Radiative heat transfer analysis of a concave porous fin under the local thermal non-equilibrium condition:application of the clique polynomial method and physics-informed neural networks

The heat transfer through a concave permeable fin is analyzed by the local thermal non-equilibrium(LTNE)model.The governing dimensional temperature equations for the solid and fluid phases of the porous extended surface are modeled,and then are nondimensionalized by suitable dimensionless terms.Further,the obtained nondimensional equations are solved by the clique polynomial method(CPM).The effects of several dimensionless parameters on the fin's thermal profiles are shown by graphical illustrations.Additionally,the current study implements deep neural structures to solve physics-governed coupled equations,and the best-suited hyperparameters are attained by comparison with various network combinations.The results of the CPM and physicsinformed neural network(PINN)exhibit good agreement,signifying that both methods effectively solve the thermal modeling problem.

A Multiple-Relaxation-Time Lattice Boltzmann Model for Natural Convection in a Hydrodynamically and Thermally Anisotropic Porous Medium under Local Thermal Non-Equilibrium Conditions

To investigate the natural convective process in a hydrodynamically and thermally anisotropic porous medium at the representative elementary volume(REV)scale,the present work presented a multiplerelaxation-time lattice Boltzmann method(MRT-LBM)based on the assumption of local thermal non-equilibrium conditions(LTNE).Three sets of distribution function were used to solve the coupled momentum and heat transfer equations.One set was used to compute the flow field based on the generalized non-Darcy model;the other two sets were used to solve the temperature fields of fluid and solid under the LTNE.To describe the anisotropy of flow field of the porous media,a permeability tensor and a Forchheimer coefficient tensor were introduced into the model.Additionally,a heat conductivity tensor and a special relaxation matrix with some off-diagonal elements were selected for the thermal anisotropy.Furthermore,by selecting an appropriate equilibrium moments and discrete source terms accounting for the local thermal non-equilibrium effect,as well as choosing an off-diagonal relaxation matrix with some specific elements,the presented model can recover the exact governing equations for natural convection under LTNE with anisotropic permeability and thermal conductivity with no deviation terms through the Chapman-Enskog procedure.Finally,the proposed model was adopted to simulate several benchmark problems.Good agreements with results in the available literatures can be achieved,which indicate the wide practicability and the good accuracy of the present model.

Local non-equilibrium thermal fluctuation,internal noise and dissipation in gaseous heat conduction systems with high values of Prandtl number

By means of a stochastic model suggested in this paper for the systems with local non-equilibrium excited thermal fluctuations, the famous Shannon entropy is extended to include the heat conduction processes controlled externally by boundary constraints of constant temperature gradients at two sides.Meanwhile,using the description of master equation for the continuous Markov processes a balance equation of stochastic entropy production valid for one dimension gaseous heat conduction systems with high values of Prandtl number has been also established.Based on it,a general expression for both the stochastic entropy production and the entropy production of fluctuations have been further deduced by theΩ-expansions.In this formalism,all kinds of stochastic contributions to the dissipation from the non-equilibrium thermal fluctuation and internal noise turn explicit.

激光诱导等离子体LTE态判定方法研究

针对目前等离子体温度测量中常用的Boltzmann平面法和双线法的测量精度较差的问题,提出结合Boltzmann-Maxwell分布和Saha-Eggert公式来提高等离子温度的测量精度;根据高斯公式的面积与峰值关系建立了发射谱线线宽的简便算法,并通过谱线的Stark展宽计算等离子体的电子密度;建立了以McWhirter准则的等离子局部热平衡（LTE）态判据。以铝为被测样品的实验结果表明,随着激光能量的增加,等离子体温度和电子密度随之呈线性上升趋势;激光能量在127~510mJ范围内的等离子体电子密度变化范围为1.305 32×10^17~1.873 22×10^17 cm^-3,等离子体温度的变化范围为12 586~12 957K,根据McWhirter准则本实验中所有等离子体均满足LTE态阈值条件;针对在光谱仪波段内可观测到的处于同一电离态谱线相对较少的铝元素,在不适合用Boltzmann平面法计算温度时,利用Saha-Boltzmann方法对100组铝等离子体光谱进行温度测量的相对标准偏差（RSD）为0.4%,相比于双线法的1.3%,大幅提高了测量精度。该计算方法可用于快速计算等离子体温度、电子密度及判断等离子体LTE态,在自由定标、光谱有效性分析、谱线的温度校正、确定最佳采光位置以及等离子体LTE分布状态等研究中都有较高的应用价值。

