Experimental research on heat transfer enhancement and pressure drop in tube fitted with foam copper on the shape of twisted tape

Mechanism of coupled energy transfer and pressure drop in cryogenic propellant sloshing through improved phase change modeling

Elevating blood pressure in neurogenic orthostatic hypotension: Investigating the efficacy and tolerability of rebreathing therapy.

The present study investigated the enhancement of convective heat transfer in horizontal tubes using twisted tape inserts, particularly emphasizing the influence of modifications to their geometrical configurations. Three twisted tape models were designed using SolidWorks: a plain tape, a tape with curved edges, and a tape with curved edges and holes. Two twist ratios were considered, namely TR1 = 6.666 and TR2 = 5. Computational Fluid Dynamics (CFD) simulations were performed to evaluate the velocity and temperature fields, Nusselt number, and friction factor over a Reynolds number range of 15,000–25,000. The results indicate that employing twisted tape with curved edges and perforations leads to the greatest enhancement in heat transfer. Specifically, the Nusselt number increases from 410 for curved edges without perforations to 460, whereas the plain tape achieves 380 at Re = 25,000 and TR2. The tape with curved edges (without holes) demonstrated the most favorable improvement in friction factor, attaining a value of 0.024 versus 0.029 for the plain tape, corresponding to a 20.8% reduction. As a result, the performance evaluation factor achieved a peak value of 1.24, indicating a 30.5% improvement. These findings demonstrated that optimized twisted tape geometries significantly enhanced heat transfer performance while maintaining reasonable pressure drop penalties. This highlights their potential applicability in thermal system design, particularly in compact and energy-efficient heat exchangers.

Monolithic adsorbent with low pressure drop and high cycling stability enabled by an anchor effect for direct air CO2 capture

Multi-channel functionalized nanofiber membranes with high mechanical strength for formaldehyde degradation, air purification, and dye degradation.

Analysis of pressure drop and power density in oscillatory baffled reactors combining experiments and CFD simulations

• Air flow direction affects the pressure drop under dehumidifying conditions. • A correlation for the mass of retained condensate is proposed. • A method to estimate pressure drop under dehumidifying conditions is proposed. • Heat transfer increases owing to dehumidification. An experimental investigation was conducted on wavy fin-and-tube heat exchangers with fin pitches of 4 mm and 5 mm to evaluate their thermal-hydraulic performance under dehumidifying conditions, considering both upward and downward airflow directions. As anticipated, condensation was found to enhance heat transfer. However, it also significantly influenced relative air-side pressure drop, with upward airflow resulting in higher relative pressure drops than downward airflow. At a face velocity of 3 m/s, reversing the airflow direction from downward to upward increased the relative air-side pressure drop by 79 %, indicating a strong dependence on flow orientation under dehumidifying conditions. An empirical correlation was developed to estimate the mass of retained condensate under downward airflow conditions, based on measurements for both fin pitches, with a coefficient of determination (R 2 ) of 0.895. Furthermore, an empirical method was proposed to characterize relative air-side pressure drop behavior as a function of retained condensate mass, face velocity, and fin pitch. The root-mean-square error (RMSE) of the prediction was 0.0593. Based on the experimental findings, upward airflow is not recommended under dehumidifying conditions, particularly at higher face velocities.

This study combines experimental and numerical approaches to investigate flow behavior downstream of bluff bodies placed at the mid-span of a rectangular sudden expansion configurations common in combustion chambers, burners, flame stabilizers, and chemical mixers. The three-dimensional, steady, incompressible, and turbulent flow was analyzed for varying Reynolds numbers, bluff body shapes (square, diamond, circular, triangular-arrow-left and arrow-right), sizes, and streamwise positions. Introducing a bluff body significantly modified flow field, intensifying adverse pressure gradients and delaying reattachment compared with configuration without a bluff body. The pressure recovery coefficient strongly depended on geometry; at Re = 74,200, the diamond body achieved a value 179% higher than that of the triangle–arrow-left configuration. Increasing bluff body size consistently reduced pressure recovery and increased losses, for instance, enlarging a cylindrical body by 2.2 times at Re = 93,734 increased the upper-wall pressure drop by 240%. Numerical simulations, validated against experiments with less than 2% deviation, revealed multiple recirculation zones and complex wake vortices that expanded with Reynolds number. Flow asymmetry occasionally appeared due to combined effects of geometry, size, and position. Drag increased with Reynolds number, with the triangle–arrow-right body producing the highest drag. Overall, the results demonstrate a strong dependence of sudden-expansion flow characteristics on bluff body parameters, providing valuable insights for optimizing engineering systems involving flow control and pressure recovery.

