Operation optimization of prefabricated light modular radiant heating system:Thermal resistance analysis and numerical study

The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,this new heating method presents an opportunity for the development of comprehensive facilities.The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature.In this paper,thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation.The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44℃ to−0.44℃ and a heat flux discrepancy of less than 7.54%,which can meet the requirements of practical engineering applications,suggesting a foundation for the prefabricated radiant heating system.

Breaking Through Bottlenecks for Thermally Conductive Polymer Composites:A Perspective for Intrinsic Thermal Conductivity,Interfacial Thermal Resistance and Theoretics

Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.

Analog-experiment analysis of ash-deposition monitoring model of boiler economizers in power plants

Ash deposition is a form of particulate fouling, and appears usually in boiler economizers. The ash deposition increases capital expenditure, energy input and maintenance costs. An analog experiment for monitoring ash deposition was performed from the analogous objective of a 410 t/h boiler economizer to verify the rationality and reliability of the ash-deposition-monitoring model presented in order to increase the security and economy in economizer running. The analog experiment platform is a tube-shell exchanger that conforms well to the conditions of a self-modeling area. The analog flue gas in the shell side is the heated air mixed with ash, and in the tube side the fluid is water heated by the flue gas. The fluid state in the water side and the flue gas side follows the second self-modeling area. A 4-factor-3-level orthogonal table was used to schedule 9 operation conditions of orthogonal experiment, with the 4 factors being heat power, flue gas velocity, ashes grain diameter and adding ashes quantity while the three levels are different values due to different position classes in every factor. The ash deposition thermal resistances is calculated by the model with the measure parameters of temperature and pressure drop. It shows that the values of the ash deposition thermal resistances gradually increase up to a stable state. And the experimental results are reliable by F testing method at α= 0.001. Therefore, the model can be applied in online monitoring of ash deposition in a boiler economizers in power plants and provides scientific decision on ash deposition prediction and sootblowing.

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation;these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoffs law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermal conduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.

A Feature Weighted Mixed Naive Bayes Model for Monitoring Anomalies in the Fan System of a Thermal Power Plant

With the increasing intelligence and integration,a great number of two-valued variables(generally stored in the form of 0 or 1)often exist in large-scale industrial processes.However,these variables cannot be effectively handled by traditional monitoring methods such as linear discriminant analysis(LDA),principal component analysis(PCA)and partial least square(PLS)analysis.Recently,a mixed hidden naive Bayesian model(MHNBM)is developed for the first time to utilize both two-valued and continuous variables for abnormality monitoring.Although the MHNBM is effective,it still has some shortcomings that need to be improved.For the MHNBM,the variables with greater correlation to other variables have greater weights,which can not guarantee greater weights are assigned to the more discriminating variables.In addition,the conditional P(x j|x j′,y=k)probability must be computed based on historical data.When the training data is scarce,the conditional probability between continuous variables tends to be uniformly distributed,which affects the performance of MHNBM.Here a novel feature weighted mixed naive Bayes model(FWMNBM)is developed to overcome the above shortcomings.For the FWMNBM,the variables that are more correlated to the class have greater weights,which makes the more discriminating variables contribute more to the model.At the same time,FWMNBM does not have to calculate the conditional probability between variables,thus it is less restricted by the number of training data samples.Compared with the MHNBM,the FWMNBM has better performance,and its effectiveness is validated through numerical cases of a simulation example and a practical case of the Zhoushan thermal power plant(ZTPP),China.

Prediction and parametric analysis of 3D borehole and total internal thermal resistance of single U-tube borehole heat exchanger for ground source heat pumps

The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D borehole and total internal thermal resistance(R_(b,3D)and R_(a,3D))and analyze the impacts of parameters on the R_(b,3D)and R_(a,3D).Firstly,eight parameters affecting the R_(b,3D)and R_(a,3D),including the borehole diameter,pipe diameter,pipe-pipe distance,borehole depth,soil thermal conductivity,grout thermal conductivity,pipe thermal conductivity,and fluid velocity inside the pipe,were considered and an L-54 design matrix was generated.Then,the 3D numerical model,coupling with the four-resistance model,was proposed to calculate R_(b,3D)and R_(a,3D)for each case.After that,the response surface methodology was employed to obtain and verify the correlation of R_(b,3D)and R_(a,3D),which were compared with the existing resistance calculation methods.Lastly,analysis of variance was carried out to reveal parameters that have statistically significant impacts on the R_(b,3D)and R_(a,3D).Results show that the rationality and accuracy of the correlation of R_(b,3D)and R_(a,3D)can be verified by the determination coefficient and P value of regression model,as well as the P value of lack-of-fit.The existing resistance calculation methods are more or less inaccurate and the discrepancies in some cases can be up to 86.74%and 111.35%for the borehole and total internal thermal resistance.The pipe and grout thermal conductivity,pipe and borehole diameter,and the pipe-pipe distance can be seen as the significant contributory factors to the variation of R_(b,3D)and R_(a,3D).

