Laminar Water Flow Research Articles

Experimental studies on heat transfer augmentation and friction factor characteristics for laminar flow of water in a square duct induced by full-length helical tapes

Experimental studies on heat transfer augmentation and friction factor characteristics for laminar flow of water in a square duct induced by full-length helical tapes

Dropwise and liquid-jet laminar flow of subcooled water falling over horizontal tube banks

Falling-film heat exchangers are widely used to promote heat and mass transport within industrial environments. In contemporary condensers, for example, liquid films continuously form over a tube row and impact multiple tubes beneath, resulting in a rich variety of two-phase flow phenomena, including the classical Rayleigh-Plateau instability. It is widely known that altering the contact angle of the tubes influences the heat exchangers’ heat and mass transfer characteristics by changing the falling films’ flow behaviour (i.e. dropwise or jet). Therefore, resolving interfacial flow characteristics, such as the Rayleigh-Plateau instability, is crucial for falling film studies as this instability may change the state of the falling film from being jet flow to dropwise/jet flow or even just dropwise. To explore this aspect, three-dimensional direct numerical simulations are used in the present work to replicate the jet instability behaviour. By employing certain mesh refinement strategies demonstrated from various case studies, the interfacial flow behaviour and jet instability have been captured, showing good agreement with experimental and theoretical data previously published. This is determined from the increased jet bifurcation and a maximum error of 2.2% of the film thickness in comparison to Nusselt's result within the bulk region of the tube. In addition, the average and local heat transfer coefficients across the first tube were compared with numerical solutions to give an average error of 3.2 and 14 %. Jet instability is found to be directly related to the amplitude of the axial pressure variations which is augmented by the growth rate of the capillary wave that travels upstream. Specifically, for contact angles of 30 and 60°, the flow is in a dropwise and dropwise/jet state due to the emergence of the Rayleigh-Plateau instability. Notably, the additional satellite droplets that materialize from the unstable jet lead to an increase in the local heat transfer coefficient of the film compared to without the Rayleigh instability improvement.

Analysis of hydrothermal performance for laminar forced convective flow through a wavy channel with porous blocks

Purpose The purpose of this paper is to investigate computationally the hydrothermal characteristics for forced convective laminar flow of water through a channel with a top wavy wall and a flat bottom wall having metallic porous blocks. Design/methodology/approach The governing equations are solved computationally using a finite element method–based numerical solver COMSOL Multiphysics® for the following range of parameters: 10 ≤ Reynolds number (Re) ≤ 500 and 10–4 ≤ Darcy number (Da) ≤ 10–1. Findings The presence of porous blocks significantly influences the heat transfer rate, and the value of local Nusselt number increases with the increase in Da. The value of the average Nusselt number decreases with Da for the top wall and the same is enhanced for the bottom wall of the wavy channel with porous blocks (WCPB). The value of the average Nusselt number for WCPB is significantly higher than that of the wavy channel without porous block (WCWPB), plane channel without porous block (PCWPB) and plane channel with the porous block (PCPB) at higher Re. For PCPB, the performance factor (PF) is always higher than that of WCWPB and WCPB for Da = 10–4 and Da = 10–3. Also, PF for WCPB is higher than that of WCWPB for higher Re except for Da = 10–4. Further, the value of for WCPB is higher than that of PCPB at Da = 10–2 and 10–1 at Re = 500. Practical implications The current study is useful in designing efficient heat exchangers for process plants, solar collectors and aerospace applications. Originality/value The analysis of thermo-hydraulic characteristics for laminar flow through a channel with a top wavy wall and a flat bottom wall having metallic porous blocks have been analyzed for the first time. Further, a comparative assessment of the performance has been performed with a wavy channel without a porous block, a plane channel without a porous block and a plane channel with porous blocks.