Robust integrated-energy management of shared transmission systems for renewable fuels and refined oil considering decision-dependent pressure drop uncertainty

The pressure loss coefficient is used to calculate and predict the pressure drop in 90° bends. Unlike some technical tables and handbooks that give a fixed value for the pressure loss coefficient, many studies have found that the coefficient varies with the Reynolds number, especially for Reynolds number ranges under 200,000. Several empirical equations have been proposed to determine the pressure loss coefficient at different Reynolds numbers. However, the coefficients obtained from different literature vary greatly, although they all share some common patterns. To compare the dependence of the pressure loss coefficients in a uniform way, the pressure loss coefficients were converted to the relative values by taking the pressure loss coefficient at Re = 200,000 as a reference value and the Re-dependence factor was defined. This paper presents the first experimental findings as part of a broader investigation on the Reynolds number dependence of pressure loss coefficients in duct bends and gives the variation curve of Re-dependence factor with relative curvatures, which provides a new means of evaluating empirical equations and predicting the bend pressure drop.

Flow restrictions, such as U-bends, are commonly used in nuclear reactor systems. The geometric effects stemming from the flow channel curvature could be of interest for analyzing hydrodynamic phenomena in these systems. However, existing U-bend studies are limited to the small radius of curvature and low-flow conditions. This study experimentally investigates air-water two-phase flows through a vertical U-bend with a curvature-to-diameter ratio of 9 over a wide range of flow rates. A detailed database for global and local two-phase flow parameters was established using four-sensor conductivity probes, a pressure transmitter, and a high-speed video camera. The obtained data were used to investigate U-bend effects on two-phase flow parameters, including pressure drop, void fraction, interfacial area concentration, and bubble velocity. An analysis of bubbly flows showed bubble accumulation near the inner side of the pipe at the U-bend’s apex and exit, influenced by secondary flow and liquid inertia. Around three diameters downstream, the bubbles dispersed, indicating the dissipation of the U-bend effects, while a dual-peaked void fraction profile emerged at around eight diameters downstream, corresponding to the core regions of the secondary-flow vortices. Farther downstream, the profile gradually became center peaked. This study found that the pressure change due to acceleration or deceleration across the U-bend can contribute up to 18% of the total pressure loss under high void fraction conditions. The Lockhart-Martinelli correlations with C = 34 and C = 68 predicted two-phase pressure drops within ±10% for the vertical upward and downward sections, respectively, while a modified correlation by Kim et al. with C = 40 , k = 0.10 and C = 85 , k = 0.20 , effectively modeled frictional losses in the vertical upward elbow and U-bend. The area-averaged void fraction α changed significantly across the U-bend due to pressure and bubble velocity variations. The void-weighted bubble velocity ⟨ ⟨ v g ⟩ ⟩ varied primarily with bubble distribution, exhibiting an opposite trend to α , while the interfacial area concentration a i followed a similar trend pattern to α . The data suggest that additional mechanisms may influence flow between L / D VD = 0 to 3, offering insights for interfacial area transport modeling across the U-bend.

The aim of this study was to evaluate the role of hemodynamic parameters in predicting the efficacy of microvascular decompression (MVD) in patients with classic trigeminal neuralgia (CTN) using computational fluid dynamics (CFD). Patients with unilateral CTN were recruited from May 2022 to December 2023. Preoperative time-of-flight MR angiography was used to identify neurovascular compression sites. CFD simulations were performed to analyze hemodynamic parameters such as peak systolic flow (PSF), peak systolic pressure drop (PSPD), maximum wall shear stress (WSS), and oscillatory shear index (OSI). Logistic regression analysis was used to develop predictive models for MVD efficacy. Fifty-six patients were included (28 in the effective MVD group and 28 in the ineffective MVD group). The effective group exhibited significantly lower PSF (mean 0.202 [SD 0.136] vs 0.306 [SD 0.142] ml/sec, p = 0.007) and higher PSPD (mean 33.239 [SD 20.122] vs 22.864 [SD 15.624] Pa, p = 0.036), maximum WSS (median 3.231 [interquartile range (IQR) 2.084-4.359] vs 2.197 [IQR 1.592-3.445] Pa, p = 0.024), and OSI (median 0.001 [IQR 0.001-0.002] vs 0.001 [IQR 0.001-0.001], p = 0.029). Logistic regression analysis identified PSF and maximum WSS as significant predictors of MVD efficacy. The developed prediction models showed high accuracy, with model 2 (using the backward logistic regression method) achieving an area under the receiver operating characteristic curve of 0.920 and both sensitivity and specificity of 90%. Hemodynamic parameters, particularly PSF and maximum WSS, significantly predict MVD efficacy in CTN. Integrating these parameters into clinical practice could improve surgical outcomes and guide personalized treatment strategies.

