Search

Fluids in computational hydrodynamics are often considered Newtonian, meaning a constant viscosity, but that is just a crude approximation for many real-world examples. Accounting for Non-Newtonian behaviour can provide a significant improvement in simulation accuracy. We present a meshless solution for the natural convection of a power-law non-Newtonian fluid driven by differentially heated cavity walls. The Navier-Stokes and heat transport equations are coupled using the Boussinesq approximation and numerically solved with the generalized finite differences, explicit Euler stepping and Chorin's projection method.

Thermal energy storage (TES) effectively contributes in the energy efficiency improving and the energy supply/demand discrepancy eliminating of solar thermal technology. Among the different types of TES, phase change materials (PCMs) exhibit a high thermal energy density per unit mass. The present work numerically investigates the melting process of PCM (RT82) in a quadruple tube heat exchanger (QTHX). ANSYS (Fluent) version 18.2 software program is used to develop a 2D numerical model for the melting process of the QTHX, and pure conduction and natural convection are considered in the simulation. Two models of QTHXs are studied with respect to the PCM position in the tubes. In model (a), the PCM inserted in the first tube and the third tube while in model (b), the PCM inserted in the second tube and the fourth tube. Moreover, the melting process of the QTHX is compared with a triplex tube heat exchanger (TTHX) and double pipe heat exchanger (DPHX). The computational results indicated that the melting rate of model (b) was achieved in a 63.2% of that of model (a). In addition, the results indicated that PCM was melted earlier in the QTHX compared to TTHX and DPHX. The numerical model was validated with a previous experimental work. Numerical results show a consistent agreement with the experimental results.

Magnetic barrier coupled primary permanent magnet linear motor (MBCPPMLM) has broad application potential in rail transit drive system. In order to improve the operation reliability, this paper studies the temperature field of MBCPPMLM. Based on the analysis and elaboration of the heating mechanism of the motor, with the help of the finite element analysis software, the three-dimensional simulation model of the motor is built, the temperature field is simulated and analyzed, and the temperature field distribution law of the motor under the condition of natural convection is obtained. The fan cooling system is used to suppress the temperature rise of the motor. Through the finite element analysis software, the highest temperature of this kind of motor is armature winding. Under the natural convection condition, the highest temperature can reach 111.79 °C. After using the fan cooling system, the highest temperature of armature winding drops to 65.86 °C, decreasing by 45.93 °C. It has a significant effect on the temperature rise control of the motor. It provides a reference value for the research of temperature rise and cooling system of this kind of motor.

Thermal performance of the pin-fin heat sink cooled by natural convection is numerically investigated when the fin density is allowed to vary along the flow direction. The distribution of the fin density is thermally optimized by using a compact modeling method, in which the pin-fin heat sink is modeled as a fluid-saturated porous medium. In the porous region, the volume-averaged governing equations are used; the Brinkman-Forchheimer-extended Darcy equation for fluid flow and the one-equation model for heat transfer. Based on the analogy between convective heat transfer between the fin and air and that carried by the fluid flowing through the porous medium, a new model for the effective thermal conductivity is proposed. The proposed model is validated by the experimental data available in literature and the numerical results obtained from a direct numerical simulation. For minimal thermal resistance, optimization is conducted using the Kriging method under the constraint of fixed base plate and fin height dimensions. As a result, the optimal distribution of the fin density is obtained as a function of the porosity (ϕ) along the flow direction. The optimal distribution of the fin density is found to be monotonically increasing from ϕ = 0.898 to ϕ = 0.946, which indicates the densely-populated fins in the lower part and the coarsely-populated fins in the upper part. Consequently, the optimized pin-fin heat sink with variable fin density has 11% lower thermal resistance and 30% less weight than those of the uniformly-populated pin-fin heat sink with ϕ = 0.891 optimized using an existing correlation. Owing to its improved thermal performance and reduced weight, the pin-fin heat sink with variable fin density is expected to be a promising solution for more efficient thermal management of electronics cooled by natural convection.

