Non-uniform Heat Research Articles

Heat transfer analysis of MHD Casson nanofluid flow over a nonlinear stretching sheet in the presence of nonuniform heat source

This study examines how a chemical reaction and a nonuniform heat source effect the flow of an MHD Casson nanofluid over a nonlinear stretching sheet. By incorporating viscous dissipation, the energy equation is strengthened. Brownian diffusion, thermophoresis diffusion effects are taken place. By using the necessary similarity transformations, the governing equations for the current flow are converted into a nonlinear system. The RKF technique yields a numerical solution along with a shooting technique for the condensed system. Thereafter, to better understand the physical interpretation of flow and heat transfer, the flow-controlling parameters are shown graphically and in tabular form in the current work. Based on the present study’s numerical results, a fair connection is found between this analysis and previous studies. Some of the observations are velocity profile is decreased for the effects of magnetics and stretching parameter variations and Eckert number plays a great role in the increase of temperature profile.

A numerical approach to the modeling of Thompson and Troian slip on magnetized flow of Al2O3–PAO nanolubricant over an inclined rotating disk

In automotive fluids, hydraulic, gear, and bearing oils, as well as in applications operating in extremely high or cold temperatures, PAO is widely employed. In present work, we have made an attempt to develop a mathematical model to discuss the flow of magnetized [Formula: see text] nanolubricant over an inclined rotating disk in Darcy-Forchheimer porous medium with Thompson and Troian slip at the boundary. The effects of mixed convection, nonlinear heat radiation, viscous dissipation, Joule heating, and non-uniform heat source/sink are also included in the modeling. We have solved the proposed model numerically with the help of MATLAB built-in bvp-4c method after metamorphosing the PDEs to ODEs. The enhancing values of inertial parameter and velocity slip parameter decrease the tangential and radial velocities of the nanolubricant. The temperature of the nanolubricant [Formula: see text] enhance significantly by strengthening the magnetic field, whereas radial and tangential velocities get retarded. The non-uniform heat source/sink parameters play a vital role in controlling heat transmission phenomenon. The increasing values of Eckert number, radiation parameter, and non-uniform heat generation parameters tend to increase the value of Nusselt number. The value of Nusselt number drops with rising values of Biot number and non-uniform heat sink parameters.

Role of Interfacial Evaporation Process in Thin Vapor Chambers With Variable Pillar Spacing and Nonuniform Heat Flux

This paper reports the results of our numerical studies on the performance of thin film evaporation, mostly seen in the evaporator of a thin vapour chamber, using micropillar arrays of varying pitch and under both uniform and non-uniform heat flux conditions. The dry-out heat flux and evaporator surface temperature have been used as the performance metrics. A numerical model has been formulated to solve the fluid flow and phase change heat transfer considering the capillary pumping action (wicking action). The model is next exercised to study the performance of the evaporator with variable pitch of the micropillar array and with both uniform and non-uniform heat flux at the base. The pitch variations are done either by maintaining the mean pitch to be constant (same number of pillars) or by keeping the limiting pitch (maximum) equal to the uniform pitch scenario. The results show that a linearly decreasing pillar spacing arrangement along the downstream direction, i.e., along the flow direction (+ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> direction), results in significant enhancement of the cooling limit up to 1.5 times along with the reduction in overall evaporator surface temperature when compared to uniform pillar spacing where increase in cooling limit is accompanied with increase in overall evaporator surface temperature. In addition, the interplay of variable spacing and non-uniform heat flux results in design guidelines for pillar arrangements for given power maps while throwing new insights into the complex fluid flow and heat transfer phenomena encountered in this process. A higher concentration of pillars is found to result in lower evaporator surface temperatures, thereby recommending more number of pillars in high heat flux zones.

Regular and chaotic Rayleigh Bénard convection in hybrid Casson nanoliquid under the effect of non-uniform heat source

Regular and chaotic Rayleigh Bénard convection in hybrid Casson nanoliquid under the effect of non-uniform heat source

A novel structure tube for supercritical CO2 turbulent flow with high non-uniform heat flux

