Upward Flow Research Articles

Recent advances in vertical temperature profiler instrumentation and flux estimation methods facilitate groundwater – Surface water exchange studies in environments with strong discharge zones

Groundwater fluxes to many surface water systems are spatially heterogeneous with discharge focused into discrete, high-flux zones. Quantifying fluxes in these preferential discharge zones is critical to a range of surface water habitat and water quality processes, but characterization can be difficult due to short-scale spatial and temporal variability. Passive heat-as-a-tracer methods employing vertical temperature profiler (VTP) data can provide the necessary spatial and temporal resolution, but upward fluid flow strongly attenuates the thermal signals used for estimating fluxes. In preferential discharge zones it becomes difficult to measure the signals in the subsurface and the flux parameter can become insensitive in the analysis models, leading to large uncertainties. We use data from a high-flux site of contaminant-loaded groundwater discharge to the Quashnet River on Cape Cod, Massachusetts, USA, to demonstrate how recent advances in VTP instrumentation that allow for the acquisition of high-resolution (0.001 °C) temperature data at short (1 cm) offsets near the ground surface, combined with advances in flux estimation methods that exploit the information content of the high-resolution data, facilitate heat-as-a-tracer approaches for characterizing groundwater-surface water exchanges and make it possible to obtain accurate and statistically robust results in a preferential discharge zone with a specific discharge of ∼1 m/d.

Towards understanding effects of ultrasonic waves on subcooled boiling using particle image velocimetry

In this study, effects of ultrasonic waves on heat transfer, bubble behavior and temporal variation of liquid flow near the heating surface in subcooled boiling was investigated with the help of high-speed particle image velocimetry method. Experimental results show that the enhancement effect of ultrasound on heat transfer and critical heat flux considerably depends on subcooling and boiling space height. In nucleate boiling regime, the ultrasound-induced acoustic streaming alters the upward liquid flow and changes the vortex structure associated with bubble growth, departure and rising. As heat flux increases, the bubble-induced convection accelerates and competes with the acoustic streaming near the heating surface, weakening the ultrasonic effect on heat transfer. In transition boiling regime, effects of ultrasonic waves on heat transfer of microbubble emission boiling depends on the competition between acoustic streaming and oscillating flow resulting from vapor film oscillation, with enhancement occurring when acoustic streaming dominates the liquid flow near the heating surface. Based on the visualization results, a scaling law is developed to determine the potential effects of ultrasound on critical heat flux.

Local characteristics of bubbly flow in rods assembly 3 × 3

This study focuses on the experimental investigation of local characteristics of upward bubble flow in a 3 × 3 square rod bundle assembly. The experiments were conducted at Reynolds numbers ranging from 4000 to 11000 and gas void fractions up to 10%. The distribution of the gas phase around the central rod of the assembly was measured using a frontal conductivity probe, while the wall shear stress on the central rod was obtained through the electrodiffusion method. It is shown that the gas phase distribution does not exhibit the symmetry characteristic of the assembly cross-section. Furthermore, as the distance from the spacer grid increases, a reconfiguration of void fraction profiles is observed. This explains the non-monotonic dependence of wall shear stress and wall shear stress fluctuations on the distance to the spacer grid.

Geochemical characteristics, Li source and genesis mechanism of thermal mineral water in Sichuan Basin, SW China