Thermal storage can be implemented using Phase-Change Materials (PCM), which absorb significant latent heat with a relatively small temperature change. PCM phase-change processes are transient and are driven by thermal diffusion and natural convection – the latter, especially for melting process. Modeling and simulation of PCM heat exchangers is typically computationally intensive due to the relative complex time-dependent underlying physics. This paper presents a study investigating a single straight tube with circular transverse fins in the vertical orientation, using PCM’s with 37°C nominal melting temperature, leveraging automated parametric CFD simulations. The computational domain is reduced to 2D axisymmetric for a segment of the HX comprising a region in between two fins with constant wall temperature as boundary condition. This approach allows for faster evaluations of the transient thermal characteristics for a given design space of interest. Correlations and reduced order models (ROM’s) are developed. Results indicate that the ROM’s reproduce the CFD simulations with high accuracy for designs from the training data set, however, designs from cross-validation and test sets do not always have good agreement. The limited number of designs in the training set is a possible cause for the lack of robustness of the ROM’s and thus additional training designs will be added in future work. The ROM’s solve the simulations on average 500,000 times faster than CFD.

In this paper, numerical simulations are carried out on steady natural convection of Al 2 O 3 -H 2 O nanofluids within a square enclosure, and the interaction effects of an inclined magnetic field and heat transfer behaviors are investigated. The Buongiorno’s two-phase mixed model is adopted with two slip mechanisms: thermophoresis and Brownian diffusion. The heat transfer transition is first detected by increasing nanoparticle volume fraction for various Rayleigh numbers. Effects of magnetic intensity and magnetic declination are further investigated. It is found that the critical Rayleigh number changes nonlinearly with the increase of the inclined angle, and the heat transfer deduces with the raise of the magnetic strength. The relationship between the heat transfer rates and the magnetic inclination is dominated by the strength of magnetic field, where the distribution changes from asymmetric mode to symmetric mode with the growth of magnetic intensity.

The three-dimensional flow of Water based Graphene Oxide (GO-W) and Ethylene Glycol based Graphene Oxide (GO-EG) nanofluids amongst the binary upright and parallel plates is considered. The unsteady movement of the nanofluid is associated with the porous medium and the uniform magnetic field is executed in the perpendicular direction of the flow field. The basic governing equations have been altered using the Von Karman transformation, including the natural convection in the downward direction. The solution for the modeled problem has been attained by means of optimal homotopy analysis method (OHAM). The influence of the physical parameters on the momentum boundary layer, pressure, and temperature fields is mainly focused. Moreover, the comparison of the GO-W and GO-EG nanofluids under the impact of physical constraints has been analyzed graphically and numerically. The imperative physical constraints of the drag force and heat transfer rate have been computed and discussed. The results have been validated using the error analysis and the obtained outcomes have been shown and discussed. The obtained results are compared with the numerical ND-Solve method. It is obtained that the increasing order of the iterations reduces the absolute error and the results go to the strong convergence. Moreover, the impact of the physical parameters is more precise in the GO-EG nanofluid due to its higher thermophysical properties.

A novel flexible woven heat sink (FWHS) composed of sintered copper braided belts was proposed here to meet the heat dissipation requirements of the flexible radiator installed in a narrow space. The sintering treatment was employed to ameliorate the tensile and bending properties as well as the thermal conductivity of the FWHS. The thermal resistance network model and the temperature field analysis in cases of natural convection and forced convection were presented to evaluate the thermal performance of the FWHS. The results show that the FWHS sintered at 850 °C with the expanded shape at a compressed height of 55 mm can reduce the temperature of heat source by 17.1% compared to the uncompressed FWHS, which demonstrates its outstanding advantage of maintaining high efficiency of heat dissipation under compressive deformation.

This research paper deals with the study of hybrid nanofluid flow with free convection in a permeable media using CVFEM. Hybrid nanoparticle (Fe3O4 + MWCNT) with base fluid H2O has been assumed. The magnetic effect is applied on hybrid nanofluid. In addition, the Non-Darcy model is used and the source term of radiation influence has designated for innumerable forms of nanofluids. Flow design was described for wide range of examined parameters. It proved that augmenting the porousness factor can increase the Nusselt number, but converse performance is conveyed for Lorentz forces. The convective nanomaterials flow intensity enhances with increase of penetrability and stronger thermal effect. Augmented magnetic field produces feebler convective flow and inferior temperature gradient. As temperature of heat source reduces with rise of Hartmann number, Nuave decreases and greater exergy loss occurs.

