Thermal Heat Sink Research Articles

A three-dimensional thermal analysis and optimization of square light edding diode subcomponents

The purpose of this paper is to assess thermal management and optimization of several parameters such as: materials, size and thickness of all subcomponents of single-chip Light Emitting Diode (LED) in order to minimize its junction temperature and thereby maximizing light output and device reliability.For this, we developed a three-dimensional code using Comsol Multiphysics that solves the systems of equations for the mass, momentum and energy. After validation of this numerical 3D code, the thermal Characterization of Subcomponents of LED system is studied numerically. This system is divided into 6 parts such as: metallization, die, die-attach, substrate, Thermal Interface Material and heat sink. Several materials which can be used in each part of the LED package from metallization to the heat sink are studied. By moving to one part to another, it was selected the best materials always allowing a minimum junction temperature.

Graphene-incorporated aluminum with enhanced thermal and mechanical properties for solar heat collectors

A simple yet innovative approach has been made through a powder metallurgy route for the synthesis of aluminum–graphene (Al–Gr) composite materials for commercially viable solar thermal collectors. The Al–Gr composite (with 1 wt. % of graphene filler content) recorded an enhanced thermal conductivity of ∼280 W/mK, which is higher than that of pristine Al (∼124 W/mK), at room temperature. It has also been found that the prepared composite has a lower coefficient of thermal expansion. The structures and morphologies of the composites have been investigated in detail with the help of X-ray diffraction technique, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, etc. Furthermore, the density measurements showed that the composites retain ∼97.5% of the density of pristine aluminum even after the sintering treatment. X-ray micro-computed tomography revealed the structural integrity and non-porous nature of the samples, free from any defects and deformations. The thermal fusing of Al-based composite materials at 630 °C is found to be satisfactory with the required strength, and the composites showed at least ∼125% increase in the thermal conductivity than that of pristine Al. These results suggest that the Al–Gr composites can be deployed as solar thermal collectors and heat sink materials for thermal dissipation.

Group theoretical analysis for magnetohydrodynamic generalized Stokes’ flow and radiative heat transfer model of a non-Newtonian nanofluid with heat generation/absorption

The fully developed boundary layer flow and heat transfer model of an unsteady, incompressible, electrically conducting, optically thick and thermodynamically compatible third-grade nanofluid are investigated from the viewpoint of Lie symmetry approach. We have studied the Stokes’ model in which flow is generated due to motion of the bounding surface with an impulsive time-dependent velocity. The mathematical model also includes the effect of thermal radiation and internal heat source or sink in the flow regime. Lie symmetry approach is employed to obtain the symmetry algebra of the governing nonlinear partial differential equations for both flow and heat transfer models. The governing nonlinear partial differential equations describing the flow and heat transfer model are reduced to different classes of nonlinear ordinary differential equations under the implication of symmetry generators. The reduced ordinary differential equations are investigated using the compatibility and generalized group theoretical method. The exact closed-form solutions for nanofluid motion and temperature distribution within the boundary layer are obtained. The effect of various thermophysical parameters on the characteristics of flow and heat transfer for Cu-water nanofluid model is explored from a physical point of view.

Unsteady Radiative Natural Convective MHD Nanofluid Flow Past a Porous Moving Vertical Plate with Heat Source/Sink.

In this research article, we investigated a comprehensive analysis of time-dependent free convection electrically and thermally conducted water-based nanofluid flow containing Copper and Titanium oxide (Cu and ) past a moving porous vertical plate. A uniform transverse magnetic field is imposed perpendicular to the flow direction. Thermal radiation and heat sink terms are included in the energy equation. The governing equations of this flow consist of partial differential equations along with some initial and boundary conditions. The solution method of these flow interpreting equations comprised of two parts. Firstly, principal equations of flow are symmetrically transformed to a set of nonlinear coupled dimensionless partial differential equations using convenient dimensionless parameters. Secondly, the Laplace transformation technique is applied to those non-dimensional equations to get the close form exact solutions. The control of momentum and heat profile with respect to different associated parameters is analyzed thoroughly with the help of graphs. Fluid accelerates with increasing Grashof number (Gr) and porosity parameter (K), while increasing values of heat sink parameter (Q) and Prandtl number (Pr) drop the thermal profile. Moreover, velocity and thermal profile comparison for Cu and -based nanofluids is graphed.

