Flow Path Research Articles

Impact of Solder Voids on IGBT Thermal Behavior: A Multi-Methodological Approach

This study investigates the thermal behavior of Insulated Gate Bipolar Transistors (IGBTs) with a focus on the influence of solder voids within the device. Utilizing a combination of Finite Element Method (FEM) simulations, X-ray imaging, and SEM-EDX analysis, we accurately modeled the internal structure of IGBTs to assess the impact of void characteristics on thermal resistance. The findings reveal that the presence and characteristics of solder voids—particularly their size, number, and distribution—significantly affect the thermal resistance of IGBT devices. Experimental measurements validate the FEM model’s accuracy, confirming that voids disrupt the heat flow path, which can lead to increased thermal resistance and potential device failure. Five regression models, including Gaussian process regression (GPR) and neural networks, were employed to predict the thermal resistance based on void characteristics, with the GPR models demonstrating superior performance. The optimal GPR RQ model consistently provided accurate predictions with an RMSE of 0.0050 and R2 of 0.9728. Using the void percentage as the only input parameter for the regression models significantly impacted the prediction accuracy, showing the importance of the void extraction method. This study shows the necessity of minimizing solder voids and offers a robust methodological framework for a better prediction of the reliability of IGBTs.

Impact of Pressure-Dependent Interfacial Tension and Contact Angle on Capillary Heterogeneity Trapping of CO2 in Storage Aquifers

Summary Carbon dioxide (CO2) capillary trapping increases the total amount of CO2 that can be effectively immobilized in storage aquifers. This trapping, manifesting itself as accumulated CO2 columns at a continuum scale, is because of capillary threshold effects that occur below low-permeability barriers. Considering that capillary pressure is dictated by heterogeneous pore throat size, the trapped CO2 column height and associated CO2 saturation will vary spatially within a storage aquifer. This variation will be influenced by two pressure-dependent interfacial parameters—CO2/brine interfacial tension (IFT) and CO2/brine/rock contact angle. Our objective is to understand how the pressure dependence of these two parameters affects the heterogeneity of capillary trapped CO2 at a continuum scale. Our conceptual model is a 1D two-zone system with the upper zone being a flow barrier (low permeability) and the lower zone being a flow path (high permeability). The inputs to this model include microfacies-dependent capillary pressure vs. saturation curves and permeability values. The input capillary pressure curves were collected in the literature that represents carbonate microfacies (e.g., dolograinstone) in a prevalent formation in the Permian Basin. We then used the Leverett j-function to scale the capillary pressure curve for the two zones that are assigned with the same or different microfacies. During scaling, we considered the influence of pressure on both the IFT and contact angle of CO2/brine/dolomite systems. We varied the zone permeability contrast ratio from 2 to 50. We then assumed capillary gravity equilibriums and calculated the CO2 saturation buildup corresponding to various trapped CO2 column heights. The CO2 saturation buildup is defined as the CO2 saturation in the lower layer minus that in the upper one. We found that the saturation buildup can be doubled when varying pressure in a storage aquifer, after considering pressure-dependent IFT and contact angles. Thus, assuming these two parameters to be constant across such aquifers would cause large errors in the quantification of capillary trapping of CO2. The whole study demonstrates the importance of considering pressure-dependent interfacial properties in predicting the vertical distribution of capillary trapped CO2. It has important implications in developing a better understanding of leakage risks and consequent storage safety.

Complex hydrology and variability of nitrogen sources in a karst watershed.