This article addresses the estimation of the thermal conductivity k and the specific heat capacity Cp of a synthetic nanocomposite, by coupling a laser-based experiment and a reduced model-based inverse problem solved via a Finite Element Method (FEM) approach. The associated multiphysics problem can be described as an optical-radiative-thermal coupled process where a laser source is irradiating the sample corresponding to an Epoxy-Based Vitrimer (EV) with dispersed gold nanoparticles (NPs). A 1D reduced model for an infinite slab (having both boundaries subjected to natural convection and under certain conditions on both experiment and material properties) has been used to solve the forward radiative transfer problem involved, in order to achieve an initial approximation for the equivalent thermal source Q. This approximation is then used in the heat transfer equation, whose solution is computed using the finite element method (FEM). The corresponding statistical solution for the thermal conductivity k and the heat capacity Cp is calculated by the inversion of the T-thermocouple temperature time series measured at the center of the irradiated specimen, using a stochastic version of the Levenberg-Marquardt algorithm by embedding the algorithm inside a Monte Carlo routine. Reduced models have been analyzed for 1D and 2D reduced geometries as well as approximations for Q in the 3D case. Results show a confidence interval for the achieved estimates of the thermal parameters in a good agreement to the Differential Scanning Calorimetry (DSC) referential values. As a conclusion, even when the performed laser remote heating experiment has been developed as a self-healing process, it also appears to be a very promising Non-Destructive Testing (NDT) methodology for retrieving the thermal parameters along with the proposed computational approach in some thermosetting polymers, such as the EV studied here.

temporal dependency of electrical conductivity of cartilage in course of laser heating by pulse periodical radiation in the condition of natural convection was studied. Various ranges of non-monotonic behaviors of temperature dependency of the conductivity have been revealed.

Overheating is one of the key factors affecting the normal service life of switch cabinets. Therefore, it is of great significance to find out methods to reduce the temperature rise of the switch cabinet. In this paper, based on a 400V low-voltage switchgear, a three-dimensional simulation model is established using the electromagnetic-thermal-fluid multi-physics coupling method. Under the conditions of simulating natural convection, considering eddy current effects, proximity effects, and skin effects, heat transfer methods such as thermal conduction, thermal convection, and thermal radiation are comprehensively used to calculate and analyze the thermal distribution characteristics of the distribution cabinet shells and three-phase current-carrying conductors. Moreover, a temperature-rise experiment is performed to verify the feasibility and accuracy of the electromagnetic-thermal-fluid multi-physics coupling method and the accuracy and effectiveness of the calculation model under the current simulation conditions. In addition, in order to reduce the temperature rise of the cabinet, A strategy for optimizing the switchgear is proposed, and the heat distribution characteristics of the optimized model is calculated using the multi-physics coupling method. The results show that the temperature rise of the switch cabinets of the scheme has been reduced in different degrees, which effectively solves the overheating problem of the switch cabinet.

Cooling of photovoltaic panels (PV) by using phase-change materials (PCM) becomes a popular research technique due to the high latent energy storage capacity of PCMs. Therefore, the acceleration of phase-change process and reducing the required time for energy charging and discharging turns out to be a crucial point in these applications. Utilization of fins is an effective way for phase-change acceleration as it promotes heat diffusion into the material and shortens the phase-change time. Besides, the branching fins are also introduced by researchers in order to further accelerate the charging/discharging process by providing larger surface area for the same volume compared to rectangular fins. However, once the melting process is completed, the natural convective heat transfer may be promoted or degraded by the fins, which is worth to be investigated. For this reason, the natural convection heat transfer in a rectangular enclosure that represents a PCM container in a PV/PCM system is numerically investigated in this study by considering three aspect ratios (AR=1, 2 and 4), three Rayleigh numbers (Ra=104, 105 and 106) and two types of fins as rectangular and tree-like branching fin. The rates of increment and decrement in the heat transfer rate are presented taking the finless enclosure as the reference case. The Prandtl number of the molten phase-change material is calculated as 41.22 and kept constant during the simulations. The outcomes of the simulations are presented in terms of streamline and isotherm contours, and mean Nusselt numbers. The computed results revealed that the natural convection can be promoted up to 13% or degraded by 4.5%, depending on Ra and AR by the inclusion of fins. Besides, it is also noticed in this study that utilizing a tree-like branching fin is not as effective as a rectangular fin with the same mass.

