Laminar Flow Research Articles (Page 1)

Purpose Understanding the flow dynamics of nano-detergents through woven textile pores is critical for enhancing cleaning efficiency at the microscale. This study aims to investigate a nano-detergent flow where a detergent-based liquid enhanced with nanoparticles interacts with an oil dirt spot embedded in a porous textile structure. Design/methodology/approach Using the Volume of Fluid method within ANSYS Fluent, simulations are conducted under laminar flow conditions to model the interfacial behavior and mass transfer between the detergent and oil phases. Five mono nanoparticles (ZnO, TiO2, Ag, SiO2 and Fe2O3) are examined, with ZnO evaluated at varying concentrations (ϕ = 0.1%–0.4%) to assess their impact on mechanical (friction factor) and thermal (Nusselt number) performance. Findings In the present investigation, the ZnO/detergent solution exhibits the highest average friction factor (2,146.49) which proves the enhanced mechanical abrasion against dirt spots. Moreover, the Ag/detergent solution demonstrates the highest average Nusselt number (3.4596), suggesting heat transfer capabilities that can help thermal breakdown of oil dirt spot. The ZnO/detergent solution also performs well in heat transfer (average Nusselt number of 3.3731) which offers a reliable performance of both mechanical and thermal aspects, thereby emerging as the most promising candidate for detergency. Increased ZnO nanoparticle concentration consistently improves both friction factor and Nusselt number. At low Reynolds numbers (Re = 0.48), the flow shows pronounced temporal fluctuations with clear peaks in friction factor and heat transfer, while higher Reynolds numbers (Re = 1.92) result in smoother, more stable flow profiles and enhanced thermal performance. An inverse correlation is observed between oil spot mass transfer rate parameter (R) and the mean friction factor, particularly at lower Re values, suggesting that as more dirt spot is removed, flow resistance decreases because of reduced drag. On the other hand, the mean Nusselt number increases with R, indicating that effective dirt spot detachment promotes better heat transfer by exposing cleaner pore surfaces. Originality/value For the first time, this study provides a comprehensive numerical framework for analyzing nano-detergent behavior in textile pore flows which offers valuable achievements in modeling technique, suitable geometry, real flow conditions, nanoparticle selection and more.

Staff qualification is essential in sterile preparation centers to ensure assigned responsibilities are clearly defined, meet established specifications, and are executed under written procedures. Traditional qualification methods often rely on checklists that may not reflect real-time performance. This study introduces an innovative methodology using visual inspection, real-time evidence collection, and in situ evaluations to enhance the accuracy and reliability of staff qualification. This applied research involved verifying staff competence through experience, training, visual inspection, and practical tests. Evaluated activities included personal hygiene, clinical and surgical handwashing, sterile gowning, entry and exit from controlled areas, laminar flow hood cleaning, and aseptic manipulation. Evidence was collected via photographs and interviews, and microbiological sampling was performed to validate aseptic techniques. During the qualification process, staff were interviewed and observed performing critical tasks. Photographic evidence was collected at each stage, including sterile gowning and laminar flow hood cleaning. Microbiological samples from personnel, equipment, and environments showed no microbial growth, confirming proper aseptic technique. All evaluated staff met acceptance criteria across all activities, demonstrating high technical competence and adherence to protocols. The implementation of this methodology significantly improved the quality of collected information and the verification of staff competence. It enabled the identification of procedural weaknesses not detectable through written tests alone. The approach provided actionable insights for targeted training and ensured compliance with sterile preparation standards. The qualification process was successfully completed with all staff receiving a 'Compliant' rating.