Streams draining karst areas with rapid groundwater transit times may respond relatively quickly to nitrogen reduction strategies, but the complex hydrologic network of interconnected sinkholes and springs is challenging for determining the placement and effectiveness of management practices. This study aims to inform nitrogen reduction strategies in a representative agricultural karst setting of the Chesapeake Bay watershed (Fishing Creek watershed, Pennsylvania) with known elevated nitrate contamination and a previous documented groundwater residence time of less than a decade. During baseflow conditions, streamflow did not increase with drainage area. Headwaters and the main stem lost substantial flow to sinkholes until eventually discharging along large springs downstream. Seasonal hydrologic conditions shift the flow and nitrogen load spatially among losing and gaining stream sections. A compilation of nitrogen source inputs with the geochemistry and the pattern of enrichment of δ15N and δ18O suggest that the nitrogen in streams and springs during baseflow represents a mixture of manure, fertilizer, and wastewater sources with low potential for denitrification. The pH and calcite saturation index increased along generalized flow paths from headwaters to springs and indicate shorter groundwater residence times in baseflow during the spring versus summer. Given the substantial investment in management practices, fixed monitoring sites could incorporate synoptic water sampling to properly monitor long-term progress and help inform management actions in karst watersheds. Although karst watersheds have the potential to respond to nitrogen reduction strategies due to shorter groundwater residence times, high nitrogen inputs, effectiveness of conservation practices, and release of legacy nutrients within the karst cavities could confound progress of water quality goals.

Optimization of Cavitation Performance of High-Speed Centrifugal Pump Based on the Meta-Model of optimal Prognosis

Abstract Using a specific type of high-speed centrifugal pump as an example, this study conducted a parameterized optimization design on geometric parameters of the impeller’s flow path. A response sample space was generated with the flow path geometric parameters as input and pressure increment and cavitation volume as output. Based on the Meta-Model of optimal Prognosis, the optimal surrogate model was fitted, and a global sensitivity analysis was conducted. The results indicated that the impeller’s inlet edge parameter and mid-curve parameter had a significant impact on the pressure increment and cavitation volume of the pump. Using a genetic algorithm, the optimal flow path geometric parameters were obtained, and numerical simulation methods were applied to verify the obtained parameters. The results showed that after optimization, the pressure coefficient of the centrifugal pump increased by 0.035, and the cavitation performance improved by 22.28%. The impeller cavitation area and void volume were significantly reduced, and the flow path pressure distribution and flow state were improved.

Prescreening surrogate-model-assisted multi-objective aerodynamic optimization design of highly loaded axial compressor in heavy-duty gas turbine

To address the challenges of numerous design variables and high evaluation costs in the aerodynamic optimization of advanced highly-loaded axial compressors, this paper presents an axial compressor aerodynamic optimization platform based on directly manipulated free-form deformation (DFFD) parameterization method, a data-driven multi-objective differential evolution optimizer, and computational fluid dynamics. The DFFD method allows for direct geometric manipulation of the target compressor, enabling efficient parameterization of the blades and flow path and reducing the number of design variables. A prescreening surrogate-model-assisted multi-objective differential evolution (Pre-MODE) optimizer is developed to obtain competitive solutions within a limited number of iterations. The surrogate model in Pre-MODE conducts real evaluations only on selected individuals in each generation, thereby reduce evaluation costs while ensuring prediction accuracy. Additionally, a parallel task management system is integrated to improve optimization efficiency. To verify the effectiveness of the optimization platform, a 1.5-stage highly-loaded compressor is aerodynamically optimized. After optimization, the adiabatic efficiency at the design point and the surge margin are increased by 2.42% and 9.04%, respectively. These results confirm the effectiveness and speed of the aerodynamic optimization platform, promoting the establishment of an integrated optimization design system for axial compressors.

Pore‐Scale Modeling of Reactive Transport with Coupled Mineral Dissolution and Precipitation

AbstractWe present a new pore‐scale model for multicomponent advective‐diffusive transport with coupled mineral dissolution and precipitation. Both dissolution and precipitation are captured simultaneously by introducing a phase transformation vector field representing the direction and magnitude of the overall phase change. An effective viscosity model is adopted in simulating fluid flow during mineral dissolution‐precipitation that can accurately capture the velocity field without introducing any empirical parameters. The proposed approach is validated against analytical solutions and interface tracking simulations in simplified structures. After validation, the proposed approach is employed in modeling realistic rocks where mineral dissolution and precipitation are dominant at different locations. We have identified three regimes for mineral dissolution‐precipitation coupling: (a) compact dissolution‐precipitation where dissolution is dominant near the inlet and precipitation is dominant near the outlet, (b) wormhole dissolution with clustered precipitation where dissolution generates wormholes in the main flow paths and precipitation clogs the secondary flow paths, and (c) dissolution dominant where all solid grains are gradually dissolved. In the three regimes, the proposed approach provides reliable porosity‐permeability relationships that cannot be described well by traditional macroscale models. We find that the permeability can increase while the overall porosity decreases when the main flow paths are expanded by dissolution and adjacent pore spaces are clogged by precipitation.

