1,720,987 research outputs found
Modeling of cavitation as an advanced wastewater treatment
No full text"This paper presents a theoretical study of cavitation as an advanced oxidation process. A. mathematical algorithm, which couples single bubble dynamics and chemical reactions for a. cavitating bubble, is proposed and compared with experimental and theoretical works. reported in the literature. The main output variable, used for comparison, is the hydroxyl. radical production. A wide range of parameter values is evaluated for the analysis of hydro-. dynamic cavitation in an orifice. Thanks to the large number of simulation, it was possible to. find a very good agreement with a design correlation proposed in the literature. Addition-. ally, a novel approach has been proposed, which consists of integrating the estimated radical. production over a typical bubble size distribution in order to predict a global oxidant pro-. duction. Moreover, by fixing the values of flowrate, pressure, and geometric parameters, a. real experimental condition of hydrodynamic cavitation in a Venturi device has been simu-. lated. This allowed the comparison of simulation results with the experimental ones reported. in the literature. A good agreement has been found in terms of cavitational yield, an estima-. tion of the process efficiency from an energetic perspective.
"Cavitational reactor for advanced treatment of contaminated water: the effect of recovery pressure"
No full textThis article deals with study of hydrodynamic cavitation in a Venturi reactor by considering the degradation of p-nitrophenol and the numerical simulation of a cavitating bubble in the explored experimental conditions. The parameters depicting the cavitation performances are reported for several experimental conditions. The best result of pNP mass removed at 30 min was found by setting the inlet pressure at 0.70 MPa and the recovery one at 0.38 MPa (≈40%), while the best performances in terms of pNP conversion per unit energy consumed were observed at 0.40 MPa (2.41 mg/MJ). The study represents a step forward in the work carried out by our research group to gain theoretical insight and optimize cavitation for advanced wastewater treatment
Thermodynamic analysis of the humidification-dehumidification-adsorption (HDHA) desalination process
No full textThe process of Air Humidification-Dehumidification (HDH) for water desalination and purification can play an important role in the field of low-carbon water production from non-conventional sources. Our research group presented a novel process scheme consisting of a multiple extraction HDH with vapour adsorption (HDHA) and brine recirculation, able to approximate a closed-air closed-water loop with bottom temperature below the environmental one. This novel work presents the strategy of process optimization through the variance analysis and a mathematical algorithm of thermodynamic balancing adapted to this novel process. The results point out the optimization strategies and allow the literature comparison to show how HDHA can overcome the performances of conventional processes at similar conditions, also reaching acceptable values of second law efficiency. In fact, HDHA can overcome the GOR of similar “balanced” water heated HDH reaching GOR around 10 even at acceptable enthalpy pinch (around 15 kJ kg−1) with three air extractions.</p
"Chemical Effect of Hydrodynamic Cavitation: Simulation and Experimental Comparison"
No full textThe chemical effect of hydrodynamic cavitation (HC) in a Venturi reactor from both the theoretical and the experimen-
tal point of view is dealt. A mathematical model is presented to simulate the global production of hydroxyl radicals; it
is based on a set of ordinary differential equations that account for the hydrodynamics, mass diffusion, heat exchange,
and chemical reactions inside the bubbles. Experimentally, the degradation of p-nitrophenol (initial concentration 0.15
g dm
23
) has been conducted in a lab scale Venturi reactor at inlet pressure ranging from 0.2 to 0.6 MPa and has been
used to estimate the hydroxyl radical production. The optimum configuration, suggested by numerical simulations, has
been experimentally confirmed. Thanks to the empirical validation, this novel modeling approach can be considered as
a theoretical tool to identify the best configuration of HC operating parameters
Numerical Analysis of VPSA Technology Retrofitted to Steam Reforming Hydrogen Plants to Capture CO2 and Produce Blue H2
No full textThe increasing demand for energy and commodities has led to escalating greenhouse gas emissions, the chief of which is represented by carbon dioxide (CO2). Blue hydrogen (H2), a low-carbon hydrogen produced from natural gas with carbon capture technologies applied, has been suggested as a possible alternative to fossil fuels in processes with hard-to-abate emission sources, including refining, chemical, petrochemical and transport sectors. Due to the recent international directives aimed to combat climate change, even existing hydrogen plants should be retrofitted with carbon capture units. To optimize the process economics of such retrofit, it has been proposed to remove CO2 from the pressure swing adsorption (PSA) tail gas to exploit the relatively high CO2 concentration. This study aimed to design and numerically investigate a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the PSA tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant using NaX zeolite adsorbent. The effect of operat-ing conditions, such as purge-to-feed ratio and desorption pressure, were evaluated in relation to CO2 purity, CO2 recovery, bed productivity and specific energy consumption. We found that conventional cycle configurations, namely a 2-bed, 4-step Skarstrom cycle and a 2-bed, 6-step modified Skarstrom cycle with pressure equalization, were able to concentrate CO2 to a purity greater than 95% with a CO2 recovery of around 77% and 90%, respectively. Therefore, the latter configuration could serve as an efficient process to decarbonize existing hydrogen plants and produce blue H2
Comparison between hydrodynamic and acoustic cavitation in microbial cell disruption
No full textCavitation phenomena are associated with the formation, growth and the collapse of microbubbles and consequently, to the generation of very high pressures, shear stresses and temperatures, locally. Thanks to the cited features, the application of cavitation is a reliable tool for cell damage and hence disruption. In this paper a theoretical model for quantifying the mechanical effect of hydrodynamic cavitation (HC) and acoustic cavitation (AC) in killing micro-organism is reported. A physical model accounting for bubble dynamics, fluid turbulence, shear stress and pressure pulse generated from cavity collapse is developed, aimed at calculating the turbulent shear generated and the extent of microbial disinfection. The theoretical results are compared with the mechanical resistance of microbial cells in order to estimate the damaging effect. Numerical results provide a practical tool for the estimation of process efficacy and parameter optimization, both for HC and AC devices. The effect of parameters is estimated and typical experiments from the pertinent literature are simulated in order to estimate the treatment efficiency. Results are in agreement with the related; moreover, from the energy efficiency point of view, it was observed that HC is almost an order of magnitude more energy efficient than AC
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