Vertical Upward Research Articles

Numerical Analysis of Mechanism on Heat Transfer Deterioration of Hexamethyldisiloxane in a Vertical Upward Tube at Supercritical Pressures

Numerical Analysis of Mechanism on Heat Transfer Deterioration of Hexamethyldisiloxane in a Vertical Upward Tube at Supercritical Pressures

Variability and connectivity in populations of different limpet species across rockpool-generated mosaic landscapes

Limpets are keystone grazers on rocky shores. We studied spatial patterns of four co-occurring patellids (Patella ulyssiponensis, Patella depressa, Patella rustica, Patella vulgata) and one siphonariid (Siphonaria pectinata) across rockpools and their surrounds. Our approach considered each rockpool as a concentric system of three micro-habitats where limpets were censused (species, counts, and size of individuals): inside rockpool, edge zone, and surrounding open-rock. The whole intertidal zone was sampled on six rocky shores with contrasting landscape variability (amount of open-rock and other micro-habitats) in Southwest Portugal. Additionally, open-rock surfaces far away (>25cm) from rockpools were surveyed on the mid-shore. Three groups of predictors (“physical, habitat-composition, and connectivity variables”) were assessed for each rockpool system. Limpets of various sizes of the three most common species—P. ulyssiponensis, P. depressa, and S. pectinata—were found to coexist inside and outside rockpools on all shores, with rockpools extending their vertical distribution upwards. Patella vulgata was rare; P. rustica was absent from rockpools and their edges. Intra-specific connectivity (correlations in density of the same species between adjacent micro-habitats) showed a decreasing gradient with distance from the pool, being sharper for P. ulyssiponensis (a largely rockpool-resident) than for P. depressa and S. pectinata (suggesting their emergence from rockpools to edges and surrounding open-rock). Abundance and size structure of both P. depressa and S. pectinata were similar on mid-shore open-rock surrounding rockpools and far from rockpools. Landscape variability explained distribution of P. depressa (shores with less open-rock had more and smaller limpets). Habitat-composition (assemblages and substrata) was more important than physical predictors in explaining among-rockpool variability of each limpet species. Densities of P. ulyssiponensis and P. depressa inside rockpools were positively associated with cover of coralline algae and negatively associated with sand cover. Less explanatory power was found in predictive models of S. pectinata, suggesting a more opportunistic nature. There was limited evidence of inter- or intra-specific competition of the three species in rockpools and open-rock. Competition between P. ulyssiponensis and P. depressa was most likely in rockpool edges. Rockpool-generated mosaic landscapes are linked by intra-specific connectivity of limpet populations and modulated by interactions among different limpet species.

Numerical simulation of boiling behavior in vertical microchannels

High heat flux electronic devices put forward new requirements for heat dissipation, and boiling heat transfer technology is widely used because of its higher heat dissipation capacity. In this study, the volume of fluid method was employed, along with the incorporation of the Lee phase-change mass transfer model, to investigate two-phase flow and heat transfer in vertical upward rectangular microchannels. The heat flux was varied within the range of 10–40 kW/m2, while the mass flux was varied within the range of 200–600 kg/m2 s. With the increase in heat flux, bubble flow, slug flow, churn flow, and annular flow were found successively. A phase diagram was established to predict the flow pattern transition during the boiling process. When the flow pattern changes to the churn and the annular flow, the active nucleation site density increases obviously with the Boiling number (Bo). A new correlation was proposed for two-phase flow boiling heat transfer, suitable for vertical upward channels in microscale fluids. The friction factor obtained using the Darcy friction factor equation agrees well with the simulation results at a high-pressure drop. The instability in microchannels increases with the increase in heat flux, particularly in annular flow, resulting in more severe wall temperature fluctuations.

