Bulk Flow Of Liquid Research Articles

An investigation of phase change induced Marangoni-dominated flow patterns using the Constrained Vapor Bubble data from ISS experiments

Kinetic models of liquid-vapor phase change often implicitly assume that the interface is in equilibrium. This equilibrium assumption can be justified for large flat interfaces far from the source of thermal energy, but it breaks down when the liquid surface is near a solid wall, or there is significant interface curvature. The Constrained Vapor Bubble (CVB) experiments conducted on the International Space Station (ISS) provide a unique opportunity to probe this common assumption and also provide unique data and insight into phase change-driven flow physics. The CVB experiment consists of a quartz cuvette partially filled with pentane such that a vapor bubble is formed at the center. The setup is heated and cooled at opposite ends, resulting in simultaneous evaporation and condensation. CVB data from the NASA Physical Science Informatics (PSI) database was used to reconstruct the entire 3D interface shape using interferometric image analysis and obtain an estimate of the net heat input to the bubble. The reconstructed interface shape is used to develop a liquid-only CFD model embedded with a custom-built “active surface” method that sets a variable interfacial temperature/phase change flux boundary condition. Phase change flux varies in both the axial and transverse directions, leading to a small (∼1 K) but discernible temperature variation along the liquid-vapor interface. The positive phase change flux near the heater end (denoting evaporation) gradually reduces and becomes negative near the cooler end (denoting condensation), resulting in an axial bulk flow of liquid from the cold to the hot end. There is also a higher flux in the thin film as opposed to the thick film, resulting in a transverse bulk flow. However, the interfacial temperature gradients along both axial and transverse directions induce a separate thermocapillary flow in a direction opposite to the bulk flows, leading to complex “wavy” flows with recirculation. A qualitative analysis of the flow pattern is presented in this paper and correlated with optical signatures from experimental images.

Evaporation of sessile drops: a three-dimensional approach

The evaporation of non-axisymmetric sessile drops is studied by means of experiments and three-dimensional direct numerical simulations (DNS). The emergence of azimuthal currents and pairs of counter-rotating vortices in the liquid bulk flow is reported in drops with non-circular contact area. These phenomena, especially the latter, which is also observed experimentally, are found to play a critical role in the transient flow dynamics and associated heat transfer. Non-circular drops exhibit variable wettability along the pinned contact line sensitive to the choice of system parameters, and inversely dependent on the local contact-line curvature, providing a simple criterion for estimating the approximate contact-angle distribution. The evaporation rate is found to vary in the same order of magnitude as the liquid–gas interfacial area. Furthermore, the more complex case of drops evaporating with a moving contact line (MCL) in the constant contact-angle mode is addressed. Interestingly, the numerical results demonstrate that the average interface temperature remains essentially constant as the drop evaporates in the constant-angle (CA) mode, while this increases in the constant-radius (CR) mode as the drops become thinner. It is therefore concluded that, for increasing substrate heating, the evaporation rate increases more rapidly in the CR mode than in the CA mode. In other words, the higher the temperature the larger the difference between the lifetimes of an evaporating drop in the CA mode with respect to that evaporating in the CR mode.

Experimental investigation of the thermal interactions of nucleation sites in flow boiling

An experimental setup was designed to perform nucleate boiling experiments in upward saturated flow conditions, in order to investigate the influence of vertically aligned vapor bubble nucleation sites on one another. Experiments were performed by activating two bubble generators, of which the inter-site distance can be varied by steps of 2 mm. Depending on mass flow rate, flow direction and heat fluxes to both bubble generators, nucleation sites have been shown to interact at any nucleation site distance. The results have shown two major trends. The first trend is caused by additional convection (not by bubbles) from the upstream bubble generator, BG2, to the downstream bubble generator, BG1, increasing its nucleation frequency and bubble detachment diameter. The influence of additional convection on bubble frequency and diameter diminishes with increasing inter-site distance, S , and initial bubble nucleation frequency at BG1. The influence of added convective heat is enhanced by increasing the liquid bulk flow rate. The second trend is seen when BG2 initiates its own bubble nucleation. Vapor bubbles that nucleate at BG2 and pass by BG1 in close proximity have an inhibitive effect on bubble nucleation at BG1. The effect of this inhibitive trend diminishes with increasing nucleation frequency at BG1. Because of the significance of the effect of hydrodynamic interaction on the number of active nucleation sites and bubble size at detachment, mechanistic modeling of nucleate flow boiling is expected to benefit from the quantifications presented in this study.

