Search

Accurate prediction of the hydraulic effect of hydrate deposition and plug location is critical to the safety and operability of natural gas transport pipelines, especially for gas-dominant subsea pipelines where maintenance and intervention activities are more difficult. To achieve this, the present work improved an existing two-phase pressure drop relation due to friction, by incorporating the hydrates deposition rate into the equation. In addition, a model has been developed to predict the pipeline plugging time. The transient pressure drop predictions in the present study for all six cases at high and low velocities are within 4% mean relative error. Similar predictions by Di Lorenzo et al. are within 40% maximum relative error, while the mean relative error of the transient pressure drop predictions by Zhang et al. was 7.43%. In addition, the plugging flowtime model underpredicts the plugging time by a mean relative error of 9%. [ABSTRACT FROM AUTHOR]

A hydro-dynamic thermal fully developed forced convective heat transfer analysis of magneto-hydrodynamics fluid flow through an annular sector duct is presented in this paper. Two types of thermal boundary conditions i.e., axially uniform heat flux along with peripherally uniform temperature (known as H1-condition) and, axially and peripherally uniform temperature (known as T condition), have been considered to carry out the thermal analysis of fluid. The velocity components along r and θ direction are transformed into algebraic form by using power law discretized scheme, whereas cross-sectional pressure P (r , θ) is estimated with the help of well know technique S I M P L E R. The governing partial differential equations are solved by numerically with the help of M A T L A B code. Furthermore, simulated results have been compared with the existing results of literature to validate the results. From the results, it is noted that hydro-dynamically and thermally impacts relate directly by increasing the Hartman number, (M). It is further reported that the effect of magnetic field becomes insignificant for the higher number of fins, N. The findings of the present analysis will be applicable in various types of thermal systems. [ABSTRACT FROM AUTHOR]

The detonation propagation characteristics of the mixtures, 2H 2 + O 2 +3Ar and CH 4 + 2O 2 , were investigated. Accordingly, the mixtures were tested in round tube with inner diameter of D = 80 mm and annular tubes with widths of w = 25 mm, 15 mm, and 5 mm. The two mixtures represent stable mixture with regular cell pattern and unstable mixture with irregular cell pattern, respectively. Smoked foils were utilized to record cellular structure under various initial conditions. Subsequently, the length scale L dsc was measured, which represents the length from the start of the test section to the position where the cellular structure changes drastically (the cell size obviously increases or the structure disappears). The results reveal that both mixtures can successfully propagate in round tube and annular tubes of 25 mm and 15 mm, but fail in 5 mm annular tube. The L dsc value of 2H 2 + O 2 + 3Ar is higher than that of CH 4 + 2O 2 in 80 mm and 15 mm tubes, but it is opposite in 25 mm tube. Moreover, the relationship between L dsc and hydraulic diameter D H was analysed. For a given tube, the values of L dsc and L dsc / D H increased when the initial pressure increased. And the variation trend of L dsc and L dsc / D H of CH 4 + 2O 2 is steeper. Furthermore, the mixtures 2H 2 + O 2 + 3Ar and CH 4 + 2O 2 resulted in over-driven detonation in 15 mm and 25 mm annular tubes, respectively. The ratio between the total reaction length (sum of the induction length and exothermic length) and the hydraulic diameter (D H /(Δ i + Δ e)) correspond to critical values of 18 for hydrogen-oxygen-argon and 6 for methane-oxygen, below which the detonation will fail. [ABSTRACT FROM AUTHOR]

