Optimization of Heat Spreader Design for Electronic Cooling

The continuing increase in IC （Integrated Circuit） power levels and microelectronics packaging densities has resulted in the need for detailed considerations of the heat sink design for integrated circuits. One of the major components in the heat sink is the heat spreader which must be designed to effectively conduct the heat dissipated from the chip to a system of fins or extended surfaces for convective heat transfer to a flow of coolant. The heat spreader design must provide the capability to dissipate the thermal energy generated by the chip. However, the design of the heat spreader is also dependent on the convection characteristics of the fins within the heat sink, as well the material and geometry of the heat spreader. This paper focuses on the optimization of heat spreaders in a heat sink for safe and efficient performance of electronic circuits. The results of the study show that, for air-cooled electronics, the convective effects may dominate the thermal transport performance of the heat spreader in the heat sink.

2-Dimensional CFD Simulation and Correlation Development for Optimization of Fin Heatsinks in Electronic Cooling

CFD has penetrated into the field of electronic cooling for some time. Both parallel and staggered plate fin heatsinks are widely used in modern computers. This paper presents the ways to make most use of CFD in optimization design of those heatsinks: the flow and heat transfer of staggered and parallel plate fm heatsinks of various geometry were simulated by using Fluent 5.0 commercial CFD code. Based on 60 different simulation solutions, two correlations, concerning Nusselt number and friction factor as the functions of geometrical and operational parameters of the heatsinks were developed. The presentation parameter examination was also performed by comparing the numerical solutions with the analytical solutions of parallel plate arrays, showing that the correct parameters are used in the correlations.

Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology

During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cool- ing techniques for electronic and microelectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection,liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.

Design of a Prototype EHD Air Pump for Electronic Chip Cooling Applications

This paper presents the design,optimization and fabrication of an EHD air pump intended for high-power electronic chip cooling applications.Suitable high-voltage electrode configurations were selected and studied,in terms of the characteristics of the generated electric field,which play an important role in ionic wind flow.For this purpose,dedicated software is used to implement finite element analysis.Critical design parameters,such as the electric field intensity,wind velocity,current flow and power consumption are investigated.Two different laboratory prototypes are fabricated and their performances experimentally assessed.This procedure leads to the fabrication of a final prototype,which is then tested as a replacement of a typical fan for cooling a high power density electronic chip.To assist towards that end,an experimental thermal testing setup is designed and constructed to simulate the size of a personal computer’s CPU core of variable power.The parametric study leads to the fabrication of experimental single-stage EHD pumps,the optimal design of which is capable of delivering an air flow of 51 CFM with an operating voltage of 10.5 kV.Finally,the theoretical and experimental results are evaluated and potential applications are proposed.

Absolute dielectronic recombination rate coefficients of highly charged ions at the storage ring CSRm and CSRe

Dielectronic recombination(DR)is one of the dominant electron-ion recombination mechanisms for most highly charged ions(HCIs)in cosmic plasmas,and thus,it determines the charge state distribution and ionization balance therein.To reliably interpret spectra from cosmic sources and model the astrophysical plasmas,precise DR rate coefficients are required to build up an accurate understanding of the ionization balance of the sources.The main cooler storage ring(CSRm)and the experimental cooler storage ring(CSRe)at the Heavy-Ion Research Facility in Lanzhou(HIRFL)are both equipped with electron cooling devices,which provide an excellent experimental platform for electron-ion collision studies for HCIs.Here,the status of the DR experiments at the HIRFL-CSR is outlined,and the DR measurements with Na-like Kr25^(+)ions at the CSRm and CSRe are taken as examples.In addition,the plasma recombination rate coefficients for Ar12^(+),14^(+),Ca14^(+),16^(+),17^(+),Ni19^(+),and Kr25^(+)ions obtained at the HIRFL-CSR are provided.All the data presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00113.00092.