Local Government Vertical Upward Accountability, Oversight, and the Intervention Mechanism in South Africa

Since democratisation, South Africa has struggled to create a stable system of local governance. There are constant municipal failures. Higher levels of government have to intervene in municipalities regularly. This study, therefore, set out to assess the effect of intervention mechanisms, including preventative measures, as part of the broader accountability and oversight setting. Based on a qualitative research approach, this paper argues that both prospective and retrospective accountability forms are weak. Post-factum interventions yield only limited results. Overall, these mechanisms are not able to form stable local governments and prevent municipal failures. Ultimately, this paper infers that strengthening prospective accountability and oversight mechanisms has the capacity to increase the stability of the local governance system. This finding has important implications for developing new accountability and oversight practices in South Africa and elsewhere.

Spatio-Temporal Analysis of Simulated Summer Extreme Precipitation Events under RCP4.5 Scenario in the Middle and Lower Reaches of the Yangtze River Basin

In the context of global warming, the frequency and intensity of extreme climate events, especially extreme precipitation events, have increased. The middle and lower reaches of the Yangtze River Basin are important areas for economic development, and are also one of the areas where rainstorms and flood disasters frequently occur in China. Improving the prediction of future summer extreme precipitation in this region under the greenhouse gas emission pathway that aligns with sustainable economic development (Representative Concentration Pathway 4.5, RCP4.5) will help decision-makers better cope with the impact of increased natural disasters, such as floods. The medium-resolution CESM1.0 (Community Earth System Model 1.0) data (1° × 1°) has limitations in capturing regional climate differences. Therefore, we designed a downscale experiment using the WRF3.8 (Weather Research and Forecasting 3.8) model to obtain the daily summer precipitation grid data with 0.25° × 0.25° latitude and longitude resolution over the middle and lower reaches of the Yangtze River Basin from May to September in 2006–2030 (WRF025). The research shows that the WRF025 data is reliable in simulating the summer extreme precipitation events over the middle and lower reaches of the Yangtze River Basin, especially in the lower reaches of the Yangtze River. Compared to CESM1.0 data, WRF025 data significantly improves the ability to simulate the numerical value and distribution of summer extreme precipitation in the middle and lower reaches of the Yangtze River. Under the RCP4.5 scenario, compared to 2006–2014, there is no significant change in daily summer precipitation in the middle and lower reaches of the Yangtze River Basin during 2015–2030, with a significant decrease in daily summer extreme precipitation. There are significant regional differences in spatial distribution, with a significant decrease in Hunan and Hubei, and a significant increase in Jiangxi and Fujian. Under high-pressure control, the lower reaches of the Yangtze River are dominated by downdraft, resulting in more sunny days and less precipitation. The increase (decrease) in water vapor transport and divergence may be the reason for the increase (decrease) in extreme precipitation. The most direct factor leading to an increase (decrease) in extreme precipitation is the vertical movement upwards (downwards). Furthermore, the anomalous descent (ascent) can be well explained by the easterly (westerly) wind anomaly on the southern (northern) side of the anomalous anticyclone via the isentropic gliding mechanism.

Reassessment of Geophysical Investigation of Zinc(Z), Cupper (Cu) and Lead (Pb) Potential Mineralization Deposits using Aeromagnetic Data in Wase Middle Benue Trough, Nigeria

Abstract: This effort aims to delineate structures responsible for exploring mineral resources in the Wase middle Benue trough area of Northcentral, Nigeria by evaluating the aeromagnetic data over that region. Oasis Montaj version 6.4 was used to qualitatively and quantitatively evaluate the aeromagnetic data. Techniques for Source Parameter Imaging (SPI) interpretation, including First Vertical Derivative, Analytical Signal, Upward Continuation, and Tilt Derivative, were used in the study. Analytic signal and tilt derivative maps showed different patterns of magnetic signatures independent of magnetization direction with amplitude ranging from 0.1 to 0.2nT/m and -1.3 to 1.4nT/m. They also showed qualitative interpretation applied aids enhance linear features at the expense of deep intrusive bodies like lineaments, fractures, and fault zones which trend Northeast Southwest (NE- SW) in the map of the study area. The boundaries of the geologically interesting anomalies were noticeably accentuated by the upward continuation done at 2 km. Nonetheless, this provides an approximation of the depth of the source of magnetic signatures in the area. The depth measured by SPI ranged from 103.9 to 1473.0 m. In the Eastern and Western regions of the region, respectively, shallow and deep-seated bodies are seen. The depth of the analysis was about 2000m, in conclusion, it was believed that the linear characteristics in the area that are trending northeast to southwest are possible structures for the prospecting of mineral deposits like zinc, copper, and lead

