Laminar Water Flow Research Articles

An optical field regulation method for waterjet-guided laser: Reducing taper and improving deep-processing capability

Waterjet-guided laser (WGL) processing technology has the advantages of low thermal damage, no contact stress and ultra-fine processing. However, the energy distribution of the existing technology in the laminar flow water column is still characterized by Gaussian distribution, which leads to taper effect in the processing of thick plate materials and affects the deep-processing capability. To address these shortcomings, a novel waterjet laser-field regulation (WLR) method is proposed in this paper. Optical simulation and coupling experiments confirm the method's ability to modulate the energy within the waterjet into a circular distribution, which solves the problem of low power density near the surface of the waterjet. Waterjet-guided laser cutting experiments were conducted based on the WLR method, and the taper was significantly reduced compared to the conventional WGL. At a power of 12 W, the taper was reduced from 5.85° to 2.28°, a reduction of 61 %. In terms of processing depth, the WLR method cuts slightly lower groove depths with a low number of cuts, but as the number of cuts increases, the groove depth steadily increases and exceeds that of the conventional WGL. At 500 cuts with a laser power of 20 W, the groove depths obtained by the WLR method increased by 115 % compared to that of the conventional WGL. This study has important implications for the processing of thick materials by waterjet-guided laser.

Influence of pin fins and channel geometry on the hydrothermal performance of hexagonal mini-channel heat sink for cooling cylindrical batteries

This study numerically and experimentally examined the effects of pin fin configuration and channel geometry on the performance of a hexagonal mini-channel heat sink (HMCHS) to cool cylindrical lithium-ion battery cells. Various configurations of HMCHS with circular pin fins are studied, including circular fins centrally positioned within flat channels, circular fins positioned within grooved channels, circular fins situated within hybrid channels transitioning between wavy and straight channels and circular fins placed within hybrid channels that incorporate secondary flow channels between the primary flow channels. This numerical study utilized the finite volume method to investigate the laminar water flow at Reynolds numbers below 800. Findings showed that the HMCHS exhibited superior thermal performance compared with the conventional cylindrical mini-channel heat sink design. Moreover, the incorporation of pin fins into the HMCHS design was more effective in enhancing the Nusselt number than simply increasing the Reynolds number across various configurations. Meanwhile, the hybrid channel design with secondary channels, combined with the addition of pin fins, achieved the optimal overall performance of the HMCHS, resulting in the highest performance index of 1.88.

One-dimensional consolidation analysis of layered unsaturated soils: An improved model integrating interfacial flow and air contact resistance effects

Layered unsaturated soils exhibit complex mechanical and physical properties. Owing to the roughness between unsaturated soil interfaces and the presence of irregularly distributed micro-pores, this study explores the laminar flow of pore water and counter-cyclonic flow of pore air through these channels at low velocities. In response to the complex consolidation behavior of unsaturated soils influenced by the flow and air contact resistance, an improved model is developed. The model incorporates the flow contact transfer coefficient (Rω), flow partition coefficient (ηω), air contact transfer coefficient (Ra) and air partition coefficient (ηa). Semi-analytical solutions for pore water pressure, pore air pressure and settlement in layered unsaturated soils are derived by employing the Laplace transform and its inverse transform. The rationality of the model is validated through comparative analysis with existing solutions. Analysis of the improved model yields critical insights: the presence of flow and air contact resistance leads to the development of relative pore pressure and air pressure gradients at interfaces, which diminishes the influence of the permeability coefficients of the water phase (kω) and air phase (ka) on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.

Exploring heat transfer augmentation and entropy generation in nanofluid flow induced by vibration: Influence of velocity and rheological properties

