Showing papers on "Convection published in 2021"

Hall and ion slip impacts on unsteady MHD convective rotating flow of heat generating/absorbing second grade fluid

Abstract: We have explored theoretically the Hall and ion slip impacts on an unsteady laminar MHD convective rotating flow of heat generating or absorbing second grade fluid over a semi-infinite vertical moving permeable surface. The non-dimensional equations for the governing flow are solved to the most excellent possible investigative solution using perturbation methodology. The effects of parameters on velocity, temperature and concentration are demonstrated graphically and described in detail. For engineering curiosity, the shear stresses, Nusselt number and Sherwood number are obtained analytically, represented computationally in a tabular format as well as explained with respect to foremost parameters. It is concluded that, the resultant velocity is increased with an increasing in Hall and ion slip parameters throughout fluid region. The thermal and solutal buoyancy forces contribute to the resultant velocity ever-increasing to high. The temperature distribution is trim downs through an increasing in heat source parameter. The concentration is reduced with an increase in the chemical reaction parameter in the entire fluid region. Rotation parameter is to diminish the skin friction, whereas it is augmented through an increase of the Hall and ion slip effects. The rate of mass transfer is increased with increasing chemical reaction parameter.

Numerical investigation on thermal behaviour of 5 × 5 cell configured battery pack using phase change material and fin structure layout

Abstract: Lithium-ion battery, the indispensable part of electric vehicles or hybrid electric vehicles because of their high energy capacity and power density but usually suffer from a high temperature rise due to heat generation within a battery. This heat generation is mainly a function of the state of charge and charge/discharge rate. A passive technique like phase change material cooling has receiving a wide recognition due to its high latent heat, compact nature, and lightweight without consuming any external power. In this article, the thermal performance of the battery module containing 5 × 5 lithium-ion battery arranged in series and parallel is evaluated using phase change material. Initially, the performance of a battery module is examined with and without PCM at different discharge rate. It was found that more heat is accumulated at the interior portion of the battery pack due to mutual heating and low heat dissipation ability of PCM at a higher discharge rate. To improve such interior heat dissipation, different fin structure layout like Type I, Type II, Type III and Type IV are proposed and analysed using maximum temperature and average temperature distribution in a PCM based battery pack. It reveals that fin structure layout of Type III minimizes heat accumulation at the interior with adequate melting time among all. Furthermore, charge and discharge characteristics are investigated at different rate using rest time, convection effect and fin structure. The results indicated that use of rest time and increasing convection effect not only reduces maximum temperature but also recover melting fraction of PCM. Results also illustrate that the thermal performance of PCM based battery pack slightly get affected with the use of fin structure at lower convection, but decreases the maximum temperature by 8.17% at higher convection. Heat source a function of the state of charge and charge/discharge rate are given using Ansys-Fluent code and results are reported in the form of maximum temperature, average temperature and melting fraction.

Battery thermal management system based on the forced-air convection: A review

Abstract: With the popularization of lithium ion battery cells, the battery thermal management system (BTMS) has been paid much attention since it is important in ensuring the safety and performance of lithium ion battery pack. Although the BTMS based on the forced-air convection with the advantage of low-cost, simple, and tight design has been favored by practical applications in electric vehicles and electrochemical energy storage stations, the forced-air convection is always criticized for its low cooling efficiency and low-temperature uniformity. Thus, extensive investigation has been conducted to optimize the BTMS based on the forced-air convection. This paper reviews the developments on the application of forced-air convection into BTMS in terms of preheating and cooling. Firstly, the thermal models for battery cells are introduced from the perspective of the lumped model and electrochemical model. Meanwhile, the methods to simulate the flow field are also presented. The computational fluid dynamics and short-cut methods have been compared in the paper. The main optimization route is summarized which includes optimization of pure forced-air convection, the combination with phase change material(PCM), and integration with heat pipe. For the optimization of the pure forced-air convection, four technical routes are concluded, which are the location of inlets and outlets, flowing tunnel, controlling strategy, and flowing state. As for the hybrid BTMS based on forced-air convection with heat pipe and PCM, some extra structures such as mesh or finned structure are also included for enhancing the heat dissipation. Finally, some perspectives and outlooks on BTMS based on the forced-air convection are put forward for future development.