Background: In coronary hemodynamics, laminar flow is a protective mechanism, and turbulent flow is a detrimental factor. In clinical practice, for patients with unstable angina, the necessity of intervention for moderate lesions (50-70% stenosis) is always questioned. In this study, we comprehensively evaluated the risk factors that may lead these plaques to progress to myocardial infarction using angiography, IVUS, and Deep Learning. Hypothesis: Vulnerable lesions are usually associated with plaque eccentricity and stagnant flow, causing chest pain. Methods: Patients with a single lesion admitted with diagnosed of unstable angina underwent the dynamic angiographic technique with IVUS support. First, the coronary artery was fully injected with contrast. After the injection stopped, the blood (white) began streaming in to replace the contrast (black). The flow characteristics and movements will be recorded through the disappearance of the contrast opacity with 15 frames/second. In aditionally, the arterial phase (AP) was calculated as the time from frames with full contrast to frames with washed-out contrast. Moreover, IVUS was performed for evaluate plaque features (eccentricity, calcification and vulnerable). At the same time, deep learning (DL) models were built based on independent datasets (225 angiogram videos). The DL program was constructed using a combination of U-Net and DenseNet-121. The segmentation model and a convolutional neural network were used to detect the starting frame, ending frame of AP. Results: Fifty patients met inclusion criteria (72% males) with a mean age of 66.2 ± 9.5 years. IVUS analysis revealed that 84% (42 patients) had plaque eccentricity without (or minimal) calcification. Contrast stagnation was observed for a longer duration in eccentric coronary regions compared to non-eccentric plaque regions, as quantified by DL analysis of the arterial phase (24.5 +/- 1.6 frames vs 30.1+/- 1.4 frames, p < 0.05). After stenting, the stagnant flow was eliminated, and flow was restored to 25 ± 2.1 frames. Conclusion: Plaque eccentricity along with a prolonged arterial phase (stagnant flow) are causes of chest pain in unstable angina. This is a personalized indication for PCI, even if they are moderate lesions.<div id="gtx-trans" style="position: absolute; left: 393px; top: 368.844px;"><div class="gtx-trans-icon"> </div></div>

We present experiments of settling and dissolving sugar grains continuously sieved above a water tank with varying grain size and mass flux. Through drag and dissolution, grains force a downward flow whose dynamics are analysed in a laser sheet through particle image velocimetry and the use of home-made fluorescent sugar to track the negatively buoyant sugary water. We reveal different regimes, mostly controlled by the grain size, from a particle-constrained laminar flow at large grain size, to a turbulent plume with an effectively fluid-like behaviour when grains are small. The transitions between regimes are predicted from dimensionless numbers quantifying fluid–particle coupling, collective effects between grains and the possible onset of a Rayleigh–Taylor instability at the source. When a quasi-steady regime is reached, all grains dissolve above a finite depth, below which the flow is exclusively driven by dissolved sugar. We derive simple idealised models based on the source properties that predict the depth of this dissolution layer as well as the characteristic flow velocity.

A study on the influence of dimension and thickness on the formation of laminar and turbulent flows in gyroid and diamond structures

Recent research has extensively investigated the rheological and thermal behaviors of nanofluids. The present work provides a detailed numerical investigation of heat transfer and pressure drop characteristics in sinusoidal and straight tubes using two types of nanofluids: water-based and ethylene glycol-water-based suspensions with nanoparticles. The simulations were conducted under laminar flow conditions using ANSYS CFX software with a constant and uniform heat flux boundary condition. Different nanoparticle sizes and concentrations were examined to evaluate their impact on heat transfer enhancement. The research gap addressed in this work lies in the limited number of studies that have simultaneously integrated sinusoidal tube geometry and nanofluid properties to enhance heat exchanger performance. This paper bridges that gap by numerically comparing the heat transfer characteristics of sinusoidal tubes against traditional straight tubes under identical operating conditions. The results demonstrate that increasing Reynolds number and nanoparticle concentration significantly enhances the heat transfer coefficient. Overall, sinusoidal tubes combined with nanofluids achieved up to 25–30% improvement in the Nusselt number compared to straight tubes, highlighting their potential for compact and energy-efficient heat exchangers. The research gap lies in the limited studies that simultaneously integrate sinusoidal tube geometry and nanofluid properties to enhance heat exchanger performance. The results clearly demonstrate that increasing the Reynolds number and nanoparticle volume concentration significantly enhances the heat transfer coefficient. Overall, sinusoidal tubes combined with nanofluids provided up to 25% improvement in Nusselt number compared to straight tubes, highlighting their potential for compact and efficient heat exchangers.

