Mass Flux Research Articles

Numerical investigation of flow boiling characteristics in narrow rectangular channels using two-fluid Eulerian CFD model covering a wide range of pressures

Narrow channel heat exchange technology is one of the key technologies for the development of integrated small modular reactors (SMR). The ‘wall heat flux partitioning’ (WHFP) model in conjunction with an Eulerian–Eulerian Multiphase Flow (EEMF) method is found to be an important tool for two-phase hydrothermal analysis. In this paper, the accuracy of the EEMF-WHFP method with various sub-models is systemically evaluated over a large database of boiling flows in narrow rectangular channels. Prediction results using a total of 9 model combinations, are compared with data from 22 experimental conditions covering a range of the mass flux of 134.2 to 2200 kgm-2s-1, the inlet fluid subcooling of 7.2 to 74.2 K, the pressure of 0.1 to 14 MPa and the heat flux of 9.54 to 1700 kWm-2 in narrow rectangular channels with gaps of 1.0 to 3.0 mm. The evolution of distributions of void fraction, wall temperature and the net vapor generation (NVG) point along the flow channel is simulated and compared with experimental data. It is found that due to the limitation of the range of applicability of sub-models, certain models produced better prediction results under different pressure ranges than others, and the recommended combinations are given according to the quantitative assessments. In addition, the ability of the model combinations to predict the NVG point, as well as the flow structure and boiling process in narrow channels is investigated. The critical local void fraction near the wall at the NVG point is quantitatively estimated based on numerical results. The research conclusions in this paper can be used in thermal–hydraulic calculations in a wide range of operating pressures covering the applications of compact heat exchangers, flat plate fuels, climbing/falling film plate evaporators and the cooling of microelectronics, among other applications.

Solute transport in unsaturated porous media with spatially correlated disorder

Solute transport in unsaturated porous media is of interest in many engineering and environmental applications. The interplay between small-scale, local forces and the porous microstructure exerts a strong control on the transport of fluids and solutes at the larger, macroscopic scales. Heterogeneity in pore geometry is intrinsic to natural materials across a large range of scales. This multiscale nature, and the intricate links between two-phase flow and solute transport, remain far from well understood, by and large. Here, we use high-resolution direct simulation to quantify solute mixing and dispersion behavior within correlated porous media during drainage under an unfavorable viscosity ratio. Through analysis of flow and transport at multiple realizations, we find that increasing spatial correlations in pore sizes increase the size of the required Representative Elementary Volume (REV). We show that increasing the correlation length enhances solute dispersivity through its impact on the spatial distribution of low-velocity (diffusion-dominated) and high-velocity (advection-dominated) regions. Fluid saturation is shown to directly affect diffusive mass flux among high- and low-velocity zones. Another indirect effect of correlated heterogeneity on solute transport is through its control of the drainage patterns via repeated alteration in the connectivity of flowing pathways. Our findings improve quantitative understanding of solute mixing and dispersion under two-phase conditions, highly relevant to some of our most urgent environmental problems.

Effects of adding micro/nano-scale surface roughness on upward flow boiling of R-134a through annular tubes

The enhancement of heat transfer efficiency is crucial for development of high-performance thermal systems in various industrial applications. This study investigates heat transfer and pressure drop during upward saturated flow boiling of R-134a in annular tubes featuring smooth and micro/nano-scale roughened copper surfaces achieved through sandblasting and chemical etching. A high-pressure chamber with a glass side is designed to observe surface wettability and measure contact angles of R-134a on both surfaces. The annular tubes, with inner and outer diameters of 28.6 and 42 mm respectively, and a total heated length of 1000 mm, undergo varying mass flux, vapor quality, and saturation pressure within ranges of 6.73–20.19 kg m−2 s−1, 0.14–0.95, and 530–1000 kPa, alongside heat flux variations from 608 to 2432 W m−2. Results indicate that the application of micro/nano-scale roughness to copper surfaces minimally reduces the contact angle of R-134a which slightly improves its wettability. However, this modification significantly increases the heat transfer coefficient by 256 % compared to the smooth tube, albeit with an associated increase in pressure drop. Additionally, increasing mass flux and vapor quality increases both the heat transfer coefficient and pressure drop. Furthermore, higher heat flux results in a higher heat transfer coefficient with a small increase in pressure drop. Also, the experimental results are compared with some of the available correlations in the literature. The novelty and significance of this work advances our understanding of effect of surface roughness on flow boiling characteristics. Understanding these phenomena is crucial for optimizing the design and performance of heat exchangers and other thermal systems used in various industries, including refrigeration, air conditioning, and power generation.

