共查询到20条相似文献,搜索用时 15 毫秒
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This paper deals with the numerical and analytical modelling of two‐dimensional heat and moisture transfer during drying of a spherical object. Drying is considered to be a process of simultaneous heat and moisture transfer whereby moisture is vapourized by means of a drying fluid (e.g. air), as it passes over a moist object. Numerical modelling of two‐dimensional heat and moisture transfer during drying of a spherical object is carried out using an explicit finite‐difference approach. Temperature and moisture distributions inside the object are determined by using the developed computer code. Moreover, the results predicted from the present model are compared with the experimental data available in the literature and a considerably high agreement is found. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Rabah Djedjig Salah-Eddine OuldboukhitineRafik Belarbi Emmanuel Bozonnet 《International Communications in Heat and Mass Transfer》2012
This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25 °C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs. 相似文献
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为了深入研究逆流形式下废液与非饱和空气热湿传递过程中传热驱动力与传质驱动力之间的关系,建立了逆流形式下废水和非饱和空气的热质交换耦合模型,利用数学方法对该模型的热湿传递驱动力进行解耦分析。将利用根据文献中逆流除湿/再生搭建的实验装置和本文搭建的废液再生实验装置得到的实验数据进行比较、验证。结果发现:相互耦合的温度差驱动力Δt和含湿量差驱动力Δω可以由相互独立的焓差驱动力Δh和相对湿度差驱动力Δφ表示,这两个相互独立的驱动力可以用来独立表征废液和非饱和空气的传热传质过程;相关文献中的和该装置中的实验结果与解耦分析的数值模拟结果一致:非饱和空气出口的所有参数在相互独立的驱动力所界定的范围内变化。 相似文献
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Predicting ground temperature is an important part of the analysis of geothermal resources assessment and use. Thus, we develop and validate one-dimensional numerical model for heat and mass transfer in partially frozen soils. The model is implemented in HVACSIM Plus and used to simulate the thermal regime of soil profile. In addition to modeling heat conduction, model variations also includes moisture transfer, snow accumulation and melting, and soil freezing and thawing. The results are compared against experimental measurements of ground temperature for three locations in Montana, USA. The differences between simulated depth temperature with and without snow cover and freezing and thawing of soil reveal that ground temperatures are predominantly influenced by these two factors. Considering moisture transfer slightly improves temperature predictions, although it increases computational time by one order of magnitude. To balance computational efficiency with prediction accuracy, we propose an equivalent moisture content of 40–60% saturation in predicting ground temperature. 相似文献
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珠状凝结与膜状凝结相比是一种高效的、有相变的换热方式,得到了广泛关注。介绍了关于珠状凝结换热在实验和理论模型方面的研究状况,并进行了对比。并且考虑了接触角、促进层以及裸露表面强制对流换热的影响,建立了新的计算珠状凝结换热特性的模型,新模型可以计算不同工况下的不同换热结果。将新模型的计算结果与实验数据进行对比,发现二者较为吻合。为进一步研究珠状凝结换热提供了一定的理论依据。 相似文献
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Modeling heat and moisture transfer through fibrous insulation with phase change and mobile condensates 总被引:1,自引:0,他引:1
This paper reports on a transient model of coupled heat and moisture transfer through fibrous insulation, which for the first time takes into account of evaporation and mobile condensates. The model successfully explained the experimental observations of Farnworth [Tex. Res. J. 56 (1986) 653], and the numerical results of the model were found to be in good agreement with the experimental results of a drying test. Based on this model, numerical simulation was carried out to better understand the effect of various material and environmental parameters on the heat and moisture transfer. It was found that the initial water content and thickness of the fibrous insulation together with the environmental temperature are the three most important factors influencing the heat flux. 相似文献
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Size effect on microscale single-phase flow and heat transfer 总被引:1,自引:0,他引:1
