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Solar thermal energy is one of the important sources of renewable energy. The solar thermal energy gives clean energy which can be utilized for industrial applications. Industrial heaters which require heat energy for many industrial uses can be attained using these solar thermal absorbers. The solar thermal absorber is designed using a layer design that consists of material compositions of Titanium (Ti) and Stannic selenide (SnSe 2) for ground and substrate sections respectively. A graphene layer which has the good properties to be used in solar absorbers is added between the Aluminum and SnSe 2 material. A thin graphene section is inserted above the SnSe 2 substrate and below the Ti resonator. To catch the good absorption in the current design, the best four wavelengths (micrometer) have been attached such as 0.22, 0.8, 2.46, and 2.85. This design's contribution can be studied in 4-atm regimes (from UV, V to NIR, and MIR). According to the wavelength and bandwidth ranges, the current absorption explores more than 97% (97.4%) in between 2.4 and 3 μm (600 nm) bandwidth and exceeds 95% (95.2%) from 0.2 to 1 μm (800 nm) respectively. To the overall range of design, it extracts 90.3% for the 2800 nm band between 0.2 and 3 wavelength regime. The flow of the presentation of the proposed paper is (i) Introduction (ii) Design and Parameters, and (iii) Results and Discussions. The explored absorber can be effective in water heating and swimming pool heating for homes. Moreover, it can also be applied in large industries as a solar thermal absorber for heating applications. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

It is difficult to alter the thermal performance of a minichannel heat sink with a fixed structure under constant operating conditions. In particular, if the local heat transfer of the substrate cannot be regulated in real time, the dynamic heat dissipation needs of high-power electronic components cannot be met in the electrical servo systems of flight vehicles. In this paper, a new minichannel heat sink structure based on the classical rectangular channel is proposed and a piezoelectric oscillating fin (POF) is introduced to replace the fixed fin. The thermal performance of the heat sink can then be regulated using the swing of the POF, with supercritical carbon dioxide (S–CO 2) as the coolant. Transient numerical simulations are applied to investigate the influence of various POF operating parameters on the heat transfer of the channel, such as the oscillation amplitude and frequency. The results demonstrate that a channel with a POF can allow for dynamic and rapid adjustment of the thermal performance through control of the oscillation frequency and amplitude of the POF, with a constant channel configuration, coolant, and operating conditions. The heat transfer can be enhanced significantly by the swing of the POF, with the local Nusselt number growing up to 8.3 times and the overall one up to 1.14 times. Both the oscillation frequency and amplitude have a positive correlation with the intensity of heat transfer. The POF also contributes to a greater pressure drop and fluctuation in pumping power. A comprehensive evaluation coefficient shows that the POF is effective at improving the overall thermal performance with a low-frequency swing, while high-frequency operation enhances the local heat transfer and decreases the local temperature near the tail end of the POF. Finally, considering the effects of the frequency and amplitude of the POF, as well as the variable thermophysical properties of the supercritical coolant, a heat transfer correlation based on the Dittus–Boelter equation is established to predict the thermal performance of the channel with a POF. This prediction has a maximum error of ±0.56%. • A minichannel introducing piezoelectric oscillating fin (POF) to replace the fixed fin is proposed. • The thermal performance of the minichannel heat sink is regulated using the POF and S–CO 2. • The influence of oscillation frequency and amplitude of the POF on heat transfer is investigated. • A heat transfer correlation for POF channel based on the Dittus–Boelter equation is established. [ABSTRACT FROM AUTHOR]

This paper deals with the analytical and experimental analysis of heat transfer in the xylem of trees and the determination of stem water content (WC). The aim of this paper was to derive and verify a new approach to WC calculation from measured temperature differences around a continuously heated needle. The configuration of heater and thermocouples of the heat field deformation (HFD) method for sap flow measurements was taken for this purpose. The suggested formula is derived from the heat conduction equation with a continuous linear source of heating. The ability of the HFD method to non-destructively determine the radial distribution of the local conditions of sap flow measurements under zero flow (referred to as K-value) was used to derive the radial distribution of WC. Examples of the application of our method on several contrasting species with different plant hydraulic architecture are given where calculated WC along stem xylem radius was compared with its direct gravimetrical measurements or with relative determination of wetness of cross-sectional stem discs using a modified differential translucence method. The proposed method enables water content measurements during continuous linear heating and is important for information about WC and sap flow together per day or season when there is possible to extrapolate the temperature difference for zero flow condition. [ABSTRACT FROM AUTHOR]