Control of crystal growth of intermetallic compounds in Aluminum alloys and their application to novel high thermal conductivity heat sink products

Control of crystal growth of intermetallic compounds in Aluminum alloys and their application to novel high thermal conductivity heat sink products

Lightweight, Superelastic Yet Thermoconductive Boron Nitride Nanocomposite Aerogel for Thermal Energy Regulation.

Conventional three-dimensional (3D) thermal conductors or heat sinks are normally bulky solids with high density, which is cumbersome and not portable to satisfy current demands for soft and flexible electronic devices. To address this issue, here, a lightweight, superelastic yet thermally conductive boron nitride (BN) nanocomposite aerogel is designed by a facile freeze-drying method. The attained aerogel constituting of tailored interconnected binary inorganic-organic network structure exhibits low bulk density (6.5 mg cm-3) and outstanding mechanical performances for compression, clotting, and stretching. Meanwhile, the aerogel has promising thermal stability and high thermal conductivity over wide temperature ranges (30-300 °C), validating the application even in extremely hot environments. Moreover, the aerogel can serve as a lightweight and elastic heat conductor for the enhancement of thermal energy harvest. Interestingly, during alternate strain loading/unloading under heating, the superelasticity and the anisotropy of thermal conductive transduction make the aerogel enable the elastic thermal energy capture and dynamic regulation. Therefore, our findings provide a potential use for the thermally conductive aerogel in future green energy applications.

Soret and Aligned Magnetic Field Effects on an Unsteady MHD Free Convection Casson Fluid Flow Past an Exponentially Infinite Vertical Plate Through Porous Medium in the Presence of Thermal Radiation, Chemical Reaction and Heat Source or Sink

Soret and Aligned Magnetic Field Effects on an Unsteady MHD Free Convection Casson Fluid Flow Past an Exponentially Infinite Vertical Plate Through Porous Medium in the Presence of Thermal Radiation, Chemical Reaction and Heat Source or Sink

Performance and economic limits of passively cooled hybrid thermoelectric generator-concentrator photovoltaic modules

Concentrator photovoltaic technology has doubled the efficiency of conventional non-concentrating photovoltaic systems. However, still ≈60% of the incident energy is dissipated as heat, and costs of concentrator photovoltaics need to be lowered for these systems to be competitive. One promising way for taking advantage of the heat generated in the solar cells is the hybridization with thermoelectric generators. The feasibility of hybrid concentrator photovoltaic-thermoelectric modules has been shown in recently published work for enhancing the efficiency and lowering the cost, with special emphasis on actively cooled designs. However, if feasible, the use of simple and reliable passive cooling would accelerate the development of new hybrid prototypes. The performance and cost reduction limits achievable with passively cooled designs have not yet been studied in detail. In this paper, an electric/thermal/economic model of concentrator photovoltaic-thermoelectric module is developed. As the main novelty, the model allows the thermoelectric generator area to be adjusted. Some optimisation problems are formulated and solved to evaluate the efficiency improvement and cost reduction of the hybrid system in comparison to a typical 800x light concentration factor and 36.4% efficiency concentrator photovoltaic-only module. The analysis showed that optimising the thermoelectric generator area is essential for the cell operating temperature limits not to be exceeded, and that conventional passive cooling is enough for achieving efficiency gains and cost reduction considering a state-of-the-art highly efficient 3 mm × 3 mm triple junction solar cell. With advanced thermoelectric materials and cell temperature of 100 °C, a maximum efficiency of 39.2% for the hybrid system can be achieved at 800x concentration factor by using low thermal resistance heat sinks, and a maximum cost reduction of 46.0% can be achieved at the maximum analysed concentration factor (1900x) by using moderate thermal resistance heat sinks. A trade-off between enhancing the efficiency and lowering the cost was observed. The sensitivity analysis on the thermoelectric parameters showed that parameters other than thermoelectric generator area and ZT figure-of-merit barely influence the results. The existing experimental concentrator photovoltaic-thermoelectric prototypes are far from the efficiency and cost benefits predicted in this paper. Thus, the study can help in the development of future prototypes.