Application of support vector machines for accurate prediction of convection heat transfer coefficient of nanofluids through circular pipes

Abstract: Convection is one of the main heat transfer mechanisms in both high to low temperature media. The accurate convection heat transfer coefficient (HTC) value is required for exact prediction of heat transfer. As convection HTC depends on many variables including fluid properties, flow hydrodynamics, surface geometry and operating and boundary conditions, among others, its accurate estimation is often too hard. Homogeneous dispersion of nanoparticles in a base fluid (nanofluids) that found high popularities during the past two decades has also increased the level of this complexity. Therefore, this study aims to show the application of least-square support vector machines (LS-SVM) for prediction of convection heat transfer coefficient of nanofluids through circular pipes as an accurate alternative way and draw a clear path for future researches in the field.,The proposed LS-SVM model is developed using a relatively huge databank, including 253 experimental data sets. The predictive performance of this intelligent approach is validated using both experimental data and empirical correlations in the literature.,The results show that the LS-SVM paradigm with a radial basis kernel outperforms all other considered approaches. It presents an absolute average relative deviation of 2.47% and the regression coefficient (R2) of 0.99935 for the estimation of the experimental databank. The proposed smart paradigm expedites the procedure of estimation of convection HTC of nanofluid flow inside circular pipes.,Therefore, the focus of the current study is concentrated on the estimation of convection HTC of nanofluid flow through circular pipes using the LS-SVM. Indeed, this estimation is done using operating conditions and some simply measured characteristics of nanoparticle, base fluid and nanofluid.

Numerical study of bio-convection flow of magneto-cross nanofluid containing gyrotactic microorganisms with activation energy.

Abstract: In this study, a mathematical model is developed to scrutinize the transient magnetic flow of Cross nanoliquid past a stretching sheet with thermal radiation effects. Binary chemical reactions and heat source/sink effects along with convective boundary condition are also taken into the consideration. Appropriate similarity transformations are utilized to transform partial differential equations (PDE's) into ordinary ones and then numerically tackled by shooting method. The impacts of different emerging parameters on the thermal, concentration, velocity, and micro-rotation profiles are incorporated and discussed in detail by means of graphs. Results reveal that, the escalation in magnetic parameter and Rayleigh number slowdowns the velocity and momentum of the fluid. The increase in Biot number, radiation and heat sink/source parameters upsurges the thermal boundary but, converse trend is seen for escalating Prandtl number. The density number of motile microorganisms acts as a growing function of bioconvection Lewis number and declining function of bioconvection Peclet number.

Thermophysical properties of graphene-based nanofluids

Abstract: Heat transfer operations are very common in the process industry to transfer a huge amount of thermal energy, i.e., heat, from one fluid to another for different purposes. Many fluids are used as heat transfer fluid (HTF), in which water is the most common HTF due to its high specific heat, availability, and affordability. However, conventional HTFs, including water, have a lower thermal conductivity, which is the most critical thermophysical property, hence decreased heat transfer efficiency. The addition of solid particles of highly thermally conductive material, specifically at nano-size, i.e., nanoparticles NPs, result in nanofluid NF, which has evolved over the last two decades as efficient HTF and have been investigated in a wide range of applications. Among NPs, graphene (Gr) based materials have shown very high potential as NF due to the very high thermal conductivity up to 5,000 W/m.K, hence higher thermal conductivity NF. This work aims to thoroughly discuss the thermophysical properties of Gr-based NFs, including thermal conductivity, heat capacity, density, and viscosity. The discussion focus on the thermophysical properties as it is the ultimate determinator of the heat transfer characteristics of the HTF, such as the convective and the overall heat transfer coefficient as well as the heat transfer capacity of the NF. The discussion expands to the relative enhancement in such thermophysical properties reaching up to a 40% increase in thermal conductivity, as the most critical thermophysical property. The discussion shows that Gr-based NF has a much higher thermal conductivity relative to widely studied metal oxide NF and at much lower content, and lower density and viscosity increase, which is critical for determining the pumping power requirements. Critical challenges facing the application of Gr-based NFs such as cost, stability, increased density and viscosity, and environmental impacts are thoroughly discussed with mitigation recommendations given.

