Thermal Resistance Of Heat Sink Research Articles

인덕션 쿡탑 기구물 형상변경이 Heatsink 및 Coil 냉각성능에 미치는 영향에 대한 연구

A numerical study on the IPM/Bridge Diode cooling and coil cooling has been performed. Results are presented as plots of thermal resistance, temperature drop and RPM-ratio. CFD analysis for conventional cooling system has been performed as a reference case. As the RPM-Ratio was increased, heatsink thermal resistance and coil temperature were decreased. IPM/Bridge Diode thermal resistance and temperature of the coil is tended to be trade-off. The temperature of coil closest to the AC-motor fan showed the most significant change in accordance with duct design. The temperature of coil located at the top of DC-motor fan showed the most significant variation as the cooling air passes the heatsink fin area.

Optimization of a staggered pin-fin for a radial heat sink under free convection

The design of a staggered pin-fin radial heat sink was optimized for light-emitting diode (LED) device cooling. A numerical model for various pin-fin array heat sinks was developed and verified experimentally. The design variables were determined from sensitivity analysis. Multidisciplinary optimization was conducted based on the heat sink thermal resistance and mass, using an evolutionary algorithm. From the analysis results, the staggered pin-fin radial heat sink was identified as the optimal configuration, demonstrating improved thermal performance by up to 10% while maintaining the same mass or reducing the mass by up to 12% for a given thermal resistance.

Computational Analysis of Conjugate Heat Transfer in Gaseous Microchannels

A fully conjugate heat transfer analysis of gaseous flow in short microchannels is presented. Navier–Stokes equations, coupled with Maxwell and Smoluchowski slip and temperature jump boundary conditions, are used for numerical analysis. Results are presented in terms of Nusselt number, heat sink thermal resistance, and resulting wall temperature as well as Mach number profiles for different flow conditions. The comparative importance of wall conduction, rarefaction, and compressibility are discussed. It was found that compressibility plays a major role. Although a significant penalization in the Nusselt number, due to conjugate heat transfer effect, is observed even for a small value of solid conductivity, the performances in terms of heat sink efficiency are essentially a function only of the Mach number.

Heat Sinks for Miniature Thermoelectric Coolers: Selection and Characterization

The effect of heat sink (HS) thermal resistance on the performance of a thermoelectric cooler (TEC) has been studied. A method of HS characterization is proposed for the typical case of substantial mismatch in the dimensions of these components. This dimension mismatch causes significant heat spreading resistance in the HS base plate which is highly dependent on the lack of conformity of the components. In this study we investigated modern a HS whose thermal resistance Rd was determined experimentally by use of a dummy heater of fixed dimensions. An analytical method is proposed for predicting HS thermal resistance for arbitrary heater dimensions using the certified Rd value as sole reference point. The method is based on an HS thermal model with three-dimensional heat spread in its base plate. This theoretical approach was used for characterization of HS from Alpha Company, a manufacturer of HS for microelectronics. HS with low pressure drop were considered under conditions of natural and forced convection. It is shown that their thermal resistance, which depends on TEC dimensions, can differ substantially from the certified value.

自然对流下LED集成芯片整体式热管散热器性能实验研究

In order to solve the problem of cooling LED multi-chip LED module,an integrated heat pipe heat sink was designed and fabricated. Heat dissipation experiments were conducted to study effects on heat load,filling ratio and inclination angle on the thermal performance of the heat sink in nature convection. The results show that the efficient heat transfer of the heat pipe can reduce the thermal resistance of the heat sink effectively and the optimum filling ratio is 30% in this research.Inclination angle in the range of 0°- 50° has little effect on heat transfer capability of heat pipe at lower heat load. When the angle reaches 75°,heat transfer of heat pipe and thermal resistance of heat sink are all subject to a significant deterioration. The time heat sink enters stable state is about30 min and is not affected by the magnitude of the power. However,the heat sink works stably after40 min when angle is 75°. Compared to traditional parallel plate fins and sunflower fins heat sink,the chip junction temperature with integrated heat pipe heat sink is smallest.