格子Boltzmann方法模拟泡沫金属内相变材料热传导融化传热过程

基于局部热非平衡条件下泡沫金属内热传导融化相变传热的非线性双温度方程,在表征单元尺度上构建双温度分布函数格子Boltzmann模型,其中相变非线性源项处理采用焓法迭代求解。数值模拟了金属骨架与相变材料的温度分布情况,重点分析了孔径、金属骨架与填充材料热传导比和Stefan数等对局部热非平衡效应的影响。模拟结果表明,孔径越大、金属骨架与填充材料热传导比越大,局部热非平衡效应越明显;相变过程的存在,加大了局部热非平衡效应,并且Stefan数越低局部热非平衡效应则越大。

网格划分对埋地管道传热计算的影响分析

采用多种网格加密方法对埋地管道计算区域进行了划分,设计了5种网格划分方案,分析了计算区域的能量守恒。通过数值模拟结果分析,在埋地管道传热模拟计算中,同时加密管道和地面边界比只加密一种的计算误差小。在加密管道和地面边界后,适当减少计算区域内部网格有助于提高计算效率,并且可以减小计算误差。

间断等温边界下多孔介质方腔内非热平衡自然对流传热数值模拟

采用局部非热平衡模型,在方腔两侧壁面布置间断式等温边界,采用SIMPLER算法数值研究了固体骨架发热多孔介质方腔内的稳态非达西自然对流,探讨了6种等温边界布置方案、孔隙率ε及Da数对方腔内自然对流与传热的影响规律。计算结果表明:在左右对称的等温边界条件下,多孔介质方腔内的流场、温度场分布出现了左右对称分布特性。孔隙率ε及Da数的增加有利于提高多孔介质方腔的整体传热量,当Da数小于10-5时,传热量Q值随Da数变化不大,且不同等温边界布置方案的Q值差别不大。随着Da数的增大,多孔介质方腔内的热对流逐渐得到发展,此时不同传热方案的Q值出现了显著的差异,并随着Da数的增大而增加。

空调开启后的人体生理热反应研究

在人工气候室,对室温由29℃分别降至23,25,27℃的3种空调运行环境中室内环境温度和人体6个部位皮肤温度进行了连续测量和主观问卷调查,采用灰色关联度分析方法,研究了空调环境下人体局部皮肤温度、局部热感觉和整体热感觉的变化特性及三者之间的相互关系。结果显示:人体皮肤温度和热感觉呈动态变化,其降低幅度和达到稳定的时间随环境控制温度的降低而增大和延长;控制温度分别为23℃和25℃时局部皮肤温度与局部热感觉显著线性相关,29→27℃工况下线性相关度降低;足背和小腿是空调环境中影响人体整体热感觉的2个关键部位,其影响的重要度随空调环境降温速率的增大而增大。

圆板在局部Gauss温度场作用下的响应分析

基于薄板热弯曲理论,推导了圆板在Gauss(高斯)温度场作用下的挠度和热应力解析表达式,分析了边界条件和局部温度参数对圆板挠度和热应力的影响,为局部温度变化薄板结构的热力学分析提供理论依据.研究结果表明:圆板中心处的挠度和压应力有最大值;在热影响区内,圆板内一点的挠度随着该点到板中心距离的增大呈Gauss型减小趋势;在热影响区外,圆板挠度的变化趋势与圆板边界约束形式和辐照因子有关,辐照因子越大,边界简支圆板挠度越先呈线性减小趋势;圆板挠度的解析解与有限元解一致.在热影响区内,圆板内一点的热应力随着该点到板中心距离的增大呈Gauss型减小趋势,两种边界约束圆板的热应力变化趋势相似;在热影响区外,圆板热应力的变化趋势与圆板边界约束形式和辐照因子有关.