Numerical Scrutinization of Darcy-Forchheimer Relation in Convective Magnetohydrodynamic Nanofluid Flow Bounded by Nonlinear Stretching Surface in the Perspective of Heat and Mass Transfer

Abstract: The aim of this research is mainly concerned with the numerical examination of Darcy-Forchheimer relation in convective magnetohydrodynamic nanofluid flow bounded by non-linear stretching sheet A visco-elastic and strictly incompressible liquid saturates the designated porous medium under the direct influence of the Darcy-Forchheimer model and convective boundary The magnetic effect is taken uniformly normal to the flow direction However, the model is bounded to a tiny magnetic Reynolds number for practical applications Boundary layer formulations are taken into consideration The so-formulated leading problems are converted into highly nonlinear ordinary problems using effectively modified transformations The numerical scheme is applied to solve the governing problems The outcomes stipulate that thermal layer receives significant modification in the incremental direction for augmented values of thermal radiation parameter Rd Elevation in thermal Biot number γ1 apparently results a significant rise in thermal layer and associated boundary layer thickness The solute Biot number is found to be an enhancing factor the concentration profile Besides the three main profiles, the contour and density graphs are sketched for both the linear and non-linear cases Furthermore, skin friction jumps for larger porosity and larger Forchheimer number Both the heat and mass flux numbers receive a reduction for augmented values of the Forchheimer number Heat flux enhances, while mass flux reduces, the strong effect of thermal Biot number The considered problem could be helpful in any several industrial and engineering procedures, such as rolling, polymeric extrusion, continuously stretching done in plastic thin films, crystal growth, fiber production, and metallic extrusion, etc

A Machine Learning Approach to Predicting the Heat Convection and Thermodynamics of an External Flow of Hybrid Nanofluid

Abstract: This study numerically investigates heat convection and entropy generation in a hybrid nanofluid (Al2O3–Cu–water) flowing around a cylinder embedded in porous media. An artificial neural network is used for predictive analysis, in which numerical data are generated to train an intelligence algorithm and to optimize the prediction errors. Results show that the heat transfer of the system increases when the Reynolds number, permeability parameter, or volume fraction of nanoparticles increases. However, the functional forms of these dependencies are complex. In particular, increasing the nanoparticle concentration is found to have a nonmonotonic effect on entropy generation. The simulated and predicted data are subjected to particle swarm optimization to produce correlations for the shear stress and Nusselt number. This study demonstrates the capability of artificial intelligence algorithms in predicting the thermohydraulics and thermodynamics of thermal and solutal systems.

Vapor condensation with daytime radiative cooling.

Abstract: A radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor This effect has been known for centuries, and is exploited by some insects to survive in dry deserts Humans have also been using radiative condensation for dew collection However, all existing radiative vapor condensers must operate during the nighttime Here, we develop daytime radiative condensers that continue to operate 24 h a day These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies

A Study of Daytime Convective Vortices and Turbulence in the Martian Planetary Boundary Layer Based on Half-a-Year of InSight Atmospheric Measurements and Large-Eddy Simulations

Abstract: Studying the atmospheric planetary boundary layer (PBL) is crucial to understand the climate of a planet. The meteorological measurements by the instruments onboard InSight at a latitude of 4.5°N make a unique rich data set to study the active turbulent dynamics of the daytime PBL on Mars. Here we use the high‐sensitivity continuous pressure, wind, and temperature measurements in the first 400 sols of InSight operations (from northern late winter to midsummer) to analyze wind gusts, convective cells, and vortices in Mars’ daytime PBL. We compare InSight measurements to turbulence‐resolving large‐eddy simulations (LES). The daytime PBL turbulence at the InSight landing site is very active, with clearly identified signatures of convective cells and a vast population of 6,000 recorded vortex encounters, adequately represented by a power law with a 3.4 exponent. While the daily variability of vortex encounters at InSight can be explained by the statistical nature of turbulence, the seasonal variability is positively correlated with ambient wind speed, which is supported by LES. However, wind gustiness is positively correlated to surface temperature rather than ambient wind speed and sensible heat flux, confirming the radiative control of the daytime Martian PBL; and fewer convective vortices are forming in LES when the background wind is doubled. Thus, the long‐term seasonal variability of vortex encounters at the InSight landing site is mainly controlled by the advection of convective vortices by ambient wind speed. Typical tracks followed by vortices forming in the LES show a similar distribution in direction and length as orbital imagery.

