Water Mass Flux Research Articles

A large-area, all-plastic, flexible electroosmotic pump

A large-area, fabric-like pump would potentially have applications, for example, in controlling water transport through a garment, such as a rain jacket, regardless of the external temperature and humidity. This paper presents an all-plastic, flexible electroosmotic pump, constructed from commercially available materials: A polycarbonate membrane combined with the electrochemically active polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate that actively transports water using an electric potential that can be supplied by a small battery. By using electrochemically active polymer electrodes instead of metal electrodes, the electrochemical reaction that drives flow avoids the oxygen and hydrogen gas production or pH changes associated with water electrolysis. We observe a water mass flux up to 23 mg min−1 per cm2 polycarbonate membrane (porosity 10–15%), at an applied potential of 5 V, and a limiting operating pressure of 0.3 kPa V−1, similar to previously reported membrane-based electroosmotic pumps.

Development of a passive sensor for measuring vertical cumulative water and solute mass fluxes in lake sediments and streambeds

This paper introduces the sediment bed passive flux meter (SBPFM) as a new tool for in situ measurements of vertical volumetric water and contaminant mass fluxes across hyporheic and hypolentic zones (i.e., stream or lake bed sediments that function as the contiguous zone between the overlying surface water body and the underlying aquifer). The device is a direct-push probe which contains a permeable internal sorbent located between two screened intervals. In the presence of a vertical hydraulic gradient the screens allow water flow through the SBPFM's internal sorbent matrix that is impregnated with resident tracers. These tracers are displaced from the sorbent at rates proportional to the water flux through the sorbent. At the same time, dissolved contaminants present in the intercepted sediment water are retained on the SBPFM sorbent at rates proportional to the ambient contaminant mass flux in the hyporheic zone. Potential flow theory is applied to convert observations of water and contaminant fluxes through the SBPFM into estimates of undisturbed ambient vertical water and contaminant fluxes in the sediment. To validate the theory and demonstrate the SBPFM as a potential site characterization tool, multiple bench-scale sediment bed experiments are performed. Results demonstrate that water and contaminant mass fluxes are accurately measured in the laboratory and that future field tests are warranted.

Experimental study of air accumulation in vapor condensation across horizontal tube

In this study, air accumulation in vapor condensation across a horizontal tube was investigated experimentally. A total of 16 thermistors were mounted uniformly on the horizontal tube wall along the circumference of z=0.17m and z=0.63m to measure wall temperature. Results show that vapor exists as a three-dimensional diffusion flow and air is carried by vapor toward the downstream at θ=135°–225° and z=0–0.6m, and forms a saturated moist air region there, whereas another region is full of moist vapor. A vapor flowing front lies at the joint of two regions, where interdiffusion between vapor and air is in dynamic equilibrium. In the saturated moist air region, the ratio of gas film layer to overall thermal resistance is within the range of 0.92–0.97, the air mole fraction on the gas–liquid interface is within the range of 0.75–0.87, and the heat transfer coefficient at the condensation side is less than 300Wm−2K−1. An increase in cooling water mass flux pushes the vapor flowing front forward, expanding the moist vapor region, ultimately enlarging the vapor condensation area. The present experimental results were compared with the results of the works of Zhou and Rose (1996), Sherkriladze and Gomelauri (1966), Rose (1984), Fujii et al. (1972), Memory et al. (1993), and Chen and Lin (2009). The wall temperature distribution and Nu‾/Rel0.5 variation are reasonable.

Monitoring nutrients fate after digestate spreading in a short rotation buffer area.