辐射耦合空调系统的局部热舒适实验研究及仿真分析

为研究辐射冷板与独立新风耦合系统下人体局部热舒适,以长沙某住宅小区某用户房间为研究对象,进行了实验研究;并对该热环境相关参数进行仿真分析。通过实测数据与仿真数据对比,从辐射温度不对称、室内气流分布、人体垂直温差和地面温度四个方面定量分析了辐射耦合空调系统的热舒适环境。同时,通过多表面模型与离散坐标模型模拟结果的对比,分析了两种辐射模型的适用性。结果表明:在采用辐射冷板+独立新风空调系统而且空间包含人体热源的情形下,DO辐射模型的仿真结果更接近实验测试结果;室内测试及仿真结果符合ASHRAE对局部热舒适的标准要求;利用CFD仿真方法可以对局部热舒适进行较准确的分析。

通风方式对辐射空调房间人体热感觉及皮肤温度的影响

采用主观问卷与实验测试相结合的方法,探讨了辐射顶板+混合通风与辐射顶板+地板送风2种通风方式下房间内人体热舒适性的差异,分析了通风方式对人体热感觉及皮肤温度的影响。结果显示:不同通风方式下各部位皮肤温度的差异与相应部位热感觉的差异存在不一致情况;通风方式对受试者整体热感觉的影响较小,而对局部皮肤温度及局部热感觉的影响较大。

长时间处于地板辐射供冷环境中的人体热反应模拟研究

辐射空调近年来在建筑中的应用案例数量上升迅速,如何预测在辐射空调环境下的人体舒适度,成为工程设计参数确定中需要解决的基础问题。本文依据人工环境舱内热反应实验中的实际情况,采用伯克利热舒适模拟软件对地板供冷工况进行模拟得出皮肤温度和热感觉值;将模拟值与实验结果从稳定时间和稳定值两方面进行对比,对该模拟软件在长时间暴露于地板辐射供冷环境中的人体热反应预测的适用性进行验证。结果表明,模型能够在一定程度上反映不对称辐射环境下的人体不同部位皮肤温度分布,以及热感觉和热舒适差异随时间的动态变化过程,大部分部位的偏差在可接受范围内,但在前臂、手背和足背等部位偏差较大,皮肤温度偏差值超过2℃,热感觉偏差接近-1,需通过后续研究进行修正。

Thermal physiological response to local heating and cooling during sleep

For a healthy and productive life, good steep is essential, which has prompted studies on how comfortable sleep can be achieved. Understanding the relationship between thermal environment and physiological responses such as skin and core temperatures, and psychological responses such as thermal and sleep sensations is necessary to identify the most suitable thermal environment for steep. As an energy-saving and practical method of creating the most appropriate thermal environment for sleep, local heating or cooling is sometimes used, which takes into consideration the differences in local thermal responses. We performed this study to identify the most effective thermal environment for inducing comfortable sleep by identifying the physiological responses during sleep on the basis of sleep experiments conducted under local body heating or cooling conditions. We also used a human thermal model, which can be applied for predicting physiological responses. In the experiments, the feet of the subject were the primary area to be heated or cooled, which was achieved by installing a flexible duct with an outlet placed close to the subject＇s feet and inlet connected to an air conditioner. Differences in the fluctuation of body temperature and sleep stage depended on the airflow direction from the duct to the feet. When air was blown downward towards the feet, body temperature decreased and the subject was able to sleep well. Measured skin and core temperatures were calculated using an improved 27-node human thermal model that was originally developed for use in subjects who are not in steep. Although skin

PLC在区域供冷自控系统中的应用及分析

详细地介绍了单体建筑空调机房的控制任务及远程监控系统网络,控制系统选型及配置,空调机房的设备自动控制逻辑。

UnsteadyMHD Non-Darcian Flow Over a Vertical Stretching Plate Embedded in a Porous Medium with Thermal Non-EquilibriumModel

An analysis is performed to study the influence of local thermal nonequilibrium(LTNE)on unsteadyMHDlaminar boundary layer flowof viscous,incompressible fluid over a vertical stretching plate embedded in a sparsely packed porous medium in the presence of heat generation/absorption.The flow in the porous medium is governed by Brinkman-Forchheimer extended Darcy model.A uniform heat source or sink is presented in the solid phase.By applying similarity analysis,the governing partial differential equations are transformed into a set of time dependent non-linear coupled ordinary differential equations and they are solved numerically by Runge-Kutta Fehlberg method along with shooting technique.The obtained results are displayed graphically to illustrate the influence of different physical parameters on the velocity,temperature profile and heat transfer rate for both fluid and solid phases.Moreover,the numerical results obtained in this study are compared with the existing literature in the case of LTE and found that they are in good agreement.