Design and characterization of a scalable airlift flat panel photobioreactor for microalgae cultivation

A novel flat panel photobioreactor prototype with bulk liquid flow driven by an external airlift was designed, modeled, and experimentally characterized for the purpose of developing scalable industrial photobioreactors. Baffles were built inside the flat panel part of the reactor, directing the liquid bulk flow in a serpentine way, and the external airlift drove the liquid flow and facilitated gas mass transfer. The gas holdup, liquid flow velocity, and oxygen mass transfer of this prototype were experimentally determined and mathematically modeled, and the performance of the reactor was tested by cultivating two species of microalgae, Scenedesmus obliquus and Chlorella sorokiniana. The model-predicted trends correlated well with experimental data, indicating that the reactor might be scaled up using these models. A high cell concentration of C. sorokiniana was achieved under controlled indoor cultivation conditions although serious biofouling occurred in the case of S. obliquus cultivation. The results favor the possibility of scaling up the reactor to industrial scales, based on the models employed, and the potential advantages and disadvantages of the reactor are discussed regarding this industry-oriented photobioreactor configuration in comparison with current industrial photobioreactors.

Accumulation and Separation of Membrane-Bound Proteins Using Hydrodynamic Forces

The separation of molecules residing in the cell membrane remains a largely unsolved problem in the fields of bioscience and biotechnology. We demonstrate how hydrodynamic forces can be used to both accumulate and separate membrane-bound proteins in their native state. A supported lipid bilayer (SLB) was formed inside a microfluidic channel with the two proteins streptavidin (SA) and cholera toxin (CT) coupled to receptors in the lipid bilayer. The anchored proteins were first driven toward the edge of the lipid bilayer by hydrodynamic forces from a flowing liquid above the SLB, resulting in the accumulation of protein molecules at the edge of the bilayer. After the concentration process, the bulk flow of liquid in the channel was reversed and the accumulated proteins were driven away from the edge of the bilayer. Each type of protein was found to move at a characteristic drift velocity, determined by the frictional coupling between the protein and the lipid bilayer, as well as the size and shape of the protein molecule. Despite having a similar molecular weight, SA and CT could be separated into monomolecular populations using this approach. The method also revealed heterogeneity among the CT molecules, resulting in three subpopulations with different drift velocities. This was tentatively attributed to multivalent interactions between the protein and the monosialoganglioside G(M1) receptors in the lipid bilayer.

Transport properties of the mesothelium and interstitium measured in rabbit pericardium

The contribution of the pleural mesothelium to pleural liquid and protein transport is still vigorously debated. Recent in vitro studies of stripped pleural membrane and free-standing pericardium have demonstrated active ion solute coupled transport of liquid and transcytosis of protein. However, the relative contribution of the passive transport properties of the pleural mesothelium compared to the pleural interstitium has not been extensively studied. In in vitro studies, we measured the albumin diffusion coefficient, reflection coefficient, hydraulic conductivity and electrical resistance of rabbit pericardium. We used two techniques, treatment with 40 μM nocodazole and a 1-min hypotonic cell lysis with distilled water, to eliminate the effect of the two mesothelial layers on diffusional and hydraulic resistances. Each technique increased the albumin diffusion coefficient and hydraulic conductivity 3- to 4-fold. In hydraulic conductivity experiments using tracer 125I-albumin, nocodazole reduced the reflection coefficient to zero, rendering the pericardium completely permeable to albumin. We applied the cell-lysis technique to the pleural and pericardial mesothelium in sequence to evaluate the separate contribution of each mesothelium. Both diffusional and hydraulic resistances, but not electrical resistance, of the mesothelium were overestimated by the cell-lysis technique. The pleural mesothelium contributed at most 30% of diffusional resistance, 10% of hydraulic resistance and 14% of electrical resistance of the total pericardial resistances. We conclude that the pleural mesothelium is not the primary barrier to protein diffusion or bulk flow of liquid from the pericardial microcirculation to the pleural liquid.

