Measurement of temperature inside die and estimation of interfacial heat transfer coefficient in squeeze casting

As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.

An Efficient Acceleration of Solving Heat and Mass Transfer Equations with the First Kind Boundary Conditions in Capillary Porous Radially Composite Cylinder Using Programmable Graphics Hardware

With the latest advances in computing technology, a huge amount of efforts have gone into simulation of a range of scientific phenomena in engineering fields. One such case is the simulation of heat and mass transfer in capillary porous media, which is becoming more and more necessary in analyzing a number of eventualities in science and engineering applications. However, this procedure of numerical solution of heat and mass transfer equations for capillary porous media is very time consuming. Therefore, this paper pursuit is at making use of one of the acceleration methods developed in the graphics community that exploits a graphical processing unit (GPU), which is applied to the numerical solutions of such heat and mass transfer equations. The nVidia Compute Unified Device Architecture (CUDA) programming model offers a correct approach of applying parallel computing to applications with graphical processing unit. This paper suggests a true improvement in the performance while solving the heat and mass transfer equations for capillary porous radially composite cylinder with the first type of boundary conditions. This heat and mass transfer simulation is carried out through the usage of CUDA platform on nVidia Quadro FX 4800 graphics card. Our experimental outcomes exhibit the drastic overall performance enhancement when GPU is used to illustrate heat and mass transfer simulation. GPU can considerably accelerate the performance with a maximum found speedup of more than 5-fold times. Therefore, the GPU is a good strategy to accelerate the heat and mass transfer simulation in porous media.

An Efficient Acceleration of Solving Heat and Mass Transfer Equations with the Second Kind Boundary Conditions in Capillary Porous Composite Cylinder Using Programmable Graphics Hardware

With the recent developments in computing technology, increased efforts have gone into simulation of various scientific methods and phenomenon in engineering fields. One such case is the simulation of heat and mass transfer in capillary porous media, which is becoming more and more important in analysing various scenarios in engineering applications. Analysing such heat and mass transfer phenomenon in a given environment requires us to simulate it. This entails simulation of coupled heat mass transfer equations. However, this process of numerical solution of heat and mass transfer equations is very much time consuming. Therefore, this paper aims at utilizing one of the acceleration techniques developed in the graphics community that exploits a graphics processing unit (GPU) which is applied to the numerical solutions of heat and mass transfer equations. The nVidia Compute Unified Device Architecture (CUDA) programming model caters a good method of applying parallel computing to program the graphical processing unit. This paper shows a good improvement in the performance while solving the heat and mass transfer equations for capillary porous composite cylinder with the second kind of boundary conditions numerically running on GPU. This heat and mass transfer simulation is implemented using CUDA platform on nVidia Quadro FX 4800 graphics card. Our experimental results depict the drastic performance improvement when GPU is used to perform heat and mass transfer simulation. GPU can significantly accelerate the performance with a maximum observed speedup of more than 7-fold times. Therefore, the GPU is a good approach to accelerate the heat and mass transfer simulation.

基于圆台波浪形换热管的潜热储热单元性能分析

为提高潜热储热单元(latent heat storage unit,LHSU)的储热性能,提出了三种优化换热管结构的新型LHSU,分别为圆台形换热管潜热储热单元、波浪形换热管潜热储热单元和圆台波浪形换热管潜热储热单元(frustum wavy heat transfer tube latent heat storage unit,FW-LHSU)。基于数值模拟方法,比较了传统圆柱形换热管潜热储热单元(cylindrical heat transfer tube latent heat storage unit,C-LHSU)和三种新型LHSU的储热性能。此外,针对FW-LHSU研究了换热管壁面倾斜角度对储热性能的影响。结果发现,所提出的三种新型换热管结构均能增强储热性能,其中FW-LHSU储热效果最好,与C-LHSU相比,FW-LHSU的熔化时间缩短了32.64%,储热速率密度提高了48.1%。当增加FW-LHSU的换热管壁面倾斜角度时,其储热性能可进一步提高。当换热管倾斜角度从2°增加到8°时,FW-LHSU的储热时间可缩短37.00%、储热速率密度可提高48.44%。