One of the main sources of reactive nitrogen pollution is animal manure. The disposal of digestate (material remaining after the anaerobic digestion of a biodegradable feedstock) in agricultural soils could solve both the problems of soil fertilization and waste removal, but the fate of digestate in the environment must be assessed carefully before its massive utilization. To investigate whether digestate could be safely employed as a soil fertilizer, an agricultural field located in Monastier di Treviso (Northern Italy) and characterized by the presence of low hydraulic conductivity clay soils, was selected to be amended with bovine digestate. The experimental site was intensively monitored by a three-dimensional array of probes recording soil water content, temperature, and electrical conductivity, to solve the water and bulk mass fluxes in the unsaturated zone. High-resolution soil coring allowed the characterization of soil water composition over two hydrological years. Chloride, found in high concentrations in the digestate, was used as environmental tracer to track the fate of the percolating water. The study concluded that digestate could be confidently employed in short rotation buffer areas at an average rate of 195±26kg-N/ha/year in low hydraulic conductivity soils not affected by diffuse fracturing during dry periods.

QUENCH FRONT PROPAGATION IN THE ANNULAR CHANNEL

Understanding the quench front propagation during bottom core reflooding is crucial for the effective cooling during the LOCA accident. The results presented in this paper were obtained on an experimental loop with an annular test section. The test section consists of a vertical electrically heated stainless steel tube with outer diameter 9 mm and length of 1.7 m. The heated tube is placed inside a glass tube with the inner diameter 14.5 mm. Water mass flux during the reflooding is in the range from 100 kg.m<sup>−2</sup>.s<sup>−1</sup> up to 140 kg.m<sup>−2</sup>.s<sup>−1</sup> and the initial wall temperature of the stainless steel tube is in the range from 250 °C up to 800 °C. The presented results show the influence of the initial conditions on the quench front propagation and the complexity of the phenomenon.

Large Eddy & Interface Simulation (LEIS) of disturbance waves and heat transfer in annular flows

A numerical method for forced convective boiling in an annulus needs to be developed in order to elucidate the reason for nucleation enhancement by disturbance waves. We first developed a numerical strategy to model the development of disturbance waves in annular flows where the highly turbulent gas core flow drives the laminar liquid flow upwards using advanced CFD tool TransAT. In which, the interface tracking method (e.g. Level-set) combined with a scale-resolving turbulence simulation technique (Large Eddy Simulation) was employed to capture dominant turbulence and interfacial scales. Then, the disturbance wave phenomenon in a vertical steam-water annulus system was investigated and analyzed. The finding reported in the present work provides insight into the evolution of disturbance wave and its influence on the heat transfer in annular flow. The modeling results revealed that locally hot ‘spots’ occurred upstream of disturbance wave. These locally overheated zones could play key roles in activating the nucleation boiling sites. In addition, the inception criteria of disturbance wave were explored by adjusting the mass flux of saturated water. And it was found no disturbance waves occurred at liquid film Reynolds number lower than the critical value, 225.

Experimental investigation on flow boiling heat transfer in conventional and mini vertical channels

An experimental investigation was carried out to study the flow boiling heat transfer mechanism in the vertical channels with different inner diameters. The heating section of the test-section was stainless steel tube, and the transparent sections were equipped at inlet and outlet of the test-section, respectively. The flow patterns at outlet were recorded by a high speed camera, and the corresponding experimental parameters were measured simultaneously. In this study, the characteristics of flow boiling heat transfer with different inner diameters, inlet water temperatures, mass fluxes, and heat fluxes were analyzed in detail. Moreover, a modified correlation on the Chen correlation was proposed to predict the heat transfer coefficients in the vertical channels, and this correlation was verified with good agreement.

Toward Improving Ice Water Content and Snow-Rate Retrievals from Radars. Part I: X and W Bands, Emphasizing CloudSat