Supercritical CO2 has been a promising alternative working medium in coal-fired power plants, high-temperature solar power systems, and fuel cells. In these cases, supercritical carbon dioxide is in a round tube under high temperature and pressure with high non-uniform heat flux. In this study, a novel structure tube is proposed by optimizing the coupling between circumferential heat flux and tube thickness on the heat-absorbing side to improve its comprehensive performance. A thermal-fluid-mechanical coupling model was developed. The novel structure can reduce maximum temperature and temperature difference effectively for the half-cycle uniform and non-uniform heat flux. The maximum thermal stress decreased by 23 and 29% and the maximum temperature decreased by 29.6 and 24.8 K for half-cycle uniform and non-uniform heat flux when the Eccentricity increased from 0 to 0.4. A comparison was made between the proposed structure, thin-walled tube, and traditional tube. Results showed that the performance of the proposed tube is the best. The maximum temperature decreases by approximately 55 K compared with the traditional and thin-walled tubes. The maximum equivalent stress of proposed tube is the smallest. Furthermore, the structure will improve the safety and economics of the tube.

Cubic Chemical Autocatalysis and Oblique Magneto Dipole Effectiveness on Cross Nanofluid Flow via a Symmetric Stretchable Wedge

Exploration related to chemical processes in nanomaterial flows contains astonishing features. Nanoparticles have unique physical and chemical properties, so they are continuously used in almost every field of nanotechnology and nanoscience. The motive behind this article is to investigate the Cross nanofluid model along with its chemical processes via auto catalysts, inclined magnetic field phenomena, heat generation, Brownian movement, and thermophoresis phenomena over a symmetric shrinking (stretching) wedge. The transport of heat via nonuniform heat sources/sinks, the impact of thermophoretic diffusion, and Brownian motion are considered. The Buongiorno nanofluid model is used to investigate the impact of nanofluids on fluid flow. Modeled PDEs are transformed into ODEs by utilizing similarity variables and handling dimensionless ODEs numerically with the adoption of MATLAB’s developed bvp4c technique. This software performs a finite difference method that uses the collocation method with a three-stage LobattoIIIA strategy. Obtained outcomes are strictly for the case of a symmetric wedge. The velocity field lessens due to amplification in the magneto field variable. Fluid temperature is amplified through the enhancement of Brownian diffusion and the concentration field improves under magnification in a homogeneous reaction effect.

Performance analysis of sCO2 tube with high non-uniform heat flux: Thermal-fluid-structural evaluation and optimization

A supercritical carbon dioxide (sCO2) tube is an important component in a sCO2 power system for a wide range of heat sources. The sCO2 tubes experience high temperature and pressure with high non-uniform heat flux when fossil fuel and solar energy are used as heat sources. Herein, a novel tube structure is proposed to match the circumferential thermal resistance with the non-uniform heat flux by changing the Eccentricity. A three-dimensional multi-physical coupling model was constructed to compare the proposed structure with a conventional tube. The fluid dynamics, thermal stress, and coupled heat transfer characteristics were analyzed, and the key working parameters were explored. The maximum temperature of the proposed structure was effectively reduced by 13–36 K and the maximum thermal stress was significantly reduced by approximately 25–33% under all the simulated working conditions when the Eccentricity changed from 0 to 0.4. The proposed novel structure will facilitate the safety and conserve tube material, and the results can serve as a reference for the development of sCO2 power systems for industrial applications.

Dynamics of Melting Heat Transfer of a Micropolar Nanofluid over an Electromagnetic Actuator with Irregular Thickness and Non-uniform Heat Source

Dynamics of Melting Heat Transfer of a Micropolar Nanofluid over an Electromagnetic Actuator with Irregular Thickness and Non-uniform Heat Source

Study on the uneven flow distribution and non-uniform heat transfer in microchannels

The power module is one of the main heating sources with non-uniform heat flux in high-power electrical servo systems used for flight vehicles. Faults in the power module are usually caused by a high or a non-uniform temperature. Given the environment of heat dissipation during flight, a regenerative cooling method is typically used, and the cooling system is designed as a microchannel heat sink with supercritical fuel. This is an effective means of solving thermal problems in the flight vehicles. However, because of the high heating power and non-uniform heat distribution of the power module, it is necessary to optimize its heat sink to restrict the high temperature rise and suppress the non-uniform distribution of temperature. In light of these considerations, a 3D numerical model of the microchannel heat sink of a power module with non-uniform heat flux was established in this study to examine the heat transfer and the thermal performance of the cooling channels. Based on the validation of the mesh and numerical method, the simulations of the flow distributions of the channels were performed to assess the thermal performance of the heat sink. It included investigating the effects of the inlet location of the manifold and its injection angle on the flow distribution in the channels, and the influences of the flow distribution and the operational parameters on the thermal performance of the heat sink. The results revealed that the Z30 configuration provided the best location and injection angle of the inlet to match the non-uniform heat flux of the power module. In this case, the values of Stanton number and buoyancy parameter of channel 4 yielded the minimum values of all channels owing to its higher flow rate and gradual rise in temperature. The deviation in the rate of mass flow Φ changed slightly corresponding to the various operational parameters, only the total heat flux would bring a bigger fluctuation. The tiny difference in temperatures among the observation areas on the substrate verified the positive influence of the flow distribution in matching the non-uniform heat flux.

