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The accurate estimation of flow resistance has significant practical value and is one of the long-standing challenges that has vexed the engineering community. Traditional methods often rely on specific assumptions or empirical approaches, resulting in resistance formulas with limited accuracy and poor generalizability. Additionally, current machine learning methods in practice are constrained by limited model complexity and poor interpretability, encountering bottlenecks in estimating flow resistance. To address the aforementioned issues, this paper establishes a flow resistance estimation model based on Deep Forest (DF) and employs Shapley Additive Explanations (SHAP) to interpret its outcomes. This innovative approach overcomes the predictive limitations of traditional models by incorporating techniques such as layer-by-layer processing and in-model feature transformation. Meanwhile, grounded in game theory, SHAP ensures the model’s outputs are comprehensible. Utilizing field data from the Yellow River Basin, a flow resistance estimation experiment is conducted with the Froude number, width-to-depth ratio, volumetric suspended sediment concentration, and diameter-to-depth ratio as input features for both the DF and benchmark models. The results indicate that the DF model, with an optimized Nash-Sutcliffe efficiency of 0.752, shows improvements in accuracy of 0.67%, 1.48%, 3.87%, 22.88%, and 269.75% compared to Random Forest, Light Gradient-boosting Machine, Artificial Neural Network, Zhang’s formula, and Brownlie’s formula, respectively. Additionally, the SHAP analysis reveals that the Froude number is the most significant variable in calculating flow resistance, underscoring its critical role in the model’s performance. [ABSTRACT FROM AUTHOR]

Dunes formation in sandy rivers significantly impacts flow resistance, subsequently affecting water levels, flow velocity, river navigation, and hydraulic structures performance. Accurate prediction of flow resistance and dune geometry (length and height) is essential for environmental engineering and river management. The current paper introduces two models to evaluate the flow resistance and geometry of dunes formed in sand-bed channels. The first model, RANN–AHA is a hybrid artificial intelligence model using the recurrent artificial neural network (RANN) linked with the artificial hummingbird optimization algorithm (AHA) to optimize the biases and weights of the neural network model. The second model uses gene expression programming (GEP) as a nonlinear approach based on a genetic algorithm (GA) and genetic programming (GP) to explicitly determine dune characteristics. For both models, the input parameters include flow and sediment characteristics, while Manning's roughness coefficient (n M), and relative dune height, h / H or h / L , were used as output parameters where h is the dune height, H is the flow depth above the dune crest, and L is the dune length. Five different published flume data sets were compiled for the analysis. Sensitivity analysis was done using different combinations of input parameters. It was found that the combination of hydraulic radius divided by median diameter (R H / d 50), Reynolds number (Re), Particle densimetric Froude number (F ∗), and grain Froude number (F G) yielded the best prediction accuracy for estimating Manning n M and relative height, h / H or h / L , with a root mean square error (RMSE) = 0.00027, 0.0504, and 0.0078 and a correlation coefficient (R) = 0.9989, 0.942, and 0.9272, respectively. Model verification proved that the RANN–AHA model outperformed the GEP model and most of the previous studies available in the literature when predicting the roughness coefficient and dune geometry in sand bed channels. • An optimized-recurrent artificial neural network (RANN–AHA) model is developed to predict the characteristics of dunes formed in sand bed channels (roughness and geometry). • Artificial hummingbird algorithm (AHA) is employed to optimize the (RANN) model biases and weights. • Gene expression programming (GEP) is utilized to deduce an explicit solutions for dunes characteristics (Manning's roughness coefficient, relative height and ratio of dune height to dune length). • Sensitivity analysis was performed to test the influence of each or possible combinations of the input parameters on the model outputs (roughness and geometry). • The performance of both models was assessed and compared to each other and to previous studies available in literature using the Taylor diagram in terms of root mean square error (RMSE), correlation coefficient (R), and standard deviation (SD) as statistical measures. [ABSTRACT FROM AUTHOR]

