Non-uniform Heat Research Articles

Heat Flux Identification of Aircraft Structure with Artificial Neural Network Compensation

Aerodynamic heating measurement of reusable hypersonic vehicles has always been an important aspect of hypersonic vehicle design. In this paper, a mechanistic-model-based heat flux identification method with artificial neural network (ANN) compensation is established to determine the spatially distributed heat flux of the aircraft structure. A one-dimensional heat conduction model is used to estimate heat flux by a robust and efficient algorithm integrating Tikhonov regularization with Levenberg–Marquardt method. The one-dimensional estimated heat flux has large errors for not considering multidimensional heat conduction effects. The proposed mechanistic-model-based method is then utilized to compensate the multidimensional heat conduction by ANN. The performance of the proposed method will be assessed by the determination of the heat flux of a two-dimensional plate and aircraft structure. Results show that compared with the one-dimensional inversion results, ANN compensation method can significantly improve the accuracy of estimated heat flux and is also applicable for larger levels of heat flux. The proposed compensation method is an effective technique to identify the nonuniform surface heat flux of multidimensional structures.

Fraction Frequency and Random Scanning Mode for Electron Beam Thermal Assessment

Development of thermal assessment technology is crucial to the security assessment of hypersonic vehicles. A strategy of high-precision reconstructions of nonuniform heat flux and temperature field characteristics of a hypersonic vehicle surface by a scanning electron beam is constructed, and a fraction frequency and random scanning mode that can significantly reduce the temperature fluctuation of materials is proposed. The reconstruction effects in this scanning mode are successively investigated in the HIFiRE-5b flight condition and the reentry condition of the capsule of Apollo 6, showing that the reconstruction accuracies of the heat flux and temperature fields are within 2 and 5%, respectively, and the temperature history is accurately reconstructed with an amplitude of temperature fluctuation below 11 K. This research is expected to promote the electron beam thermal assessment to reconstruct the thermal boundary conditions of hypersonic vehicles more realistically.

Effect of Uneven Heat Sink/Source and Nonlinear Radiation on Hydromagnetic Casson Fluid Flow Past an Inclined Elongating Sheet

Objectives: The present article investigates the steady flow of hydromagnetic Casson fluid flow past an inclined stretched sheet with the existence of nonlinear radiation and Joule heating effects. Methods: A numerical model is established and then solved using the BVP4c MATLAB technique. Findings: In this present work we described about the influence of the Grashof number, non-uniform heat source, Biot number, Casson fluid parameter, hydrodynamics, nonlinear radiation, chemical reaction, local Grashof number and Schmidt number parameters on the flow of mass and rate of heat transport was discussed through tabular result and graphs. It is clear that the rate of heat transport decreases with Joule heating and is higher with an increase in Biot numbers. Increases the amount of thermophoresis parameter and decreases with the rate of heat transport. Novelty: To the best extent of the authors’ belief so far, no attempt is made to inspect the flow, thermal and mass transfer of uneven heat sink/source and non-linear radiation on hydromagnetic and embedded with the viscous dissipation, thermophoresis, Brownian diffusion, Joule heating and Casson fluid. Keywords: NonUniform Heat Sink/Source; Casson Fluid; Joule Heating; NonLinear Radiation; Hydromagnetic

Topology design of cold plates for pouch battery thermal management considering heat distribution characteristics

The topology optimization technique was applied to the structural design of the cold plate for pouch Lithium-ion batteries in this study, aiming to boost its overall performance. With maximum heat transfer and minimum flow resistance as the optimization objectives of the cold plate channel, we proposed a topology approach for non-uniform heat generation, motivated by the inhomogeneous cell heat distribution. The optimization iteration yielded a non-uniform channel structure (N-type) with a denser channel distribution in the hot zone. According to the topology results, a simplified cooling system model for the 50 V battery module was constructed and investigated numerically. Under constant and dynamic current conditions, the N-type cold plate was compared to cold plates with other two channel structures: the uniform channel type and the straight channel type. As a result, the N-type cold plate showed the best comprehensive performance. Furthermore, the optimal design of the cooling system with different inlet and outlet layouts, channel depths and inlet mass flow rates was explored. The N-type cold plate with bottom inlet-top outlet layout, channel depth of 2.5 mm, inlet width of 15 mm and mass flow rate of 8 g s-1 is the ideal choice for the cooling system at 2C discharge. The j/f factor reached the maximum value of 3.42, with the pump power consumption and the Nusselt number being 2.53×10-3W and 39.26, respectively. The topology cold plate and optimization method proposed in this study can be used to increase the performance of BTMS.