This paper presents a methodology to evaluate and analyze the volumetric power density of planar magnetics used in power electronics converters. The power density is computed for various EE and E/PLT cores considering optimal configurations for the planar transformers' design and for its cooling heatsink. The analysis is performed for three cooling configurations: natural convection without heatsink, single sided cooled component with one heatsink, and double sided cooled with two heatsinks. This study can be very useful for designers to evaluate their design specifications and to adapt their technological choices to achieve the desired planar magnetics' characteristics.

Passively cooled housings for modern power electronic converters with high power density require maximum heat dissipation over little surface area. To determine the power dissipation budget, this paper presents thermal measurement based convection modeling with temperature dependent heat transfer coefficients and the derivation of efficiency requirements for given housing dimensions.

IEEE Standard 1407 provides guidance on accelerated insulation aging experiments on multiple medium voltage (MV) power cables using water-filled tanks. An applied cable current increases the temperature within the water tank and thus provides the accelerated aging conditions for the cables. Understanding the precise nature of the temperature distribution within the water tank and within the cable insulation is important to quantify and calculate the effective aging of the cables. This paper presents initial finite element analysis (FEA) simulation studies that evaluate the temperature distribution within a water filled tank and across submerged power cables when multiple cables are supplied with current. Two scenarios are evaluated and compared, namely the temperature profiles of cables when the water in the tank is treated (a) as a solid material, and (b) as a fluid with natural convection. The importance of applying effective water circulation mechanisms are also highlighted.

This work describes the electromagnetic and coupled thermo-fluid dynamic analysis of an oil-natural air-natural (ONAN) distribution transformer with the main objective of studying the changes in the heat dissipation performance when the fluid employed to cool the machine is a biodegradable ester instead of mineral oil. The distribution transformer under analysis has a rated power of 315 kVA with a voltage ratio of 13.2 kV / 0.4 kV. The heat losses in the magnetic core and the windings are computed with the ANSYS Maxwell software on suitable finite element meshes. These heat losses are then transferred as volume heat source terms to appropriate finite volume meshes which are used to compute the heat conduction in the core and windings, then the heat dissipates to the oil by convection, afterwards to the walls of the oil tank and to the radiators panels and finally to the surrounding air. In the thermo-fluid dynamic model, the natural convection of the fluid flow is taken into account using a temperature-dependent density. Moreover, the heat conduction through the metal sheet of the oil tank and the radiators panels are considered. The coupled thermo-hydraulic problem is solved with Code_Satume software. The experimental data of the total power losses provided by the unit manufacturer were employed to validate the electro- magnetic model. Because the thermo-fluid dynamic numerical model is computationally expensive, only one quarter of the transformer is modelled. In addition, equivalent anisotropic thermal conductivity in the core and windings are calculated to simplify the heat conduction model in the active parts. The differences in the temperature distribution and oil flow observed between the transformer working with a standard mineral oil and a biodegradable ester are discussed. This work is carried out as part of the EU Horizon 2020 BIOTRAFO project.

Thermal management is necessary to dissipate heat from semiconductors while keeping system efficiency high. There is a clear need for compact, effective, reliable, high-capacity, and quiet, passive cooling systems in the power electronics industry. A novel Smith-Volterra-Cantor (SVC) set fractal heat-sink is introduced and numerically investigated for natural convection. The SVC fractal pattern increases the heat transfer area and interrupts the thermal and aerodynamic boundary layers. The heat-sink mass and size are reduced with the SVC fractal design compared to the classical ones that make compact passive cooling system design feasible. The thermal performance of the fractal heat-sink is detailed, considering the fin scale and surface heat flux. The analysis indicates mass normalized fin effectiveness is improved, and the temperature is more uniformly distributed for fractal design. These results are applicable for the development of compact power-electronics passive thermal management design for telecommunication and aviation applications with reduced parasitic powers, noise, and vibration.