空气源分体式热管-热泵供暖系统在煤矿井口防冻中的特性研究

为提高空气源热泵的性能,同时更好地满足煤矿井口防冻特殊工艺要求,将空气源热泵与热管技术相耦合,使用小压比热泵机组搭建了空气源分体式热管-热泵供暖系统实验平台。该耦合系统中蒸发器和冷凝器两端均采用相变传热的方式,并对其进行不同运行工况下的性能特性研究,结果表明:该耦合供暖系统即使在0℃左右的室外条件下,耦合机组的系统制热性能仍可达到4.5以上,远远优于传统空气源热泵机组。

叉排微通道换热器的换热性能

[目的]探究叉排微通道换热器在船用燃气轮机间冷过程中的实验换热性能及其影响因素.[方法]针对增材制造加工的叉排微通道换热器,在低流动工况条件下进行对流换热实验,从结构和流动因素研究叉排微通道换热器的换热性能.[结果]通道宽度减小0.50 mm使叉排换热器换热性能增强106.9%~61.9%;通道数增加1.6倍导致同流量下换热性能平均降低21.9%~50.8%,而同流速下换热性能平均降低11.6%;进口流量增加6.3倍,换热器换热性能提升44.0%;但换热性能受热侧空气进口温度的影响较小,相邻工况条件计算值变化最大仅为5.4%.[结论]工艺条件允许下减小通道尺寸可提升叉排微通道换热器性能,而增加通道数量则会带来负面影响;冷侧水进口流量增大能提升叉排微通道换热器换热量,从而增强换热性能;热侧空气进口温度的影响则较为复杂.

溴化锂吸收式冷水机组吸收器传热管腐蚀特性研究

本文采用挂样试验的方式,通过模拟溴化锂吸收式冷水机组吸收器与发生器中溴化锂溶液浓度45%与61%条件下,氧含量分别为0.5%、1%、5%、10%、20%、30%时对B30传热管的腐蚀情况,研究了B30传热管的有氧腐蚀特性,分析了溴化锂溶液浓度与氧含量的腐蚀影响因素与机理,结果表明当溴化锂溶液浓度为45%时,只要氧含量高于5%,B30传热管就会出现麻点状腐蚀,氧含量高于20%,B30传热管明显点蚀,深度达到0.5mm;当溴化锂溶液浓度为61%时,只有当氧含量达到30%,B30传热管才会出现明显的腐蚀麻坑。

烧结冷却烟气低温余热ORC系统建模与热经济性能

本文以烧结冷却烟气低温余热为有机朗肯循环(organic Rankine cycle,ORC)系统热源,建立超临界ORC系统热力和经济模型,并选取R134a为ORC工质,研究变温热源下膨胀机的进口温度和压力,以及工质冷凝温度对系统热经济性能的影响。研究结果表明:系统净输出功随膨胀机进口温度的增加而增加,随膨胀机进口压力和工质冷凝温度的增加而减小,但系统单位温度的传热量随之均减小。当系统热力参数一定时,热源进口温度越大,系统净输出功和单位温度的传热量越大。在实际操作过程中,存在适宜的热源进口温度和系统热力参数使得ORC系统获得较大的净输出功和较小的单位温度传热量。

液体循环热回收系统性能参数模拟与优化设计

为了降低洁净室全新风空调系统的能耗,基于深圳某生物医药洁净车间的液体循环热回收系统,采用效能-传热单元数法建立盘管数学模型,模拟系统性能参数,并设计正交试验分析因素主次和优方案,最后提出一种加强换热的措施。研究结果表明:水流量在2.5kg/s时,盘管换热量达到峰值。室外温湿度增加,热回收量最大增幅88%,室内温湿度增加,热回收量最大减幅14%。通过正交试验结果表明:影响热回收量的因素主次为水流量、室外温度、室内温度、室外相对湿度、室内相对湿度,优方案为水流量3.5kg/s,室内温度24℃,室内相对湿度50%。加强换热后系统总体节能20kW。

