Heat Dissipaters Research Articles

A review on Aluminium based thermal interface materials for heat transfer application

Thermal management is the capability of a system to maintain its temperature with the support of thermodynamics and heat transfer-based technologies. Thermal Interface Materials (TIMs) are any kind of material that is inserted between two components in order to enhance the thermal coupling between them hence the heat transfer rate. It is commonly used in many systems for heat dissipation. Thermal Interface Material with higher thermal conductivity value will improve the heat transfer performance of such devices. The conventional heat dissipaters are typically made up of materials like aluminum and copper which are quite heavy (density of Al-2.7 g/cm3, density of Cu-8.96 g/cm3) and have low thermal conductivity value (for Al-207 W/mK, Cu-385 W/mK) in pure form. This paper is an effort to review and summarize the recent developments in the research area of Thermal Management. Aluminium based metal matrix composites used as heat sink are an ongoing research interest as they enhance the thermal conductivity and finds application in aerospace, automobile, electronic equipment’s and building materials.

Synergic effect of metallic fillers as heat dissipaters in the tribological performance of a nonasbestos disk brake pad

Brake friction linings are made of materials with a highly complex formulation that helps in improving the braking performance. The selection of friction materials with good physical, mechanical, and thermal properties is vital, which will decide the braking performance. Apart from giving good physio-mechanical properties, metallic fillers act as heat dissipaters. The objective of this work is to study the synergetic effect of prominent heat dissipaters, namely copper fibers, brass fibers, and zinc powders. Three simplified formulations were developed with 10, 14, and 18 wt.% of these heat dissipaters and named DB1, DB2, and DB3, respectively. It was observed that the addition of heat dissipaters increased the thermal properties. Tribological properties are tested based on SAE J661 standards. It was observed that DB2 had a consistent and higher coefficient of friction of 0.503 with a higher wear rate (7.6%) while DB3 had adequate μ and lower wear rate. The same batches of brake pads were tested in an inertia brake dynamometer following JASO C406 and a wear test was carried out. It was observed that % fade and % recovery were better for DB2 in both cycles. The wear rate in terms of thickness was lesser for DB2 followed by DB1 and DB3. The wear mechanism was analyzed using a scanning electron microscope. The preference selection index method of optimization was used to evaluate the overall performance parameters of the brake friction composites. Heat dissipaters with 14 wt.% have proved to be the better performers, followed by 10 and 18 wt.%.

Improvements in the Organic-Phase Hydrothermal Synthesis of Monodisperse M x Fe3-x O4 (M = Fe, Mg, Zn) Spinel Nanoferrites for Magnetic Fluid Hyperthermia Application.

In the quest for optimal heat dissipaters for magnetic fluid hyperthermia applications, monodisperse MxFe3–xO4 (M = Fe, Mg, Zn) spinel nanoferrites were successfully synthesized through a modified organic-phase hydrothermal route. The chemical composition effect on the size, crystallinity, saturation magnetization, magnetic anisotropy, and heating potential of prepared nanoferrites were assessed using transmission electron microscopy (TEM), dynamic light scattering, X-ray diffraction (XRD), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), atomic absorption spectroscopy (AAS), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer (VSM) techniques. TEM revealed that a particle diameter between 6 and 14 nm could be controlled by varying the surfactant ratio and doping ions. EDS, AAS, XRD, and XPS confirmed the inclusion of Zn and Mg ions in the Fe3O4 structure. Magnetization studies via VSM revealed both the superparamagnetic nature of the nanoferrites and the dependence on substitution of the doped ions to the final magnetization. The broader zero-field cooling curve of Zn-doped Fe3O4 was related to their large size distribution. Finally, a maximum rising temperature (Tmax) of 66 °C was achieved for an aqueous ferrofluid of nondoped Fe3O4 nanoparticles after magnetic field activation for 12 min.