Implementing the finite element numerical approach to optimize thermosolutal convection (TSC) energy imparted by discrete heat and solute sources in generalized Newtonian fluid flow in square enclosure

AbstractMesmerizing utilizations of thermosolutal convection (TSC) have been found in metallurgical and petrochemical procedures, crystal growth, thermal exchangers, nuclear waste disposal, and building environment control. In the current study, we considered three heat and solute sources on the left boundary of the cavity, which raises the significance of studying multiple chemical and civil engineering phenomena. Therefore, the prime motivation to commence this work is to attain the optimization of thermosolutal attributes characterized by non-Newtonian (power–law) liquid in the presence of installed sources. For this purpose, the natural convective flow governed by the nonpersistent impact of buoyancy forces is encompassed in the square enclosure. In addition to the source location, the vertical boundaries are considered to be cold, whereas the horizontal boundaries are kept insulated. Owing to the free convective flow, no compositional and thermal gradients are induced by lid movement, and all walls are prescribed with no-slip constraints. To examine the transport mechanism, structuring of problem is attained in the form of dimensional governing expressions by employing conservation laws. Subsequently, constitutive equations in a dimensionless format are accessed through similar variables. The finite element approach is employed to find the solution using COMSOL Multiphysics software. The deviations in the thermal and solutal fields are examined against the involved physical parameters by illustrating graphs and tables. Quantities of interest, such as the mean Nusselt and Sherwood numbers, are also computed against sundry parameters. The assurance of the computed results is validated by constructing a comparison with published studies. A grid sensitivity test is also executed to ensure the credibility of the built-in software (COMSOL). It is observed that the averaged heat and mass flux coefficient diminishes with an elevation in the magnitude of the power-law index (n), irrespective of the change in other involved parameters. The average Sherwood number tends to increase for a positive magnitude of (N) in contrast to negative values of (N). The average heat flux and average mass flux coefficients increase until the Prandtl number (Pr) reaches a value of 5 in shear thinning case at $$Ra\ge {10}^{5},$$ R a ≥ 10 5 , whereas, for n > 1 there is no substantial effect on either the average heat flux coefficient or average mass flux coefficient.

Analytical Solution for Contaminant Transport through a Soil–Bentonite (SB)/Geosynthetic Clay Liner (GCL)/Soil–Bentonite (SB) Composite Cutoff Wall and an Aquifer

This study develops a one-dimensional analytical solution for contaminant advection, diffusion and adsorption through a soil–bentonite (SB)/geosynthetic clay liner (GCL)/SB–aquifer composite cutoff wall (CCW) system. The solution agrees well with an existing double-layer model. Adopting toluene as a representative contaminant, using the present solution, the analysis systematically investigates the impact of hydraulic gradient (i) and the hydraulic conductivities of GCL (kgcl) and SB (ksb). The results show the following: (1) Increasing i from 0.1 to 1 reduces the concentration breakthrough time (tcb) from 20 to 11 years and mass flux breakthrough time (tfb) from infinite to 11 years, indicating lower i significantly extend both tcb and tfb, which is crucial for optimizing CCW barrier performance; (2) lowering kgcl from 5.0 × 10−11 m/s to 1 × 10−12 m/s and reducing ksb from 1.0 × 10−9 m/s to 1.0 × 10−11 m/s, would increase the tcb by 36% and 100%, respectively. It demonstrates that reducing kgcl and ksb could enhance barrier performance. (3) To achieve equivalent barrier performance, soil–bentonite cutoff wall (SBCW) requires greater thickness compared to SB/GCL/SB CCW, indicating that GCL reduces the required amount of bentonite; and (4) CCWs can use SB with lower adsorption capacity to achieve equivalent performance, further reducing bentonite requirements. The present solution can aid in the design and optimization of GCL-enhanced CCWs.