Relating hydrodynamic test data with aerodynamics using t-DHI

An optical full-field non-invasive technique is introduced to study hydrodynamic interactions within a scale water tunnel as a simile of a wind tunnel. The ad-hoc water tunnel is a transparent chamber that allows the observation of the hydrodynamics generated from the water's interaction with the objects in it. A slow laminar water flow circulates into the tunnel serving as the surrounding media for the samples to be studied. This interaction is monitored with a transmission digital holographic interferometer (t-DHI) that uses a high-speed camera to analyze the changing flow in short periods. As proof of principle, three different tests are presented: the first test is to verify the laminar flow inside the water tunnel. Hence, no sample is inside the chamber. The second uses a barrier placed perpendicularly to the flow to modify the fluid's direction by blocking half of the chamber's path. The last test uses a scale car model, showing how the liquid deviates around the car, similar to the information reported when using a wind tunnel. The t-DHI system used to monitor the ad-hoc water tunnel proves the latter's potential to be used as a wind tunnel in a down-scaled and simple form. For this, as a first-order approximation, consider that a more significant water displacement implies a faster flow; and a slow flow results in small water displacements.

Heat transfer and flow characteristics of varying curvature wavy microchannels

This paper compares the thermohydraulic performance of varying curvature wavy microchannels, namely elliptical-wavy and sinusoidal-wavy microchannels. The amplitude of microchannels is fixed at 0.6 mm, and wavelengths are varied from 3 mm to 8 mm. Simulations are performed for the laminar flow of water (160 ≤ Re ≤ 900) considering three-dimensional conjugate heat transfer using ANSYS Fluent version 2020R2. The computational model has been validated by performing experiments on a serpentine-wavy microchannel, a special case of the elliptical-wavy microchannel, using micro-particle image velocimetry (μ-PIV) test facility. Both Nusselt number and friction factor increase with the increase in waviness. Elliptical-wavy microchannels have superior thermohydraulic performance than sinusoidal-wavy microchannels except for the channel of highest waviness at Re = 160. A microchannel with lower entropy generation has a higher thermohydraulic performance. Further, we observe centrifugal instabilities in both sinusoidal-wavy and elliptical-wavy microchannels at higher Reynolds numbers. Centrifugal instabilities in the elliptical-wavy differ from those in the sinusoidal-wavy microchannel by the asymmetric formation of additional vortices about the horizontal midplane in the channel cross-section.

THERMAL ANALYSIS OF LAMINAR WATER FLOW OVER A BACKWARD FACING CHANNEL WITH CARBON NANOPARTICLES

In the last few years, the thermo-hydraulic simulation of nanofluid flow bifurcation phenomena has become of great interest to researchers and a useful tool in many engineering applications. FVM has been employed in this article to numerically explore the laminar water flow over a backward facing channel with or without carbon nanoparticles (CN). The problem formulated in this paper has been solved by considering the effects of nanoparticle weight percentages (𝑤%), such as 0.00, 0.12, and 0.25 for different Reynolds number (𝑅𝑒). Nusselt number distribution (𝑁𝑢(𝑥)), coefficient of skin friction (𝐶𝑓), characteristics of pressure drop (Δ𝑝), velocity contours, static temperature, pumping power (𝑃𝑝) and thermal resistance factor (𝑅) have been investigated to know the behavior of thermo-hydraulic flow bifurcation phenomena. The present study shows that the surface temperature and coefficient of heat transfer can be reduced due to the effect of 𝑅𝑒 or w%. For different w%, it has been found that in the rise in the values of 𝑅𝑒 causes the increase of vortex length and as a result velocity gradient and Δ𝑝 arises. Furthermore, it has also been studied that the enhancement of 𝑅𝑒 causes the increaseof 𝑃𝑝 and Δ𝑝.