Considering significant worldwide use of electricity for general lighting, the implementation of energy efficient technologies is highlighted in many platforms with the use of light emitting diodes (LEDs). Because of its environmentally friendly nature, LEDs offer a promising solution to minimize inefficient use of energy as the demanding operating conditions pose new challenges. Reduction of lumen output, shorter lifetime and degradation of light characteristics with increasing package temperatures are critical issues that need to be addressed with innovative solutions. Especially in high power LEDs exposed to raised heat fluxes, standard cooling methods fail to remove the dissipated heat effectively. Recently, immersion cooling of LEDs with suspended phosphor particles in a dielectric liquid has been offered as a viable option to dissipate a vast amount of heat, ensuring a uniform distribution of temperature, and removal of local hot spots in a high brightness LED package. Therefore, understanding the fluid flow and particle motion due to natural convection in the package is crucial to improve thermal and optical design of an LED system. Temperature distribution and light extraction of a package can be considerably affected by material characteristics, flow regime and flow direction. In this study, the impact of different heat generation rates of an LED package is investigated considering natural convection currents and corresponding phosphor particle trajectories inside a fluid domain. A discrete phase model of a high-power white LED package is created in order to keep track of individual particles interacting with the carrier fluid and heat flow in a closed LED system. Current findings provide good basis for smart control of phosphor particles to maximize thermal and optical performance of both RGB and white LED packages.

This study aimed to investigate performance of ARM-based computer clusters using two-phase immersion cooling (IC) approach, and demonstrate its potential benefits over the air-based natural convection (NC) and forced convection (FC) approaches. ARM-based clusters were created using Raspberry Pi (Rpi) model 2 and 3, a commodity-level, single-board computer. The IC mode utilized two types of dielectric liquids, HFE-7100 and HFE-7000. Experiments involved running benchmarking programs Sysbench, and the combination of Sysbench and High-Performance Linpack (HPL), in order to quantify the key parameters of device junction temperature, operating frequency, execution time, computing performance, and energy consumption. Results indicated that the device junction temperature has direct effects on the computing performance and energy consumption. In the reference NC cooling mode, as the temperature approached the preset limit, the Rpi-3 cluster either decreased its operating frequency to save the internal cores from damage, leading to decrease in computing performance and increase in execution time and energy consumption (in the Sysbench test), or shut down all the nodes (in the HPL test). When the Rpi-3 cluster was exposed to a heavy load (combined Sysbench and HPL test) the IC modes compared to the FC mode indicated similar execution time, up to 3% higher computing performance, and up to 10% lower energy consumption. Although the results for the considered Rpi clusters do not represent a significant improvement, this study demonstrates that the two-phase IC method with its near-isothermal, high heat transfer capability would enable fast, energy efficient and reliable operation, particularly benefiting high performance and large scale computing applications where conventional air-based cooling methods would fail.

Electrical equipment and microprocessors distribute power and generate and/or dissipate heat due to the resistance and impedance of the various electrical components in any given circuit. That results in complications pertaining to the device functioning, failure, or damage to the component. As such, the electronic component’s temperature should be kept below a safe temperature by employing efficient thermal management system to prevent premature component failure. Numerous cooling techniques for electrical systems have been investigated such as heat sinks, direct and indirect cooing, thermoelectric coolers, and heat pipes. Traditionally, heat sinks have been notable and well-known form of electronic cooling in which they harness forced as well as natural convection to cool electronic components. On the other hand, indirect channel cooling using structured channels have been of interest for developing cooling systems for different applications. In this work, indirect air-cooling utilizing turbulence promoters in structured channel flow is investigated numerically. Numerical modeling is employed and the results are verified against experimental data in literature. Grid independence study is performed and the flow field characteristic and thermal advantage of structured ribbed channels are analyzed.

