Effect of chip spacing in a multichip module on the heat transfer for paraffin slurry flow

The experiments were conducted by using water and paraffin slurry to investigate the effect of a chip spacing in the multichip module on the cooling characteristics from an in-line 4 × 3 array of discrete heat sources which were flush mounted on the top wall of a channel, The experimental parameters were chip spacing in a multichip module, heat flux of simulated VLSI chip, mass fraction of paraffin slurry, and channel Reynolds number. The removable heat flux at the same chip surface temperature decreased as the chip spacing decreased at the first and fourth rows. The local heat transfer coefficients for the paraffin slurry were larger than those for water, and the chip spacing on the local heat transfer coefficients for paraffin slurry influenced less than that for water. The enhancement factor for paraffin slurry showed the largest value at a mass fraction of 5% regardless of the chip spacing, and the enhancement factors increased as the chip spacing decreased. This means that the paraffin slurry is more effective than water for cooling of the highly integrated multichip module.     

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width) ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity caused by more active mixing of the jet flow.     

微/小通道冷板在某型相控阵天线上的对比分析

微通道换热是近年来电子机械工程抗恶劣环境研究的热点之一。由于其具有良好的换热特性,现在逐渐被应用于高热流密度电子设备的冷却散热系统设计之中。相控阵天线具有热源集中、热流密度极高等特点。文中将新型微通道冷板与某型相控阵天线进行有机结合,提出了一种新的相控阵天线冷却方式。同时,通过基于有限体积法的仿真分析表明,微通道冷板相较于小通道冷板更有利于控制天线中T/R模块的温度。     

基于多功能结构的相控阵天线一体化设计

为了满足星载有源相控阵天线对轻量化以及承载、热控等多功能一体化的迫切需求,文中开展了轻质多功能结构相控阵天线的设计理论、制备工艺、控温特性和力学性能等研究,提出了一种基于多功能结构的星载有源相控阵天线一体化设计技术,利用轻质多功能复合安装板结构,合并平面正交一体桁架热管,在内部空间嵌埋有源功能模块,融合低剖面辐射阵面形成天线功能,制备了集控温、承载、电磁辐射于一体的多功能结构的轻质相控阵天线,并对多功能结构天线子阵进行了一体化设计和验证。结果表明,多功能结构天线系统布局改善了微波部件互联的性能,提高了有源阵列的散热和辐射效率以及系统性能,显著减小了天线阵列的剖面,大幅降低了有源阵列天线的重量。     

相控阵阵面热设计及流量分配研究

为解决某有源相控阵中T/R组件散热及组件之间温度差异问题,文中针对相控阵阵面布局特点,采取冷板并联、流量均分的热设计方案。运用定性分析与数值计算相结合的方法确定阵面总流量及流量分配,根据流量分配对最长冷板进行了热仿真分析,分析结果表明流量分配满足T/R组件散热要求。对于影响T/R组件之间温度差异的流量分配问题,通过定性分析各冷板通路流阻组成,介绍了如何利用等流阻匹配实现流量均分。最后通过全阵T/R组件温度测试验证了热设计方案满足T/R组件散热及组件之间温度差异要求。     

Modeling 3D magnetic fields for precision magnetic actuators that use non-periodic magnet arrays

In this paper we use the Fourier transform to model and simulate the three-dimensional magnetic field created by finite, planar permanent magnet arrays that are Fourier-transformable and possess vertical magnetization. This approach captures the three-dimensional characteristic of the fields, including the field components near the ends of the array. These end effects are important in small-scale precision actuators where geometric constraints preclude the use of larger finite arrays that emulate the behavior of infinite arrays. We demonstrate how to model and compute the field characteristics along a plane using two-dimensional Fast Fourier transforms. Model predictions are compared with analytical solutions for a simple prototype magnet array, measured values of a magnet array's flux density, and a meso-scale actuator's behavior. The difference between measured and predicted values is less than 5%.     