Influence of fin orientation on the natural convection of aqueous-based nano-encapsulated PCMs in a heat exchanger equipped with wing-like fins

Abstract: The heat transfer enhancement in pin-fin heat exchangers is achieved by fluid mixing, disruption of the thermal-viscous boundary and the extension of the effective surface area for maximum heat exchange. The orientation and configuration of the fins are among the prime factors influencing the performance of these heat exchangers. Therefore, the present study investigates the combined influences of fin angle ( 0 ≤ ζ ≤ 270 ), arrangement and position of the wing-like fins on the natural convection of aqueous-based nano-encapsulated phase change material (PCM) in a fin heat exchanger. The analysis is performed for Rayleigh and Stefan numbers of 1e3-1e5 and 0.2 respectively by considering the PCM concentration of 0.05. The flow is assumed to be laminar, incompressible and Newtonian. The results demonstrate that the vertical alignment of the fins contributes to the augmentation of the thermal performance compared to the horizontally arranged fins. At the larger Rayleigh number, the mode of heat transfer is predominantly convective and thermal performance slightly deteriorates due to the blockage caused by adjacent fins. For low Rayleigh number, the conduction is the primary mode of heat transfer between the source and sink fins. This phenomenon is crucial to determine the heat exchanger thermal performance.

Impact of Soret and Dufour on MHD Casson fluid flow past a stretching surface with convective–diffusive conditions

Abstract: The intension of current inquiry is to highlight the impact of magnetohydrodynamic Casson fluid flow across a convective surface with cross diffusion, chemical reaction, non-linear radiative heat are accounted. Convection and diffusive boundary conditions are deemed. The governing flow equations for the flow fields are converted into non-dimensional form by using appropriate similarity variables. These ODEs are solved by fourth order Runge–Kutta and Shooting method. The outcomes are bestowed with plots and table for the influence of diverse flow variables on the flow fields. We observed that depreciate temperature and appreciate concentration with the upsurge in Sorret number, whereas a negative impact is perceived with Dufour number. A decrement in Nusselt number and an enhancement in Sherwood number are observed for the intensification of non-linear radiative parameter.

Sensitivity analysis of Marangoni convection in TiO 2 –EG nanoliquid with nanoparticle aggregation and temperature-dependent surface tension

Abstract: The sensitivity analysis of the magnetohydrodynamic thermal Marangoni convection of ethylene glycol (EG)-based titania (TiO2) nanoliquid is carried out by considering the effect of nanoparticle aggregation. The rate of heat transfer is explored by utilizing response surface methodology and estimating the sensitivity of the heat transfer rate toward the effective parameters: radiation parameter (1 ≤ R ≤ 3), magnetic parameter (1 ≤ M ≤ 3) and nanoparticle volume fraction $$(1\% \le \phi \le 5\%$$ ). The heat transfer phenomenon is scrutinized with thermal radiation and variable temperature at the surface. The effective thermal conductivity and viscosity with aggregation are modeled by using the Maxwell–Bruggeman and Krieger–Dougherty models. The governing equations are solved by using the apposite similarity transformations. It is found that when the effect of aggregation is considered, the velocity profile is lower. A positive sensitivity of the Nusselt number toward thermal radiation is observed. Further, a negative sensitivity of the heat transfer rate is observed toward the magnetic field and nanoparticle volume fraction.

Heat Source Location Effects on Buoyant Convection of Nanofluids in an Annulus

Abstract: In this paper, the impacts of the location of a thermal source on buoyant convection of nanofluids in an annular region are analyzed numerically through the finite volume technique. Five different thermal source positions along the inner cylinder of the annulus have been analyzed. The prime objective is to identify the optimal position of the source to maximize or minimize the thermal transport at different values of Ra and diverse volume fractions of the nanoparticle ranging from 0 to 10%. The location of the thermal source has a profound impact on the flow and temperature patterns as well as thermal transfer from the discrete source to the nanofluid. Further, the volume fraction of nanoparticles also controls the heat transport in the annular geometry.