Abstract: To decrease the regeneration temperature of silica gel (an excellent desiccant), the non-heating regeneration method with ultrasonic has been proposed and studied in our previous papers in which the effect of acoustic parameters as well as drying air temperature on the regeneration process was investigated experimentally by desiccant-weighing method. In this paper, the effect of drying air temperature and humidity on the ultrasonic-assisted regeneration and the following adsorption features of silica gel will be further studied by measuring the states of drying air. Different inlet air conditions, i.e., 40, 50, 60 and 70 °C in temperature combined with 0.01, 0.015 and 0.02 kg/(kg dry air) in humidity, are designed for the experimental study. The mass of dry silica gel sample used in this study is measured as 175 ± 0.1 g, and the acoustic frequency and power of ultrasound are 23 kHz and 60 W, respectively. The two indexes, AERR (Average Enhancement Ratio of Regeneration) and AERA (Average Enhancement Ratio of Adsorption), are used to estimate the effect of ultrasonic on the regeneration and the following adsorption of silica gel. The experimental results show that the effect of ultrasound on the regeneration will first rise and then decline when the drying air temperature rises from 40 °C to 70 °C, while it decreases with the drying air humidity increasing from 0.01 to 0.02 kg/(kg dry air). Similar regular patterns can be found for the effect of regeneration assisted by ultrasonic on the adsorption of silica gel. Meanwhile, a theoretical model is developed to predict the regeneration rate of silica gel assisted by ultrasound and validated by experiments. [Copyright &y& Elsevier]

Abstract Semiconducting single-walled carbon nanotube (s-SWNT) arrays attract much attention due to the ideal configuration for high performance electronics. A recent approach based on the nanoscale thermocapillary flow enabled the achievement of aligned arrays of highly purified s-SWNTs by removing the metallic SWNTs (m-SWNTs) in as-grown arrays by direct pulsed current injection. Thermal management of this process is critically important since the cumulative heating from the m-SWNT array yields a high temperature increase to cause the difficult control of thermocapillary flow. In this paper, an analytical heat transfer model combining a two-dimensional transient thermal model and a three-dimensional steady state thermal model is established for predicting the temperature increase of the SWNT array under a pulsed current injection with a period step function. The analytical predictions agree well with three-dimensional finite element analysis. Effects of parameters (such as duty cycle, period, spacing, etc.) on the temperature distributions and the maximum temperature increase are investigated systematically. These results can help guide the purification process to reduce the adverse thermal effects to obtain highly purified s-SWNTs. Highlights • An analytical thermal model is established for the aligned arrays of metallic single-walled carbon nanotubes by pulsed heating. • The analytical thermal model combines a two-dimensional transient analysis and a three-dimensional steady state analysis. • Effects of loading and geometric parameters on the temperature distributions and the maximum temperature increase are studied. • These results can help optimize the process to purify the horizontally aligned single-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

The paper deals with the study of the heat transfer phenomena within a vertical enclosure containing PCM integrated inside a test cell with the dimension of (0.5, 0.5, 0.5 m 3 ). An experimental framework was conceived and installed in the Thermal Processes Laboratory in Borj Cedria, Tunisia. The experimental investigation was carried out by measuring the temperature and the heat fluxes exchanged throughout the PCM vertical enclosure. It was found that during the heating phase the temperature inside the test cell equipped with the PCM vertical enclosure is about 28 °C. It was also found that once the PCM vertical enclosure is omitted the cell temperature inside the test cell ranges between 29 and 40 °C. A complete model was also formulated by taking into account various modes of heat transfer inside the PCM vertical enclosure. The numerical model was performed by following the temperature changes at the bottom position and at the high position of the PCM vertical enclosure. The numerical model followed also the evolution of the melting front during the melting process. The model was then exploited for the evaluation of the melting front evolution during the charging and the discharging processes. Another TRNSYS simulation was achieved to evaluate the feasibility of integrating the PCM vertical enclosure in a real building envelop. The results of the TRNSYS simulation showed that the integration of a well dimensioned PCM vertical enclosure enhances the thermal comfort of the occupant by reducing the thermal fluctuation and by improving the thermal inertia of the walls. [ABSTRACT FROM AUTHOR]

