Isotherm Contours Research Articles

Systematic Characterization of High-Power Short-Duration Ablation: Insight From an Advanced Virtual Model

Background: High-power short-duration (HPSD) recently emerged as a new approach to radiofrequency (RF) catheter ablation. However, basic and clinical data supporting its effectiveness and safety is still scarce.Objective: We aim to characterize HPSD with an advanced virtual model, able to assess lesion dimensions and complications in multiple conditions and compare it to standard protocols.Methods: We evaluate, on both atrium and ventricle, three HPSD protocols (70 W/8 s, 80 W/6 s, and 90 W/4 s) through a realistic 3D computational model of power-controlled RF ablation, varying catheter tip design (spherical/cylindrical), contact force (CF), blood flow, and saline irrigation. Lesions are defined by the 50°C isotherm contour. Ablations are deemed safe or complicated by pop (tissue temperature >97°C) or charring (blood temperature >80°C). We compared HPSD with standards protocols (30–40 W/30 s). We analyzed the effect of a second HPSD application.Results: We simulated 432 applications. Most (79%) associated a complication, especially in the atrium. The three HPSD protocols performed similarly in the atrium, while 90 W/4 s appeared the safest in the ventricle. Low irrigation rate led frequently to charring (72%). High-power short-duration lesions were 40–60% shallower and smaller in volume compared to standards, although featuring similar width. A second HPSD application increased lesions to a size comparable to standards.Conclusion: High-power short-duration lesions are smaller in volume and more superficial than standards but comparable in width, which can be advantageous in the atrium. A second application can produce lesions similar to standards in a shorter time. Despite its narrow safety margin, HPSD seems a valuable new clinical approach.

Comparison of thermal performances between copper and stainless steels on application of graphene coatings

Computational Fluid Dynamics (CFD) and heat transfer simulations are conducted for a cross flow heat exchanger. The heat exchanger consists of a linear pipe carrying a heated fluid. The thermal interactions between the heated fluid having a laminar flow and the walls of the pipe have been studied under the influence of an external environment of water having a turbulent flow, in a direction normal to the pipe. A RANS model with a k-ε variant was used to model the behavior of different material pipes which were observed under the varying conditions of turbulence, velocity, pressure and vorticity. When subjected to the same conditions, plots of the temperature gradient, isothermal contours, heat transfer coefficient against Reynolds number and thermal conductivity modelled against the various graphene coating thicknesses studied have shown that out of Copper and Stainless Steel the former has shown the most significant increase in thermal conductivity on the addition of a Graphene coating. Furthermore, to check for optimum efficiency, the same study was conducted with an internal coating of a Graphene layer for the aforementioned materials. It has been observed that an outer coating was not only more economically feasible, but also showed better thermal performance compared to an inner coating of graphene for copper, however it did improve the thermal performance of Stainless Steel significantly.

MHD natural convection in nanofluid filled square cavity with isothermally heated hexagonal block

This article explores the influence of natural convection heat transfer in a square enclosure with hexagonal block filled by Al2O3-H2O nanofluid in presence of external magnetic field. The two vertical walls of the enclosure are kept at constant cold temperature, Tc, and the top horizontal wall is insulated whereas the remaining walls of the enclosure are maintained high temperature, Th. The governing equations are formulated using Boussinesq approximations and solved numerically employing built-in-finite element method and then presented graphically in terms of streamlines, isotherms, average Nusselt number and average temperature. It is found that the different values of physical parameters: Rayleigh number (Ra = 103 -106), nanoparticle volume fraction (ϕ = 1% -5%) and Hartman number (Ha = 0-100) affects the streamlines, isotherm contours and heat transfer rate. Comparison of the present results with previously published results on the basis of special cases has been performed and found to be a good agreement.

