上喷式矿井排风热回收装置内液滴运动模型及其优化计算

Optimized calculation model for the moving droplets sprayed via an up-jet diffuser and a heat-retriever attached to the mining ventilator

为了减小常见下喷式装置风吹水损失大的问题,设计了上喷式矿井排风热回收装置。通过液滴受力及运动分析,将上喷式液滴的运动划分为2个阶段。根据牛顿第二定律,建立了简化的液滴动量方程;在该方程的基础上,结合运动阶段划分,得到临界条件下的力平衡关系式;利用该式,在10个不同相对速度下,得到了上喷式与下喷式的保证液滴不被吹飞的临界直径。应用变量替换,将液滴动量方程变换为液滴运动距离的微分式;继而,根据液滴及空气之间的雷诺数组合,导出了液滴最大上升高度的5个积分计算式。应用这些积分式,数值计算了不同迎面风速、液滴粒径及液滴初速度下,上喷式中液滴最大上升高度、下喷式中液滴最大下降高度。对比计算结果,相比下喷式,上喷式具有节水、液滴选择范围宽和低耗高效的优势。

The given paper would like to propose a new exchanger with the up-jet spraying water to solve the problem of serious water loss,the great system resistance and the low efficiency for a general downward-jet device. The whole research idea of ours has been laid on the basis of the principle of the force equilibrium and the relationship between the resistance and the Reynolds number,with the vertically rising motion of a single droplet that can be divided into two stages. In the vertical direction,the momentum equation of this droplet can be deduced in accordance with the Newton＇s Second Law,according to which the equation may have a simplest formula,when the acceleration of this equation is equal to zero. In accordance with the formula,the diameter of a droplet can avoid being blown away on the conditions of the airflow velocity with 6 m / s and its relative velocities to the droplet is equal to3-12 m / s. The critical diameter of a droplet sprayed by an up-jet can be listed in a detailed way,in comparison with those sprayed by the downward jet. Substituting a ratio of differential rising distance to the velocity of a droplet for the time varying in accordance with the momentum equation,the differential distance can be expressed by the transformation of the aforementioned equation. Besides,on the basis of Reynolds numbers of a droplet and that of itself relative to the air phase,it is possible to deduce the five formulae of the integrated distance,with the maximum height of the vertically rising droplet sprayed by the up-jet. What is more,on the conditions when the air flow velocities are 6 m / s and 8 m / s,it is possible to work out the distance with the initial velocities and diameters of the droplets through numerical integration of MATLAB. Hence,the results：（ 1） When the ratio of the initial velocity to that of the air flow is lower than 2,the distance will be primarily affected by the initial velocity of a droplet;（ 2）When the ratio is from 2 to 3,the distance should be prevailingly affected by the initial as well as the air flow velocities;（ 3） When the ratio is greater than 3,the distance is supposed to be affected by the initial and the air flow velocities,in addition to the diameter of a droplet. Therefore,as compared with the numerical results of a down-jet exchanger,the given up-jet one should be endowed with the three advantages for reducing the water loss,the decreasing head of a water pump supplied for the exchanger in addition to heightening the efficiency.