Electronic devices continue to become smaller, more sophisticated and faster performing, needing to dissipate the heat generated in smaller areas. Researchers have turned to unconventional methods to enhance the local heat transfer rate in small, confined spaces, such as synthetic jets. These jets use oscillating flow, which have a zero net mass flux, to produce jet flow through a given orifice. These devices have a significant momentum flux, creating vortex rings that increase mixing and the heat transfer rate. Previous experiments have shown that a contracting orifice diameter can produce a higher momentum flux, enhancing the heat transfer rate by up to 6 times that of natural convection. This used a mechanical aperture, which presented problems with miniaturization as well as fatigue strength. To avoid this issue, a virtual orifice is developed, which siphons fluid via a bypass slot and redirects it radially inward to the primary flow as it exits the orifice. The virtual aperture reduces the complexity of the design and the volume needed. Computational fluid dynamics simulations were used to optimize the geometry for the design, selecting dimensions for optimal exit speeds and impingement plate cooling. Simulations demonstrated that the virtual orifice synthetic jet produced a 5% increase in convective heat transfer rate compared to an ordinary synthetic jet with the same characteristic dimensions. The design was fabricated and used to cool a square heater mounted on an impingement plate. The heater temperatures were measured for distances ranging from 2 to 8 jet diameters, showing comparable performance to the simulations. The virtual orifice design did not prove as promising as originally hoped, only providing a 3% increase in heat transfer, and should be looked at for other applications such as flow control or propulsion.

The energy yield loss of PV modules due to soiling is an important performance factor and can become catastrophic in dusty environments. As the environmental conditions vary from region to region, soiling also varies, and its evaluation is a challenging element in the field of PV research. For that reason, an advanced laboratory soiling setup was developed for the evaluation of the anti-soiling performance of glass coatings under different soiling and controlled environmental conditions. The sequential methodology allows for testing the impact of environmental parameters individually. Within this study, we present an in-depth analysis of the influence of surface and ambient temperatures, relative humidity as well as tilt angle on the dust deposition. It is shown that - depending on particle size - the effects of natural convection, thermophoresis, capillary condensation and rebound can have crucial impact on soiling and the outcome of laboratory soiling tests.

A numerical model is built to simulate two-phase flow and heat transfer performance in an axial rotating heat pipe. The volume of the fluid is used to describe two-phase flow and heat transfer characteristics. A mixed phase transition model with pure heat conduction and natural convection is studied. Based on mixed phase transformation model, the change rules are analyzed on the characteristics of two-phase flow and heat transfer such as heat load, filling, rotating speed and working medium. The results are compared with the experimental results in order to explore the mixed phase transformation model. The results show that the mixed phase transformation model is agree with the experimental results. The heat load and filling make little effect on the heat transfer performance. As the rotating speed increase, the heat transfer performance is enhanced. The physical properties of working medium have great influence on the heat transfer performance. It is concluded that the numerical model is a useful method to simulate the flow and heat transfer in an axial rotating heat pipe.

We performed 3D simulations of the temperature field and velocity field in the Czochralski (Cz) process by using computational fluid dynamics (CFD) analysis software. With the obtained velocity field and temperature field in the Cz process, we showed the relative intensity of natural convection and forced convection under different rotation speeds of the growth process based on the Boussinesq approximation and by considering the conduction, convection, and radiation of heat. We simultaneously simulated the change of natural convection and forced convection due to the fall of the liquid surface level in the crucible used for Cz growth. The results will help guide Nd:YAG Cz growth with large diameters and high quality.

A key component of the concept of Smart City is the use of energy efficient technology for household and nonresidential building applications. In this context, the study presents an experimental setup with phase change material (PCM) encapsulated in spherical shells and an analysis of phase change materials for energy efficient cold storage applications using air as heat transfer fluid. The solidification and melting processes are investigated and compared with the thermal behavior indicated by the differential scanning calorimetry (DSC) signals generated at cooling and heating rates of 0.1 K/min. The solidification and melting experiments were carried out at a mean air velocity of 0.837 and 0.833 m/s, respectively. The temperature differences between the peak phase change temperature and the mean air temperature are 20.87 and 17.21 °C, for solidification and melting, respectively. It was observed that melting occurred at a higher rate than solidification due to natural convection. Melting completes (3–12) minutes faster than solidification depending on the position of the sphere in the thermal setup. Because of the natural convection some deviations between the experimental and differential scanning calorimetry heating rates were observed. The experimental thermal storage is capable to reduce the air temperature with approximately (7.54-14.61) °C, at melting.