The supply and exhaust system of the experimental rack on the Chinese space station is a complex integrated system. In this paper, a multi-stage simulation, testing, and verification method is designed for a multi-team, multi-location, and multi-stage integrated gas system. This method is designed to solve the problem of missing input parameters between the gas supply system and the exhaust system. Preliminary tests and strategy verifications were carried out through theoretical simulation and semi-physical simulation, and good calculation results were obtained for the single-rack product. The external systems were tested using a simulation system, and a calculation method was designed to obtain relatively accurate parameters. In the early stage, the performance of the product was predicted using the parameter library of Flomaster and semi-physical simulation methods, but the error was large. In the middle and late stages of development, as some products became realistic, multi-stage testing was carried out using a vacuum simulator, simulated flow resistance, and other methods, achieving a performance prediction with an error of 12% before ground testing. The final ground test and on-orbit test showed that the design and calculation method of this paper is effective. The multi-stage design method proposed in this paper was successfully applied to the integrated gas system of the Chinese space station, which can provide a reference for the design of fluid components in long-term system engineering. [ABSTRACT FROM AUTHOR]

Vegetation plays a crucial role in mitigating and controlling soil erosion caused by overland flow. However, variations in the hydraulic characteristics of overland flow induced by the spatial distribution of vegetation with different row and column spacings are often overlooked in existing literature, potentially leading to significant deviations in predicting these characteristics. In this study, 180 lab‐scale runoff tests were conducted to clarify the hydraulic characteristics of overland flow considering six α (the ratio of the lateral distance of vegetation to stem diameter) levels, six β (the ratio of the slope distance of vegetation to stem diameter) levels, and three slope angles (θ) under five flow discharges (Q) conditions. The results show that the observed flow regime of overland flow belongs to the transition flow regions, shifting from slow to rapid as α and/or β increase. The friction coefficient and the proportion of frictional resistance in the total flow resistance increase with increasing α and β. The local resistance dominates the total flow resistance of bare glass slopes. The local resistance coefficient ξ decreases with increasing α and β, however, it initially increases and then decreases with increasing θ. The impact of β on the local resistance is greater for gentle slopes, whereas the impact of α is more significant for steep slopes. ξ exhibits a negative correlation with Re and the ξ‐Re curves gradually level off as α or β increases, while they become steeper with increasing θ. A prediction model for the total flow resistance was established taking into account the combined effects of Re, α, β and θ, which provides better prediction performance than two other relevant models. The results obtained from this study provide valuable insights into the hydraulic characteristics of overland flow and offer clear guidance for vegetation management in controlling soil erosion on slopes with heterogeneous vegetation coverage. [ABSTRACT FROM AUTHOR]

Quantifying turbulent friction holds significant importance, not only for understanding the fundamental flow physics but also for enriching system performance across a wide range of engineering applications. This vision article presents the state of the science of the turbulent friction in canonical flows, shedding light on its current status through a combination of theoretical developments and experimental observations. First, the article discusses the law of the wall, including the scaling behavior, the possible origin of the logarithmic law, and the effects of wall roughness. Then, it provides an overview of roughness height and its connection with the wall topography. The scaling behaviors of the logarithmic and power laws of turbulent friction are thoroughly appraised, offering insights into their implications. Additionally, the phenomenological models of turbulent friction based on the spectral and co-spectral budget theories are furnished. The behavior of turbulent friction for extremely large Reynolds number flows is examined, based on theoretical models and experimental data. The semiempirical finite Reynolds number model for turbulent friction is reviewed, emphasizing the pertinent scaling laws in various forms. The scaling laws of turbulent friction in curved-pipe and axisymmetric boundary layer flows are discussed. Finally, future research directions are outlined, highlighting the key challenges to be addressed. [ABSTRACT FROM AUTHOR]