Lung Fluid Balance During Development

After completing this article, readers should be able to: 1. Describe the major driving forces for liquid formation in and liquid removal from the lumen of the fetal lung. 2. Delineate the role of a normal volume of liquid within the lumen of the fetal lung for normal lung growth during development. 3. Describe the effects of labor on Na,K-ATPase activity in lung epithelial cells and clearance of lung liquid after birth. 4. Explain the route by which most residual liquid drains from the lung. 5. List the conditions associated with preterm birth that may contribute to delayed removal of fetal lung liquid. Curious students of mammalian development recognized more than a century ago that the lungs are filled with liquid during fetal life, (1) but the origin of that liquid remained obscure until 1948, when an unexpected discovery by two French scientists dispelled the prevailing view that fetal lung liquid derived from intrauterine inhalation of amniotic fluid. In studies designed to explore the ontogeny of the pituitary-adrenal axis, tracheal ligation of fetal rabbits for 9 days resulted in fluid distention of the lungs. (2) This serendipitous finding, subsequently confirmed and embellished by others, (3)(4)(5) established that the fetal lung itself, rather than the amniotic sac, is the source of the liquid that fills the lung during development. This liquid forms a slowly expanding structural template that prevents collapse and promotes growth of the fetal lung. Subsequent studies, conducted mostly with sheep, showed that liquid in the lumen of the fetal lung forms as a result of chloride secretion in the respiratory epithelium, (6)(7) a process that can be inhibited by diuretics that block Na,K-2Cl cotransport. (8)(9) In vitro experiments using cultured explants of lung tissue and monolayers of epithelial cells harvested from human fetal lung have …

HIGH INTENSITY DRYING

ABSTRACT A mathematical model simulating the heat and mass transfer process during high intensity drying of paper and board has been developed. The model is successful in predicting the vapor pressure developments, pressure driven bulk flow of liquid and vapor, and increased drying rates during high-intensity drying, closely matching the experimental determination. The model predicts substantial amounts of water removal in the liquid form during high-intensity drying being pushed out of the web by pressurized vapor zone. Water removal by pressure flow of liquid could account for as much as one-third of the total water removed. Similar to drying under conventional conditions, the existence of a dry zone, wet zone and an intermediate zone with accompanying advancing heat pipe has also been shown for drying under high intensity conditions.

On the suspension of particles in an agitated vessel

The purpose of the work was twofold. The first aim was to develop a technique, based on video recordings, to measure the velocities of the particles and the liquid bulk flow which is parallel to, and at the bottom of, the vessel. The second aim was to use the obtained experimental data to investigate Wichterle's model

Secretion of 35SO4-labeled proteins from isolated rat hepatocytes.

Sulfation is a Golgi-specific modification of secretory proteins. We have characterized the proteins that are labeled with 35SO4 in cultures of rat hepatocytes and studied their transport to the medium. Analysis by polyacrylamide gel electrophoresis showed that of the five most heavily labeled proteins, four had well-defined mobilities--apparent molecular masses of 188, 142, 125, and 82 kDa--whereas one was electrophoretically heterogeneous--apparent molecular mass of 35-45 kDa. Judging by their relatively high resistance to acid treatment, the sulfate residues in the 125- and 35-45-kDa proteins were linked to carbohydrate. Some of the secreted proteins were sialylated. In samples of pulse-labeled cells, there appeared to be no unsialylated forms, indicating that sulfation occurred after sialylation, presumably in the trans Golgi. Kinetic experiments showed that the cellular half-life was the same for all the sulfated proteins--about 8 min--consistent with the idea that transport from the Golgi complex to the cell surface occurs by liquid bulk flow.