Performance Of LED Employing Metal Oxide Mixed Thermal Interface Material By Structure Function Analysis

LED industries are currently focusing on the thermal management to reduce the junction temperature as well as the total thermal resistance for high power solid state lighting application. Metal powder or metal oxide filled thermal paste (TP) using as a thermal interface material is one kind of approach to solve the problem. In connection with that, milled TiO 2 and Cr 2 O 3 powder were mixed in different ratio with commercial thermal paste. Cumulative structure function (CSF) analysis was used to characterize the metal oxide mixed thermal paste as thermal interface material (TIM) for 3W LED. TiO 2 mixed TIM showed good performance on reducing junction temperature ( ΔT J = 1.19 oC) for driving current at 350 mA. Overall, TiO 2 mixed TP shows low value of board to heat sink thermal resistance ( R th-b-hs ) compared to all other results. Energy Dispersive Spectrum (EDS) analysis results revealed the percentage of mixed powder as low when compared with mixed ratio. O 2 content in mixed paste showed immense effect on reducing total thermal resistance. DOI: http://dx.doi.org/10.11591/ijpeds.v3i4.4150

Nonlocal Modeling and Swarm-Based Design of Heat Sinks

Cooling electronic chips to satisfy the ever-increasing heat transfer demands of the electronics industry is a perpetual challenge. One approach to addressing this is through improving the heat rejection ability of air-cooled heat sinks, and nonlocal thermal-fluid-solid modeling based on volume averaging theory (VAT) has allowed for significant strides in this effort. A number of optimization methods for heat sink designers who model heat sinks with VAT can be envisioned due to VAT's singular ability to rapidly provide solutions, when compared to computational fluid dynamics (CFD) approaches. The particle swarm optimization (PSO) method appears to be an attractive multiparameter heat transfer device optimization tool; however, it has received very little attention in this field compared to its older population-based optimizer cousin, the genetic algorithm (GA). The PSO method is employed here to optimize smooth and scale-roughened straight-fin heat sinks modeled with VAT by minimizing heat sink thermal resistance for a specified pumping power. A new numerical design tool incorporates the PSO method with a VAT-based heat sink solver. Optimal designs are obtained with this new tool for both types of heat sinks, the performances of the heat sink types are compared, the performance of the PSO method is discussed with reference to the GA method, and it is observed that this new method yields optimal designs much quicker than traditional approaches. This study demonstrates, for the first time, the effectiveness of combining a VAT-based nonlocal thermal-fluid-solid model with population-based optimization methods, such as PSO, to design heat sinks for electronics cooling applications. The VAT-based nonlocal modeling method provides heat sink design capabilities, in terms of solution speed and model rigor, that existing modeling methods do not match.

Thermal pulse energy harvesting

This paper presents a new method to enhance thermal energy harvesting with pulsed heat transfer. By creating a phase shift between the hot and cold sides of an energy harvester, periodically pulsed heat flow can allow an available temperature gradient to be concentrated over a heat engine during each thermal pulse, rather than divided between the heat engine and a heat sink. This effect allows the energy harvester to work at maximum power and efficiency despite an otherwise unfavorable heat engine–heat sink thermal resistance ratio. In this paper, the analysis of a generalized energy harvester model and experiments with a mechanical thermal switch demonstrate how the pulse mode can improve the efficiency of a system with equal engine and heat sink thermal resistances by over 80%, although at reduced total power. At a 1:2 engine–sink resistance ratio, the improvement can simultaneously exceed 60% in power and 15% in efficiency. The thermal pulse strategy promises to enhance the efficiency and power density of a variety of systems that convert thermal energy, from waste heat harvesters to the radioisotope power systems on many spacecraft.

Thermal Performance of Higher Aspect Ratio Microchannels Using TiO<SUB>2</SUB>-Water Nanofluids

An experimental setup was developed to study the heat transfer and fluid flow characteristics in rectangular copper microchannels with hydraulic diameter 29.4 microm using TiO2-Water nanofluids. The experimental facility is validated using existing correlations and subsequently tested with 0.1% and 0.3% concentrations of TiO2 nanofluids. The thermal resistance of heat sink with nanofluids is compared with the base fluid. It is inferred that 0.3% TiO2-Water nanofluids have 18% lower thermal resistance as compared to base fluid having for the same operating conditions.

