Hydrodynamic and environmental characteristics of a tributary bay influenced by backwater jacking and intrusions from a main reservoir

The construction of large reservoirs results in the formation of tributary bays, and tributary bays are inevitably influenced by backwater jacking and intrusions from the main reservoir. In this paper, a typical tributary bay (Tangxi River) of the Three Gorges Reservoir (TGR) was selected to study the hydrodynamic and environmental characteristics of a tributary bay influenced by the jacking and intrusions from the main reservoir. The flow field, water temperature, and water quality of Tangxi River were simulated using the hydrodynamic and water quality model CE-QUAL-W2 (thomas and Scott, 2008), and the eutrophication status of the tributary bay was also evaluated. The results showed that the main reservoir had different effects on its tributary bay in each month. The tributary bay was mainly affected by backwater jacking from the main reservoir when the water level of the main reservoir dropped and by intrusions from the main reservoir when the water level of the main reservoir rose. An obvious water quality concentration boundary existed in the tributary bay, which was consistent with the regional boundary in the flow field. The flow field and water quality on both sides of the boundary were quite different. The results of this study can help us figure out how the backwater jacking and intrusions from the main reservoir influence the hydrodynamic and water environment characteristics of the tributary bay and provide guidance for water environment protection in tributary bays.

Enhancement of the air gap membrane distillation system performance by using the water gap module

The negative effect of an air gap layer presented between the membrane and cooling plate on air gap membrane distillation (AGMD) performance was diminished largely by inserting a water gap membrane distillation (WGMD) module in series. The new design of air-gap–water-gap membrane distillation (AG-WG)MD was evaluated experimentally by comparing with an AGMD system under different operating conditions. In theory, mass and heat transfer in the new (AG-WG)MD and imitative AGMD systems were analyzed. Experimental outcomes showed that a new (AG-WG)MD design profoundly enhanced flux (Pd) and gained output ratio (GOR), and greatly decreased energy consumption (STEC) and heat input (EH.I). At a concentration of 5,000 mg/L, coolant temperature of 20 °C, and flow rate of 18 L/h, Pd was promoted by 76.26%, 40.84%, 35.45%, 30.91%, and GOR by 46.38%, 33.46%, 31.27%, 26.65%, in addition to STEC being reduced about 55.63%, 46.81%, 43.66%, 38.30%, and EH.I around 31.31%, 25.84%, 23.53%, 20.55%, from the AGMD to (AG-WG)MD system at feed temperatures of 50 °C, 60 °C, 70 °C, and 80 °C, respectively. The outcomes proved that the AGMD performance could be significantly promoted by integrating with WGMD in a combined MD system. This combination increased the temperature difference across the membrane and decreased thermal-concentration boundary layers for the AGMD system.

Numerical Simulation of Carbon Dioxide Absorption by Monoethanolamine Solution with Super Mini Ring Contactor

Carbon capture storage provides an alternative to reducing global warming. In order to reduce the cost of carbon capture storage, high mass transfer packings for CO2 absorption from flue gas is an alternative. The study modeled and numerically simulated CO2 absorption by monoethanolamine solution with super mini ring contactor. The model considered the effect of the mass and momentum transfers, as well the chemical reaction. The simulation results show that the driving force of the reactive absorption is higher than the ordinary absorption in term of the low concentration of CO2 in the liquid phase. The CO2 concentration in the bulk gas is approximately 7.56 mol/m3. It decreases to around 5.75 mol/m3 after crossing the concentration boundary layer.

The Role of Gravity in the Evolution of the Concentration Field in the Electrochemical Membrane Cell

The subject of the study was the osmotic volume transport of aqueous CuSO4 and/or ethanol solutions through a selective cellulose acetate membrane (Nephrophan). The effect of concentration of solution components, concentration polarization of solutions and configuration of the membrane system on the value of the volume osmotic flux ( J v i r ) in a single-membrane system in which the polymer membrane located in the horizontal plane was examined. The investigations were carried out under mechanical stirring conditions of the solutions and after it was turned off. Based on the obtained measurement results J v i r , the effects of concentration polarization, convection polarization, asymmetry and amplification of the volume osmotic flux and the thickness of the concentration boundary layers were calculated. Osmotic entropy production was also calculated for solution homogeneity and concentration polarization conditions. Using the thickness of the concentration boundary layers, critical values of the Rayleigh concentration number ( R C r ), i.e., the switch, were estimated between two states: convective (with higher J v i r ) and non-convective (with lower J v i r ). The operation of this switch indicates the regulatory role of earthly gravity in relation to membrane transport.