Review on fabrication and experimental study of microchannel heat sinks for cooling of electronic components

Microchannels are widely used in electronic components for higher heat dissipation rate and for providing optimum performance and durability for electronic devices. In this paper, various aspects of microchannel including its fabrication and experimental study are being reviewed. fabrication of microchannels can be done using machining techniques like micro-milling, electric discharge machining, laser beam machining, lithography, injection molding, dry and wet etching. Experimental comparison of fluid flow and heat transfer characteristics in manufactured microchannel heat sinks utilising laminar water flow as a coolant in common applications. Also, coolants like hybrid and non-hybrid nanofluids, ethylene glycol, phase changing material, graphene, etc. are used to enhance the thermal conductivity and heat dissipation rate in microchannel heat sinks. Experimental studies on various output parameters like surface roughness, tool wear rate, and material removal rate are examined. Complex structured microchannel heat sinks are also considered. The variations in process parameters with respect to material removal rate and surface roughness can be found using an experimental study. Also, optimization of various process parameters along with material removal rate and surface quality can be performed using numerical analysis. Heat dissipation performance based on the geometry of the microchannel heat sink is explored. These aspects determine the pressure drop characteristics as well as fluid flow and heat transfer capability of a microchannel heat sink. It is inferred that fabrication, experimental and numerical factors have a remarkable influence on the fluid flow and heat dissipation performance of the microchannel heat sink.

Near-infrared imaging to quantify the diffusion coefficient of sodium pentaborate aqueous solution in a microchannel

• The solution concentration was estimated from NIR absorption of water. • The concentration distribution behavior of solutions was visualized. • The diffusion coefficient of aqueous solutions of sodium pentaborate was estimated. • The temperature dependence of the diffusion coefficient was determined. Borated water is injected into boiling-water reactors as a neutron absorber, and it is, therefore, essential to understand the effect of the solution concentration on its diffusion. We have developed a technique for measuring concentration distributions using a microchannel and near-infrared imaging. This measurement technique was applied to borated water in the present study, precisely an aqueous solution of sodium pentaborate. Laminar flows of water and this aqueous solution with 0.12 mol/L, 0.24 mol/L, and 0.32 mol/L at temperatures from 30 °C to 70 °C were mixed in a microchannel at Reynolds numbers of less than 2, and images were acquired at a wavelength of 1900 nm. From the obtained images, the concentration distribution was visualized, and the diffusion coefficient was estimated as being between 3.6 × 10 −10 m 2 /s and 9.8 × 10 −10 m 2 /s. The diffusion coefficient was correlated positively with both temperature and concentration.

A novel method of measuring microtube wall temperatures by thermocouples to investigate sCO2 flows

Experimental study on convective heat transfer through microtubes encounters many challenges such as measuring the wall temperature of the tube with a reasonable uncertainty, relatively high heat loss from the outer surface of the tube, and difficulty in measuring the fluid bulk temperature at the tube outlet. These issues become exacerbated with flow at low Reynolds numbers. The present study presents a new method to measure the tube wall temperature with a small solder cast where a thermocouple is embedded. The net heat flux to flows, determined with the heat loss on the outer surface and the axial heat conduction, is integrated to obtain the local mean enthalpy of fluid and then the fluid mean temperature along the tube. Thus, convection heat transfer coefficients are calculated without measuring the mean temperature at the outlet. The new method is successfully validated with laminar water flows through a horizontally configured microtube, 0.501 mm in inner diameter. All Nusselt numbers are found to lie between 4.36 and 4.36 + 10%. Finally, the method developed in this study is applied to supercritical CO2 flowing upward at 8.0 MPa through a microtube, 0.509 mm in inner diameter. For both high and low mass flow rates, a local maximum of the convection heat transfer coefficient is observed at a location where the film temperature is close to the pseudo-critical temperature. On the other hand, the second local maximum of the convection heat transfer coefficient appears only at low mass flow rates.

Topology optimization for a water-cooled heat sink in micro-electronics based on Pareto frontier