Investigations on the effect of graphene coating on thermophysical properties of aluminium and mild steel for cross flow heat exchanger

In a cross-flow heat exchanger, heat transfer and fluid dynamics studies were conducted to observe the performance of graphene coated pipes. The heat exchanger consists of a linear pipe made of Aluminum 6061-T6 and Mild Steel in separate studies carrying a heated fluid. The thermal interactions between the heated fluid having a laminar flow and the walls of the pipe have been studied under the influence of an external environment of water having a turbulent flow, in a direction normal to the pipe. A RANS model with a k-ε variant was used to model the behavior of different material pipes which were observed under the varying conditions of turbulence, velocity, pressure, and vorticity. When subjected to the same conditions, plots of the temperature gradient, isothermal contours, heat transfer coefficient against Reynolds number and thermal conductivity modelled against the various graphene coating thicknesses studied have shown that out of Aluminum 6061-T6 and Mild Steel, the former has shown a significant increase in thermal conductivity on the addition of a Graphene coating. Simulation results showed an increase in Aluminium 6061 T6′s conductivity by 6.8975% with a continuous decrease in the heat transfer coefficient, whereas Mild Steel showed an anomaly in the heat transfer coefficient value which peaked at 1.2 mm thickness of graphene coating with a value of 3858.862 W/m2K.

Thermofluidic transport phenomena of hybrid nanofluid in a porous wavy enclosure imposing magnetic fields

The present work outlines an analysis of thermo-fluidic transport phenomena in an undulated walled porous enclosure filled with hybrid nanofluid imposing magnetic field under the free-convective mode of heat exchange. The complex wavy enclosure is heated isothermally from the bottom, whereas the wavy sidewalls are cold. The enclosure is packed with porous material and Cu/Al2O3 water-based hybrid nanoliquid. The externally generated magnetic field acts partially perpendicular to the left sidewall. The governing equations are solved numerically utilizing FORTRAN-based code adopting the finite volume method. The porous structure is modeled using the Brinkman-Forchheimer-Darcy model. The key parameters are judged for the study as modified-Rayleigh number Ram (reflects the convective strength), Darcy number Da (reflects the permeability of the porous structure), Hartmann number Ha (reflects the magnetic field intensity), the volume fraction of hybrid nanoparticles, etc. The results are presented systematically using streamlines, and isotherms contours. The assessment of heat transport is illustrated using the average Nusselt number (Nu) under a wide range of control parameters. It is found that the thermo-fluid flow alters significantly depending on the control parameters. The presence of flow dampening magnetic field and porous structure causes decrement of heat transfer, which is compensated (increment ∼ 9.4%) using the hybrid nanoliquid. The outcome of this analysis can be very useful for designing any device/ system involving thermal energy transportation in diverse fields of applications.

Comsolic solution of an elliptic cylindrical compressible fluid flow

In this article, the primary focus is to investigate the heat transfer effects with viscous compressible laminar flow in the permeable elliptic cylinder. The Reynolds number is kept 100 for flow to be laminar. The physics of heat transfer is selected to be coupled with the laminar flow. The results for particular step-size time for Velocity distribution, pressure profile, temperature profile, isothermal temperature contours, and drag coefficient have been analyzed. Mesh has been generated through COMSOL, mesh entities have been elaborated statistically. The maximum and minimum velocity profile is observed at the elliptical cylinder’s walls and upper, lower boundary respectively. The maximum velocity observed is 2.22 m/s. Pressure profile around elliptic corners is found maximum, distinct patterns are observed even under the influence of applied heat. Temperature is observed maximum at walls but it gradually increases as moving from the upper boundary towards the lower boundary. The isothermal contour patterns are observed maximum near the walls, drag coefficient of gradual decrease is observed. COMSOL multi-physics is utilized for mathematical modeling of problems and the Backward-Differentiation-Formula has been exploited to handle problems numerically. The results will help greatly to understand the characterizations of viscous fluids and in industries like air furnaces and automobile cooling systems.

