensively studied.
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The aim of this study was to investigate the use of bovine serum albumin (BSA) as a solubility enhancer for indometacin (IND) as a model drug. IND-BSA solid dispersions were prepared ...by both spray drying and freeze drying techniques using IND:BSA solution (20:1 Molar Ratio (MR)) and IND:BSA suspension (100:1 MR). The solid state of IND in solid dispersions was characterised by SEM, DSC and XRD. The aqueous solubility of IND in the presence of increased amounts of BSA was evaluated. Additionally, IND dissolution and release profiles were evaluated. IND in solid dispersions with BSA showed significantly higher solubility in water than that of the physical mixture of both. Enhancement factors of 24,000 and 100,000 were obtained for the solid dispersion formulated in 20:1 MR and 100:1 MR, respectively. Dissolution studies in-vitro indicated a significant increase in the dissolution rate of IND from solid dispersions compared to that of the free drug, with almost 95% of the drug dissolved in the first 5min. Furthermore, an immediate release of IND from BSA solid dispersions was shown. The potential use of albumin as solubility enhancer for poorly soluble drugs, particularly, for immediate release volume-limited dosage forms is reported.
The study has described through the extrapolation method the roles of those precursors' ions as main substances accompanying the progress of electroplating processes that have been used mainly in the ...deposition of semiconductor thin film and in the fabrication of solar cells. The role of some materials as primary salts have been compared to each other according to their structures, and through the extrapolation method the atomic structures of the metals included in those salts have been reviewed in 3D forms, investigated and compared. The nuances, on the other hand, cannot be denied. However, the study has reached a plausible point of comparison to substantiate the pieces of evidence of these ions’ role in the aqueous solitons. Definitely, the aim is to build up the ultimate steps to finally disclose the essential role of some inorganic or organic compounds in the deposition solution, claiming a step ahead for particular purposes about some elements in the periodic table. Basically, the study cannot rebuke that the available data play an innate part in this study and the next investigating steps in the future. This attempt has somehow illustrated the role of sulfate, nitrate and chloride as accompanying ions in the major salts that have been used to get the desired results in solar cells fabrications. Also, the study has confirmed the basics of mechanisms in which those ions could be compared to each other. For instance, sulfate, nitrate and chloride ions can compare the final results of some metals electrodeposition according to the positions of those metals in the periodic table when fabricating the solar cells. The thickness or the atomic composition of Cu and Zn deposits can be increased at considerably higher voltages starting from IB to IIB columns, whilst for Ga and In deposits, they can be increased starting from the top to the bottom of IIIA column.
Sulfate, Nitrate, Chloride, Electrodeposition, Solar cells.
The reduction of Cu(II) has been investigated in the presence of Alizarin Red S in two different background solutions namely KCl and acetate buffer through this study. The electroactive intermediate ...species have been extensively characterised by using Direct Current Polarography and Deferential Pulse Polarography techniques. It has been observed that Cu
2+
was reduced to elemental copper in a two-step single-electron transfer process. However, the kinetics of charge transfer is dampened in the presence of Alizarin due to the complexation of active copper ions with ionised Alizarin, making the electrodeposition more controlled. In the first technique, the peaks of the 57 mM-Cu
2+
reduction and for the 57 mM-Alizarin reduction have been observed. Using the second technique, the voltammograms exhibit the peaks at pH = 2, 3, where the first peak is for the reduction process of two carbonyl groups in Alizarin, and the second one is for Cu
2+
reduction as one-step two-electron transfer. At pH = 5, the complex formation reveals that copper can be hardly reduced on the cathode, whereas Alizarin has two small peaks for two carbonyl groups after being in the investigated alkali mediums. The clear peak at pH = 11 indicates that copper is no more in the structure of a complex. The stoichiometries of the salt and complex have been also verified where both are (1:1). Coating experiments were carried out at 25 °C, 35 °C and 60 °C to investigate the relations between the current efficiency and pH, current density, molarity concentration and time and obtain the optimal operating conditions for copper electrodeposition on steel and stainless steel.
Coating of silica-supported sulfonic acid catalysts with hydrophobic ionic liquid leads to a significant improvement of catalyst selectivity. Many organic reactions, including Prins cyclization, ...cycloaddition of epoxide to aldehyde, and dehydrative etherification of secondary benzyl alcohols, proceed well in formalin or pure water. In particular, tandem dehydration/Prins cyclization reactions of tertiary and secondary alcohols with formaldehyde were developed for the first time.
Here we report that sulfonated crystal-like benzene-silica is much more robust and active than conventionally used periodic mesoporous silica for catalyzing aqueous organic reactions.
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