This study numerically investigates the heat transfer and entropy generation of nanofluid flow under mechanical vibration, employing approved formulations to model the nanofluid density, specific heat, viscosity, and conductivity. Specifically, the impact of vibration on laminar forced convection thermal flow of both pure water and Al2O3-water nanofluid within a pipe is explored using CFD. Various Reynolds numbers are examined under constant heat flux conditions, with nanofluid properties determined using established correlations. Results indicate that applying Al2O3 nanofluid slurry instead of pure water at low Reynolds numbers reduces entropy generation, proving advantageous. Vibration enhances heat transfer by intensifying fluid agitation and promoting particle dispersion near the wall, resulting in a significantly more uniform temperature distribution along the pipe, approximately 100 times more than steady-state flow. Analysis reveals vibration’s effectiveness in reducing irreversibility, especially at lower Reynolds numbers, with substantial enhancements in heat transfer coefficients, up to approximately fivefold compared to steady-state flow, particularly for nanofluid flows. Optimal conditions for maximizing heat transfer enhancement emphasize nanoparticle size and concentration. Mechanical vibration with different frequencies produces significant improvements in heat transfer compared to amplitude variations, primarily influenced by the Reynolds number. Overall, this study offers valuable insights into the intricate relationship between vibration, fluid dynamics, and heat transfer in nanofluid flows, with practical implications for optimizing thermal management systems across various engineering applications.

New Insights into Turbulent and Laminar Flow Relationships Using Darcy–Weisbach and Poiseuille Laws

Analytical solutions for turbulent and laminar water flow conditions are developed considering the drainage process of a simple tank reservoir, using the Darcy–Weisbach and the Poiseuille laws, respectively. Near the critical value of the Reynolds number, the Darcy–Weisbach and the Poiseuille laws do not match, and there is a gap regarding the possibility of describing the drainage analytically. This gap corresponds to the critical zone of the Moody diagram, where theoretically a constant discharge occurs under a decreasing hydraulic gradient. In the critical zone, this hydraulic behavior of the flow reflects the different energy losses occurring during the drainage, as the laminar flow is a more efficient flow condition than the turbulent one. In natural systems (e.g., springs and karst aquifers), a smooth transition from the turbulent to the laminar water flow occurs due to the heterogeneity in the medium.

Optimization of simultaneous utilization of air and water flow in a hybrid cooling system for thermal management of a lithium-ion battery pack

The present study provides a simulation of a battery pack (BCK) comprising lithium-ion battery cells positioned within an air channel utilizing Finite Element Method (FEM). A tube containing a flowing liquid, which serves the purpose of cooling BCK, sits at center of the BCK. Laminar nanofluids (NFs) or water flow enters tube, and air flows inside channel. A transient investigation is conducted on BCK temperature, heat transfer coefficient (HTC), and air and liquid outlet temperatures by varying airflow rate (AFR). The results demonstrate that raising airflow decreases the BCK's average temperature (TAE) and maximum temperature (TMM). The TAE of the BCK is more sensitive to changes in flow rate. Furthermore, as the AFR increases, the HTC increases because liquid and air leaving the outlet are cooled. Using NFs instead of water in the tube causes the average and TMM of the BCK to decrease and the HTC to enhance. The results show that The TMM and the TAE of the BCK are increased until the first 25 min and then are reduced. Using NFs instead of water reduces the outlet air and water temperature when AFR is low. Using NFs for battery cooling typically results in better performance than water.

A New Water Film Depth Prediction Model for Pavement Surface Drainage

The prediction of the water film depth (WFD) on the road surface can help with road skid resistance research and reduce the risk associated with driving on rainy days. At present, there are many empirical and analytical models based on drainage length, slope, rainfall intensity and other parameters. Considering the influence of road surface runoff and starting from the Reynolds number formula of road surface water flow, a new road surface WFD calculation formula that considers the movement state of laminar water flow is derived. The results show that the changing trends of various parameters in the prediction model (drainage length, rainfall intensity, road slope) affecting WFD are consistent with those of the existing model. It is also found that the initial water film depth, initial speed of rainwater, and rainfall angle have little impact on WFD. The predicted value of the model has a suitable matching degree compared with the classical empirical model, which provides a new approach to the prediction of road water film depth.