Thermal mineral water (temperature >25 °C) is a valuable resource, especially when it contains a certain amount of Li. In this study, an attempt was made to elucidate the factors affecting spatial distribution of lithium (Li) resources and interpret the formation mechanisms of thermal mineral waters in the Sichuan Basin. The spatial distribution, reservoir temperatures, and hydrochemical characteristics of thermal mineral waters were systematically analyzed in the Sichuan Basin, preliminarily revealing Li sources through hydrochemical methods. Results are showed as follows: (1) The Li-bearing (Li ≥ 1 mg/L) thermal mineral waters are mainly distributed in the southwestern part of the Sichuan Basin. There are three sites of thermal mineral waters with Li content greater than 25 mg/L with the hydrochemical type of Cl–Na type: Pengji Well (37.7 mg/L), Foguanghu Well (99.5 mg/L) and Zhougongshan New Well (118.0 mg/L). Among them, the Foguanghu Geothermal Well and the Zhougongshan New Well have high Li content and low Mg/Li (10.7 and 2.5), indicating great potential for utilization. (2) The Li-bearing thermal mineral waters are mainly formed in the fissure and pore reservoirs of the Middle–Lower Triassic. They are mainly affected by the dissolution of halite minerals and the deeply buried ancient seawater of the Triassic. The Li-bearing thermal mineral waters possess high contents of total dissolve solids (TDS) (4.3–230.0 g/L), Cl (0.7–142.9 g/L), Na (0.5–76.7 g/L), K (0.1–52.0 g/L), B (4.1–739.6 mg/L), and Li (1.5–118.0 mg/L). Moreover, the temperature of the geothermal reservoir ranges from 40 to 150 °C. The geothermal reservoir temperatures calculated by K–Mg and Mg–Li geothermometers are positively correlated with the Li content. (3) The Li source of the thermal mineral waters of the Sichuan Basin are dominated by multiple factors: first, Li concentration by evaporation, concentration and deep-seated metamorphism of ancient Triassic seawater; second, water–rock interaction between deep thermal mineral waters and mung bean rock or Emeishan basalt; and third, active tectonic activity and deep faulting induced upward flow of Li in deep fluids. This research enhances understanding of the formation of thermal mineral waters in the Sichuan Basin, offering scientific basis for the exploitation of Li resource.

In situ measurements of dissolved gases in xylem sap as tracers in plant physiology

Abstract Trees transport gases from the ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in the tree sap in situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2 and CO2) from the soil, through the trees, into the atmosphere. We constructed and inserted custom-made semi-permeable membrane probes in the xylem of a fir tree and measured gas abundances at different heights using a portable gas equilibrium membrane-inlet mass spectrometer (‘miniRUEDI’). With this method, we were able to continuously measure the abundances of He, Ar, Kr, N2, O2 and CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of the concept that trees do uptake dissolved gases in soil water, we irrigated the tree with He-enriched water in a tracer experiment and were able to determine upward sap flow velocity. Measurements of inert gases together with reactive species, such as CO2 and O2, allowed separation of the physical transport and exchange of gases derived from the soil or atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in situ measurements of gases in the tree sap.

CFD analysis in effects of spacer-vane on thermal–hydraulic performance of two-phase flow in annular channel

Spacer performs a key function in the construction of nuclear rod assembly. It is utilized to ensure the appropriate spacing and firmness of the rods in assembly. In rod bundle structures, spacers are typically incorporated with vanes to promote turbulence and improve heat transfer. The aim of this work is to analyze the impacts of spacer-vane on the thermal–hydraulic performance of two-phase flow in an annular channel. CFD model of an upward flow annular channel with spacer-vane has been developed. In addition, an annular channel model with a spacer but without vane has been generated and modeled in order to examine the impact of the spacer-vane in a two-phase flow. Transient simulations were performed with flow considerations of mass flux 714.4 kg/m2s, liquid temperature 330 K, volume fraction 0.35, heat flux 197.2 kW/m2, and atmospheric pressure conditions. CFD results have been validated with experimental data. Results show that the core zone of the annulus gap exhibits the highest level of turbulent intensity, and the outer pipe wall temperature is lower for spacer-vane relative to spacer alone. It is observed that the majority of water vapor is concentrated at the center of the channel in the farthest downstream location.

Gravity-driven close contact melting heat transfer in gradient latent heat storage units

Numerical modeling of efficient close contact melting (CCM) has been a significant challenge in phase-change heat transfer research. This work addresses this issue by developing a modified equivalent heat capacity method to construct a universal CCM model, considering physicals such as conduction, heat convection, and solid sinking. The enhanced heat transfer mechanism of CCM compared to conventional constrained melting (CM) in finned latent heat storage (LHS) units is investigated. The results reveal that the early stages of CM and CCM are dominated by heat conduction, while natural convection and mixed convection are induced in the late stage of CM and CCM, respectively. The CM and CCM performance is optimized under upward and downward flows, respectively. The complete melting time of CCM is reduced by a substantial 36.7% and 29.7% compared to CM for both downward and upward flow cases. The inlet temperature and volume flow rate are positively correlated with CM and CCM performance, but the effect of volume flow rates is smaller. The gradient fin maximizes melting performance at a height gradient of 1. Compared to the uniform layout, the complete melting time of CM and CCM in the optimized gradient LHS unit is reduced by 5.6% and 8.5%.

