1,721,290 research outputs found
Salinity Gradient Heat Engines
No full textSalinity Gradient Heat Engines classifies all the existing SGHEs and presents an in-depth analysis of their fundamentals, applications and perspectives. The main SGHEs analyzed in this publication are Osmotic, the Reverse Electrodialysis, and the Accumulator Mixing Heat Engines. The production and regeneration unit of both cycles are described and analyzed alongside the related economic and environmental aspects. This approach provides the reader with very thorough knowledge on how these technologies can be developed and implemented as a low-impact power generation technique, wherever low-temperature waste-heat is available. This book will also be a very beneficial resource for academic researchers and graduate students across various disciplines, including energy engineering, chemical engineering, chemistry, physics, electrical and mechanical engineering
Simulation of a regeneration plant for spent pickling solutions via spray roasting
Full text linkNowadays, pyrohydrolysis techniques are widely applied for regeneration of spent pickling liquors providing an excellent environmental and economical strategy to the problem of waste disposal/recovery, also thanks to the high acid recovery efficiencies (>99%) achieved1. In fact, in these processes, iron chlorides are converted into iron oxides and hydrogen chloride at high temperature in spray roasting or fluidized bed reactors2. Though the state-of-the-art technologies have been successfully applied only to large scale plants, the development of small scale units, able to perform a delocalized regeneration of spent solutions where these latter are actually produced, would be strongly needed in order to minimize the transportation of hazardous spent pickling and fresh HCl solutions to/from pickling factories from/to large centralized regeneration plants. In the present work, a steady state simulation model for regeneration of spent pickling liquor via spray roasting has been developed, aiming at the analysis of performance of a small-scale unit. The simulation and optimization of the process has been carried out using ASPEN Plus simulator. A simplified model of the spray roaster, based on data collected from studies reported in the literature3, has been implemented and exported from ASPEN Custom Modeler. Solid recovery from roaster off-gases has been obtained by a cyclone and a Venturi scrubber, where the spent pickling liquor is concentrated prior to be sprayed into the reactor. Hydrogen chloride is absorbed in an adiabatic absorber, where a sub-azeotropic (18-20 wt%) hydrochloric solution is obtained. Prior to the stack, a scrubber is required to wash off the exhaust gases. Several parametric studies have been performed. Different designs of solid separators have been compared in order to investigate the particulate separation efficiency of the process, while absorption column’s packing types and rinse water flowrates have been varied in order to investigate their effects on HCl recovery and acid gas emissions
Influence of thermal buoyancy on heat transfer in spacer-filled channels for Membrane Distillation
Full text linkNumerical results are discussed for the flow in a horizontal plane channel filled with a novel sphere-rod spacer and exchanging heat from both the top and the bottom sides. Direct Numerical Simulations (DNS) are compared with RANS ones based on different turbulence models in the Reynolds number range 100~2000. Preliminary comparisons for non-buoyant flow show that models using wall functions perform poorly, grossly overpredicting Nusselt numbers, while ω-based models resolving the viscous-conductive sublayer all yield satisfactory results. In the presence of buoyancy, simulations using either DNS or the k-ω model yield a thermal asymmetry between top and bottom wall, confirmed by experiments and related to the stable or unstable thermal stratification occurring in the lower and upper layers of the channel. The asymmetry, large at low Re, becomes negligible for Re≥1000. The Spalart-Allmaras model yields satisfactory results in the absence of buoyancy but grossly overpredicts Nu in buoyant flows
Reverse electrodialysis – Multi effect distillation heat engine fed by lithium chloride solutions
Full text linkSalinity Gradient Heat Engines (SG-HEs) have been proposed as a promising technology for converting low-temperature heat into electricity. The SG-HE includes two different processes: (i) a salinity gradient process where the salinity gradient between two solutions is converted into electricity and (ii) a thermal regeneration process where low-grade heat (T<100°C) is used to re-establish the original salinity gradient of the two streams. Among the proposed working solutions, aqueous solution of lithium chloride has been identified as one of the most promising thanks to its remarkable solubility and activity. In this work, a process model to study the performance of a SG-HE constituted by a Reverse ElectroDialysis (RED) unit coupled with a Multi Effect Distillation (MED) unit fed with lithium chloride solution is presented. The influence of the concentration of the inlet solution in the RED unit and the temperature difference in the evaporators of the MED unit on the performance were evaluated by considering ideal membranes. Furthermore, the impact of membrane permselectivity and resistance on the system performance was evaluated. Results showed promising system efficiencies, making this technology attractive for conversion of low-grade heat (<100°C) into electricity, but membrane properties should be enhanced
Effects of shell-side non-ideal flow in hollow fibre membrane contactors operating in cross-flow
No full textHollow fibre membrane contactors are very common today in many areas of separation process technology. The main applications include, but are not limited, to membrane distillation, reverse osmosis, ultrafiltration, gas separation, blood oxygenation and haemodialysis. In some applications (e.g., membrane distillation, haemodialysis) two fluids occupy two separate compartments, the lumen- and the shell-side, whereas in others (e.g., reverse osmosis, ultrafiltration) it is the portion of the feed crossing the membrane that passes from one compartment to another. The cylindrical shell housing includes bundles of several thousand hollow fibres, made of semipermeable membranes allowing for the selective passage of some species from a fluid to another. A common issue of these systems is the management of non-ideal effects on the shell-side fluid dynamics. The main relevant phenomenon, known in the literature as channelling, causes the fluid to flow mainly along preferential passages while some regions of the contactor are essentially stagnant. It is typical of axial, cross- and mixed flow across non-uniform bundle distributions, as already observed, among others, by Bao and Lipscomb [1-2]. Recently, several authors have dealt with