Heat Transfer and Energy Utilization of Waste Heat Recovery Device with Different Internal Component

Steel industry is high energy-consuming industry, and its waste?heat recovery is critically?important for energy utilization. In this study, pipeline bundle is used to enhance heat transfer in?waste?heat recovery device,?and?associated gas-solid heat transfer and energy utilization performance with different pipeline arrangement, pipe diameter and shape of internal component are further analyzed. The temperatures of gas and particle in device with pipeline bundle periodically fluctuate in horizontal direction, and those in staggered system distribute more uniformly than those in paralleled system. Compared with paralleled device, exergy and waste heat utilization efficiency of staggered device have been improved, and they are both higher than?those without pipeline. As pipe diameter increases, exergy and waste heat utilization efficiency first increases and then decreases, and they reach the maxima with optimal pipe diameter.?As the width of internal component keeps constant, influence of its shape on heat transfer is very little.

Analyzing Heat Extraction and Sustainability of EGS with a Novel Model

We investigate the subsurface heat exchange process in EGS （enhanced geothermal systems） with a previously developed novel model. This model treats the porous heat reservoir as an equivalent porous medium of a single porosity. However, it considers local thermal non-equilibrium between solid rock matrix and fluid flowing in the factures and employs two energy conservation equations to describe heat transfer in the rock matrix and in the fractures, respectively, enabling the modeling and analyses of convective heat exchange in the heat reservoir. Another salient feature of this model is its capability of simulating the complete subsurface heat exchange process in EGS. The EGS subsurface geometry of interest physically consists of multiple domains： open channels for injection and production wells, the artificial heat reservoir, and the rocks enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties （porosity and permeability, etc.）. This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. This model is used to perform a comprehensive parametric study with respect to an imaginary doublet EGS. Effects of several parameters, including the permeability of heat reservoir, heat exchange coefficient in the heat reservoir, the specific area of fractures in the heat reservoir, and thermal compensation from surrounding rocks, on the heat extraction efficiency and EGS lifetime are analyzed.

矿井局部降温系统设计研究

为了解决深井热害问题,研发了矿用气动蓄冰空调系统。该系统整合了降温除湿和空气净化两大系统,主要用于避难硐室,具有广阔的市场前景与良好的社会效益。矿用气动蓄冰空调系统的优点主要有:(1)无电化设计,可避免二次灾害发生,具有较高的安全性和可靠性;(2)自动控制,准确可靠;(3)制冷功率大;(4)降温、空气净化及除湿一体化设计;(5)采用蓄冰球蓄冷及释冷,制冷和释冷效率高;(6)采用机械通风,风量大,强制对流,降温速率快;(7)适用环境温度范围宽。

Experimental and numerical analysis of the hydraulic and thermal performances of the gradually-varied porous volumetric solar receiver

A gradually-varied porous structure is designed to increase the thermal performance of the porous volumetric solar receiver.Based on the replica method and multilayer recoating technique, the silicon carbide porous ceramic with linear-changed geometrical parameters is fabricated. The performances of the uniform and gradually-varied porous volumetric solar receivers are studied by both experiment and numerical simulation. An optimization method combining genetic algorithm and computational fluid dynamics analysis is applied to determine the optimum porosity distribution. The results present that porous volumetric solar receiver with linear-changed geometrical parameters exhibits better thermal performance than the uniform porous volumetric solar receivers, especially when the thickness of the receiver is small. Larger porosity in the front is beneficial for increasing the solar radiation penetration depth, which limits the reflectance and thermal radiative losses. Smaller porosity in the rear traps more solar radiation and increases the convective heat transfer. When the receiver’s thickness is larger, the performance of the gradually-varied volumetric solar receiver is nearly identical to that of the uniform receiver with largest porosity. The double-layer configuration is found to be the optimized structure of the gradually-varied porous volumetric solar receiver. The thermal efficiency could be further improved using genetic algorithm with an 11 K increase of the outlet temperature.

冷端边界条件对发汗冷却解析解的影响

发汗冷却多孔区域的非热平衡模型数值计算中,冷端边界条件对多孔介质内流固温度分布有着非常明显的影响。该文针对发汗冷却多孔壁面内部非热平衡模型理论求解方法中冷端边界条件的设置问题,比较了3种不同的冷端边界条件设置模型。结果表明:在流动Reynolds数较小时,假设冷端流体温度等于初始温度的等温边界且假设边界绝热的边界条件会导致冷端附近流固温度偏低;而假设等温边界同时存在冲击冷却边界会使得流固温度整体范围内偏低。该文分析了量纲为1的数对不同边界条件模型计算结果的影响,指出量纲为1的冷却剂流量与多孔体Biot数增加会使流体冷端进口温度等于远端温度假设成立,并提出了热平衡假设成立的条件方程。