Carbon Macrosegregation Pattern in 30Cr15Mo1N Ingot: Impact of Pouring Rate

The effect of the pouring rate on the carbon macrosegregation in 30Cr15Mo1N ingots has been clarified by investigating changes in the content of carbon‐containing precipitated phases, cooling rate, secondary dendrite arm spacing (SDAS) and the flow characteristics of molten steel. During the solidification process, the solute‐enriched liquid steel migrates toward the center of the ingot under the action of convection, resulting in an increasing segregation ratio from the edge to the center. However, the growth of equiaxed grains partially restricts the flow of solute‐enriched liquid steel, which leads to a maximum segregation ratio not at the center but at approximately a quarter radius from the center. Furthermore, due to the upward flow of molten steel in the center, positive segregation occurs at the top. An increment in the pouring rate reduces the SDAS by enhancing the cooling rate, and thus the permeability decreases. It aggravates the carbon macrosegregation horizontally. However, increasing the pouring rate decreases the carbon macrosegregation vertically. This is due to the more intense flow of molten steel and the larger liquid phase region at higher pouring rate, which reduces the solute enrichment degree and promotes compositional homogeneity above and below the ingot.

Dynamics of a cantilevered pipe conveying fluid and partially subjected to a confined counter-current external axial flow of a different fluid

A linear analytical model has been developed for prediction of fluid-elastic instabilities of brine-strings during product retrieval in salt-mined caverns. These caverns are utilized for storage and subsequent retrieval of hydrocarbons, hydrogen gas or compressed air in Compressed Air Energy Storage (CAES) plants. The retrieval operation involves pumping brine downwards through a long cantilevered pipe (“brine-string”) into the cavern, causing the lighter-than-brine gaseous or liquid “product” stored in the cavern to flow upwards and out of the cavern through a shorter annular passage formed by a concentric casing surrounding the upper portion of the pipe. The presence in the cavern of two different fluids with a variable interface level is taken into account. Employing a Newtonian derivation of the equation of motion solutions were obtained via the Galerkin modal decomposition technique, demonstrating that the brine-string may develop buckling or flutter at high-enough flow rates, depending on the system parameters. Extensive computations investigated the influence of system parameters on the dynamics. It is shown that simplifying the system by considering a single fluid in the cavern, and so for the flows within and around the brine-string, leads to unrealistically high critical flow velocity predictions.

Simulation of natural convection flow for vertical heated rod by using ANSYS/Fluent

The decay heat removal by natural convection is very important in case of Station blackout (SBO) of nuclear reactor. The computational fluid dynamic (CFD) is helpful to simulate the flow and temperature field. However, the CFD simulation models need to be validated by the experimental data. Thus, in this report, the Anslys/Fluent is applied to simulate the natural convection induced by single heater rod. The vertical heated rod with a diameter of 12 mm and a length of 225 mm is immersed at the center of a vertical pipe made of acrylic with a diameter of 146 mm and a height of 500 mm. In this simulation, the coupled scheme algorithm is also applied. Regarding to experimental method, the optical method such as Particle Image Velocimetry (PIV) was applied for 2-dimensional velocity distribution and pointwise temperature measurement. As a result, the predicted flow and temperature field are well agreed with experimental data. Accordingly, the thermal plumes are well estimated by ANSYS/Fluent, in which the buoyant plumes induced by different temperatures vertically go up along the heater rod's upper part until the container's isolated upper wall. The complicated flow occurs in the middle part of the container by mixing the downward flow on the top and the upward flow from the heater rod.

