Heat Sink Device Research Articles

Significant improvement in the interface thermal conductivity of graphene-nanoplatelets/silicone composite

Heat conducting silica gel sheets with graphene nanoplatelets (GNPs) filler prepared by high pressure homogenization were fabricated. The dispersed GNPs filler in silica gel significantly affects the thermal conductivity of GNPs silica gel sheets (GNPs-SGS). The thermal conductivity of GNPs-SGS with 5 wt% GNPs reaches 0.43 W(m · k)−1 which increased by 110% and 50% comparing to the pure silica gel sheets (Pure-SGS) and graphite silica gel sheets (GP-SGS) with the same mass fraction. The efficient of heat conduction of heat-sink device which made of GNPs-SGS with 5 wt% is higher than the one which made of Pure-SGS. Besides, The temperature of the thermal plate is 22 °C lower when using 5 wt% GNPs-SGS compared to the bare one measured by thermal management simulator (TMS), proving its good heat radiation ability. FE-SEM was used to observe the fillers and the section of gel sheets, it can be clearly observed the layered and the uniform distribution of GNPs in the matrix. The facile process of high pressure homogenization to exfoliate GNPs is a feasible program for industrial production.

Investigation of Impact Jets Flow in Heat Sink Device of Closed-Circuit Cooling Systems

The flow simulations of impact jets in the heat sink device of the closed-circuit cooling systems are presented. The analysis of the rate of fluid flow in the heat sink device with the jet supply coolant is given.

Numerical analysis of a multi-channel active cooling system for densely packed concentrating photovoltaic cells

The efficiency of concentrating photovoltaic cells (CPVs) is highly affected by the cell temperature. The main problems for the cooling devices are insufficient heat dissipation and uneven heat distribution. In this study, a novel cooling manifold with multi-channels for densely packed CPVs were proposed and numerical investigated. The effects of coolant type, inlet flow rate and channel dimensions on the cooling performance of the manifold heat sink device were examined. The influence of solar irradiance was also investigated at four solar terms in Shenzhen, China. The results show that great cooling performance and temperature distribution uniformity can be achieved by the novel cooling manifold. Thermal resistance of the studied manifold is also lower than those reported in the literature.

Conditions for the in-situ formation of carbide coatings on diamond grains during their sintering with Cu[sbnd]WC binders

In present work, self-assembled WC/W coatings on diamond grains, sintered with Cu matrix were firstly obtained by gas phase transport mechanism. Conditions for spontaneous coating formation were also determined. The coatings can improve adhesion strength between diamond grains and a binder. Discovered method can be used for production of heat sink and heat spreader devices, as well as cutting tools. As functional additives (precursors) for coating formation, WC and WO3 were used. Morphology and composition of the coatings were identified by XPS, SEM, and TEM techniques. Coating consisting of mixture of metallic tungsten and tungsten carbide is formed on diamond when the Cu+WC binder is used. No coating is formed when copper is modified with WO3 nanoparticles; introduction of 20% Fe to the binder leads to formation of a coating containing 100% tungsten in metallic form. Hence, conditions for formation of the tungsten (tungsten carbide) coating onto the diamond surface during sintering with a metal binder include the presence of a nucleating agent WC and a metal that catalyzes graphitization. It was found that the driving force for spontaneous coating formation is a chemically activated gas-phase mass transfer of WO3 to the diamond surface, its chemisorption and subsequent reduction.

Optimizing the design for a two-phase cooling loop heat pipe: Part A: Numerical model, validation and application to a case study

High-power light-emitting diodes can dissipate several times more heat power than conventional lighting devices, while keeping the junction temperature below a security value, in order to assure reliability and low light decay. No fans are usually permitted, so the heat dissipation solution should adopt new technological advances that are required in the form of lighter, shape-embedded heat-sink devices. The present study addresses the implementation of a special heat-dissipation technology, known as a loop heat pipe, consisting of an evaporator, a condenser, a compensation chamber, and vapor and liquid lines for cooling particular types of devices, such as light-emitting diodes, through the phase-change cooling method. In this paper a new algorithm to simulate this loop heat pipe is presented. This mathematical model is based on steady-state energy balance equations for each main component. Finally, a validation procedure through a fully monitored experimental test is performed to show the effects of different key parameters on the heat load such as radius and length of the vapor line, wick thickness and condensing temperature. It produces an effective optimization of the original design, representing an innovative tool for design assessment, to determine the influence of these key performance parameters for each particular application. Finally, a case study is presented for the optimization of a loop heat pipe design, applied to the cooling of an 80 W street lamp.