• Knowledge of the drag coefficient is necessary in channels with rigid vegetation. • A drag coefficient was proposed in the past as function of vegetation density only. • This drag coefficient allows two different sets of profiles to be drawn correctly. • The effective width was taken into account in the profile computation. • In profile computations, the boundary condition in subcritical flows must be downstream. Although vegetation in watercourses has an important ecological function, from a hydraulic point of view, it increases flow resistance, determinates higher water levels and generates a greater risk of flooding. In engineering practice, to determine water levels, the drag coefficient must be known, whose experimental values, in literature, are provided for uniform or quasi-uniform flow. In this paper, the expression of a drag coefficient, previously proposed by the authors for the case of emergent rigid vegetation arranged in a linear manner, was used to simulate experimental water surface profiles, employing the effective width for the first time. The formula was validated by simulating 26 experimental profiles observed at the University of Calabria, over 1100 points in total, plus 8 published in literature. In some of these applications, the vegetation density was much higher than that for which the drag coefficient expression was derived. For this reason, it is possible to consider a new, wider field of validity for it. The proposed equation is independent of the Reynolds stem number, so that it can be used in natural streams and rivers, provided that viscosity effects can be considered negligible. Finally, some comments are offered on the application of a new formula proposed in literature regarding the computation of the profile when downstream depth is taken as a boundary condition. [ABSTRACT FROM AUTHOR]

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

The paper investigates experimentally the thermal performance and flow resistance of two-phase flow shell-and-tube heat exchangers (STHEs). STHE is configured with flat surface baffles (FSB), 4 mm amplitude-20 mm pitch sinusoidal baffles (SB), and 2 mm amplitude-20 mm pitch SB. The heat exchangers have the same geometrical design and tube count, with the exception of the baffles. The working fluids in the shell and tube side are hot water and cold air-water mixture, respectively. During the experiment, the hot water flow rate ranged from 1.63 to 2.718 kg/s, while the cold air-water mixture flow rate was set at constant value of 2.14 kg/s. The results show that the Nusselt number and overall heat transfer coefficient were highest and lowest in STHE with 2 mm amplitude-20 mm pitch SB and STHE with 4 mm amplitude-20 mm pitch SB, respectively, in comparison to STHE with FSB. When compared to STHE with FSB, and STHE with 4 mm amplitude-20 mm pitch SB, the STHE with 2 mm amplitude-20 mm pitch SB shows improvement in Nusselt number of about 36% and 21.44%, respectively. The two SB heat exchangers had lower Euler values, which indicates that their flow resistance is lower than that of STHE with FSB. Compared to STHE with FSB, there is a reduction of approximately 36% and 19%, respectively, for Euler's values for STHE with 2 mm amplitude-20 mm pitch SB and 4 mm amplitude- 20 mm pitch SB. This study demonstrates that the use of SB in the shell side of a twophase flow STHE tremendously improves thermal performance without a corresponding increase in shell side flow resistance or pumping power. Hence, energy saving and improved heat transfer capacity are possible with SB type heat exchanger. [ABSTRACT FROM AUTHOR]

Murray’s law, as the best-known optimal relationship between bifurcation calibers, is obtained based on the assumption of steady-state Poiseuille blood flow and is mostly accurate in small vessels. In middle sized and large vessels such as the aorta and coronary arteries, the pulsatile nature of the flow is dominant and deviations from Murray law have been observed. In the present study, a general scaling law is proposed, which describes the optimum relationship between the characteristics of bifurcations and pulsatile flow. This scaling law takes into account the deviations from Murray law in large vessels, and proposes optimal flow (i.e. less flow resistance) for the full range of the vascular system, from the small vessels to large ones such aorta. As a general scaling law, it covers both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is that bifurcation characteristics solely depend on the Womersley number of parent vessels. The diameter ratios suggested by this scaling law are in acceptable agreement with available clinical morphometric data such as those reported for coronary arteries and aortoiliac bifurcations. A numerical simulation of pulsatile flow for several Womersley numbers in bifurcation models according to the proposed scaling law and Murray law has been performed, which suggests that the general scaling law provides less flow resistance and more efficiency than Murray law in pulsatile flow. [ABSTRACT FROM AUTHOR]

Brush seals are extensively used in rotating equipment, such as gas turbines and compressors, providing effective sealing while accommodating radial, axial, and angular movements between components. In this study, the performance of brush seals with and without clearances was predicted through axisymmetric 2D computational fluid dynamic (CFD) simulations using a porous media model. Because the accurate modeling of a brush seal requires the appropriate porosity to be determined and the flow resistance to be calculated, a porosity correction was performed based on the brush seal's geometry and pressure ratio. The corrected porosity was then used to calculate the flow resistance and the leakage flow rate was predicted. Based on the results, the corrected porosity significantly improved the accuracy of the previously unreliable leakage flow rate predictions, regardless of the presence of clearances. For cases with a clearance, the blow-down effect was determined through CFD simulations for the given geometry and was compared with experimental data. The leakage flow rate predictions were highly accurate, with a relative error of less than 5% across a pressure ratio range of 1.5–4. [ABSTRACT FROM AUTHOR]