Understanding the formation of laser-induced melt pools with both wire and powder feeding in directed energy deposition

Wire-powder fed directed energy deposition (WP-DED) has been applied to produce high-performance metal parts. Compared to DED with the feed of a single filler (either powder or wire), simultaneous WP-DED exhibits more complex interactions between fillers and laser-induced melt pools, such as additional powder collisions by wire, different filler properties, intricated heat transfer paths, etc. At present, there is little mechanistic understanding of the interactions among wire, powder particles, and laser-generated melt pools in the WP-DED. In this work, we discovered the filler-melt pool interactions in a coaxial wire-powder fed DED (CWP-DED) process by in situ experimental characterizations. In particular, we investigated the wire-influenced particle dynamics before entering the melt pool. When in-flight particles interact with the melt pool, the temporal-varied melt pool geometry as well as melt flow dynamics were characterized. The bubble formation and evolution in CWP-DED were also revealed. We found that the extruded wire would affect the trajectory of in-flight particles and reduce their velocity before the entry of melt pool due to the inelastic collision. The melt pool size decreased with powder feed rate; however, the powder feed rate had limited influences on the melt pool oscillation. Four modes of fluid flow were observed in the melt pool, including backward flow, upwards flow to the wire-melt pool interface, rebounded flow, and clockwise flow. At a high powder feed rate, more gas-induced bubbles occurred along the melt pool boundary and wire-melt pool interfaces. This study provides a fundamental understanding of filler-melt pool interactions during the CWP-DED process to advance the development of next-generation, fast-rate additive manufacturing technology.

Pockmarks and associated fresh submarine groundwater discharge in the seafloor of Puck Bay, southern Baltic Sea

This is the first well-documented report on the occurrence of pockmarks in Puck Bay. Pockmarks in the seafloor of Puck Bay were discovered during a hydroacoustic survey carried out in 2020. They are located at a depth of 25–27 m in the southwestern part of the bay. Significant depletion of chloride (Cl−) concentrations in sediment pore water was found within the depressions. Most likely, the formation of pockmarks was due to groundwater flow through the Miocene–Pleistocene system of aquifers, which extends from land to the bay area. One-dimensional modeling of vertical Cl− concentration profiles in pore water revealed the upward flow of freshened groundwater within the pockmarks. The magnitude of submarine groundwater discharge (SGD) was estimated to vary from 1.53·10−2 to 18·10−2 L·m−2·h−1. The effect of groundwater seepage was also observed at 3 cm above the seafloor within the pockmarks, which was identified as a decrease in salinity of approximately 0.12 PSU compared to reference sites.Furthermore, due to the effect of water advection, SGD can be detected even several meters above the seafloor as a decrease in salinity values within the thermocline layer.

Probing the Kinematic Signatures of Planet Formation in the Gas Disk of MWC 480

The disk around MWC 480 has shown multiple substructures in both dust and gas observations, possibly suggesting ongoing planet formation in situ. In this paper, we explore the gas kinematics of the MWC 480 disk by analyzing the archival Atacama Large Millimeter/submillimeter Array observations of 12CO (J = 2-1), 13CO (J = 2-1), and C18O (J = 2-1). By modeling the line-of-sight velocities, inferred from the Doppler shifts of the emission lines, we are able to decompose the three-dimensional (3D) velocity field of the disk into rotational, radial, and vertical components. Further analysis reveals the presence of large-scale gas flows in the (r, z) plane. Notably, we identify potential meridional flows across various heights as traced by all three CO isotopologues in the 80–120 au region, possibly associated with ongoing planet formation activities in this region. Moreover, we find upward flows near 200 au for all three CO isotopologues, which may point to the presence of disk winds.

Modeling and simulation of air-water upward annular flow characteristics in a vertical tube using CFD

