Heat Transfer最新文献

This study investigates the various uses of density of motile microorganisms in the context of the flow of a binary base fluid with double diffusion past a vertical surface. The research aims to comprehend the interactions between motile microorganisms and the fluid dynamics, as well as the heat and mass transport mechanisms in this system. The analysis involves mathematically constructing the governing equations, transforming them into dimensionless nonlinear ordinary differential equations using similarity transformations, and numerically solving them using the MATLAB bvp4c solver. An analysis of the influence of several parameters on the profiles of velocity, temperature, concentration, nanoparticle concentration, and density of motile microorganisms is conducted using graphical representation. The findings demonstrate that boosting the thermophoresis parameter intensifies the temperature profile. In addition, an increase in the nanofluid Schmidt number results in a larger concentration of nanoparticles, whereas a higher bioconvection Lewis number reduces the density of the motile microorganism profile. These findings may find use in biomedical engineering as well as industrial processes that include enhancing the efficiency of mass transfer and bioconvection. Numeric simulation prophesies 99.9% for both shear stress and heat transfer rate intensification for Prandtl values are noticed.

Pressure-driven movement is a fundamental concept with numerous applications in various industries, scientific disciplines, and fields of engineering. Its proper execution is vital for promoting revolutionary innovations and providing solutions in numerous sectors. Therefore, this article scrutinizes the pressure-driven flow of magnetized Casson fluid between two curved corrugated walls. The geometry of the channel is represented mathematically in an orthogonal curvilinear coordinate system. The corrugation grooves are described by sinusoidal functions with phase differences between the corrugated curved walls. The boundary perturbation method is used to find the analytical solution for the velocity field and volumetric flow rate, taking the corrugation amplitude as the perturbation parameter. The results show that the peak of the velocity increases with the radius of curvature and the width of the channel for a constant pressure gradient. The velocity exhibited a declining trend due to an increase in the Casson fluid parameter. For a sufficiently large corrugation wavenumber, the flow rate decreases, and the phase difference becomes irrelevant. However, the reduction in flow can be minimized by decreasing the channel radius of curvature. In general, a smooth curved channel will give the maximum flow rate for a large corrugation wavenumber. The model can be used to simulate blood flow in arteries with varying geometries and magnetic fields, aiding in the study of cardiovascular diseases and the design of medical devices like stents.

The current study presents a computational investigation of mixed convective heat transfer in a square enclosure containing power-law fluid. An active flow modulator is employed in the form of a flat plate with negligible thickness, and the mixed convection is achieved through clockwise rotation of the plate. The rotation of the plate is modeled by incorporating a moving mesh technique. The solution is then obtained by applying the Finite Element Technique under the arbitrary Lagrangian–Eulerian framework. Numerical validation is performed with contemporary research studies consisting of rotating plates to justify the accuracy of the present study. The study is conducted at constant Prandtl number Pr = 1.0 and Reynolds number Re = 500 while varying the power-law index (0.6 ≤ n ≤ 1.4) and the Richardson number (0.1 ≤ Ri ≤ 10.0). The results have been presented in terms of the flow and thermal fields, spatially averaged Nusselt number, spatially averaged power consumption by the plate, and the velocity and temperature profile in the enclosure. The numerical findings indicate that a higher Richardson number encourages heat transfer. For the shear-thinning fluid, a 37% thermal augmentation is observed in comparison to the Newtonian fluid at Ri = 10. However, in the case of shear-thickening fluid, thermal performance was reduced by 21.13%. Small thermal oscillations are observed in naturally dominated mixed convection for shear-thinning fluids, but none are observed for shear-thickening or Newtonian fluids. In addition, the findings demonstrate that the flow modulator has a positive impact on heat transfer for the shear-thickening fluids (n > 1) and an adverse effect for the shear-thinning fluids (n < 1). Furthermore, the power consumption decreases as Ri increases, and it becomes negative beyond Ri = 1.0 due to the increase in natural convection strength.