Some recent progress in reactor core thermal-hydraulics modelling

In the last more than ten years the research groups of the present authors have been working on some of the key phenomena or parameters widely used in sub-channel thermal-hydraulics (SCTH) codes, e.g. (a) transversal exchange between sub-channels, (b) circumferential non-uniform heat transfer in fuel assemblies with tight or semi-tight lattice (pitch-to-diameter ratio smaller than 1.25), (c) PDO heat transfer and rewetting and (d) CFD analysis of two-phase flow and heat transfer, incl. critical heat flux. Among others, three transversal exchange phenomena were studied, i.e. turbulent mixing coefficients, void drift and wire wrap induced sweeping flow. New models for various turbulent mixings, void drift and wire wrap induced cross flow were developed based on analytical analysis and CFD simulations. Importance of the non-uniform heat transfer behavior inside single sub-channel was identified in fuel assemblies with tight or semi-tight lattice. Correlations for predicting the non-uniform heat transfer coefficient were proposed, which were implemented into SCTH codes, to accurately determine the local hot spot on the fuel pin surface. A large experimental data base containing more than 60,000 data points of PDO heat transfer and rewetting was established. Based on the data base a new empirical correlation of PDO heat transfer was proposed. In addition, dynamic behavior of droplets (droplet size and velocity) and the thermal non-equilibrium were experimentally measured, which can be used for the validation and improvement of mechanistic models of PDO heat transfer and rewetting, also proposed by the research groups of the present authors. For the CFD prediction of CHF, a new and robust method for wall boiling heat transfer was developed to calculate the near wall void fraction and its connection to CHF.

Natural Convection of Ternary Hybrid Nanofluid in a Differential-Heated Enclosure with Non-Uniform Heating Wall.

In the field of convective energy transfer, natural convection is one of the most studied phenomena, with applications ranging from heat exchangers and geothermal energy systems to hybrid nanofluids. The aim of this paper is to scrutinize the free convection of a ternary hybrid nanosuspension (Al2O3-Ag-CuO/water ternary hybrid nanofluid) in an enclosure with a linearly warming side border. The ternary hybrid nanosuspension motion and energy transfer have been modelled by partial differential equations (PDEs) with appropriate boundary conditions by the single-phase nanofluid model with the Boussinesq approximation. The finite element approach is applied to resolve the control PDEs after transforming them into a dimensionless view. The impact of significant characteristics such as the nanoparticles' volume fraction, Rayleigh number, and linearly heating temperature constant on the flow and thermal patterns combined with the Nusselt number has been investigated and analyzed using streamlines, isotherms, and other suitable patterns. The performed analysis has shown that the addition of a third kind of nanomaterial allows for intensifying the energy transport within the closed cavity. The transition between uniform heating to non-uniform heating of the left vertical wall characterizes the heat transfer degradation due to a reduction of the heat energy output from this heated wall.

New Insight Into Crack-Healing Mechanism via Electropulsing Treatment

A combination of experiment and numerical simulation was employed to study the healing mechanism of fatigue crack via a novel route of electropulsing treatment (EPT) named dual-step EPT processing. By applying cyclic loads, similar cracks were generated in 316L stainless steel samples. Then, cracked specimens were subjected to electropulsing treatment under different conditions in order to find the optimum EPT condition to effectively heal the crack. The geometry of the fatigue crack before and after EPT was investigated in 3D by Micro-CT. SEM-EBSD was used to evaluate the microstructure of the healed region. To understand the dominant mechanism of crack healing by EPT, the temperature and stress/strain fields were evaluated by the finite element method (FEM) considering non-uniform Joule heating. The results demonstrate that complete crack healing requires a balanced combination of melting and compressive stress as well as increased peak current density regarding the reduced crack length. The simulations also suggest that Joule heating alone is sufficient to induce the observed melting in the examined samples. The fatigue crack after EPT was found to be effectively healed, as indicated by the similar crack growth rate compared with the samples without electropulsing treatment. In addition, a refined microstructure can be achieved after EPT.

