Volume Flux Of Water Research Articles

Long-term ferry-based observations of the suspended sediment fluxes through the Marsdiep inlet using acoustic Doppler current profilers

Long-term measurements with a hull mounted acoustic Doppler current profiler (ADCP) under the ferry, crossing the Marsdiep inlet between the mainland and the island of Texel (the Netherlands), were used to determine the volume flux and the flux of suspended particulate matter (SPM) through this inlet for the period 2003–2005. Profiles of the SPM concentration were estimated from profiles of the acoustic backscatter intensity in which the shift between the low and the high turbulent regime is taken into account. Calibration constants and tuning parameters were estimated by using data collected during 7 different 13hour anchor stations. The residual (water) volume flux through the inlet appears to vary strongly on a variety of time scales from daily to inter-annual. A regression analysis indicates that the daily residual volume transport correlates well with the daily mean wind component from the south; the latter likely drives the residual flow along the coast of Holland. The observed residual SPM transport of 7 to 11Mton/yr is dominated by the correlation between tidal velocity and SPM concentration variations. This leads to an import as currents and SPM concentrations during flood were higher than those during ebb, a process generally known as tidal asymmetry. Our analysis has shown that regular observations with a ferry mounted ADCP is an effective method to monitor the volume and SPM transport processes in an estuary.

Spring 2009 water mass distribution, mixing and transport in the southern Adriatic after a low production of winter dense waters

Enhanced mixing of North Adriatic Dense Water (NAdDW) occurs in a strong frontal region as this cold and fresh intermediate water enters the southern Adriatic basin and meets warm and salty Modified Levantine Intermediate Water (MLIW) coming from the Ionian Sea. This study examines how NAdDW was mixed and transformed as it traveled southward from the Gargano to the Bari region and investigates the pathway and intrusion patterns of MLIW in late winter/spring 2009. Hydrographic data are analyzed to compute source water fractions via a least-squares analysis method and combined with ADCP data to compute source water volume fluxes. Results show that despite an anomalous low year for NAdDW production in the Adriatic, a warmer, fresher and lighter version of traditional NAdDW (i.e. 2009 NAdDW) endured its journey from Gargano to Bari. In the Gargano region, 2009 NAdDW (with fractions up to 80–90%) traveled southward in a non-continuous thin, dense vein between 35m and 100m isobaths, with diluted cores (>50%) extending to 140m depth, and with fluxes of −0.05Sv, to the southeast, south of Palagruz˘a Sill. Near the sill, 2009 NAdDW was further mixed and diluted with MLIW and surface water. By the time it reached the Bari region, the 2009 NAdDW fraction in the water column was reduced to about 20%. MLIW intrusions observed over the Sill and in northern sections of the study area suggest a splitting of MLIW pathways (stemming from the main South Adriatic rim pathway) towards the central Adriatic. Source water fraction results combined with velocity and seismic oceanography data show that eddies in the study area are one mechanism for the generation of MLIW intrusions towards the northwest.

Spray Measurements of an Upright Fire Sprinkler

Measurements were conducted to characterize the spray patterns of an upright fire sprinkler in the near and far field of the sprinkler. The spatial distribution of droplet size, velocity and number density in the spray was measured using a laser-based shadow-imaging system. The water volume flux distribution was measured by an array of pressure-transducer-equipped water collection tubes and containers. A large-scale traverse was constructed to move the laser optics and water collection tubes and containers to the designated measurement locations. An upright fire sprinkler with a K-factor of 162 lpm/bar1/2, installed with its deflector 0.17 m below a flat horizontal ceiling, was characterized at two discharge pressures, i.e., 0.76 bar and 1.31 bar. In the near field at 0.76 m from the sprinkler, measurements were performed in a spherical coordinate at different azimuthal and elevation angles with respect to the sprinkler deflector. In the far field, the sprays were mapped out in a 110° circular sector at 3.05 m and 4.57 m below the ceiling. The shadow-imaging based water flux measurements were verified by the measurements obtained from water collection containers. Except for the pipe effect, the azimuthal distributions of the flow rate showed that the spray pattern was more influenced by the frame arms than by the deflector tines and slots. The gross droplet size distribution was expressed as a combination of a log-normal function and Rosin–Rammler function. The median droplet diameter was correlated as an empirical function of the sprinkler orifice diameter and operating pressure. The near-field distributions of the droplet size, velocity and flux can be used to prescribe the starting spray conditions for numerical simulations of spray transport. The far-field measurements are useful in evaluating the spray transport calculations.

