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在微尺度燃烧过程中,由于在很小的范围内各种中间组分和燃烧产物的传质和传热过程以及化学反应过程相耦合,因此微燃烧室内部的对流传质问题比较复杂.基于金属Pt壁面催化微燃烧室的模拟结果,分析了燃烧化学反应过程中组分OH的浓度梯度、传质和流动过程的计算结果,并结合无量纲分析法,推导出传质准则数舍伍德数Sh的数学表达式,通过OH的截面平均Shx去表征微燃烧过程中空间气相反应的变化,并分析入口参数对Shx的影响及空间气相反应与表面催化反应之间的抑制作用. 相似文献
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太阳辐射力和水平来流惯性力引起的壁面热羽流会对建筑表面的污染物跨楼层扩散传播产生明显影响。采用风洞实验和数值模拟,研究6层居民建筑在不同强度热羽流影响下,气溶胶污染物沿建筑立面不同楼层扩散分布特性。采用理查德森数Ri表示建筑立面热羽流的强弱。研究表明,建筑立面的热羽流对气溶胶污染物的扩散分布有明显影响。当Ri < 2.28时,污染物主要向迎风面近地面聚集,导致近地面污染物浓度较高;当Ri ≥ 2.28时,污染物向高处扩散,将引起严重的污染物跨楼层扩散传播风险。 相似文献
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利用数值模拟方法研究了多孔介质中存在温度梯度、浓度梯度并具有热质渗透壁面时的受迫对流对传热传质的影响。采用有限容积法在同位网格上离散控制多孔介质内流体流动与热质传递方程守恒方程(即N-S),对流项采用二阶精度的QUICK格式,扩散项采用中心差分格式。利用SIMPLE算法求解压力和速度耦合问题。利用所发展的程序研究了在不同孔隙率,不同的温度、浓度边界条件下,流场、温度场和浓度场以及Nu和Sh的变化规律。 相似文献
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驻波作为薄液膜表面波中的一种波,其流动稳定性受界面热不平衡效应的影响。基于边界层理论和界面热不平衡效应,推导出沿倾斜璧面下降的在蒸发、等温和冷凝状态下普遍适用的二维表面驻波空间稳定性方程,从理论上深入分析了热不平衡效应、流体物性、壁面倾角和雷诺数对驻波稳定性的影响。研究表明:热不平衡效应对驻波稳定性的影响仅在小雷诺数下较为明显,在高雷诺数下,稳定性主要取决于惯性力和粘性力;流体物性和壁面倾角在整个雷诺数范围内均起着非常明显的作用。 相似文献
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建立了湿工况下2排叉排平直翅片管换热器空气侧对流传热传质模型,利用Fluent软件进行了模拟,通过编写UDF(User-Defined Function)添加潜热换热质量源项、能量源项。模拟结果表明空气迎面风速、相对湿度以及壁面过冷度对显热换热系数的影响不大,但会对冷凝对流换热系数产生重要影响。 相似文献
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【摘要】 目的 研究流固耦合作用下室内维医沙疗对人体股动脉血流动力学的影响,探讨维医沙疗对动脉粥样硬化成因的作用机制及对血管破裂的影响。方法 在室内维医沙疗实验中对年轻健康受试者进行维医沙疗研究,对受试者心率、股动脉血流速度峰值及内径作统计学分析;重构人体股动脉三维流固耦合模型,将正弦函数作为初始条件,用Fluent软件分别对沙疗前后血液流动作非定场双向流固耦合模拟,分析维医沙疗对股动脉壁面切应力及von Mises等效应力的影响。结果 维医沙疗前后受试者心率平均值分别为(76.32±11.40)次/min、(92.69±16.09)次/min,差异有统计学意义(P<0.05);沙疗前后股动脉血流雷诺数分别为1855.35、2518.43;沙疗对股动脉壁面切应力及von Mises等效应力增高的影响较为明显。结论 维医沙疗可增大股动脉血流雷诺数,改善人体股动脉血液流动状态,但沙疗后股动脉血流方式由层流变为紊流,很可能会导致血管瘤,因此对血管内壁较薄弱人群要控制埋沙时间、埋沙厚度及温度。维医沙疗可增高壁面切应力,对预防动脉壁增厚引起的动脉粥样硬化及血栓形成有一定的积极作用。维医沙疗后von Mises等效应力明显增加可加大股动脉在分叉部分破裂可能,沙疗时需谨慎。
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An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h. 相似文献
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H.-J. Steeman A. Janssens M. De Paepe 《International Journal of Heat and Mass Transfer》2009,52(5-6):1431-1442
The heat and mass transfer analogy is used in building simulation to convert heat transfer coefficients into mass transfer coefficients. The analogy is valid under strict conditions. In this paper CFD is used to investigate the accuracy of the analogy for indoor air flows when not all these conditions are met. CFD simulations confirm the possibility of applying the analogy to indoor air flows and show that when not all conditions are met, the average mass transfer coefficients remain well predicted by the analogy while the prediction of local transfer coefficients can result in large errors. 相似文献
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This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate. 相似文献
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A.C. Baytas A.F. Baytas D.B. Ingham I. Pop 《International Journal of Thermal Sciences》2009,48(4):665-673
The double diffusive natural convection between a saturated porous layer and an overlying fluid layer in an enclosure has been investigated using the non-Darcy flow model. The problem has been investigated for two cases; namely case I where the interface between fluid and porous layer is horizontal, and case II where the interface contains a step that has a height a. The fluid flow and heat and mass transfer has been investigated for different values of the step height and the Rayleigh and Darcy numbers. The results show that the height of the step at the interface has a significant effect on the flow field and heat and mass transfer from the left-hand to the right-hand walls in the composite enclosure. This is very important for insulation problems and for heat and mass blockage in enclosure systems. 相似文献
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《International Journal of Heat and Mass Transfer》2006,49(21-22):3997-4002
The unsteady geometrical 2D governing equation set for the double diffusive convection—a very complicated nonlinear partial differential equation set with 4 variables—is solved analytically in the cylindrical coordinates. Two special exact solutions describing the convection in a cylindrical tube and a circular tube respectively are derived with an extraordinary method of separating variables and some other skills. The solutions are valuable for the development of heat and mass transfer theory. Moreover, as benchmark solutions, they are very useful for the computational heat and mass transfer to check the accuracy, convergence and effectiveness of various numerical computation methods. 相似文献
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A new complete numerical model for the prediction of thermal performance of the earth-to-air heat exchangers is presented. The model describes the simultaneous heat and mass transfer inside the tube and into the soil accounting for the soil natural thermal stratification. The model is validated against an extensive set of experimental data and it is found accurate. The proposed algorithms are suitable for the calculation of the temperature and humidity variation of the circulating air and for the temperature and humidity distribution inside the ground. The presented model was developed within the TRNSYS environment and can be easily coupled with building or greenhouse simulation codes in order to describe the impact of the earth-to-air heat exchangers to indoor environments. 相似文献