Optimization with genetic algorythms of PVT system global efficiency

Photovoltaic (PV) solar panels generally produce electricity in the 6% to 12% efficiency range, the rest being dissipated in thermal losses. To recover this amount, hybrid photovoltaic thermal systems (PV/T) have been devised. These are devices that simultaneously convert solar energy into electricity and heat. A significant amount of research on PV/T collectors has been carried out over the last decade and water PV/T glazed flat plate collector systems turned out to be the most promising to develop (Zondag[1]). It is thus interesting to study the PV/T system as part of a closed loop single phase water CDU (coolant distribution unit) in laminar forced convection. In particular, the analysis was conducted on the optimal cooling performance of the thermal part, testing polynomial channel profiles of varying order (from zero to fourth) for channels of a real industrial module heat sink, under the following conditions: ideal flux of 1000 W/m² on one side, insulation on the opposite side, periodic conditions on the remaining sides, fully developed thermal and velocity profile in laminar flow of water. Through the use of a genetic algorithm, we have optimized the shape of the channel’s sidewalls in terms of heat transfer maximization. In terms of Nusselt number, results show that fourth order profiles are the most efficient. When limits to allowable pressure loss and module weight are introduced, these bring generally to a lower efficiency of the system than the unconstrained case.

Innovative aquaculture cage “Flow2Vortex” ensures a sustainable biomass delivery for low trophic level aquaculture

The increasing global demand for seafood, coupled with the limitations of current fish stocks and aquaculture practices, requires the development of sustainable aquaculture solutions. In this context, this study explores the potential of a novel cage technology - Flow2Vortex - for the cultivation of jellyfish, a low-trophic-level organism with increasing market demand. The unique cage design creates a laminar and circular water flow, providing optimal conditions for cultivating fragile planktonic species. Indoor experiments demonstrated the successful growth of jellyfish in the cage, with growth rates of up to 11.6% per day. In addition, field tests in open waters confirmed the cage's ability to maintain a diffuse and controlled flow inside, even under strong external currents. The cage also maintained significantly higher zooplankton concentrations than the surrounding environment, offering a consistent food source for the cultivated jellyfish. These findings highlight the potential of the Flow2Vortex cage for scalable indoor and outdoor cultivation of low-trophic-level organisms, such as jellyfish, contributing to the diversification and sustainability of aquaculture practices.

Optical and hydrodynamic performance of photocatalytic monoliths of different shapes in a solar photoreactor with compound parabolic collector

Radiative transfer and hydrodynamic analyses are carried out to study the performance of solid macroscopic pieces (monoliths) of TiO2 photocatalyst in a CPC solar reactor. The absorbed photonic flux distribution was solved through Monte Carlo simulations for different monolith geometries: asterisk and flower shapes. In the case of the asterisk geometry, different numbers of arms (lobes) are considered. The performance of the monoliths in a tubular Pyrex photoreactor is numerically studied under both diffuse and collimated UV solar irradiation on the CPC. Also, the case of a homogeneous diffuse illumination on the glass tube, without CPC reflection, is considered. Hydrodynamic simulations are also carried out to determine the overall friction factors in the presence of the different pieces. Significant differences are observed for the results between different monoliths. Absorbed power varies up to 36%. On the other hand, the peak flux is the same for all pieces, but the standard deviation of its distribution may be up to 65%. The effect of partial specularity in the reflection by the TiO2 surface is also studied, resulting in a maximum deviation of just 4.2% in the flux values between 25% and 75% specularity. Two different positions for a monolith inside the glass tube were considered, with some significant differences in the flux distribution, but with changes below 4% in total absorbed power. With regards to the hydrodynamics, laminar flow of water along the pieces inside the tube was considered. Differences higher than one order of magnitude are observed in the friction factor for different pieces, being the void fraction inside the tube the main parameter affecting this change. The results of this work are relevant to understanding the potential effect of using catalyst pieces with different geometry on a photocatalytic reactors performance; inadequate geometrical design of this component may lead to diminished light collection or substantially increased pressure drops for scaled up systems.