Abstract Non‑circular cylinders can manipulate separation and wake dynamics for mixing, heat transfer, and energy harvesting. This study investigates flow past a dodecagonal cylinder and benchmarks it against a circular cylinder across steady and unsteady laminar regimes, with the goal of identifying the conditions under which the dodecagonal section is preferable to the circular one. We perform numerical, time-resolved simulations using the lattice Boltzmann method (LBM) over
Re = 4,10,20,40,100,125, covering steady (Re≤40) and unsteady laminar (Re=100,125) regimes. We report drag coefficient C_D, lift coefficient C_L, and Strouhal number S_t. In the steady regime, the dodecagon shows a more stable, narrower wake and lower drag: C_D =6.47 vs 6.69 at Re=4 (-3.29%), 3.36 vs 3.46 at Re=10 (-2.89%), 2.27 vs 2.33 at Re=20 (-2.58%), and 1.64 vs 1.67 at Re=40 (-1.80%). In the unsteady regime, the trend reverses. Mean drag is higher for the dodecagon 1.36 vs 1.33 at Re=100 (+2.3%) and 1.38 vs 1.32 at Re=125 (+4.5%), and lift oscillations are stronger (±0.34 vs ±0.29 at Re=100 (+17.2%); ±0.46 vs ±0.40 at Re=125 (+15.0%). Strouhal number is slightly higher for the dodecagon than for the circle (0.159 vs 0.154 at Re = 100; 0.168 vs 0.165 at Re = 125), i.e., by 3.2% and 1.8%, respectively. These findings provide quantitative guidance: in steady laminar flow (Re ≤ 40), choose the dodecagon for energy-efficient operation. In the unsteady laminar regime
(Re ≈ 100-125), choose the dodecagon for stronger periodic forcing, and select the circle when the priority is to minimize mean drag and load amplitudes. 

Hemodynamics significantly impact the biology of endothelial cells (ECs) lining the blood vessels. ECs are exposed to various hemodynamic forces, particularly frictional shear stress from flowing blood. While physiological flows are critical for the normal functioning of ECs, abnormal flow dynamics, known as disturbed flows, may trigger endothelial dysfunction leading to atherosclerosis and other vascular conditions. Such flows can occur due to sudden geometrical variations and vascular abnormalities in the cardiovascular system. In the current study, a microfluidic system was used to investigate the impact of different flow conditions (i.e, normal vs. disturbed) on ECs in vitro. We particularly explored the relationship between specific flow patterns and cellular pathways linked to oxidative stress and inflammation related to atherosclerosis. Here, we utilized a 2D cell culture perfusion system featuring an immortalized human vascular endothelial cell line (EA.hy926) connected to a modified peristaltic pump system to generate either steady laminar flows, representing healthy conditions, or disturbed oscillatory flows, representing diseased conditions. EA.hy926 were exposed to an oscillatory flow shear stress of 0.5 dynes/cm2 or a laminar flow shear stress of 2 dynes/cm2 up to 24 h. Following flow exposure, cells were harvested from the perfusion chamber for quantitative PCR analysis of gene expression. Reactive oxygen species (ROS) generation under various shear stress conditions was also measured using DCFDA/H2DCFDA fluorescent assays. Under oscillatory shear stress flow conditions (0.5 dynes/cm2), EA.hy926 ECs showed a 3.5-fold increase in the transcription factor nuclear factor (NFκ-B) and a remarkable 28.6-fold increase in cyclooxygenase-2 (COX-2) mRNA expression, which are both proinflammatory markers, compared to static culture. Transforming growth factor-beta (TGFβ) mRNA expression was downregulated in oscillatory and laminar flow conditions compared to the static culture. Apoptosis marker transcription factor Jun (C-Jun) mRNA expression increased in both flow conditions. Apoptosis marker C/EBP homologous protein (CHOP) mRNA levels increased significantly in oscillatory flow, with no difference in laminar flow. Endothelial nitric oxide synthase (eNOS) mRNA expression was significantly decreased in cells exposed to oscillatory flow, whereas there was no change in laminar flow. Endothelin-1 (ET-1) mRNA expression levels dropped significantly by 0.5- and 0.8-fold in cells exposed to oscillatory and laminar flow, respectively. ECs subjected to oscillatory flow exhibited a significant increase in ROS at both 4 and 24 h compared to the control and laminar flow. Laminar flow-treated cells exhibited a ROS generation pattern similar to that of static culture, but at a significantly lower level. Overall, by exposing ECs to disturbed and normal flows with varying shear stresses, significant changes in gene expression related to inflammation, endothelial function, and oxidative stress were observed. In this study, we present a practical, optimized system as an in vitro model that can be employed to investigate flow-associated diseases, such as atherosclerosis and aortic aneurysm, thereby supporting the understanding of the underlying molecular mechanisms.