AbstractMicrophysical data and radar reflectivities (Ze, −15 < Ze < 10 dB) measured from flights during the NASA Tropical Clouds, Convection, Chemistry and Climate field program are used to relate Ze at X and W band to measured ice water content (IWC). Because nearly collocated Ze and IWC were each directly measured, Ze–IWC relationships could be developed directly. Using the particle size distributions and ice particle masses evaluated based on the direct IWC measurements, reflectivity–snowfall rate (Ze–S) relationships were also derived. For −15 < Ze < 10 dB, the relationships herein yield larger IWC and S than given by the retrievals and earlier relationships. The sensitivity of radar reflectivity to particle size distribution and size-dependent mass, shape, and orientation introduces significant uncertainties in retrieved quantities since these factors vary substantially globally. To partially circumvent these uncertainties, a W-band Ze–S relationship is developed by relating four years of global CloudSat reflectivity observations measured immediately above the melting layer to retrieved rain rates at the base of the melting layer. The supporting assumptions are that the water mass flux is constant through the melting layer, that the air temperature is nearly 0°C, and that the retrieved rain rates are well constrained. Where Ze > 10 dB, this Ze–S relationship conforms well to earlier relationships, but for Ze < 10 dB it yields higher IWC and S. Because not all retrieval algorithms estimate either or both IWC and S, the authors use a large aircraft-derived dataset to relate IWC and S. The IWC can then be estimated from S and vice versa.

Prediction of subcooled flow boiling characteristics using two-fluid Eulerian CFD model

The present study concerns a detailed analysis of flow boiling phenomena under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4mm was considered as the modeled domain. Two different uniform heat fluxes and three saturation pressures were applied to the channel wall, whereas water mass flux of 900kg/m2s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of the CFD technique for estimation of the wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Changes in factors applied in the modeling of the interfacial heat transfer coefficient and bubble departure frequency were suggested, allowing a better prediction of the void fraction along the heated channel. The commercial CFD solver FLUENT 14.5 was used for the model implementation.

Amplitude characteristics of pressure oscillation caused by steam jet condensation in a confined channel

Steam jet injector is a prospective device with advantages of impact volume, strong heat transfer, without moving part, which can be applied in various industrial fields such as nuclear/conventional power plant, heat-supply system and heat recovery system, etc. However, as the steam jet injector is driven by high speed steam jet condensation in subcooled water flow in the mix chamber, the instability of steam-water direct contact condensation will lead to loud noise and severe vibration. Thus, loud noise will evolve into environmental pollution, and vibration will endanger the equipment, which prevent the promotion of this device in induatrial applications. Moreover, the published works generally involved in the pressure oscillation caused by steam jet condensation in large space water pool, where the water was considered to be stagnant. However, the case becomes more complex when direct contact condensation occurs in a confined channel like in a steam jet injector, where the effect of turbulence on water side and wall can not be ignored. Thus, the reported results can not be applied in the present condition. So it is necessary to study the mechanism of the instability of steam-water direct contact condensation in a confined channel. In this paper, experimental investigation was performed on the amplitude characteristics of pressure oscillation caused by direct contact condensation in a confined channel, aiming at revealing the mechanism of noise and vibration and providing some guidance for the design and operation of the steam jet injector. In order to better observe the behavior of the steam-water interface, a special visualized test section was designed and a high speed camera was applied. The dynamic pressure data was obtained by a dynamic pressure transducer arranged on the wall of channel. Three main inlet parameters, including steam mass flux, water mass flux and water temperatures were tested in the ranges of 150–600 kg/m2s, 6×103–18×103 kg/m2s and 15–40°C, respectively. The results indicated that when direct contact condensation occurred in a confined channel, flow patterns could be divided into two categories-unstable and stable flow patterns with respect to the interface behavior. The effect of the inlet parameters on amplitude characteristics of pressure oscillation was discussed. With the increase of water mass flux, the amplitude altered slightly in stable flow pattern region, but increased suddenly and dramatically in unstable region. With the increase of steam mass flux, the amplitude increased a little in unstable region, but decreased suddenly in stable region and then increased again. And the increase of water temperature leaded to the increasing of amplitude in all flow pattern regions. In a word, the equipment would bear stronger impact load when operating in unstable flow pattern region.

