Size Of Heat Sink Research Articles

Effect of non-uniform heating on the performance of the microchannel heat sinks

The present study experimentally investigates the performance of a 2-pass microchannel heat sink subject to non-uniform heating. The size of the microchannel heat sink is 132mm×82mm×6mm with a rectangular channel of 1mm×1mm. Three independent heaters having identical size (96mm×38.5mm×1mm) is placed consecutively below the microchannel heat sink. Two kinds of manifolds are used for testing of the microchannel, one with a side entrance (type A) and the other with a front entrance (type B). Test results show that both maximum temperature and average temperature rise with the total input power, and this is applicable for both manifolds. For uniform heating condition, the maximum temperature for type B manifold is much lower than that for type A manifold due to a better flow distribution and heat transfer performance. The pressure drop is slightly reduced with the rise of supplied power. For non-uniform heating, the maximum temperature and the average temperature depend on the location of heaters. For the same supplied power with non-uniform heating, it is found that heater being placed at the inlet of the microchannel will give rise to a higher maximum temperature than that being placed at the rear of the heat sink. This phenomenon is especially pronounced when the inlet flowrate is comparatively small and becomes less noted as the inlet flowrate is increased to 0.7L/min.

Placement Optimization of Power Components in Static Power Converters under Spatial and Thermal Constraints

This paper deals with an optimization approach of 3D space placement of power components under volume and thermal constraints. It consists in optimizing semiconductors positions on a heat sink by respecting the components junction temperatures and minimizing the heat sink size. The aim is to remove risks on the 3D converter components placement and ensure their effective integration before carrying out the first physical prototype. This approach is based on coupling an optimization environment with a thermal finite element simulation tool. A pre-sizing step using analytical models is performed to set the optimization computations coupled to numerical simulation.

A Closed-Form Expression for Estimating the Maximum Radiated Emissions From a Heatsink on a Printed Circuit Board

A closed-form expression is derived for determining the maximum possible radiated emissions from a heatsink over a printed circuit board or chassis plane as a function of the maximum voltage between the heatsink and plane. Two modes of radiation are considered: a patch-antenna mode and a monopole-antenna mode. The maximum emissions are the sum of the emissions due to each of these modes. Circuit board dimensions are assumed to be large compared to the heatsink dimensions. The most relevant parameters affecting the emissions are the dimensions of the heatsink. The closed-form expression is validated by comparing its results to full-wave simulation results for a variety of heatsink sizes and shapes.

Control of DFIG based Wind Turbine Converter using Continuous and Discontinuous PWM: A Comparative Study

Pulse width modulation (PWM) has been widely employed in voltage source converter (VSC) due to its superior output waveforms. PWM types are generally grouped into continuous (CPWM) and discontinuous (DPWM). Each has its own performance characteristic, which contrasts from the other. CPWM has lower total harmonic distortion (THD) compared with DPWM at the same value of carrier frequency. However, DPWM has lower switching losses compared with CPWM in a similar condition. Concerning power quality issue, reduction in THD injected into the grid is necessary to fulfill the standard harmonic requirement. The reduction in converter losses could help reduce thermal stress on power switches and reduce the size of heat sink, thereby aiding the design of compact power converters. In VSC based doubly fed induction generator (DFIG), applying PWM techniques for both line side converter (LSC) and machine side converter (MSC) can affect overall performances of the system. The performances are different depending on four possible PWM combinations. This paper compares four combinations of PWM techniques through conceptual discussion and based on simulation results. The results show that each combination has its own performance advantages which can give an idea on designing DFIG controller based on desired objectives.

Permanent Magnet Biased Bearing of Suspension System

PM (Permanent Magnet) biased magnetic bearing with PM to replace the magnetic field produced by electromagnet an Active Magnetic Bearing generated static bias magnetic field, it can reduce the power consumption of power amplifier to reduce the number of turns of magnet safety, reduce the volume of magnetic bearings, reducing electromagnetic coil operating current, thereby reducing the power amplifier power control system and heat sink size, magnetic bearings significantly reduce power loss, and fundamentally reduce the cost of bearing. In this paper, a kind of PM biased magnetic bearings, describes its structure and working principle, derived a mathematical model of magnetic bearing and magnetic circuit of PM biased magnetic bearings are calculated, given the specific PM biased magnetic bearing size and accordingly calculate the parameters of magnetic bearings. A magnetic model constructed using Simulink simulation method, and constructed using this method, magnetic bearing specific mathematical model simulation results show that the rotor position in the balance, X and Y decoupling between the control winding, while the deviation from equilibrium position time, X and Y control coupling between the windings, the simulation results and the calculation results.