Property of water-nanoparticle flow and heat transfer in the double-tube heat exchanger with nanofluid

The three-dimensional numerical simulation is conducted to study the impact of Al2O3/water nanofluid on the flow property and heat transfer of a counter flow double-tube heat exchanger where a laminar flow of cold water is in the outer tube, and in the inner tube there is a turbulent flow of hot nanofluid with particle volume concentrations ranging from 0.05% to 3%. The effects of temperature, flow rate, and particle volume concentration on the property of nanofluid flow and heat transfer are explored. The results show that the friction factor decreases with the increase of temperature and flow rate, and the pressure drop increases with increasing particle volume concentration. The temperature of the nanofluid at the outlet first decreases rapidly with time and then increases gradually to a stable value. Along the flow direction, the temperature of nanofluid decreases slowly at x/D < 10, and the axial temperature gradient increases at the full development stage. At a constant Reynolds number, the lower the temperature or the larger the particle volume concentration, the stronger the heat transfer. The local heat transfer coefficient on the wall of the inner tube decreases rapidly after reaching the peak x/D = 2.3, and then increases slowly until the outlet. The particle number density decreases sharply at x/D < 5, and then slowly decreases, while the change of the geometric mean diameter of particles is just the opposite. Increasing the flow rate or the temperature will strengthen particle coagulation, resulting in the decrease of particle number density and the increase of geometric mean diameter of particles.

Examining the effect of backward/forward-facing wavy channels on the thermohydraulic performance of a printed circuit heat exchanger under the laminar flow regime

The printed circuit heat exchanger (PCHE) has been used in many important engineering applications because of its advantages, including its small size and high efficiency. This study aims to enhance the thermohydraulic characteristics of the PCHE by using new channels characterised by a three-dimensional flow path. These proposed backward/forward-facing wavy channels (BFFWCs) are a combination of a wave path in the horizontal plane and a U-shape path in the vertical plane. Under laminar water flow on both sides of the PCHE, a numerical study was conducted to assess the thermohydraulic characteristics of the proposed PCHEs with various wave amplitudes for channels and angles of attack for six models of BFFWCs on the basis of the conventional PCHE. The evaluation parameters that were adopted are the Nusselt number, friction factor, thermohydraulic performance criterion, and PCHE's effectiveness. Two models of the PCHE were manufactured and tested—one for the straight channels and the other for the proposed channels—to verify the accuracy of the numerical simulation results by comparing them with the experimental outcomes. Results indicated that the three-dimensional flow path has a positive influence on enhancing the heat transfer rate of the exchanger, with a slight increase in the pressure loss. The Nusselt number and friction factor increase with increasing wave amplitude and angle of attack. Compared with conventional PCHE, the maximum improvement in the Nusselt number is as much as 71 % and 78 % for model 3 (amplitude = 0.8 and angle of attack = 30°) and model 6 (amplitude = 0.8 and angle of attack = 60°). The thermohydraulic performance of model 3 was better than that of model 6. The maximum obtained thermohydraulic performance criterion reaches about 1.43 and 1.40 for models 3 and 6, respectively.

Etude numérique de l’effet des générateurs de vortex longitudinaux sur le transfert thermique d’un écoulement laminaire traversant un micro-canal

We conducted, in this work, a three-dimensional numerical study of forced convection heat transfer of a laminar flow of water passing through micro-channels with and without longitudinal vortex generator, using the CFD code “Ansys- Fluent”. This work aimed to elucidate the effect of vortex generators on the dynamic and thermal behavior of the micro-fluidic flow. The results obtained show that the increase in the Reynolds number leads to an improvement in the quality of heat transfer in both cases of the study. Rectangular micro-channel with LVG can improve heat transfer compared to smooth rectangular micro-channel while consuming more pressure drop. In the range of Reynolds numbers between 200 and 1200, a 2-21% increase in the mean Nusselt number was observed for micro-channels with LVG compared to smooth micro-channels. This occurs through better mixing of the fluid, reduction in the thickness of the thermal boundary layer, and increased heat transfer area. In addition, the friction factor has been increased by more than 50% compared to smooth micro-channels, due to the local resistance of LVGs and the presence of secondary flows.

Cohesive bond strength of marine aggregates and its role in fragmentation

Marine aggregates are one of the main contributors to carbon sequestration in the deep sea through the gravitational settling of biogenic particles formed from the photosynthetic products of phytoplankton. The formation of large particles due to aggregation processes has been the focus of studies in the past, but recent findings on the spatio-temporal distribution of particles suggests that the fragmentation of aggregates plays an important role in aggregate dynamics. Here, we assessed the yield strength of aggregates derived from natural planktonic communities in order to analyze the cohesive bond strength and further understand fragmentation. The experimental approach was designed around the use of a Couette device, which produces a constant laminar shear flow of water. Aggregates were found to have a higher yield strength (~289 ± 64 nN) during phases of nutrient depletion than those of mineral particles such as montmorillonite. Based on an estimated cohesive bond strength of 96 nN a numerical model to predict the temporal variation of aggregate size was created. The output of this model indicates that cohesive bond strength is a major determinant of the size of aggregates in motion. Our findings suggest that the dynamics of marine aggregates are greatly influenced by cohesive bond strength and the role in fragmentation.