Computational thermal fluid dynamic analysis of Hypervapotron heat sink for high heat flux devices application

In fusion devices, plasma is the environment in which light elements fuse producing energy. More than 20% of this power reaches the surface of plasma facing components (e.g. the divertor targets, first wall), where the heat flux local value can be several MW/m2. In order to handle such heat fluxes several coolants are proposed such as water, helium and liquid metals along with different heat sink devices, such as Swirl tubes, Hypervapotrons, Jet cooling, Pin-fins, etc. Among these, Hypervapotron concept, operating in highly subcooled boiling regime with water as a coolant is considered as one of the potential candidates. In this paper, a Computational Fluid Dynamic (CFD) approach is used to analyze the boiling flow inside Hypervapotron channel using two different boiling models: Rohsenow boiling model and Transition boiling model, these models are available in the commercial CFD code STARCCM+, and uses Volume of Fluid approach for the multiphase flow analysis. They are benchmarked using experimental data obtained from experiments conducted at Joint European Torus, UK. The simulated results are then compared with each other and also with other simulated data available to test the quantitative, qualitative features of boiling models in modeling nucleate as well as hard boiling regimes.

Development of heat sink device by using topology optimization

Small scale fluid flow systems have been studied for various applications, such as chemical reagent dosages and cooling devices of compact electronic components. This work proposes to present the complete cycle development of an optimized heat sink designed by using Topology Optimization Method (TOM) for best performance, including minimization of pressure drop in fluid flow and maximization of heat dissipation effects, aiming small scale applications. The TOM is applied to a domain, to obtain an optimized channel topology, according to a given multi-objective function that combines pressure drop minimization and heat transfer maximization. Stokes flow hypothesis is adopted. Moreover, both conduction and forced convection effects are included in the steady-state heat transfer model. The topology optimization procedure combines the Finite Element Method (to carry out the physical analysis) with Sequential Linear Programming (as the optimization algorithm). Two-dimensional topology optimization results of channel layouts obtained for a heat sink design are presented as example to illustrate the design methodology. 3D computational simulations and prototype manufacturing have been carried out to validate the proposed design methodology.

Assessment of an active-cooling micro-channel heat sink device, using electro-osmotic flow

Non-uniform heat flux generated by microchips causes “hot spots” in very small areas on the microchip surface. These hot spots are generated by the logic blocks in the microchip bay; however, memory blocks generate lower heat flux on contrast. The goal of this research is to design, fabricate, and test an active cooling micro-channel heat sink device that can operate under atmospheric pressure while achieving high-heat dissipation rate with a reduced chip-backside volume, particularly for spot cooling applications. An experimental setup was assembled and electro-osmotic flow (EOF) was used thus eliminating high pressure pumping system. A flow rate of 82 μL/min was achieved at 400 V of applied EOF voltage. An increase in the cooling fluid (buffer) temperature of 9.6 °C, 29.9 °C, 54.3 °C, and 80.1 °C was achieved for 0.4 W, 1.2 W, 2.1 W, and 4 W of heating powers, respectively. The substrate temperature at the middle of the microchannel was below 80.5 °C for all input power values. The maximum increase in the cooling fluid temperature due to the joule heating was 4.5 °C for 400 V of applied EOF voltage. Numerical calculations of temperatures and flow were conducted and the results were compared to experimental data. Nusselt number (Nu) for the 4 W case reached a maximum of 5.48 at the channel entrance and decreased to reach 4.56 for the rest of the channel. Nu number for EOF was about 10% higher when compared to the pressure driven flow. It was found that using a shorter channel length and an EOF voltage in the range of 400–600 V allows application of a heat flux in the order of 10 4 W/m 2, applicable to spot cooling. For elevated voltages, the velocity due to EOF increased, leading to an increase in total heat transfer for a fixed duration of time; however, the joule heating also got elevated with increase in voltage.

An experimental method to measure initiation events during unstable stress-inducedmartensitic transformation in a shape memory alloy wire

An experimental configuration is demonstrated that captures features of the initiation ofunstable stress-induced transformation in a shape memory alloy (SMA). The apparatususes circulating fluids through the grips and a heat sink and thermoelectric devices tocontrol the temperature profile of a specimen within a mechanical testing machine. Theconfiguration can be used to restrict the initiation of phase transformation toa small region of interest of the free length, while permitting full-field opticaltracking, infrared imaging, use of laser extensometry, and monitoring of loadand extension. In this way, some longstanding difficulties in the measurement ofthermo-mechanical phenomena in SMA wire have been resolved. The size of initiationstress peaks can be accurately measured for both transformation directions withoutchanging the wire geometry, the temperature of a region of interest can be selectedover a wide range, and imaging can be performed for multiple loading cyclesand for events that occur from static to near dynamic rates. The motivation forthis work is to produce high quality data for use in calibrating numerical modelsthat study thermo-mechanical coupling during unstable transformation behavior.