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Double-diffusive natural convection in a fluid saturated porous cavity with a freely convecting wall
P. Nithiarasu T. Sundararajan K.N. Seetharamu 《International Communications in Heat and Mass Transfer》1997,24(8):1121-1130
Double — diffusive natural convection in fluid saturated porous medium has been investigated using a generalised porous medium model. One of the vertical walls of the porous cavity considered is subjected to convective heat and mass transfer conditions. The results show that the flow, heat and mass transfer become sensitive to applied mass transfer coefficient in both the Darcy and non-Darcy flow regimes. It is also observed that the Sherwood number approaches a constant value as the solutal Biot number increases. 相似文献
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Qun Chen Jianxun Ren Zengyuan Guo 《International Journal of Heat and Mass Transfer》2008,51(3-4):873-881
The field synergy principle has been validated to be an effective tool for enhancing convective heat transfer capability. Since convective mass transfer is analogous to convective heat transfer, the field synergy principle has been extended to convective mass transfer analyses to enhance the overall decontamination rate of indoor ventilation systems. According to the field synergy principle, the overall decontamination capability and the utilization efficiency of the air are both influenced by the synergy between the velocity vectors and the contaminant concentration gradients. Furthermore, in order to derive a method to improve the synergy based on the essence of convective mass transfer, the mass transfer potential capacity dissipation function is defined, and then the convective mass transfer field synergy equation is obtained by seeking the extremum of the mass transfer potential capacity dissipation function for a set of specified constraints. The convective mass transfer field synergy equation can be solved to find the optimized air velocity distribution to increase the field synergy and the overall decontamination capability. The optimized air velocity field provides guidance for optimizing ventilation system designs. 相似文献
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The impact of Cattaneo heat flux law in the solid on the onset of double‐diffusive Darcy porous convection with local thermal nonequilibrium temperatures is investigated. The Fourier law of heat transfer is invoked for the fluid, whereas the Cattaneo heat flux law used to transfer heat in solid skeleton alters the temperature equation from parabolic to hyperbolic. The results are obtained for porous skeletons of aluminum and copper oxides. Both Cattaneo and solute concentration effects reinforce in controlling the onset of oscillatory convection and some novel consequences are observed. Compared with the results perceived in the absence of solute concentration, a manifestation of oscillatory convection with scaled‐interphase heat transfer coefficient as well as solid thermal relaxation time parameter initiates earlier in its presence. The effect of increasing interphase heat transfer coefficient and the Lewis number is to delay and hasten the onset of stationary and oscillatory convection. Besides, the increase in the value of solid thermal relaxation time parameter advances the oscillatory onset. Although the increase in the solute Darcy–Rayleigh number is to delay the stationary onset, it shows a twofold behavior on the onset of oscillatory convection. Before the onset of oscillatory convection, the size of the convection cell gets narrower and after which it becomes much wider. The existing results are retrieved as limiting cases from the current study. 相似文献
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Effect of laser radiation upon heat and mass transfer in two-component elastic semitransparent layer
Taras Kournyts’kyi Stanis?aw Matysiak 《International Journal of Heat and Mass Transfer》2004,47(5):977-985
In present paper the effect of the correlation between spectral radiative characteristics of different lasers and absorptive characteristics of laser irradiated two-component elastic semitransparent material upon coupled thermal, diffusive and elastic processes in the layer is examined. Irradiated material is supposed to consist of elastic matrix and gaseous admixture. Investigations are carried out within the model applied early to the study of mentioned coupled processes in the layer subjected to thermal infrared radiation. Calculations were carried out for four different infrared lasers. Peculiarities of heat and admixture mass transfer caused by laser irradiation are established and discussed. 相似文献