Flow and heat transfer characteristics of regenerative cooling parallel channel

Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass ratio,has not been systematically carried out.In this paper,the heat transfer and flow characteristics of related high temperature fuels are studied by using typical engine parallel channel structure.Through numeri⁃cal simulation and systematic experimental verification,the flow and heat transfer characteristics of parallel chan⁃nels under typical working conditions are obtained,and the effectiveness of high-precision calculation method is preliminarily established.It is known that the stable time required for hot start of regenerative cooling engine is about 50 s,and the flow resistance of parallel channel structure first increases and then decreases with the in⁃crease of equivalence ratio(The following equivalence ratio is expressed byΦ),and there is a flow resistance peak in the range ofΦ=0.5~0.8.This is mainly caused by the coupling effect of high temperature physical proper⁃ties,flow rate and pressure of fuel in parallel channels.At the same time,the cooling and heat transfer character⁃istics of parallel channels under some conditions of high heat-mass ratio are obtained,and the main factors affect⁃ing the heat transfer of parallel channels such as improving surface roughness and strengthening heat transfer are mastered.In the experiment,whenΦis less than 0.9,the phenomenon of local heat transfer enhancement and deterioration can be obviously observed,and the temperature rise of local structures exceeds 200℃,which is the risk of structural damage.Therefore,the reliability of long-term parallel channel structure under the condition of high heat-mass ratio should be fully considered in structural design.

Effect of Different Shapes of Conformal Cooling Channel on the Parameters of Injection Molding

Cooling system improvement is important in injection molding to get betterquality and productivity. The aim of this paper was to compare the different shapes of theconformal cooling channels (CCC) with constant surface area and CCC with constantvolume in injection molding using Mold-flow Insight 2016 software. Also the CCC resultswere compared with conventional cooling channels. Four different shapes of the CCC suchas circular, elliptical, rectangular and semi-circular were proposed. The locations of thecooling channels were also kept constant. The results in terms of cooling time, cycle timereduction and improvement in quality of the product shows that no significant effect ofCCC’s shapes when surface area of CCC kept constant. On the other hand, the rectangularCCC shows better result as compared to other shapes of CCC when volume of CCC werekept constant.

Cycle Time Reduction in Injection Molding by Using Milled Groove Conformal Cooling

This paper presents simulation study on Milled Grooved conformal cooling channels(MGCCC)in injection molding.MGCCC has a more effective cooling surface area which helps to provide efficient cooling as compared to conventional cooling.A case study of Encloser part is investigated for cycle time reduction and quality improvement.The performance designs of straight drilled are compared with MGCCC by using Autodesk Moldflow Insight(AMI)2016.The results show total 32.1% reduction of cooling time and 9.86% reduction of warpage in case of MGCCC as compared to conventional cooling.

Air Cooling of Mini-Channel Heat Sink in Electronic Devices

Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.

Numerical Study of High Heat Flux Performances of Flat-Tile Divertor Mock-ups with Hypervapotron Cooling Concept

The hypervapotron（HV）,as an enhanced heat transfer technique,will be used for ITER divertor components in the dome region as well as the enhanced heat flux first wall panels.W-Cu brazing technology has been developed at SWIP（Southwestern Institute of Physics）,and one W/CuCrZr/316 LN component of 450 mm×52 mm×166 mm with HV cooling channels will be fabricated for high heat flux（HHF） tests.Before that a relevant analysis was carried out to optimize the structure of divertor component elements.ANSYS-CFX was used in CFD analysis and ABAQUS was adopted for thermal-mechanical calculations.Commercial code FE-SAFE was adopted to compute the fatigue life of the component.The tile size,thickness of tungsten tiles and the slit width among tungsten tiles were optimized and its HHF performances under International Thermonuclear Experimental Reactor（ITER） loading conditions were simulated.One brand new tokamak HL-2M with advanced divertor configuration is under construction in SWIP,where ITER-like flat-tile divertor components are adopted.This optimized design is expected to supply valuable data for HL-2M tokamak.