A Correction Factor-Based General Thermal Resistance Formula for Heat Exchanger Design and Performance Analysis

Methods for the analysis of heat exchangers with various flow arrangements modeling,design,and performance are essential for heat transfer system modeling and its integration with other energy system models.This paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer rate.Additionally,we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance,as a function of correction factor,heat transfer coefficient,and surface area.Based on the effective thermal conductance,we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer law.Moreover,for parallel-flow,cross-flow,and 1-2 Tubular Exchanger Manufacturers Association(TEMA)E shell-and-tube heat exchangers,we derived and obtained alternative correction factor expressions without introducing any temperatures.Two cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are accurate.Finally,the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer performance.That is,the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.

An Analytical Model for the Thermal Assessment of a Vertical Double U-Tube Ground-Coupled Heat Pump System in Steady-State Conditions

An analytical model was built to predict the thermal resistance of a vertical double U-tube ground-coupled heat pump that operates under steady-state conditions.It included a geometry obstruction factor for heat transfer throughout the backfill medium due to the presence of the second loop.The verification of the model was achieved by the implementation of five different borehole configurations and a comparison with other correlations in the available literature.The model considered a U-tube spacing range between(2)and(4)times the U-tube outside diameter producing a geometry configuration factor range of(0.29-0.6).The results of the model were utilized for the assessment of the DX ground heat exchanger coupled heat pump system.For similar geometrical configurations,the borehole thermal resistance experienced a decrease as the geometry factor increased.The single U-tube borehole thermal resistance was higher than that of the double U-tube heat exchanger by(10-27)%for the examined geometry configurations.The borehole thermal resistance at tube spacing of twice the tube diameter was higher than the predicted value at the triple diameter and fell in the range of(18-34)%.

Thermal Analysis of Vehicular Twin-Tube Hydraulic Gas-Precharged Shock Absorbers

In this study of temperature rising in vehicular twin-tube hydraulic gas-precharged shock absorbers,thermodynamic analyses were conducted via simulations.Equations on heat conduction,heat convection as well as radiation were derived by applying certain laws governing heat transfer;an equivalent thermal resistance network model of a shock absorber undergoing heat transfer was established innovatively;moreover,the shock absorber’s thermodynamic model of control volume system was built by using the first law of thermodynamics;and finally,time required for shock absorber to reach thermal equilibrium and corresponding value of steady temperature were calculated by programming.In this way,a lower thermal equilibrium temperature will be achieved,hence help to improve reliability of shock absorbers in work by offering low ambient temperature,by reducing amplitudes and frequencies of external incentives exerted on them and by increasing flow rate of ambient air passing around them.

基于自产热和外传热的锂离子电池热学模型参数辨识方法

锂离子电池热学模型参数(热容和热阻)的准确辨识对电池热电耦合建模及状态参数估计至关重要。然而传统测量方法成本高且测试周期长,如何利用充放电工况结合产热和传热机理研究快速热参数辨识方法具有重要意义。以8A×h软包锂离子电池为研究对象,建立分布式热路模型;设计双向脉冲工况实验,采用自适应粒子群算法(APSO)进行辨识;同时采用其他工况进行验证,实验和仿真温度误差小于0.1℃。另外,将热容和热阻转换为比热容和导热系数,并与其他文献中同类电池的参数进行比对,量级接近。研究结果表明,该方法可以有效解决层叠式软包锂离子电池热学模型参数辨识难的问题,且简便易行、成本低。

