Performance analysis of air-cooled microchannel absorber in absorptionbased miniature electronics cooling system

Theoretical analysis and simulation of performance of an air-cooled microchannel absorber is reported in this study. It is shown that the air-cooled microchannel absorber can be integrated into an absorption-based miniature electronics cooling system by which the chip junction temperature can be maintained near room temperature, while removing 100 W of heat load. Water/LiBr pair is used as the working fluid and refrigerant vapor is intended to counter-currently flow against aqueous LiBr solution flow. Parametric study is carried out to determine the effects of several operating parameters, including inlet temperature and mass flow rate of the coolant, and inlet temperature of LiBr solution. To facilitate the air-cooling of microchannel absorber, an offset-strip-fin array is adopted, by which enhanced air-side heat transfer coefficient and large heat transfer area are obtained. The performance of the air-cooled absorber is compared to liquid-cooled absorber.     

Visualization of flow pattern in thermosyphon by ECT

Visualization of the liquid flow in a two-phase closed thermosyphon (TPCT) is studied using electrical capacitance tomography (ECT) with optimal step lengths for iterative image reconstruction algorithm. Measurements are made under a range of heating rates. Experimental results demonstrated ECT’s capability of reconstructing images of thin films of the order of μm in thickness. Results are compared with the established theory and agreements and discrepancies are observed for different thresholds. ECT images of the liquid distributions in the TPCT show clear dependence on the variation of working conditions, which reveals the potential of ECT as an advanced technique for monitoring the operation of TPCT.     

Instability of a two-phase loop thermosyphon

The instability of two-phase loop thermosyphons was investigated experimentally and analytically. Three orifice type inserts were used to study the effect of change in the pressure drop in the flow channel of the TLT on the flow instability and temperature fluctuation. It is observed that a decrease in the size of the orifice insert from 3.7 mm (no insert) to 0.71 mm drastically reduced the fluctuation of the temperature, especially at the evaporator section of the TLT. With the orifice type insert of 0.71 mm for the TLT, the overall temperature fluctuation was almost completely eliminated, especially at higher power input to the TLT. The analysis based on the Kelvin-Helmholtz instability theory seems to predict reasonable well the loop stability state of the TLT with experimentally determined constant factors.     

Thermal flow analysis of vehicle engine cooling system

This paper deals with theoretical model developed for analyzing the heat transfer of automotive cooling systems. The model has a modular structure which links various cooling system submodels. From the model, heat transfer rate of automotive cooling systems can be predicted, providing useful information at the early stages of the design and development. The aim of the study is to develop a simulation program for automotive cooling system analysis and a performance analysis program for analyzing heat exchanger. Heat release rate from combustion gas to coolant through the cylinder wall in engine cylinder was analyzed by using an engine cycle simulation program. In this paper, details of each submodel are described together with the overall structure of the vehicle model.     

聚胺酯泡塑富集-石墨炉原子吸收法测定痕量钯的研究

在强酸性条件下 ,利用聚氨脂泡沫塑料对样品中钯 (II)离子的选择性吸附作用 ,对钯离子进行富集 ,泡塑经HNO3、HClO4 等消解处理 ,然后加入基体改进剂Ni(NO3) 2 ,经石墨炉原子吸收法 (GFAAS)测定其中金属钯元素的含量。实验结果显示 ,金属元素钯在 0～ 72ng/mL范围内线性关系良好 ,线性方程为A =0 0 1115 +0 0 0 6 6 5×C(ng/mL) ,相关性系数r=0 9984 3,检出限为 0 4 887ng/mL。标准矿样加标回收率为 10 7%左右 ,尘土样品加标回收率为 98 1%～ 10 2 1% ,结果令人满意     

A study on the tribological characteristics of graphite nano lubricants

Many researchers have tried to improve the tribological characteristics of lubricants to decrease friction coefficients and wear rates. One approach is simply the use of additives in the base lubricant to change its properties. Recently, nanoparticles have emerged as a new kind of additive because of their size, shape and other properties. A nano lubricant is a new kind of engineering lubricant made of nanoparticles, dispersant, and base lubricant. In this study, graphite nanoparticles were used to fabricate nano lubricants with enhanced tribological properties and lubrication characteristics. The base lubricant used was industrial gear oil, which has a kinematic viscosity of 220 cSt at 40°C. To investigate the physical and tribological properties of nano lubricants, friction coefficients and temperatures were measured by a disk-on-disk tribotester. The surfaces of the fixed plates were observed by a scanning electron microscope and an atomic force microscope to analyze the characteristics of the friction surfaces. The results show that when comparing fixed plates coated with raw and nano lubricants, the plate coated with a nano lubricant containing graphite nanoparticles had a lower friction coefficient and less wear. These results indicate that graphite nanoparticle additives improve the lubrication properties of regular lubricants.     