• An efficient Pareto frontier based design strategy for heat sinks is proposed. • A fitting formula of the Pareto frontiers is introduced to accelerate the design. • The 2D topology design results are validated by 3D CFD simulations. • Effects of temperature dependent properties on the results are significant. Topology optimization has been increasingly adopted as a non-intuitive methodology for heat sink design in the thermal management of microelectronics. In this work, a bi-objective topology optimization method for heat sink design in micro-electronics is suggested by considering the trade-off between two contradicting objectives, i.e., the heat transfer and hydraulic performances. The method in this work focused on the laminar water flow with Reynolds number less than 100 based on the channel width for a wide temperature range that covers different types of micro-electric devices. A series of Pareto frontiers were acquired for heat sink designs with different topologies, which can be used to decide the optimum design in respect of heat transfer and pressure drop. Particularly, an analytical formula in terms of inlet Reynolds numbers was obtained for the fast generation of the Pareto frontiers under different working conditions which help to determine the weight parameters of two contradicting objectives readily. The new strategy for weight parameter determination significantly reduces the workload of trial-and-error during the weight parameter determination in the traditional bi-objective topology optimization and thus accelerates the design process. Besides, the temperature-dependent physical properties (viscosity and thermal conductivity) in the design model were considered and were found to affect the design results significantly. Finally, the 3D heat sink model was reconstructed from the 2D topology optimization, and the thermal-fluid analyses were conducted. The results indicate that the 3D reconstructed model can well satisfy the design objective specified in the topology optimization, thereby confirming the validity and robustness of our design method.

A Motion Model of a Remotely Operated Underwater Vehicle: CFD Simulation

The article is directly related to the authors’ previous study of the remotely operated underwater vehicle’s (ROV) motion, where the mathematical model of the ROV motion is derived for laminar flow of water. This solution of the ROV motion has been improved by using the three-dimensional computational fluid dynamics (CFD) simulation that allows simulating the turbulent flow, which is mainly generated by propellers. Both methods were coupled to obtain more accurate values of hydrodynamic damping coefficients for the improved determination of the ROV motion velocity. Results of the solution are discussed and some of them are compared with the experiment.

A Motion Model of a Remotely Operated Underwater Vehicle: CFD Simulation

The article is directly related to the authors’ previous study of the remotely operated underwater vehicle’s (ROV) motion, where the mathematical model of the ROV motion is derived for laminar flow of water. This solution of the ROV motion has been improved by using the three-dimensional computational fluid dynamics (CFD) simulation that allows simulating the turbulent flow, which is mainly generated by propellers. Both methods were coupled to obtain more accurate values of hydrodynamic damping coefficients for the improved determination of the ROV motion velocity. Results of the solution are discussed and some of them are compared with the experiment.

Effect of amplitude of walls on thermal and hydrodynamic characteristics of laminar flow through an asymmetric wavy channel

In this work, we investigate the hydrothermal characteristics for laminar forced convective flow of water through sinusoidal asymmetric wavy channel of three types: linearly increasing amplitude channel (LIAC), linearly decreasing amplitude channel (LDAC) and constant amplitude channel (CAC). The computed velocity and temperature fields are analyzed by varying the Reynolds number (Re) and slope (A) of the linearly varying amplitude in the following ranges: 5 ≤Re≤ 200 and 0.02≤A≤ 0.04. The value of average Nusselt number is almost independent on the geometry of the channel at lower values of Re and A. At higher Re values, the average Nusselt number is the highest for LIAC followed by LDAC, and CAC. The combined effects of heat transfer increase in the wavy channel compared to plane channel and the associated pumping power is assessed using performance parameter (PF). For lower Re values the highest PF is obtained for CAC. For higher values of Re the PF is the largest for LDAC at A = 0.02 and 0.03, and the value of PF for A = 0.04 is the highest for CAC.

The 2-D Cu-water nanofluid-flow and heat transfer over an inclined wall and between two inclined walls: The numerical solution of PDE and ODE

In this paper, we attempt to investigate the steady and laminar flow of incompressible water based nanofluid between inclined plates and over an inclined plate. A uniform and external magnetic field is applied in order to control the non-fluid-flow. The Cu-water based nanofluid can be also used for heat transfer enhancement. We can gain additional thermal energy in the fluid by increasing the volume fraction of Cu nanoparticles in the base fluid and improving the thermophysical parameters for the single-phase model. The results also show that adjusting the Prandtl and Eckert numbers causes the velocity profile to change fast. According to our findings, fluid elements may be more intensively accelerated by raising the nanoadditive concentration and enhancing the thermo-physical characteristics of the fluid.