用于IGBT模块温度观测的3-D降阶混合型热模型

IGBT模块温度在线监测是提高大容量变流器可靠性的关键技术。在IGBT模块在线温度监测方法中,热阻模型法可对IGBT模块内部的温度分布进行估计,因而受到关注。结合了传感器数据的温度观测器可基于热阻模型,实时修正材料老化、参数温度依赖性和功率损耗计算误差等不确定因素对温度估计造成的影响。然而现有热模型无法同时兼顾系统可观性和建模准确性,且阶数相对较高,难以应用于温度观测器的在线运行。因此,该文提出了一种适用于风冷散热多芯片IGBT模块3-D温度观测器,同时满足可观性、准确性和实时性要求的混合型降阶热模型。首先,分析了热阻模型的拓扑结构及其参数辨识的方法,并探究了模型的状态空间生成规律;然后,基于非线性优化算法对该模型的参数进行修正,以减小因计算流体力学(CFD)仿真模型参数与实际参数不一致所引入的热阻模型与实验物理对象间的误差;随后,使用平衡截断法对热阻模型降阶,相对于现有集总参数热阻模型,进一步提高了实时求解效率;最后,通过仿真和实验验证了所提模型的准确性。

牵引变流器功率器件结温在线监测方法综述

功率器件结温在线监测对牵引变流器安全可靠运行至关重要,准确的结温监测是牵引变流器失效分析、运行状态监测、健康管理和剩余服役寿命预测的基础。因此,面向功率器件结温在线监测开展了大量研究。在此基础上,概述了以热网络模型法和温敏参数法为主的功率器件结温在线监测方法,以此为分类基准梳理了现有功率器件的结温监测方法并讨论了在牵引变流器中在线实现的可能,详细介绍了功率器件结温监测方法针对在线应用及客观因素干扰的发展与改进。最后,总结并对比了现有功率器件结温在线监测方法的演变、联系与差异,在分析现有结温监测方法面临挑战的基础上,展望功率器件结温在线监测在人工智能技术辅助下的前景。

不同季节影响下复合道面力学响应分析

为了研究复合道面在不同季节时的力学响应,以中原地区某机场改造项目为项目背景,借助三维有限元软件,建立了道面有限元模型,分析了复合道面在温度影响下的力学响应,并与机场监测数据进行对比,验证了模型的准确性。研究发现:大气温度所能影响的道面深度范围在0.56 m以内,和大气温度相比,道面面层温度峰值远大于气温峰值;道面内部不同结构层之间温度变化趋势相同,随着道面深度的加深,温度峰值逐渐递减,并且出现时间具有延迟现象;在不同季节,道面在相同机型作用下所产生的变形不同,说明温度对于道面的受力是有影响的,其中混凝土层在冬季时所产生的应变值比夏季所产生的减少约74%,变化比较明显。

火电厂智能化系统架构及智能监盘模型研究

数字化智能化技术是加速火电清洁低碳转型的关键,结合《火力发电厂智能化技术导则》及智能发电系统ICS、ISS建设理念,针对不同类型电厂自动化信息化现状,提出了融合热工电气一体化的智能化系统实施架构及接口设计,可满足智能发电运行控制与运维管理两类应用的实施与扩展。在此基础上,面向火电机组少人值守需求,结合运行人员实际监盘过程,针对关键运行参数趋势预警,提出了基于趋势分析、热力系统变工况、神经网络等算法的机组智能监盘模型,可有效降低运行人员监盘强度,提高机组运行安全性,最后对提高智能化应用的实用化程度进行了探讨。

基于土壤分层当量物性的地埋管换热器换热模型研究

文章综合考虑了土壤分层与地下水渗流等情况,结合实测数据,通过地埋管外壁温度计算得出地埋管内部流体温度与不同分层土壤的热物性参数,根据土壤当量物性进行分层,据此建立地埋管换热模型。经过对比验证实验发现,分层换热模型比常规均质模型更接近实测值,误差更小;基于土壤分层当量物性的地埋管换热器换热模型模拟出水温度与实测值平均绝对误差为0.21℃,模拟进、出口换热温差与实测值平均绝对误差为0.14℃,具有较高的准确度,可为工程设计提供依据并作为后续地埋管换热优化研究的基础。

基于热电堆的微型热流传感器制备及性能研究

航空发动机内部温度和热辐射的不均匀分布可能导致叶片表面出现热点,引起叶尖等区域的材料损坏。因此,监测单位时间内通过叶片表面的热量十分重要。热电堆型热流传感器以其测量范围广、稳定性好、精度高等优点,成为监测高温环境热流参数的常用方法。本文采用丝网印刷和高温烧结工艺,在10 mm×10 mm×1 mm的99%Al_(2)O_(3)陶瓷基片上制备了Pt-Rh10/Pt热电堆型热流传感器,并搭建了热流实验平台对传感器进行测试。结果表明,该热流传感器在1 019.4℃的高温环境下,所测热流密度为179.67 kW/m^(2),输出电压为0.462 3 mV。经过3次热循环测试可知,该热流传感器的重复性偏差小于5%,具有较好的重复性。

