THE RELATION OF THE THRESHOLD VELOCITY OF COAL DUST TO ITS SIZE AND HUMIDITY

On the ground of wharf and a station where coal is piled up,the sources polluting theatmosphere are mainly the raised coal dust.According to the principle of mechanics,withthe consideration of the gravities of coal dust particles and liquid droplets,coal dust size andhumidity,under the condition of force balance when the coal dust was raised,the authorsobtained a theoretical formula for the threshold velocity of coal dust with humidity.Finally,the theoretical values from the formula gave a good agreement with the experimental datafrom some wind tunnels.     

三涡旋模式理论中小涡旋的二元和三元速度关联函数和网格湍流的衰变

在三种涡旋分开考虑的湍流模式里,我们用到了小涡旋的二元和三元速度关联函数。本文对小涡旋的二元和三元速度关联函数进行了讨论,并且对它们展开式的头几项中常用到的系数给出了表达式,最后,用它们讨论了网格湍流的衰减问题.计算结果与G.K.Batchelor和A.A.Townsend的实验相符合得很好.     

煤粉起动速度与粒径及湿度的关系

在煤码头和车站的煤堆积场上,煤粉的扬起是污染环境的主要原因之一.作者根据力学的基本原理,考虑颗粒和液滴重力、煤粉颗粒尺寸和湿度的影响,利用煤粉颗粒起动时的力平衡条件,推导出在风的作用下,具有一定湿度的煤粉颗粒开始扬起的起动风速的理论表达式.最后.根据煤粉起动速度与煤粉颗粒粒径及湿度的关系,将理论公式和风洞实验结果进行了比较,理论和实验结果符合得相当好.     

脉动压力脉动速度变形平均项的表达式

脉动压力脉动速度变形平均项,最初是Rotta改写压力梯度做功项得来的.但是,这项处理起来都很困难,从Rotta开始,以后Launder等人都对这项做过一些假定.本文根据脉动速度所满足的方程解出脉动压力,然后进而求出脉动压力乘上脉动速度变形的平均值,得到了脉动压力脉动速度变形平均项的完整表达式.这个表达式说明了Rotta和Launder等人的有限表达式是有一定道理的.本文所得的完整表达式分为两种情形加以讨论.一种是几种涡旋不分开的情形,另一种是三种涡旋分开考虑的情形.由此,本文为雷诺应力模式和三涡旋模式等湍流模式提供了完整的脉动压力脉动速度变形平均项的表达式.     

密相两相流基本方程组的封闭性和分散相在壁面处的剪应力

本文对将连续相和分散相分别作连续介质考虑的两相流基本方程组,通过分析密相下两相流动的物理机制,提出了分散相的应力满足宾汉流体的本构方程,并用分散相在壁面处剪应力作为分散相的一个边界条件,从而得到了一个封闭的处理密相系统的两相流数学模型.最后,还讨论了分散相在壁面处剪切力的表达式.     

AN ANALYTIC SOLUTION OF DENSE TWO-PHASE FLOW IN A VERTICAL PIPELINE

According to a mathematical model for dense two-phase flows presented in theprevious paper,a dense two-phase flow in a vertical pipeline is analytically solved,and theanalytic expressions of velocity of each continuous phase and dispersed phase arerespectively derived The results show that when the drag force between two phases dependslinearly on their relative velocity,the relative velocity profile in the pipeline coincides withDarcy’s law except for the thin layer region near the pipeline wall,and that the theoreticalassumptions in the dense two-phase flow theory mentioned are reasonable.     

EXPRESSIONS FOR PRESSURE-VELOCITY-GRADIENT CORRELATIONS

The term for pressure-velocity-gradient correlation was initiated by Rott’srewriting the correlation between the pressure fluctuation gradient and velocity fluctuation.However,it is very difficult to consider the effect of this term.Since Rotta’s work,Launderet al.has made some estimates of this term.In this paper according to the equations forvelocity fluctuation,the pressure fluctuation is solved so that the average value of theproduct of the pressure fluctuation and the velocity fluctuation gradient is obtained.Thus,the whole expressions for the pressure-velocity-gradient correlation are derived.The resultexplains that the limited expressions by Rotta and Launder are reasonable to a certaindegree.The whole expressions in this paper are discussed respectively in two situations:oneis without a separate consideration of large and small vortexes;the other is with a separateconsideration of three kinds of vortexes.Therefore,the paper gives the whole expressions forpressure-velocity-gradient correlation     

A CLOSED SYSTEM OF EQUATIONS FOR DENSE TWO-PHASE FLOW AND EXPRESSIONS OF SHEARING STRESS OF DISPERSED PHA’E AT A WALL

In this paper.each of the two phases in dense two-phase flow is considered ascontinuous medium and the fimdamental equations for two-phase flow are described inEulerian form.The generalized constitutive relation of the Bingham fluid is applied to thedispersed phase with the analysis of physical mechanism of of dense two-phase flow.Theshearing stress of dispersed phase at a wall is used to give a boundary condition.Then amathematical model for dense two-phase flow is obtained.In addition.the expressions ofshearing stress of dispersed phase at a wall is derived according to the fundamental,model ofthe frictional collision between dispersed-phase particles and the wall.