Effect of hydrothermal conductivity on thermal resistance of porous materials

Results of experimental study for dependency of thermogradient coefficient on moisture in porous material have been presented. These experimental data were used for estimating the effect of hydrothermal conductivity on heat transfer.     

非均匀多孔介质有效热导率分析

本文采用控制容积法,界面调和平均导热系数值以及图形处理方法对典型非均匀多孔介质硬质聚氨酯泡沫材料的导热过程进行了分析与模拟计算。结果表明:多孔介质的内部结构是影响温度分布和热量传递的主要的因素,其影响程度与骨架和孔隙的导热系数,孔隙的大小和分布有关;计算得到的有效热导率值与文献中实验测量结果吻合较好。本文的研究结果可以推广到更为复杂的非均匀多孔介质的场合,从而可以进一步认识非均匀多孔介质中的导热规律,为工程计算提供更精确的计算方法。     

Amélioration du transfert thermique par un dépôt poreux sur la paroi d'un échangeur tubulaire

A study of flow regime and heat transfer in an annular heat exchanger partially filled with a porous medium is presented in this work. Constant heat flux and constant wall temperature boundary conditions on the inner cylinder are considered, while the outer cylinder is assumed adiabatic. The study is for both the thermal entry region and the thermally fully developed region. The flow in the porous region is modelled either by the Darcy-Brinkman equation for which an exact solution is developed or by the Darcy-Brinkman-Forchheimer equation in order to take into account inertial effects. For this case a numerical solution based on a control volume method is discussed. The results emphasize the effect of the porous layer attached to the inner cylinder on the thermal development length and heat transfer rate. It is shown that the porous substrate reduces the thermal entry length. When the effective thermal conductivity of the saturated porous medium is of the order of the fluid thermal conductivity, the local Nusselt does not vary monotonically with the thickness of the substrate. However, the use of a porous matrix always leads to an increase in the heat transfer rate provided its thermophysical properties and thickness are well chosen.     

前沿领域综述–多孔介质强制对流换热研究进展

多孔介质的强制对流换热主要涉及渗流、对流换热、热弥散和热辐射等方面的内容, 文中对这个几个方面的国内外研究进展和发展趋势进行了逐一综述. 同时对主要理论模型、实验研究和经验关联式进行了分类整理, 总结了它们的特点、适用范围和局限性, 并对主要研究成果进行了对比分析, 指出了将来进一步研究的方向和难点所在. 而且通过简化计算得到高温多孔介质冷却过程何时需要考虑辐射换热. 所有这些对多孔介质的理论研究和工程应用都具有指导性的意义. 关键词： 多孔介质 对流换热 渗流 热弥散     

微尺度换热器的研究及相关问题的探讨

本文对微风度换热器产生的背景、研究现状及存在的问题进行了综述和初步分析。对在微小槽道内流体的流动和传热与常规尺度下的差异的原因和机理进行了简单分析。发现有些用气体所做的实验研究，很有可能是处于有速度滑移和温度跳跃的滑流区。速度滑移和温度跳跃致使阻力系数减小、传热减弱。对微小槽道和多孔介质对传热的强化效果进行厂比较。多孔介质对传热的强化效果更好，但同时压力损失也更大。     

温室内多孔蓄热墙传热与流动特性

本文采用一维稳态饱和多孔介质能量双方程模型,对温室内多孔蓄热墙的传热与流动特性进行了研究.结果表明:多孔蓄热墙的固体骨架与空气之间的换热取决于空气的入口流速、多孔材料的孔隙率、渗透率和固体骨架的导热系数,由于多孔蓄热墙接受的太阳辐照是不均匀的,因此推荐采用具有不同孔隙率的新型复合多孔蓄热墙,以减少这种不利的影响.     