An axial flow tubular heat exchanger has been experimentally investigated to augment the heat transfer rate with a novel swirl flow of air past the heated tubes. The novel design has been made on the circular baffle plates provided with trapezoidal air deflectors of various inclination angles α, which is the angle made by the deflector surface with baffle plane. The arrangement of tubes, which were supported on baffle plates, was kept the same throughout the experiment analogy with the peripheral longitudinal air flow directed on it. All the tubes were maintained at constant heat flux condition over the entire surface. There were four deflectors developed on each of the baffle plate each deflector with equal inclination angle which generates air swirls inside the circular duct carrying the heated tubes that increase air side turbulence and hence the surface heat transfer rate. For every Re the baffle plates were placed equidistant from each other at different pitch ratios (PR = 0.6, 0.8, 1.0, and 1.2). The Reynolds number Re was kept in the range of 93 500–160 500. The effect of pitch ratios and the inclination angles on the thermo-fluid performance of the heat exchanger has been studied. The investigations reveal an average improvement of 25.1% in the thermo-fluid performance for a heat exchanger provided with the deflector baffle plates (DBP) having an inclination angle of 50° and a pitch ratio of 1.2 compared to that of a heat exchanger with a segmental baffle plate (SBP) tested under similar conditions of operation. [ABSTRACT FROM AUTHOR]

Abstract Our aim is to recreate the distinct patterns observed in gravel-bed river channels for studies involving physical modeling by designing a morphological configuration and investigating bed resistance. We used a 10x0.56x0.4m experimental channel that scaled-down a natural river at a ratio of 1:20, utilizing sand as the bed material. Employing both field data and measuring instruments such as a laser profiler and pitot tube, we conducted a total of 12 tests spanning 27 hours. In the initial 15-hour phase, we closely monitored deformations and sediment transport under various flow rates. Subsequently, we adjusted the flow rates and proceeded with testing. The results indicated that a larger diameter of the movable bed led to increased flow resistance, evident in parameters like n, f, and C. Additionally, we observed the deposition of fines within intergrain voids and noted an increase in ks with reduced discharge volume, illustrating the influence on flow dynamics and sediment transport. Furthermore, this preliminary study provides valuable insights into the physical processes governing water and sediment transport, which are crucial considerations for future physical simulation studies.

The investigation of frictional pressure drops in wire-wrapped bundles at low flow velocities is crucial for thermal-hydraulic studies of sodium-cooled fast reactor cores. This study aims to refine empirical formulas for predicting friction factors in wire-wrapped bundles by addressing their limitations in accurately calculating friction factors during transition regime. By analyzing existing empirical formulas and meticulously observing frictional pressure drop experiments conducted under low-flow conditions that reported in the literature, the study proposes and demonstrates the mechanism of the laminar-to-transitional regime transition in wire-wrapped bundles. Additionally, experimental research was conducted on the frictional pressure drop of a 37-rod wire-wrapped bundle. A novel high-precision differential pressure measurement technique, the photographic liquid column manometer, was employed to enhance frictional pressure drop measurement accuracy. This innovative method achieves a measurement uncertainty of less than 2 Pa within a range of 0 to 300 Pa. The mass flow rate of the fluid was measured and converted to obtain the flow velocity through the assembly, further improving the accuracy of flow velocity measurements. The analysis and experiments reveal that the transition from the laminar to transitional regime does not occur uniformly but initiates locally in certain subchannels before spreading across the assembly as flow velocity increases. Significant increases in the frictional pressure drop occur only after a sufficient number of subchannels have undergone transition. This perspective is supported by extensive existing literature, which report that in assemblies with fewer rod bundles, smaller P/D and H/D values, and constructed from hard metal materials such as stainless steel, the friction factor at the initial stage of the transitional regime shows a significant increase or remains constant with increasing Reynolds number. Under these conditions, the high consistency of the P/D ratio within the assembly causes the fluid to transition within a narrow range of flow velocities, leading to a marked increase in the friction factor with Reynolds number. The research results also indicate that the prediction accuracy of the critical Reynolds number for the laminar-to-transitional flow transition significantly impacts the calculation accuracy of empirical formulas at low flow velocities. Formulas using smaller predicted values of the critical Reynolds number show better agreement between predicted values and the measured results in this study. Therefore, the study recommends adopting smaller critical Reynolds numbers and interpolation indices in empirical formulas to facilitate an early onset and smooth transition of laminar-to-transitional regime behavior in friction factors, thereby improving the accuracy of calculated friction factors.