Simulation Analysis on the Characteristics of Aerosol Particles to Inhibit the Infrared Radiation of Exhaust Plumes.

Aerosol infrared stealth technology is a highly effective method to reduce the intensity of infrared radiation by releasing aerosol particles around the hot exhaust plume. This paper uses a Computational Fluid Dynamics (CFD) two-phase flow model to simulate the exhaust plume fields of three kinds of engine nozzles containing aerosol particles. The Planck-weighted narrow spectral band gas model and the Reverse Monte Carlo method are used for infrared radiation transfer calculations to analyze the influencing factors and laws for the suppression of the infrared radiation properties of exhaust plumes by four typical aerosol particles. The simulation calculation results show that the radiation suppression efficiency of aerosol particles on the exhaust plume reaches its maximum value at a detection angle (ϕ) of 0° and decreases with increasing ϕ, reaching its minimum value at 90°. Reducing the aerosol particle size and increasing the aerosol mass flux can enhance the suppression effect. In the exhaust plume studied in this paper, the radiation suppression effect is best when the particle size is 1 μm and the mass flux is 0.08 kg/s. In addition, the inhibition of aerosol particles varies among different materials, with graphite having the best inhibition effect, followed by H2O, MgO, and SiO2. Solid particles will increase the radiation intensity and change the spectral radiation characteristics of the exhaust plume at detection angles close to the vertical nozzle axis due to the scattering effect. Finally, this paper analyzed the suppression effects of three standard nozzle configurations under the same aerosol particle condition and found that the S-bend nozzle provides better suppression.

Assessment of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) Mass Flux and Distributions in a Lake System Using Sediment Bed Passive Flux Meters and Ceramic Dosimeters

AbstractPer‐ and polyfluoroalkyl substances (PFAS) are persistent in the environment due to their chemical stability and can spread quickly in a lake system due to mixing. Passive samplers allow for time‐weighted average concentration monitoring and the ability to detect low concentrations, which are difficult to measure with conventional grab sampling. This study demonstrates the feasibility of deploying both ceramic dosimeters and Sediment Bed Passive Flux Meters (SBPFMs) to assess time integrated PFAS concentrations and fluxes, respectively, at a historically contaminated PFAS lake near Baden‐Baden, Germany. Long‐term surface water grab samples resulted in the detection of PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFBS, PFHxS, and PFOS at a total concentration of approximately 1 μg/L. Dosimeters were deployed for 66 and 126 d, resulting in detected concentrations ranging from approximately 250 to 380 ng/L and 120 to 460 ng/L, respectively. The 66 d deployment resulted in the detection of PFPeA, PFHxA, PFHpA, and PFOA, whereas the 126 d deployment additionally detected PFBA, PFNA, PFDA, PFUnDA, PFDoDA, PFTeDA, PFBS, PFPeS, PFOS, PFNS, and PFDS. SBPFMs resulted in the detection of PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFUnA, PFTrDA, and PFBS and the determination of a total mass discharge of 5.6 g/d into the lake. Overall, dosimeters and SBPFMs are more sensitive than grab samples at detecting PFAS at low concentrations and can be used to better understand spatial distribution of PFAS in a lake system.