Effects of the nozzle-to-nozzle distance on the performance of the water condensation growth-based virus aerosol concentrator

Efficient collection of airborne viruses is crucial for monitoring and preventing the spread of respiratory diseases. The laminar flow water condensation-based growth tube collector (GTC) is a microbial sampler extensively used to collect virus aerosol particles owing to its high recovery of viable viruses. The GTC involves multiple nozzles and eight tubes for sampling flow rates of 6–8 L per minute (LPM). To allow the GTC to operate at a higher flow rate, optimizing GTC performance through investigation of the effects of nozzle-to-nozzle distance is essential. Herein, we examined these effects on the collection efficiency and viability of airborne MS2 viruses collected by the growth-based virus aerosol concentrator (GVC), which is a lab-made single-tubed GTC, at flow rates of up to 6 LPM per tube. The flow interactions between adjacent jets were analyzed by observing the particle deposition patterns. The collection efficiencies of MS2 virus aerosol particles and the enrichment ratio of the GVC increased with increasing nozzle-to-nozzle distance. The infectious virus concentration relative to that in the virus suspension (RIVC) ranged from 0.0093 to 0.095 for 5 min of sampling. At flow rates of 1 and 6 LPM, the RIVC decreased as the nozzle-to-nozzle distance decreased, which may be ascribed to the higher shear stress at shorter nozzle-to-nozzle distances applied to the viruses collected through the cross-flows driven by adjacent jets. These measured RIVC values are much larger than those collected by the BioSampler. These findings can provide important insights into optimizing multiple nozzles in high-flow-rate GTCs.

Heat transfer enhancement in laminar water flow through a square channel by streamwise ultrasound irradiation

This research focuses on the heat transfer of laminar water flow in a square channel under 28–120 kHz and 60–120 W ultrasonic waves, irradiated along the streamwise direction. The experiment was conducted at Reynolds numbers of 400–2000, and the uniform surface heat flux of the pipe was set as 3.1–12.9 kW/m2. In this study, ultrasound-induced streaming was investigated using a particle image velocimetry (PIV) technique, and cavitation bubbles were detected using a digital camera. From the results, the maximum heat transfer enhancement was 155% with 28 kHz and 120 W ultrasound at q = 12.9 kW/m2, Re = 400, and x/Dh = 2.58. The Nu ratio, which represents the capability of ultrasound-induced heat transfer enhancement, was also determined. A maximum Nu ratio of 2.017 was achieved with 28 kHz and 120 W ultrasound at q = 7.2 kW/m2 and Re = 400 or St = 28.16 × 104. With a relatively low Re, the poorest heat transfer was observed at St values ranging from 40 × 104 to 120 × 104. This study provides a predictive formula for the Nu ratio, with deviations ranging from 6.89 to 13.2%. Furthermore, the PIV analysis suggested that acoustic streaming of Eckart type appears under the ultrasound irradiation and its velocity enhancement effect becomes maximal under the conditions for the maximum Nu ratio. It is also confirmed that the ultrasound irradiation can enhance the nucleation of bubbles at the pipe wall; ultrasound-induced dynamics of these nucleated bubbles are expected to further disturb near-wall liquid motion and contribute to heat transfer enhancement.