The thermal performance of different cross-sectional areas of a U-shape ground-coupled heat exchanger (GCHE) is numerically investigated for summer and winter conditions in the present paper. The four different cross-sectional tubes, viz. square, circular, triangular, and rectangular, of fixed hydraulic diameter and length are considered. Numerical simulations are carried out for different velocities ranging from 2 m/s − 5 m/s using K-epsilon turbulent model. It is found that the rectangular cross-sectional area GCHE provides a more stable air temperature for both summer and winter conditioning, and a maximum temperature drop/rise is observed at a shorter length in this condition. The temperature drop of 14.2 K is observed at a length of 12.6 m in the case of GCHE with rectangular cross-section, while the same drop is reported at 19.2 m, 17.4 m, and 16.5 m for circular, square, and triangular cross-sectional areas, respectively. A maximum temperature rise of 8.3 K is reported at 14.8 m, 20.7 m, 18.2 m, and 17.5 m in rectangular, circular, square, and triangular cross-sectional GCHE for heating conditions. Therefore, the rectangular cross-section GCHE may be preferred for space constraints. The net temperature difference is found to be dependent on inlet air temperature. It increases with an increase in the inlet air temperature for summer cooling conditions and reverses in winter conditions. The inlet velocity greatly influences the thermal performance of GCHE, and optimum performance is found at a lower velocity of 2 m/s due to the more settling time. The effectiveness is found to increase initially along the length, and it attains a maximum value at a shorter length in the case of rectangular cross-section compared to other sections. The maximum effectiveness is achieved between 14 m to 15 m length of the pipe for the case of rectangular cross-sectional GCHE. [ABSTRACT FROM AUTHOR]

• Flow and heat transfer characteristics in CW-type PSHE are numerically studied. • The effect of hydraulic diameter is analyzed. • The effect of airflow shuttling on heat transfer enhancement is explained. • The local thermal resistance analysis method is applied. This paper numerically investigates the flow and heat transfer characteristics in the primary surface heat exchanger (PSHE) with cross-wavy (CW) structures. The comprehensive performance affected by hydraulic diameters is evaluated. Moreover, the airflow shuttling behavior at the mixing area of CW-type PSHE is discussed, showing rapid heat transfer enhancement. The advection thermal resistance method and local thermal resistance analysis is proposed, while the impacts of longitudinal pitch and flowrates are considered. Results show that the case with a large hydraulic diameter displays much better comprehensive performance at lower flowrates. When raising the hydraulic diameter from 1.58 mm to 15.8 mm, the heat transfer rate per unit pumping power grows by 36.1 %. However, the priority of large channel is gradually disappeared after increasing the flowrates. Meanwhile, the larger longitudinal pitch of the CW channel may result in pronounced improvement on the heat transfer performance due to the presence of airflow shutting behavior at the mixing area as well as the secondary flow near the channel boundary layers. When no airflow shuttling exists, very high advection thermal resistance region can be observed due to the formation of boundary layers. It can be recognized that the case with airflow shuttling behavior can display similar heat transfer improvement compared to that with increasingly high Reynolds numbers, yet the pressure loss is rarely increased. [ABSTRACT FROM AUTHOR]

The relevance of the work is caused by the wide use of porous media, both in the design and optimization of compact heat exchangers and in the engineering calculations of the characteristics of heat and mass transfer in the channels with a grainy medium and when flowing around the bodies immersed in the porous medium. The main aim of the research is the experimental study of heat transfer in an annular channel filled with a granular medium at various modes of liquid filtration; to obtain semi-empirical correlations for heat transfer in the inertial mode of fluid filtration in an annular channel. Objects: annular channel with a porous insert consisting of glass beads of the same diameter with different types of both regular and chaotic pakings. Methods: experimental methods for finding the patterns of heat exchange processes. In experiments, using thermocouples, the temperature of the heated outer wall of the annular channel was measured in four sections and the temperature of the heater at two different points. The temperatures at the inlet to the working station and at the output of it were measured as well. Simultaneously with thermal investigation, the fluid flow was measured when filtering through a porous insert. Porosity was determined by the usual weighty way. In special calibration experiments, the heat losses of the working section were determined separately. The calculation of the heat transfer coefficient was carried out according to the flow of heat to the outer wall of the annular channel, taking into account heat losses and, along the difference in the measured wall temperature and the medium-mass fluid temperature in this section. The paper introduces the results of the experimental study of liquid filtration flow heat exchange with the walls of the annular channel filled with a porous medium at constant heat flux on the outer wall. The study was conducted on ring channels with different widths. The width of the channel was laid either one layer of the balls of one diameter with two types of packages: cubic and rhombohedral, or several layers of balls, but already with arbitrary packaging (from 3 to 10 ball width). When processing the experimental data, hydraulic grain diameter is selected as the determining geometric parameter. It is shown that, depending on the filtration mode, various laws of heat exchange exist through a porous insert. So for the turbulent filtering mode, the obtained data for heat exchange is well summarized by the universal «law of two-thirds». The paper introduces the comparison with the data of other authors, both for heat exchange in the annular channel and in a round tube. It is shown that in the inertial mode of filtration, the heat exchange corresponds to the regularity of Nu~Re1/2.