The thermally induced limitations of SiC SBDs operation conditions

In the paper, the DC current–voltage characteristics of silicon carbide Schottky barrier diodes are analyzed, with special attention paid to the critical current and junction temperature estimation. The self-heating phenomenon, interpreted as an electro-thermal positive feedback, is taken into account. The measurements of isothermal and non-isothermal I–V characteristics, as well as adequate calculations, are shown and discussed. The electro-thermal models, based on various descriptions of temperature-dependent series resistance of the device, are proposed. It is also shown that the shapes of I–V characteristics depend on the current range and on the heat-sink size.

Analysis of Thermal Resistence for High-Power Light-Emitting Diodes

This paper measures the LED thermal resistance characteristic by thermal transient tester (T3Ster) obtained the cumulative structure functions curve and differential structure functions curve. The actual K factor and optical power are obtained by testingⅠ. The thermal resistance characteristic of each layer for LED structure are analyzed by testingⅡ in different cases. The experimental results show that the bonding method and the heat sink size have tremendous influence on the LED thermal resistance’s reduce, and the contact thermal resistance takes up a great proportion in LED total thermal resistance. The contact thermal resistance may reduce by pressure on interface and by a change of the attach material and the roughness of interface.

Multiobjective Evolutionary Optimization of Splayed Pin-Fin Heat Sink

This paper presents the use of a multiobjective evolutionary algorithm, namely population-based incremental learning (PBIL), for the design/optimization of a splayed pin-fin heat sink. An innovative design strategy based on evolutionary optimization is presented for the enhancement of the heat sink’s performance. The design problem is to simultaneously minimize the junction temperature and the fan pumping power of the heat sink. Design variables determine the sizes and geometry of the heat sink. The new encoding/decoding process of the design variables, using surface spline interpolation, is detailed. There are 24 design parameters including fin number, fin height, fin width, heat sink base thickness and size, fin bevel, and inlet air velocity. Manufacturing tolerances, such as the heat sink aspect ratio and the device free space, are taken as design constraints. Computational fluid dynamics is used for the objective function evaluation. Numerical results show that PBIL is a powerful tool for the optimal design of a splayed pin-fin heat sink. This new design approach results in heat sinks with variation in fin heights, and it is said to be superior to available commercial splayed pin-fin heat sinks.

A Study of Liquid Cooling Heat Sink Fabrication and Development in Notebook

Liquid cooling heat sink has excellent heat dissipation ability at the personal computer. It can also produce the similar effect at the notebook when the same heat sink is used. However, under the installing space is limited in notebook, the size and weight of heat sink must be limited too. Therefore a novel liquid cooling heat sink was fabricated herein to understand the heat dissipation efficiency in the notebook. Wire electrical discharge machining (WEDM) uses heat erosion effect to remove material and only produces little cutting force on the working surface. Therefore, WEDM has excellent ability to fabricate the straight micro fins (high 1000 μm, width 250 μm, fin gap 400 μm). The WEDM parameters were used to find the precision micro fins in this experiment. The precision micro fins were made when the cutting path offset was 185 μm in WEDM. WEDM would produce over cutting during long pulse duration and it caused oblique micro fins. The appropriate off time in cutting process would promote the WEDM efficiency. However, a liquid cooling heat sink with uniform micro fins and slits was obtained using WEDM.

Numerical Thermal Analysis to Study the Effect of Static Contact Angle on the Cooling Rate of a Molten Metal Droplet

ABSTRACT The present study is conducted to simulate the effect of molten metal droplet wettability on the solidification rate of a molten metal droplet. The effect of heat sink size, i.e., the thickness of substrate is also studied with respect to droplet solidification. It is found that the variation of contact angle has significant effect on the solidification time but the heat sink size does not effectively change the solidification time. It is also observed that the thermal diffusivity of substrate plays a dominant role in multimaterial systems.

An integrated methodology for multiobjective optimal component placement and heat sink sizing

The advances in power electronics packaging resulting from the integration of various high power devices into single programmable blocks are projected to significantly increase heat dissipation rates up to 2-3 W/mm/sup 2/ within the next decade. Conventional thermal management schemes such as air-cooled heat sinks are inadequate at these high power levels, requiring the use of forced liquid cooled heat sinks, or cold plates. A primary issue concerning the thermal-packaging designers today is the selection of a suitable cold plate and the optimum placement of components on it. This paper focuses on a methodology for selection of cold plates and the optimal placement of power modules on them. The basis of the methodology is the integration of computationally efficient reduced or "compact" thermal models within a genetic algorithm based multiobjective optimization framework. This methodology is used to optimize the placement of multiple power modules on a cold plate. It is also extended to perform a tradeoff analysis between multiple competing objectives for cold plate selection. Compact thermal models for power electronics and heat sinks are developed, validated, and integrated within the optimization framework. The effectiveness of the methodology as a rapid scouting tool to arrive at an optimum tradeoff solution set for further analysis by detailed numerical simulation is discussed. The methodology is general in the sense that it allows for incorporation of changes in optimization criteria or improvements in the heat transfer solver.