Laminar Flow and Heat Transfer Enhancement in Helical Twisted Tube with Twisted Tape Inserted

BACKGROUND: Cryopreservation is a crucial technique for the long-term conservation of endangered plant germplasm. However, desiccation-sensitive seeds, such as those of Citrus indica Yu. Tanaka and Citrus latipes (Swingle) Yu. Tanaka, require optimized dehydration protocols to prevent cryo-injury. Enhancing post-thaw recovery through antioxidant supplementation is a promising approach to mitigate oxidative stress-induced damage. OBJECTIVE: This study aimed to establish an optimized dehydration-based cryopreservation protocol of seeds for C. indica and C. latipes while evaluating the protective effects of sodium nitroprusside (SNP) and tocopherol on post-cryopreservation recovery. MATERIALS AND METHODS: Mature seeds of C. indica and C. latipes were subjected to controlled dehydration to moisture contents of 22.7 and 30.1 using a laminar air flow chamber before liquid nitrogen storage. Post-thaw viability was assessed through germination studies, physiological assays (chlorophyll content and malondialdehyde estimation), and biochemical analyses (antioxidant enzyme activities). SNP (0.4 ??M) and tocopherol (25 ??M) were used as post cryopreservation supplements to enhance seedling recovery. RESULTS: Optimal seed moisture content prior to freezing was 24.9% for C. indica and 32.0% for C. latipes, maximizing post-thaw germination. SNP and tocopherol supplementation significantly reduced lipid peroxidation, improved chlorophyll retention, and enhanced superoxide dismutase, catalase, and peroxidase activities. CONCLUSION: SNP and tocopherol effectively mitigate cryo-induced oxidative stress, improving post-thaw recovery of C. indica and C. latipes seeds. These findings provide critical insights into cryopreservation strategies for conserving endangered citrus germplasm.

Experimental evaluation of airborne spread of contaminations in operating room air under laminar air flow and mixing ventilation

Reduction of fluid forces on a circular cylinder in the laminar flow regime using a pair of airfoils

Targeted gene delivery of shear-responsive forkhead box C1 using hyaluronic acid modified chitosan nanoparticles suppresses atherosclerosis through Hippo-YAP signaling pathway.

The turbulent skin-friction theory of van Driest II (involving transformation to incompressible flow) is employed to calculate the local and mean friction coefficients. A wall-wake velocity profile is proposed and employed in the numerical evaluation of the displacement and boundary-layer thicknesses. The proposed velocity profile is shown to be successful in a realistic representation of a compressible boundary layer for given Mach and Reynolds numbers. Values of the calculated variables are compared with existing correlations and experimental/computational data reported in the literature. A two-stage regression analysis is applied to the predicted data to obtain expressions for the streamwise variations of the mean flow properties as functions of the Reynolds and Mach numbers. Explicit correlations for the local and mean friction coefficients, displacement, momentum, and boundary-layer thicknesses are presented for air flow in the Mach number range from 2 to 7 and the Reynolds number range from 7×105 to 7×109. In contrast to the laminar flow case, the thickness of the turbulent boundary layer depends weakly on the Mach number.

Design and Testing of a laminar flow windows high-temperature optical cell

Thermo-hydraulic performance of offset fin microchannel heat exchanger in molten salt laminar flow

A time-resolved luminescence assay using time-to-space conversion strategy for the sensitive detection of influenza virus on a microfluidic chip.

