共查询到20条相似文献,搜索用时 93 毫秒
1.
2.
快速干燥过程中多孔介质内部湿分迁移机理的研究 总被引:13,自引:0,他引:13
本文对快速干燥过程中多孔介质内部湿分迁移机制进行了实验研究和理论分析。实验本体是一台X-650扫描电子显微镜;实验样品分别为大蒜;胡萝卜和土豆片。提出了压力梯度作用下的毛细管通道内的挤压流动是高强度干燥过程中湿分迁移的主要机理并对单毛细管通道内的挤压流动进行了理论分析。 相似文献
3.
在第三类边界条件下测定含湿多孔介质热湿迁移特性的方法 总被引:3,自引:0,他引:3
本文研究了含湿多孔介质表面和大气接触时湿分向空气中扩散的过程,在此基础上,提出了一种在第三类边界条件下同时测定含湿多孔体有效导温系数、质扩散系数和热质扩散系数的方法。本方法以电子分析天平作为主要测试手段,可避免瞬态测定含湿量场变化的困难。 相似文献
4.
5.
6.
多孔介质对流干燥降速段热质传递规律的研究 总被引:8,自引:0,他引:8
文献[1]提出的耦合等效扩散模型成功地反映了多孔介质在升速段和恒速段热质传递的规律。对于恒速段终了后的降速段,由于多孔介质内部热质传递现象的复杂性,文献[1]中的分析还有待引伸。本文采用同一模型的基本思路,将其引伸到降速段。过程特点的分析提供了干区起始点的判定方法。按过程特点进行的数值计算与实验结果满意地相符。 相似文献
7.
多孔物料干燥时的耦合传热传质效应 总被引:10,自引:0,他引:10
1引言多孔物料干燥时的传热传质过程是一个典型的耦合过程,物料内的质扩散通量不仅受湿度梯度控制,而且还和温度梯度有关[1~5]。在对流干燥过程中,热量总是从物料表面向内部传递,而湿分总是从物料内部向表面迁移,然后扩散至干燥介质中,故物料内部的温度梯度和湿度梯度方向相反,由Luikov理论可知,向内的传热过程总是阻止物料中的湿分向表面迁移,从而减小质通量,降低干燥速度。显然,为了提高干燥速度,可以通过采用辅助加热或改变加热方式来减小物料内部逆向温度梯度、甚至改变温度梯度的方向以加快物料内部湿分向表面… 相似文献
8.
《工程热物理学报》2021,(8)
保温材料广泛应用于建筑中的制冷与空调等领域,保温多孔介质材料的内部结构复杂无规律且孔隙分布具有不确定性,热质传递作用机理复杂多变,目前的分析方法和研究模型普适性差,对一些微观热质传递机理问题尚未提出解决方法。本文基于表征体元REV,建立了保温多孔介质材料传热计算"三箱"分析模型。利用"三箱"模型对保温多孔介质材料传热过程进行分析,并给出各模型下多孔介质导热系数计算公式。基于保温多孔介质材料传热计算"三箱"分析模型,对不同孔隙率、孔隙通道分布系数和迂曲度的硅酸钙材料进行了计算和模拟并研究了其对保温多孔介质材料导热系数的影响,总结出其变化规律。本文所做工作,不仅为保温多孔介质材料传热分析研究提供了新模型与新方法,在其他类型多孔材料研究中也有借鉴意义。 相似文献
9.
10.
11.
The hydromagnetic convective boundary layer flow past a stretching porous wall embedded in a porous medium with heat and mass transfer in the presence of a heat source and under the influence of a uniform magnetic field is studied. Exact solutions of the basic equations of motion, heat and mass transfer are obtained after reducing them to nonlinear ordinary differential equations. The reduced equations of heat and mass transfer are solved using a confluent hypergeometric function. The effects of the flow parameters such as a suction parameter (N), magnetic parameter (M), permeability parameter (K p ), wall temperature parameter (r), wall concentration parameter (n), and heat source/sink parameter (Q) on the dynamics are discussed. It is observed that the suction parameter appears in the boundary condition ensuring the variable suction at the surface. Transverse component of the velocity increases only when magnetic field strength exceeds certain value, but the thermal boundary layer thickness and concentration distribution increase for all values. Results presented in this paper are in good agreement with the work of the previous author and also in conformity with the established theory. 相似文献
12.