Accurate Measurements of Aerosol Hygroscopic Growth over a Wide Range in Relative Humidity

Using a comparative evaporation kinetics approach, we describe a new and accurate method for determining the equilibrium hygroscopic growth of aerosol droplets. The time-evolving size of an aqueous droplet, as it evaporates to a steady size and composition that is in equilibrium with the gas phase relative humidity, is used to determine the time-dependent mass flux of water, yielding information on the vapor pressure of water above the droplet surface at every instant in time. Accurate characterization of the gas phase relative humidity is provided from a control measurement of the evaporation profile of a droplet of know equilibrium properties, either a pure water droplet or a sodium chloride droplet. In combination, and by comparison with simulations that account for both the heat and mass transport governing the droplet evaporation kinetics, these measurements allow accurate retrieval of the equilibrium properties of the solution droplet (i.e., the variations with water activity in the mass fraction of solute, diameter growth factor, osmotic coefficient or number of water molecules per solute molecule). Hygroscopicity measurements can be made over a wide range in water activity (from >0.99 to, in principle, <0.05) on time scales of <10 s for droplets containing involatile or volatile solutes. The approach is benchmarked for binary and ternary inorganic solution aerosols with typical uncertainties in water activity of <±0.2% at water activities >0.9 and ∼±1% below 80% RH, and maximum uncertainties in diameter growth factor of ±0.7%. For all of the inorganic systems examined, the time-dependent data are consistent with large values of the mass accommodation (or evaporation) coefficient (>0.1).

Mass transfer enhancement for LiBr solution using ultrasonic wave

The methods were studied to improve the cooling performance of the absorption refrigeration system (ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boiling mass transfer in LiBr solution was also analyzed with experiment. The experimental results indicate that, under the driving heat source of 60–100 oC and the ultrasonic power of 20–60 W, the mass flux of cryogen water in LiBr solution is higher after the application of ultrasonic wave than auxiliary heating with electric rod of the same power, so the ultrasonic application effectively enhances the heat utilization efficiency. The distance H from ultrasonic transducer to vapor/liquid interface significantly affects mass transfer enhancement, so an optimal H opt corresponding to certain ultrasonic power is beneficial to reaching the best strengthening effect for ultrasonic mass transfer. When the ultrasonic power increases, the mass transfer obviously speeds up in the cryogen water; however, as the power increases to a certain extent, the flux reaches a plateau without obvious increment. Moreover, the ultrasound-enhanced mass transfer technology can reduce the minimum temperature of driving heat source required by ARS and promote the application of solar energy during absorption refrigeration.

Dynamics of Particle Size on Inhalation of Environmental Aerosol and Impact on Deposition Fraction.

Inhalation of elevated levels of particulate air pollution has been shown to elicit the onset of adverse health effects in humans, where the magnitude of the response is a product of where in the lung the particulate dose is delivered. At any point in time during inhalation the depositional flux of the aerosol is a function of the radius of the droplet, thus a detailed understanding of the rate and magnitude of the mass flux of water to the droplet during inhalation is crucial. In this study, we assess the impact of aerosol hygroscopicity on deposited dose through the inclusion of a detailed treatment of the mass flux of water to account for the dynamics of particle size in a modified version of the standard International Commission on Radiological Protection (ICRP) whole lung deposition model. The ability to account for the role of the relative humidity (RH) of the aerosol prior to, and during, inhalation on the deposition pattern is explored, and found to have a significant effect on the deposition pattern. The model is verified by comparison to previously published measurements, and used to demonstrate that ambient RH affects where in the lung indoor particulate air pollution is delivered.