某液冷冷板换热特性实验研究

针对电子设备冷却用液冷冷板设计,选用了3种新型的锯齿型翅片作为冷板内芯。为了验证新型冷板的换热特性,应用稳态电加热法,分别对内芯为矩形、梯形和侧向梯形锯齿型翅片的3种冷板以蒸馏水为介质的换热特性进行了实验研究,分别获得了在一定雷诺数范围内的换热无量纲准则式,并对液冷冷板的换热特性进行了比较。结果表明,在小流量区域,3种冷板换热系数差别不大;随着流量增大,侧向梯形锯齿型翅片对冷板通道内的扰动更强,换热性能更好。本实验为液冷冷板设计提供了参考。     

板式空冷器波纹板片内的流场和温度场分布研究

通过创建二维、三维波纹板束模型,采用流体计算软件对模型进行模拟分析,研究波纹板片的流场和温度场的分布,并与平行板片的传热效果相比较,分析波纹板片传热效果提高的原因.     

涡轮动叶表面气膜冷却换热实验研究

这里在大尺寸低速叶栅传热风洞中，对某型涡轮动叶表面有无气膜冷却的换热情况进行了详细的实验研究，实验结果表明，不同孔位出流的换热由于孔排下游表面来流速度及叶片表面曲率的不同而有着不同的规律，即主流雷诺数对叶片表面特别是压力面和前缘区域的换热系数比的影响较小，吹风比对换热系数影响较大，并且随气膜孔位置和来流雷诺数的变化而情况复杂。     

A study on heat transfer characteristics for staggered tube banks in cross-flow

Cross-flow over tube banks is commonly encountered in practice in heat transfer equipments. The local and average heat transfer characteristics for staggered tube banks are investigated in the present study. A naphthalene sublimation technique is employed to obtain the local heat transfer coefficients, and experiments are performed for various tube spacings, tube locations and Reynolds numbers. The variation of the local heat transfer coefficients is quite different from the first tube to the third tube, but they are similar afterwards. The average Nusselt number increases more than 30% and 65% on the second and third tubes, respectively, in comparison with that of the first tube. And the empirical correlations for average heat transfer coefficients are compared with the conventional heat transfer correlations.     

An experiment on thermosyphon boiling in uniformly heated vertical tube and asymmetrically heated vertical channel

Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made by two parallel rectangular plates was carried out in this study for possible application of the direct immersion cooling. Fluorinert FC-72 as a working fluid was used in this experiment. Asymmetric heated channel of open periphery with gap size of 1, 2, 4 and 26 mm and uniformly heated vertical tubes with diameter of 9, 15 and 20 mm were boiled at saturated condition. The boiling curves from tested surfaces exhibited the boiling hysteresis. It was also found that the gap size is not a significant parameter for the thermosyphonic boiling heat transfer with this Fluorinert. Rather pool boiling characteristics appeared for larger gap size and tube diameter. The heat transfer coefficients measured were also compared with the calculation results by Chen’s correlation.     

Numerical investigation of fluid flow past a square cylinder using upstream,downstream and dual splitter plates

A two-dimensional numerical study is carried out to analyze the drag reduction and vortex shedding suppression behind a square cylinder in presence of splitter plate arranged in upstream, downstream and both upstream and downstream location at low Reynolds number (Re = 160). Computations are performed using a Single relaxation time lattice Boltzmann method (SRT-LBM). Firstly, the code is validated for flow past a single square cylinder. The obtained results are compared to those available in literature and found to be in good agreement. Numerical simulations are performed in the ranges of 1 ≤ L ≤ 4 and 0 ≤ g ≤ 7, where L and g are the length of splitter plate and gap spacing between the splitter plate and main square cylinder, respectively. The effect of these parameters on the vortex shedding frequency, time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualization and force exerted on the cylinder are quantified together with the observed flow patterns around the main cylinder and within the gap spacings. The observed results are also compared with a single square cylinder without splitter plate. We found that at some combinations of L and g, the mean drag coefficient and Strouhal number reach either its maximum or minimum value. It is found that the drag is reduced up to 62.2 %, 13.3 % and 70.2 % for upstream, downstream and dual splitter plates, respectively as compared to a single square cylinder (without splitter plate). In addition, in this paper we also discussed the applications of SRT-LBM for suppression of vortex shedding and reduction of the drag coefficients.     