Analytical prediction of the maximum temperature of non-uniform heated surface with channel cooling

Active cooling of aircraft skin has garnered significant attention from researchers in recent years due to the increasing flight speeds.The determination of the maximum temperature plays a crucial role in the design of active cooling systems as it dictates the selection of suitable materials for aircraft skin.This research presents two analytical models for predicting surface temperatures in aircraft skin with active cooling channels:one for densely arranged channels and another for sparsely arranged channels.The application criteria of these two models are obtained.The analytical models offer several advantages,including handling non-uniform heat fluxes and providing direct predictions of maximum temperature and its location.Numerical simulations validate these models,demonstrating their accurate estimation capabilities across various solid materials,Reynolds numbers,and thermal conductivities.This investigation lays the foundation for rapid and cost-effective design of optimal cooling channels based on solid thermal conductivity,cooling flow rate,channel spacing,and temperature limits under non-uniform heat flows.Furthermore,an examination of channel aspect ratios reveals that larger ratios result in lower heated surface temperatures.Overall,these analytical temperature prediction models serve as efficient tools for selecting appropriate design parameters for active cooling channels.

Research on a Manifold Micro-channel Heat Sink Applied in High Concentrated Solar Cells

该文对歧管式微通道冷却技术在聚光电池冷却方面的应用进行了理论和实验研究。歧管式微通道冷却技术有助于在较小的空间内实现高热流密度冷却，较为适合高聚光比的密集阵列聚光电池系统。文中对歧管式微通道热沉热阻的计算方法进行改进，建立该种结构完全基于半经验公式的一维传热模型，并分析影响总热阻的主要因素。同时，对电池-热沉系统进行实验。实验结果表明，在此范围内实验与计算结果具有良好的一致性，电池-热沉系统的整体热阻低于1×10-4 m2·℃/W。结合聚光电池的性能模型，可获得电池的最大输出功率、效率、温度等性能参数随聚光比的变化情况。

A multi-objective study on the constructal design of non-uniform heat generating disc cooled by radial-and dendritic-pattern cooling channels

A three-dimensional disc model with non-uniform heat generating is built.A series of cooling channels are inserted to cool this disc which is strewn in a hierarchical pattern.To reveal thermal and flow characteristics,a composite objective function comprised of the maximum temperature difference(MTD)and pumping power is constructed.The deployment pattern of cooling channels contains two cases,i.e.,the radial-pattern and dendritic-pattern.By capitalizing on constructal design method together with finite element method,the diameter of radial-pattern cooling channels is optimized in the first place.Next,the diameter,angle coefficient and length coefficient of dendritic-pattern cooling channels are three degrees-of-freedom to be stepwise optimized at different heat generating conditions.Furthermore,NSGA-II algorithm is introduced into the multiobjective problem.Upon obtaining its Pareto optimal solution set,Topsis method is invoked to yield the optimal solutions under given weighted coefficients.The heat generation over the entire body and the volume ratio of cooling channels operate as the primary constraints.Based on these premises,constructal design will be stepwise performed by varying three degrees-offreedom.The obtained results state that more heating components or devices should be installed as close to the cooling water inlet as possible.This can further reduce MTD at the same cost of pumping power,thereby improve thermal and flow performance and prolong the lifespan of devices.As optimized with two degrees-of-freedom,the MTD is reduced by 18.6%compared with the counterpart obtained from single degree-of-freedom optimization,while the pumping power is increased by 59.8%.As optimized with three degrees-of-freedom,the MTD is decreased by 6.2%compared with the counterpart from two degrees-of-freedom optimization,while the pumping power is increased by 3.0%.It is manifest that when two sub-objectives form a composite objective,the performance improvement of one sub-objective will inevitably elicit the vitiation of the alternative.

Finite Element Analysis on the Injection Molding and Productivity of Conformal Cooling Channel

The study proves that the conformal cooling channel can overcome the disadvantages of the conventional cooling channel resulting from the limitation in complicated shape.The simulation analyses of the fragrance lamp with different cooling layouts show that the conformal cooling channel can offer a more uniform heat dissipation,lower volume shrinkage and shorter time to freeze than the conventional channel,which indicates significantly improvements in productivity and quality.

