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一个多孔有机织物热湿传递过程的数学模型 总被引:1,自引:0,他引:1
利用多孔介质中的Darcy定律建立了一个多孔有机织物中热湿传递过程的数学模型,并提出了一个描述多孔有机织物中液相水重力与表面张力的对比关系的数H=5gρldcLτlεl1/3/2σcosФε1/3采用Crank—Nicolson方法数值求解了该模型,得到了在相同初始和边界条件下,不同有机材料织物中的热湿传递过程,并给出了多孔有机织物中的水蒸汽的浓度场分布、温度场分布以及纤维中的含水量的分布。计算结果与实验结果是吻合的。 相似文献
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混凝土中化学-热-湿-力耦合过程的数值方法 总被引:4,自引:0,他引:4
提出了一个火灾下混凝土中化学-热-湿-力耦合过程分析的两级数学模型. 混凝
土模型化为充满两种非混溶孔隙流体的非饱和变形多孔多相介质. 数学模型基于控制干空
气、湿份及基质溶解物的质量守恒、混凝土介质混合体的动量守恒和焓(能量)守恒的耦合
偏微分方程组. 模型中特别考虑到了高温下的脱盐过程. 构造了一个用于数值模拟
化学-热-湿-力耦合行为的有限元求解过程的混合弱形式. 并且针对其中具有非自伴随算子特性的
双曲线控制方程的空间离散进行了特殊考虑. 数值结果例题显示所发展的数学模型和数值方
法在重现火灾条件下的混凝土中化学-热-湿-力耦合行为的有效性. 相似文献
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环境热舒适是衡量建筑物等级的重要指标。据大量实验与现场研究表明,PMV热舒适模型存在一定的偏差,有待完善、改进。现有PMV计算模型计算的各散热项、热负荷、PMV值与实际存在偏差;适用于PMV评价模型“接近热中性”环境条件、人体热负荷定义及其计算方法还存在异议。通过理论分析,本研究提出了新的“接近热中性”环境条件、新的人体热负荷定义及其计算方法,提出了新的PMV计算模型,并经对比分析发现,新的模型修正了在偏热环境下的现有PMV预测偏差。另一方面,在新的热负荷计算方法下,PMV与热负荷之间的函数关系KM必须进行相应调整,要获得准确的KM函数关系,必须获得较准确的人体平均皮肤温度与环境参数间的关系。 相似文献
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针对不同气体模型对高超声速飞行器喷流反作用控制系统(RCS)热喷干扰流场模拟的计算效率和准确性问题, 基于喷流燃气物理化学模型, 通过数值求解含化学反应源项的三维N-S方程, 建立了飞行器RCS热喷干扰流场数值模拟方法, 分别采用化学反应流、反应冻结流、二元异质流以及空气喷流四种气体模型开展了典型外形热喷干扰流场的数值模拟, 研究了不同气体模型对热喷干扰流场结构、飞行器气动力热特性的影响, 分析了不同马赫数、飞行高度下的变化规律. 研究表明: 化学反应流模型计算精度较高, 计算与风洞试验数据的吻合程度优于其他三种简化模型; 在本文的低空条件下, 采用简化模型进行热喷干扰流场数值模拟, 会低估分离区大小, 使飞行器气动力特性预测出现偏差, 同时也会低估表面热环境, 对防热系统设计不利, 随着马赫数增加, 简化模型对气动力热特性预估的误差进一步增大, 同时不同简化模型之间的差异也进一步增大; 飞行高度较高时, 模型之间的差异减小, 此时可采用简化模型进行计算以提高计算效率. 本文的研究结果可为飞行器热喷干扰流场数值模拟及喷流反作用控制系统设计提供参考. 相似文献
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油藏多孔介质热质传递“三箱”分析模型研究 总被引:1,自引:0,他引:1
油藏多孔介质孔隙组成及结构变化多样,一些特性参数很难全部获得,精确描述和分析困难;另外,多孔介质内渗流过程水力条件和作用机理复杂,存在热流固耦合作用,目前的一些分析方法和研究模型具有一定的局限性.提出了油藏多孔介质的表征单元体(representative elementary volume,REV)描述表征方法;基于表征单元体建立了多孔介质的黑箱模型、灰箱模型和白箱模型,据此提出了多孔介质的“黑箱→灰箱→白箱”分析过程.基于黑箱模型和灰箱模型推导了REV导热系数计算公式、给出了REV热质传递过程的热平衡方程.结合中国油藏热采情况,对多孔介质导热系数变化规律和蒸汽驱热质传递特性进行了分析,得到了一些有意义的结果.该工作为多孔介质热质传递过程分析提供了新思路和新方法. 相似文献
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基于压力隧洞模型的复合材料横向热残余应力分析 总被引:1,自引:1,他引:0
考虑碳纤维横向刚度情况下,将复合材料横向热残余应力问题简化为压力隧洞模型.利用该模型推导出复合材料固化成型过程中形成的横向热残余应力,其中分析得出了单纤维与树脂的接触压力以及该压力传递到纤维和树脂后的分布情况.结果表明接触压力传递到纤维内部后成一固定值,传递到树脂后以正比于r.函数衰减.在其基础上提出场叠加方法,得出纤维之间相互耦合的接触压力与残余应力场.通过有限元模拟,理论模型和数值模拟基本一致. 相似文献
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Wassim Kriaa Salma Bejaoui Hatem Mhiri Georges Le Palec Philippe Bournot 《Heat and Mass Transfer》2014,50(2):235-251
In this study, we developed a two-dimensional Computational Fluid Dynamics (CFD) model to simulate dynamic structure and heat and mass transfer of a vertical ceramic tiles dryer (EVA 702). The carrier’s motion imposed the choice of a dynamic mesh based on two methods: “spring based smoothing” and “local remeshing”. The dryer airflow is considered as turbulent (Re = 1.09 × 105 at the dryer inlet), therefore the Re-Normalization Group $k - \in$ model with Enhanced Wall Treatment was used as a turbulence model. The resolution of the governing equation was performed with Fluent 6.3 whose capacities do not allow the direct resolution of drying problems. Thus, a user defined scalar equation was inserted in the CFD code to model moisture content diffusion into tiles. User-defined functions were implemented to define carriers’ motion, thermo-physical properties… etc. We adopted also a “two-step” simulation method: in the first step, we follow the heat transfer coefficient evolution (Hc). In the second step, we determine the mass transfer coefficient (Hm) and the features fields of drying air and ceramic tiles. The found results in mixed convection mode (Fr = 5.39 at the dryer inlet) were used to describe dynamic and thermal fields of airflow and heat and mass transfer close to the ceramic tiles. The response of ceramic tiles to heat and mass transfer was studied based on Biot numbers. The evolutions of averages temperature and moisture content of ceramic tiles were analyzed. Lastly, comparison between experimental and numerical results showed a good agreement. 相似文献
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Influence of the air gap between protective clothing and skin on clothing performance during flash fire exposure 总被引:1,自引:0,他引:1