Conception of minichannel cooling for a PVT heat exchanger

In the paper, a new construction of a compact plate heat exchanger dedicated to PVT cooling was numerically tested. The efficiency of photovoltaic panels decreases as their temperature increases, but cooling improves efficiency. A model counter-current heat exchanger with rectangular minichannels was presented. A heated wall of the heat exchanger was a photovoltaic cell. There were laminar flows of Fluorinert FC-72 and distilled water in the minichannels. FC-72 was heated by the photovoltaic panel. The CAD model of a minichannel heat exchanger was proposed. CFD calculations were performed using Simcenter STAR-CCM+ software. The fluid temperature and velocity profile in the minichannels were determined to finally obtain the values of the heat transfer coefficient. The main parameters taken into consideration in the computations concerned: meshes, physics, and geometry. Finally, local heat transfer coefficients were determined.

Numerical Investigation of Geometric Parameters Effects on Heat Transfer Enhancement in a Manifold Microchannel Heat Sink

Microchannel heat sink has been employed and as a part of electronic equipment extensively investigated. In this investigation, heat transfer and fluid flow features of laminar flow of water in a manifold microchannel heat sink (MMHS) was numerically simulated. Selected heat flux was 100 W/m^2 and water was as working fluid. The effect of length of inlet/outlet ratio (λ=Linlet/Loutlet), the height of microchannel (Hch), and width of the microchannel (Wch) at Reynolds number (Re) range from 20 to 100 as independent parameters on the fluid flow and heat transfer features were examined. Obtained results demonstrate that in MMHS, the impinging jet on the bottom channel surface, inhibits the growth of hydrodynamic and thermal boundary layers, resulting in an enhanced heat transfer rate. Also, by increasing Re and keeping the geometric parameters constant, the heat transfer rate increases. Based on the present investigation, for low Re, it is better to choose a λ=Linlet/Loutlet >1 and for high Re, choose a λ<1. For low Re, maximum of performance evaluation criterion (PECmax) is obtained at Hch=300µm, and for high Re, PECmax is obtained at Hch=240µm. for Re=20 to 100, the maximum of PECmax is 1.765 and obtained at Re=100 and Hch=240µm.

Biotherapic of Trypanosoma cruzi 17x controlled histopathological alterations in mice infected by this protozoon

Introduction: about 10 million people worldwide suffer from Chagas’ disease [1]. The World Health Organization (WHO) has explicitly acknowledged the significance of this condition and supports the use of Complementary and Alternative Medicine by health systems integrated with conventional treatments. Even so, one century after its discovery it still represents a global challenge [1,2]. Biotherapics are ultradiluted medicines and the infection of mice by Trypanosoma cruzi is an excellent model to understand their effect [3,4]. At 8 weeks, mice are physiologically more developed than at age 4 weeks, including a more competent immune system [5].&#x0D; &#x0D; Aim: the aim of this study was to assess the effect of biotherapic of T. cruzi in dilution 17x on liver and spleen tissue of mice of different ages infected by this protozoon.&#x0D; &#x0D; Method: in a blind, randomized controlled trial 12 male Swiss mice aged 4 and 8 weeks, infected by 1,400 blood trypomastigotes T. cruzi Y strain were divided into groups control – treated with 7% hydroalcoholic solution (CI-4=3 animals or CI-8=3 animals) and treated with biotherapic 17x (BIOT-4=3 animals or BIOT-8=8 animals). Treatment (0.2 ml biotherapic/day/animal, per gavage) started after infection was verified (4th day) and animals were sacrificed on the 3rd day of treatment. For histopathological exam, the liver and spleen were removed and fixated in 4% paraformaldehyde for 24 hours and then processed for inclusion in paraffin. Semi-serial 7mm cuts were made and subjected to hematoxylin-eosin stain. It was performed a quantitative analysis of the number of nests of amastigotes and inflammatory foci in the liver. Slides were observed under microscope Olympus BX41 (Tokyo, Japan) and images captured with camera Qcolor3 (Olympus) coupled to the microscope. In the spleen it was counted the number of nests of amastigotes and the number of foreign-body giant cells. In each organ, 20 microscopic fields/cut were counted under power 40x totaling 120 fields/animal with microscope Olympus CBA (Tokyo, Japan). To analyze data it was used software Statistica 8.0. For data not exhibiting normal distribution it was used Kruskal-Wallis’ test at 5% significance and ANOVA for the ones with normal distribution. Chi-square test was used to compare percentages. Biotherapic 17d was prepared by adding 0.9 ml of blood with T. cruzi (10E+7 trypomastigotes/ml) to 9.1 ml of distilled water in laminar flow. Following dilutions were prepared in 86% hydroalcoholic solutions up to 16x. Dilution 17x was prepared with 7% hydroalcoholic solution [6]. It was performed microbiological control and in vivo biological risk of the biotherapic. Results showed a number of colony forming units proper for use (&gt;1CFU/ml). Intraperitoenal inoculation of the biotherapic did not cause infection in animals. This study was approved by the Ethics Committee for Animal Experimentation/UEM protocol 030/2008.&#x0D; &#x0D; Results and Discussion: in the liver, animals of group BIOT-8 exhibited less nests of amastigotes (p