Tailored morphology and highly enhanced phonon transport in polymer fibers: a multiscale computational framework

Although tremendous efforts have been devoted to enhance thermal conductivity in polymer fibers, correlation between the thermal-drawing conditions and the resulting chain alignment, crystallinity, and phonon transport properties have remained obscure. Using a carefully trained coarse-grained force field, we systematically interrogate the thermal-drawing conditions of bulk polyethylene samples using large-scale molecular dynamics simulations. An optimal combination of moderate drawing temperature and strain rate is found to achieve highest degrees of chain alignment, crystallinity, and the resulting thermal conductivity. Such combination is rationalized by competing effects in viscoelastic relaxation and condensed to the Deborah number, a predictive metric for the thermal-drawing protocols, showing a delicate balance between stress localizations and chain diffusions. Upon tensile deformation, the thermal conductivity of amorphous polyethylene is enhanced to 80% of the theoretical limit, that is, its pure crystalline counterpart. An effective-medium-theory model, based on the serial-parallel heat conducting nature of semicrystalline polymers, is developed here to predict the impacts from both chain alignment and crystallinity on thermal conductivity. The enhancement in thermal conductivity is mainly attributed to the increases in the intrinsic phonon mean free path and the longitudinal group velocity. This work provides fundamental insights into the polymer thermal-drawing process and establishes a complete process–structure–property relationship for enhanced phonon transport in all-organic electronic devices and efficiency of polymeric heat dissipaters.

Total internal reflection shell for light-emitting diode bulbs.

A total internal reflection (TIR) shell capable of generating illuminating light with a wide-angle distribution from light-emitting diodes (LEDs) is proposed. The TIR shell can be used to create an LED light bulb with enclosed heat dissipaters to release the heat generated by the LEDs. The TIR shell has light-scattering areas on its inner surface and a mirror-polished free-form outer surface that can guide all rays emitted from the LEDs to the scattering areas by the TIR. The rays diffused by the light-scattering areas are emitted from the TIR shell in a wide-angle light distribution. A prototype of the LED light bulb with a metal shell for heat dissipation inside the TIR shell shows favorable features such as a half-intensity angle of 330°, lighting efficiency of 81%, and glare-free lighting emitted from the entire surface area of the TIR shell.

Experimental performance investigation of minichannel water cooled-thermoelectric refrigerator

An experimental performance analysis of minichannel water cooled-thermoelectric refrigerator in this study is presented. The cooling system of refrigerator is consists of two thermoelectric modules integrated with the minichannel heat sinks in its hot side and the heat dissipaters in its cold side. The experiments carried out for different system voltages and different flow rates of cooling water in the minichannel. The results show that the inner temperature of water cooled-thermoelectric refrigerator is about 2°C for 0.8L/min flow rate while it is about −0.1°C for 1.5L/min flow rate at the end of 2-h experiment. COP value of thermoelectric refrigerator is 0.23 in the flow rate 1.5L/min while COP is 0.19 in the flow rate 0.8L/min at the end of 25min cooling times. When it comes to 8V system voltages, COP of the thermoelectric refrigerator is about 0.41 at the end of 25min operating period for the flow rate 1.5L/min. This study concludes that the performance of minichannel heat sink used in this study has as good as other liquid water cooled systems used to absorb heat from thermoelectric modules hot side.

Optimization of Design Parameters for Lateral Circular Perforated Fin Arrays under Forced Convection

Heat dissipation is an important issue in compactness and weight of equipment. Heat dissipaters are not only chosen for their thermal performance but also for other design parameters such as weight, cost and reliability depending on applications. The present paper reports an experimental study to investigate the heat transfer enhancement over vertical rectangular fin arrays equipped with lateral circular perforations. The cross-sectional area of the rectangular duct was 200 mm × 80 mm. The data used in performance analysis were obtained experimentally for aluminum at 200 Watts heat input, by varying the fin thickness, size of perforations and varying Reynolds number range 2.1 × 104 to 8.7 × 104. Using the Taguchi experimental design method, optimum design parameters and their levels were investigated. Average Nusselt number was considered as a performance characteristics. An L9 (33) orthogonal array was selected as an experimental plan. Optimum results were found by experimenting with porosity, Reynolds number and thickness of the fin. It is observed that the Reynolds number and maximum porosity have a larger impact on Nusselt number.