Free Convection of Ag/H2O Nanofluid in Square Cavity with Different Position and Orientation of Egg Shaped Cylinder

A numerical simulation was conducted to study the free convection of Ag/H2O nanofluid between a square cavity with cold walls and an egg shaped cylinder with a hot wall. Utilizing the egg equation, dimensionless governing equations were solved using the Galerkin Finite Element Method (GFEM). In this work, several parameters were studied, i.e. Rayleigh number (103 ≤ Ra ≤ 106), volume fraction (0 ≤ φ ≤ 0.05), position (-0.2 ≤ Y ≤ 0.2), and orientation angle (-90° ≤ γ ≤ 90°). The numerical results are presented as streamline contours, isotherm contours, and local and average Nusselt numbers. Moreover, the results were used to analyze the fluids’ structure, temperature distribution, and heat transfer rate. The numerical results confirmed that the stream intensity value increased with an increase of the Rayleigh number as well as the movement of the cylinder towards the bottom wall for all values of the orientation angle. Variation of the vertical position of the cylinder inside the cavity had a noticeable effect on , which increased by 50% at γ = -90°, and by 58% at γ = -45°. However, at Y = -0.2, increased by 58% at γ = -45° and decreased by 7% at γ = -90°. The highest heat transfer rate was obtained at high Rayleigh number (Ra = 106), volume fraction (φ = 0.05), negative position (Y = -0.2), and the highest positive orientation angle (γ = 90°).

Numerical investigation of transient mixed convection of nanofluid in a cavity with non-Darcy porous inner block and rotating cylinders with harmonic motion

Mixed convection of nanofluid in a 2D square enclosure with a porous block in its center and four rotating cylinders, which are forced by a simple harmonic function, was studied numerically. The porous zone was studied by considering the Forchheimer–Brinkman-extended Darcy model. Effects of various parameters including Darcy number (10–5 ≤ Da ≤ 10–2), porosity (0.2 ≤ ɛ ≤ 0.7), Richardson number (0.1 ≤ Ri ≤ 10), and volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.03), on heat transfer, entropy generation, PEC, velocity, streamline and isotherm contours were demonstrated. The results show that decreasing the Darcy number as well as reducing the Richardson number leads to an increase in the average Nusselt number. However, porosity changes had no decisive effect on heat transfer. Maximize the volume fraction of copper nanoparticles in the base fluid enhanced heat transfer. In the case of the high permeability of the porous medium, the impact of the harmonic rotation of the cylinders on the flow patterns became more pronounced.

Effect of Linearly Varying Heating Inside a Square Cavity under Natural Convection

Telecommunication devices such as ADSL Modems or Wi-Fi routers are being widely used around the globe. Thermal management of such equipments are of critical importance as the increased power consumptions caused by technological upgrades results in increased heat generation within these systems. The heat transfer process inside such sealed and passively cooled equipments can be simplified as natural convection inside enclosures. Studying actual conditions inside electronic enclosure are necessary for their effective thermal management. This study aims at investigating the effect of non-isothermal heating inside such enclosures with linearly varying temperature distribution on free convection inside square enclosure. The issue of free convection of air interior of a square chamber with linearly varying temperature distributions on the left partition is studied numerically. The effect of change of Rayleigh number, temperature distributions, on flow and temperature field and rate of transfer of heat are analysed. Rayleigh number is chosen to vary in between 103 and 106. Four different cases of linearly varying temperature distributions are considered. The outcomes are presented as stream line plot, isotherm contour and average Nusselt number. The outcomes depicted that case of linearly increasing temperature along the height gives higher Nusselt number than other cases.

Comparative analysis of thermoelectric behavior of molybdenum silicide (MoSi2) and bismuth telluride (Bi2Te3)

A comparative analysis of the thermoelectric behavior of Molybdenum Silicide and Bismuth Telluride using the COMSOL-Multiphysics platform is presented. Parameters like temperature distribution, potential distribution, figure of merit all the way through the length of the model and isothermal contours for these materials are reported. The outcomes of the modeling and simulation have revealed the potential use of Bismuth Telluride in thermoelectric applications at low temperature applications whereas Molybdenum Silicide is utilized as thermoelectric materials at high temperatures applications.