A mass-momentum consistent THINC-scaling scheme for CLSVOF method on co-located grid

Accurate numerical simulation of practical two-phase flows characterized by high density ratios are indeed challenging as spurious interfacial currents may disrupt the solution. To address such complexities, the present work considers a conservative discretization of the incompressible Navier-Stokes equation that advects the mass and momentum consistently on a co-located grid. An algebraic Coupled Level Set and Volume Of Fluid (CLSVOF) approach, based on THINC (Tangent of the Hyperbola for INterface Capturing)-scaling scheme is used to capture the interface. The numerical methodology relies on a balanced treatment of the pressure and other interfacial forces at the discrete level while emphasizing a compatible calculation of mass and momentum fluxes. Effectiveness of the present Consistent Mass-Momentum Transport (CMMT)-based THINC-scaling method is demonstrated by the thorough numerical analysis of advection of a high density drop. The obtained results signify the requirement of a balanced force CMMT framework for accurate and stable simulation of multiphase flows. Furthermore, performance of the present in-house multiphase solver is evaluated from practical tests like capillary wave, dam break, bubble rise and Rayleigh-Taylor instability. The present work is significant as it presents the capability of the CMMT-based THINC-scaling method to resolve precise interface profiles while preserving close to second order spatial accuracy.

Influence of Aluminum Content and Agglomerates Initial Velocity on Erosion in Solid Rocket Motor

Abstract Despite the aluminized propellants offering a high specific impulse, the challenge of nozzle erosion adversely impacts the rocket's performance and its potential for reusability. This study presents a numerical model aiming to predict the mechanical erosion of the propulsion chamber nozzle. The model employs an Eulerian/Lagrangian approach to simulate the complexity of the flow field within the rocket combustion chamber and the interactions between the continuous phase and particles. The model also includes a simplified representation of the aluminum particle combustion process, besides the consideration of secondary breakup phenomena in liquid droplets. Experimental and numerical data from the literature were used to validate the numerical model. Subsequently, the model was utilized to explore the impacts of increasing propellant aluminum content and varying particles' injection velocities on the nozzle mechanical erosion. The outcomes indicated that higher aluminum content leads to a 4-10% increase in nozzle erosion compared to the 15% content case. Furthermore, the aluminum particles tend not to fully burn within the combustion chamber and contribute to nozzle erosion. Lastly, particles with higher initial velocity at the inlet of the combustion chamber increase the nozzle mechanical erosion despite the observed decrease in incident mass flux.

Nanoparticle shape factor impact on double diffusive convection of Cu-water nanofluid in trapezoidal porous enclosures: A numerical study

Enclosures that contain both fluid and porous regions are utilized in various industries and geophysical processes to enhance heat and mass transfer. These enclosures find applications in fields such as geothermal engineering, drying of porous solids, cooling of electronics, metal solidification, and many others. In line with the motivation behind these applications, the present study explores double diffusion in the naturally convective flow of water-based nano fluid saturated in the trapezoidal porous enclosure and containing Copper (Cu) nano particles. The impact of uniformly applied radiative heat flux and nano particle shape factor is also accounted. A numerical investigation was carried out using a finite difference methodology integrated into a computational MATLAB code for numerical simulation. The simulation aimed to study the effect of nanoparticle shape factor on the effectiveness of a porous medium, which is exposed to two distinct objectives: enhancing heat transfer and optimizing mass transfer within a fluid-saturated porous medium. This research conducts a meticulous parametric exploration, underscoring the pivotal roles played by Darcy number (Da), nanofluid shape factor (m), Rayleigh number (Ra), thermal radiation (Rd), buoyancy ratio (Nr), and Lewis number (Le) in shaping the dynamics of flow, heat, and concentration transfer. The analysis of Nusselt and Sherwood numbers reveals that changing the shape of nano-particles from spheres to bricks increases the heat flux and mass flux coefficients by approximately 0.33% and 1.37% respectively. The results show a significant increase in Nusselt and Sherwood numbers, with blade-shaped nanoparticles demonstrating approximately a 2.97% and 10.82% improvement, respectively, compared to sphere-shaped nanoparticles. The outcome of this analysis yields an exhaustive dataset encompassing Nusselt and Sherwood numbers can be written as mathematical functions based on the parameters we talked about earlier.