Blood flow within biomedical devices and vascular models is characterized by laminar dynamics at relatively low Reynolds numbers, where shear-dependent viscosity governs hemodynamic behavior. This behavior is commonly observed in biomedical applications, such as nozzles, and accurate modeling is essential. In this study, numerical simulations of laminar non-Newtonian blood flow are performed in OpenFOAM using the Bird-Carreau viscosity model to examine the influence of flow conditions and nozzle geometry. The FDA benchmark nozzle is employed as a reference geometry, and the computational setup is validated against available experimental data prior to the parametric study. Five throat Reynolds numbers, $Re = 100, 300, 500, 1000,$ and $1500$, are investigated together with two collector cone angles, $20^\circ$ and $40^\circ$, as well as three throat diameters, $D_t = 3, 4,$ and $5$ mm, to assess geometric effects. The results show that narrower throats and higher Reynolds numbers significantly increase both velocity and shear stress, highlighting the strong sensitivity of hemodynamics to geometric constriction. Pressure drop analysis further reveals that enlarging the throat diameter can substantially reduce losses; for example, at $Re=1000$ and $1500$, increasing the throat from 3 mm to 4 mm lowers the pressure drop by nearly 50%, while a further increase to 5 mm reduces it by about 40%. Overall, the study demonstrates that both geometric variations and flow conditions lead to significant changes in blood flow physics, underscoring their importance in hemodynamic applications.

The treatment of glioblastoma (GBM) presents significant challenges, with median survival rates remaining low despite standard-of-care therapies. A novel approach, cytostatic hypothermia (CH), is under development against GBM; it is a window of temperature (typically 20-25°C) which halts tumor growth in vivo. This feasibility study expands upon the findings through the computational evaluation of a fully implantable system. Our simulations evaluate a thermoelectric cooler with a microwire array (NeuraTEC) and a novel ambient recirculating core (ARC) to achieve uniform cooling of a region in the brain without overheating local skin temperature. Finite-element modeling was employed to simulate coupled bioheat transfer and laminar non-isothermal fluid flow dynamics. Our results indicate that NeuraTEC can attain local tissue temperatures within a cytostatic range while minimizing thermal gradients. The use of multiple narrow, thermally conductive wires enhances cooling uniformity with minimal tissue displacement. The ARC provides a unique form of heat management that enables full implantability and hence portability. This work suggests it can facilitate the transfer of heat from a brain region to the skin. Future work will focus on device prototyping and validation through in vitro and in vivo studies in large animal models. These simulations suggest that the proposed intracranial cooling system could make CH a practicable approach against GBM. Furthermore, this approach to internal heat management may also open new avenues for treating neurological conditions through local and chronic hypothermia, extending beyond the short-duration (acute) cooling methods currently tested.

The Stokes boundary layer (SBL) is the oscillating flow above a flat plate. Its laminar flow becomes linearly unstable at a Reynolds number of $\textit{Re} = U_0 \sqrt {T_0/\nu } \approx 2511$ , where $U_0$ is the amplitude of the oscillation, $T_0$ is the period of oscillation and $\nu$ is the fluid’s kinematic viscosity, but turbulence is observed subcritically for $\textit{Re} \gtrsim 700$ . The state space consists of laminar and turbulent basins of attraction, separated by a saddle point (the ‘edge state’) and its stable manifold (the ‘edge’). This work presents the edge trajectories for the transitional regime of the SBL. Despite linear dynamics disallowing the lift-up mechanism in the laminar SBL, edge trajectories are dominated by coherent structures as in other canonical shear flows: streaks, rolls and waves. Stokes boundary layer structures are inherently periodic, interacting with the oscillating flow in a novel way: streaks form near the plate, migrate upward at a speed $2\sqrt {\pi }$ and dissipate. A streak-roll-wave decomposition reveals a spatiotemporally evolving version of the self-sustaining process (SSP): (i) rolls lift fluid near the plate, generating streaks (via the lift-up mechanism); (ii) streaks can only persist in regions with the same sign of laminar shear as when they were created, defining regions that moves upward at a speed $2 \sqrt {\pi }$ ; (iii) the sign of streak production reverses at a roll stagnation point, destroying the streak and generating waves; (iv) trapped waves reinforce the rolls via Reynolds stresses; (v) mass conservation reinforces the rolls. This periodic SSP highlights the role of flow oscillations in sustaining transitional structures in the SBL, providing an alternative picture to ‘bypass’ transition, which relies on pre-existing free stream turbulence and spanwise vortices.