Power-Law Fluid Flow and Heat Transfer via Vertical, Parallel Porous Walls with Varying Thermal Conductivity and Viscosity, As Well As Nth Order Chemical Reaction

This analysis examines a non-uniform heat source or sink, the flow of a power-law fluid induced by vertical parallel plates, and heat transfer using variable viscosity and thermal conductivity. Temperature likely exponentially changes viscosity and thermal conductivity. The implicit finite difference approach solves governing partial differential equations. Power-law index, Prandtl number, variable viscosity, and thermal conductivity are analysed. Skin friction, Nusselt number, and Sherwood number are graphically depicted to analyse channel fluid behaviour.

Anisotropic slip impact on nanofluid flow over a biaxial exponentially stretching sheet with Hall current: Corcione's correlation

This study introduces the Corcione correlation that accentuates the role of fluid temperature, particle volume fraction, and sizes in the increment of the nanofluid heat transfer rate and thermal conductivity. Here, the flow of nanofluid comprising Al2O3/H2O over a biaxial exponentially stretching sheet is considered. The analysis is performed for nanoparticles’ sizes 28, 30, and 45 nm and volume concentrations up to 7%. The mathematical model is strengthened by the anisotropic slip and convective boundary conditions. The momentum and heat equations are enriched with the inclusion of the Hall current and the non-uniform heat generation/absorption terms respectively. The nonlinear, coupled momentum and heat nondimensionalized ordinary differential equations (ODEs) are formulated with appropriate transformations and are solved numerically. The effects of many relevant factors are depicted using graphs. It is scrutinized that by enhancing the diameter of nanoparticles (Al2O3), the skin friction coefficient enhances and the heat transfer rate in the case of different nanoparticle sizes boosts for gradually growing estimations of the volume fraction. It is also deduced that surface slip increases pumping power and the insertion of the nanoparticles into the working fluid enhances heat transmission. To support the thesis, the presented model's validation is also provided.

Effect of Laser Scribing on Coating, Drying, and Crystallization of Absorber Layer of Perovskite Solar Cells

Large‐area perovskite solar modules fabrication has been demonstrated with a rapid process of large‐area slot‐die coating, drying, and crystallization using near‐infrared radiation in ambient air, in which the laser‐scribing process is applied to fabricate the modules. However, defective coating of perovskite layer near laser‐scribed P1 line which isolates the front electrode of transparent conductive oxide (TCO) results very low module efficiencies. Therefore, systematic study is conducted to investigate the root cause, mechanism and solution of the defective coating and crystallization of the perovskite layer. Scanning electron microscope, energy‐dispersive X‐ray spectroscopy, and atomic force microscopy are used to characterize the TCO film before and after P1 scribing. It is found that P1 laser‐scribing process changes surface morphology of TCO at the area near P1 line, which decreases the surface wettability and results discontinuous coating of precursor solution near P1 lines. The absence of TCO material in the P1 trench induces nonuniform heating during NIR annealing step, which is verified by thermal analysis via numerical simulation. After tuning laser process recipes, a large module with an active area of 46 cm2 is fabricated with a power conversion efficiency of 7.2% and geometry fill factor of 93.8%.

A study on optimization of the air supply system for the electric heating solid heat storage unit

An experimental and simulation study was carried out on the air supply system of the electric heating solid heat storage unit, aiming to improve the uniformity of the air supply system, thereby increasing the overall heating efficiency of the solid heat storage unit. The experiments show that non-uniform air distribution of the air system may cause non-uniform heat release of the heat accumulator, and the uniformity of the air supply system is greatly affected by the air supply structure and air inlet. By establishing a model of the heat storage device and conducting numerical simulation, the air distribution law of the air supply system was studied. According to the study results, the uniformity index of the air system was effectively improved by increasing the air cabin width and the air inlet angle, and adding a static pressure box at the air supply outlet, so that the flow velocity distribution of the air supply system was more uniform, which is of great significance to the overall optimization of the solid heat storage and heating system.

Non-uniform heat generation and Stefan blowing on nonlinear radiative Casson-nanofluid flow through microorganisms through leading-edge accretion or ablation

The effect of Stefan blowing on bioconvection of microorganisms mixed on non-Newtonian fluid with water-based nanofluids to an accretion/ablation of the leading edge was investigated in this current analysis. The effects of convective heat boundary conditions are one more important physical parameter in the flow investigation and have been studied for that analysis. Furthermore, the influence of nonlinear thermal radiation and irregular heat source or sink was more integrated. Even systems of conservative governing PDEs were transformed within the dimensionless structure of equations by utilising the appropriate conversion. The recent systems of equations including comparable transformed boundary conditions were again defined numerically for the use of the finite element method. It is notable about the accuracy and validity of the current numerical solution was an attractive understanding of the actual definite results in the literature. It is observed that velocity decreases by increasing Casson fluid parameter.