Identifying the structure as a hot water outflow path using gravity in Jatimulyo, South Lampung

Abstract Geothermal manifestations have been utilized as a tourist attraction (geo-tourism) worldwide. Geothermal manifestation systems could be found in many forms such as hot springs. The path of the hot water flow is controlled by the existence of geologic structures such as faults as the medium. Geophysical methods in general have been used to image and characterize subsurface layers. The gravity method using the natural source has been employed to determine the geological structure, such as faults. This study aims to identify the structure related to the outflow path which is part of the geothermal system using gravity method in Jatimulyo Village, Jati Agung, South Lampung. The result shows the contrast anomaly indicating the existence of a fault that could be a hot water path. An outflow zone which is characterized by low temperatures because it is far from heat sources. The complete Bouguer Anomaly is used to create 2D forward modelling where the model is divided in 2 layers. The first layer is indicated as Lampung Formation (QTl) with density of 1.8 g/cc, and second layer recognized as bedrock with denser rock of 2.78 g/cc representing Tertiary Paleozoic (Pzg) Gunung Kasih Complex Formation.

Design and Performance Prediction of a Vortex Pump Based on CFD for High Concentration Sludge Dredging

Abstract Aiming at solving the problems of clogging and severe wear of the delivery pump in the sludge dredging project, a design method for a vortex pump was summarized. An open impeller and a cross shaped blade was designed with good passing ability, simple structure, and easy maintenance. The volute flow path profile of the vortex pump was designed as a spiral, and the relationship between the width of the vaneless cavity and the diameter of the impeller was established. Based on CFD, the external characteristics of the DRC45-200-VLS vortex pump were simulated and predicted, with a flow rate of 600 m3/h, a head of 20 m, and a water efficiency of 50%. The effects of medium viscosity, solid phase distribution, and gas phase distribution on the flow field of the vortex pump were analyzed. The results showed that the designed vortex pump had good adaptability to transport high concentration sludge and aerated sludge. Combined with a municipal sludge dredging project, a vortex pump transportation scheme for high concentration sludge dredging was formed.

Transient temperature measurement of silicon carbide Schottky barrier diode based on thermal reflection.

In this article, we present a transient temperature detection device for silicon carbide (SiC) Schottky barrier diodes (SBDs) based on thermal reflection theory. We constructed a thermal reflection temperature measurement device based on a 530-nm green laser. This device is more suitable for transient temperature measurement of SiC SBDs than previous thermal reflection equipment. The accuracy of temperature measurement by our device was confirmed by comparison with the results of infrared thermal imaging. The high temporal resolution characteristics of the thermal reflection technology allowed the detection of millisecond-level transient temperature changes in SiC SBDs. In addition, we investigated the complementarity of transient temperature change curves during heating and cooling processes, as well as the reasons for the differences between these curves. Finally, we used the structural function method combined with the Bayesian deconvolution algorithm to obtain the thermal resistance along the heat flow path of the device and validated the results using an established thermal resistance testing method.

Combined effects of rainfall‐runoff events and antecedent soil moisture on runoff generation processes in an upland forested headwater area

AbstractIn this study, we investigate the combined effect of different rainfall‐runoff event types and antecedent soil moisture (ASM) on runoff processes in the headwater elementary discharge area of a small forested upland catchment. The study focuses on (i) the relationship between soil moisture thresholds and runoff generation; (ii) the combined effect of ASM and tree vicinity and (iii) the relationship between different rainfall‐runoff event types and different types of runoff (baseflow and stormflow). The results suggest that ASM has a strong impact on local runoff generation processes. Soil water content (35%–36%) threshold exceedance was related to stormflow runoff generation caused by the activation of quick preferential flow paths in the soil during storm events, especially in the upper and the deepest soil layers. At the same time, unexpected non‐linear increases in baseflow runoff ratios were documented during dry, precipitation‐free, periods and when the 31%–34% soil moisture threshold was exceeded, presumably due to the hydrological connection of farther slope areas during these conditions. Multiple stormflow periods, which exhibited the lowest runoff coefficient, were the most significant events in terms of water retention and soil water recharge due to increased vertical hydrological connectivity enabling more rapid transport to deeper soil layers. However, this rainfall type occurred least often over the study period. The important role of forest stands (individual trees) in creating spatial patterns of soil moisture and preferential infiltration paths to deeper soil layers was also confirmed. These results contribute towards a better conceptualisation of hydrological behaviour in elementary headwater discharge areas and highlight the potential dangers associated with expected increases in extreme weather events.