Thermal Performance of Mini Cooling Channels for High-Power Servo Motor with Non-Uniform Heat Dissipation

High-power servo motor is widely employed as a necessary actuator in flight vehicles.The urgent problem to be solved restraining the working performance of servo motor is no longer the torque and power,but the heat dissipation capability under high-power working conditions,which may cause the overheat,even burn down of motor or other potential safety hazards.Therefore,a structure of mini cooling channels with appropriate channel density is designed in accordance with the non-uniform heat flux of servo motor in this paper.Combined with the regenerative cooling method,the cryogenic fuel supercritical methane is served as the coolant,which is easy to be obtained from the propulsion system,and the heat from the servo motor can be transported to the combustion for reusing.According to the actual working cases of servo motor,a numerical model is built to predict the thermal performance of cooling channels.In order to better represent the secondary flow of coolant in the cooling channels,especially the turbulent mixed flow in the manifold,the k-εRNG model with enhanced wall treatment is employed resulting from its precise capacity to simulate the secondary and wall shear flow.On this basis,the heat transfer mechanism and thermal performance of cooling channels,as well as the influence of various heat flux ratios are investigated,which can offer an in-depth understanding of restraining excessive temperature rise and non-uniformity distribution of the servo motor.By the calculation results,it can be concluded that under the adjustment of the channel density according to the corresponding heat flux,the positive role of the appropriate channel density and the manifolds on heat transfer is manifested.Moreover,the maximum temperature difference of heating wall can be kept within an acceptable range of the servo motor.The heat transfer coefficient in the manifold is nearly 2–4 times higher compared with that in the straight cooling channels.The effect of buoyancy force cannot be neglected even in the manifold with turbulent mixed flow,and the pattern of heat transfer is mixed convection one in all the flow regions.The thermal resistance R and overall Nusselt number Nu are affected remarkably by all the operation parameters studied in the paper,except the pressure,while the overall thermal performance coefficientηdemonstrates differently.The strong impact of heat flux ratio is implied on thermal performance of the cooling channels.Higher heat flux ratio results in the stronger non-uniform temperature distribution.Meanwhile,only tiny temperature differences of the fluid and inner wall in manifolds among various heat flux ratios are demonstrated,resulting from the positive effect of mixture flow on heat transfer.

Conjugate Heat Transfer Characterization in Cooling Channels

Cooling technology of gas turbine blades,primarily ensured via internal forced convection,is aimed towards withdrawing thermal energy from the airfoil.To promote heat exchange,the walls of internal cooling passages are lined with repeated geometrical flow disturbance elements and surface non-uniformities.Raising the heat transfer at the expense of increased pressure loss;the goal is to obtain the highest possible cooling effectiveness at the lowest possible pressure drop penalty.The cooling channel heat transfer problem involves convection in the fluid domain and conduction in the solid.This coupled behavior is known as conjugate heat transfer.This experimental study models the effects of conduction coupling on convective heat transfer by applying iso-heat-flux boundary condition at the external side of a scaled serpentine passage.Investigations involve local temperature measurements performed by Infrared Thermography over flat and ribbed slab configurations.Nusselt number distributions along the wetted surface are obtained by means of heat flux distributions,computed from an energy balance within the metal domain.For the flat plate experiments,the effect of conjugate boundary condition on heat transfer is estimated to be in the order of 3%.In the ribbed channel case,the normalized Nusselt number distributions are compared with the basic flow features.Contrasting the findings with other conjugate and convective iso-heat-flux literature,a high degree of overall correlation is evident.

锂离子电池叶脉状液冷散热通道设计与优化

为提升锂离子电池组热安全性,提出了一种具有叶脉状仿生通道的液冷锂电池热管理结构。使用流体力学软件STAR-CCM+对模型的散热性能进行分析与优化,采用正交试验极差法,研究了冷却板通道数N、通道宽度W、入口流量Q等多参数耦合对电池最高温度T_(max)、平均温度T_(avg)、表面温差ΔT和冷却液压降Δp的影响。结果表明,N和Q是影响冷却性能的主要因素,W是次要因素,并且在N=12,W=8 mm,Q=25 g/s时冷板的综合性能最佳,优化后的叶脉状冷板比S型冷板的T_(max)低了1.32%,T_(avg)低了0.64%,Δp低了88.2%。