The objective of this paper is to analyze the effect of hydraulic diameter and channel shape on the thermal and hydrodynamic characteristics of a microchannel cooled by Graphene–Platinum/water hybrid nanofluid for electronic cooling applications. The study was performed numerically using mathematical software called Maple 19.0. Microchannels having square and rectangular cross-sections, and hydraulic diameters ranging from 200 µm to 1,000 µm were taken into consideration. Thermal resistance, heat transfer coefficient, pressure drop, and friction factor were evaluated for different conditions and their corresponding graphs are presented and discussed. It was evident from the results that low thermal resistance and high heat transfer coefficient was achieved upon decreasing the hydraulic diameter, which is favorable for the cooling of electronic chips and devices. Based on the Reynolds number, the heat transfer coefficient increased by 2–4 times for both rectangular and square microchannels, on decreasing the hydraulic diameter from highest value (1,000 µm) to lowest value (200 µm). However, friction factor and pressure drop increased for channels with lower hydraulic diameters. In addition, rectangular microchannels exhibited better heat transfer performance, while square microchannels had lower friction factor and pressure drop. Rectangular microchannels presented a maximum enhancement of 30% in heat transfer coefficient and a reduction of 18% in thermal resistance, when compared to square microchannels. The results also suggested that the performance of microchannels with 500 µm hydraulic diameter is balanced, considering both heat transfer performance and pressure drop constraints. [ABSTRACT FROM AUTHOR]

Extreme climatic events that are expected under global warming expose forest ecosystems to drought stress, which may affect the growth and productivity. We assessed intra-annual growth responses of trees to soil water content in species belonging to different functional groups of tree-ring porosity. We pose the hypothesis that species with contrasting carbon allocation strategies, which emerge from different relationships between wood traits and canopy architecture, display divergent growth responses to drought. We selected two diffuse-porous species (Acer saccharum and Betula alleghaniensis) and two ring-porous species (Quercus rubra and Fraxinus americana) from the mixed forest of Quebec (Canada). We measured anatomical wood traits and canopy architecture in eight individuals per species and assessed tree growth sensitivity to water balance during 2008–2017 using the standardized precipitation evapotranspiration index (SPEI). Stem elongation in diffuse-porous species mainly depended upon the total number of ramifications and hydraulic diameter of the tree-ring vessels. In ring-porous species, stem elongation mainly depended upon the productivity of the current year, i.e., number of vessels and basal area increment. Diffuse-porous and ring-porous species had similar responses to soil water balance. The effect of soil water balance on tree growth changed during the growing season. In April, decreasing soil temperature linked to wet conditions could explain the negative relationship between SPEI and tree growth. In late spring, greater water availability affected carbon partitioning, by promoting the formation of larger xylem vessels in both functional groups. Results suggest that timings and duration of drought events affect meristem growth and carbon allocation in both functional groups. Drought induces the formation of fewer xylem vessels in ring-porous species, and smaller xylem vessels in diffuse-porous species, the latter being also prone to a decline in stem elongation due to a reduced number of ramifications. Indeed, stem elongation of diffuse-porous species is influenced by environmental conditions of the previous year, which determine the total number of ramifications during the current year. Drought responses in different functional groups are thus characterized by different drivers, express contrasting levels of resistance or resilience, but finally result in an overall similar loss of productivity. [ABSTRACT FROM AUTHOR]