Illuminating the “Invisible”: Substantial Deep Respiration and Lateral Export of Dissolved Carbon From Beneath Soil

AbstractDissolved organic and inorganic carbon (DOC and DIC) influence water quality, ecosystem health, and carbon cycling. Dissolved carbon species are produced by biogeochemical reactions and laterally exported to streams via distinct shallow and deep subsurface flow paths. These processes are arduous to measure and challenge the quantification of global carbon cycles. Here we ask: when, where, and how much is dissolved carbon produced in and laterally exported from the subsurface to streams? We used a catchment‐scale reactive transport model, BioRT‐HBV, with hydrometeorology and stream carbon data to illuminate the “invisible” subsurface processes at Sleepers River, a carbonate‐based catchment in Vermont, United States. Results depict a conceptual model where DOC is produced mostly in shallow soils (3.7 ± 0.6 g/m2/yr) and in summer at peak root and microbial respiration. DOC is flushed from soils to the stream (1.0 ± 0.2 g/m2/yr) especially during snowmelt and storms. A large fraction of DOC (2.5 ± 0.2 g/m2/yr) percolates to the deeper subsurface, fueling deep respiration to generate DIC. DIC is exported predominantly from the deeper subsurface (7.1 ± 0.4 g/m2/yr, compared to 1.3 ± 0.3 g/m2/yr from shallow soils). Deep respiration reduces DOC and increases DIC concentrations at depth, leading to commonly observed DOC flushing (increasing concentrations with discharge) and DIC dilution patterns (decreasing concentrations with discharge). Surprisingly, respiration processes generate more DIC than weathering in this carbonate‐based catchment. These findings underscore the importance of vertical connectivity between the shallow and deep subsurface, highlighting the overlooked role of deep carbon processing and export.

Leakage flow mixing in shrouded axial turbines and its control strategies using casing optimization

The geometry of the shroud cavity, which accommodates the rotor shroud leakage flow, is very important due to its impact on the leakage flow path as well as the interaction between the leakage flow and mainstream. The research in this paper numerically investigates the potential for reducing the leakage loss by optimization to the casing. The spatial loss audit and the loss breakdown based on loss mechanisms undertaken in the first part of this study are the foundation to develop promising strategies for minimizing the leakage loss. The profiled casing in the exit cavity effectively deflects the leakage jet into the axial direction when it re-enters the mainstream. The mixing loss is significantly reduced due to the notable decrease in axial velocity disparity of the two streams. On this basis, the exit and inlet cavity are further shaped to both form a step. Reductions in the shroud leakage loss are achieved by alleviating the flow nonuniformity in the exit cavity and reducing the leakage flow rate, respectively. The work in this study contributes to the refinement of control methods for the shroud leakage loss.

RATIONALE FOR THE TECHNOLOGY OF PROTECTING THE METAL SURFACE IN THE FLOW PATH OF A HYDRAULIC TURBINE TO REDUCE CAVITATION WEAR

The relevance of the problem is due to the significant scale of cavitation destruction of hydraulic turbines of many operating hydroelectric power stations and the high economic costs of major repairs of hydraulic units. Methods for restoring surfaces damaged by cavitation in the flow path of hydraulic turbines at hydroelectric power stations are considered. Based on a review and comparison of existing technologies, recommendations are made that significantly increase the periods between major overhauls of hydraulic turbine parts. It has been shown that material damage due to cavitation can be minimized by using cavitation-resistant materials. A feasibility study for a combined method of repairing a hydraulic unit is presented.