Local condensation heat transfer analysis of three-component mixture refrigerant R455A in plate heat exchanger

Plate heat exchangers are gaining popularity as condensers for their compact design and high efficiency. However, the uneven fluid distribution in channels poses a challenge to effective heat transfer. Existing literature lacks experimental analysis of local heat transfer coefficients for pure and zeotropic mixture refrigerants in plate heat exchangers. This study experimentally analyzed the local heat transfer of the three-component zeotropic mixture R455A at various conditions (mass flux 20, 30, and 50 kg m−2 s−1 and saturation temperatures 30 and 35 °C). Results show that the heat transfer coefficient increases with flow rates and decreases with saturation temperature. However, results indicated lower heat transfer coefficients compared to pure refrigerants due to mixture effects. In addition, the local distribution of the heat transfer coefficient revealed that the heat transfer coefficient is highest at the center compared to the edges of the channel due uneven distribution of refrigerants within the channel. This HTC pattern confirms an asymmetrical flow within the plate. A new correlation is being developed to predict the heat transfer coefficient of the ternary mixture, showing improved accuracy than previously proposed correlations.

Non-Fourier computations of heat and mass transport in nanoscale solid-fluid interactions using the Galerkin finite element method

PurposeTo improve the thermal performance of base fluid, nanoparticles of three types are dispersed in the base fluid. A novel theory of non-Fourier heat transfer is used for design and development of models. The thermal performance of sample fluids is compared to determine which types of combination of nanoparticles are the best for an optimized enhancement in thermal performance of fluids. This article aims to: (i) investigate the impact of nanoparticles on thermal performance; and (ii) implement the Galerkin finite element method (GFEM) to thermal problems.Design/methodology/approachThe mathematical models are developed using novel non-Fourier heat flux theory, conservation laws of computational fluid dynamics (CFD) and no-slip thermal boundary conditions. The models are approximated using thermal boundary layer approximations, and transformed models are solved numerically using GFEM. A grid-sensitivity test is performed. The accuracy, correction and stability of solutions is ensured. The numerical method adopted for the calculations is validated with published data. Quantities of engineering interest, i.e. wall shear stress, wall mass flow rate and wall heat flux, are calculated and examined versus emerging rheological parameters and thermal relaxation time.FindingsThe thermal relaxation time measures the ability of a fluid to restore its original thermal state, called thermal equilibrium and therefore, simulations have shown that the thermal relaxation time associated with a mono nanofluid has the most substantial effect on the temperature of fluid, whereas a ternary nanofluid has the smallest thermal relaxation time. A ternary nanofluid has a wider thermal boundary thickness in comparison with base and di- and mono nanofluids. The wall heat flux (in the case of the ternary nanofluids) has the most significant value compared with the wall shear stresses for the mono and hybrid nanofluids. The wall heat and mass fluxes have the highest values for the case of non-Fourier heat and mass diffusion compared to the case of Fourier heat and mass transfer.Originality/valueAn extensive literature review reveals that no study has considered thermal and concentration memory effects on transport mechanisms in fluids of cross-rheological liquid using novel theory of heat and mass [presented by Cattaneo (Cattaneo, 1958) and Christov (Christov, 2009)] so far. Moreover, the finite element method for coupled and nonlinear CFD problems has not been implemented so far. To the best of the authors’ knowledge for the first time, the dynamics of wall heat flow rate and mass flow rate under simultaneous effects of thermal and solute relaxation times, Ohmic dissipation and first-order chemical reactions are studied.

When are galactic winds molecular?