Endothelial barrier dysfunction in diabetic conduit arteries: a novel method to quantify filtration

The endothelial barrier plays an important role in atherosclerosis, hyperglycemia, and hypercholesterolemia. In the present study, an accurate, reproducible, and user-friendly method was used to further understand endothelial barrier function of conduit arteries. An isovolumic method was used to measure the hydraulic conductivity (L(p)) of the intact vessel wall and medial-adventitial layer. Normal arterial segments with diameters from 0.2 to 5.5 mm were used to validate the method, and femoral arteries of diabetic rats were studied as an example of pathological specimens. Various arterial segments confirmed that the volume flux of water per unit surface area was linearly related to intraluminal pressure, as confirmed in microvessels. L(p) of the intact wall varied from 3.5 to 22.1 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 7-180 mmHg. Over the same pressure range, L(p) of the endothelial barrier changed from 4.4 to 25.1 × 10(-7) cm·s(-1)·cmH(2)O(-1). During perfusion with albumin-free solution, L(p) of rat femoral arteries increased from 6.1 to 13.2 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 10-180 mmHg. Hyperglycemia increased L(p) of the femoral artery in diabetic rats from 2.9 to 5.5 × 10(-7) cm·s(-1)·cmH(2)O(-1) over the pressure range of 20-135 mmHg. In conclusion, the L(p) of a conduit artery can be accurately and reproducibly measured using a novel isovolumic method, which in diabetic rats is hyperpermeable. This is likely due to disruption of the endothelial glycocalyx.

Spray characterization measurements of a pendent fire sprinkler

The spray patterns of a pendent fire sprinkler were characterized through experimental measurements in the near and far field of the sprinkler. A laser-based shadow-imaging system was used to measure the droplet size, velocity and number density in the spray. An array of pressure-transducer-equipped water collection tubes and containers provided a separate set of water volume flux measurements. A large-scale traverse was constructed to move the laser optics and water collection tubes and containers to the designated measurement locations. A pendent fire sprinkler with K-factor of 205lpm/bar1/2 (14.2gpm/psi1/2) was characterized at two discharge pressures 3.5bar and 5.2bar (50 and 75psi). In the near field at 0.76m from the sprinkler, measurements were performed in a spherical coordinate at different azimuthal and elevation angles with respect to the sprinkler deflector. In the far field, the sprays were mapped out in a 110° circular sector at 3.05m and 4.57m below the ceiling. The shadow-imaging based water flux measurements were verified by the measurements obtained from water collection containers. The measurements show that the spatial distributions of water volume flux, droplet size and velocity of sprinkler sprays are strongly influenced by the sprinkler frame arms and the configuration of sprinkler deflector’s tines and slots. For the purpose of fire protection analysis, empirical correlations were developed from the near-field measurements to prescribe the spray starting conditions for the numerical modeling of spray transport through fire plumes. The far-field measurements can be used to evaluate the spray transport calculations.