Case study of autocatalysis reactions on tetra hybrid binary nanofluid flow via Riga wedge: Biofuel thermal application

Ethanol and biodiesel, which both belong to the first generation of biofuel technology, are the two most popular forms of biofuels now in use. In order to create next-generation biofuels using waste, cellulosic biomass, and algae-based resources, the Bioenergy Technologies Office (BETO) is working with business. The present article is designed to study the effect of tetra hybrid nanoparticles with the utilization of the novel Hamilton and Crosser model and catalytic reaction on binary fluid with the consideration of ethanol biofuel as a base fluid. Ethanol comprising tetra hybrid nanoparticles and heterogeneous catalytic reaction amplifies thermal conductivity and significantly increases brake thermal efficiency and reduces brake-specific fuel consumption in diesel engines. Therefore, the aim of this article is a theoretical checkup that is related to heat and mass transport of biofuel flow considering binary fluid accompanied with autocatalysis reaction and novel tetra hybrid nanoparticles on biofluid flow subjected to a Riga wedge. Transportation of heat via nonuniform heat source/sink, thermal radiation, and thermal conductivity are in our consideration. The mathematics of the assumed problem generates the system of non-linear partial differential equations from basic equations of momentum, energy, and mass. The usage of non-dimensional variables gave a system of non-linear ODEs with boundary conditions which are further dealt with in the Lobatto111A scheme. The results are obtained for stretching/shrinking wedge with several parameters. From obtained results, it is observed that the velocity field diminishes owing to magnification in Weissenberg number and Casson fluid parameter. The temperature field diminishes by amplifying heat generation, thermal radiation, and variable thermal conductivity parameter. Concentration distribution escalates by rising homogeneous reaction parameters.

Dynamics of gyrotactic microorganisms for chemically reactive magnetized 3D Sutterby nanofluid flow comprising non-uniform heat sink-source aspects

This presents a theoretical and computational evaluation of the unsteady 3D Bioconvection flow of Sutterby fluid, which has non-linear nonlinear radiation features as well as gyrotactic microorganisms, illuminating the novelty of the work. Furthermore, the influences of magnetic field, activation energy, chemical reactions, mixed convection and non-uniform heat sink-source are likewise indebted. Boundary layer theory is entreated to progress the elementary PDEs designed for microorganism field, momentum, nanoparticles concentration and energy also then condensed to the extremely nonlinear ODEs through the variable’s transformation. Numerical solutions for the existing investigation are obtained by bvp4c method in MATLAB software. Numerical calculations intended for Sherwood number, density number of microorganism and wall heat transfer are correspondingly accompanied. The graphic illustrations for exemplifying features of diverse embryonic parameters on dimensionless measures are designated systematically. It is fascinating to observed that the concentration as well as microorganism field is progressed for developed approximations of the bioconvection Rayleigh number and the magnetic parameter. The temperature of the fluid develops as a implied reaction to the magnetic parameter, the radiation parameter, Biot number and temperature ratio parameter.

Natural Convection Flow of Radiative Casson Fluid Past a Stretching Cylindrical Surface in a Porous Medium with Applied Magnetic Field and Joule Heating

This study is based on the exploration of MHD Casson fluid flow past a stretching cylinder in the presence of non-uniform heat generation, thermal radiation and Joule heating. Boussinesq approximation is also put into consideration due to density difference in the fluid. The governing equations and their corresponding boundary conditions are changed into system of ordinary differential equations with the aid of appropriate similarity variables. The obtained ordinary differential equations are solved numerically using Runge-Kutta Fehlberg method alongside shooting technique. The flow and thermal fields are investigated in the presence of emerging parameters, namely Grashof number, Prandtl number, radiation parameter, curvature parameter, Eckert number, Casson parameter, permeability parameter, magnetic number, space and temperature dependent heat generation parameter. In this study, enhancement in velocity distributions is noticed as values of Grashof number grow but velocity profiles are depreciated by permeability parameter and curvature parameter.

Imaging system aberrations through optical windows with nonuniform laser heating.