This study experimentally investigates the impact of flow resistance in risers and downcomers on the heat transfer performance of two-phase thermosyphon loops (TPTLs) with CO2, R134a, and R410A refrigerants. Variations in the heat transfer limit and thermal resistance of the TPTLs were analyzed. The results show that the three TPTLs respond differently to changes in flow resistance. For the CO2 TPTL, the effects of the riser and condenser resistances on thermal performance are similar. When the opening angle of the riser or condenser valve decreases from 90° to 30°, the heat transfer limit of the CO2 TPTL decreases from 1 200 W to 700 W. For the R134a and R410A TPTLs, when the opening angle of the riser valve decreases from 90° to 30°, the heat transfer limit of the R410A TPTL decreases from 1 300 W to 700 W, and the R134a TPTL does not reach normal operating conditions, resulting in substantial superheating and subcooling inside the pipes and a substantial increase in thermal resistance for both types. An increase in the condenser resistance has little effect on the thermal performances of the R134a and R410A TPTLs. For practical design considerations, the same or similar diameters should be used for the riser and downcomer of a CO2 TPTL. However, for R134a and R410A TPTLs, the riser diameter should be significantly larger than the downcomer diameter to achieve material cost savings.

Murray’s law, as the best-known optimal relationship between bifurcation calibers, is obtained based on the assumption of steady-state Poiseuille blood flow and is mostly accurate in small vessels. In middle sized and large vessels such as the aorta and coronary arteries, the pulsatile nature of the flow is dominant and deviations from Murray law have been observed. In the present study, a general scaling law is proposed, which describes the optimum relationship between the characteristics of bifurcations and pulsatile flow. This scaling law takes into account the deviations from Murray law in large vessels, and proposes optimal flow (i.e. less flow resistance) for the full range of the vascular system, from the small vessels to large ones such aorta. As a general scaling law, it covers both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is that bifurcation characteristics solely depend on the Womersley number of parent vessels. The diameter ratios suggested by this scaling law are in acceptable agreement with available clinical morphometric data such as those reported for coronary arteries and aortoiliac bifurcations. A numerical simulation of pulsatile flow for several Womersley numbers in bifurcation models according to the proposed scaling law and Murray law has been performed, which suggests that the general scaling law provides less flow resistance and more efficiency than Murray law in pulsatile flow.

Relative submergence of macroroughness elements such as boulders and bedrock outcrops, or large bed elements (LBEs), collectively, is a primary control on hydraulics and morphodynamics in steep, coarse-bedded rivers. However, in practice, the property is typically represented by singular, often reach- or cross-section-averaged values that mask bed-surface heterogeneity and joint distributions of local flow depths. By coupling sub-meter resolution two-dimensional (2D) hydrodynamic modeling with spatially explicit mapping of LBEs from a 13.2 km segment of a boulder-bedded mountain river, we present complete distributions of LBE relative submergences at multiple spatial scales and explore their dynamism across discharges. Through distribution fitting and statistical analysis of resultant discharge-dependent LBE relative submergence datasets, it was confirmed that segment- and reach-scale datasets exhibited similar statistical properties and were able to be drawn from the same type of distribution. Further, the rate at which statistical and parametric properties changed between discharge-dependent datasets were statistically equivalent between spatial domains, which we term “process-based similarity”. Commonality in distribution type and the uniform between discharge–scaling relationships suggest mutual self-organizing processes associated with the size-frequency distribution, spatial arrangement, and submergence of LBEs were present between most domains.

Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied successfully for non-submerged conditions whereas its suitability for submerged conditions requires further development. This study investigates the vegetative flow resistance at low relative submergences and extends existing LAI-based approaches building upon new flume data and prior experiences from field-scale applications. We provide advanced LAI-based formulas for modelling the flow resistance from emergent to submerged conditions, with water depth up to three times higher than the vegetation height. Such low relative submergences are highly relevant in hydraulic analyses of riverbank and floodplain flows but not adequately represented in existing formulas. The use of the deflected vegetation height as the characteristic height provided the most accurate modelling results, whereas the use of undeflected height resulted in significant errors. As a new development for submerged conditions, we proposed von Kármán scaling factor for improved model predictions. Overall, the results proved that LAI-based modelling is suitable also at low relative submergences for a wide range of vegetation densities (LAI = 1–5) and mean flow velocities (0.05–1.2 m s−1). For both emergent and slightly overtopped vegetation the JAR and VAS approaches outperformed the BAPmod-LAI approach that does not account for reconfiguration. For modellers, we provide a workflow and guidance on the use of the newly developed LAI-based formulas in 1D/2D hydrodynamic models for both emergent and submerged conditions. [ABSTRACT FROM AUTHOR]

Morphologies of the porous materials influence the processes of solar radiation transport, flow, and thermal behaviors within volumetric solar receivers. A comprehensive comparative study is conducted by applying pore scale numerical simulations on volumetric solar receivers featuring various morphologies, including Kelvin, Weaire-Phelan, and foam configurations. The idealized unit cell and X-ray computed tomography scan approaches are employed to reconstruct pore scale porous models. Monte Carlo ray tracing and pore scale numerical simulations are implemented to elucidate the radiative, flow, and thermal behaviors of distinct receivers exposed to varying thermal boundary conditions and real irradiation situations. The findings demonstrate that the foam structure exhibits greater solar radiation absorptivity, while Kelvin and Weaire-Phelan structures enhance the penetration depth under non-perpendicular solar irradiation. In comparison with Kelvin and Weaire-Phelan configurations, the foam structure presents efficient convective heat transfer, with the Weaire-Phelan structure showing pronounced thermal non-equilibrium phenomena. The variance in convective heat transfer coefficient between Kelvin and Weaire-Phelan configurations is approximately 8.4%. The foam structure exhibits higher thermal efficiency and flow resistance under non-perpendicular irradiation compared to Kelvin and Weaire-Phelan structures, attributed to its smaller pore size and intricate flow channels. An increase of 1.3% in thermal efficiency is observed with a substantial rise in pressure drop of 32.2%. [ABSTRACT FROM AUTHOR]

A theoretical simulation is performed to evaluate how microcracks affect the flow resistance in tumors during the convection-enhanced delivery (CED) of nanofluids. Both Darcy's law and the theory of poroelasticity are used to understand fluid transport with or without microcrack introduction and/or enlargement. The results demonstrate significantly altered pressure and velocity fields in a spherical tumor with a radius of 10 mm due to the presence of a microcrack with a radius of 0.05 mm and length of 3 mm. The non-uniform fluid pressure field enlarges the original cylindrical microcrack to a frustum, with the crack volume more than doubled. Due to the larger permeability and porosity in the microcrack, flow in the tumor is much easier. One finds that the flow resistance with the enlarged microcrack is reduced by 14% from the control without a microcrack. Parametric studies are conducted to show that larger crack radii, longer crack lengths and higher infusing pressures result in further resistance reductions. The largest resistance reduction occurs when the infusing pressure is 4 × 105 Pa and the microcrack is 9 mm long, up to 18% from the control. We conclude that introducing a microcrack is an effective way to facilitate nanofluid delivery in porous tumors using CED. [ABSTRACT FROM AUTHOR]