ABSTRACT The molecular phase of supernova-driven outflows originates from the cold, molecular gas in the disc of a star-forming galaxy, and may carry a substantial fraction of the wind mass flux in some galaxies, but it remains poorly understood. Observations of this phase come mostly from very nearby galaxies due its low-surface brightness and covering fraction, and simulations often lack the spatial resolution necessary to resolve it. Here, we analytically estimate the survivability of this phase in order to understand under what conditions a galactic wind can contain a significant molecular phase. We show that the molecular content of outflows is primarily determined by two dimensionless numbers: a generalized Eddington ratio describing the strength of the outflow and the dissociation parameter, an ionization parameter-like quantity describing the strength of the radiation field per baryon. We apply this model to a sample of galaxies and show that, while any molecules entrained in the winds of normal star-forming galaxies should be destroyed close to the galactic disc, the outflows of strong starburst should become increasingly dominated by molecules.

Effect of twisted tapes and surface extensions in enhancing the condensation heat transfer of high-temperature saturated steam in a circumferential rectangular channel

This article numerically investigates the impact of twisted tapes and extended surfaces (fins) on enhancing high-temperature steam flow in a circumferential rectangular channel, akin to the external jacket cavity of a tyre cure press. The passive enhancement techniques for improving the mold warm-up time of the tyre curing process have received limited attention in previous studies, which have primarily focused on enhancing heat transfer in configurations and working conditions typical of heat exchanger applications. The objective of this article is to enhance the condensation heat and mass transfer rate by geometrically modifying the internal flow path of the circumferential rectangular channel, resembling an external jacket cavity of a tyre cure press, using twisted tapes and extended surfaces. Four configurations are simulated: i) conventional circumferential rectangular channel, ii) channel with twisted tapes, iii) channel with surface extension, and iv) channel with both twisted tapes and surface extension. The heat transfer performance of all the modified channel configurations derived from the simulation results is assessed in comparison to the conventional channel. The channel, featuring a design that includes five twisted tapes with a twist ratio of 8 and 54 extended surfaces, records a substantial 36.85% rise in heat flux along with a notable 24% increment in the condensation mass flux. The simulation results are validated using an in-house experimental study. The tyre cure press in the experimental setup is modified to align with the design proposed by the simulation results, and a warm-up study is conducted. The warm-up time for the modified mold to attain the desired temperature is reduced by 33%, with no accompanying increase in steam consumption, compared to the warm-up time for the conventional mold. This significant reduction in mold warm-up time holds immense potential in enhancing the productivity rate, an ongoing requirement of the automobile industry.

Frictional pressure drop correlation of steam-water two-phase flow in helically coiled tubes

Helically coiled tubes are utilized as the heat transfer tubes for High-Temperature Gas-cooled Reactor (HTGR) steam generators due to their compactness, thermal expansion accommodation and high heat transfer coefficient. A clear understanding of the pressure drop characteristics is important for the design and operation of steam generators. In this study, experiments were conducted to investigate the frictional pressure drop characteristics in helically coiled tube with a very large curvature ratio of 0.109. The experiments were carried out in a steam quality range of 0.1–0.9, system pressure range of 3.5–7 MPa, mass flux range of 320–1100 kg/m2s. The results indicate that the frictional pressure drop increased with the increase of mass flux, decreased with the increase of system pressure. It first increased with the increase of steam quality, and reached a maximum value at a steam quality of approximately 0.8, then decreased until steam quality reached unity. Based on the present work and existing experimental database, 25 existing correlations are evaluated and none of them could satisfactorily fit all the data. Therefore, a new correlation based on the Martinelli and Nelson correlation was proposed. Compared with existing correlations, it has a broader range of applicability (operating pressure from 0.75 to 8 MPa, mass flux from 200 to 1100 kg/(m2·s), steam quality from 0.03 to 0.99, and curvature ratio from 0 to 0.109.), and higher accuracy (weighted mean MAPE of 8.92 % and arithmetic mean MAPE of 8.81 %). It also has better compatibility with straight tubes.