某毫米波功放组件液冷散热设计

随着雷达技术的提升,阵列化排布的毫米波功放组件逐渐应用于相控阵体制的雷达之中。体积小、散热量大、热流密度高是毫米波功放组件的典型特征。如何在极小的体积内实现功放组件的液冷散热集成成为毫米波相控阵体制雷达应用的瓶颈。文中通过对功放组件的结构进行优化设计,实现在5 mm组阵间距条件下功放组件的液冷散热集成,对毫米波功放组件的流量特性与温度特性进行数值求解,通过电气补偿电路消除核心芯片温度分布的影响。     

贴附型局域共振声子晶体双层板的带隙特性

针对板面之间周期性贴附柱状散射体的局域共振声子晶体双层板结构,采用有限元法计算了该结构能带结构、特征模态所对应的位移场以及相应有限周期双层板结构的传输曲线,对其展现出的带隙特性进行了研究。数值结果和分析表明,当激励点和响应点位于上下异侧板时,一条起始频率低并且带隙宽的完全带隙可以被打开。该带隙的打开可以认为是共振单元的振动模态和上下板的板振动模态相互耦合作用的结果。同时,由双板间空气声腔所带来的声振耦合效应对带隙的影响可以忽略不计。此外,双层板结构展现出许多相应单板结构共同的带隙特性,但其拥有单板所无法比拟的宽带隙特性。通过改变结构相关参数,可以实现对带隙的有效调节。     

A numerical study on the flow and heat transfer characteristics in a noncontact glass transportation unit

Vertical sputtering systems are key equipment in the manufacture of liquid crystal display (LCD) panels. During the sputtering process for LCD panels, a glass plate is transported between chambers for various processes, such as deposition of chemicals on the surface. The minimization of surface scratches and damage to the glass, the rate of consumption of gas, and the stability of the floating glass-plate are key considerations in the design of a gas pad. To develop new, non-contact systems of transportation for large, thin glass plates, various shapes of the nozzle of a gas pad unit were considered in this study. In the proposed nozzle design, negative pressure was used to suppress undesirable fluctuations of the glass plate. After the nozzle’s shape was varied through numerical simulations in two dimensions, we determined the optimal shape, after which three-dimensional analyses were carried out to verify the results from the two-dimensional analyses. The rate of heat transfer from the glass plate, as a result of the gas jet, was also investigated. The average Nusselt number at the glass surface varied from 22.7 to 26.6 depending on the turbulence model, while the value from the correlation for the jet array was 23.5. It was found that the well-established correlation equation of the Nusselt number for the circular jet array can be applied to the cooling of the glass plates.     

单相阶段板式多喷嘴阵列喷雾冷却的试验研究

喷雾冷却由于在较小的工质流量下可以实现很高的散热能力,在高热流密度散热、电子元器件热控等领域具有广阔的应用前景。针对较大面积的发热表面的温度控制和热量散出,本文建立闭式喷雾冷却循环系统,并选取板式多喷嘴阵列,对其在单相阶段瞬态和稳态时的换热特性进行研究。系统选取水为工质,冷却30mm×30mm的发热表面。试验中测试了板式多喷嘴阵列的雾化性能,并得出了在单相阶段时瞬态的温度变化曲线和不同体积流量下的喷雾冷却曲线。试验结果表明,板式多喷嘴阵列的雾化特性较为均匀,且喷雾冷却在单相阶段能达到较高换热性能,而流量对换热影响明显,在更大的流量下换热性能更显著。     

An invariant descriptor for conjugate forced convection-conduction cooling of 3D protruding heaters in channel flow

In this research, the temperatures of three-dimensional (3D) protruding heaters mounted on a conductive substrate in a horizontal rectangular channel with laminar airflow are related to the independent power dissipation in each heater by using a matrix G⁺ with invariant coefficients, which are dimensionless. These coefficients are defined in this study as the conjugate influence coefficients (g⁺) caused by the forced convection-conduction nature of the heaters’ cooling process. The temperature increase of each heater in the channel is quantified to clearly identify the contributions attributed to the self-heating and power dissipation in the other heaters (both upstream and downstream). The conjugate coefficients are invariant with the heat generation rate in the array of heaters when assuming a defined geometry, invariable fluid and flow rate, and constant substrate and heater conductivities. The results are numerically obtained by considering three 3D protruding heaters on a two-dimensional (2D) array by ANSYS/Fluent^TM 15.0 software. The conservation equations are solved by a coupled procedure within a single calculation domain comprising of solid and fluid regions and by considering a steady state laminar airflow with constant properties. Some examples are shown, indicating the effects of substrate thermal conductivity and Reynolds number on conjugate influence coefficients.     