Modeling and Experimental Evaluation of Passive Heat Sinks for Miniature High-Flux Photovoltaic Concentrators

An important consideration in the practical realization of high-concentration photovoltaic devices is the heat rejection at high power densities to the environment. Recently, optical designs for generating solar flux in excess of 1000 suns on advanced solar cells–while respecting flux homogeneity and system compactness–were suggested with the introduction of solar fiber-optic mini-dish concentrators, tailored specifically to high-flux photovoltaic devices [1]. At the core of the design is the miniaturization of the smallest building block in the system–the concentrator and the cell–permitting low-cost mass production and reliance on passive heat rejection of solar energy that is not converted to electricity. First, this paper proposes a relatively simple 1-D axi-symmetric model for predicting the thermal and electrical performance of such mini-dish high-flux concentrators. Experimental measurements were performed with a real-sun solar simulator, indoors under controllable conditions, at flux levels up to 5,000 suns. A CFD (Computational Fluid Dynamics) model was also developed for model-validation. Both the modeling approaches predict heat sink temperatures within experimental uncertainty of a couple of degrees. Next, the 1-D axi-symmetric model is used to evaluate the sensitivity of different solar cell model assumptions, environmental effects (such as outdoor temperature, and the wind speed), heat sink size and geometry, thermal contact resistance, etc. It was confirmed that the miniaturization of the solar cell module permits passive heat rejection, such that solar cell temperatures should not reach more than 80 °C at peak insolation and stagnation conditions. Though the cell rated efficiency degrades by only 1-2% in absolute terms, higher cell temperatures may compromise the integrity of the cell circuitry and of the encapsulation. The 1-D axi-symmetric model also allows optimization of the heat sink geometric dimensions for a given volume. Hour-by-hour performance simulation results for such an optimized design configuration were performed for one month in summer and one month in winter for two locations namely Philadelphia, PA and Phoenix, AZ. The insight gained from this study is important for the proper design of the various components and materials to be used in PV mini-dishes. Equally important is that it allows similar types of analyses to be performed and well-informed design choices to be made for mini-dishes that have to operate under different climatic conditions with cells of different performance and concentration ratios.© 2005 American Institute of Physics.

Compact Modeling of Fluid Flow and Heat Transfer in Pin Fin Heat Sinks

In this work, a novel compact modeling method based on the volume-averaging technique is presented. Its application to the analysis of fluid flow and heat transfer in pin fin heat sinks are further analyzed. The pin fin heat sink is modeled as a porous medium. The volume-averaged momentum and energy equations for fluid flow and heat transfer in pin fin heat sinks are obtained by using the local volume-averaging method. The permeability, the Ergun constant, and the interstitial heat transfer coefficient required to solve these equations are determined experimentally and correlations for them are presented. To validate the compact model proposed in this paper, 20 aluminum pin fin heat sinks having a 101.43 mm×101.43 mm base size are tested with an inlet velocity ranging from 1 m/s to 5 m/s. In the experimental investigation, the heat sink is heated uniformly at the bottom. Pressure drop and heat transfer characteristics of pin fin heat sinks obtained from the porous medium approach are compared with experimental results. Upon comparison, the porous medium approach is shown to predict accurately the pressure drop and heat transfer characteristics of pin fin heat sinks. Finally, for minimal thermal resistance, the optimum surface porosities of the pin fin heat sink are obtained under constraints on pumping power and heat sink size. The optimized pin fin heat sinks are shown to be superior to the optimized straight fin heat sinks in thermal performance by about 50% under the same constraints on pumping power and heat sink size.

Identification of Minimum Air Flow Design for a Desktop Computer Using CFD Modeling

This paper reports the results of CFD analysis to cool the 30-W socketed CPU of a desktop computer with minimum air flow rate and minimum heat sink size. This was achieved using only the fan in the power supply for all air movement in the chassis. A duct was employed to direct the air flow over the CPU and then to the inlet air vents of the power supply. Use of this duct allowed more than 10°C reduction of the CPU case temperature, relative to an unducted design. The CFD analysis results were confirmed by experiment, and the predicted CPU case temperatures agreed within ±2.9°C of the experimental values for the ducted cases. This paper describes the methodology of CFD analysis for the heat sink/duct design, and describes experimental procedures to validate the predictions.

The graded doped trench MOS Barrier Schottky rectifier: a low forward drop high voltage rectifier

A novel high voltage Schottky rectifier, called the Graded Doped Trench MOS Barrier Schottky (GD-TMBS) rectifier, is described in this paper. It is shown to have very low forward drop with excellent reverse blocking characteristics through device simulation and electrical characterization of fabricated devices. A linearly graded drift region doping profile is shown to result in an uniform electric field in the drift region resulting in the ability to support blocking voltages proportional to the trench depth. Two-dimensional device simulations have shown that breakdown voltages of upto 200 V can be achieved with a very low forward drop of 0.54 V. The measured on-state drop of fabricated 60 and 100 V GD-TMBS are about half those of conventional Schottky rectifiers. Power dissipation analysis indicates higher operating temperatures (150°C) with reduced heat sink sizes when compared to conventional Schottky barrier diodes.