Investigations of the dielectronic recombination of phosphorus-like tin at CSRm

The electron–ion recombination for phosphorus-like^（112） Sn^（35＋）has been measured at the main cooler storage ring of the Heavy Ion Research Facility in Lanzhou, China, employing an electron–ion merged-beams technique. The absolute total recombination rate coefficients for electron–ion collision energies from 0 e V–14 e V are presented. Theoretical calculations of recombination rate coefficients were performed using the Flexible Atomic Code to compare with the experimental results. The contributions of dielectronic recombination and trielectronic recombination on the experimental rate coefficients have been identified with the help of the theoretical calculation. The present results show that the trielectronic recombination has a substantial contribution to the measured electron–ion recombination spectrum of^（112）Sn^（35＋）. Although a reasonable agreement is found between the experimental and theoretical results the precise calculation of the electron–ion recombination rate coefficients for M-shell ions is still challengeable for the current theory.

Prediction Model for Cooling of an Electrical Unit with Time-Dependent Heat Generation

The satisfactory performance of electrical equipments depends on their operating temperature. In order to maintain these devices within the safe temperature limits, an effective cooling is needed. High heat transfer rate of compact in size and reliable operation are the challenges of a thermal design engineer of electronic equipment. Then, it has been simulated the transient a three-dimensional model to study the heating phenomenon with two assumption values of heat generation. To control for the working of this equipment, cooling process was modeled by choosing one from different cooling technique. Constant low speed fan at one direction of air flow was used for cooling to predict the reducing of heating temperature through working of this equipment. Numerical Solution of finite difference time domain method （FDTD） has been utilized to simulate the temporal and spatial temperature profiles through two processes, which would minimize the solution errors.

面向异构集成应用的“片上”嵌入式冷却技术的研究进展

The electronics packaging community strongly believes that Moore’s law will continue for another few years due to recent technological efforts to build heterogeneously integrated packages.Heterogeneous integration(HI)can be at the chip level(a single chip with multiple hotspots),in multi-chip modules,or in vertically stacked three-dimensional(3D)integrated circuits.Flux values have increased exponentially with a simultaneous reduction in chip size and a significant increase in performance,leading to increased heat dissipation.The electronics industry and the academic research community have examined various solutions to tackle skyrocketing thermal-management challenges.Embedded cooling eliminates most sequential conduction resistance from the chip to the ambient,unlike separable cold plates/heat sinks.Although embedding the cooling solution onto an electronic chip results in a high heat transfer potential,technological risks and complexity are still associated with the implementation of these technologies and with uncertainty regarding which technologies will be adopted.This manuscript discusses recent advances in embedded cooling,fluid selection considerations,and conventional,immersion,and additive manufacturing-based embedded cooling technologies.

Influence of the zigzag fins and inlet arrangements on the cooling proficiency of the mini-channel heat sink

Mini-channel heatsinks are one of the most effective thermal management methods for high heatflux devices due to the high performance of convective heat transfer.In recent years,various techniques have been innovated to improve the thermal proficiency of the mini-channel heatsinks.Some of these are taking advantage offins’structural designs and ar-rangements of inlets and outlets.The zigzagfins and channels were considered in the previous works in heatsinks,and researchers analyzed their cooling enhancement effects.However,in the present work,a combined cooling technique,considering new-type zigzagfins’geometrical parameters(arrangement,length,and height)causes turbulenceflow and higher convective heat transfer along with different positionings offlow inlet and outlets resulting in superior temper-ature uniformity,is proposed to evaluate their impacts on the cooling proficiency of the heat sink versus different Reynolds numbers.To assess the thermal and hydraulic performance of the proposed heatsink,different parameters,including temperature contours,Nusselt numbers,thermal resistance,and entropy generation are investigated.As a result,it is observed that in the case demonstrating the best thermal performance,the Nusselt number,pressure drop,thermal resistance,and entropy generation are respectively 37.13,4586.46 Pa,0.000078 m^(2)·K/W,and 0.1078 W/K in the best header.As well,it is found that by changing the arrangements of inlets and outlets,the Nusselt number,and thermal resistance are improved by 12%and 13%,respectively.Accordingly,the proposed mini-channel heat sink could be used as a high-performance thermal management system for electronic devices in different industries,including energy,solar,and medical sectors.