Wind forcing of salinity anomalies in the Denmark Strait overflow

Abstract. The overflow of dense water from the Nordic Seas to the North Atlantic through Denmark Strait is an important part of the global thermohaline circulation. The salinity of the overflow plume has been measured by an array of current meters across the continental slope off the coast of Angmagssalik, southeast Greenland since September 1998. During 2004 the salinity of the overflow plume changed dramatically; the entire width of the array (70 km) freshened between January 2004 and July 2004, with a significant negative salinity anomaly of about 0.06 in May. The event in May represents a fresh anomaly of over 3 standard deviations from the mean since recording began in 1998. The OCCAM 1/12° Ocean General Circulation Model not only reproduces the 2004 freshening event (r=0.96, p<0.01), but also correlates well with salinity observations over a previous 6 year period (r=0.54, p<0.01), despite the inevitable limitations of a z-coordinate model in representing the mixing processes at and downstream of the Denmark Strait sill. Consequently the physical processes causing the 2004 anomaly and prior variability in salinity are investigated using the model output. Our results reject the hypotheses that the anomaly is caused by processes occurring between the overflow sill and the moorings, or by an increase in upstream net freshwater input. Instead, we show that the 2004 salinity anomaly is caused by an increase in volume flux of low salinity water, with a potential density greater than 27.60 kg m−3, flowing towards the Denmark Strait sill in the East Greenland Current. This is caused by an increase in southward wind stress upstream of the sill at around 75° N 20° W four and a half months earlier, and an associated strengthening of the East Greenland Current.

Mixing in the stratified interface of the Faroe Bank Channel overflow: The role of transverse circulation and internal waves

The overflow of cold water across the Faroe Bank Channel sill is a significant volume flux of dense water to the North Atlantic Ocean. Using observations of hydrography, current and microstructure from a 1 week cruise and 2 month long time series from moored instruments, we address the role of transverse circulation and internal waves in mixing in the stratified 100 m thick plume‐ambient interface. The streamwise momentum budget is dominated by a balance between the pressure gradient and bottom friction; the entrainment stress is negligible. The transverse momentum budget is in geostrophic balance, and the transverse velocity variability is governed by the internal streamwise pressure gradient. The transverse geostrophic flow in the interfacial layer is opposed by the bottom Ekman transport. The shear associated with the interfacial jet lowers the Richardson number and enhances dissipation rates. Convective overturning events observed on the upslope side suggest a link between the transverse circulation and the vertical mixing on the upper slope. Several independent threads of evidence support the transverse circulation as an important mixing mechanism for the overflow plume. In the ambient, dissipation rates inferred from fine‐scale shear and density profile measurements are in good agreement with direct measurements, supporting internal wave breaking as a dominant mechanism for dissipation of turbulent energy. In the interfacial layer, spectral distribution of internal wavefield is energetic. In addition to shear‐induced mixing and entrainment in the interfacial layer, internal wave breaking is likely to be important for the dissipation of turbulent energy and should not be ignored.

Water Content Wave Approach Applied to Neutron Radiographs of Finger Flow

Finger flow along distinct paths in homogeneous soils and other porous media is well known, but its characterization and quantification with existing approaches is challenging. Neutron radiography produces 2‐d images of water content distributions that allow testing of a water content wave approach to finger flow. Neutron radiographs were taken every 25 s during finger flow in a sand box that was 200 mm wide, 400 mm deep, and 5 mm thick. The sand was sieved to 0.2‐ to 0.5‐mm diameter. The area of finger flow was 30 mm wide. We approached water content variations during infiltration and redistribution in the finger flow area with a water content wave model that assumes gravity as the driving force and viscosity to oppose it. The two model parameters are thickness of the water film F (μm) and its contact length L (m−1) per unit cross‐sectional area A (m2) between the film and the stationary parts of the sand–water–air system. The velocity vW (m s−1) of the wetting front is an exclusive function of F, while mobile water content and volume flux density are functions of L and F We observed constant vW across the entire depth of investigation, which indicates constant F despite the considerable spatial variations in bulk density and porosity. The contact length L expresses the surface area per unit volume of the medium onto which momentum dissipates. The value of L compared well with the estimated surface area per volume of the smallest sand fraction during unhampered flow; however, it increased drastically when flow was influenced by the capillary fringe at the bottom of the sand box.