The Role of the Toroidal Vortex in Cumulus Clouds' Entrainment and Mixing

AbstractShallow convective clouds play a crucial role in Earth's energy budget, as they modulate the radiative transfer in the atmosphere and participate in the vertical transport of aerosols, energy, and humidity. The parameterizations representing these complex, vital players in weather and climate models are mostly based on a description of steady‐state plumes and are a source of major uncertainty. Recently, several studies have shown that buoyant thermals are inherent in atmospheric convection and contain a toroidal (ring) vortex. This work studies those vortices in growing shallow cumulus (Cu) clouds using high‐resolution (10 m) Large Eddy Simulations that resolve these vortices in much detail. Recent analysis of such data showed that small‐scale turbulent diffusion is unable to explain the large diluted portion of the cloud. Here we advocate for the important role of the Cu toroidal vortex (TV) in cloud dilution and present the complex dynamics and structure of a Cu TV. Nevertheless, since the vortex dominates the cloud's dilution, simplicity emerges when considering the cloud's lateral mass flux profile. The cloud mixing is quantified using direct flux calculations and Eulerian tracers. In addition, Lagrangian tracers are used to identify the origin of the entrained air and its thermodynamic properties. It shows that most of the air entrained by the vortex is not recycled by the vortex, yet is significantly more humid than the environment. We suggest that the development of new models describing thermals, together with their toroidal vortices, might improve cloud parameterizations in weather and climate models.

Water quality and wetland vegetation responses to water level variations in a university stormwater reuse reservoir: Nature-based approaches to campus water sustainability

In response to climate-driven water shortages, Duke University in 2014 constructed a water reuse reservoir and wetland complex (Pond) to capture urban stormwater and recycle water to provide campus cooling and reduce downstream loading of nutrients and sediment into Jordan Lake, a regional water supply. We postulated that even with significant water level changes due to withdrawals, the Pond would function to reduce downstream nutrients and sediment once wetland plants became established in the littoral zone. Throughout the project (2015–2021), baseflow nutrient concentrations downstream decreased, with Unfiltered Total Nitrogen (UTN) falling by 44 % and Unfiltered Total Phosphorus (UTP) by 50 %. Storm mean concentrations decreased by 31 % for UTN, 54 % for UTP, and 72 % for Total Suspended Solids (TSS). The annual reductions in mass fluxes (UTN, UTP, and TSS) were between 58 and 85 % across a range of storm intensities. Regardless of water level, temperature, pH, and oxygen concentrations downstream were not significantly changed. Between 2015 and 2020, a littoral survey of planted and naturally introduced species showed that wetter years resulted in a greater number of species across a gradient of three inundation zones (i.e., moist, wet, and aquatic). Conversely, dryer years resulted in fewer species across overlapping zones. The dominant plants that successfully colonized the Pond are all obligate wetland species despite the Pond's highly variable water depths and periods of inundation. The final plant populations were dominated by invasive native species supporting the self-design theory of plant succession as nearly half of the original planted species died. The reuse Pond design (pond-wetland complex) showed the capability of using stormwater runoff for campus cooling while improving water quality services and providing habitat for wetland plants. Thus, campuses with watershed runoff capture capability should consider a nature-based recycling approach as part of their water sustainability program.

A physics-informed, data-driven framework for estimation and optimization of two-phase pressure drop of refrigerants in mini- and macro channels