A finite volume model was developed to simulate transient heat transfer in protective clothing during flash fire exposure.
The model accounts for the combined conduction-radiation heat transfer in the air gap between the fabric and skin. The variation
in the fabric and air gap properties with temperature and the thermochemical reactions in the fabric are also considered.
This study investigates the influence of the air gap in protective clothing on the energy transfer through the clothing and
hence on its performance. Different parameters that affect the conduction-radiation heat transfer through the air gap such
as the air gap absorption coefficient and the air gap width were studied. Finally, the paper demonstrates that an innovative
and potentially significant way to improve protective clothing performance is to reduce the emissivity on the backside of
the fabric. 相似文献
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One-dimensional heat and moisture transfer in the aeration region of reclaimed land is considered for two limiting cases. In the first, the heat transfer is mainly due to the thermal conductivity of the soil; in the second, to the motion of moisture. The influence of the water-table depth on the thermal regime is investigated. A solution to the problem of unsteady heat transfer in soil is found analytically by the method of matched asymptotic expansions.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 63–71, September–October, 1981.We thank V. S. Berman for discussions and valuable comments. 相似文献
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The purpose of this work was to study both theoretically and experimentally the process of moisture redistribution and heat transfer due to phase changes during the tests of thermal conductivity in aerated autoclaved concrete (AAC) moist specimens. The different moisture contents of the test samples were obtained in climatic chamber at equilibrium conditions reached with constant air temperature and variable relative humidity. The moist specimens were sealed inside highly impermeable polyethylene bag, as required by UNI 10051, and placed in a heat flow meter apparatus. During the experimental thermal conductivity measurements, the temperature and heat flow rate were measured under transient and steady state conditions. A theoretical analysis of the heat and mass transfer process was performed and then a suitable numerical model was used to predict the moisture redistribution and heat transfer due to the phase changes. The theoretical model has been compared against the experimental data. Substantial agreement between numerical results and experimental data was found. Then several numerical simulations have been performed to study the influence of the errors due to phase changes and non-uniform moisture distribution during the test of thermal conductivity of moist AAC specimens. 相似文献
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In this paper, a model of heat and moisture transport in firefighter protective clothing during a flash fire exposure is presented. The aim of this study is to investigate the effect of coupled heat and moisture transport on the protective performance of the garment. Computational results show the distribution of temperature and moisture content in the fabric during the exposure to the flash fire as well as during the cool-down period. Moreover, the duration of the exposure during which the garment protects the firefighter from getting second and third degree burns from the flash fire exposure is numerically predicted. A complete model for the fire-fabric-air gap-skin system is presented. 相似文献
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I. Dincer 《Heat and Mass Transfer》1996,32(1-2):109-113