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

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

This experimental investigation aimed to analyze the impact of a unique design of swirl generator airflow on the performance of a tubular heat exchanger operating with axial flow. To conduct the experiment, we utilized a custom‐built apparatus containing eight sawtooth air deflectors with differing space height ratios (e/h). These deflectors were oriented in a uniform manner (shutter type) and positioned at various inclination angles. Circular baffle plates, housing these deflectors, were equidistantly spaced at different pitch ratios. The arrangement of tubes within the heat exchanger remained constant throughout the study, while the Reynolds number ranged from 16,000 to 30,000. In addition, a consistent heat flux condition was maintained on the surface of the tubes. The research outcomes indicated that incorporating a deflector baffle plate with an inclination angle of 30°, an e/h ratio of 0.4, and a pitch ratio of 1.2 led to an average increase of 1.36 in the thermal enhancement factor when compared to a heat exchanger lacking a baffle plate, tested under similar conditions. [ABSTRACT FROM AUTHOR]

The Nikuradse roughness height for a river channel or, equivalently, the friction factor (f) or Manning's coefficient, are parameters required to calibrate hydrodynamic models used for flood risk management. In general, modeling hydraulic roughness includes the contributions of skin friction, related to sediment grain size, and bed-form roughness, related to bed-form geometry. Frequently, bed-form resistance is larger than the resistance due to skin friction. An empirical approach has been presented in the literature to estimating bed-form roughness, which is widely used for engineering purposes. This contribution presents an alternative physically based formulation for dune roughness estimation. Flow resistance generated by the bed form is assumed to arise from the drag force exerted by the bed, based on depth-averaged flow quantities. The new formulation agrees with existing experimental laboratory results and new field data from the Tercero (Ctalamochita) River, Córdoba, Argentina. [ABSTRACT FROM AUTHOR]

Flow resistance estimate is a challenging topic for establishing flooding propensity of streams, designing river restoration works, and evaluating the use of soil bioengineering practices. In this paper, flume measurements with rigid cylinders set in two arrangements (aligned, staggered) were used to evaluate the effect of rigid emergent vegetation on flow resistance. A well‐known theoretical flow resistance equation was firstly reviewed. Then, it was calibrated and tested by measurements performed for these arrangements with six concentrations (0.53–11.62 stems dm−2). The analysis was conducted using three approaches: (i) distinguishing the experimental runs corresponding to different arrangements and stem concentrations; (ii) using only a scale factor representing the effect of the stem concentration; and (iii) joining all available data. The results demonstrated that the flow resistance equation gives an accurate estimate of the Darcy–Weisbach friction factor f, characterized, for the best approach among the tested ones, by errors less than or equal to ±5% for 95.9% of the examined cases for the aligned arrangement and for the staggered arrangement less than or equal to ±5% for 94.2% of the examined cases. For both arrangements, the measurements demonstrated that, for a given longitudinal distance between vegetation elements, flow resistance increases for decreasing values of the transverse distance and, for a given transverse distance, f decreases for increasing values of the longitudinal distance between elements. Finally, in the range of the investigated stem concentrations, the influence of the arrangement on flow resistance resulted negligible. [ABSTRACT FROM AUTHOR]

This study investigates flow resistance in the Malina stream, located in the Zahorská lowland of western Slovakia, with a particular emphasis on refining the estimation of Manning's n in vegetated streams. Traditional flow resistance equations, such as Manning, Chézy, and Darcy-Weisbach, often assume uniform flow conditions, which limits their applicability in complex river systems characterized by bedforms and aquatic vegetation. This research evaluates various empirical equations for determining Manning's n, as well as a nondimensional hydraulic geometry approach that integrates dynamic flow characteristics and the effects of vegetation. Field measurements collected during the growing season (April to September) demonstrated that vegetation density significantly influences flow velocity and roughness coefficients. Empirical equations that rely solely on median grain size exhibited limited predictive capability in lowland streams with uniform and homogeneous beds, while the nondimensional approach produced more accurate estimates, showing a strong correlation with measured data. The findings highlight the critical need to incorporate vegetation dynamics into flow resistance calculations to enhance hydrodynamic modeling and improve predictions of sediment transport and sediment budgets in riverine ecosystems. [ABSTRACT FROM AUTHOR]