Forced convection thermal management solutions require high heat transfer coefficients, electrically efficient operation, small form factors, reliability, and low noise. Piezoelectric synthetic jets capture all of these requirements. U sing a high aspect ratio synthetic Dual Cool jet (DCJ) (AR = 44: 1), heat transfer coefficients of nearly 200 W/(m2K) were achieved while the operational frequency was maintained at 170 Hz in the vertically oriented position above a heated surface. Normalized heights of $\mathrm{y}/\mathrm{D}_{\mathrm{h}}=2,5$ , and 10 were tested over an Amkor Thermal Test Vehicle (TTV) subjected to constant heat fluxes ranging from 0.2 to 1.4 W/cm2. The TTV has a spatial resolution of 0.25” (6.6 mm), allowing for spatial temperature measurement along the major axis of the slit orifice synthetic jet. After validation of the DCJ performance over the flat plate, the effect of the inclination angle above the heated surface is examined with two DCJ's facing one another. Over the optimal operational frequency of 170 Hz, angles of 30°, 45°, and 60° were tested. Heat transfer coefficients over 250 W/(m2K) were achieved in this inclined dual DCJ configuration. Regression analysis shows a heat flux dependence on the heat transfer coefficient that exceeds that expected by laminar or turbulent free convection, suggesting that the periodic convergence and turbulent rise of the two coolant streams at the heated surface center exploits the increased energy density for improved thermal performance.

The buoyancy-driven gas flow (air) confined within an enclosed square-section cavity with isothermal walls is investigated numerically using the lattice Boltzmann method (LBM). The right side of the enclosure is partially heated by a hot chip, while, the left one is completely kept at cold temperature. However, the horizontal walls and apart from the chip are kept adiabatic. The buoyancy effect induced by the gravity acceleration, related to the convection force, is evaluated through the Rayleigh number in the range of 103-106(laminar regime). Wall heating-ratio effect on the flow properties such as temperature and velocity profiles. The heat transfer is analyzed through the Nusselt number for different chip lengths. Results show that the wall heat ratio has an interesting effect on flow behavior. Results show good agreement with those of full natural convection simulation in the literature and their experimental data.

In this work, an experimental investigation on the hybrid solar collector in a hot climate is presented. This collector consists of photovoltaic / thermal (PV/T) panel which contains a photovoltaic module and a solar thermal collector. This system produces simultaneously electricity and heat. According to PV/T uses, the collector can be operated with air / water as a using fluid. The combination of a PV panel with thermal collector contributes to temperature increase of the PV module which reduces its efficiency. In order to ameliorate the air-based PV/T efficiency, the hot air should be extracted. In this experiment, a PV/T collector with mono-crystalline cells is designed. The experimental investigation is performed for evaluate thermal and electrical efficiency. The results indicate that the global efficiency of the system is significantly improved; however the electrical efficiency is slightly increased.

Present study reports experimental and computational results obtained for a switchgear, where its critical components such as busbars, and tulip contacts are numerically modeled. In the experiment, thermocouples are used to measure the temperature at several locations of the switchgear at operating condition. One-way coupled EMAG and CFD computations are performed to obtain eddy current losses first, then the temperature and velocity distributions are obtained for the natural convection in and out of the model that is induced by the losses. Comparison of the obtained temperature distributions show that the experimental and computational results are in similar trend in general. In order to understand the causes of local discrepancies in the results, it is considered to conduct computations on a high performance computing environment for a more realistically modelled electrical components.

In this study, an investigation of thermal characteristics was carried out at two stages namely, the experimental stage and the simulation and modeling stage. In the experimental stage, the battery consists of 1 cell with a capacity of 14Ah. At the experimental stage, the battery under investigation works at the discharge currents C1, C2, and C4, with natural convection studies in insulation and non-insulation systems. The assumptions used in this study are the battery used have experienced more than 10 cycles, the heat radiation from the battery is ignored, the parameters and thermal constants are considered constant. The ambient temperature range for operation is at 24°C – 28,5°C. Experimental results show that the battery system under insulation conditions has more stable thermal characteristics compared to non-insulation systems. As well as the results of the simulation stage 1 battery cell under conditions of insulation and non-insulation. In addition, estiomation were also made for the 10 battery insulation system. The temperature rise characteristic shows an exponential graph on all simulations performed. By evaluating the measurement values in the experimental and simulation stages, the results of the non-insulation conditions show an error for the C1 discharging current of 1,77%, C2 of 1,97%, and C4 of 0,38%. The results of insulation conditions show an error for the C1 emptying current of 1,10%, C2 of 0,53%, and C4 of 0,05%.