Flux comparison of Eulerian and Lagrangian estimates of Agulhas leakage: A case study using a numerical model

Estimating the magnitude of Agulhas leakage, the volume flux of water from the Indian to the Atlantic Ocean, is difficult because of the presence of other circulation systems in the Agulhas region. Indian Ocean water in the Atlantic Ocean is vigorously mixed and diluted in the Cape Basin. Eulerian integration methods, where the velocity field perpendicular to a section is integrated to yield a flux, have to be calibrated so that only the flux by Agulhas leakage is sampled. Two Eulerian methods for estimating the magnitude of Agulhas leakage are tested within a high-resolution two-way nested model with the goal to devise a mooring-based measurement strategy. At the GoodHope line, a section halfway through the Cape Basin, the integrated velocity perpendicular to that line is compared to the magnitude of Agulhas leakage as determined from the transport carried by numerical Lagrangian floats. In the first method, integration is limited to the flux of water warmer and more saline than specific threshold values. These threshold values are determined by maximizing the correlation with the float-determined time series. By using the threshold values, approximately half of the leakage can directly be measured. The total amount of Agulhas leakage can be estimated using a linear regression, within a 90% confidence band of 12 Sv. In the second method, a subregion of the GoodHope line is sought so that integration over that subregion yields an Eulerian flux as close to the float-determined leakage as possible. It appears that when integration is limited within the model to the upper 300 m of the water column within 900 km of the African coast the time series have the smallest root-mean-square difference. This method yields a root-mean-square error of only 5.2 Sv but the 90% confidence band of the estimate is 20 Sv. It is concluded that the optimum thermohaline threshold method leads to more accurate estimates even though the directly measured transport is a factor of two lower than the actual magnitude of Agulhas leakage in this model.

Hydrodynamics of the Segara Anakan lagoon

A hydrodynamic field study of the Segara Anakan lagoon combined with a reconstruction of the recorded data using a three-dimensional numerical model provides insights into the processes driving the hydrodynamics of the lagoon. This includes bathymetry, quantification of water volume fluxes with ADCP measurements, sea level recordings, salinity measurements, water budget and numerical model results for the periods of the field studies. Salinity measurements at the Klaces village show a complete flushing of the western lagoon during neap tide in the rainy season, which is assumed to increase the sedimentation. Mean salinities of the western part are in the order of 10 and 21 g/kg, while the eastern part has a larger mean salinity of 27 and 32 g/kg for the rainy and dry season, respectively. A numerical sensitivity study shows a relationship between the Citanduy discharge and the nett water volume transport between the eastern and western part of Segara Anakan. A nett transport to the west, which differs from neap to spring tides, turns to zero when Citanduy discharges are between 300 and 400 m3/s. The flushing time of the lagoon depends on the monsoon season and is about 1–3 days at the western outlet and increases to 12 days in the central parts.

Effect of Wind and Rainfall on Water Exchange in a Stratified Estuary

This study was conducted to estimate the horizontal and vertical exchange of water in response to meteorological effects in Inohana Lake, Japan. To examine the horizontal water flow between Hamana and Inohana Lakes while monitoring horizontal and vertical exchanges of water within the lake, we determined the current velocity, salinity, and water density in the field. We performed regression analysis of the relationship between meteorological factors such as wind and rain and the horizontal water flow between the two lakes. This information was then used to construct a simple box model to estimate the average water exchange and evaluate the meteorological effect based on the average salinity and river discharge. These results revealed that the surface water-volume flux in the channel was heavily influenced by the north–south wind intensity. These findings indicate that a box model is capable of providing a good estimate of the summer-averaged water flow and the exchange rate that is influenced by wind and rain.