it. Sun et al. [3] studied the effects on the module’s performance of the radial non-uniformity of the porosity between the core and peripheral regions of the bundle. Also Cancilla et al. [4] investigated the effects of a non-uniform porosity on shell-side axial flow by means of CFD. The computational domain was a chequerboard arrangement of alternately high and low porosity regions, between which the fluid was free to move. The authors showed that non-uniformity causes a significant increase of the Darcy permeability and an even larger drop of the mass transfer coefficient. In the present work, numerical simulations around non-uniform fibre bundle distributions under creeping cross flow conditions were performed to assess the influence of non-ideal shell-side flow. Both random and chequerboard configurations were investigated. Fig. 1 reports the dimensionless mean normal permeability knorm as a function of the mean porosity ε for random 20-fibre configurations (for example, the random fibre arrangement for ε=0.5 is shown in Fig. 2(a)). For comparison purposes, results by Sangani and Mo [5] for 64-fibre random configurations, and by Cancilla et al. [6] for regular square and hexagonal arrays are also reported. At ε=0.5-0.6, the present results are above those in [5] and lie below the values of for both regular arrays. At ε=0.8-0.9, Sangani and Mo predicted values larger than those for regular arrays (~1.35 times larger for ε=0.9), while the present results practically coincide with those for regular arrays (i.e., for isolated fibres), which, in their turn, tend to become independent of the type of lattice (i.e., square vs. hexagonal). Fig. 2 shows false colour maps of the velocity module and superimposed vector plots for ε=0.5 and 0.9 and a flow attack angle of 0°. For ε=0.5, the flow field exhibits a strong interaction between any particular fibre and the neighbouring ones. On the contrary, for ε=0.9, as better shown in the inset of Fig. 2(b), the flow field around any given fibre is almost unaffected by the presence of the adjacent fibres
Design of a novel membrane-integrated waste acid recovery process from pickling solution
Full text linkHydrochloric acid pickling is a common practice in steel manufacturing industry. During the process, acid
is consumed to dissolve surface oxides and metals ions are accumulated in the solution, which becomes
less effective with time. In addition, the costly and risky waste acid disposal is another issue affecting the
hot-dip galvanizing industry.
In this work, a novel sustainable waste acid recovery process from pickling solutions based on circular
approach is proposed to tackle these issues. The innovative system allows (i) the continuous regeneration
of pickling solutions to enhance process rate and performance and (ii) minimise the highly expensive and
environmentally risky wastewater disposal. In this way, refilling pickling baths with fresh acid, as done in
conventional operation, can be avoided and can be carried out continuously under optimal working
conditions. Moreover, the recovery of valuable substances (e.g. metal hydroxide or salts solution) can be
obtained as an additional benefit. Continuous treatment and regeneration of pickling solution can be
accomplished by coupling diffusion dialysis (DD) and membrane distillation (MD) technologies with a
reactive precipitation unit where iron ions can be separated from the zinc-rich solution, in order to
recover valuable products.
To this purpose, a steady state process simulator was developed to predict the operation of the proposed
integrated process
Histological analysis of implants removed from the oral cavity, a case series
No full textOBJECTIVES Dental implants are widely used to rehabilitate maxilla of partial or to-tal edentulous patients, however, despite the increase in the implant survival rate, both early and late failures still occur. The early failure of an implant de-rives from not being able to obtain a sufficient and adequate osseointe-gration; in this case, the bone healing after the insertion of the implant is compromised and may depend on local and systemic factors such as diseases, intake of certain drugs or bad habits such as smoking, which can interfere with wound healing. Late implant failures, on the other hand, are more related to the oral microbial environment, parafunctions, or prosthetic errors. The aim of this study is to de-scribe and compare different causes of early and late implant failure through histological and ra-diographic analysis of several clinical cases. MATERIALS AND METHODS Five clinical cases are presented in this study, relating to 5 implant fail-ures, which occurred after different loading periods and due to different causes. Each case has been docu-mented both radiologically and, after the removal of the bone samples containing the implants, also histologically. These biological samples were removed from the oral cavity of the patients, in order to be able to proceed with the dental rehabilitation procedures, which had previously been agreed with the patients. In order to proceed with the histological analysis, the bone samples were subjected to a dehy-dration procedure with increasing concentrations of alcohol, inclusion in a glycol-methacrylate resin, sec-tioning with the aid of a high preci-sion diamond disc until reaching the thickness of 150 microns, sub-sequent abrasion up to about 30 microns, and coloring with acid fuchsin and toluidine blue. The analysis of the samples was carried out under a transmitted light optical microscope. RESULTS AND CONCLUSIONS Of the 5 implants presented, one represents an early failure, because removed <6 months from insertion; the other late failures, since removed between 7 and 18 years from insertion. The histological analysis has made it possible to obtain more information, relating to the actual causes of implant failure, as op-posed to radiographic images, which are useful above all for di-agnosis, but give little information regarding the real causes. In particular, while the radiological images showed only the presence of a generic radiolucency that started from the implant collar and extended towards the apical portion, in the histologic section it is possible to observe the type of cells that composed these tissues. In particular, in the histological analysis it is possible to check for the presence of inflammatory in-filtrated tissue which allows us to differentiate physiological bone resorption, part of the normal re-modeling processes, from the pathological one, due to peri-im-plantitis. CLINICAL SIGNIFICANCE In order to make a correct diagnosis and therefore decide for the best treatment, it is essential to analyze the greatest number of in-formation, both clinical and radio-logical. The use of histological analysis in some cases, however, allows us to obtain unique infor-mation, fundamental not only in research but also in the clinic
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