New family of solid sorbents for adsorptive cooling: Material scientist approach

This paper summarizes literature data concerning a new family of materials for adsorptive cooling. They are composites of a type of “salt confined to a porous host matrix” (so called selective water sorbents or SWSs). These materials demonstrate an intermediate behavior between solid adsorbents, salt hydrates, and liquid absorbents. The thermodynamic equilibrium with water vapor has been measured for more than thirty SWSs based on halides, sulphates, and nitrates of alkaline and alkaline earth metals that are confined to various matrices (silica, alumina, porous carbons, clays, MCM-41, etc.). The important advantage of the SWSs is the possibility to controllably modify their water sorption properties in a wide range by varying (a) the chemical nature of the impregnated salt, (b) the porous structure of the host matrix, (c) the amount of the confined salt, and (d) the preparation conditions. This, in principle, allows purposeful synthesis of new solid sorbents with predetermined properties that fit the demands of particular adsorptive cycles. Appropriate examples are presented in the paper. A recent study of adsorption chillers with granulated and compact layers of SWS-1L (CaCl₂ in mesoporous silica) showed an experimental COP as high as 0.6, which is larger than that reported for silica gel/water and zeolite/water systems under the same cycle conditions. The concept of matrix modification with an active salt can also be used for synthesis of efficient sorbents of carbon dioxide, methanol, and ammonia. Other practical applications of SWSs are briefly discussed, such as heat protection, gas drying, and fresh water production from the atmosphere. The text was submitted by the author in English.     

毛细多孔介质在液氮中的传热试验研究

为了研究毛细多孔介质在液氮中的传热性能,进行了在试验件中不填充和填充超细玻璃棉的试验。采用低温热电偶连续测量试验件的5个不同位置的温度,得到了5条温度曲线。分析曲线表明超细玻璃棉对传热过程有明显的强化作用,且能使试验件在一段时间内保持相对稳定的低温。并从理论上分析了换热过程,整理了换热方程组。     

考虑毛细滞后效应的未饱和含湿多孔介质传热和传质理论

毛细滞后是未饱和多孔介质中很重要的特性之一。在许多情况下，毛细滞后现象对介质中传热和传质过程有着显著的影响。本文引入最小梯度概念，用以描述多孔体中毛细水运动滞后的定量行为，进而建立了考虑毛细滞后效应的未饱和含温多孔介质传热和传质的系统理论，为进一步定量研究毛细滞后对传热传质的影响打下了理论基础。     

Fracture Characterization with NMR Spectroscopic Techniques

Determination of suitable techniques and analyses that can be implemented by NMR well logging can greatly improve the characterization of underground petroleum reservoirs and aquifers. In this paper, the feasibility for using various NMR methods for detection and characterization of fractures is explored. Analyses of experimental data obtained with a variety of samples are presented. It is shown that relaxation contrasts are useful for separating the signal contributions from fluids in the fractures and the porous matrix, and that relaxation weighting can be used in combination with other NMR techniques for enhancing fracture characterization.     

Effects of Solid Matrix and Porosity of Porous Medium on Heat Transfer of Marangoni Boundary Layer Flow Saturated with Power-Law Nanofluids

The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids,and the Marangoni boundary layer flow with heat generation is investigated.Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered.The governing partial differential equations are simplified by dimensionless variables and similarity transformations,and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique.It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.     

机械加工多孔层在大气压和高于大气压时的沸腾换热

1引言在过去的二十年中，已研制出诸如HighFI。、Thermoexcel－E、Ge、－T、CIT等多种高性能强化沸腾换热结构［‘－’］，其中ThermoexcelE型结构是机械加工多孔层中有代表性的一种，并进行了较多研究＊‘］。但迄今为止，研究工作多限于一个大气压时的沸腾工况［‘，’］，而较少涉及非大气压时的情形。本文对一种ThermoexcelE型机械加工多孔层在大气压和高于大气压时的沸腾传热进行了实验，提出了简化物理模型，进行了流动与传热分析，综合实验数据，建立了相应的传热关联式。2实验研究实验装置参见文献＊。多孔层基体为厚壁紫铜管…     

Theoretical analysis of porous radiant burners under 2-D radiation field using discrete ordinates method

This paper describes a theoretical study to investigate the heat transfer characteristics of porous radiant burners (PRBs). In the present work, a 2-D rectangular model is used to solve the governing equations for porous medium and gas flow before the premixed flame to the exhaust gas. The gas and the solid phases are considered in non-local thermal equilibrium and combustion in the porous medium is modeled by considering a non-uniform heat generation zone. The homogeneous porous media, in addition to its convective heat exchange with the gas, may absorb, emit and scatter thermal radiation. The radiation effect in the gas flow is neglected but the conductive heat transfer is taken into account. In order to analyze the thermal characteristics of porous burners, the coupled energy equations for the gas and porous medium in steady condition are solved numerically and the discrete ordinates method (DOM) is used to obtain the distribution of radiative heat flux in the porous media. Finally, the effects of various parameters on the performance of porous radiant burners are examined. The present results are compared with some reported theoretical and experimental results by other investigators and good agreement is found.     