Annular flow refers to a special type of two-phase flow pattern in which liquid flows as a thin film at the periphery of a pipe, tube, or conduit, and gas with relatively high velocity flows at the center of the flow section. This gas also includes dispersed liquid droplets. The liquid film flow rate continuously changes inside the tube due to two processes-entrainment and deposition. To determine the liquid holdup, pressure drop, the onset of dryout, and heat transfer characteristics in annular flow, it is important to have proper knowledge of flow characteristics. Especially a better understanding of entrainment fraction is important for the heat transfer and safe operation of two-phase flow systems operating in an annular two-phase flow regime. Therefore, the objective of this work is to develop a computational model for the simulation of the annular two-phase flow regime and assess the various existing models for the entrainment rate. In this work, Computational Fluid Dynamics (CFD) in ANSYS FLUENT has been applied to determine annular flow characteristics such as liquid film thickness, film velocity, entrainment rate, deposition rate, and entrainment fraction for various gas-liquid flow conditions in a vertical upward tube. The gas core with droplets was simulated using the Discrete Phase Model (DPM) which is based on the Eulerian-Lagrangian approach. The Eulerian Wall Film (EWF) model was utilized to simulate liquid film on the tube wall. Three different models of Entrainment rate were implemented and assessed through user-defined functions (UDF) in ANSYS. Finally, entrainment for fully developed flow was determined and compared with the experimental data available in the literature. From the simulations, it was obtained that the Bertodano correlation performed best in predicting entrainment fraction and the results were within the ±30 % limit when compared to experimental data.

Role of Longitudinal Temperature Gradients in Eliminating Interleaving Inclusions in Casting of Monocrystalline Silicon Ingots

Infrared analysis reveals the presence of interwoven inclusions, primarily comprised of silicon nitride and silicon carbide, in the casting process of monocrystalline silicon ingots. This study investigates how the longitudinal temperature gradient affects the removal of inclusions during the casting of monocrystalline silicon ingots through simulations and comparative experiments. Two monocrystalline silicon ingots were cast, each using different longitudinal temperature gradients: one employing smaller gradients and the other conventional gradients. CGSim (Version Basic CGSim 23.1) simulation software was utilized to analyze the melt flow and temperature distribution during the growth process of quasi–monocrystalline silicon ingots. The findings indicate that smaller longitudinal temperature gradients lead to a more robust upward flow of molten silicon at the solid–liquid interface, effectively carrying impurities away from this interface and preventing their inclusion formation. Analysis of experimental photoluminescence and IR results reveals that although inclusions may not be observed, impurities persist but are gradually displaced to the top of the silicon melt through a stable growth process.

Full-scale experiments on smoke movement in a two-story detached house with two horizontal openings at the lower-floor ceiling

This paper conducted full-scale experiments to investigate transient burning characteristics inside a two-story detached house, which had a double-pitched roof and covered an area of 14.2 m × 6.5 m. Two horizontal openings, formed by a staircase and an atrium, connected the lower floor with the upper floor. By changing the heat release rates (HRRs) and locations of the fire source, as well as the opening conditions, smoke movement and filling process were addressed, and flame shapes and temperature evolutions inside the building were presented. Based on the heat transfer analysis, it was indicated that the two horizontal openings play a significant role on smoke movement and filling process. When the burner was placed between the two openings, there was a constant upward flow through the atrium opening to the upper floor due to its lower flow resistance. While gas flow inside the staircase can be both downward and upward, caused by the competition between the inertia and thermal buoyancy, as well as the air supply to the fire source. When the burner was placed under the atrium opening, there was a steady circulation of smoke with an upward flow through this opening, and a downward flow through the other. Smoke movement was accompanied by both the transverse diffusion and the settling process. An equation was derived to estimate the smoke filling time inside the building. The calculation results demonstrate that downward flow through the staircase may lead to a decrease in the smoke filling rate in the later stage of fire on the upper floor.

Experimental study on the upward annular two-phase flow of nitrogen and ethanol aqueous solutions with different concentrations

Vertical upward annular flow experiments of nitrogen gas and ethanol aqueous solutions with volume fractions of 30 %, 60 %, and 95 % under 0.2 MPa were conducted. The characteristics of the liquid film including base, average, and maximum film thickness and height, velocity, and frequency of disturbance waves were obtained and studied based on the constant electric current method in a 5 mm inner diameter polycarbonate tube. The flow behavior was observed using a high-speed camera simultaneously. It is found that a large number of bubbles in the liquid film is critical to these characteristics. A connection between ethanol concentration and bubbles in the liquid film is found and interpreted by considering bubble stability which arises from the dynamic rise in surface tension. Our experimental investigation suggests that the effect of bubbles in the liquid film on the flow characteristics is not negligible in such annular flows under high liquid flow rates and bubble stability should be considered for annular flows employing solutions consisting of two or more components with large differences in surface tension.