On the relation between excess hydraulic head and flow in a conduit imbedded within a porous matrix

This article provides a partial answer to the question “What is the relation between excess hydraulic head and volume flux of water in a conduit within a porous matrix?”, focusing on the case that the forcing is steady. The conduit is modelled as a horizontal circular cylinder, imbedded within a porous matrix of rectangular cross section, having constant head prescribed on the sidewalls and being confined top and bottom. Laminar flow in the matrix is assumed to obey Darcy's law, while turbulent flow in the conduit is quantified using the Darcy–Weisbach equation. Analysis of the latter equation shows that the length scale of variations in the direction of the conduit is large compared with the scale of lateral and vertical variations. This permits separation of the full three-dimensional non-linear problem into a two-dimensional linear problem for head within the matrix and a one-dimensional non-linear problem for head within the conduit. Analytic solutions are obtained for the distribution of head in the matrix and in a conduit of either infinite or finite length. In both cases, the volume flux of water is proportional to the excess head to the 2/3 power, the conduit radius to the 5/3 power, the matrix permeability to the 1/3 power and gravity to the 1/3 power. The scale of variation of head along the conduit is proportional to the excess head to the −1/3 power, the conduit radius to the 5/3 power, the matrix permeability to the −2/3 power and gravity to the 1/3 power.

A Study on Process of Water Exchange in Inohana Lake

During the summer of 2005, we carried out an intensive field survey of current velocity, salinity, temperature, and water density in Inohana Lake, Japan, which is a semi-enclosed and highly stratified estuary. Field and meteorological data were used to investigate the characteristics of currents, and to estimate water-volume and salt fluxes as a measure of water and material exchanges. We undertook a test using a simple box model based on the average salinity and river discharge, and obtained the exchanges of waters between Inohana and Hamana Lakes and within Inohana Lake, respectively. In terms of water exchanges between the two lakes and within Inohana Lake, wind effects were dominant over tide. In terms of water exchange rate between the two lakes, the water-volume flux was about five times as great as freshwater inflow. The water-volume flux between two lakes estimated from the box model showed good agreement with the observed ones by the ADCR In the box model, the contribution of advection was larger than that of diffusion for the vertical water exchange. The vertical salt flux was estimated using two methods: the direct estimation from field data and a turbulent diffusion model. The turbulent diffusion model showed good agreement with the direct estimation by removing fluctuations with frequency less than 0.2 Hz from the velocity and salinity data.

Vertical and Lateral Mixing Processes Deduced from the Mediterranean Water Signature in the North Atlantic

Abstract The conservation equations of heat, salt, and mass are combined in such a way that a simple relation is found between the known volume flux of Mediterranean Water entering the North Atlantic Ocean and the effects of lateral and vertical mixing processes. The method is a form of inverse method in which the only unknowns are the vertical and lateral diffusivities. For each isohaline contour on each neutral density surface the authors develop one equation in two unknowns, arguing that other terms that cannot be evaluated are small. By considering several such isohaline contours, the method becomes overdetermined for each density layer, and results are found for both the vertical and lateral diffusivity that vary smoothly in the vertical direction, giving some confidence in the method.

An ecosystem modeling approach to predicting cod recruitment

Abstract The Norwegian Ecological Model (NORWECOM) biophysical model system implemented with the ROMS ocean circulation model has been run to simulate conditions over the last 25 years for the North Atlantic. Modeled time series of water volume fluxes, primary production, and drift of cod larvae through their modeled ambient temperature fields have been analyzed in conjunction with VPA estimated time series of 3-year-old cod recruits in the Barents Sea. Individual time series account for less than 50% of the recruitment variability; however, a combination of simulated flow of Atlantic water into the Barents Sea and local primary production accounts for 70% of the variability with a 3-year lead. The associated regression predicts increased recruitment between 2007 and 2008 from about 450–700 million individuals with a standard error of nearly 150 million.