1102 空調機器における製品機能と形状両立のための冷却設計(OS1 製品開発と設計方法論)

Up front design method for variety (DfV) is effective to minimize model change impact on the total cost of product series. However, DfV is unsuitable to adapt for re-layout of cross-functional module. So, we proposed a collaborative design method by using communication table to visualize the explicit and tacit knowledge of mechanical engineers. This paper shows a design innovation on air-conditioning system about a trade-off design optimization between heat sink layout and device performance by applying a heat pipe. As a result, effectiveness of our proposal method is demonstrated.

429 樹脂/金属押出し法を用いた極細貫通気孔を持つアルミ多孔体の創製(粉末加工)

To fabricate heatsink devices or ultra-light structural parts, a method of producing micochannels in aluminium with utilizing plastic forming is proposed. In the present study, cylindrical billets containing aluminium powder or tubes with some kinds of resin rods or fibers are extruded at an elevated temperature. It is found that aramid inserts are successful in thinning down without breakage, as a space holder, while the aluminium matrix consolidates during extrusion. The aramid inserts are burned out in the subsequent firing process, and the penetration in the extruded bar is confirmed.

Influence of probe beam multi-reflection on thermal lens measurements: Application to Nd:YAG rods

In this work time resolved thermal lens measurements were carried out in Nd-doped yttrium aluminum garnet laser crystal. We observed that due to the probe beam multi-reflection the thermal lens signal was influenced by the moving fringes that occurred in front of the detector. By using a heat sink device, this effect was minimized permitting the determination of the temperature coefficient of optical path length, the thermal diffusivity and the thermal conductivity of the sample. As a complementary technique, the thermal relaxation method was used to measure the sample specific heat.

Diffusion within a porous medium with randomly distributed heat sinks

Heat sinks filled with phase-change material, a design concept suitable for the thermal management of electronic airborne systems, find limited applicability at present due to lack of structural rigidity and poor isothermal cooling characteristics. A composite heat sink device (CHSD) is a new design concept proposed in this work, which combines the thermal benefit of the phase-change material with the structural rigidity provided by a solid porous matrix. The device consists of a solid porous matrix with pores filled with capsules containing a phase-change material. Numerical simulations of a CHSD steady-model indicate the existence of a maximum capsule density beyond which a transition from disperse diffusion (when all capsules actively participate in the diffusion process) to concentrate diffusion (when the capsules close to the heated surface shield the capsules placed further away) occurs. This observation is important for optimizing the volume of the CHSD.

4830100 Heat-pipe device and heat-sink device

4830100 Heat-pipe device and heat-sink device

Development of a passive device for freezing large amounts of transplantable skin at one time in a −70 °C mechanical refrigerator

A simple device has been developed for the simultaneous cooling of up to 9120 cm 2 of allograft skin in a flat package format. The device, named an insulated alternating-offset heat sink device, is composed of a stack of interleaved layers of 2.0-mm-thick packets of skin and 3.18-mm-thick aluminum heat sinks (each 33.0 cm long by 22.9 cm wide). Four skin packets are placed in a single layer on each heat sink plate, and the number of plates can be varied to accommodate different numbers of skin packets. Every heat sink protrudes 6.3 cm of its 33.0-cm length beyond the skin packets to make a fin for heat convection, but adjacent plates alternate the direction of their fin protrusion so that the layers of plates alternate in their 6.3-cm offset. Insulation layers of 2.54-cm-thick expanded polystyrene are placed on the exposed surfaces of the top and bottom heat sinks in the stack, and the stack is held together by rubber bands. The device is cooled in a −70 °C mechanical refrigerator. Maximal cooling rates of −1.8 °C min −1 are obtained for both 6- and 11-plate devices, and −3.0 °C min −1 for a 2-plate device. The exothermic temperature plateaus associated with skin cooled in these devices are 1.5–1.8 min in duration. Skin cooled by this technique maintains levels of glucose oxidation similar to those associated with skin cooled by liquid nitrogen vapor at a controlled rate of −1 °C min −1, provided rapid warming is employed after −70 °C storage. The development of this device provides a method for the simple, low-cost cryopreservation of the large amounts of allograft skin obtained from a cadaveric donor.

Development of a simple insulated heat sink device for large volume skin freezing

Development of a simple insulated heat sink device for large volume skin freezing