Various studies dealing with decay characteristics of circular and noncircular supersonic jets were conducted by previous researchers. But in these studies due emphasis was not given to the hydraulic diameter (Dh), shape factor (ζ) & the nozzle lip parameters which have significant impact on the characteristics of noncircular supersonic jet. In this study, it has been shown that these parameters played a significant role on supersonic core decay characteristics [2, 3, 6] of the jet. The scope of this study included supersonic core length (Lc), decay pattern, due to noncircular shaped nozzle. In the literature, the supersonic jet characterization and the related experimental correlation are available for optimum expansion conditions whereas for other expansion (under and over) conditions the experimental correlation is barely available. While investigating experimentally, new empirical relations were obtained which were the improved forms of earlier correlations for supersonic core length [4]. For experiments, six different types of nozzles (circular, hexagon, square, triangular, elliptical and rectangular) with the same exit to throat area ratio, convergent length and divergent length were used. The results obtained from the experimentally developed correlations were coherent with numerical results, experimental data and flow visualization.

• A 3D-CFD study has been carried out using RNG k–ɛ turbulence model. • Jet diameter ratio and jet height ratio are varied with Reynolds number. • A significant amount of heat transfer enhancement is achieved. • Best performance is found at jet height ratio of 0.216 with jet diameter ratio of 0.0650. • Maximum thermo-hydraulic performance parameter is determined as 3.66. Solar air heater is the simplest heating device for utilizing solar thermal energy. Jet impingement technique can be used to amplify the performance of a solar air heater by increasing the heat transfer between fluid and heated surface. Under the present study, an attempt has been made to carry out a numerical investigation on heat transfer behaviour of a solar air heater having absorber plate with impinging jet. 3D-Computational fluid dynamics (CFD) simulation using ANSYS-18.1 has been carried out with RNG k–ɛ turbulence model, and the upwind scheme is applied for the discretization of governing equations. Jet diameter ratio and jet height ratio are the considered system parameters, and their considered ranges are 0.065 to 0.195 and 0 to 0.433, respectively. The performance of solar air heater with jet impingement is investigated under different flow conditions taking Reynolds number ranging from 3500 to 17,500. It has been found that a significant increase in heat transfer for jet impinging solar air heaters is achieved in comparison to smooth solar air heater under similar operating conditions. The maximum heat transfer enhancement of 7.58 with a friction factor penalty of 9.01 times is obtained at jet diameter ratio of 0.0650 and jet height ratio of 0.216 for Reynolds number of 17,500. Maximum thermal-hydraulic performance parameter value of 3.66 is obtained correspond to jet height ratio of 0.216 and jet diameter ratio of 0.065 for Reynolds number of 15,500. [ABSTRACT FROM AUTHOR]

• Numeric analysis of the annular and circular pulse tube have been done and compared. • Heat transfer between gas and two walls has an apparent effect on the expansion efficiency of annular pulse tube. • Effects of pulse tube hydraulic diameter and wall thermal conductivity on the thermal performance are investigated. CFD models are used to study the performance of circular and annular pulse tubes working at 77–300 K. The oscillating flow and heat transfer characteristics are investigated. In terms of pulse tube impedance, simulation results indicate that the annular shape has negligible influence when the length and flow area are kept the same as circular pulse tube. However, compared with the circular pulse tube, the thermal performance of annular pulse tube apparently deteriorates which is mainly due to the increased thermal losses caused by heat transfer between the internal gas and two cylindrical tube walls (instead of one in the case of circular pulse tube). The expansion efficiency (defined as the enthalpy flow divided by acoustic power at the cold end) of annular pulse tube is lower by about 14% compared with that of circular pulse tube. Among the influencing factors, hydraulic diameter of annular pulse tube has a significant influence on the performance, and smaller hydraulic diameter leads to a reduced expansion efficiency. The effects of tube wall thermal conductivity are also discussed. This study provides a better understanding on the mechanism of annular pulse tube which sets the basis for optimizing a compact low temperature cryocooler for future applications. [ABSTRACT FROM AUTHOR]