Applicability of Single-Borehole Dilution Tests in Aquifers with Vertical Flow

A set of experimental field single-borehole dilution tests were completed in the Motril–Salobreña detrital aquifer (Spain) in a sector with coarse material in four different moments under variable hydrological conditions. The comparative study of the tracer washing, and the temperature profile patterns for the tests carried out in two wells located hundreds of m from each other, revealed the presence of ascending vertical flows in one of the wells (not detected by other means) that compromises the reliability of the tracer test. The values of both the apparent horizontal velocity and hydraulic conductivity obtained in the affected well were less than half of those estimated in the well not affected by the upward vertical flows. The repetition of the test eight times during different seasons showed that the hydraulic conductivity calculated from the apparent horizontal velocity can vary; therefore, to approximate to a representative hydraulic conductivity value, using this method is recommended to carry out tests under different hydrological conditions and average the results. The difference generated by the changes in conditions for the specific setting of the study area was 25%. Taking this into account, it was considered that an approximation to the more representative value would be an average under variable hydrological conditions, resulting in a horizontal velocity of 6.7 m/d and hydraulic conductivity of 337 m/d. This information is critical for the management of the aquifer as it has strategic resources against droughts that are becoming more frequent in the Mediterranean area.

Verification and Validation of Spectral Element Code for Supercritical CO2 Flow in Vertical Heated Tubes

The investigation of heat transfer in supercritical CO2 (sCO2) has garnered considerable attention in recent decades, given sCO2’s potential as a promising working fluid for advanced power conversion cycles. Despite previous research efforts, there are still gaps in our understanding of sCO2 heat transfer, particularly in conditions associated with heat transfer deterioration. To delve into sCO2 heat transfer more comprehensively, we propose employing the high-fidelity computational fluid dynamics code NekRS to simulate sCO2 flow using the large eddy simulation technique. Through graphics processing unit acceleration, NekRS achieves a higher computational speed than traditional CPU-based systems. However, before using NekRS in practical applications involving sCO2, it is imperative to perform verification and validation. This paper presents our efforts to verify and validate the NekRS code’s capability for simulating sCO2 using heated vertical tubes, where heat transfer deterioration usually happens. To accommodate the unique properties of sCO2, we have modified the NekRS code by integrating third-party property modules, such as REFPROP and PROPATH. Our simulations are compared with experimental and numerical data from the literature, instilling confidence in leveraging NekRS for future engineering applications. Our simulations also reveal that the accuracy of the property module significantly impacts the results, with REFPROP outperforming PROPATH for sCO2 properties. Additionally, we observed that, depending on the flow direction, buoyancy can either enhance or suppress turbulence in sCO2 flow. In upward flow, under certain conditions, the suppressed turbulence leads to heat transfer deterioration, resulting in elevated wall temperatures.

Experimental and numerical study on the pressure drop and flow pattern of liquid foam in a foam generator

In the present study, a comprehensive analysis of the pressure drop, flow pattern, and foam structural properties of vertical upward two-phase flow in a Kenics static foam generator of a compressed air foam system was carried out. A liquid with an extremely low surface tension (16.5 mN/m) was used for making the foam. The effects of the number of elements (number of individual elements combined into the mixer), aspect ratio (the ratio of length to diameter of each element), and transition angle (transition angle between elements) of the Kenics mixers on the pressure loss during foam generation were studied in detail over a wide range of Reynolds numbers through experiments and numerical simulation. A new pressure drop correlation was successfully obtained by scaling analysis and the modified Lockhart–Martinelli correlation was proposed to describe the pressure drop during foam generation. Furthermore, the experimental results validated the proposed correlation and exhibited good reliability and predictive accuracy. Finally, four flow patterns for foam generation in vertical pipes that were different from the classical gas–liquid two-phase flow patterns were proposed, and the relationships among the pressure drop, flow pattern, and foam structural properties were explored. This research expands the study of foam generation in vertical tubes containing a built-in spiral structure with low flow resistance. It provides new insights and guidance for developing continuous foam manufacturing.