多孔体内插物强化蒸汽凝结换热实用计算关联式

根据多孔体内插物显著影响凝结液膜流动状态并导致液膜波动的特性,提出了用于大空隙率多孔体内插物强化蒸汽凝结换热计算的半经验准则关联式,用实验结果对关联式的正确性进行了验证,并通过数值模拟计算结果与该关联式结果的比较,证明了提出的半经验关联式可以应用到实验范围以外。     

Theoretical prediction of the onset of thermoacoustic instability from the experimental transfer matrix of a thermoacoustic core

The aim of this paper is to propose a method to predict the onset conditions of the thermoacoustic instability for various thermoacoustic engines. As an accurate modeling of the heat exchangers and the stack submitted to a temperature gradient is a difficult task, an experimental approach for the characterization of the amplifying properties of the thermoacoustic core is proposed. An experimental apparatus is presented which allows to measure the transfer matrix of a thermoacoustic core under various heating conditions by means of a four-microphone method. An analytical model for the prediction of the onset conditions from this measured transfer matrix is developed. The experimental data are introduced in the model and theoretical predictions of the onset conditions are compared with those actually observed in standing-wave and traveling-wave engines. The results show good agreement between predictions from the model and experiments.     

Characterization of porous polar semiconductors by their optical spectra in the region of phonon and plasmon-phonon excitations

Optical properties of porous A ³ B ⁵ semiconductors (GaAs, InP, and GaP) in the far-infrared region, in particular, the specular reflection and attenuated total reflection, including the excitation regime of surface polaritons, are considered. Considering a porous material as a composite, we performed calculations in the context of the effective medium model using two modifications of it, Maxwell-Garnett and Bruggeman, which correspond to two different topologies of the composite material—matrix and statistical. The effect of porosity of the material and of such parameters as doping, anisotropy, and penetration depth of an electromagnetic wave to a porous material on optical spectra is analyzed. In addition, some experimental data are presented and the adequacy of the performed numerical simulation is demonstrated.     

考虑弥散效应的多孔介质中超绝热燃烧的数值模拟

研究多孔介质内往复流动下的超绝热燃烧。一维模型包括气体输运、多孔介质固体的辐射、导热和气固两相间的对流换热。通过数值计算研究超绝热燃烧的形成、以及弥散效应、当量比和多孔介质材料本身对超绝热燃烧特性的影响。计算结果的有效性通过实验进行了验证并取得了相同的趋势。结果表明,组分弥散效应对气体温度分布和反应热影响很小;同一工况下,不考虑气体混合物的热弥散效应,会导致过高的气体温度计算值。同时,计算结果表明小孔径的多孔介质更有利于贫可燃极限的扩展,对30 ppi的多孔介质燃烧器,得到了当量比为0．092的可燃极限。     

多孔层在高于一个大气压下的沸腾两相流与传热

在前文［１］工作的基础上，利用微型多孔壁热虹吸管蒸发段模型，对粒状多孔层在高于一个大气压下的沸腾两相流与传热进行了分析；根据实验数据，建立了传热关联式。     

热储周围岩石热补偿对增强型地热系统采热过程的影响

采用自行开发的增强型地热系统(EGS)地下热流动过程三维动态模拟软件,模拟不同地质条件下EGS的长期运行过程,分析热储周围岩体的热补偿对产热温度以及热储内岩石、流体温度演化的影响.该数值模型视热储为等效多孔介质,采用两个能量方程分别描述流体和岩石的温度场,深入探究岩石与循环流体之间的换热过程.研究发现,热储周围岩体的热补偿作用与热储内流场形态强烈相关,且并不总是提高EGS的生产温度.在深度方向上有较大的优势流动的热储中,热补偿作用在EGS运行早期甚至会降低采出流体的温度.随着EGS的运行,热储温度持续降低,热补偿将对热能开采的影响将逐渐转向正面,对生产流体温度的提高效果增强.