The Role of Headwater Streams in Downstream Water Quality1

Knowledge of headwater influences on the water-quality and flow conditions of downstream waters is essential to water-resource management at all governmental levels; this includes recent court decisions on the jurisdiction of the Federal Clean Water Act (CWA) over upland areas that contribute to larger downstream water bodies. We review current watershed research and use a water-quality model to investigate headwater influences on downstream receiving waters. Our evaluations demonstrate the intrinsic connections of headwaters to landscape processes and downstream waters through their influence on the supply, transport, and fate of water and solutes in watersheds. Hydrological processes in headwater catchments control the recharge of subsurface water stores, flow paths, and residence times of water throughout landscapes. The dynamic coupling of hydrological and biogeochemical processes in upland streams further controls the chemical form, timing, and longitudinal distances of solute transport to downstream waters. We apply the spatially explicit, mass-balance watershed model SPARROW to consider transport and transformations of water and nutrients throughout stream networks in the northeastern United States. We simulate fluxes of nitrogen, a primary nutrient that is a water-quality concern for acidification of streams and lakes and eutrophication of coastal waters, and refine the model structure to include literature observations of nitrogen removal in streams and lakes. We quantify nitrogen transport from headwaters to downstream navigable waters, where headwaters are defined within the model as first-order, perennial streams that include flow and nitrogen contributions from smaller, intermittent and ephemeral streams. We find that first-order headwaters contribute approximately 70% of the mean-annual water volume and 65% of the nitrogen flux in second-order streams. Their contributions to mean water volume and nitrogen flux decline only marginally to about 55% and 40% in fourth- and higher-order rivers that include navigable waters and their tributaries. These results underscore the profound influence that headwater areas have on shaping downstream water quantity and water quality. The results have relevance to water-resource management and regulatory decisions and potentially broaden understanding of the spatial extent of Federal CWA jurisdiction in U.S. waters.

Molecular and functional characterization of aquaporin 1 in Japanese quail kidneys

Water conservation by urine concentration is one of the most fundamental functions of avian and mammalian kidneys. Birds can produce hyperosmotic urine by a countercurrent multiplier mechanism, but the urine concentration capacity is lower than in mammals. In avian kidneys, loopless nephrons are in superficial zones, whereas looped nephrons without a thin ascending limb are in deeper zones. We reported that Japanese quail, Coturnix japonica, express a vasotocin (AVT, avian ADH)-dependent water channel (qAQP2) in apical/subapical areas of cortical and medullary collecting ducts (CDs). Enhancement of water permeability or volume flux by AVT, however, is only modest in CDs perfused in vitro, whereas normally hydrated avian kidneys reabsorb over 90% of filtered water. Hence, we hypothesized that bird kidneys should express AVT-independent water channels. Using reverse RT-PCR cloning techniques, we found a full-length cDNA encoding a 270-amino acid sequence with, respectively, 82%, 77%, and 60% identity to rat AQP1, frog FA-CHIP, and eel AQP1. The clone has six transmembrane domains, two NPA sequences, and a mercury-sensitive (C189) site. Phylogenetic analysis (Clustal X 1.83) of the AQP superfamily revealed that this clone is clustered into the AQP1 subset. The qAQP1 protein shows high water permeability and is selectively inhibited by HgCl2 in a Xenopus expressing system. qAQP1 mRNA was detected (real time-PCR) in the brain, intestine, heart, adrenal glands, liver, and kidney (higher in the superficial than in the medullary zone). Immunoreactive qAQP1 protein is expressed in proximal tubule brush-borders, but not in CDs. These results suggest that the quail kidney has a functional AQP1 homologue channel that likely accounts for water movement across proximal renal tubules. Supported by NSF grant IOB0615359 and NIH grant HL52881.

The Arctic and Subarctic Ocean Flux of Potential Vorticity and the Arctic Ocean Circulation*