Various studies dealing with decay characteristics of circular and noncircular supersonic jets were conducted by previous researchers. But in these studies due emphasis was not given to the hydraulic diameter (Dh), shape factor (ζ) & the nozzle lip parameters which have significant impact on the characteristics of noncircular supersonic jet. In this study, it has been shown that these parameters played a significant role on supersonic core decay characteristics [2, 3, 6] of the jet. The scope of this study included supersonic core length (Lc), decay pattern, due to noncircular shaped nozzle. In the literature, the supersonic jet characterization and the related experimental correlation are available for optimum expansion conditions whereas for other expansion (under and over) conditions the experimental correlation is barely available. While investigating experimentally, new empirical relations were obtained which were the improved forms of earlier correlations for supersonic core length [4]. For experiments, six different types of nozzles (circular, hexagon, square, triangular, elliptical and rectangular) with the same exit to throat area ratio, convergent length and divergent length were used. The results obtained from the experimentally developed correlations were coherent with numerical results, experimental data and flow visualization. [ABSTRACT FROM AUTHOR]

This paper investigated effects of slip length and hydraulic diameter on the hydraulic entrance length of laminar flow in superhydrophobic microchannels. Numerical investigations were performed for square microchannels with Re ranging between 0.1 and 1000. It is found that superhydrophobic microchannels have a longer hydraulic entrance length than that of conventional ones by nearly 26.62% at a low Re. The dimensionless hydraulic entrance length slightly increases with the increasing slip length at approximately Re<10, and does not vary with the hydraulic diameter. A new correlation to predict the entrance length in square microchannels with different slip lengths was developed, which has a satisfying predictive performance with a mean absolute relative deviation of 5.69%. The results not only ascertain the flow characteristics of superhydrophobic microchannels, but also suggest that super hydrophobic microchannels have more significant advantages for heat transfer enhancement at a low Re. [ABSTRACT FROM AUTHOR]

Aim: Tundra ecosystems are highly vulnerable to climate change, and climate–growth responses of Arctic shrubs are variable and altered by microsite environmental conditions and biotic factors. With warming and drought during the growing season, insect‐driven defoliation is expected to increase in frequency and severity with potential broad‐scale impacts on tundra ecosystem functioning. Here we provide the first broad‐scale reconstruction of spatio‐temporal dynamics of past insect outbreaks by assessing their effects on shrub growth along a typical Greenlandic fjord climate gradient from the inland ice to the sea. Location: Nuuk Fjord (64°30′N/51°23′W) and adjacent areas, West Greenland. Taxa: Great brocade (Eurois occulta L.) and grey willow (Salix glauca L.). Methods: We combined dendro‐anatomical and remote sensing analyses. Time series of ring width (RW) and wood‐anatomical traits were obtained from chronologies of >40 years established from 153 individuals of S. glauca collected at nine sites. We detected anomalies in satellite‐based Normalized Difference Vegetation Index (NDVI) related to defoliation and reconstructed past changes in photosynthetic activity across the region. Results: We identified outbreaks as distinctive years with reduced RW, cell‐wall thickness and vessel size, without being directly related to climate but matching with years of parallel reduction in NDVI. The two subsequent years after the defoliation showed a significant increase in RW. The reconstructed spatio‐temporal dynamics of these events indicate substantial regional variation in outbreak intensity linked to the climate variability across the fjord system. Main conclusions: Our results highlight the ability of S. glauca to cope with severe insect defoliation by changing carbon investment and xylem conductivity leading to high resilience and rapid recovery after the disturbance. Our multiproxy approach allows us to pinpoint biotic drivers of narrow ring formation and to provide new broad‐scale insight on the C‐budget and vegetation productivity of shrub communities in a widespread arctic ecosystem. [ABSTRACT FROM AUTHOR]