Experimental study on the stable steam jet in subcooled water flow in a rectangular mix chamber

Two-phase Flow Steam Injector (TFSI) was a simple device without moving parts, which had been used in several industrial applications. As an important process of the TFSI, steam-water Direct Contact Condensation (DCC) in stagnant water pool had been widely investigated. DCC had different features when occurring in a confined channel in water flow, which is more similar to the DCC process of that in TFSI. In present work, direct contact condensation of stable steam jet in subcooled water flow in a rectangular mix chamber was investigated experimentally. Rectangular steam and water nozzles were adopted to form a quasi-planar structural flow flied and two different stable steam jets including conical jet and ellipsoidal jet were observed. The transition from stable steam jet to divergent jet was observed and the transition criterion was also established. A three-dimensional regime diagram was presented and discussed based on steam mass flux, water mass flux and inlet water temperature. In addition, temperature and pressure distributions on the bottom wall center for stable steam jet were measured. The peaks in temperature distributions evidenced the compression wave, whilst the nadirs in pressure distributions were evidence to the expansion wave. Furthermore, average heat transfer coefficients predicted by interfacial transport model due to turbulent intensity were in the range of 3.83–6.24MW/m2K, which were in the same order of magnitude with previous investigations, and the discrepancies between predicted and experimental values were within ±30%.

Experimental study on the direct contact condensation of the steam jet in subcooled water flow in a rectangular channel: Flow patterns and flow field

Direct contact condensation (DCC) of steam jet in subcooled water flow in a channel was experimentally studied. The main inlet parameters, including steam mass flux, water mass flux and water temperature were tested in the ranges of 200–600kg/(m2s), 7–18×103kg/(m2s), 288–333K, respectively. Two unstable flow patterns and two stable flow patterns were observed via visualization window by a high speed camera. The flow patterns were determined by steam mass flux, water mass flux and water temperature, and the relationship between flow patterns and flow field parameters was discussed. The results indicated that whether pressure or temperature distributions on the bottom wall of channel could represent different flow patterns. And the position of pressure peak on the bottom wall could almost represent the condensation length. The upper wall pressure distributions were mainly dependent on steam and water mass flux; and the upper wall temperature distributions were affected by the three main inlet parameters. Moreover, the bottom wall pressure and temperature distributions of different unstable flow patterns had similar characteristics while those of stable flow patterns were affected by shock and expansion waves. The underlying cause of transition between different flow patterns under different inlet parameters was reflected and discussed based on pressure distributions.

Flow boiling instability characteristics in expanding silicon microgap heat sink

The effects of mass flux, heat flux and microgap configuration on flow boiling instability in expanding microgap heat sink are experimentally investigated. Characterizations of instabilities are performed for deionized water mass fluxes, G=400–1000kg/m2s, imposed effective heat flux q″eff ranging from 0 to 80W/cm2 for three different microgap configurations, straight microgap of depth 200μm and expanding microgap having same inlet depth 200μm with gradually increasing exit depth 300μm and 460μm. High speed flow visualizations are conducted simultaneously along with experiments to explore the bubble behavior in expanding microgap heat sink. Results show that two phase expanding microgap heat sink has novel potential to mitigate the flow instabilities and flow reversal issues as the generated vapor has room to expand downstream and also due to reducing shear force along the direction of expansion. Reduced share force is beneficial as it contributes to easing flow in the direction of expansion and thus, eliminates flow reversal and maintains stable flow boiling condition. In addition, inlet pressure oscillation increases gradually with the increase of mass flux and heat flux due to the extensive repetitive backward expansion of vapor slug. Whereas, wall temperature oscillation decreases with the decrease of mass flux and increase of heat flux due to the presence of stable annular flow regime at high heat flux and low mass flux condition before dryout approaches.

Experimental study on the direct contact condensation of the steam–air mixture in subcooled water flow in a rectangular channel

An experimental study was performed to investigate the direct contact condensation (DCC) of steam–air mixture in subcooled water flow in a rectangular channel. The main inlet parameters including steam mass flux, water mass flux and water temperature were tested at 150–550kg/(m2s), 6–14×103kg/(m2s) and 30°C, respectively. The air mass fraction was in the range of 0%–2%. Four different flow patterns for pure steam in subcooled water flow were filmed by a high speed camera. The effect of air on these four flow patterns was investigated by introducing air into steam. The pressure and temperatures on the wall of channel were measured without destroying the flow field. The results indicated that with the present of air, the direct contact condensation was hindered, the interface area enlarged, the mixture layer thickened and plenty of small bubbles gathered in the channel. The air had greater influence on the phase interface area of unstable flow patterns than that of stable flow patterns. This phenomenon could not only be observed in the pictures of flow patterns, but also be reflected in the bottom wall pressure and temperature distributions. The average heat transfer coefficient for pure steam jet in subcooled water flow was in the range of 3.92–6.81MW/(m2°C). Since air mass fraction increased, the average heat transfer coefficient decreased.