TCE and PCE plume persistence based on different clay types

<p>This study was performed to understand dense non-aqueous phase liquid (DNAPL) persistence by the back diffusion from the three types of clay using one-dimensional analytical solutions. The conceptual model was designed with 5 m thickness of an aquifer underlain by 0.7 m thickness of an aquitard. The aquitard was considered to be a finite domain boundary at the bottom of bentonite (B), kaolinite (K), and montmorillonite (M) layers. The tortuosity of each clay was assumed to be 0.95 (B), 0.55 (K), and 0.05 (M). A diffusion model scenario assumed a step change in concentration boundary condition representing complete removal of trichloroethylene (TCE) and tetrachloroethylene (PCE) at the source zone, after 10 years of source loading. Total accumulated mass in the aquitard during the forward diffusion showed that PCE was 57.3 (B), 44.3 (K), 13.3 (M) g/m<sup>2</sup>, and TCE was 329.2 (B), 256.2 (K), 76.8 (M) g/m<sup>2</sup>. The calculated tailing concentration of PCE at the aquifer during the back diffusion maintained higher concentrations than the maximum contaminant level (MCL, PCE = 5 μg/L) for 22 (B), 16 (K), and 11 (M) years, respectively, in the same order as the tortuosity of clays. The calculated tailing concentration of TCE above MCL (TCE = 5 μg/L) was maintained for 38 (B), 43 (K), and 19 (M) years. These results showed that the total accumulated mass of TCE was higher in the bentonite layer than the kaolinite layer, but the TCE tailing concentrations caused by back diffusion from the kaolinite layer maintained 5 years longer above MCL than those caused by back diffusion from the bentonite layer due to different values of tortuosity for bentonite and kaolinite. The results of this study indicate that the tortuosity of clays has a significant influence on plume persistence caused by back diffusion.</p>

The hydrodynamic and environmental characteristics of tributary bay influenced by backwater jacking and intrusion of main reservoir

The construction of large reservoirs results in the formation of tributary bays, and tributary bays are inevitably influenced by the backwater jacking and intrusion of the main reservoir. The hydrodynamic conditions and the environmental factors of tributary bays exhibit complex distribution characteristics and eutrophication occur frequently. Thus, exploring the distribution and evolution of the hydrodynamic and water environment characteristics of tributary bays in response to backwater jacking and intrusion is the key to solving eutrophication and other problems relevant to water environment. In this paper, a typical tributary bay (Tangxi River) of the Three Gorges Reservoir (TGR) was selected to study the hydrodynamic and environmental characteristics of the tributary bay influenced by the jacking and intrusion of the main reservoir. The flow field, water temperature and water quality of the Tangxi River were simulated using the hydrodynamic and quality model CE-QUAL-W2, and the eutrophication status of the tributary bay was also evaluated. The results showed that the main reservoir had different effects on its tributary bay in each month. The tributary bay was mainly affected by backwater jacking of the main reservoir when the water level dropped and by intrusion of the main reservoir when the water level rose. An obvious quality concentration boundary existed in the tributary bay, which was basically consistent with the regional boundary in the flow field. The flow field and water quality on both sides of the boundary were quite different. The results of this study can help us figure out how the backwater jacking and intrusion of the main reservoir influence the hydrodynamic and water environment characteristics of the tributary bay and provide guidance for water environment protection in the tributary bays.

On the effects of straight extremities on low-density lipoprotein transport in the concentration boundary layer of curved arteries

Purpose The purpose of this paper is to analyze the influence of curvature on the transport of low-density lipoprotein (LDL) through a curved artery and concentration boundary layer characteristics numerically. Design/methodology/approach By using a projection method based on the second-order central difference discretization, the authors solve the set of governing equations, which consists of Navier–Stokes, continuity and species transport. The effects of initial straight length, as well as the curvature and wall shear stress (WSS) on LDL transport in a curved artery are established in this paper. Findings The obtained numerical results imply that the LDL concentration boundary layer thickness decreases in the outer part of the curved artery and increases in the inner part for both with or without initial straight length. The effect of Reynolds number on the concentration distribution in a curved artery with initial straight length is more pronounced than that on a fully curved artery, although an opposite trend was seen for the curvature ratio. The maximum surface LDL concentration is related to the regions with minimum WSS in the inner part of the curved artery, which has more potential the formation of atherosclerosis. Originality/value The authors present a comprehensive concentration distribution of LDL in the concentration boundary layer of the curved artery. The authors also characterize and predict the influence of curvature on the formation and development of atherosclerosis within the arterial wall.

Bödewadt Flow Over a Permeable Disk with Homogeneous-Heterogeneous Reactions: A Numerical Study

We analyzed the onset of homogeneous-heterogeneous reactions in Bödewadt flow occurring over an isothermal and permeable surface. This research is based on the assumption that the homogeneous (bulk) reaction follows isothermal cubic autocatalator kinetics, whereas the surface reaction is governed by first-order kinetics. The heat energy released during the chemical reaction is assumed to be negligible. The governing equations are reducible to a set of self-similar equations, which are handled numerically. Asymptotic analysis was conducted, which revealed that the existence of a concentration boundary layer on the disk is possible only when the disk is subjected to a sufficient amount of suction. In a large suction situation, an exact formula for concentration profile ϕ was derived that strongly supports the obtained numerical solution. Our results demonstrate the mass transfer parameter considerably alters flow fields. The concentration at the wall varies substantially when the chemical reaction proceeds at a faster rate.