13.
《理论物理通讯》2017,(3)
This paper investigate the effect of slip boundary condition, thermal radiation, heat source, Dufour number,chemical reaction and viscous dissipation on heat and mass transfer of unsteady free convective MHD flow of a viscous fluid past through a vertical plate embedded in a porous media. Numerical results are obtained for solving the nonlinear governing momentum, energy and concentration equations with slip boundary condition, ramped wall temperature and ramped wall concentration on the surface of the vertical plate. The influence of emerging parameters on velocity,temperature and concentration fields are shown graphically. 相似文献
14.
《中国物理快报》2021,(3)
We prove that under the condition of closed boundary to mass flux, pure advection is not a valid mechanism to make a practical thermal diode. Among the various designs of thermal diodes, many of them involve circulating fluid flow, such as in thermosyphons. However, those designs often employ natural convection, which is basically a nonlinear process. It thus remains unclear how the pure advection of temperature field induced by a decoupled velocity field influences the symmetry of heat transfer. Here we study three typical models with pure advection:one with open boundary, one with closed boundary at unsteady state, and one with closed boundary at steady state. It is shown that only the last model is practical, while it cannot become a thermal diode. Finally, a general proof is given for our claim by analyzing the diffusive reciprocity. 相似文献
15.
The process of heat and mass transfer in a long cylindrical channel has been considered in terms of the mirror–diffuse model of the Maxwell boundary condition. The Hazen–Williams equation is used as a basic equation of the process kinetics. A constant temperature gradient is maintained in the channel. The heat and mass fluxes through the cross section of the channel versus the tangential momentum accommodation coefficient have been calculated in a wide range of the Knudsen number. The heat flux profiles have been constructed. A comparison with relevant published data has been carried out. 相似文献
16.
The present paper addresses the megnetohydrodynamic Jeffrey fluid flow with heat and mass transfer on an infinitely rotating upright cone. Inquiry is carried out with heat source/sink and chemical reaction effects. Further, constant thermal and concentration flux situations are imposed. Optimal homotopy analysis method (OHAM) is employed to achieve series solutions of the concerned differential equations. Important results of the flow phenomena are explored and deliberated by means of graphs and numerical tables. It is perceived that thermal boundary layer thickness possess contrast variations for the heat source and heat sink, respectively. The chemical reaction enhances the heat transfer rate but decline the mass transfer rate. Moreover, the precision of the existing findings is verified by associating them with the previously available work. 相似文献
17.
18.
An experimental analysis of ammonia-water absorption process was performed for the falling film and bubble modes in a plate-type absorber. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the bubble mode is superior to the falling film mode for mass transfer performance, and more heat was generated in the bubble mode. Increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, fluidization occurred in the bubble mode and influenced the thermal boundary layer. However, channeling appeared in the falling film mode and decreased the heat transfer area. Increase of the gas flow rate greatly enhanced the performance of heat transfer in the bubble mode but made it worse in the falling film mode. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and we plotted Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance. 相似文献
19.
为了方便而有效地模拟具有纵向外肋片的水平复合管外表面大空间自然对流换热的数值计算时计算区域外边界条件,本文提出一种新的边界条件处理方式。数值实验表明,用该条件计算的具有恒壁温的水平圆柱外表面自然对流换热数值解与文献中的基准解相比,平均Nu数的误差在0.5%以下。本文在极坐标系下,采用固体区与流体区耦合计算原始变量法,模拟计算了具有纵向外肋片的水平复合管外表面在不同肋片高度和肋片数下的自然对流换热量。数值计算表明,管外布置6个对称的肋片时,在肋片相对高度h/r04.0时,对换热最为有利,对应的肋片管平均肋效率为87.92%;而在相同肋片高度下,布置8个对称的肋片时,换热量最大。 相似文献
20.
Thermal Performance of Laser Diode Array under Constant Convective Heat Transfer Boundary Condition 下载免费PDF全文
Three-dimensional heat transfer model of laser diode array under constant convective heat transfer coefficient boundary condition is established and analytical temperature profiles within its heat sink are obtained by separation of variables. The influences on thermal resistance and maximum temperature variation among emitters from heat sink structure parameters and convective heat transfer coefficient are brought forward. The derived formula enables the thermal optimization of laser diode array. 相似文献