In this paper the aerothermal heating of a reusable launch vehicle with the material parameters depending on temperature is retrieved. An additional information, necessary for solving the corresponding inverse problem, is taken from the temperature values in the selected point of thermal protection system. Minimization of the constructed functional, defining the error of approximate solution, is executed with the aid of Levenberg–Marquardt method. Whereas the direct problem, needed to be solved in order to determine the value of functional mentioned above, is solved by using the implicit scheme of the finite difference method. In this approach a system composed from three layers is considered, which represents an integrated thermal protection system with material parameters depending on temperature. [ABSTRACT FROM AUTHOR]

Current heat transfer systems in the industry may result in problems such as low efficiency and environmental pollution. In this paper, the influence of heater power, speed and direction of rotation cylinders, and underfloor heating power are investigated on the Nusselt number in a water-filled enclosure with Pr = 5.4 numerically and experimentally based on the Arduino control unit. The enclosure is under constant heat flux from the bottom wall. Using the mixed-Taguchi method and according to different considered cases, 36-state experiments were designed in the range of 2 × 10 8 < R a < 8 × 10 8 and R e < 4000. The problem was simulated by using the Realizable k-ε turbulence model, in 3D steady-state mode. Isotherms and streamlines were reported for each case and analysis revealed that the speed of rotation and the heater power has a more important role than other parameters on the heat transfer rate. In the best situation with a maximum speed of cylinders (S = S (max)), maximum floor heating system ( q f ˙ = q f ˙ (max)) , and maximum power of the heater ( q r ˙ = q r ˙ (max)) the Nusselt number is 110.5 with an almost 22% increase in heat transfer rate. A polynomial surf fit for Nusselt number according to Re, Ra proposed and there are three parts to the variation range of Nusselt numbers based on Richardson numbers. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite a variety of techniques available for thermal conductivity measurement, there is a lack of methods to directly measure the radial thermal conductivity of a cylinder. This presents a critical gap in heat transfer metrology, particularly in presence of anisotropic thermal conduction, such as in a Li-ion cell, where radial thermal conductivity plays a key role in determining performance and safety. This paper reports a technique for measurement of radial thermal conductivity of a cylinder by accounting for variable heat flux into the cylinder when heated on the outside. It is shown that heat flux into the cylinder from a thin heater wrapped around its surface varies significantly with time. This variation, which was neglected in past work, is accounted for by developing a variable heat flux model for experimental data analysis. For two different materials, measurements of radial thermal conductivity using this approach are shown to be in close agreement with standard thermal conductivity measurement using the transient plane source method. Radial thermal conductivity of a 26650 Li-ion cell is measured to be 0.39 W/mK. Besides contributing a new approach for thermal metrology in cylindrical systems, this work also improves the understanding of thermal phenomena in Li-ion cells. [ABSTRACT FROM AUTHOR]

The solid-liquid phase change process in a cavity with protruding heater is of significant importance to application of phase change material (PCM). In this paper, the phase change lattice Boltzmann (LB) model has been applied and the effects of heater and inclination angle of cavity on phase change process are investigated. The results show that moving the protruding heater is able to change the temperature distribution and location of solid-liquid interface. The phase change process can be accelerated by moving the heater to middle region of cavity. Decreasing the distance between heater and cavity upper wall enhances the flow obstruction, and reduces the heat transferred through upper and right walls of heater. Furthermore, rotating the cavity changes the distance of flow from heater to cavity. Increasing inclination angle from 30° to 45° enhances the heat transfer rate of heater's upper wall and weakens that of heater's right wall. [ABSTRACT FROM AUTHOR]

An accurate model and numerical method to simulate heat transfer for radiative heating of granular media is developed based on a modified Monte Carlo – ray tracing method and the Mie scattering theory. The effect of scattering on the radiative transfer and heat diffusion in semi-transparent polymer powder beds during laser sintering process is investigated via a 3D numerical model based on Discrete Elements Method (DEM) specifically developed for this purpose. In particular we show that DEM in combination with the specially developed Monte Carlo method is far more suitable to simulate radiative heat transfer and heat diffusion in a granular bed, polymeric or metallic, than the Finite Element Method (FEM). The method presented in this paper is particularly suitable for the simulation of additive manufacturing processes where similar radiative phenomena are of central importance. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental investigation of the heat transfer performance of a phase change material (PCM) based composite 72 pin fin heat sink subjected to individual heat loading of 4 discrete heaters of equal area. The investigation is then followed by multi objective optimization of the individual heat inputs, wherein the total power of the heaters is fixed. The PCM used is n-eicosane and the heat sink is made of aluminium. First, in house experiments are conducted for different combinations of power. The hotspots imposed by spatially non uniform heat flux are seen to have a considerable effect on the melting and solidification cycle and hence on the thermal performance of the heat sink. The diversity in the performance of heat sink motivates us to perform a multi objective optimization using Non-dominated sorting genetic algorithm (NSGA-II) to determine the optimum combination of the discrete power levels, that stretches the charging period and minimizes the discharging period of the heat sink simultaneously. The solutions obtained thus obtained are validated by conducting in house experiments. This study establishes the fact that discrete heating scenarios have to be considered in the future optimization of the heat sinks. [ABSTRACT FROM AUTHOR]