Heat exchangers are crucial in transferring heat and finding applications across various industries. Numerous strategies have been devised to improve and optimize the heat transfer process within these systems. Among these, passive methods have garnered significant attention for their ability to operate without external power consumption. This article examines the recent experimental and computational studies conducted by researchers since 2018 on passive enhancement techniques, especially twisted tape, wire coil, swirl flow generator, and others, to boost the thermal efficiency of heat exchangers and aid designers in adopting passive augmentation methods for compact heat exchangers. Recently, researchers' new class of flow maldistribution devices, referred to as swirl flow devices, has gained attention; which enhances convective heat transfer by introducing swirl into the main flow and disrupting the boundary layer at the tube surface through alterations in surface geometry. Twisted tape inserts are devices that demonstrate better performance in laminar flow compared to turbulent flow. Conversely, other passive techniques like ribs, conical nozzles, and conical rings are generally more effective in turbulent flow than laminar flow. A recent research trend is the utilization of nanofluids in combination with other passive heat transfer enhancement techniques like turbulators, ribs, and twisted tape inserts in heat exchangers, which can reduce exergy losses and improve overall convective heat transfer coefficient and effectiveness of heat exchanger.

This work provides an analytical and numerical assessment, complete with correlations, of mixed convection in a double lid-driven shallow rectangular enclosure, which confines non-Newtonian fluids of the Ostwald–de Waele type and which a uniform thermal flux heats. The finite volume method with the SIMPLER algorithm is the numerical method used to solve the governing partial differential equations along with the boundary conditions, where the parallel flow concept is the analytical approach. In the limits of the explored values of the governing parameters of this study, which are the Rayleigh number, the Peclet number, and the behavior index, the results obtained by these approaches appear to be in good harmony. On the basis of the results obtained by these approaches, we established helpful correlating relations between the governing parameters to realize the contribution of mixed convection to heat transfer. This leads to the finding that the ratio Ra/Pe²⁺ⁿ is the mixed convection parameter, which is the key to distinguishing the three convective flow modes. On the basis of this parameter, which allows the transition from one regime to another, it is possible to identify the zones that designate the predominance of natural, forced, and mixed convection. The limits of these latter depend on the behavior index, n, which is diversified from 0.6 to 1.4 to account for shear thinning (0 < n < 1, low apparent viscosity, high fluid flow, and high heat transfer rate), Newtonian (n = 1), and shear thickening (n > 1, high apparent viscosity, slow fluid flow, and low heat transfer rate) fluids. On the other hand, the study presents and interprets the influences of the steering factors on heat transfer and fluid flow.

The heat transfer in power-law fluids across three corrugated circular cylinders placed in a triangular pitch arrangement is studied computationally in a confined channel. Continuity, momentum, and energy balance equations were solved using ANSYS FLUENT (Version 18.0). The flow is assumed to be steady, incompressible, two-dimensional, and laminar. A square domain of side 300D_h is selected after a detailed domain study. An optimized grid with 98,187 cells is used in the study. The convergence criteria of 10⁻⁷ for the continuity, x-momentum, and y-momentum balances and 10⁻¹² for the energy equation were used. Constant density and non-Newtonian power-law viscosity modules were used. The diffusive term is discretized using a central difference scheme. Convective terms are discretized using the Second-Order Upwind scheme. Pressure–velocity coupling between continuity and momentum equations was implemented using the semi-implicit method for pressure-linked equation scheme. Streamlines show wake development behind the cylinders, which is very dominant at large Re_N and n. Isotherm contours are cramped at higher values of Re_N and Pr_N, implying higher heat transfer. Global parameters, like, C_d and Nu, are computed for the wide ranges of controlling dimensionless parameters, such as power-law index (0.3 ≤ n ≤ 1.5), Reynolds (0.1 ≤ Re_N ≤ 40), and Prandtl (0.72 ≤ Pr_N ≤ 500) numbers. The Nu_Local plot attains a pitch near the corrugation of the surface due to abrupt changes in velocity and temperature gradients. Nu increases with Re_N and/or Pr_N and decreases with n under ot herwise identical situations. Nu is correlated with pertinent parameters, namely, Re_N, Pr_N, and n.