平板式相变储能单元空气侧表面换热性能分析

为提高平板式储能单元的换热性能,通过储能单元的换热性能实验,研究相变储能单元不同表面结构对储能单元换热特性的影响。储能单元内部的相变材料(石蜡)熔化分为2个阶段:第1阶段石蜡开始软化,相变材料侧热阻较大,因此空气侧花纹结构对总体换热影响较小;第2阶段石蜡快速熔化,相变过程中相变材料侧热阻减小,空气侧表面花纹结构强化了空气侧换热,总体换热能力得到有效强化。花纹储能单元表面的花纹通过增加传热面积、增强储能单元表面空气扰动,达到强化换热的效果,使相变材料完全熔化时长比光滑储能单元缩短27%—55%。相变储能单元瞬时热流量随时间呈现先增大后逐渐减小的趋势。

Performance of Thermal Energy Storage Unit Using Solid Ammoniated Salt (CaCl₂-NH₃System)

The exothermic chemical reaction of CaCl2 (calcium chloride) with NH3 (ammonia) can be utilized as an energy storage system. Since this reaction is a typical gas-solid reaction, the reaction rate is controlled by the heat transfer rate. In order to improve the low heat transfer rate of the ammoniation and the deammoniation of CaCl2, the influence of a heat transfer media (Ti: titanium) on the heat transfer rate of the solid ammoniated salt (CaCl2&#46mNH3) was studied and tested experimentally. The performance tests were carried out under the conditions of various weight ratios of Ti. No decrease of the activation of chemical reaction and no corrosion of experimental apparatus were observed on the repeated runs (≥30 times each). The heat transfer rate of ammoniated salt was greatly improved by adding Ti under the constant pressure (0.5 MPa). The reaction time required for the ammoniation of CaCl2 mixed with Ti was approximately 16% - 54% shorter than that of CaCl2 alone, and the reaction time required for the deammoniation was also approximately 19% - 59% shorter than that of CaCl2 alone.

圆柱形相变单元的蓄热装置蓄热特性分析

设计了基于圆柱形相变蓄热单元的相变蓄热装置,通过循环实验对蓄热装置的运行特性进行分析,研究了装置的蓄热影响因素。研究结果表明;在等质量相变材料(Phase Change Material,PCM)时,相变单元数量对装置蓄热速率的影响较大;蓄热单元布置间距对装置蓄热速率的影响较小;当增大换热流体(Heat Transfer Fluid,HTF)的流量时,装置总蓄热时间分别缩短了14.5%和29%;提高换热流体入口温度时,不仅增加了蓄热装置的总蓄热量,并且总体蓄热时间分别缩短了10.6%和16.5%。

化工原理热量传递过程的课程思政教学实践

化工原理是化工类专业的一门核心课程,也是该专业学生思政教育的主讲堂。文章以传热章节为例,设立知识传授、能力培养和价值塑造三个教学目标,深挖思政元素并创建章节思政关联图,设计并实施了“课前、课中、课后”全时域的课程思政教育方案,探索了思政教育融入专业课程的方法,提升了育人和育才的教学效果。

基于主动旋转的螺旋翅片储热单元传热性能优化分析

相变储热技术可有效缓解能源间歇性、不稳定性等问题,在电力灵活性及调度等方面起重要作用。为提高相变储热单元的储热效率,以螺旋翅片相变储热单元为研究对象,通过旋转储热单元内部螺旋翅片从而加快单元内部传热进程,并运用FLUENT软件对螺旋翅片储热单元在不同旋转速率及不同无量纲螺距下的传热过程进行数值模拟分析。结果表明:通过旋转螺旋翅片可以有效提高储热单元的传热效率,螺旋翅片旋转速率分别为3、5、7和10 rev/min的储热单元对比静止工况下储热单元完全熔化时间分别缩短了5000、2750、1250和750 s。在四种旋转速率下,储热单元的熔化强化率在0~6000 s增长迅速,并在6000 s左右达到最大值,3 rev/min的储热单元熔化强化率达到了240%,而10 rev/min的储热单元由于旋转速率过快从而破坏翅片表面对流涡胞,熔化强化率仅为180%。当螺旋翅片体积分数不变、对比其他旋转速率工况,旋转速率为3 rev/min,无量纲螺距P为0.46的储热单元传热效率最好,熔化强化率最大达到了200%。研究结果可为相变储热系统的设计优化提供参考。

导风板对空调风量及室内气流组织影响的研究

利用计算流体力学软件Star-CCM+,对四面出风嵌入式空调导风板在不同角度下的室内气流进行数值仿真,计算出各个出风口风量以及整体风量的大小,利用MATLAB采用数值拟合方法得出导风板角度与风量的数值关系,得出五次多项式能够准确描述风量与静态角度的关系;并通过对1.5 m高度平面的速度场与温度场仿真,得出导风板处于40°时,室内气流更能满足舒适性要求。