基于暖体假人的套装局部热阻及预测模型研究

对多名成年男女全年各季节着装行为进行了现场调研,得到了我国成年男女全年各季节典型着装搭配情况。在实验室条件下利用暖体假人模型进行了各季节典型着装搭配下的套装热阻测试,得到了34组成套服装的整体与局部热阻值,建立了全年各季节典型套装的局部服装热阻数据库。在此基础上分析了套装局部与整体热阻值的关系,获得了基于套装整体热阻值的局部热阻预测模型。

基于金属化薄膜电容器状态在线监测的剩余寿命评估方法

模块化多电平变流器(MMC)是柔性直流输电系统的核心装备,其中子模块(SM)金属化薄膜电容器是MMC中的薄弱环节之一,故研究金属化薄膜电容器的状态监测和寿命评估对于提高MMC运行可靠性和制定系统维护计划具有重要意义。目前,现有金属化薄膜电容器的寿命评估方法未考虑电容器老化进程对电容值和等效串联电阻(ESR)的影响,难以准确实现不同服役状态下的电容器剩余寿命评估问题。因此,该文提出考虑当前电容值状态在线监测的金属化薄膜电容器的剩余寿命评估方法。首先,在考虑电容器老化速率与温度耦合关系的基础上建立了电容器ESR和电容值的老化模型。其次,在进行寿命计算时考虑到电容器的老化效应,根据提出的容值在线监测方法得到当前的电容值,推断出电容器已使用年限及电容器目前的ESR值,并代入建立的场路协同仿真电热耦合模型中计算得到电容器温度。最后,根据提出的剩余寿命模型对电容器当前剩余寿命进行预测。该文研究成果将为设备选型、系统设计和MMC系统子模块电容器的可靠性评估提供参考。

基于无创血流动力学参数的脓毒症预测模型构建

目的:探讨超声心排血量监测(USCOM)联合临床指标对脓毒症的预测价值。方法:收集2017年2月至2018年5月广州医科大学附属第二医院EICU疑似感染患者214例为研究对象。记录患者的一般资料和实验室检查结果,并使用USCOM测量患者入院时血流动力学数据。根据脓毒症3.0诊断标准,分为脓毒症组与非脓毒症组,应用Logistic回归分析构建脓毒症的预测模型。采用受试者操作特征曲线ROC曲线下面积检验模型预测效能。结果:共收录214例疑似感染患者,其中非脓毒症组129人,脓毒症组85人。最终纳入脓毒症预测模型的预测因子分别为:每搏功(SW)、外周血管阻力指数(SVRI)、GCS评分、降钙素原(PCT)、白细胞计数(WBC)。ROC曲线下面积(AUC)为0.895,95%CI(0.837-0.938),敏感性为83.1%,特异性为83.3%,Youden指数0.6643。结论:SW、SVRI、WBC、PCT、GCS评分是预测EICU疑似感染患者的脓毒症发生的影响因素,由其构建的模型对脓毒症的发生有较高的预测价值。

基于热阻调控方法的低温光学系统二级温区传热特性分析

为了实现低温光学系统二级温区的精准控温,同时不引入额外的热负载,提出了一种热阻调控方法,建立了应用于该方法的一维数学模型,运用该数学模型研究了不同真空腔温度条件下不同热阻参数(不同材料参数和几何参数)对二级温区达到热平衡后温度水平和漏热量的影响,同时将该方法和传统的电加热调控方法进行了比较。研究结果表明:当真空腔温度为定值时,随着热阻的增大,二级温区温度升高,漏热量减小;当热阻为定值时,随着真空腔温度的升高,二级温区温度升高,漏热量增大。在文中的研究工况下,当真空腔温度为253.15 K时,二级温区温度水平调节范围为111.1~185.2 K,相应的漏热量从1.75 W减小至1.10 W;当真空腔温度为293.15 K时,温度水平调节范围为120.9~219.4 K,相应的漏热量从2.58 W减小至1.57 W。电加热调控方法使二级温区热负载达到了16.8 W,是热阻调控方法的11倍左右(真空腔温度为293.15 K,二级温区目标温度为220 K左右),随着二级温区温度的升高,电加热调控方法使得系统热负载增大,热阻调控方法与之相反。热阻调控方法使低温光学系统热负载一直处于较低的水平,同时可减少系统对电功率和散热资源的需求。研究结果可为空间应用中的类似低温光学设计提供参考。