Effects of Initial Injection Condition on Colloid Retention

AbstractThis study investigates the impact of initial injection conditions on colloid transport and retention in porous media. Employing both uniform and flux‐weighted distributions for the initial colloid locations, the research explores diverse flow scenarios, ranging from simple Poiseuille flow to more complex geometries. The results underscore the pivotal role the injection mode plays on the shape of colloid retention profiles (RPs), particularly those that display anomalous non‐exponential decay with distance. Broadly, uniform injection yields multi‐exponential profiles, while flux‐weighted injection can lead to nonmonotonic profiles in certain conditions. The study identifies preferential flow paths as a key factor in producing nonmonotonic RPs. Notably, variations in fluid velocity, colloid size, and ionic strength affect attachment rates near the inlet but do not significantly alter the qualitative transition between multi‐exponential and nonmonotonic profiles. The study emphasizes that the chosen injection mode dictates retention profile shapes, highlighting its crucial role in porous media colloid transport. These insights provide a possible partial explanation of previously observed anomalous transport behaviors, urging consideration of injection conditions in interpretations of experiments, where they can be difficult to accurately control and measure with high precision.

Experimental study on radial suction flow and its effect in water vortex unit

A water vortex unit is a non-contact adsorption unit that utilizes water as a flowing medium. Negative pressure is generated on the adsorbed surface through the high-velocity rotation of the fluid, resulting in suction force. In comparison to the air vortex unit, the water vortex unit exhibits a substantial increase in suction force and has the capability to deliver greater power. However, the presence of the central bubble in the water vortex unit weakens the suction force. To address the impact of the central bubble, a suction hole was introduced on the vortex unit to remove them. Experimental results indicate that solely removing the central bubble has almost no effect on the radial pressure gradients in the gap flow path and chamber center of the water vortex unit. However, in the cylindrical neighborhood, the radial pressure gradient increases, leading to a certain degree of improvement in suction force. Further increasing the suction flow rate induces inward radial flow within the vortex chamber. This flow field further enhances the suction force. To analyze the reasons for this pressure distribution, we indirectly obtained the radial velocity distribution by examining the relationship between the pressure gradient and tangential velocity. The results of the tangential velocity distribution indicate that the radially inward suction flow significantly increases the rotational velocity of the fluid in the chamber center, enhancing the centrifugal inertial effect. This further reduces the negative pressure, resulting in a significant improvement in the suction of the vortex unit.

Pattern transition of flow dynamics in a highly water-absorbent granular bed

An aqueous sodium chloride solution was injected at a controlled rate into a granular bed in a quasi-two-dimensional cell. The granular bed was made of dried, highly water-absorbent gel particles whose swelling rate was controlled by the salinity of the injected fluid. At a high salinity level (low swelling rate), high injection rate, and short timescale, the injected fluid percolated between the gel particles in an isotropic manner. Meanwhile, at a low salinity level (high swelling rate), low injection rate, and long timescale, the gel particles clogged the flow path, resulting in anisotropic branch-like structures of the injected fluid front. The transition of the injection pattern could be understood based on the ratio of the characteristic timescales of swelling and injection. Moreover, the clogged pattern showed an oscillatory pressure drop whose amplitude was increased with higher salinity. Such an oscillatory behavior observed in an injection process in swelling gel particles may be relevant in geological situation, such as fluid migration underground.

Redesigning the Element Profile of Air Preheater in Coal-fired power plants for Emission Reduction and Efficiency Improvement

PT PLN Nusantara Power Unit Pembangkit Tanjung Awar-Awar (UPTA) is a state-owned company that supplies electricity to areas of Java and Bali. Using coal as the main fuel, UPTA currently has two mills that each has capacity of 350 MW in coal-fired mode. Since the last few years, UPTA has been focusing on bringing efficiency into its overall operations, maximizing efforts for an improved output, modernizing machinery, and reducing emissions. After conducting routine inspection and examinations, UPTA decided to improve the air preheating element, so-called air preheater (APH), as an enabling condition to heat both the primary and secondary air to a temperature required for effective combustion in a boiler. To seek for an optimal APH, a redesign project was initiated to primarily change the element profile from a distorted wavy flow path to a linear flow path. The profile surface was coated with an added "enamel" layer, which prevents ash from adhering readily. Our measurements and calculations were based upon the data collected in October 2022 (pre- implementation) and within the periods of February to June 2023 (post-implementation). As a result, the average power consumption was reduced: from over 1740 kWh per month to become around 1377 - 1535 kWh per month, or 11% - 21%, for the induced draft fan (ID Fan) and from over 1900 kWh per month to become around 1450 - 1542 kWh per month, or 19% - 29%, for the primary air fan (PA Fan).