Abstract According to observations, the Arctic Ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges. In each deep basin, the circulation is also believed to be cyclonic. This circulation pattern has been used as an important benchmark for validating Arctic Ocean models. However, modeling this grand circulation pattern with some of the most sophisticated ocean–ice models has been often difficult. The most puzzling and thus perhaps the most interesting finding from the Arctic Ocean Model Intercomparison Project (AOMIP), an international consortium that runs 14 Arctic Ocean models by using the identical forcing fields, is that its model results can be grouped into two nearly exact opposite patterns. While some models produce cyclonic circulation patterns similar to observations, others do the opposite. This study examines what could be possibly responsible for such strange inconsistency. It is found here that the flux of potential vorticity (PV) from the subarctic oceans strongly controls the circulation directions. For a semienclosed basin like the Arctic, the PV integral over the whole basin yields a balance between the net lateral PV inflow and the PV dissipation along the boundary. When an isopycnal layer receives a net positive PV through inflow/outflow, the circulation becomes cyclonic so that friction can generate a flux of negative PV to satisfy the integral balance. For simplicity, a barotropic ocean model is used in this paper but its application to the 3D models will be discussed. In the first set of experiments, the model with a realistic Arctic bathymetry is forced by observed inflows and outflows. In this case, there is a net positive PV inflow to the basin, due to the fact that inflow layer is thinner than that of outflow. The model produces a circulation field that is remarkably similar to the one from observations. In the second experiment, the model bathymetry at Fram Strait is modified so that the same inflows and outflows of water masses lead to a net negative PV flux into the Arctic. The circulation is reversed and becomes nearly the opposite of the first experiment. In the third experiment, the net PV flux is made to be zero by modifying again the sill depth at Fram Strait. The circulation becomes two gyres, a cyclonic one in the Eurasian Basin and an anticyclonic one in the Canada Basin. To elucidate the control of the PV integral, a second set of model experiments is conducted by using an idealized Arctic bathymetry so that the PV dynamics can be better explained without the complication of rough topography. The results from five additional experiments that used the idealized topography will be discussed. While the model used in this study is one layer, the same PV-integral constraint can be applied to any isopycnal layer in a three-dimensional model. Variables that affect the PV fluxes to this density layer at any inflow/outflow channel, such as layer thickness and water volume flux, can affect the circulation pattern. The relevance to 3D models is discussed in this paper.

Assessment of fire protection performance of water mist applied in exhaust ducts for semiconductor fabrication process

Fume exhaust pipes used in semiconductor facilities underwent a series of fire tests to evaluate the performance of a water mist system. The parameters considered were the amount of water that the mist nozzles used, the air flow velocity, the fire intensity and the water mist system operating pressure. In order to make a performance comparison, tests were also performed with a standard sprinkler system. The base case served as a reference and applied a single water mist nozzle (100 bar operating pressure, 7.3 l/min water volume flux and 200 µm mean droplet size) installed in the pipe (60 cm in diameter) subjected to a 350°C air flow with an average velocity of 2 m/s. In such a case, the temperature in the hot flow dropped sharply as the water mist nozzle was activated and reached a 60°C saturation point. Under the same operating conditions, four mist nozzles were applied, and made no further contribution to reducing the fire temperature compared with the case using only a single nozzle. Similar fire protection performances to that in the base case were still retained when the exhaust flow velocity increased to 3 m/s and the inlet air temperature was increased to 500°C due to a stronger input fire scenario, respectively. Changing to a water mist system produced a better performance than a standard sprinkler. With regard to the effect of operating pressure of water mist system, a higher operating pressure can have a better performance. The results above indicate that the droplet size in a water-related fire protection system plays a critical role. Copyright © 2005 John Wiley & Sons, Ltd.

The rate of inflow and mixing during deep‐water renewal in a sill fjord

We obtained high‐resolution data on a deep‐water renewal in the basin of Gullmar Fjord, Sweden, using an autonomous profiling platform. In the middle of the fjord, where the platform is anchored, renewal starts with the passage of a gravity current front and continues with a steady thickening of the new, oxygen‐rich, low‐nitrate bottom layer and an associated lifting of the old, oxygen‐depleted, high‐nitrate bottom water. The basin continuously fills to sill level during a period of 10 d. At the mouth of the fjord, a three‐layer structure develops. Renewal is driven by the density difference between the intermediate water inside and the new deep water outside the fjord. The volume flux is well predicted by a hydraulic exchange model in which the upper layer plays a passive role. Local upwelling and downwelling of the upper halocline cause fluctuating baroclinic currents during renewal, but these seem to have little influence on the average volume flux of new deep water. Entrainment rates are small, and the associated volume flux increase seems to be balanced by detrainment.