Heat transfer characteristics in a narrow confined channel with discrete impingement cooling

Heat transfer characteristics in a narrow confined channel with discrete impingement cooling were investigated using thermal infrared camera. Detailed heat transfer distributions and comparisons on three surfaces with three impact diameters were experimentally studied in the range of Reynolds number of 3000 to 30000. The experimental results indicated that the strong impingement jet leaded to a high strength heat transfer zone in the ΔX=±2.5D;range of the impact center,which was 1.3–2.5 times of the average heat transfer value of the impingement wall. With the same coolant mass flow rate, small diameter case had lower heat transfer coefficient on both inner wall and outside wall, while the impingement wall was insensitive to the impact diameter. The surface averaged Nusselt number of inner wall was only 43%–57% of impingement wall, while the outside wall can reach up to 80%–90%. The larger the diameter, the higher heat transfer enhancement and the smaller the channel flow resistance was observed in term of Reynolds number. The surface averaged Nusselt numbers were developed as the function of Reynolds number and the impingement height-to-diameter for further engineering applications.

Thermal and Structural Insight into Lightweight Lattice Channels for Active Cooling Technology

The active cooling technology that can reduce the combustor temperature is commonly used to protect the scramjet.In order to further improve the performance of active cooling,the structural weight reduction,cooling efficiency and stress level of the cooling channel must be considered simultaneously.In this paper,new types of lattice channels for active cooling were designed and compared with the conventional cooling channel in terms of weight reduction,thermal and structural performance.The results showed that,at the same channel height,the cooling channel with staggered lattice arrays has the optimal comprehensive performance:the weight reduction effect reaches 39.93%;the wall temperature drops significantly,and the maximum Nu number is 2.155times of the conventional channel.The flow field analysis showed that horseshoe vortices formed by the impact effect and hairpin vortices near the trailing edge are the main factors of heat transfer enhancement.The disturbed boundary layer and the excited turbulent kinetic energy also contribute much to enhance the heat transfer.In addition,due to the HTE-induced increment of metal tensile strength,the system reliability of lattice channel is better than the conventional one.

Flow Structure and Heat Exchange Analysis in Internal Cooling Channel of Gas Turbine Blade

This paper presents the study of the flow structure and heat transfer,and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade.The investigations focus on heat transfer and aerodynamic measurements in the channel,which is an accurate representation of the configuration used in aeroengines.Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models.It is important to note that real engine passages do not have perfect rectangular cross sections,but include coiner fillet,ribs with fillet radii and special orientation.Therefore,this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.

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 convec- tion-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 twodimensional （2D） array by ANSYS/FluentTM 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.

Failure mode analysis on compression of lattice structures with internal cooling channels produced by laser powder bed fusion

Conformal cooling coils have been developed during the last decades through the use of additive manufacturing(AM)technologies.The main goal of this study was to analyze how the presence of an internal channel that could act as a conformal cooling coil could affect compressive strength and quasi-elastic gradient of AlSi10Mg lattice structures produced by laser powder bed fusion(LPBF).Three different configurations of samples were tested in compression at 25℃ and 200℃.The reference structures were body centered cubic(BBC)in the core of the samples with vertical struts along Z(BCCZ)lattices in the outer perimeter,labelled as NC samples.The main novelty consisted in inserting a straight elliptical channel and a 45°elliptical channel inside the BCCZ lattice structures,labelled as SC and 45C samples respectively.All the samples were then tested in as-built(AB)condition,and after two post process heat treatments,commonly used for AlSi10Mg LPBF industrial components,a stress relieving(SR)and a T6 treatment.NC lattice structures AB exhibited an overall fragile fracture and therefore the SC and 45C configuration samples were tested only after thermal treatments.The test at 25℃ showed that all types of samples were characterized by negligible variations in their quasi-elastic gradients and yield strength.On the contrary,the general trend of stress-strain curves was influenced by the presence of the channel and its position.The test at 200℃ showed that NC,SC and 45C samples after SR and T6 treatments exhibited a metal-foam like deformation.