Correlations Based on CFD and Their Applications in Optimization for Staggered and Parallel Plate Fin Heatsinks

Both parallel and staggered plate fin arrays have shown promise for use inhigh performance heatsinks regard of its individual manufacturing costs. The geometrical andoperational parameters are very important to their cooling performance as heatsinks in practicalapplications. Fluent 5.0 commercial CFD (computational fluid dynamic) code is used to simulate theflow and heat transfer of those heatsinks of different realistic parameters. Based on thosesimulations, two correlations, concerning Nusselt number and friction factor as the functions ofgeometrical and operational parameters, FB (fin-base area ratio), PR' (ratio of spanwise pitch tolengthwise pitch) and Re, were developed. From the both, the performance comparisons for optimizinggeometrical and operational parameters of a fixed dimension heatsink are shown at constant pumpingpower and constant thermal resistance. Several optimized parameters were obtained can out performthe staggered ones.

Experimental study of the effects of a transversal air-flow deflector in electronics air-cooling

This paper presents an experimental investigation of the influence of a transversal flow deflector on the cooling of a heated block mounted on a flat plate.The deflector is inclined and therefore it guides the air flow to the upper surface of the block.This configuration is simulating the air-cooling of a rectangular integrated circuit or a current converter mounted on an electronic card.The electronic component is assumed dissipating low heat power,as such,air forced convection is still a sufficient cooling way even without fan or heat sink on the component.The measurements are given by hot and cold wires anemometers and by an InfraRed camera.The results give details of the effects of the deflection on the hydrodynamic and the thermal fields on and over the block for different inclination angles.They show that the deviation caused by the deflector may significantly enhance the heat transfer from the component.Deflection is also able to avoid local overheating of the electronic component.Optimum heat transfer rate and homogenised temperature are shown to be obtained with an inclination angle =30°.

A New Method of Roughness Construction and Analysis of Construct Parameters

In micro-manufacturing,roughness is unavoidable due to the tolerance of micro-machining methods.Roughness in microchannel could have a significant influence on flow and heat transfer since the size of microchannel is very small.In our work,roughness is modeled as a superposition of waves.A simple Fourier series method is proposed to construct the rough surface.With this method,roughness is constructed on the bottom of the rectangular microchannel which has a hydraulic diameter of 0.5 mm.Two important parameters during roughness construction,triangulate size and correlation length are studied under the same relative roughness 1%.Results show that flow and heat transfer characteristics are not sensitive to triangulate size.While triangulate size is changing from 0.1 mm to 0.05 mm,the variations of pressure drop and average Nusselt number are less than 1%.Correlation length could influence the topography of roughness surface a lot,smaller correlation length will lead to more pressure drop and lower Nusselt number.

Effects of bending on heat transfer performance of axial micro-grooved heat pipe

Heat pipe is always bent in the typical application of electronic heat dissipation at high heat flux,which greatly affects its heat transfer performance. The capillary limit of heat transport in the bent micro-grooved heat pipes was analyzed in the vapor pressure drop,the liquid pressure drop and the interaction of the vapor with wick fluid. The bent heat pipes were fabricated and tested from the bending angle,the bending position and the bending radius. The results show that temperature difference and thermal resistance increase while the heat transfer capacity of the heat pipe decreases,with the increase of the bending angles and the bending position closer to the vapor section. However,the effects of bending radius can be ignored. The result agrees well with the predicted equations.

Fabrication and thermal performance of grooved-sintered wick heat pipe

Some novel grooved-sintered composite wick heat pipes(GSHP) were developed for the electronic device cooling.The grooved-sintered wicks of GSHP were fabricated by the processes of oil-filled high-speed spin forming and solid state sintering.The wick could be divided into two parts for liquid capillary pumping flow:groove sintered zone and uniform sintered zone.Both of the thermal resistance network model and the maximum heat transfer capability model of GSHP were built.Compared with the theoretical values,the heat transfer limit and thermal resistance of GSHP were measured from three aspects:copper powder size,wick thickness and number of micro grooves.The results show that the wick thickness has the greatest effect on the thermal resistance of GSHP while the copper powder size has the most important influence on the heat transfer limit.Given certain copper powder size and wick thickness,the thermal resistance of GSHP can be the lowest when micro-groove number is about 55.