The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO2 in Vertical Upward Flows

Buoyancy effects in vertical, upward laminar flows can result in an augmentation in heat transfer rates to supercritical CO2 (sCO2) near its pseudocritical temperature (TPC). This is in contrast to corresponding flows in the turbulent regime, or laminar sCO2 flows (with minimum buoyancy effects), where a deterioration in heat transfer near TPC, followed by a recovery phase, have been observed. To exploit these sCO2 heat transfer enhancement characteristics and improve heat exchange efficiencies, the location of the TPC pinch point and the variables controlling these buoyancy effects need to be identified. To fill this void, numerical simulations of sCO2 (at inlet: 8.2 MPa, 265 K) in vertical circular tubes of diameters (D) 0.2–2 mm, heated with constant wall heat fluxes (Q) of 1–4 kW/m2) and inlet Reynolds numbers (Re) of 100, 400, were carried out. The tube lengths were varied to maintain an exit temperature of 320 K (TPC~309 K). The results indicated that buoyancy-augmented laminar heat transfer rates may be expected when Gr/Re2.7 > 10−4 (Gr = Grashof number). A modified Nusselt number correlation in terms of (Gr/Re) is proposed and is observed to fit the observed variations within a mean absolute percentage error < 15%, in most regions.

Performance Comparison of ANN-Based Model and Empirical Correlations for Void Fraction Prediction of Subcooled Boiling Flow in Vertical Upward Channel

The accurate prediction of void fraction parameter in subcooled boiling flow is very important for nuclear safety since it has significant influences on the mass flow rate, the onset of two-phase flow instability, and the heat transfer characteristics in a nuclear reactor core. Many different models and empirical correlations have been established over a variety of input conditions; however, this classical approach could lead to unsatisfactory prediction due to the uncertainties of model parameter and model forms. To cope with these limitations, Artificial Neural Network (ANN) is a powerful machine learning tool for modeling and solving non-linear and complicated physical problems. Therefore, this work is aim at developing an ANN-based model to predict the local void fraction of subcooled boiling flows. The comparison results of the performance between the ANN-based model and empirical correlations for the void fraction prediction of subcooled boiling in vertical upward channel showed the potential use of ANN-based model in the Computational Fluid Dynamics (CFD) codes to accurately simulate the subcooled boiling phenomena.

Mitigation of Heat Transfer Deterioration of Supercritical CO2 Vertical Tube Upward Flows by Introducing Truncated-Ribs in Helical-Like Distribution

Abstract To effectively alleviate the heat transfer deterioration (HTD) phenomenon of supercritical CO2 flow in a vertical circular tube, this paper proposes multiple truncated ribs from a whole O-ring rib but distributed in helical-like distribution. The fluid hydraulics and thermal performance with a verified standard k–ω mode are numerically explored. The effects of the height, the distance, and the number of truncated ribs on flow characteristics, and heat transfer are observed and analyzed in detail. Results show that the heat transfer coefficient increases significantly with increasing rib height, and as the pitch decreases the fluid recirculation area behind each rib decreases, resulting in stronger mixing of swirling flow, which enhances turbulent kinetic energy in the downstream and weakens the buoyancy force, thus mitigating heat transfer deterioration. This study suggests that introducing multiple truncated ribs distributed along helices into circular vertical tubes can be a beneficial way to alleviate heat transfer deterioration and to enhance heat transfer of supercritical CO2 flow.