A comparison of two methods for estimating critical swimming speed (Ucrit) in larval fathead minnows: the laminar flow assay and the spinning task assay.

Critical swimming speed (Ucrit) is considered a good predictor of swimming capabilities in fish. To estimate Ucrit, a fish is exposed to an incrementally increasing laminar flow of water until it cannot maintain its position against the current. The spinning task assay has been proposed as an alternative method to traditional laminar flow methods; however, these methods have not been directly compared. Thus, the goal of this study was to determine whether the spinning task assay is a suitable alternative to traditional laminar flow assays. To that end, the performance of fathead minnows in each assay was compared at three time points (14, 19 and 24 days post-fertilization, dpf). In 14 dpf fish, Ucrit estimates were similar regardless of the assay used. However, at 19 and 24 dpf, Ucrit estimates derived from the two assay types were significantly different. This indicates that the assays are not equivalent to one another and that the spinning task assay is not a suitable alternative to the laminar flow assay for the determination of Ucrit.

Experimental and numerical study of a latent heat storage using sodium acetate trihydrate for short and long term applications

A flexible thermal energy storage with 137.8 kg PCM and 75 L water was introduced. The heat storage combined short-term and long-term heat storage functions by utilizing sodium acetate trihydrate as heat storage material. The thermal performance and flow characteristics of the heat storage were investigated by experiments and by CFD simulations. The result show that after a full charge to 92 °C, the heat storage can flexibly release heat in two steps: In the first step, 13.7 kWh sensible heat can be released for short-term use; in the second step, 7.8 kWh latent heat can be released for long-term use. When releasing heat, there is laminar flow of water and a high degree of thermal stratification in the tank. During discharge of the sensible heat, the heat storage can provide 294 L hot water with an average temperature of 68.2 °C. During discharge of the latent heat, 334 L hot water with an average temperature of 46.7 °C were drawn from the heat storage. In the charging process, a fluid short circuit existed inside the water region. Part of hot water flows out of the tank before sufficiently heated. There was no obvious thermocline inside the tank during charging. The flow rate has a big influence on the thermal characteristics of the heat storage during the charge and discharge periods. By increasing the flow rate from 4 L/min to 14 L/min, the charging time was shortened by 67% from 276 min to 92 min while the discharging time was shortened by 65% and 83% respectively in releasing sensible heat and latent heat.

Effect of Laser Shock Peening Parameters on Residual Stresses and Corrosion Fatigue of AA5083

Aluminium alloy 5083 was subjected to Laser Shock Peening both with (LSP) and without protective coating (LPwC) at multiple pulse densities. A second LPwC treatment was conducted fully submersed under water, in addition to the standard laminar water flow condition. The results show that compressive residual stresses were generated in all cases, although their character varied depending on the peening strategy and method of confinement. In all cases, higher pulse density lead to an increase in compressive stresses with a saturation point of −325 MPa at 1089 p/cm2 for the LPwC treatments. Corrosion fatigue testing of sensitized samples then showed 59% and 69% improvement in fatigue strength after the LSP and LPwC treatments, respectively.