TEMPERATURE CALCULATION OF IGBT MODULE FREQUENCY CONVERTOR AT START OF INDUCTION MOTOR

The most effective and economical way to a smooth start and control the rotor speed of the induction motor is to change the frequency of the voltage supply. During acceleration of the motor it is necessary to ensure not only the actuator static torque, and the dynamic inertia overcoming. Thus, the value of the dynamic moment of inertia depends on the time of increasing the motor rotational speed. To overcome this dynamic torque on the engine during acceleration, stator windings create additional magnetic field due to increase current consumption. Typically, it is desirable that the duration of the engine acceleration was minimal, i.e. , the acceleration is maximized. This may cause excessive increase in the output current of the frequency converter and damage of bipolar transistors with insulated gate (IGBT), which power switches are used. To ensure reliable operation of AC Drivers the method to perform calculations to determine the type of IGBT module, temperatures structures of transistor and inverse diode of the inverter, when starting the engine, depending on the load torque and the moment of inertia of the actuator is proposed. Method for determination of the values of the polynomials coefficients that approximate energy IGBT switching losses and reverse diode recovery losses depending on the value of the collector current IGBT is proposed. A method for determination of the required values of heat sink thermal resistance, which cool IGBT module is proposed. Charts of the transistor temperature dependence and inverse diode values of the acceleration duration and of induction motor inertia – the actuator are shown.

Optimal design of thermoelectric devices with dimensional analysis

The optimum design of thermoelectric devices (thermoelectric generator and cooler) in connection with heat sinks was developed using dimensional analysis. New dimensionless groups were properly defined to represent important parameters of the thermoelectric devices. Particularly, use of the convection conductance of a fluid in the denominators of the dimensionless parameters was critically important, which leads to a new optimum design. This allows us to determine either the optimal number of thermocouples or the optimal thermal conductance (the geometric ratio of footprint of leg to leg length). It is stated from the present dimensional analysis that, if two fluid temperatures on the heat sinks are given, an optimum design always exists and can be found with the feasible mechanical constraints. The optimum design includes the optimum parameters such as efficiency, power, current, geometry or number of thermocouples, and thermal resistances of heat sinks.

H143 自然空冷型冷却システムの低熱抵抗化(OS-3:電子機器・デバイスの熱課題(4))

Reduction of thermal resistance of naturally-cooled cooling system has been investigated. Pin-fin type heat sink was utilized as to clarify the effect of pin arrangement on the thermal performance of heat sink. The pitch of fins was set 1, 2, 3, 4, 5mm where the surface area of all heat sink was set as the same. The results show that the thermal resistance of heat sink decreases with increasing pitch of fin arrangement from 1 to 4mm, whereas the thermal resistance gets increase when the pitch was set 5mm. The results also show that even the slight decrease in fin efficiency causes the increase in the thermal resistance.

Vapor chamber heat sink with hollow fins

A new vapor chamber heat sink with maximum fin efficiency is presented. The fins are hollow, so the vapor generated at the base flows up to the top of the fins. As a result, the heat sink is practically isothermal. A prototype of the hollow fin vapor chamber heat sink was built and tested. The prototype presented 20% less overall thermal resistance than conventional pin fin heat sinks with the same mass and volume. A theoretical model for the heat sink thermal resistance was developed and the agreement between the model and the experimental data is fair.

Experimental analysis of flow and heat transfer in a miniature porous heat sink for high heat flux application

A novel miniature porous heat sink system was presented for dissipating high heat fluxes of electronic device, and its operational principle and characteristics were analyzed. The flow and heat transfer of miniature porous heat sink was experimentally investigated at high heat fluxes. It was observed that the heat load of up to 280W (heat flux of 140W/cm2) was removed by the heat sink with the coolant pressure drop of about 34kPa across the heat sink system and the heater junction temperature of 62.9°C at the coolant flow rate of 6.2cm3/s. Nu number of heat sink increased with the increase of Re number, and maximum value of 323 for Nu was achieved at highest Re of 518. The overall heat transfer coefficient of heat sink increased with the increase of coolant flow rate and heat load, and the maximal heat transfer coefficient was 36.8kW(m2°C)−1 in the experiment. The minimum value of 0.16°C/W for the whole thermal resistance of heat sink was achieved at flow rate of 6.2cm3/s, and increasing coolant flow rate and heat fluxes could lead to the decrease in thermal resistance. The micro heat sink has good performance for electronics cooling at high heat fluxes, and it can improve the reliability and lifetime of electronic device.

On the Color Stability of Phosphor-Converted White LEDs Under DC, PWM, and Bilevel Drive

Most commercial white LEDs are made from nitride-based blue LEDs coated with yttrium aluminium garnet phosphor, which produce spectra that shift in opposite directions under the influences of drive current and junction temperature changes. This property gives rise to different emitted spectra, hence chromaticity properties, when the LED is driven/dimmed by different current waveforms. By using a commercial white LED sample, LUXEON K2, the effects of drive current and junction temperature on the changes of chromaticity coordinates are studied experimentally. The impact of dc, pulse width modulation (PWM), and bilevel current waveform is discussed through a graphical analysis, followed by experimental verification. It is proven that dc offers the best color stability over dimming due to the counteracting influences of drive current and junction temperature variations, whereas an LED constantly suffers from noneliminable chromaticity changes when driven by the PWM. Theoretical explanations are given to justify these cases, and it is found that, for the case of dc drive, an ideal heat sink's thermal resistance can be selected based on a simple equation to minimize the overall chromaticity change over dimming. This paper provides an in-depth discussion on the relations between the chromaticity properties of phosphor-converted (pc) white LEDs and the driving/dimming methods used.