Heat transportation enrichment and elliptic cylindrical solution of time-dependent flow

The main focus of this article is to examine the effects of heat transfer for a compressible time-dependent laminar flow pass the two distinctly positioned elliptic cylinders. The Mac number is chosen below 0.3 to keep the flow laminar. The heat transfer feature has been added and coupled with the laminar flow. The heat transfer feature adjusted for constant pressure. The arising Naiver-Stokes equations have been addressed numerically. The mesh has also been created and its entities have been elaborated statistically. The outcomes of velocity distribution, pressure distribution, 2D temperature plots, isothermal contours, drag coefficient, streamlines, and surface volume of fluid are discussed. The BDF technique has been employed to tackle the problem numerically. It was observed that the velocity profile at the boundaries of the elliptic cylinder has a maximum value, 3.85 m/s. The pressure distribution is observed maximum around elliptic cylinders. The heat transfer coefficient has maximum values at the upper and lower boundaries, the maximum temperature value observed is 290K. The isothermal contours, streamlines, and velocity volume were also studied. The drag coefficient is observed increasing but the drag force is decreasing. The mathematical modeling of the current problem has been designed in COMSOL.

An Efficient Numerical Simulation of 2D Natural Convection in an Inclined Cavity with Internal Heat Generation Using Differential Quadrature Method

Natural laminar convective fluid flow has been simulated inside inclined rectangular cavities with and without internal heat generation for different aspect ratios and inclination angles. The most important basic dimensionless parameters for this problem are the external Rayleigh number (RaE) and the internal Rayleigh number (RaI), where RaE refers to the effects of the differential heating of the side walls and RaI refers to the amount of heat produced internally. Results were obtained for 4 cases with 192 tests: case (1), RaI = 0 without internal source generation, and cases (2, 3, and 4) with internal source generation for RaI = RaE, 10 RaE, and 100 RaE, respectively. In all cases, the parameters of study changed as 103 ≤ RaE ≤106, 0 ≤ RaI ≤ 107, inclination angle from 0 to 60 deg., and aspect ratios of the enclosure from 0.5 to 2. Results were represented graphically for flow and thermal fields as a streamline, isothermal contours, and Nusselt number. The computed results show that the strength of convection currents is measured by the internal energy. Finally, it is illustrated that by using a few grid points and a shorter CPU time for calculation, the present method can produce accurate numerical results. Also, increase in RaI leads to increasing heat transfer rate and its direction out from the cavity at both hot and cold walls. For lower values of RaI, heat transfer diffusion is more prominent, while for higher values of RaI, convection outweighs diffusion.
 HIGHLIGHTS
 
 Natural laminar convective fluid flow inside inclined rectangular cavities with and without internal heat generation for different aspect ratios and inclination angles has been simulated
 The most important basic dimensionless parameters, the external Rayleigh number (RaE) and the internal Rayleigh number (RaI) are studied
 DQ method performance was excellent
 The obtained computational results indicate that the strength of the convection currents depends on the internal energy
 Accurate numerical results can be obtained by the present method using a few grid points and shorter CPU time for calculation
 
 GRAPHICAL ABSTRACT

Augmentation of Pure Mixed Convection Heat Transfer in a Non-Newtonian Power-Law Fluid Filled Lid-Driven Trapezoidal Cavity With Double Rotating Cylinders

Abstract In this study, a numerical investigation on mixed convection inside a trapezoidal cavity with a pair of rotating cylinders has been conducted. Three different power-law fluid indexes (n = 1.4, 1.0, and 0.6) have been considered to model different sets of non-Newtonian fluids. Four separate cases are considered based on the rotational orientation of the cylinders within the cavity. In the first two cases, the cylinders rotate in the same direction, i.e., both counterclockwise (CCW), and both clockwise (CW), whereas, in the other two cases, cylinders rotate in opposite directions (CW–CCW and CCW–CW). Simulations have been carried out over a broad range of Reynolds number (from 0.5 to 500) and angular speeds (a dimensionless value from 0 to 10). The average Nusselt number values at the isothermal hot inclined cavity surface are determined to evaluate heat transfer performance in various circumstances. Streamlines and isotherm contours are also plotted for a better understanding of the effects of different cases for various parameters on thermal and fluid flow fields. It is found that the Nusselt number varies nonlinearly with different angular speeds of the cylinders. The combined effect of the mixing induced by cylinder rotation and viscosity characteristics of the fluid dictates the heat transfer in the system. Predictions from the numerical investigation provide insights into the sets of key parametric configurations that have a dominant influence on the thermal performance of the lid-driven cavity with double rotating cylinders.