Three-Dimensional Numerical Simulation of Pyrolysis of Polymethyl Methacrylate under Non-Uniform Radiative Heating.

PMMA material is widely used in the building and household industries, and its pyrolysis behavior is important for fire safety. In real fire conditions, polymethyl methacrylate (PMMA) material will receive non-uniform distributed radiative heat flux from heat sources (such as fire). However, most of the existing work on this subject is limited to one dimensional geometry with uniform heat flux. This paper investigates the heat transfer and pyrolysis mechanism of PMMA material under non-uniform radiative heat flux. A three-dimensional model is developed to this end with a consideration of in-depth radiation and surface heat loss. The results show that temperature and density contours are highly non-uniform inside the solid and there is both a high-temperature core and low-density core beneath the surface. The maximum temperature occurs at a location under the top surface.

Second law analysis on EMHD with variable viscosity and thermal conductivity of hybrid nanofluid over a rotating disk: an application in solar systems

This current attempt explores the characteristics of variable viscosity and variable thermal conductivity of EMHD flow in which the shape factors like spherical versus laminar is considered for comparison purpose. Also, non-uniform heat source/sink and entropy generation are taken into count. We consider ethylene glycol of 50% and water of 50% mixture as base fluid. To convert the governing equations into ordinary differential equations (ODEs), self-similarity variables are used. The RK Fehlberg method has been used successfully to solve numerical sequential of ODEs. Active parameters such as magnetic field, electric field, Biot number, variable viscosity and variable thermal conductivity parameters are plotted on velocity profile, entropy, temperature and Bejan number. For the variable viscosity and thermal conductivity factors, the temperature rate increases. At the highest values of these parameters, the heat transmission rate is extremely high. This theoretical study is important for solar energy collectors, solar water heaters, solar energy conversion devices, solar PV (Photovoltaic) systems, solar thermal power fabrication, solar thermoelectric cells and radiators, among other things.

An elliptical inhomogeneity under nonuniform heat flux

We use complex variable techniques to study the decoupled two-dimensional steady-state heat conduction and thermoelastic problems associated with an elliptical elastic inhomogeneity perfectly bonded to an infinite matrix subjected to a nonuniform heat flux at infinity. Specifically, the nonuniform remote heat flux takes the form of a linear distribution. It is found that the internal temperature and thermal stresses inside the elliptical inhomogeneity are quadratic functions of the two in-plane coordinates. Explicit closed-form expressions of the analytic functions characterizing the temperature and thermoelastic field in the matrix are derived.

Mathematical modeling and computational outcomes for the thermal oblique stagnation point investigation for non-uniform heat source and nonlinear chemical reactive flow of Maxwell nanofluid

Owing to fine thermal prospective of nanomaterials, different applications have been addressed in nanotechnology and thermal management systems. Multidisciplinary applications of such nanomaterials are commonly observed in nuclear reactors, thermal systems, transportation systems, industrial products cooling, power industry, renewable energy etc. The motivated work aims to predicts improved thermal consequences of Maxwell nanofluid with applications of non-uniform heat source and radiated phenomenon. The heat transfer analysis is assessed by using the Cattaneo-Christov theories. The thermal phenomenon is controlled with interference of slip effects. The flow pattern is based on the oblique stagnation point flow confined by stretched cylinder. The Keller Box numerical determination of problem is worked out with fine accuracy. The physical dynamic of flow parameters is visualized graphically. It is claimed that control of thermal transportation phenomenon is resulted when the slip effects are dominant. The exponential heat source with nonlinear radiated phenomenon is important when enhancement in thermal process needed.

Darcy-Forchheimer flow of Prandtl-Eyring nanofluid subjected to a Riga plate of varying thickness along with Brownian diffusion, thermophoresis and non-uniform heat source/sink effects

This article is subjected to the characteristics of an electro-magnetohydrodynamic (EMHD) boundary layer movement of a nanofluid induced by a Gailitis device with variable thickness. A viscous incompressible Prandtl-Eyring nanofluid saturates the porous medium through Darcy-Forchheimer expression. Heat transfer process involves the influence of non-linear thermal radiation, viscous dissipation, non-uniform heat source/sink, and convective boundary conditions. Moreover, Brownian motion and thermophoresis mechanisms are taken into consideration. The governing mathematical model is transmuted with appropriate similarity transformations into a non-dimensional system of ordinary differential equations (ODEs). Numerical solution for this system is acquired through the bvp4c solver in MATLAB software. Velocity, temperature, and concentration profiles are scrutinized through graphical representation for various flow controlling parameters. The impact of these parameters on local values of skin friction coefficient, Nusselt number, and Sherwood number is analyzed through computational data specified in a tabular form.