Experimental Research on the Flow and Heat Transfer Characteristics of Subcritical and Supercritical Water in the Vertical Upward Smooth and Rifled Tubes

Experiments were conducted to investigate the heat transfer and flow characteristics of the vertical upward smooth and rifled tubes from subcritical to supercritical pressure. The distributions of wall temperature and heat transfer coefficient (HTC) were obtained, and the HTC correlations and friction resistance coefficient correlations were fitted with experimental data. In addition, the influences of heat flux and type of tube on heat transfer performance were analyzed. The research shows that heat flux has different influences on the heat transfer characteristics under different pressures. The increase in heat flux improves the heat transfer characteristics in the nucleate boiling region, yet it leads to the advance in heat transfer deterioration. However, for supercritical water, the increase in heat flux reduces the heat transfer ability. In addition, using the rifled tube not only improves the heat transfer performance, but also inhibits the occurrence of heat transfer deterioration. The fitted correlations have great predictive ability for the heat transfer coefficient and friction resistance coefficient, and the average relative fitting errors are limited to 20%.

Experimental Investigation on Heat Transfer and Pressure Drop of Supercritical Carbon Dioxide in a Mini Vertical Upward Flow

Experiments on the convection heat transfer and pressure drop of supercritical carbon dioxide in a mini vertical upward flow were investigated in a smooth tube with an inner diameter of 2 mm. The experiments were conducted with pressures ranging from 7.62 to 8.44 MPa, mass fluxes ranging from 600 to 1600 kg·m−2·s−1, and heat flux ranging from 49.3 to 152.3 kW·m−2. Results show that the peak of heat transfer occurs when the bulk fluid temperature is below the proposed critical temperature and the wall temperature is above the proposed critical temperature. For the 2 mm vertical upward flow, the radial buoyancy effects are relatively weak, and the axial thermal acceleration effect cannot be negligible. In this study, a new modified Jackson correlation for the supercritical carbon dioxide is proposed for convective heat transfer. To reflect the effect of flow acceleration on heat transfer, a dimensionless heat flux was introduced to construct a new semi-correlation of heat transfer. The new correlation of friction factor taking into account the variation of density and dynamic viscosity was proposed with 146 experimental data within a ±20% error band.

A Modified Turbulent Model for the Supercritical Water Flows in the Vertical Upward Channels

The supercritical water undergoes drastic changes in the thermal physical properties near the pseudo-critical point. It is necessary to evaluate whether the conventional turbulent models could successfully capture the wall temperature variations. In this study, the heat transfer of the supercritical water in the vertical tube and multiple fuel rods channel is numerically investigated using different turbulent models. The numerical results are compared with the experimental data. The comparisons indicate that the realisable k - ɛ model, k – ω SST model, and the Reynolds stress model generally give a better agreement with the experimental data on the predictions of the wall temperatures. A new variable turbulent Prandtl model is proposed. Selected better performance turbulent models coupled with the proposed turbulent Prandtl model are assessed. The modified turbulent model shows a great improvement in the prediction of the wall temperatures, especially for the condition in a multiple fuel rods channel.

Modeling of Wetting Pattern Under a Linear Drip Source Buried in Layered Soil

This study aims to model the wetting patterns of the homogeneous and stratified soil profile, and to derive an equation to estimate the discharge rate during the application time. The study included conducting 8 experiments to monitor the progress of the wetting patterns over time in a homogeneous and stratified soil profile. Two types of soils were used (silty clay loam and sandy Loam). The emitter was installed at a depth of 45 cm below the soil surface, and soil profiles were prepared in two different sequences and the location of the interface between the soils was changed (at the dripper, 10 cm below the dripper, 10 cm above the dripper). The results showed that there is a good agreement between the measured and estimated advancement distances, where the determination coefficient R2 ranges between 0.826 to 0.989. Moreover, the results showed that the emitter discharge gradually decreases and continues to decline with the continuation of the operating time until it reaches an almost constant value. This reduction in emitter discharge increases by increasing the clay content, soil bulk density, emitter depth, and initial moisture content. The results also showed that the largest wetting front advance distance in the horizontal and vertical directions was in the sandy loam soil profiles, while it was the least valued in the silty clay loam profiles for the same operating time. The interface between the layers also helped in the horizontal and vertical diffusion, especially when the silty clay loam soil was placed below the dripper, which helped in the spreading of water in the horizontal and vertical direction upwards.