The numerical work presented in this paper concerns the three-dimensional simulation of the natural convection in a liquid film contained in a cylindrical container with a bottom of solid substrate heated from below by a non-uniform heat flux. Both buoyancy and thermocapillarity are considered in addition to heat conduction within the solid substrate. The Navier–Stokes and energy equations are solved by a 3D finite volume method. Original morphologies of stationary convective cells (type and number) are observed. The flow patterns were found to depend on several studied dimensionless numbers, which are Rayleigh, Biot and Marangoni numbers, and on the ratio of the thermal conductivities of the solid substrate and the fluid. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a numerical study of heat transfer from spheres settling under gravity in a box filled with liquid. Three-dimensional Lattice Boltzmann Method is applied to simulate fluid-particle interaction. Firstly the developed numerical model is validated in comparison with experimental and numerical data for a falling sphere in a box filled with liquid. Then the effects of Reynolds, Prandtl and Grashof numbers (Re, Pr, Gr) are investigated for a settling particle at fixed/varied temperature. The time variations of velocity, height and Nusselt number of the settling particle are also investigated. The results depict that the maximum settling velocity of the particle at varied surface temperature is higher at lower Reynolds numbers. As the Reynolds number increases, the settling velocity of the particle for both cases of constant and varied temperature is the same. However, the Nusselt number of the particle at varied temperature is lower compared with that for the particle at constant surface temperature. Increasing the Grashof number leads to slower settling and larger average Nusselt number. Finally sedimentation of 30 hot spherical particles in an enclosure and their hydraulic and heat transfer interactions with the surrounding fluid are studied. The results depict how the presence of heat transfer phenomena can significantly alter the behavior of settling particles. [Copyright &y& Elsevier]

Abstract: This paper deals with the numerical solution of a three-dimensional model of nonstationary nonlinear heat transfer in the sapwood of trees during sap flow measurement by a thermodynamic method based on volumetric heating of a stem segment (Trunk Heat Balance – THB – method). The model respects the dependence of physical properties on temperature and moisture and also the anisotropic nature of wood. The corresponding partial differential equation is then solved by finite element method. The main aim of this study was to analyze the thermal inertia of the THB method with horizontal references thermocouples. We compared the results of the simpler stationary and the more complex nonstationary model and we can conclude that the thermal inertia of the THB method is not negligible (mainly for smaller flows around 0.01 kg m−2 s−1). In addition, the authors have shown that the influence of moisture on the recorded sap flow data Q rec is negligible but there is small influence on Q fic and hence on the resulting sap flow measurement as was shown in their previous work. We also tested two new variants of temperature sensors arrangement and proved that the difference between them is very small and can be ignored. [Copyright &y& Elsevier]

Abstract: Patients with obesity often suffer pain and risks arising from complications in their pursuit for a trimmer figure. Therefore, an effective and safe treatment for obesity is urgently needed. In this paper, we propose a novel minimally invasive way to treat the target obesity tissues via alternative cooling and heating produced by a microprobe. The validity of the method was evaluated through both numerical simulation and differential scanning calorimetry (DSC) experiments. Theoretical prediction presents the significant effect of typical surgery and assesses the influence of various temperature boundary conditions on the microprobe to obtain the ideal therapeutic effect. An estimation standard was also established on the basis of cryolipolysis and hyperthermia. The DSC test confirms physical and chemical changes in cells during the cooling and heating process. The treatment planning will be varied with operational target, such as longer or shorter treatment time, one or multiple probes, etc. The 3D reconstruction employing MATLAB shows a simulated destruction area. This work is expected to serve as the foundation for identifying a new cure for obesity. [Copyright &y& Elsevier]