Experimental and theoretical study on the onset of nucleate boiling in non-uniform heating tube bundle channel

The transverse non-uniform heating tube bundle exists in steam generator and will affect the heat transfer and flow conditions in the shell side. It is important for the operational performance of the steam generator. In this study, a non-uniform heating tube bundle channel experimental device was set up. The channel consisted of two groups of heating tube bundles which were non-uniform heating in the transverse direction and uniform heating in the axial direction. Experiments and theoretical analysis were conducted to evaluate the influence of transverse non-uniform heating on the Onset of Nucleate Boiling (ONB). The locations of ONB during the experiments were determined from the heat transfer coefficient variations and the tube wall temperature variations. Experimental results at ONB were compared with existing well-known correlations under uniform heating conditions. And then under non-uniform heating conditions, the experimental wall superheat at ONB were furthermore compared with results predicted by the verified existing correlation. It was found that the correlation can’t predict the experimental wall superheats well under transverse non-uniform heating conditions. Therefore, the influence of transverse non-uniform heating on ONB was theoretically analyzed. Correction factors were theoretically introduced and a new correlation was proposed. This new correlation was examined with experimental data and the result showed the correction factors need to be further studied.

Optimization of fin layout in liquid-cooled microchannels for multi-core chips

When the dense pin-fins array distributed uniformly is used to dissipate the non-uniform heat source, it is easy to generate excessive cooling at the non-hot spot, which leads to unnecessary heat dissipation loss. In this study, a three-dimensional model of a multi-core chip-microchannel heat sink is established. Fin layout in the chip-microchannel is optimized under the conditions of non-uniform power-partition chip based on constructal theory. The total volume of fins in a channel is selected as the constraint condition. A genetic algorithm is used to seek the optimal construct. Comparing the optimal fin layout with the dense pin-fins array, the results demonstrate that the maximum temperature can be reduced by 6.75 K when Re number is 750, and the total pressure loss can be reduced by 54.1% when Re number is 750. Namely, under the condition of non-uniform heat source, the fins with a certain total volume were distributed reasonably, which can maintain the optimal balance of heat dissipation capacity and heat dissipation cost, so that the accurate and efficient thermal design is realized, and the better comprehensive benefits are obtained.

Thermal-Hydrodynamic Behavior and Design of a Microchannel Pin-Fin Hybrid Heat Sink.

A three-dimensional convective heat transfer model of a microchannel pin-fin hybrid heat sink was established. Considering the non-uniform heat generation of 3D stacked chips, the splitting distance of pin-fins was optimized by minimizing the maximum heat sink temperature under different heat fluxes in the hotspot, the Reynolds numbers at the entrance of the microchannel, and the proportions of the pin-fin volume. The average pressure drop and the performance evaluation criteria were considered to be the performance indexes to analyze the influence of each parameter on the flow performance and comprehensive performance, respectively. The results showed that the maximum temperature of the hybrid heat sink attained a minimum value with an increase in the splitting distance. The average pressure drop in the center passage of the microchannel first increased and then decreased. Furthermore, the optimal value could not be simultaneously obtained with the maximum temperature. Therefore, it should be comprehensively considered in the optimization design. The heat flux in the hotspot was positively correlated with the maximum heat sink temperature. However, it had no effect on the flow pressure drop. When the Reynolds number and the pin-fin diameter increased, the maximum heat sink temperature decreased and the average pressure drop of the microchannel increased. The comprehensive performance of the hybrid heat sink was not good at small Reynolds numbers, but it significantly improved as the Reynolds number gradually increased. Choosing a bigger pin-fin diameter and the corresponding optimal value of the splitting distance in a given Reynolds number would further improve the comprehensive performance of a hybrid heat sink.

Responses of an axially rotated tube versus twisted tube design as two solutions to enhance the thermal performance under a non-uniform heat flux condition: A numerical study