DCMD modelling and experimental study using PTFE membrane

This research work aims to investigate the performance of direct contact membrane distillation (MD) unit under different conditions. A mathematical model was developed to evaluate the experimental values of the membrane water mass flux, heat transfer coefficients, the membrane/liquid interface temperatures, the temperature polarisation coefficient and the evaporation efficiency. This model was solved numerically using MATLAB® software, and its results were used to predict the actual performance of the membrane unit. The MD coefficient was evaluated from the computer model data and was subsequently used to estimate water fluxes. Experimental tests were performed using 0.0572 m2 of PTFE membrane manufactured by membrane solution (85% porosity, 45μm thickness, 0.22μm nominal pore size). Feed solutions were aqueous NaCl solutions with 1,000–200,000 mg/L (0.1–20%) in concentration and its temperatures were 40–80°C, and feed flow rate was 2 L/min. The temperature and flow rate of permeate water was fixed at 20°C and 3 L/min, respectively. The experimental observation showed that the vapour mass flux through the membrane pores increased with feed temperature, but decreased with feed concentration. It was found that the predicted mass fluxes agreed reasonably with the experimental data, except at a high feed concentration. The temperature polarisation coefficients increased with concentration and decreased with increasing temperature. The membrane heat transfer rates and the permeate flux have been discussed in this paper.

Flow boiling heat transfer and pressure drop characteristics in expanding silicon microgap heat sink

The present flow boiling experiments are performed for deionized water mass fluxes, G=400–1000kg/m2s, imposed effective heat flux qeff″ ranging from 0W/cm2 to 80W/cm2 for three different microgap configurations having same inlet depth 200μm and gradually increasing exit depth 200μm, 300μm and 460μm to explore expanding microgap effect on heat transfer and pressure drop performances. High speed flow visualizations are conducted simultaneously along with experiments to explore the bubble behavior in expanding microgap heat sink. The results of this study show that expanding microgap maintains a more uniform wall temperature than straight microgap heat sink and also delays dryout phase. In addition, expanding microgap of exit depth 300μm performs best for both heat transfer and pressure drop performances among all configurations.

A research on water desalination using membrane distillation

This research work aimed to investigate the performance of direct contact membrane distillation (MD) unit under different conditions. A mathematical model was developed to evaluate the experimental values of the membrane water mass flux, heat transfer coefficients, the membrane/liquid interface temperatures, the temperature polarization coefficient (TPC) and the evaporation efficiency. This model was solved numerically using MATLAB® software, and its results were used to predict the actual performance of the membrane unit. The MD coefficient was evaluated from the computer model data and was subsequently used to estimate water fluxes. Experimental tests were performed using 0.0572 m2 of poly-tetra-fluoro-ethylene membrane manufactured by membrane solution (85% porosity, 45-µm thickness, 0.22-µm nominal pore size). Feed solutions were aqueous NaCl solutions with 1,000–200,000 mg/L (0.1–20%) in concentration, its temperatures were 40–80°C and feed flow rate was 2 l/min. The temperature and flow rate of permeate water was fixed at 20°C and 3 l/min, respectively. The experimental observation showed that the vapour mass flux through the membrane pores increased with feed temperature, but decreased with feed concentration. It was found that the predicted mass fluxes agreed reasonably with the experimental data, except at a high feed concentration. The temperature polarization coefficients increased with concentration and decreased with increasing temperature. The membrane heat transfer rates and the permeate flux have been discussed in this paper.