Unsteady MHD natural convection flow of a nanofluid inside an inclined square cavity containing a heated circular obstacle

Abstract The phenomena of unsteady magnetohydrodynamics (MHD) natural convection flow in an inclined square cavity filled with nanofluid and containing a heated circular obstacle at its center with heat generation/absorption impact are examined numerically. The cavity’s right and left walls are maintained at low temperatures, while the remaining walls are adiabatic. The volumetric external force, MHD, is applied across the inclined cavity. A penalty formulation-based finite element method is used to solve the nonlinear set of governing equations iteratively. The numerical scheme and results are validated through a comparison with the benchmark results, and it shows that our solutions are in good agreement with them. The results are shown in terms of contours of streamlines, isotherms, and average Nusselt number. It is observed that MHD alters the streamlines, isotherms, and average Nusselt number and dominates the flow as compared to any other physical parameter. The average Nusselt number is found sensitive to the central obstacle’s size, and it reduces sufficiently when the radius of the inner cylinder increases. For all the parameters, the streamlines’ symmetric pattern holds, such that the anti-clockwise cells on the left side of the cavity have their symmetric clockwise cells on the right side.

Applying Humboldt's holistic perspective in China's sustainability

Alexander von Humboldt, was a great German geobotanist, educator and naturalist who greatly influenced science and humanities for more than two hundred years. In addition to scientific contributions (such as the understanding of vegetation distribution, the concepts of isotherm and pressure contours, and the initial concept of continental drift theory), he firmly believed in the concept of the interconnection of everything and the methodological approach of a holistic perspective to development, which has significance in achieving the UN Sustainable Development Goals, because they include both synergy and trade-offs among these goals. China has undergone tremendous changes since its reform and opening up in 1978 and now faces severe challenges in sustainable development. The scientific methods applied by Chinese scientists in sustainability fulfil the Humboldtian holistic perspective of nature. Here I provide four successful cases and their significant implications for addressing the increasingly severe water shortage, biological conservation, and conflicts between human well-being and land. The four examples discussed in this article are enlightened to establish a strong, just, and influential government and require empirical research to implement sustainable development plans. I believe that it's vital to encourage and supervise public participation for a successful program; for example, the participants should not be restricted to project executors, i.e., farmers or workers, but also students and scientists. Eradicating poverty must be prioritized, and well-being is the ultimate goal for sustainable development. This review article provides an extremely valuable reference for other developing or even developed countries to address sustainability challenges.

Heatline visualization of MHD natural convection heat transfer of nanofluid in a prismatic enclosure

Temperature transfer by virtue of natural convection for visualizing heat transport characteristics through heatline method within a prismatic cavity filled with Cu-H2O nanofluid considering two different temperature boundary conditions is performed numerically. Two top inclined walls are warmed-up at low temperature whilst the bottom wall is heated two different heated conditions such as uniform temperature condition and linear temperature condition. Two vertical walls are insulated. Finite element technique of Galerkin weighted residual form is employed for solving nonlinear partial differential equations for numerical calculation. Heatlines, isotherm contours, streamline contours, and Nusselt number are employed for displaying numerical simulated results for the model parameters entitled nanoparticles volume fraction, Hartmann number and Rayleigh number. The outcomes indicate that heat transfer rate has a significant impact on thermal boundary condition and shape of the nanoparticles. The temperature transfer value enhances significantly for higher Rayleigh number as well as nanoparticles volume fraction. Hartmann number has a positive impact on fluid flow and temperature transport. The characteristics of heat transport using heatlines method are also performed for predicting the better energy transform compared to isotherm contours. In addition, different types of nanofluids are also employed to examine the best heat transport performance.

Impact of uniform and non-uniform heated rods on free convective flow inside a porous enclosure: finite element analysis

A numerical study of laminar natural convective flow in a porous rectangular cavity having two heated rods is performed in this article. Both heated rods are placed in the middle of the cavity. Further, it is assumed that the flow and isothermal contours are influenced by permeable medium. Physical laws transform this physical setup into the mathematical form, which is expressed as partial differential equation. Finite element method is adopted to get the solution of these partial differential equations, the results against various flow controlling variables are presented in contour plots and line graphs. Results illustrate that in the case of non-uniform heating, the heat transfer rate is suppressed with the enhancement Rayleigh parameter as compared to uniform heating. In addition, with the increase in heated length of rods, flow field gets stronger due to stronger buoyancy effects. Moreover, the velocity distribution and Nusselt number are enhanced with the rise of permeability of porous medium.