Thermal Analysis of Melting Occurring Inside a Finned Rectangular Enclosure Equipped with Discrete Pulsed Protruding Heat Sources

This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources.The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources,in sensible and latent forms.The heat sources are assumed to simulate electronic components undergoing a superheating technical issue.By extracting heat from the electronics,the PCM plays the role of a heat sink.To analyze the thermal behavior and predict the cooling performance of the proposed cooling system,we derive a nonlinear mathematical model based on mass,momentum and energy conservation laws.Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink.Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume.A comparison between our numerical results and experimental data selected from the literature shows a good agreement.The main conclusion is that the presence of the fin leads to a slight increase in the melting time.

Research on the detuning system of a cooling electron beam for the dielectronic recombination experiment at CSRm

The storage ring equipped with an electron cooler is an ideal platform for dielectronic recombination （DR） experiments. In order to fulfill the requirement of DR measurements at the main Cooler Storage Ring, a detuning system for the precision control of the relative energy between the ion beam and the electron beam has been installed on the electron cooler device. The test run using 7.0 MeV/u C6＋ beam was performed with recording the Schottky spectra and the ion beam currents. The influence of pulse heights and widths of the detuning voltage on the ion beam was analyzed. For the small pulse height, the experimental results from the Schottky spectra were in good agreement with the theoretical results. The frequency shift in the Schottky spectra was significantly reduced for the short pulse width. For the large pulse height, an oscillation phenomenon was observed and some effective ways to reduce the oscillation were pointed out. The detailed description of the phenomenon and the theoretical model based on the plasma oscillation was discussed in this paper. The overall results show that the new detuning system works properly, and could fulfill the requirements of future DR experiment.

An Experimental Study on the Performance of a Stainless Steel-Water Loop Heat Pipe under Natural Cooling Condition

Aiming to improve the thermal characteristics of modern electronics, we experimentally study the performance of a stainless steel/water loop heat pipe(LHP) under natural cooling condition. The LHP heat transfer performance, including start-up performance, temperature oscillation and total thermal resistance at different heat loads and with different incline angles have been investigated systematically. Experimental results show that at an optimal heat load(i.e. 60 W) and with the LHP being inclined 60 to the horizontal plane, the total thermal resistance is lowered to be ~0.24 K/W, and the temperature of evaporator could be controlled steadily at around 90 C.

Injection method of barrier bucket supported by off-aligned electron cooling for CRing of HIAF

A new accelerator complex, HIAF （the High Intensity Heavy Ion Accelerator Facility）, has been approved in China. It is designed to provide intense primary and radioactive ion beams for research in high energy density physics, nuclear physics, atomic physics as well as other applications. In order to achieve a high intensity of up to 5× 10^11 ppp 23Su34＋, the Compression Ring （CRing） needs to stack more than 5 bunches transferred from the Booster Ring （BRing）. However, the normal bucket to bucket injection scheme can only achieve an intensity gain of 2, so an injection method, fixed barrier bucket （BB） supported by electron cooling, is proposed. To suppress the severe space charge effect during the stacking process, off-alignment is adopted in the cooler to control the transverse enfittance. In this paper, simulation and optimization with the BETACOOL program are presented.

Commissioning of electron cooling in CSRe

The 400 MeV/u 12C6＋ ion beam was successfully cooled by the intensive electron beam near 1 A in CSRe.The momentum cooling time was estimated near 15 s.The cooling force was measured in the cases of difierent electron beam profiles,and the difierent angles between the ion beam and electron beam.The lifetime of the ion beam in CSRe was over 80 h.The dispersion in the cooling section was confirmed as positive close to zero.The beam sizes before cooling and after cooling were measured by the moving screen.The beam diameter after cooling was about 1 mm.The bunch length was measured with the help of the signals from the beam position monitor.The difiusion was studied in the absence of the electron beam.

Commissioning of electron cooling in CSRm

A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108 particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10-4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy, electron beam current, electron beam profile, expansion factor and injection interval have been performed. The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.