• Remote sensing indexes and tree-rings/wood anatomy data were compared. • High variability among sites and tree species in their responses to drought. • Ash seem to perform better then oak in terms of growth under drought. • Relevant effect for forest management and ecosystem services. Drought reduces canopy cover, productivity and tree growth in forests. However, there is still little knowledge on how drought affects coupling between canopy greenness assessed by remote sensing and hydraulic conductivity detected by wood anatomy. This combination could improve the understanding of forest response to climate change. Thus, we investigated the impacts of a hot drought, which occurred in summer 2017, on radial growth, earlywood hydraulic diameter (Dh), a proxy of conductivity, and several remote-sensing indices in mixed Mediterranean hardwood forests (Quercus pubescens Willd. – Fraxinus ornus L.). In general, growth showed a higher coherence among trees and a higher responsiveness to climate. Growth decreased during the drought year, particularly for Q. pubescens , which showed high defoliation and dieback intensity. Both species showed a decline of Dh in 2018 after the drought and subsequent warm winter conditions. We found positive relationships between Dh and remote-sensing data for Q. pubescens in some of these vulnerable sites, where (i) growth was constrained by dry spring-summer conditions and (ii) Dh and growth covaried. These findings indicate a high variability among sites and tree species in their responses to drought considering earlywood anatomy, growth canopy cover and water content. However, some common patterns emerge such as links between potential hydraulic conductivity (Dh), tree cover and Dh-growth covariation in the most impacted sites. Further, F. ornus seem to perform better in terms of growth under drought conditions, showing less mortality and dieback than Q. pubescens. Future studies could explore how water transport and changes in canopy cover respond to dry and warm conditions and if that covariation indicates vulnerability to drought. [ABSTRACT FROM AUTHOR]

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of Dh = 50, 100, 150, and 200 μm with constant channel aspect ratio of 0.5 and length of 2.4 mm were examined. Due to the different Dh, the applied heat and mass flux values varied between 20 to 200 kW/m2 and 150 to 2400 kg/m2s, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number Nuglob was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with Dh of 200 μm and four-parallel rectangular microchannels, each having a hydraulic diameter Dh of 50 μm. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance R¯l compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the R¯l by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms.

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An experimental study is conducted to investigate the effect of hydraulic diameter on the saturated flow boiling characteristics of deionized water in parallel rectangular microchannels. Experiments have been performed for the mass fluxes of 51, 65, 78 and 93 kg m−2 s−1, and the hydraulic diameters of 100, 150, 200 and 250 μm. The wall heat flux ranges from 35.9 to 105.6 kW m−2. To eliminate the effect of aspect ratio and to address clearly the effect of hydraulic diameter, all the channels are designed with square cross section. Flow visualization studies are performed for a better understanding of the underlying physical phenomena. Effects of heat flux, mass flux and vapor quality on the heat transfer and total pressure drop have been investigated, too. It is concluded that hydraulic diameter has significant influence on both of the local two phase heat transfer coefficient and the total pressure drop. [ABSTRACT FROM AUTHOR]

Anatomical traits such as xylem conduit diameter and vessel connectivity are fundamental characteristics of the hydraulic architecture of vascular plants. Stem xylem conduits are narrow at the stem apex, and this confers resistance to embolisms that might otherwise be induced by large, negative water potentials at the top of tall trees. Below the apex, conduits progressively widen and this characteristic minimizes effects of path length on total hydraulic resistance. While interconnections among xylem vessels have been noted for decades, their role(s) are not fully clarified. For example, we do not know if they allow water to bypass embolized vessels, or increase the risk of spread of embolisms, or how their arrangement varies within a tree. Here we demonstrate the benefit of removing the independent effect of stem length on assessment of effects of external (e.g. climatic) factors on such xylem traits. We measured the hydraulic diameter (Dh) and vessel conductivity index (VCI) along the stem of 21 shrubs/trees of similar height (1.19 < H < 5.45 m) belonging to seven Acacia species, across a wide aridity gradient in Australia. All trees showed similar scaling exponents of Dh (b = 0.33) and VCI (b = 0.53) vs axial distance from the apex (L), thus conforming with general patterns in woody plants. After de-trending for L, neither Dh (P = 0.21) nor VCI (P = 0.109) differed across the aridity gradient. We found that across a wide gradient of aridity, climate had no effect on xylem anatomy of Acacia spp, which was instead dictated by axial distances from stem apices. We argue that the use of standardization procedures to filter out intrinsic patterns of vascular traits is an essential step in assessing climate-driven modifications of xylem architecture. [ABSTRACT FROM AUTHOR]