An Experimental Investigation of Heat Transfer Characteristics for Steam Cooling in a Rectangular Channel with Parallel Ribs

An experimental study of heat transfer characteristics in superheated steam cooled rectangular channels with parallel ribs was conducted.The distribution of the heat transfer coefficient on the rib-roughed channel was measured by IR camera.The blockage ratio(e/Dh) of the tested channel is 0.078 and the aspect ratio(W/H) is fixed at3.0.Influences of the rib pitch-to-height ratio(P/e) and the rib angle on heat transfer for steam cooling were investigated.In this paper,the Reynolds number(Re) for steam ranges from 3070 to 14800,the rib pitch-to-height ratios were 8,10 and 12,and rib angles were 90°,75°,60°,and 45°.Based on results above,we have concluded that:In case of channels with 90° tranverse ribs,for larger rib pitch models(the rib pitch-to-height ratio=10 and12),areas with low heat transfer coefficient in front of rib is larger and its minimum is lower,while the position of the region with high heat transfer coefficient nearly remains the same,but its maximun of heat transfer coefficient becomes higher.In case of channels with inclined ribs,heat transfer coefficients on the surface decrease along the direction of each rib and show an apparent nonuniformity,consequently the regions with low Nusselt number values closely following each rib expand along the aforementioned direction and that of relative high Nusselt number values vary inversely.For a square channel with 90° ribs at Re= 14800,wider spacing rib configurations(the rib pitch-to-height ratio=10 and 12) give an area-averaged heat transfer on the rib-roughened surface about8.4%and 11.4%more than P/e=8 model,respectively;for inclined parallel ribs with different rib angles at Re=14800,the area-averaged heat transfer coefficients of 75°,60° and 45° ribbed surfaces increase by 20.1%,42.0%and 44.4%in comparison with 90° rib angle model.45° angle rib-roughened channel leads to a maximal augmentation of the area-averaged heat transfer coefficient in all research objects in this paper.

圆弧抽芯注塑模具优化设计

基于圆弧抽芯注塑模具,根据塑件结构及材料性能特点,对浇口的位置及结构进行了优化设计,通过CAE模拟分析得到位于填充末端、最大壁厚处的塑件最大变形量为0.739 mm,变形量在设计允许范围内。以油缸作为驱动动力源,通过齿条驱动齿轮、内齿轮旋转,实现抽芯动作;将内齿轮设计为异形非标齿轮,减少了所占空间,实现了1模2腔布局。为解决圆弧型芯冷却水路难以加工的问题,设计的加工工序为先按照直型芯进行粗加工,钻孔加工型芯冷却水路,然后,将型芯加热弯曲为所需形状,并进行调质处理,最后对型芯进行精加工使其满足设计要求,达到了随形冷却效果。传动机构关键参数采用理论计算与CAE模拟分析相结合的法验证,测试结果表明,计算校核效率提高了约4倍。

注塑模具随形冷却管道自动生成技术

作为一种新颖的水路结构,随形水路以其优越的冷却效果在模具工程中得到了越来越多的应用。然而由于随形水路的特殊性,其管道的创建过程并不容易。针对注塑模具随形水路传统设计方法中普遍存在的操作复杂耗时且易出错的问题,受莲藕内部导管结构的启发,结合实际模具工程中随形水路的设计要求,提出了一种随形水路自动生成算法。该算法的基本思路是首先沿模具型芯高度方向建立一系列基准面,作为切片层,通过对模具零件进行分层切片,获得每一个切片层上的型芯轮廓线。然后在每一个切片层上以指定管径按照逐点扫描的方法进行曲线干涉检查,筛选出样条曲线的控制点,并制定连线策略使用样条曲线依次连接各个切片层上的控制点,从而获得样条曲线。最后以样条曲线作为管道扫描中心线,扫描形成随形冷却管道实体。以NX为算法实现平台,开发了随形水路自动设计系统与NX无缝衔接,实例验证表明,该方法大幅度缩短了设计时间,减轻了设计人员的工作负担,提高了随形水路的设计效率和质量。