Prediction Algorithm of Pressure Drop for Impingement Cooling of Heat Sinks with Longitudinal Fins.

This paper is a semi-empirical report on the development of a prediction algorithm of pressure drop for impingement cooling of heat sinks with longitudinal fins. The inlet rectangular orifice (slit) is about the heat sink size in length, less than 1/4 of the heat sink size in width and is placed over the center of the heat sink. A physical model suitable for heat sinks with longitudinal fins is considered based on the flow visualization results of our previous study. According to this model, the flow region is divided into five parts : (i) the region of inlet orifice, (ii) the region between the fins under the inlet orifice, where the flow is perpendicular to the fin base, (iii) the region between the fins where the flow is parallel to the fin base except under the inlet orifice, (iv) the outlet of the heat sink, and (v) the region distant from the heat sink. Values are predicted for pressure drop of the heat sinks with longitudinal fins for a variety of orifice width, gaps, fin heights and number of fins. These values agree with the experimental data within ±30%.

A Preliminary Investigation of the Cooling of Electronic Components With Flat Plate Heat Sinks

Flat rectangular plate heat sinks are often used to cool large electronic components by the combined effects of natural convection and thermal radiation. There is, however, a paucity of rational design techniques for these devices. Thus, a systematic program to investigate the use of flat, rectangular plate heat sinks with surface coatings to enhance the net radiative exchange with the surroundings has been undertaken. The preliminary results of this program are presented in this work. A two-dimensional numerical model of a single electronic component mounted on a vertically oriented, flat rectangular plate heat sink that is located immediately above an upward-facing, horizontal component board was developed for this investigation. This model, which is solved using a control volume method based on the SIMPLER algorithm, accounts for the fully-coupled natural convection, conduction and radiative heat transfer processes that occur in the two-dimensional heat sink configuration described above. The results of a parametric study performed with the numerical model confirm the necessity of employing a heat sink, since for the ranges of values investigated, from 64 to 88 percent of the energy dissipated in the component is transferred to the surroundings from the heat sink. The parametric study examines the effects of component power, heat sink size (height), the thickness and emissivity of the heat sink, the vertical location of the component on the heat sink, and the temperature of the horizontal component board on the temperature of the component mounted on the heat sink.

Low forward drop JBS rectifiers fabricated using submicron technology

This paper demonstrates the impact of using submicron technology (0.5 /spl mu/m design rules) on JBS Rectifiers to achieve very low forward voltage drops while maintaining good high temperature reverse blocking characteristics. Two dimensional numerical simulations show that decreasing P/sup +/-junction width and depth improves the on-state voltage drop by improved utilization of the active area for the Schottky region and improved spreading of majority carrier current from the Schottky contact. Experimental results that demonstrate the capability to reduce the forward drop from 0.5 V to 0.25 V, while operating at up to 125/spl deg/C-175/spl deg/C with good reverse blocking capability, are presented. The tradeoff curves between forward drop and reverse leakage current show 45/spl times/ reduction in leakage current for the same forward drop as compared to previous reports on JBS rectifiers. Power dissipation analysis indicates higher operating temperatures, (100/spl deg/C for Ti-JBS and 175/spl deg/C for Cr-JBS rectifiers) with reduced heat sink sizes for the JBS Rectifiers when compared to the conventional Schottky Barrier Diode (SBD).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Effect of the London-Van Der Waals Dispersion Force on Interline Heat Transfer

A theoretical procedure to determine the heat transfer characteristics of the interline region (junction of liquid-solid-vapor) from the macroscopic optical and thermophysical properties of the system is outlined. The analysis is based on the premise that the interline transport processes are controlled by the London-van der Waals dispersion force between condensed phases (solid and liquid). Numerical values of the dispersion constant are presented. The procedure is used to compare the relative size of the interline heat sink of various systems using a constant heat flux mode. This solution demonstrates the importance of the interline heat flow number, A¯h/fgν−1, which is evaluated for various systems.

Analysis of thermal impedance for conventional and beam lead IC chips

The thermal impedance of conventional and beam lead IC packages is evaluated from the partial differential equations, which govern the temperature and heat flow within the chip and substrate, and transmission line analogy. The mounting and the geometry dependance of the thermal impedance for various heat sink and chip sizes are presented for both beam lead and conventional IC packages. The variation of thermal impedance with the number of leads and the various Ceramic sizes is shown for the beam lead IC chip.The lumped and the distributed heat sources have been considered for the different mounting structures.