An optical window is a critical component of an imaging system. When operating in harsh environments with extreme heating, nonuniform temperature changes occur throughout the window and cause nonuniform refractive index changes and mechanical deformations due to thermal expansion, which can degrade the imaging system's performance. In this paper, we present results collected from an experimental setup developed to characterize these aberrations. This setup includes a C O 2 laser for sample heating, an infrared camera for measuring front and back surface temperatures, and a visible imaging system and a wavefront sensor for measuring degradations of a collimated beam from a point source transmitted through the heated window. Sapphire samples are laser heated with a Gaussian profile to temperatures in excess of 500K with surface temperature gradients in excess of 15K/mm. These measurements are compared with first principles models, which show quantitative agreement for window temperatures and qualitative agreement with the transmitted wavefront and imaged point source.

Enhanced magneto-convective heat transport in porous hybrid nanofluid systems with multi-frequency nonuniform heating

In high-performance thermal systems, convective heat transport is a critical phenomenon for sustainable operation from an energy efficiency standpoint. This study examines the convective heat transport dynamics of a hybrid nanofluid (aluminum oxide-copper–water nanofluid) under spatially varying nonuniform temperature conditions within a porous thermal system in the presence of a magnetizing field. The flow domain experiences nonuniform heating (following a half-sinusoidal profile) from both sidewalls and is cooled from the top, while the lower wall remains adiabatic. The flow domain is filled with a porous substance and a hybrid nanoliquid. The non-dimensional governing equations are derived and numerically solved using a finite volume method-based solver. To accurately capture thermal behavior, available experimental data on hybrid nanofluid thermophysical properties are utilized. The study analyzes significant control variables such as half-sinusoidal heating amplitude, frequency, and offset temperature, as well as flow control variables such as Darcy number (Da), modified-Rayleigh number (Ram), and Hartmann number (Ha). The analysis shows that non-uniform heating consistently enhances transfer by up to approximately 722% compared to uniform heating. The three temperature-controlling parameters (amplitude, frequency, and offset temperature) play a crucial role in enhanced heat transfer, and the higher their magnitudes, the higher the heat transfer. Heat flow dynamics between the heat source and the heat sink are well visualized through heat function and heatlines. Heat transfer is an increasing function of Ram and frequency, which is opposite to the rising Da or Ha. An optimum frequency at which thermal convection is maximum is about 70 for the considered range of Ram. Furthermore, mathematical correlations that combine control variables are developed for predicting heat transfer characteristics.

New Laboratory Experiments to Study the Large-Scale Circulation and Climate Dynamics

The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this “classical” design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control.

Analysis of auto cubic catalysis and nanoscale heat transport using the inclined magnetized Cross fluid past over the wedge

In this study, the chemical procedure is presented in the nanomaterial flow, which contains the astonishing topographies. Nanoparticles contain physical and chemical properties, which are continuously used in almost every field of nanotechnology and nanoscience. Therefore, the idea to implement of these investigations is related to the heat and mass transport based on the nanomaterial flow along with the Cross model, chemical process via autocatalysis and an inclined magnetic dipole over shrinking/stretching wedge. Moreover, heat transportation with non-uniform heat source/sink, thermophoretic diffusion impacts, and Brownian motion are also studied. The assumed problems in the mathematics generate the system of nonlinear partial differential equations using the basic form of momentum, energy, and mass. Non-dimensional variables provide the system of equations using the boundary conditions, which are further updated with the shooting method to reduce into the initial value problem. The solution of the nonlinear model is presented through the MATLAB built-in procedure Bvp4c to find the numerical solutions.

Numerical investigation of flow and heat transfer of supercritical carbon dioxide in the vertical helically-coiled tube under half-side heating condition

ABSTRACT The supercritical boiler is one of the ways to enable sustainable energy development. Its revolution cannot be separated from the study of the characteristics of supercritical carbon dioxide in a spiral pipe. This research article provided an industrially compliant model of a water-cooled wall spiral pipe with one-side heating for heat transfer. The simulation was set for various parameters including P = 30.42 MPa, Tin = 578–643 K, q = 105–180 kW/m2, G = 1784–2348 kg/m2s. The article discussed in detail factors such as buoyancy and secondary flow for these cases. The results showed that in the range of high parameters, mass fluxes, heat fluxes, and inlet temperature all had a substantial influence on the temperature and velocity fields, with the mass flux showing a non-monotonic trend on the HTC and the heat flux having a more subtle influence on the HTC. The inhomogeneous heating pattern affected the buoyancy and secondary flow motion, changing the temperature field in the tube, and enhancing the velocity field at the bend and on the heating side. A new empirical correlation for supercritical CO2 with non-uniform heating was proposed.