The present discussion will focus on the size effect induced by the variation of dominant factors and phenomena in the flow and heat transfer as the device scale decreases. Due to the larger surface to volume ratio for microchannels and microdevices, factors related to surface effects have more impact to microscale flow and heat transfer. For example, surface friction induced flow compressibility makes the fluid velocity profiles flatter and leads to higher friction factors and Nusselt numbers; surface roughness is likely responsible for the early transition from laminar to turbulent flow and the increased friction factor and Nusselt number; the relative importance of viscous force modifies the correlation between Nu and Ra for natural convection in a microenclosure and, other effects, such as channel surface geometry, surface electrostatic charges, axial heat conduction in the channel wall and measurement errors, could lead to different flow and heat transfer behaviors from that at conventional scales. 相似文献
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可呼吸墙体中不仅有热传递,还伴随着湿传递及空气渗透,并且3个过程互相影响,协同作用。在分析国内外相关资料的基础上,采用热力学方法,并根据多孔介质中多相流体流动描述的体积平均方程,建立了热、湿和空气耦合作用下的可呼吸墙体热质传递模型。推导出热、湿和空气耦合传递等效扩散方程;找到可呼吸墙体热、湿及空气耦合作用下热质传递过程的主要影响因素湿容量Lθ、气压pG和温度T;根据等效扩散方程,通过TDM A算法,可以求得可呼吸墙体内的湿容量分布、气压分布和温度分布,并进行了数值模拟。 相似文献
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M. Piechowski 《国际能源研究杂志》1998,22(11):965-979
Validation of ground heat exchanger (GHE) model is presented using the experimental data obtained for both single and double pipe horizontal GHE. Sensitivity analysis of the GHE model shows the influence of the variation in the soil thermal conductivity, specific heat and density on the thermal performance of a GHE. Finally, the thermal performance of a GHE is analysed using both heat and mass transfer models, and conduction only model, as well as the influence of the initial soil moisture content on the thermal performance of a GHE. © 1998 John Wiley & Sons, Ltd. 相似文献
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This article presents an effective analytical model for determining the moisture diffusivities and moisture transfer coefficients for solid objects (namely, infinite slab, infinite cylinder, sphere; and also for irregularly shaped objects, by using a shape factor) subject to drying applications in a medium. The unsteady-state moisture diffusion analysis is used on the basis of two important criteria: 0·1 <Bi < 100 and Bi > 100. The drying coefficients and lag factors were employed. The analytical models are then verified using available experimental data taken from the literature. The results show that the method presented here can be used to determine the moisture diffusion coefficients and moisture transfer coefficients for such solid objects in a simple and accurate manner for a variety of drying applications. 相似文献
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基于流体体积函数法(volume of fluid,VOF)建立垂直平行平板通道内膜状冷凝传热预测数值模型,膜状冷凝传热传质过程模拟通过在VOF模型守恒方程中施加基于界面能量平衡方法的源项实现。通过数值分析研究发现,在壁面的顶部,冷凝液膜最薄,存在层流区域;冷凝液向下流动,一系列不规则的波纹随之出现;影响冷凝传热的主要因素是蒸汽的流速、液膜厚度及流动状态等。 相似文献
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为了获得翅片间距Pf对平直翅片管换热器的传热与阻力特性的影响规律,根据相似模化原理对3种不同Pf的平直翅片管换热器进行了试验研究。结果表明:雷诺数Rea在4 000~8 000范围内,努赛尔数Nua数随Rea的增大而增加,欧拉数Eua随Rea的增大而降低;同一Rea下,Nua随Pf减小而增加,但增加不明显,Eua随Pf增大而降低;同一Rea下,Pf越大,综合流动传热性能越好,但实际换热面积会减小,需综合考虑。研究成果可为汽轮发电机平直翅片管换热器的结构和性能优化提供依据。 相似文献
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为了强化工业供热中的汽汽换热,通过CFD技术对不同类型换热管的流动及换热特性进行了研究。结果显示:光滑壁面时管壁两侧的高、低温蒸汽的温度梯度沿着流向逐渐变化,对流换热逐渐增强;相比于光滑管,采用内波节管和内螺纹波节管时,高温蒸汽侧的温度梯度增大,而低温蒸汽侧的壁面温度梯度明显增大;采用壁面异型结构能够改变管壁内温度梯度,采用内螺纹波节管尤甚。采用内波节管和内螺纹波节管的平均Nu相比于光滑管显著提高,最大值分别提高了26%和30%。 相似文献
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Review of research on heat generation characteristics during charging and discharging of lithium ion batteries 下载免费PDF全文
ZHANG Zhichao ZHENG Lili DU Guangchao FENG Yan WANG Dong DAI Zuoqiang ZHANG Hongsheng 《储能科学与技术》2019,8(Z1):32-37
电动车辆的性能和成本很大程度上取决于动力电池组的性能和使用寿命,而电池组的性能和使用寿命又受到电池单体产热的影响。研究锂离子电池充放电过程中的产热特性及影响因素,对锂电池的开发及使用具有指导意义。本文从环境温度、充放电倍率、电池材料、荷电状态和老化程度五个方面入手,综述了各因素对锂离子电池产热的影响。 相似文献