تحلیل ترمودینامیکی یک آرایش جدید ترکیبی با استفاده از چاه های زمین گرمایی سبلان و انرژی سرد گاز طبیعی مایع شده

A new configuration base on the Sabalan geothermal wells is proposed to utilize two wells with different thermodynamic properties in Sabalan region in Iran and generate more power as well as supply of natural gas from liquefied natural gas. A Kalina cycle and Transcritical CO2 Rankine cycle are using Sabalan geothermal wells as a heat source and liquefied natural gas as a thermal heat sink. A comprehensive parametric study is investigated to understand the characteristics of the system. The results show that the thermal and exergy efficiencies can be increased by increasing separator 1&2 pressures. Also decreasing the higher pressure of the Kalina cycle and pinch point temperature of evaporators lead to increasing the net output power, thermal and exergy efficiencies. Additionally, exergy analysis results showed that the highest exergy destruction rate belongs to the heat exchanger 1&2. Optimization of the proposed cycle is performed by using genetic algorithm method, and it is observed in the optimal condition that the net output power, thermal efficiency, and exergy efficiency can be obtained as 30610 kW, 29.16%, and 56.92%, respectively. The results of this study indicate that the net output power and thermal efficiency is better performance compared to the previous studies.

Theoretical aspects of thermophoresis and Brownian motion for three-dimensional flow of the cross fluid with activation energy

The current review proclaims the forced convective flow and heat–mass transfer characteristics of cross nanofluid past a bidirectional stretched surface. The most significant aim of the current review is to incorporate the features of Buongiorno relation, activation energy, nonlinear thermal radiation and heat sink–source for a three-dimensional flow of the cross fluid. Appropriate transformations are employed to transform the modelled partial differential equations (PDEs) of momentum, temperature and concentration into coupled nonlinear ordinary differential equations (ODEs). The governing boundary value problem is numerically integrated with the help of bvp4c scheme. The obtained numerical data are plotted for the temperature and concentration profiles of nanofluid for various converging values of physical parameters. The dependence of increasing thermophysical parameters on temperature and concentration profiles of the cross nanofluid is graphically demonstrated. Furthermore, detailed study reveals that the concentration of the cross nanofluid decreases for increasing values of Brownian motion parameter. It is also perceived from the sketches that the concentration of the cross nanofluid decreases for higher values of chemical reaction parameter. The validity of the achieved numerical outcomes is ensured by making a comparison with the existing work as special cases.

Effect of Hall Current on Unsteady Magneto Hydrodynamic Flow Past an Exponentially Accelerated Inclined Plate with Variable Temperature and Mass Diffusion

The present study is carried out to examine the effect of Hall current on unsteady flow of a viscous, incompressible and electrically conducting fluid past an exponentially accelerated inclined plate with variable wall temperature and mass diffusion in the presence of transversely applied uniform magnetic field. The plate temperature and the concentration level near the plate increase linearly with time. The governing equations involved in the present analysis are solved by the Laplace-transform technique. The velocity profile is discussed with the help of graphs drawn for different parameters like thermal Grashof number, mass Grashof number, Prandtl number, Hall current parameter, acceleration parameter, the magnetic field parameter and Schmidt number, and the numerical values of skin-friction have been tabulated. It is observed that the flow pattern is affected significantly with plate acceleration, Hall current. The importance of the problem can be seen in cooling of electronic components of a nuclear reactor, bed thermal storage and heat sink in the turbine blades.

A study of methods to enhance infrared emissivity of Molybdenum surfaces

Single crystal Molybdenum is one of the most promising materials for the First Mirror (FM) of ITER optical diagnostics due to its high resistance to erosion under neutral atom bombardment. Other advantages are: low CTE, high thermal conductivity, and advantageous mechanical properties at elevated temperatures. The FMs are normally located in the front-end of ITER port plugs, being subject to volumetric heat loads up to ∼1 W/cm3 and higher. Active cooling of Mo mirrors by water or gas flow has limited applicability due to remote handling, integration and risk requirements. An athermal design with radiative cooling was developed for the H-alpha FM unit (FMU) with an all-Mo/TZM structure comprising a TZM housing, two Mo mirrors and the TZM cleaning electrodes. The main idea is to minimize mirror angular displacements and to keep the alignment at temperatures up to ∼350 °C. That requires a balance between thermal contact and radiative heat sinks. The most uniform temperature profile is obtained by weak thermal contact between FMU and support structure, but that leads to the highest FM temperature, since the normal as-milled Mo surface has a very low effective emissivity (ε < 0.1 at 200…400 °C). Well-known tools for surface blackening are: enhanced roughness, oxidation, V-grooving, and coatings, which should be analyzed for outgassing rate, thermal radiation and long-term stability in Hydrogen environment. In this study, a number of techniques to enhance Mo surface effective emissivity were tested: V-grooving, detonation spray coating, drilling and surface electro-erosion. Spectral emissivity of the test samples was measured by Bruker Vertex-70 infrared Fourier spectrometer and the effective values were derived for subsequent thermal analyses. Alumina coatings were found to be the most effective tool with ε ≈ 0.8…0.9. However, V-grooving and drilling also provide acceptable results (εeff ≈ 0.25…0.3) and do not require qualification for applicability to ITER. The trade-off between different techniques is discussed in detail.