Thermal conduction of stable graphite suspensions considering structural characteristics of graphite aggregations

In this article, a new simple approach that can investigate thermal conduction of graphite suspensions is discussed. Using the three-level homogenization model, the fractal dimension (df) of graphite suspensions is determined as df = 1.76 and 1.70 for graphite/EG and for graphite/PAO, respectively. From these values, the highly anisotropic heat conduction is expected to be dominant through aggregations of graphite flake. Based on these observations, a simple thermal expression is proposed to describe the anisotropic heat conduction of graphite suspensions incorporating the effect of the interfacial thermal resistance. The effects of aggregated sphere (AS) distribution on thermal irreversibilities of nanofluids are also investigated by comparing the entropy creations between spatially uniform and random distributions of AS.     

Internet-based electronics manufacturing troubleshooting tool for surface mount PCB assembly

Increasing product complexity, decreasing component size, and using double-sided boards have made surface mount technology (SMT) based electronics manufacturing (EM) components more difficult to assemble. This has resulted in the economic troubleshooting of EM defects being one of the main problems facing all manufacturers. Although the authors have made significant improvements in the EM process, it has been shown that the implemented changes in the automated lines have not yet produced a high enough percentage of reliable finished products. The objective of this current development is to make a contribution towards these EM processes by creating an Internet-based intelligent system of circuit board defect detection so that EM process flaws that necessitate rework operations can be identified prior to manufacturing runs. With the development of this system, the need to rework the defective components will be minimized for any assembly line and assembly line process parameters, which cause some reliability problems (such as solder balls, insufficient solder at joints, burnt joint connections, bridged leads, voids, skewed leads, and unformed joints) will be troubleshot directly, and the rework will be greatly reduced from the EM assembly line. This paper reports the current development and its structure.     

A numerical study on flow and heat transfer characteristics of film cooling with a compound angle hole

A numerical simulation has been performed for the investigation of flow and heat transfer characteristics of a film cooling system injected through a hole with compound angle orientation. The finite volume method is employed to discretize the governing equations based on the non-orthogonal coordinate with non-staggered variable arrangement. In order to analyze flow and heat transfer characteristics, velocity, temperature, aerodynamic loss coefficient, skin friction and vorticity are calculated with the variation of the skew angle. The maximum longitudinal vorticity and aerodynamics loss depend strongly on the skew angle. For the symmetric case of β=0 deg, a pair of counter-rotating vortices are formed and the maximum value of the film cooling effectiveness has appeared in the center plane where the skin friction is the minimum. For the skew angle of β=30 deg and above, only one strong counter-clockwise vortex remains in the downstream region and the maximum value of the film cooling effectiveness are obtained on the right side of the vortex. The predicted results for the film cooling effectiveness show good agreements with previous experimental data except the near-hole region.     

发动机短舱冷却的计算研究

采用一维的方法对发动机短舱冷却进行了研究,介绍了两种不同的冷却形式,并且给出了这两种冷却形式中短舱冷却空气流量和换热的计算公式,对某型发动机短舱在四种不同状态下的流动及换热进行了计算,并对计算结果进行了分析。     

The surface failure and wear of graphite seals

Exfoliated graphite rings are now the most common form of die-formed seal for valve stems, and other stuffing box applications. However, there is very little fundamental knowledge of what determines their friction and wear. In earlier papers, it was shown that the mechanical properties of this material could be represented approximately by a geotechnical model designed for soils or rocks. In this paper, a simple test is described for measuring the friction and wear of seals against steel sliders in a controlled atmosphere. The results, which are rather surprising, can be explained by applying the geotechnical model referred to above, to the case of sliding.     