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN A NOVEL HEAT SINK BY MEANS OF ALUMINA NANOFLUIDS

In this paper, heat transfer characteristics of a miniature heat sink cooled by Al2O3–water nanofluids were investigated experimentally. Based on plate fin heat sinks, a new type of plate pinfinnned heat sink is developed which is composed of a plate fin heat sink and columnar pins between the plate fins. The heat sink was fabricated from aluminum and insulated by plexiglass cover plates and consisted of five pin-finned rectangular channels with a length of 42 mm. The volume fraction of the Al2O3–water nanofluid particles was in the range from 0.5 to 2%. Mixtures were prepared without a dispersion agent. Tests were performed while supplying a 180 W/cm 2 heat flux to the bottom of heat sink. Experimental results showed that dispersion of Al2O3 nanoparticles in water increased significantly the overall heat transfer coefficient, while the thermal resistance of heat sink decreased. Also, the plate pin-finned heat sink showed an increase in the heat transfer coefficient up to 20% in comparison with the conventional plate fin heat sink.

Design and Tests of a Water-Cooling Micro-Channel Heat Sink Made by WEDM

The purpose of this research is to design a new heat sink of water-cooling. With the aid of CAE (computer aided engineering), WEDM (wire electrical discharge machining), and the concept of micro-channel design, a heat sink of water-cooling can then be built with the merit of a smaller volume and lower thermal resistance. From this paper, results of the experiment indicate that the thermal resistance of heat sink can be decreased to 0.12 °C/W with input power of 60W, flow rate of 0.6 LPM, and a better heat dissipation with the in input power of 100W or 140W can be revealed.

Design and Tests of a Water-Cooling Micro-Channel Heat Sink Made by WEDM

The purpose of this research is to design a new heat sink of water-cooling. With the aid of CAE (computer aided engineering), WEDM (wire electrical discharge machining), and the concept of micro-channel design, a heat sink of water-cooling can then be built with the merit of a smaller volume and lower thermal resistance. From this paper, results of the experiment indicate that the thermal resistance of heat sink can be decreased to 0.12 °C/W with input power of 60W, flow rate of 0.6 LPM, and a better heat dissipation with the in input power of 100W or 140W can be revealed.

Experimental and numerical investigation of heat transfer in a miniature heat sink utilizing silica nanofluid

In this paper, heat transfer characteristics of a miniature heat sink cooled by SiO 2–water nanofluids were investigated both experimentally and numerically. The heat sink was fabricated from aluminum and insulated by plexiglass cover plates. The heat sink consisted of an array of 4 mm diameter circular channels with a length of 40 mm. Tests were performed while inserting a 180 W/cm 2 heat flux to the bottom of heat sink and Reynolds numbers ranged from 400 to 2000. The three-dimensional heat transfer characteristics of the heat sink were analyzed numerically by solving conjugate heat transfer problem of thermally and hydrodynamically developing fluid flow. Experimental results showed that dispersing SiO 2 nanoparticles in water significantly increased the overall heat transfer coefficient while thermal resistance of heat sink was decreased up to 10%. Numerical results revealed that channel diameter, as well as heat sink height and number of channels in a heat sink have significant effects on the maximum temperature of heat sink. Finally, an artificial neural network (ANN) was used to simulate the heat sink performance based on these parameters. It was found that the results of ANN are in excellent agreement with the mathematical simulation and cover a wider range for evaluation of heat sink performance.

Heat Sink Matching for Thermoelectric Generator

Heat sink does affect on the performance of thermoelectirc generator according to the studies of many authors. In this paper, an analytical model inculding the number of thermocouples and the thermal resistance of heat sink is derived. The match between the thermoelectric module and heat sink is discussed by numerical calculation also. The results show that the thermal resistance of thermoelectric module should be designed to match that of heat sink in order to get the highest output power for a given heat sink. But for a given thermoelectric module, the output power increases with the decrease of heat sink thermal resistance, and there is a suitable heat sink due to the limit of the temperature difference between the heat source and coolant.