• Heat transfer in rotating and twisted tubes are studied and compared numerically. • A maximum increase of 137% in Nusselt number occurs at N=10.5 for the 3-meter pipe. • Pipe rotation eliminates the liquid stratification phenomenon in the pipe. • A maximum increase of 2.5% in outlet temperature occurs at twist ratio S=0.1. • A maximum loss in the pressure coefficient reaches 32.8% at twist ratio S=0.1. Enhancement of heat transfer in tubes exposed to non-uniform heat flux applications is a key factor in increasing such applications' efficiency. In the present study, heat transfer in an axially rotating pipe with concentrated heat flux at the lower section of the pipe is numerically investigated and compared to the twisting technique in such applications. The effects of pipe’s length (1, 2, and 3 meters) and rotation rate (N=0-10.5), which is the ratio between the rotational and axial Reynold’s numbers, are studied numerically using ANSYS Fluent while the effect of the twist ratio (S=0.1-1) is studied in the twisted tube. The numerical analysis reveals that the pipe axial rotation has a negative impact on the average outlet temperature where a maximum decrease of 7.7% is reached in the 3-meter pipe at a rotation rate of N=10.5 with respect to the stationary pipe while the effect of the twisting technique was significant as the outlet temperature has a maximum increase of 9.3% at S=0.1. On the other hand, the pipe rotation increases the temperature homogeneity between the liquid layers thus reducing the liquid stratification phenomenon in the pipe. The average reduction percentage in the temperature difference between the pipe wall and the fluid center is 69.7% at N=10.5, however; this reduction reached a maximum value of only 11% at twist ratio S=0.1. This is evidenced by the increase in the Nusselt number where the numerical results show a maximum increase of 137% in the Nusselt number at N=10.5 for the 3-meter pipe whereas this increase reached 9.8% at a twist ratio of S=0.1 compared to the plain tube. Therefore, pipe axial rotation increases the temperature homogeneity by reducing the temperature gap between the pipe wall and the fluid center by reducing the pipe wall temperature thus making the pipe capable of absorbing greater heat amounts at larger lengths while the twisting technique increases the outlet temperature taking into consideration that this is a passive technique that does not consume power.

Radiation effect on MHD three-dimensional stagnation-point flow comprising water-based graphene oxide nanofluid induced by a nonuniform heat source/sink over a horizontal plane surface

This research aims to study the 3D magnetohydrodynamics stagnation-point flow (SPF) over a horizontal plane surface (HPS) carrying water-based graphene oxide (GO) nanoparticles caused by an irregular heat source/sink used in heat transfer procedures. In addition, a Tiwari–Das model is used to inspect the dynamics of fluid flow behavior and heat transmission features of the nanoparticles with experiencing the impacts of thermal radiation. The acquired nonlinear set of partial differential equations (PDEs) is transfigured to a system of ordinary differential equations (ODEs) using similarity transformations. The accumulative dimensionless ODEs are then further tackled in MATLAB using the bvp4c solver. Tables and figures are prepared for the execution of several relevant constraints along with nodal/saddle indicative parameter, internal heat source/sink parameter, radiation parameter and nanoparticles volume fraction which divulges and clarify more accurately the posited quantitative data and graphical findings. Also, the velocity profile decelerated in the axial and transverse coordinate axes for a higher value of the nanoparticle volume fraction but the dimensionless temperature distribution is augmented. Additionally, thermal boundary layer thickness and profile of temperature enriches with higher impressions of radiation constraint. However, the internal heat sink factor declines the profiles of temperature while escalating with the superior value of the internal heat source parameter.

Eulerian multiphase study of direct steam generation in parabolic trough with OpenFOAM

AbstractDirect steam generation (DSG) in parabolic trough solar collectors is a feasible option for economic improvement in solar thermal power generation. Three‐dimensional Eulerian two‐fluid simulations are performed under OpenFOAM to study the turbulent flow in the evaporation section of the parabolic trough receiver and investigate the phase change, and pressure drop of water as a heat transfer fluid. First, the model's validity has been tested by comparing the numerical results of a laboratory scale boiler with the available correlations and semi‐correlations of boiling flows from the literature. Simulations agreed well with Rouhani–Axelsson correlation for horizontal tubes, with a mean relative error of less than 7.1% for all studied cases. However, despite a mean relative error of less than 13.19% compared to the experimental data in the literature, the reported pressure drop factor remains valid; overprediction remains tolerable for most engineering applications. Second, the scaling effect on the mathematical model, from laboratory to commercial‐scale configuration, was tested with experimental data of the DISS test loop in Platforma Solar de Almeria, Spain. The Monte Carlo Ray Tracing method under the Tonatiuh package allowed for obtaining the nonuniform heat flux distribution. Due to the large size of the evaporation section in the DISS loop (eight collectors), each collector is considered independently in the simulations. Thus, simulations follow each other, taking the numerical results of each collector output as input data in the next collector and so on until the last. The numerical results showed an excellent agreement for the void fraction with 3.53% against the Rouhani–Axelsson correlation. Frictional pressure losses are within a 17.06% error of the Friedel correlation, in the range of previous work in the literature, and the heat loss is less than 4.69% error versus experimental correlation.