Cooling of the plasma-facing first wall is challenging in the design of blanket components because of the high heat flux (on the order of MW / m 2) from the plasma, especially when a low thermal mass medium like helium is chosen as the coolant. Therefore, heat transfer enhancement in which the convective heat transfer rate is augmented by the addition of turbulence-promoting structures becomes a key initiative for providing sufficient cooling capability with helium. Previously, computational fluid dynamics simulations had been performed on pipe flows with different transverse and longitudinal ribbed geometries at Oak Ridge National Laboratory to compare the enhancement performance among different ribbed geometries. Rib shape morphing had been conducted to obtain an optimized rib profile. In the work presented here, the adjoint method is adopted in the ANSYS Fluent solver for turbulence model augmentation, and the Generalized k-ω (GEKO) turbulence model is employed because of its ability of tuning the turbulence model. The Nusselt number and pressure drop obtained from the channel flow with bottom ribbed wall experiments are used as the targets. Sensitivity analysis provides information as guidance to improve the turbulence model accuracy. The augmented GEKO model is tuned for the studied ribbed channel geometry and flow conditions, providing improved predictive accuracy within this context. Extension to other configurations offers potential but may require additional tuning and validation.

Efficient ortho–para hydrogen conversion is essential to suppress spontaneous heat release and boil-off losses during cryogenic liquid hydrogen storage and pre-liquefaction processes. In this study, a novel catalyst-filled wavy plate-fin heat exchanger (CFHE) is proposed to simultaneously enhance heat transfer and ortho–para hydrogen conversion under cryogenic conditions. Compared with conventional straight-fin configurations, the wavy-fin structure introduces controlled flow perturbations and increased specific surface area, thereby intensifying transport processes. Three-dimensional computational fluid dynamics (CFD) simulations, using the SST k–ω turbulence model, coupled with an ortho–para hydrogen conversion kinetic model were performed to quantitatively investigate the effects of key geometric parameters and catalyst loading on hydrogen conversion, heat transfer, and pressure drop within a Reynolds number range of 941–1577 and a temperature range of 35–20 K. Within the same CFHE configuration, the para-hydrogen fraction remains nearly unchanged without catalyst but increases significantly with catalyst loading. However, the catalyst reduces the global average Colburn j-factor by about 25%. Despite higher friction losses, the outlet–inlet temperature difference decreases to about 0.866 times that of the non-catalyst case, indicating improved temperature uniformity. A comprehensive performance index e, integrating heat transfer enhancement, flow resistance, and conversion efficiency, was introduced and optimized using a genetic algorithm. The optimized CFHE achieves an outlet para-hydrogen fraction exceeding 95% of the thermodynamic equilibrium value while maintaining hydrogen entirely in the gaseous phase to avoid catalyst deactivation. Overall, the catalyst-packed wavy channel configuration demonstrates superior conversion efficiency, enhanced thermal uniformity, and improved overall performance compared with straight-fin structures, providing quantitative design guidance for high-performance heat exchangers in cryogenic hydrogen liquefaction systems.

Ground-level ozone poses a serious threat to human health. However, developing catalytic membranes with high ozone conversion, low resistance, and long-term durability under humid conditions remains challenging. Here, we introduce a selective swelling-induced segmental reorganization strategy for fabricating perforating catalyst-embedded nanofibrous membranes for efficient ozone decomposition. Using polysulfone-block-poly(ethylene glycol) (PSF-b-PEG, abbreviated as SFEG) as a scaffold, the controlled swelling process generates interconnected through-channels within individual nanofibers, enhancing the accessibility of catalytically active sites. In combination with the interconnected inter-fiber pores formed by fiber stacking during electrospinning, a continuous through-pore network is established, enabling efficient gas transport at a low pressure drop. Also, migrated PEG segments create a moisture-compatible environment that regulates water interaction, thereby maintaining high catalytic activity under humid conditions. Versatility of this approach enables the fabrication of diverse catalyst-embedded membranes, exhibiting outstanding performance in ozone elimination. Nearly complete ozone conversion (∼100%) is achieved with a pressure drop of only 0.15% of atmospheric pressure, while long-term filtration efficiency maintains over 99% for 600 h under humid conditions. This membrane-engineering strategy paves the way for the development of advanced catalytic membranes for sustainable air purification applications.