Previous works that investigated the characteristics of heat transfer and fluid flow in channels with corrugated walls have been extensively reviewed in this study. In accordance with the fast increase in power consumption requirements, many researchers have investigated a new approach for cooling techniques that can enhance the cooling performance of devices without consuming more power. To improve the efficiency of energy systems, many investigators and engineers implement promising techniques such as surface optimization and additives as passive methods to augment the rates of heat transfer. Researchers investigated different corrugation profiles along with various working fluids as well as external power devices to further improve the heat exchange process of thermal systems. The aim of this article is to give a clear preview of the effects of different parameters such as wave parameters, Reynolds number, type of working fluid, and pulsating flow condition on the average and local Nusselt number, the pressure drop, the performance factors, and irreversibility. The main findings are listed in tables and depicted in figures, the matter that helps engineers and researchers to choose a suitable channel shape for their applications.

Photothermal radiometry has recently been investigated for use in the multidimensional thermal characterization of anisotropic samples. In application, there are two principal thermal models available for such characterization: a Cartesian model for the heat equation, which requires the application of three Fourier transforms to arrive at a solution (dubbed the Fourier technique), and a cylindrical model for the heat equation, which requires the application of a Hankel transform and a single Fourier transform (dubbed the Hankel technique). The Fourier technique allows for three-dimensional characterization, while the Hankel technique is expected to greatly reduce the computational time required. As these models can be very computationally expensive, the potential to reduce this cost is of great interest. In this work, these multidimensional models are presented after which they are compared for accuracy, computational time, and assumption limitations. It was found that both the Fourier and Hankel techniques could accurately arrive at desired thermal properties, but that the Hankel Technique reduced the computational time by between 100× and 250× depending upon mesh spacings. Accuracy limitations were found as the eccentricity of the heating laser was increased with a less than 13% error being induced from a beam with a 3–1 axis ratio. The Hankel technique shows ideal application in computationally expensive models which employ a relatively circular beam shape.

Flow-control techniques have attracted significant attention in many scientific areas due to their ability to improve the effectiveness and regulate the flow of aerodynamic devices. This study explores the latest developments in flow-control techniques, specifically concentrating on the cutting-edge technologies of plasma vortex generators (PVGs) and actuators. By taking advantage of the ionization of gases or air, plasma actuators have become a viable method for modifying an object's aerodynamic properties without needing physical moving parts. These actuators create localized plasma discharges that interact with the surrounding flow to provide accurate separation control, boundary-layer dynamics, and aerodynamic forces on aircraft wings, wind turbine blades, and other surfaces. PVG, which produce controlled vortical structures, offer a novel way to manipulate airflow with plasma actuators. These generators create swirling motions through plasma discharges that can be used in various technical applications, such as automotive, marine, and aviation, to modify boundary layers, reduce drag, and improve lift characteristics. This study offers an overview of recent work, focusing on the theoretical underpinnings, experimental validations, and practical applications of plasma-based flow-control technologies. Advances in plasma-generating techniques, computational modeling approaches, and experimental configurations to optimize and comprehend the intricate fluid–structure interactions are covered in the debate. Moreover, the study delves into incorporating plasma-based flow management into cars, renewable energy systems, and next-generation aerospace designs, highlighting the possibility of increased agility, decreased emissions, and efficiency. It also discusses the difficulties and potential paths for developing these technologies further for use in business and industry, highlighting the necessity of dependable, scalable, and durable solutions. Finally, this study summarizes the most recent advancements in vortex generators and plasma actuators for flow control. It demonstrates how they have the power to revolutionize fluid dynamics and aerodynamics in a variety of engineering fields.