Effect of polymer additives and viscous dissipation on natural convection in a square cavity with differentially heated side walls

This study presents an extensive numerical investigation on how the addition of polymer molecules into a Newtonian solvent would tend to influence the natural convection heat transfer phenomena in a differentially heated square cavity. The rheological behaviour of the resulting polymer solution is modelled based on the FENE-P viscoelastic constitutive equation, which along with other governing equations, namely, mass, momentum, and energy equations, have been solved using the open source CFD code OpenFOAM over the following ranges of conditions: Rayleigh number, 103≤Ra≤106; Weissenberg number, 1≤Wi≤100; polymer extensibility parameter, 10≤L2≤500, polymer viscosity ratio, 0.5≤β≤0.9 and for a fixed value of the Prandtl number of Pr=7. At low values of the Rayleigh number, the average Nusselt number gradually increases with the Weissenberg number. However, at high values of it, the average Nusselt number first increases steeply up to a critical value of the Weissenberg number, and beyond that, it remains almost constant as the Weissenberg number further increases. The average Nusselt number is seen to decrease with the increasing values of both the polymer extensibility paramter and polymer viscosity ratio. The viscous dissipation tends to deteriorate the heat transfer rate in comparison to that seen in the absence of it; however, the extent of this deterioration is found to be independent on the values of Wi,L2 and β. Furthermore, a detailed discussion of the results in terms of the streamline profiles, isotherm contours, distribution of local Nusselt number, variation of velocity components, etc., is also presented. Finally, from an application standpoint, a simple correlation for the average Nusselt number is presented, which can be used for the interpolation of the present results for the intermediate values of the governing parameters in a new application.

Parametric study of natural convection heat transfer from an inclined rectangular cylinder embedded in a square enclosure

ABSTRACT This paper presents the effects of aspect ratio , Rayleigh number () and inclination angle of the heated rectangular cylinder on heat transfer and fluid flow characteristics due to natural convection in air around heated rectangular cylinders of different sizes inside a cold square enclosure. Galerkin finite element method was adopted for the solution of the developed model. The walls of the enclosure were maintained at an isothermal cold temperature while the boundaries of the rectangular cylinder were kept at a constant hot temperature. The results are presented in the form of isothermal contours, stream functions, local and average Nusselt numbers. It has been found that for the range of aspect ratio and Rayleigh number considered, the rate of heat transfer increases with increasing aspect ratio and Rayleigh number. Furthermore, the orientation angle of the rectangular cylinder was found to generally augment heat transfer rate except at value of , where the average Nusselt number declines beyond for all the range of Rayleigh numbers considered. Results from the present study could be applied to nuclear reactor technology and cooling of electronic chips system optimisation.

Optimum Placement of Heating Tubes in a Multi-Tube Latent Heat Thermal Energy Storage

Utilizing phase change materials in thermal energy storage systems is commonly considered as an alternative solution for the effective use of energy. This study presents numerical simulations of the charging process for a multitube latent heat thermal energy storage system. A thermal energy storage model, consisting of five tubes of heat transfer fluids, was investigated using Rubitherm phase change material (RT35) as the. The locations of the tubes were optimized by applying the Taguchi method. The thermal behavior of the unit was evaluated by considering the liquid fraction graphs, streamlines, and isotherm contours. The numerical model was first verified compared with existed experimental data from the literature. The outcomes revealed that based on the Taguchi method, the first row of the heat transfer fluid tubes should be located at the lowest possible area while the other tubes should be spread consistently in the enclosure. The charging rate changed by 76% when varying the locations of the tubes in the enclosure to the optimum point. The development of streamlines and free-convection flow circulation was found to impact the system design significantly. The Taguchi method could efficiently assign the optimum design of the system with few simulations. Accordingly, this approach gives the impression of the future design of energy storage systems.