The magnetorheological effect of the pinch-mode magnetorheological valve (pinch-mode MR valve) depends on the complex coupling between nonlinear gradient magnetic fields and magnetorheological fluids, especially for the configuration with multiple non-magnetic edges, which is rarely investigated. In this study, a magneto-hydrodynamic coupling model of pinch-mode MR valve with multiple non-magnetic edges is established to capture the interactions between non-uniform magnetic fields and hydrodynamic behavior, firstly. Secondly, the experimental data of pressure drop between the inlet and outlet is utilized to verify the model accuracy. The comparison results show that the established model, considering the wall movement to describe the flow separation of MR flow dynamics caused by the pinch effect, can describe the variable properties of the viscous damping and pre-yield damping with different magnetic fields and fluid flow with relative agreement. Finally, through the parameter sensitivity analysis based on the established model, it is shown that the pinch-mode MR valve with about 6.5 mm channel diameter can provide a better performance in absolute pressure drop adjustment range and pinch effect. Besides, the width of the coil bracket can be utmost designed without the magnetic saturation in steel yoke, improving the damping properties of the pinch-mode MR valve.

BackgroundEustachian tube (ET) dysfunction is associated with middle ear pathologies; however, the quantitative relationship between ET opening and pressure equalization remains insufficiently characterized. Computational fluid dynamics (CFD) offers a robust tool for analyzing middle ear pressure dynamics, particularly in elucidating pressure equilibrium mechanisms under partial ET opening conditions.ObjectiveThis study aimed to investigate pressure dynamics in the tympanic cavity, mastoid antrum, and air cells during ET opening using CFD, to compare pressure distributions between full and partial openings, and to determine whether partial opening can achieve equilibration equivalent to full opening.MethodsEight normal temporal bones were reconstructed from high-resolution computed tomography scans of four healthy adults. ET openings were simulated at 10%, 30%, 50%, and 100% patency using CFD, and results were validated against in vivo Tubomanometry data. Pressure variations in the tympanic cavity, mastoid antrum, and air cells were monitored throughout the process. Mesh independence was verified to ensure reliability, and statistical analyses were conducted using SPSS 27.0, with P < 0.05 considered significant.ResultsCFD simulations revealed distinct pressure dynamics within the ET–middle ear system. Airflow velocity peaked at the narrow isthmus, generating a localized pressure drop. Effective middle ear pressure equilibration—across the tympanic cavity, antrum, and mastoid air cells—was achieved with partial ET opening in most cases: 30% opening sufficed for full equilibration in two ears, while 50% opening achieved complete equilibration in six. This equivalence to full patency was consistently observed during pressurization, stabilization, and depressurization phases.ConclusionEffective middle ear pressure equilibration can be achieved with partial ET opening (50%) in most cases (75% of ears). These findings provide valuable insight into middle ear physiology and its response under pathological conditions, offering a theoretical basis for optimizing the management of ET dysfunction.

Viscoelastic flow of an Oldroyd-B fluid through a slowly varying contraction-expansion channel: pressure drop and elastic stress relaxation

Polymer based microfluidics, using polydimethylsiloxane (PDMS), are highly adaptable platforms for electrochemical studies commonly used for numerous applications. Deformations of these PDMS devices due to the flow pressure drop in microchannels have been widely documented in literature but cannot be prevented in all applications even though it is critical to measure quantitative data. In this work, we show that in electrochemical microfluidic devices used in energy conversion systems, the velocity profiles and channel deformations can be quantitatively measured based on spectro-electrochemistry and numerical simulations of Hagen-Poiseuille flows. PDMS deformations are found amplified in the case of large channel aspect ratios (i.e. close to 100), with deformation Δ h / h 0 &gt; 100 % at 50 kPa, and start to be non-negligible &gt; 10 % for channel internal pressure above 5 kPa. Finally, by considering these channel deformations in the Beer-Lambert law, we show that accurate absorbance and concentration measurements can be obtained using visible spectroscopy regardless the channel internal pressure.