Initiation of an Emulsion Microinfusion: Flow Direction Influences Delivery Onset Rate

Critically ill and anesthetized patients commonly receive life-sustaining medications by pump-driven continuous intravenous infusion. Microinfusion refers to delivering concentrated drugs with low flow carriers to conserve fluid administration. Most infused medications are water-soluble. Delivery onset lag times have been identified for microinfusions of water-soluble drugs or experimental surrogates. Drugs may be formulated as emulsions. Initiation of emulsion microinfusions has not been described. We tested in vitro the hypothesis that an emulsion's physical characteristics would influence its microinfusion delivery onset. We adapted an established in vitro model of pump-driven continuous intravenous microinfusion to compare the delivery of methylene blue as a surrogate for water-soluble drugs and a 10% lipid emulsion as a surrogate for a drug formulated as an emulsion. The drug surrogates joined the carrier with carrier flow vertically upwards, vertically downwards or horizontally. We measured the times to 5%, 50% and 95% of plateau delivery. Emulsion entry into a vertical (upwards) carrier flow resulted in a rapid initial emulsion delivery exceeding predictions of delivery models. Emulsion entry into both horizontal and vertical (downwards) carrier flows resulted in long lag times to steady state. Methylene blue delivery was unaffected by carrier flow orientation. Initiating microinfusion emulsion delivery with upward flow can result in a relative bolus, whereas long delivery lags would be expected with horizontal or downwards flow. An emulsion might carry a high potency drug having significant physiologic effects, e. g. clevidipine. Unrecognized, differences in initial emulsion delivery kinetics depending on carrier flow orientation may have clinical implications for both efficacy and safety.

Visualization Experiments and Piston Effect of Heat Transfer on Supercritical Carbon Dioxide in a Mini Vertical Upward Flow

Visualization Experiments and Piston Effect of Heat Transfer on Supercritical Carbon Dioxide in a Mini Vertical Upward Flow

Testbed for Experimental Characterization of Indoor Visible Light Communication Channels

In this paper, we describe an experimental testbed designed to evaluate indoor visible light communications (VLC) in realistic scenarios. The system is based on a mockup where the location and orientation of the optical receiver can be modified with precision for a static configuration of walls and ceiling lamp arrangements. The system utilizes a timing synchronization method, which is based on evaluating the training sequence periods used for channel response estimation, which enables robust frame synchronization. In addition, an adaptive rate orthogonal frequency-division multiplexing (OFDM) scheme is used to assess the VLC performance throughout the receiver plane emulating a real communication. The preliminary results obtained with this prototype, considering a multiple-input single-output (MISO) scenario, demonstrate that reflection on walls yields a significant increase in data rates, which can be additionally improved if appropriate orientation of the receiver is implemented. However, vertical orientation upward of the optical receiver still constitutes a simple solution but efficient enough. Moreover, a good agreement between simulation and experimental results is observed, which confirms the suitability of the mockup as an experimental testbed for practical evaluation of indoor VLC systems, where system performance for different lamp arrangements and receiver designs, including multi-user communications, can be studied.

A framework for conceptualising the organisational communications of a project management office

The project management office (PMO) plays a key role in linking the strategic and operational levels of a project-based enterprise. Fulfilling this mission requires effective collaboration with stakeholders since PMOs can no longer operate in organisational silos. This research aims to tackle the knowledge gap regarding the conceptualisation of the content of PMO communications in project-based organisations. A critical literature review and qualitative synthesis were conducted to draw conclusions concerning the existing theoretical discussions on the topic. The results are presented in the form of a framework explaining 11 categories of stakeholders and respective potential communications with them in four directions: horizontal, vertical upward, vertical downward and external. This study extends the literature by introducing a new theoretical framework of PMO communications and providing an insight into the main constituents required for maintaining effective relationships with stakeholders in practice.