Effect of heat source area on the thermal resistance of the wick columns vapor chambers

The results of the spreading thermal resistance, heat transfer and flow characteristics of the vapor chamber embedded with plate fin are investigated. The experiments are performed with the vapor chambers with wick plate and wick columns embedded plate fin. Parametric studies including different heat fluxes, heated surface areas, flow rate of coolants on the cooling performance in terms of the spreading thermal resistance and heat transfer characteristics are considered. A three-dimensional heat and mass transfer model for the vapor chamber with wick plate and wick columns are developed. The velocity and pressure distributions of liquid phase and vapor phase inside the vapor chamber obtained from the simulation are shown. By comparing the experimental results with numerical results, reasonable agreement is obtained. It can be found that the heat input and heat source area have significant effect on the decreasing of the boiling and condensation thermal resistances while they are slightly effect on the decreasing of the convective thermal resistance. Due to the wick plate and wick columns, the capillary force has significant effect on the working fluid circulation, evaporation rate and flow directions of the liquid and vapor phases inside the vapor chamber. The results of this study are of technological importance for the efficient design of cooling system of the personal computer or electronic devices to enhance cooling performance of the vapor chamber.

     

Thermal characteristics of a multichip module using PF-5060 and water

The experiments were performed by using PF-5060 and water to investigate the thermal characteristics from an in-line 6 x 1 array of discrete heat sources for simulating the multichip module which were flush mounted on the top wall of a horizontal, rectangular channel of aspect ratio 0.2. The inlet temperature was 15°C for all experiments, and the parameters were the heat flux of simulated VLSI chips with 10, 20, 30, and 40W/cm² and the Reynolds numbers ranging from 3,000 to 20,000. The measured friction factors for PF-5060 and water gave a good agreement with the values predicted by the modified Blasius equation within ±6%. The chip surface temperatures for water were lower by 14.4-21.5°C than those for PF-5060 at the heat flux of 30W/cm². From the boiling curve of PF-5060, the temperature overshoot at the first heater was 3.5°C and was 2.6°C at the sixth heater. The local heat transfer coefficients for water were larger by 5.5-11.2% than those for PF-5060 at the heat flux of 30W/cm², and the local heat transfer coefficients for PF-5060 and water reached a uniform value after the fourth row. This meant that the thermally fully developed condition was reached after the fourth row. The local Nusselt number data gave the best agreement with the values predicted by the Malina and Sparrow’s correlation and the empirical correlations for Nusselt number were provided at the first, fourth and sixth rows for a channel Reynolds number over 3,000.     

Heat/mass transfer measurement on concave surface in rotating jet impingement

The objective of this paper is to investigate the heat/mass transfer characteristics on a concave surface for rotating impinging jets. The jet with Reynolds number of 5,000 is applied to the concave surface and the flat surface, respectively. The rotating experiments have been carried out at the rotating speed of 560RPM which is corresponding to Ro number of 0.075. The two jet orientation (front and trailing orientation) are considered. Detailed heat/mass transfer coefficients on the target plate were measured using a naphthalene sublimation method. The result indicates that the rotation leads to change in local heat/mass transfer distributions and the slight increase in the Sh level. The front orientation induces asymmetric Sh distributions, whereas the trailing orientation shows the shifted heat/mass transfer feature due to rotation-induced flow behavior. The crossflow effect on heat/mass transfer is also observed as the streamwise direction increases. Compared to flat surface, the heat/mass transfer on the concave surface is enhanced with increasing the spanwise direction due to the curvature effect, providing the higher averaged Sh value. It is proved that the difference of surface geometry affects somewhat the local and averaged heat/mass transfer regardless of rotation condition. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.