At present, there is no universally accepted approach for forecasting the flow boiling heat transfer in the scientific literature. The objective of this study is to predict and optimize the two-phase pressure drop (2ϕΔP) for different refrigerants in both mini and macro-sized channels under various operating conditions. The dataset is amassed from open literature and consists of 1954 points that include seven different refrigerants, including R12345yf, R1234ze, R134A, R410A, R22, R744, and R717 containing heat flux (Q) in the range 0–40 kW/m2, hydraulic diameters (Dh) in the range 0.509–14 mm, mass flux in the range 55 < G < 1800 kg/m2s, saturation temperature (Tsat) in the range -40 – 43 °C, and flow qualities (x) in the range 0.001–0959. The first step involves conducting feature engineering operations to select the most significant and impactful features for estimating the considered output. The interpretation by Pearson’s correlation highlighted that Dh, Tsat, x, Q, and G were the most impactful params. The Bayesian optimization incorporated with surrogacy was used to determine the required hyper-parameters, which were then deployed to form multi-layer deep neural network (DNN) for estimating 2ϕΔP. A metaheuristic algorithm known as differential evolution (GA) was used to estimate Dh, Tsat, x, Q, and G to minimize the pressure drop. The performance of the established model was determined to be highly accurate with an accuracy of 0.9985. Additionally, an appropriate 2ϕΔP value for each refrigerant was provided to obtain the optimized values of the different input features. The optimized ML (regression) models performed better than the existing semi-empirical pressure drop correlations. This approach can be beneficial for the development and improvement of various engineering systems, particularly those involving the 2ϕΔP of numerous refrigerants.

Unsteady MHD‐radiative thin film flow with heat transfer over a stretching surface in porous media

AbstractThis study conducts a computational analysis to explore how magnetic fields, radiation, heat, and mass transfer collectively influence a horizontal stretching sheet within a porous medium. The research focuses on elucidating the dynamics of thin film flow through the formulation of time‐dependent equations and subsequent transformation of fluid flow equations into ordinary differential equations via similarity transformation. The numerical solution is attained employing the Runge–Kutta fourth‐order method coupled with a shooting technique. MATLAB software is utilized to generate graphs and numerical values, offering a detailed representation of engineering‐relevant physical quantities in tabular form. The investigation revealed notable trends associated with varying parameters. Increasing unsteadiness parameters lead to a reduction in velocity, temperature, and concentration fields, while the temperature distribution demonstrates a positive correlation with radiation parameters. Moreover, elevated Prandtl numbers and unsteadiness parameters correspond to augmented heat and mass flux, respectively. Of particular significance is the observed heightened heat transfer rate during the transition from a Prandtl number of 1 (representing air) to 2 (representing oil), alongside an increased mass transfer rate with the escalation in Schmidt number from 0.62 (representing hydrogen) to 0.78 (representing ammonia). A comparative analysis of the numerical findings with existing literature demonstrates excellent agreement, affirming the validity and relevance of the present study. These insights offer valuable implications for understanding and optimizing heat and mass transfer processes in porous media, with potential applications in various engineering and scientific domains.

A new paradigm in critical flow analysis: Combining Buckingham Pi theorem with neural network for improved predictions in microchannels

Critical flow phenomena are prevalent in many chemical engineering processes, such as microchannel heat exchangers, nuclear safety analysis, jet pump modeling, and industrial systems utilizing subcooled or two-phase pressurized fluids. Understanding the impact of various physical parameters on critical flow and accurately predicting critical flow mass flux is essential in these processes. This article collects extensive experimental data on subcooled water two-phase critical flow and supplements it with additional experimental data from actual micro-cracked channels, constructing a comprehensive benchmark database. The database covers an inlet pressure range of 1.82–16.29 MPa, an inlet subcooling range of 0.3–119.35 K, and a microchannel hydraulic diameter range of 0.09–2.2 mm. By integrating the classical Buckingham Pi theorem with a data-driven active subspace method, the dominant dimensionless numbers in subcooled water two-phase critical flow were identified, addressing some limitations of the Buckingham Pi theorem by ranking the influences of these dimensionless numbers. Based on these dominant dimensionless numbers, the impact of physical quantities on two-phase critical flow was accurately identified, leading to a concise predictive correlation for critical flow mass flux with a mean absolute percentage error of 20.3 % across 1071 experimental data points, outperforming commonly used critical flow models. Furthermore, leveraging the dominant dimensionless numbers improved existing model results, enhancing the Henry-Fauske model’s overall prediction accuracy from a mean absolute percentage error of 47.6 % to 17.8 %. This study outlines a promising path for discovering physical characteristics and mechanisms in data-driven critical flow, facilitating a deeper understanding of critical flow phenomena.