Laboratory-Scale Low-Speed Water Tunnel: Comparison of Experimental Flow Visualization and Computer-Aided Simulation

This study aimed at developing the laboratory-scale low-speed water tunnel design by first evaluating the effect of varying the number of wide-angle diffuser vanes and then confirming flow visualization against object geometries tested by experiments and computer-aided simulation. The low-speed water tunnel design in this study consists of a wide-angle diffuser, a honeycomb, a convergent section, and a working section. To ascertain the laminar flow of water would act in the experiment, a prior simulation using 3, 6, and 12 vanes and without a vane was conducted. Some geometries, including tube, triangle, aerofoil, and car models have been tested and then compared to the experimental results. The results indicate that the twelve vanes diffuser is more effective in minimizing turbulent flow and producing a streamlined pattern in the water tunnel. Laminar flow with a Reynolds number of 2238 and flow velocity of 0.008 m/s was obtained in the working section. The flow visualization by experiment and computational fluid dynamics simulation was almost similar.

Numerical Investigation of the Hydrothermal Characteristics of Water Flow in Compound Microchannel Heat Sinks

In the present work, three-dimensional numerical simulations of laminar forced convection flow of water in unique compound microchannel heat sinks (MCHSs) were investigated using computational fluid dynamics (CFD) modeling. The newly proposed MCHS is made up of circular microchannels slotted from the top within a trapezoidal shape, and its cooling effectiveness was compared to that of traditional rectangular MCHS. Each MCHS under consideration has the same hydraulic diameter and heat transfer surface area. Water volumetric flow rates (Qin) with a wide range of values are used, ranging from 40 to 90 ml/min, with the fluid inlet temperature set to 20 oC. A constant heat flux boundary condition of 100 W/cm2 is supplied on the MCHS bottom. The results demonstrated that the inclusion of reentrant trapezoidal shapes can disrupt both hydrodynamic and thermal boundary layers, as well as accelerate fluid flow and mixing in the main flow, resulting in a significant heat transfer enhancement. Furthermore, at Qin=90 ml/min, the average Nusselt number (Nuavg) of compound MCHS increased by 2.16%, while total pressure drop and total thermal resistance decreased by 1.73% and 1.57%, respectively, when compared to the straight rectangular counterpart.

Numerical and experimental thermohydraulic performance evaluation of multi-minichannel heat sinks considering channel structure modification

Heat transfer and fluid flow behaviour have been studied numerically and experimentally in multi-mini channel heat sinks (MM-CHS). The proposed designs of MM-CHS are utilizing more than one passive technique in order to enhance the thermohydraulic performance with different inlet/outlet arrangements. Three curved channels have been considered including (arc, S, and wave) combined with two passive techniques of interruptions and ribs–cavities. Numerical simulations are performed on laminar water flow for the considered Reynolds number less than 500. In the experiment, four MM-CHSs with different channel structures that include straight channels, wave channels, wave channels with interruptions and wave channels with ribs–cavities are manufactured and tested to validate the simulation model and compare the performance improvement of the MM-CHS resulting from the adoption of both proposed techniques. Results show an effective improvement in the performance of the MM-CHS after using interruptions and ribs–cavities but with the pressure loss penalty. Compared with the interrupted curve channel, a ribbed curved channel with cavities is more effective in improving wall temperature uniformity along the channel length of MM-CHS. The best thermohydraulic performance is achieved by the wave channel with ribs and cavities, where the performance evaluation criterion reached about 1.68.

Turbulence via Intermolecular Potential: Viscosity and Transition Range of the Reynolds Number

Turbulence in fluids is an ubiquitous phenomenon, characterized by spontaneous transition of a smooth, laminar flow to rapidly changing, chaotic dynamics. In 1883, Reynolds experimentally demonstrated that, in an initially laminar flow of water, turbulent motions emerge without any measurable external disturbance. To this day, turbulence remains a major unresolved phenomenon in fluid mechanics; in particular, there is a lack of a mathematical model where turbulent dynamics emerge naturally from a laminar flow. Recently, we proposed a new theory of turbulence in gases, according to which turbulent motions are created in an inertial gas flow by the mean field effect of the intermolecular potential. In the current work, we investigate the effect of viscosity in our turbulence model by numerically simulating the air flow at normal conditions in a straight pipe for different values of the Reynolds number. We find that the transition between laminar and turbulent flow in our model occurs, without any deliberate perturbations, as the Reynolds number increases from 2000 to 4000. As the simulated flow becomes turbulent, the decay rate of the time averaged Fourier spectrum of the kinetic energy in our model approaches Kolmogorov’s inverse five-thirds law. Both results are consistent with experiments and observations.