Carbon nanotubes as heat dissipaters in microelectronics

We review our recent modelling work of carbon nanotubes as potential candidates for heat dissipation in microelectronics cooling. In the first part, we analyze the impact of nanotube defects on their thermal transport properties. In the second part, we investigate the loss of thermal properties of nanotubes in presence of an interface with various substances, including air and water. Comparison with previous works is established whenever is possible.

English

Heat dissipation is a drastic issue to tackle due to continued integration, miniaturization, compacting and lightening of equipment. Heat dissipaters are not only chosen for their thermal performance; but also for other design parameters that includes weight, cost and reliability, depending on application. The present paper reports an experimental study to investigate the heat transfer enhancement over horizontal flat surface with rectangular fin arrays with lateral square and circular perforation by forced convection. The cross sectional area of the rectangular duct was 200 mm x 80 mm. The data used in performance analysis were obtained experimentally for fin arrays of material aluminum, by varying geometry and size of perforation as well as by varying Reynolds number from 21 10 4 to 8.7 10 4 . It is observed that the Reynolds number and size perforation have a larger impact on Nusselt number for the both type of perforations.

Advanced thermal enhancement and management of LED packages

Thermal management of packages consists of external cooling mechanisms, heat dissipaters, and thermal interfaces. While keeping cooling condition constant, junction temperature of LEDs with higher thermal resistance increases more rapidly; hence the luminous efficiency decreases more obviously. This paper includes the discussion about the calculation methods of the lighting's heat transfer. The calculation process has been demonstrated by an example of cooling of LEDs lighting in this paper. In particular, the operation package heat transfer enhancement is required by most package manufacturers with a decrease of 20% ~ 30% of the thermal resistance over conventional package geometries.

Shorter Field Life in Power Cycling for Organic Packages

The importance of power cycling as a mean of reliability assessment was revisited for flip chip plastic ball grid array (FC-PBGA) packages. Conventionally, reliability was addressed empirically through accelerated thermal cycling (ATC) because of its simplicity and conservative nature of life prediction. It was well accepted and served its role effectively for ceramic packages. In reality, an assembly is subjected to a power cycling, i.e., nonuniform temperature distribution with a chip as the only heat source and other components as heat dissipaters. This non-uniform temperature distribution and different coefficient of thermal expansion (CTE) of each component make the package deform differently than the case of uniform temperature in ATC. Higher substrate CTE in a plastic package generates double curvature in the package deformation and transfers higher stresses to the solder interconnects at the end of die. This mechanism makes the solder interconnects near the end of die edge fail earlier than those of the highest distance to neutral point. This phenomenon makes the interconnect fail earlier in power cycling than ATC. Apparently, we do not see this effect (the die shadow effect) in ceramic packages. In this work, a proper power cycling analysis procedure was proposed and conducted to predict solder fatigue life. An effort was made for FC-PBGA to show the possibility of shorter fatigue life in power cycling than the one of ATC. The procedure involves computational fluid dynamics (CFD) and finite element analyses (FEA). CFD analysis was used to extract transient heat transfer coefficients while subsequent FEA–thermal and FEA–structural analyses were used to calculate temperature distribution and strain energy density, respectively.

Plates of the Dinosaur Stegosaurus : Forced Convection Heat Loss Fins?

It is suggested that the plates along the arched back and tail of Stegosaurus served an important thermoregulatory function as forced convection "fins." Wind tunnel experiments on finned models, internal heat conduction calculations, and direct observations of the morphology and internal structure of stegosaur plates support this hypothesis, demonstrating the comparative effectiveness of the plates as heat dissipaters, controllable through input blood flow rate, temperature, and body orientation (with respect to wind).

"Sun Leaves" and "Shade Leaves": Differences in Convective Heat Dissipation

Temperatures of radiantly heated sun and shade leaves of white oak (Quercus alba L.) were measured in a low—speed wind tunnel. In either still air or a gentle updraft the difference between ambient and leaf temperature is about 20% less for the sum leaves than for the shade leaves. Consequently the former are more effective heat dissipaters.