Establishment and verification of the prediction model of soil wetting pattern size in vertical moistube irrigation

AbstractTo solve the difficulty of observing the soil wetting pattern of vertical moistube irrigation, the HYDRUS-2D software is used to simulate wetting pattern data under different conditions. Based on the analysis of Origin 9.0 and summarizing the law of simulation data, an empirical model for predicting wetting pattern size is constructed, with the reliability of the model verified by experimental data. The results show that the power function is used to fit the relationship between the size of wetting pattern and irrigation time. The power function exponent has small changes in three directions (vertical upward, horizontal, and vertical downward) of the moistube. Further analysis shows that the power function coefficient is in accordance with the power function relationship with soil-saturated hydraulic conductivity, the steady permeability of the moistube, and the difference between soil-saturated moisture content and initial moisture content. The average absolute error of statistical indicators of the built model is between 0.30 and 1.42 cm, the root mean square error is between 0.42 and 1.65 cm, and the Nash–Sutcliffe efficiency coefficient is not less than 0.93. The model has a good prediction effect and can provide a scientific basis for the design, operation, and management of the moistube irrigation engineering.

Firing pin impressions: a valuable feature for determining the orientation of the weapon at the time of shooting

Sometimes the firearm forensic examiner is required to provide information useful to discriminate between suicide, homicide or accident, or between contradictory reconstructions of the events (like attempted murder versus accidental discharge). In such situations, knowledge of the position and orientation of the firearm at the time of firing can be of fundamental help for the reconstruction of events. To achieve these goals, the analysis of the firing impressions is very important. In this study, the cartridge cases shot with three different revolvers aiming at three different spatial orientations (vertical upwards, horizontal or vertical downwards) were studied. The depth and morphology of the firing pin impression was characterised by optical microscopy and quantified by a surface topography analysis. The orientation of the firearm significantly modified the morphology and depth of the firing pin impression: ammunition fired upwards had the deepest firing pin impression, those fired downwards had the shallowest. Such behaviour was attributed to the different geometry of the firing pin-primer cup interaction and to the different pressure exerted by the primer as the orientation of the weapon changes. Therefore, this work has shown that a suitable protocol of morphological and topographical analysis can be set up to understand if a shot by a revolver was fired holding the weapon upwards, downwards or horizontally.

Separate-effect experiments and modeling for two-phase flow under geometric restrictions

While significant efforts have been made to investigate two-phase flows in vertical upward channels, limited work has been performed to study the effects stemming from geometric configurations on two-phase flow transport, such as flow restrictions and change in flow orientation. This presents significant shortcomings in the application of predictive models to practical systems, including nuclear power reactors. It has been well observed that geometric restrictions (e.g., elbows, spacer-grid, and inlet configurations) and change in flow orientation (e.g., upward-to-horizontal, horizontal-to-downward) can cause significant effects on the hydrodynamics of two-phase flow. In view of these, high-resolution separate-effect experiments have been performed to establish a two-phase flow database that is accurate, extensive and good enough for multi-phase CFD codes development, to develop predictive models accounting for geometric effects, and to improve the performance of nuclear reactor system analysis codes. Recent studies on the effects of the vertical-upward and vertical-downward 90-degree elbows, spacer grid, inlet configurations, and change in flow orientation are summarized. Some of the major two-phase flow phenomena investigated in the present study include flow regime transition, pressure loss, two-phase flow parameters, flow development, and interfacial drag. To demonstrate the functionality of the newly developed models, the one-dimensional steady-state one-group interfacial area transport equation is employed to predict two-phase flow transport under geometric effects.