Exergoeconomic optimization of a novel cascade Kalina/Kalina cycle using geothermal heat source and LNG cold energy recovery

Abstract In recent studies, cascade power generation systems are introduced as promising methodologies in power plants for recovering the waste heat of topping cycle, resulting in low waste heat rejection from the heat exchangers of the single-stage power plant. Due to the importance of this topic, a cascade Kalina cycle (CKC) power plant is proposed using geothermal energy as heat source and liquefied natural gas (LNG) as thermal heat sink. The proposed system is integrated from a high pressure KC (HPKC) as topping cycle and a low pressure KC (LPKC) as bottoming cycle. Energy, exergy and exergoeconomic analysis of the proposed system are conducted to give more detail information for designers. In addition, single- and multi-objective optimizations of the proposed system are performed, using genetic algorithm (GA) method. It is demonstrated that the optimum net power, thermal efficiency, exergy efficiency and total sum unit cost of product of the proposed system can be obtained 9044 kW, 29.87%, 43.19% and 127.8 $/GJ, respectively. Exergy analysis results demonstrated that among all components, the second heat exchanger accounts for the biggest exergy destruction rate. To obtain a better understanding from characteristics of the proposed system, a comprehensive parametric study is conducted showing that the thermal efficiency of system can be optimized based on the geothermal inlet temperature as well as the basic ammonia concentrations of HPKC and LPKC. In addition, it is found that a higher thermal efficiency can be obtained by increasing vapor generator pinch point temperature difference and turbines expansion ratio or by decreasing the second heat exchanger's temperature. Moreover, it is concluded that the exergy efficiency can be increased by increasing the first and second turbines' expansion ratios, geothermal inlet temperature, and basic ammonia concentration of HPKC or by decreasing the second heat exchanger's temperature, third turbine's expansion ratio and vapor generator pinch point temperature difference. In addition, the total sum unit cost of product of system can be decreased by increasing of the geothermal inlet temperature, second heat exchanger temperature, basic ammonia concentration of HPKC and basic ammonia concentration of LPKC or by decreasing of the vapor generator pinch point temperature difference and turbines' expansion ratios.

Grain boundary thermal resistance and finite grain size effects for heat conduction through porous polycrystalline alumina

Design of high performance materials for thermal insulation or heat sinking requires understanding of the mechanisms controlling heat flow. The effect of grain size on the effective thermal conductivity of porous alumina ceramics has been investigated. After uniaxial pressing of a fine α-alumina powder, control of firing temperature and duration yielded ceramics with variations in grain size. Values of thermal conductivity corresponding to equivalent 100% dense ceramics were determined from laser flash measurements using Landauer’s relation to take porosity into account. These exhibited a strong decrease from 33 W m−1 K−1, for grain sizes larger than 2 μm, down to 8 W m−1 K−1 for an average grain size of 0.25 μm.A method to separate the contributions of localized thermal resistance (Kapitza resistance) at grain boundaries and grain conductivity for each sample is presented. The larger grain size samples (>0.5 μm) yield values for the effective grain boundary thermal resistance in the range 0.6–0.8 × 10−8 m2 K W−1 and a grain conductivity close to 35 W m−1 K−1. For smaller grain samples (<0.5 μm), the grain boundary thermal resistance increases to 2 × 10−8 m2 K W−1 while the grain conductivity reduces to 23 W m−1 K−1. Thus grain size controls both the number of grain boundaries in the heat path and the grain conductivity itself.