In this paper, the development of new models to determine heat and mass transfer parameters (HMTPs) in terms of the thermal diffusivity, heat transfer coefficient, moisture diffusivity and moisture transfer coefficient for slab, cylindrical, and spherical products being deep-fried was presented. In the model development, two cases of the Biot number, i.e., 0<Bi<100, and Bi≥100 in the transient heat and mass transfer were considered. In order to verify the models, frying experiments were performed using the cylindrically shaped potatoes as test samples, and these samples were fried in a deep fryer at 180°C. The lag factor and frying coefficient for a frying process, which affect heat and mass transfer parameters, were first-defined and considered most important process parameters. By using the temperature and moisture measurements, the frying coefficient and lag factor were determined and incorporated into the models. The HMTPs were determined in a simple and effective manner. In this respect, we can conclude that the present models are useful tools for determining the HMTPs for the products during frying and will be beneficial to the practical applications. 相似文献
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Yin Hu Dongmei Huang Zhengkun Qi Song He Hui Yang Heping Zhang 《Heat and Mass Transfer》2013,49(4):567-573
Experiments and research on heat transport through firefighting protective clothing when exposed to high temperature or intensive radiation are significant. Phase change material (PCM) takes energy when changes from solid to liquid thus reducing heat transmission. A numerical simulation of heat protection of the firefighting protective clothing embedded with PCM was studied. We focused on the temperature variation by comparing different thicknesses and position conditions of PCM combined in the clothing, as well as the melting state of PCM and human irreversible burns through a simplified one-dimensional model. The results showed it was superior to place PCM between water and proof layer and inner layer, in addition, greater thickness increased protection time while might adding extra burden to the firefighter. 相似文献
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The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in con-junction with heat transfer enhancement in particle-laden turbulent flows.The effects of particles on momentum and heat transfer are analyzed,and the possibility of drag reduc-tion in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed.We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow,which shows the heat transfer reduction when large inertial parti-cles with low specific heat capacity are added to the flow. However,we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved.The present results show that particles,which are active agents,interact not only with the velocity field,but also the temperature field and can cause a dissimilarity in momentum and heat transport.This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of par-ticles with different thermal properties. 相似文献
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A model is proposed to investigate heat and moisture transfer in porous media during freezing process based on Luikov’s model
by considering the effect of variation of phase transformation number, ε. This parameter has been mostly used as a constant by researchers. Three-dimensional Luikov’s equations are considered and
solved numerically. The model is compared with obtained experimental data. It is shown that the effect of variable phase transformation
number is noticeable in heat and moisture transfer process. 相似文献
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Thermal protective clothing has steadily improved over the years as new materials and improved designs have reached the market.
A significant method that has brought these improvements to the fire service is the NFPA 1971 standard on structural fire
fighters’ protective clothing. However, this testing often neglects the effects of cylindrical geometry on heat transmission
in flame resistant fabrics. This paper deals with methods to develop cylindrical geometry testing apparatus incorporating
novel skin bioheat transfer model to test flame resistant fabrics used in firefighting. Results show that fabrics which shrink
during the test can have reduced thermal protective performance compared with the qualities measured with a planar geometry
tester. Results of temperature differences between skin simulant sensors of planar and cylindrical tester are also compared.
This test method provides a new technique to accurately and precisely characterize the thermal performance of thermal protective
fabrics. 相似文献