Abstract: Fluid flow with phase change heat transfer in a three-dimensional porous channel with asymmetrically heating from one side is numerically studied in this paper. The “modified” Kirchhoff method is used to deal with the spatial discontinuity in the thermal diffusion coefficient in the energy equation. The velocity and temperature fields, as well as the liquid saturation field on the heated section of the wall with different Peclet and Rayleigh numbers are investigated. The results show that the liquid flow bypasses the two-phase zone, while the vapor flows primarily to the interface between the sub-cooled liquid zone and the two-phase zone. An increase in the Peclet number decreases the two-phase region while an increase in the Rayleigh number helps to spread the heat to a larger region of the domain. The distribution of the liquid saturation on the heated section of the wall indicates that the minimum liquid saturation increases with the increase of both the Peclet and Rayleigh numbers. [ABSTRACT FROM AUTHOR]

Abstract: The transient behavior of two-phase flow and heat transfer in a channel filled with porous media was numerically studied in this paper. Based on the two-phase mixture model, numerical solutions were obtained using the Finite-Volume Method (FVM). Two methods to treat the discontinuous diffusion coefficient in the energy equation, i.e. the harmonic mean method and the “modified” Kirchhoff method were compared. It was found that the “modified” Kirchhoff method was better in dealing with the rapid change in the diffusion coefficient. Three different cases, with discrete heat flux applied at (1) the upper wall, (2) lower wall and (3) both the upper and lower walls were studied. The velocity and temperature fields for these cases were discussed. The results show that the liquid and vapor flow fields, as well as the temperature and liquid saturation fields have distinctly different features with the change in heating location. An analysis of the vapor volume fraction indicates that the largest amount of vapor with the highest vapor generation rate was for the case in which the heat flux is applied from the lower wall. [Copyright &y& Elsevier]

Abstract: The effect of internal absorption and emission of radiation on the heating and melting of a semitransparent solid particle has been theoretically studied by characterizing the local radiative transfer inside the particle. Different radiative models affecting the heating and melting processes are discussed in the paper. The study reveals that the melting rate of a particle is significantly enhanced by the internal absorption of radiation. For small particles, the interior temperature distributions in the solid phase are rather uniform throughout the melting process. From the numerical results obtained it is evident that the uniform volumetric absorption and emission of radiation model may be an acceptable approach for evaluating the melting rate of a spherical semitransparent particle if the computation time is of major concern. [Copyright &y& Elsevier]

New heating technologies are constantly being developed worldwide, specially the electrical ones that take advantage of renewable energy. In this paper, the Basic Cell of Energy Transference (BCET) is proposed as an innovative fluid heater, carrying a microwave-fed heat transfer plate for thermal contact. A fully-dimensional thermo-fluid analysis was implemented and validated to determine the key design parameters and operation features for heat transfer to temperature-sensitive working fluids. Circulation patterns were observed, when using certain fluids, in turn causing strong temperature non-uniformities. As fluid treatment in the heater relies on the thermal contact at its active plate, the model was used to ascertain the undesired excess/lack temperature range for quality/safety treatments, with reference to a final effective process temperature. Therefore, a geometry optimization by means of internal baffles was carried out which ensured variation to fluid pattern and more uniform active plate temperature. In a base case, the new design allowed to limit the uncontrolled temperature excess by almost 30%, while favouring the pressure drop reduction across the flow device by more than 10%. [ABSTRACT FROM AUTHOR]

In this paper, effect of the heaters' clearance on mixed convective cooling performance in a discretely heated horizontal duct is examined. Tests are carried out for a constant value of the modified Grashof number (G r D h * = 1.15 × 107), and for Reynolds numbers (R e D h ) between 792 and 3,962. In the analysis, surface to surface radiation and wall conduction are coupled with convective heat transfer. Experiments involve measurements of surface temperatures and air velocity while ANSYS Fluent is used to conduct numerical simulations. Variations of the local surface temperatures, hot spot temperature, global conductance (C) and effective Nusselt number (N u e f f ) with Reynolds number (R e D h ) are presented. Finally, it is disclosed that up to 10.77% reduction in the hot spot temperature and an improvement of up to 20.84% in the system's global conductance can be achieved with an increase in the clearance. • Mixed convection in a discretely heated horizontal duct is investigated experimentally and numerically. • Varying combinations of active and passive heat sources are examined. • Increasing the clearance has a positive effect on cooling performance. [ABSTRACT FROM AUTHOR]