The study investigated an unconventional heat exchanger design that utilizes swirling airflow to enhance heat transfer over heated tubes. This innovative system incorporates a perforated round baffle plate, accompanied by multiple rectangular air deflectors oriented in opposite directions at varying inclination angles. These deflectors are symmetrically arranged at different pitch ratios alongside consistently spaced tubes forming a circular configuration, all subject to a uniform heat flux. Enclosed within a circular duct with longitudinal airflow, the combined baffle plate and tube assembly bring forth efficient heat transfer. The air-side turbulence intensified by the deflectors induces a chaotic motion, contributing to enhanced surface heat transfer. Each baffle plate has twelve opposite-oriented deflectors, resulting in opposing swirl flows that further promote flow recirculation and augment surface heat transfer. The performance of this heat exchanger was evaluated by considering different pitch ratios and inclination angles across a Reynolds number range of 16000-30000. The findings demonstrate that the heat exchanger with rectangular flow deflectors on the baffle plate exhibits significant improvements in thermo-fluid performance. Notably, an average enhancement of 1.88 was observed at an inclination angle of 50 degrees and a pitch ratio of 1.2 when compared to an exchanger without baffle plates, emphasizing the considerable impact of these design aspects.

In this study, ultrasonic technology is combined with twisted belts to explore the comprehensive performance, and this study also investigated the effect of different Reynolds numbers, ultrasonic frequencies, and number of transducers on the performance of circular and twisted band tubes. It was found that ultrasonic waves applied on the tube plate enhanced the heat transfer performance of the heat exchanger tubes, reduced the flow resistance, and improved the overall performance, and the lower the ultrasonic frequency, the better the heat transfer and resistance reduction ability, and at the experimental condition frequency of 21 kHz, the maximum increase of Nu is 19.06%. With the increase of Reynolds number, the better the ultrasonic enhancement heat transfer performance, but the worse the resistance reduction performance. For different heat exchanger tube structures, the synergistic enhanced heat transfer effect of ultrasonic waves with the twisted belt is better than round tubes, and the synergistic drag reduction effect with the round tube is better than the twisted tape round tube. When the installed ultrasonic transducers are two, the heat transfer performance of the heat exchanger tube is the best, and the maximum increase in the value of Nu was 28.06%.

Macro-roughness elements such as boulders and bedrock outcrops, collectively referred to as large bed elements (LBEs), are key features influencing hydrodynamics and morphodynamics in mountain rivers. Where LBEs are abundant and account for a substantial portion of total flow resistance, existing geomorphic theory, previous physical experiments, and limited field observations support the theory that LBE configurations adjust to maximize flow resistance. However, methods to explicitly map individual features along entire river segments are lacking, thus limiting analysis of LBE spatial structure in boulder-bedded rivers. In addressing these gaps, this study sought to develop a procedure for mapping LBEs from 3D point-clouds, explore LBE spatial structure in a real boulder-bedded river, and test the hypothesis that LBE configurations were organized to maximize flow resistance. The mapping procedure applied a ground classification algorithm to produce a roughness surface model, from which LBEs were extracted by a marker controlled watershed algorithm. Implementing the procedure, 42,176 LBEs were mapped in 13.2-km of the mountainous Yuba River (Northern California). Scale and discharge-dependent LBE concentration and spacing metrics were quantified for multiple laterally and/or hierarchically nested spatial domains and classified to differentiate three flow-resistance based hydrodynamic regimes: isolated roughness, wake interference, and skimming flow. Of these regimes, wake interference corresponds to a state of maximum resistance, so hypothesis testing involved determining if this regime was dominant. Results confirmed 25 of 28 segment- and reach-scale LBE concentrations were in the wake interference regime. However, spacing metrics classified 24 of these same spatial domains in the skimming flow regime. Concentration metrics, which quantify LBE density in a given spatial area, differ from spacing metrics, which represent LBE proximity to one another. While comparison of segment and reach-scale regime classifications by each metric concluded concentration was superior to spacing for regime classification purposes, these disparities leave open questions about this extremal model of geomorphic adjustment. Lastly, lateral variability of metrics across the river corridor had implications for discharge-dependent resistance.