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Abstract : Investigation of Membrane-Based Total Heat Exchangers with Different Structures and Materials
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Abstract: Membrane-based total heat exchangers are devices to recover both sensible heat and latent heat from the exhaust air. The performances of exchangers assembled with different structures and membranes vary dramatically. To investigate performances, five modules are fabricated for comparison. A test rig is built to measure the performance of these total heat exchangers. The heat and moisture transfer in the cores are studied simultaneously. These cores can be divided into two categories: with different structures and with different membranes. For the first category, parallel-plates, plate-fins and cross-corrugated structures are used. For the second category, three kinds of membranes, i.e. one-step hand-made CA membrane, hydrophobic-hydrophilic composite membrane and machine-made CA membrane are used. The heat and mass transfer coefficients, sensible cooling and latent effectiveness are obtained through experimental measurements. The experimental results show that the cross-corrugated ducts can enhance heat and mass transfer effectively. And the one-step hand-made CA membrane has the lowest resistance in heat and moisture transfer. Keywords: Total heat exchanger, core structure, membrane materials, energy recovery, comparison.Download Full Article |
Abstract : Applications of Open Channel Membrane Modules to Treat and Reuse Wastewater
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Abstract: Local utilities often face problems of domestic wastewater, local industrial wastes, storm water disposal due to existing strict regulations. For many local industries, the problem of wastewater treatment and discharge into surface reservoirs can’t be solved through the use of conventional biological treatment techniques. Current discharge standards require very strict removal of a number of impurities such as ammonia, nitrates, phosphate, etc. To reach this level of removal, modern modified biological treatment facilities (membrane bioreactors etc.) are used. This article suggests a new technical approach to treat directly domestic wastewater and storm water to completely reuse them for technical needs. The modern concept of rational water resources management requires the development of new efficient techniques that provide wastewater treatment and reuse. As RO membranes simultaneously reject all dissolved impurities such as BOD, TDS, ammonia, phosphates etc., they become very attractive for the direct treatment of wastewater without biological stage. To treat wastewater, specially designed membrane "open channel" modules are used that do not possess "dead areas" that cause fouling or require pretreatment. A solution to RO concentrate disposal problem is presented that consists of reducing of initial wastewater volume by 100 times. Concentrate is withdrawn from membrane unit as sludge moisture. The efficient use of membrane RO techniques is connected with a salt balance in water system. Thus, to provide high ecological efficiency of developed techniques, all components of water supply and wastewater discharge systems should be accounted for. Keywords: Reverse osmosis, open channel membrane module, wastewater reuse, domestic wastewater, storm water, ammonia reduction, oil reduction, car wash effluents.Download Full Article |
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Abstract: It appeared that malic acid solubilized both Al3+ and Cr3+ in aqueous solutions at all pH-values in 0.1 M NaNO3 at 25 oC. The detailed potentiometric measurements indicated that these free tri-valent metal ions released a net of three protons (3H+’s) into the solution. Free malic acid released a net of (2H+’s) into the solution from the two carboxylates. However, in the presence of metal ions malic acid effectively releases a net of three protons (3H+’s) into the solution; two from the two carboxylates and the third from the alcoholic group. The reaction mixture of Al3+:malic acid indicated the formation of a dimeric species. The proposed structure of this dimeric species is in good agreement with what has been shown in the literature. We are presenting a dimeric species that may play an important role in malate transportation across cell membrane. Formation of the Al3+-malic acid complexes cover the span of a total of 400 mV; from +250 mV to -150 mV. The Cr3+-malic acid reaction mixture indicated the formation of a dimeric species as well. Keywords: Aqueous solutions, Dimeric species, Malic acid, Al3+, Cr3+, and Speciation diagrams.Download Full Article |
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Abstract: The main objective of this work is to study the heat stability of refined palm oil produced from membrane-based refining process. Two novel routes of refining process have been proposed in which the first one was to integrate conventional refining process with ultrafiltration (UF) membrane technology while the second route was based on the integration between conventional refining process and UF membrane-solvent extraction process. The results revealed that the two novel refining routes showed improvement on free fatty acid (FFA) stability compared with the conventional technique throughout 5-day studied period. With respect to peroxide value (PV), it is found that only the first proposed route showed very similar increasing trend with the conventional refining process. In addition to this, it is also found that the two refining routes which were operated at 260oC showed slightly better colour stability in comparison to conventionally-produced oil. Keywords: Membrane technology, solvent extraction, crude palm oil, free fatty acid, phospholipids.Download Full Article |
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Abstract: Physical and gas transport properties of the asymmetric hyperbranched polyimide (HBPI) -silica hybrid membranesprepared with a dianhydride, 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and an asymmetric triamine, 2,4,4’-(triaminodiphenyl)ether (TADE), were investigated and compared with those of the symmetric HBPI-silica hybrid membranes prepared with a symmetric triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB). The HBPI-silica hybrid membranes were prepared via sol-gel reaction using hyperbranched polyamic acid of which end groups were modified with silane coupling agents, water and tetramethoxysilane. The thermal mechanical and dynamic mechanical analysis measurements confirmed that the rigidity of asymmetric HBPI was higher than that of symmetric HBPI because of the rigid and asymmetric structure of TADE monomer. In addition, the degree of branching of asymmetric HBPI is lower than that of symmetric HBPI because of the different reactivity of the three amino groups included in TADE. The rigidity and linearity of HBPIs had an effect on the progression of sol-gel reaction, consequently the gas transport properties. The increasing of the gas permeability coefficient of the asymmetric dianhydride(DA)-HBPI-silica hybrid membranes with increasing silica content was smaller than those of symmetric DA- and amine(AM)-HBPI-silica hybrid membranes. In addition, the gas permeability coefficient of the asymmetric AM-HBPI-silica hybrid membranes decreased with increasing silica content. This was due to the fact that the dispersibility of silica in the asymmetric HBPI-silica hybrids, of which polymer chain was more rigid and linear than those of symmetric HBPI-silica hybrid, was not as fine as in the symmetric HBPI-silica hybrids, and that the long and tortuous diffusion path was newly formed by hybridization with silica. Keywords: Hyperbranched Polyimide, Silica hybrid, Gas permeability, Asymmetric, Symmetric.Download Full Article |