A model for saturated–unsaturated flow with fractures acting as capillary barriers

AbstractHigh‐resolution modeling of the flow dynamics in fractured soils is highly complex and computationally demanding as it requires precise geometrical description of the fractures in addition to resolving a multiphase free‐flow problem inside the fractures. In this paper, we present an idealized model for saturated–unsaturated flow in fractured soils that preserves the core aspects of fractured flow dynamics using an explicit representation of the fractures. The model is based on Richards’ equation in the matrix and hydrostatic equilibrium in the fractures. While the first modeling choice is standard, the latter is motivated by the difference in flow regimes between matrix and fractures, that is, the water velocity inside the fractures is considerably larger than in the soil even under saturated conditions. On matrix/fracture interfaces, the model permits water exchange between matrix and fractures only when the capillary barrier offered by the presence of air inside the fractures is overcome. Thus, depending on the wetting conditions, fractures can either act as impervious barriers or as paths for rapid water flow. Since in numerical simulations each fracture face in the computational grid is a potential seepage face, solving the resulting system of nonlinear equations is a nontrivial task. Here, we propose a general framework based on a discrete‐fracture matrix approach, a finite volume discretization of the equations, and a practical iterative technique to solve the conditional flow at the interfaces. Numerical examples support the mathematical validity and the physical applicability of the model.

Groundwater recharge sources and mechanisms in the Ethiopian central Afar rift: Insights from isotopic and hydrogeochemical tracers.

Groundwater flow and recharge mechanisms in the central Afar rift and the associated western marginal grabens and Northwestern Plateau (NWP) are poorly understood because of the complex geology and spatial heterogeneity in the aquifer systems. The major aquifers in the region include the Oligocene and Pliocene to recent volcanics and recent alluvio-lacustrine sediments. We employed hydrogeochemical, stable isotopes of water (18O and 2H), and geological structures insights to identify groundwater recharge sources and mechanisms, aiming to develop a representative conceptual groundwater flow model. Water samples from groundwater and surface water were collected based on lithological/aquifer variation and geomorphological setup for isotope and hydrochemical analysis. Findings reveal distinct isotopic differences between the deep (>350 m) and shallow groundwater systems of the Afar rift, with deep systems showing relative isotopic depletion, indicating varying recharge sources. The deep groundwater exhibited a similar isotopic signature to that of the marginal grabens and NWP. The distribution of major ion chemistry and electric conductivity (EC) of groundwaters from the western plateau to the Afar rift show significant spatial variability. However, in some corridors of western parts of the rift, there is a clear geochemical evolution along the flow paths inferring groundwater flow continuity between aquifers. The results revealed the existence of preferential deep groundwater recharge from the NWP through the highly fractured linking zones, interacting fault zones in between the marginal grabens, to the deeper volcanic aquifers of the central Afar rift. The proposed groundwater flow model of this study illustrates the deep groundwater flow from the NWP to the Afar rift is primarily directed by the orientations of the faulted marginal grabens and the highly fractured interacting zones. This model is pivotal for understanding groundwater dynamics in similar continental rift environments, offering insights for effective groundwater management.

Vibration energy transfer in forced laminated composite box structure

This study investigates the dynamics of laminated composite box structures from the viewpoint of energy flow transmission. Using a substructure-based technique, the power flow and dynamic responses are defined and obtained. The relationship between natural frequencies and the fiber orientations is explored. The influence of excitation frequencies, fiber angles, and boundary conditions on power flow and energy transmission paths (ETPs) is examined. The fiber orientations of box structure and boundary conditions are shown to have a substantial impact on ETPs and the positions of sinks. By modifying fiber angles, vibration suppression of box structure can be achieved.