弓形导流板对“V”型直接空冷单元流动传热特性的影响

采用CFD软件对“V”型直接空冷单元在环境横向风影响下的流动传热特性进行模拟研究。为缓解翅片管束出口温度分布不均匀的问题,在“V”型直接空冷单元风机出口处加装弓形导流板。首先对加装导流板前后空冷单元的内部流场进行对比分析;随后探究了弓形导流板不同数量、倾角及高度对内部空气流动和传热特性的影响,并对参数进行了优化;最后比较了空冷单元内加装最优化的弓形与矩形导流板的换热效果。结果表明:在空冷单元的风机出口加装弓形导流板可有效减弱环境风的不利影响,使散热器出口的速度及温度分布更加均匀,局部高温区域逐渐消失,改善了空冷单元的换热性能;在弓形导流板数量为4块、倾角为20°、高度为0.8m时导流效果最佳;与矩形导流板相比,弓形导流板对空冷单元散热效果的改善较为明显。论文所得结果可为空冷单元的优化设计提供一定理论依据。

液体循环热回收系统性能参数模拟与优化设计

为了降低洁净室全新风空调系统的能耗,基于深圳某生物医药洁净车间的液体循环热回收系统,采用效能-传热单元数法建立盘管数学模型,模拟系统性能参数,并设计正交试验分析因素主次和优方案,最后提出一种加强换热的措施。研究结果表明:水流量在2.5kg/s时,盘管换热量达到峰值。室外温湿度增加,热回收量最大增幅88%,室内温湿度增加,热回收量最大减幅14%。通过正交试验结果表明:影响热回收量的因素主次为水流量、室外温度、室内温度、室外相对湿度、室内相对湿度,优方案为水流量3.5kg/s,室内温度24℃,室内相对湿度50%。加强换热后系统总体节能20kW。

核电机组高低压加热器U形传热管涡流检测法对比

核电机组不同类型加热器U形传热管通常采用不同的涡流检测法,从检测原理、方案实施、缺陷分析等方面将常规涡流检测与远场涡流检测进行对比。结果表明:常规涡流检测对于凹陷的检测灵敏度较高,远场涡流检测对于一定深度的内外伤的检测灵敏度较高,高低压加热器缺陷主要集中在U形传热管外圈及直管与弯管之间的过渡段区域,可以为类似核电机组高低压加热器U形传热管的涡流检测提供参考。

换热器在石化装置中的智能化应用

换热器在运行过程中,易产生结垢、腐蚀、泄漏、振动和性能下降等问题,会影响换热器甚至整个生产装置的效率、安全和可靠性。主要阐述了适用于石化装置中换热器设备状态监测和故障诊断的智能化方法与系统,详细说明了基于MQTT和OPC协议的两种数据采集方法,以及主成分分析(PCA)、有效度-传热单元数法、对数平均温差法三种用于换热器运行状态分析的算法;介绍了三种基于信息技术的换热器智能化运维系统的应用,实现换热器状态的实时监测,故障诊断和性能优化等功能,以满足石化装置长周期运行生产需要。

天然气脱轻烃装置制冷剂循环系统的多参数优化

为降低制冷装置区能耗及确保主冷箱最大传热温差低于25.00℃的综合控制目标,使用化工稳态流程模拟软件Aspen Hysys V 10版,对中国石油长庆油田(榆林)油气有限公司1.09万t/a天然气脱轻烃装置混合制冷剂制冷循环供冷(MRC)系统进行了建模,并构建了主冷箱冷热复合曲线,进行了多参数灵敏度分析优化。结果表明:该MRC系统关键控制参数的制冷剂分离器温度、主冷箱高压制冷剂流量最优值分别为1.75℃,64 960.00 m^(3)/h,制冷剂压缩机入口、出口压力的最优值分别为270.00,2 940 kPa;在该最优工况下运行的主冷箱内最大传热温差为23.47℃,较优化前降低了2.37℃,制冷装置区能耗为5 799.17 kW,较优化前降低了2 256.82 kW,降幅为28.01%。