超级计算机热设计

主要阐述了超级计算机热设计的原则、方法和步骤,结合具体的工程应用,介绍了各种冷却措施。认为热设计工程师应从冷却系统的功能、可用性规定指标和冷却系统的投资费用等一些基本原则出发,研制出一些更为有效的冷却方法,以适应发展形势的需求。     

细长塑件的冷却及模具设计

阐述细长塑件注射模具冷却系统的设计方法,重点介绍该模具细长型芯的冷却。     

注塑模冷却时间优化设计

针对冷却系统在塑胶模注射成型过程中的重要地位,利用专业模流分析软件MOLDFLOW对注塑抽屉的冷却系统中冷却时间的优化进行了研究。重点介绍了MOLDFLOW软件对模具冷却系统进行计算机模拟分析的过程,主要对模具冷却回路和冷却时间进行了优化设计,获得了高预测质量的产品,进一步说明合理的冷却系统设计对提高产品质量、缩短成型周期、提高生产率和降低能耗提供了有利保证。     

基于MATLAB的轧辊精细冷却模糊控制的仿真

主要介绍了轧辊精细冷却的工作原理,构建了精细分段冷却的模糊控制的模型,并对其进行MATLAB的实现及仿真。通过采用模糊控制原理控制精细分段冷却系统中各个喷嘴的流量,有效克服了系统非线性、时变大、纯滞后等问题,提高了板形控制的能力。     

Influence of graphite nodules on the particles erosion of spheroidal graphite cast irons

The influence of graphite nodules on the normal angle erosion of the spheroidal graphite cast irons with four different matrices, namely ferrite, upper bainite, lower bainite and martensite, was investigated. The results indicate that, in the range investigated (10-15 area pet), graphite nodules (with variations in area percent and size) did not exert any influence in the irons with ferrite or upper bainite matrix. However, in the case of the spheroidal graphite cast iron with martensitic matrix, both increasing area percent and decreasing diameter of graphite nodules did in fact raise the erosion rate; moreover, those cast in metal molds consistently experienced higher erosion rate than those cast in sand molds. For the irons with a lower bainite matrix, increasing the amount of graphite nodules raises the erosion rate for those cast in sand molds, but did not affect the erosion rate for those cast in metal molds; furthermore, the erosion rate of the sanded-molded irons was consistently higher than their metal molded counterparts. The different roles of graphite nodules on the erosion rates of the spheroidal graphite cast irons are discussed.     

某塑料模具的石墨电极数控加工工艺

分析石墨电极数控加工的特点和难点,应用Mastercam数控加工技术,采取适当的工艺措施和合理的工艺路线,完成石墨电极的数控加工。     

Tribological behaviors of graphite/epoxy two-phase composite coatings

To obtain a composite coating possessing both good conductivity and high wear resistance, a series of coatings with conductive graphite and epoxy resin were designed. The seepage critical value (SCV) of conductive coatings was used to identify the transformation between continuous phase and dispersed phase for graphite/epoxy composite coatings. Before SCV, the coatings were insulated with epoxy resin as continuous phase and the wear behavior was primarily characterized of adhesive wear with local adhesive spalling of epoxy resin. After SCV, the coatings appeared conductivity and the surface resistance decreased monotonically with the increase of graphite content. Both the curves of friction coefficient vs. graphite content and wear rate vs. graphite content showed the same model with two valleys at graphite content of 30% and 50%, respectively. At graphite content of 50%, an optimal solid lubricant film was obtained which leaded to the lowest friction coefficient and wear rate, due to a possible dynamic equilibrium between the transfer and spalling of debris. The tribological behaviors of these coatings were evaluated using a ring-on-block tribo-tester under dry sliding friction.     

YY3型横向加热平台石墨管结构性能的改进

讨论了部分元素在YY2和YY3型横向加热平台石墨管中的原子化行为,考察了元素的灵敏度、精密度、准确度。实验表明,YY3圆形横向加热平台石墨管的原子化性能比较优越,可以推广使用。     

旋转燃烧室冷却结构设计研究

针对新型旋转燃烧室的传热与冷却问题进行了深入研究。根据燃烧室的热传导特点,列出其热传导微分方程,讨论了传热问题的边界条件,使用有限元方法对燃烧室壁进行了温度场和应力场计算,结合实验修正取得了各个冷却通道之间的换热量及换热系数。在此基础上提出了双层螺旋通道的冷却方案。分析计算结果与实验结果相吻合。