In this article simulated the process of the emergence of dynamic and temperature boundary layers near a vertically located rod, which is a heat source. The formulated system of partial differential equations with boundary conditions is solved numerically and its algorithm is implemented using the DELPHI graphical environment. The Chart component was used to draw graphs.

A multitude of parameters affect the speed, maximal yield, quality of obtained biogas and several other important factors in the complex process of anaerobic digestion. One of these parameters is the temperature distribution inside the digester. It was noticed that when no form of stirring takes place inside the digester, a temperature gradient forms due to the natural convection phenomenon. The presence of this gradient is undesirable in most anaerobic digestion applications, since it would cause the anaerobic bacteria to suffer from upsetting temperature changes, triggering a noticeable slowdown and even a failure of the process. As stirring would fix this temperature gradient issue, an alternative low-cost solution is investigated in this study. This potential solution manifests in changing the placement of the solid waste layer inside the liquid recirculation digester to allow it to always be at an optimal temperature. Experiments and simulations have been conducted to better understand the thermal behavior of the digester, then a model was developed and validated to numerically simulate the observed phenomena. It was concluded that the occurrence of this gradient is independent of the contents of the digester, while in the same time it was established that the optimal location for the solid waste layer is between the heating elements.

Hollow concrete blocks are the most commonly used materials in building construction due to several factors, including their lightweight, mechanical strength and low cost. This study focuses on the identification of the thermal performances of hollow concrete blocks used in Sale City, Morocco, using the 1D-approximate suggested in EN ISO-6946 [1]. An iterative algorithm based on the equivalent thermal resistance network is described and applied to hollow structures. It should be noted that the heat transfer through the hollow blocks is coupled with conduction., natural convection., and radiation. Firstly., the thermal properties of the basic materials used as input to the numerical calculation were estimated based on experimental methods. In this context., the present work is intended to contribute to a better understanding of the feasibility of using Multilayer wall technology in order to achieve potential energy savings and acceptable thermal comfort condition for the six Moroccan climate zones. The obtained results show that the thermal insulation system must be applied to comply with the requirements of the RTCM.

An experimental study in a naturally ventilated building was conducted in August 2016. It aimed to highlight the energy charge and discharge of a concrete-slab floor submitted to the day-night-cycles heat exchanges in the southwestern part of France and to identify the heat transfer phenomena that take place in both processes (charge and discharge). To highlight the energy charge and discharge processes, heat flux, temperature, and airspeed measurement techniques were implemented. Measurement zones were distributed all over the concrete-floor surface. To identify the heat transfer phenomena that take part in the charge and discharge process, some important dimensionless numbers were used, along with correlation analysis. Experimental data showed that during the charge period, on the floor surface, radiative heat exchanges were significantly higher compared to convection. The contrary was found during the discharge period. After correlation analysis with dimensionless numbers, results showed that forced and natural convection coexist during the discharge period, where more accurate correlations with the Peclet number than with the Rayleigh number were found. This may suggest that forced convection is stronger than natural convection. Yet, airspeed levels encountered suggest that it is natural convection that should take place rather than forced convection.

This paper presents a thermal network model in a steady state condition for thermal management of future smart glasses. It is accomplished by disassembling the state wearing smart glasses into some parts, creating the equivalent thermal resistance circuit for each part, approximating heat generating components such as ICs to simple physical structures, setting power consumption to the heat sources, and providing heat transfer coefficients of natural convection in air. The average temperature difference between the thermal network model and a commercial thermal solver is 0.9°C when the maximum temperature is 62°C. Moreover, the thermal analysis results using the model reveal some important points for thermal design of smart glasses.

The two-dimensional flow structure in a vertical slice with variously heated walls, the dynamics of the vortex structures origination, formation, and interaction were studied. The influence of nonlinear thermal characteristics on the process of heat propagation in the liquid layer is taken into account. A numerical-analytical study of conjectured convective currents of a heterogeneous fluid was carried out using the FreeFem++ software package.