Studies of membrane phenomena. Part 5.—Bulk flow through membrane

A theory was developed for the bulk flow of liquid through an ionized membrane which separates aqueous solutions of a 1:1 electrolyte of different concentrations, C1 and C2(C1 < C2). The main assumptions used were : (i) the activity coefficients and mobilities of mobile ions in the membrane phase are given by the expressions proposed previously; (ii) the velocity of the local centre of mass is proportional to the sum of mechanical and electric forces acting on the volume element considered; (iii) the osmotic pressure acting between two phases at the membrane surface is proportional to RT times the difference in molar concentration of thermodynamically effective ions across the phase boundary considered. The derived expression for the volume rate of bulk flow (Jν)c was the sum of three effects : interdiffusion of solute and solvent components, flow due to pressure gradient, and electro-osmotic flow due to electric-potential gradient. Methods to evaluate three parameters associated with these three kinds of flow from a set of experimental data for (Jν)c were developed, and applied to systems of oxidized collodion membrane and typical 1 : 1 electrolyte (KCl, LiCl, KIO3). With the values of the parameters so determined, the values of (Jν)c at various fixed values of C2/C1 were calculated as a function of ln C1 from the theoretical equation derived. The resulting curves displayed an N-shaped feature similar to the observed results and agreed numerically with the latter in all cases examined.

Studies on the Filter-thickener

There are several types of filter-thickener now available in commercial scale, but in this experiment, we studied the fundamental characteristics of the simplest type of filter-thickener as shown in Fig. 1. This filter-thickener consists of a cylindrical settling tank (50cm in diameter and 90cm in depth) with perforated floor covered with a filter medium. (Poly-vinyl chloride filter cloth).A part of the liquid contained in the sludge sedimented on the bottom of the settling tank is withdrawn as filtrate through the filter cloth by liquid head and suction of the gear pump. The cake sludges on the filter cloth are scraped and gathered to the centre of the tank bottom and withdrawn by the reciprocating diaphragm pump as thickened sludges. Overflow, underflow and filtrate are all sent back to the reservoir, where they are mixed by the stirrer, and recirculated by the pump.After a long and continuous running under constant feed-, underflow- and filtration-rate conditions. the whole system comes to its equilibrium. Then the concentration distribution of slurry along the height of the settling tank and the underflow concentration are measured. The results obtained are shown in Table 1 and Fig. 5.According to our study of the capacity of the ordinary continuous thickener, the concentration Cu of underflow sludge is determined mainly by the underflow rate per unit settling area (Qu/A) and the settling characteristics of that slurry. Solid flux G which may settle down across a horizontal unit area of the slurry layer with a concentration C, is represented by the equation, G=C(R+Qu/A), where R is a settling velocity of slurry having a concentration C and Qu/A is a downward bulk flow of liquid induced by the withdrawal of underflow. As shown in Fig. 6 (dotted curve), solid flux G at a constant rate Qu/A takes a minimum value Gm at a certain value of C(Cmu), and the slurry layer of that concentration controlls the capacity of the thickener.From the material balance, the underflow concentration to be obtained under this condition may be calculated by means of the following equation.Gm=Cmu(Rcmu+Qu/A)=CuQu/AIn the filter-thickener, besides the underflow Qu, the filtrate Qff is withdrawn from the bottom of the tank. Therefore the downward bulk flow of liquid in the lower part of the settling tank becomes (Qu+Qff)/A.If the sum of Qu and Qff is designated by Qu', solid handling capacity in the settling part of the filter-thickener is the same as that of ordinary thickener with an underflow rate Qu'. Then if all the sludge (Qu') but no filtrate is withdrawn as underflow, the concentration of the underflow sludge becomes Cu' in Fig. 6.If Qu (one part of Qu') is withdrawn as underflow and Qff (=Qu'-Qu) as filtrate, the concentration of the thickened sludge becomes Cu2 in Fig. 6. In other words, the volume of sludge decreases from Qu' to Qu, and solids contained remain the same, so the sludge concentration increases from Cu' to Cu2 which equals Cu'×Qu'/Qu. Accordingly, when corrected values of observed Cu2 at various operating conditions are plotted as Cu2Qu2/Qu' against