Thermal modeling of wide bandgap semiconductor devices for high frequency power converters

The emergence of wide bandgap semiconductors has led to development of new generation semiconductor switches that are highly efficient and scalable. To exploit the advantages of GaNFETs in power converters, in terms of reduction in the size of heat sinks and filters, a thorough understanding of the thermal behavior of the device is essential. This paper aims to establish a thermal model for wideband gap semiconductor GaNFETs commercially available, which will enable power electronic designers to obtain the thermal characteristics of the device more effectively. The model parameters is obtained from the manufacturer’s data sheet by adopting an exponential curve fitting technique and the thermal model is validated using PSPICE simulations. The model was developed based on the parametric equivalence that exists between the thermal and electrical components, such that it responds for transient thermal stresses. A suitable power profile has been generated to evaluate the GaNFET model under different power dissipation scenarios. The results were compared with a Silicon MOSFETs to further highlight the advantages of the GaN devices. The proposed modeling approach can be extended for other GaN devices and can provide a platform for the thermal study and heat sink optimization.

English

English

Simulation and Performance Comparison of Si and SiC Based on a Proposed H6 Inverter for PV Grid-tied Applications

Multilevel transformerless inverters are widely employed in PV grid-tied applications because of their significant benefits in reducing switching losses and enhancing system efficiency. Wide bandgap (WBG) semiconductor devices such as SiC MOSFETs can increase the system performance and reduce the total losses due to their superior features over Si switching devices. This paper investigates a three level transformerless inverter based on H6 topology. The proposed topology is implemented with SiC MOSFETs and a modulation approach is adopted to reduce the number of conducting switches. Also, a detailed comparison of the use of SiC and Si switching devices in terms of switching and conduction losses, high switching frequency operation, filter size reduction, and thermal analysis and heat sink volume is presented. Simulation results show that total conduction and switching losses are reduced by about 50%, which allow a significant increase in either the switching frequency or the inverter power rating level for the same switching device losses. Additionally, operating at higher switching frequencies using SiC MOSFET leads to a significant reduction in volume and weight of the inductor filter. Furthermore, a thermal analysis is performed using COMSOL software to investigate the heat sink requirement.

Heat and Mass Transfer of Unsteady Hydromagnetic Free Convection Flow Through Porous Medium Past a Vertical Plate with Uniform Surface Heat Flux

AbstractSimultaneous effects of thermal and concentration diffusions in unsteady magnetohydrodynamic free convection flow past a moving plate maintained at constant heat flux and embedded in a viscous fluid saturated porous medium is presented. The transport model employed includes the effects of thermal radiation, heat sink, Soret and chemical reaction. The fluid is considered as a gray absorbing-emitting but non-scattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. The dimensionless coupled linear partial differential equations are solved by using Laplace transform technique. Numerical results for the velocity, temperature, concentration as well as the skin friction coefficient and the rates of heat and mass transfer are shown graphically for different values of physical parameters involved.

A computational theoretical model for radiofrequency ablation of tumor with complex vascularization

Radiofrequency ablation (RFA) for liver tumors is a minimally invasive procedure that uses electrical energy and heat to destroy cancer cells. One of the critical factors that impedes its successful outcome is the thermal heat sink effects from complex vascular systems that give rise to incomplete destruction of the target tumor tissue, resulting in therapy failure. To better understand the thermal influence of the complex vascular system during RFA, this work proposes the employment of two 3D fractal tree-like branched networks to investigate which key factors of the tree-like vascular system impact heating process. A three-dimensional finite difference analysis is employed to simulate the RFA treatment. Based on the data acquired from the measured experiments, the simulated results derived from combining the Pennes bioheat model and the boundary condition-enforced immersed boundary method (IBM) have demonstrated close agreement with experimental data with a maximum discrepancy of ±8.3%. We employed the orthogonal design approach to analyze 3 factors, namely, the blood vessel's volume, the average distance between probe center and the blood vessel system and the number of the selected part's branches at three different levels. Results have revealed that the distance between RFA probe and blood vessel plays a major role during the heating process compared with the other two factors. In addition, both the ablating rates and the volume of damaged tissue are slightly reduced with increasing number of blood vessel branches.

Thermal stability and heat sink of microalgae aviation fuels

Thermal stability and heat sink of microalgae aviation fuels