Abstract In this paper methodologies are described for the analysis of the porous structure of cylindrical and annular packed beds consisting of spheres when the coordinates and sizes of the spheres are known. Methodologies to determine the overlap between adjacent spheres and between the spheres and the walls of the container; axial variation in the porosity and hydraulic diameter; and the radial variation in the porosity are described. The determination of the overall bulk porosity, as well as the average porosity of selected regions, from the results are also discussed. The methodologies are based on analytical geometry and Simpson's rule is used to perform the numerical integration of the relevant integrals. The validity of the methodologies is demonstrated and the application of the methodologies to analyse the porous structure of selected packed beds is illustrated. Graphical abstract Unlabelled Image Highlights • Analyse porous structure of packed bed when coordinates and size of spheres known. • Use analytical and semi-analytical methods to analyse porous structure. • Areas integrated using Simpson's rule with angular or axial increments. • Perform analysis of axial variation in porosity and hydraulic diameter. • Perform analysis of radial variation in porosity using line- and area-based methods. [ABSTRACT FROM AUTHOR]

Highlights • Air–water flow in serpentine mini and microchannels visualized by high speed camera. • Influence of orientation on flow regimes disappears for micro channel. • Horizontal orientation of serpentine micro channel prone to mal-distribution. • Serpentine micro channel favors the formation of annular flow. • Vertical serpentine micro channel drains water easily, desired for PEMFC. • Modified friction factor proposed for predicting the pressure drop. Abstract Ex-situ experimental investigation of air–water two phase flow characteristics are carried out in rectangular serpentine mini and micro-channels. The test sections to be studied are made up of acrylic and are of three different hydraulic diameters of 1.65 mm, 1.00 mm and 0.65 mm with the corresponding length of 50 mm. Experiments are performed for different combinations of superficial velocities of air and water ranging between 0.0011 m/s and 0.33 m/s and 0.33 m/s to 16.66 m/s, respectively. The effect of channel orientation on various parameters is also studied. The visualisation of two phase is accomplished by high-speed camera. The flow pattern maps developed by closely scrutinizing each flow rate combinations are presented. Mal-distribution occurred in horizontal orientation of micro channel. However, vertical orientation of micro channel favoured draining of water, thereby encountered lesser pressure drop than mini channel. New correlation based on various dimensionless numbers has been proposed for modelling the pressure drop. [ABSTRACT FROM AUTHOR]

Improper sizing of pipelines and production tubings in the petroleum industry is often caused by lack of understanding of three-phase flow, which is characterized by gas flowing together with an immiscible water-oil mixture. There is the presence of a continuous liquid phase and a liquid dispersed phase, as observed in liquid-liquid flows, i.e., one can observe either a dispersion or emulsion of oil in water (o/w) or dispersion or emulsion of water in oil (w/o). The transition from o/w to w/o, or the other way around, is defined as phase-inversion. This phenomenon is characterized by a sharp increase in the pressure gradient, leading to significant pressure loss in the oil production system. The goal is to investigate the effects of oil viscosity, channel geometry (circular pipe or annular duct) and superficial gas velocity on the phenomenon of phase inversion in vertical liquid-liquid-gas flows, using oil with three different viscosities (ranging from 70 mPa s to 280 mPa s), tap water and compressed air as working fluids. The experiments were carried out in three different geometries: (i) glass pipe of 50 mm i.d., (ii) glass pipe of 95 mm i.d. and (iii) concentric annular duct with 95 mm of hydraulic diameter (glass outer pipe and PVC internal pipe). The experiments were performed under equivalent Reynolds number to evaluate the geometry effect. New data as total pressure gradient and volumetric fractions were obtained for all geometries. The results suggest that the extrapolation of results obtained in circular pipes with low viscosity oil and low gas flow rates to annular-duct flow with viscous oils and high gas flow rates can lead to significant errors. [ABSTRACT FROM AUTHOR]

Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R2 > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R2 = 84.11%) for the whole set of experiments