环形分布器内变质量流动的CFD模拟研究

环形分布器是实现导热介质在列管式固定床反应器壳程均匀流动的关键部件,文中采用计算流体力学方法(CFD)对环形分布器内的变质量流动进行了模拟研究。首先计算了环形通道内的速度和静压力分布,在此基础上研究了穿孔阻力系数随开孔几何结构以及入口流体流速的变化规律。模拟结果表明:环形通道内存在较明显的速度梯度和压力梯度;随着流体不断分流,在流道内的流动速度不断减小,静压力逐渐增大。因此,需要沿流动方向将开孔直径逐渐减小,以增大穿孔阻力,从而实现流体的均布。对穿孔阻力系数变化规律的研究结果表明:穿孔阻力系数ξ与出口和主流道的流速比ui/u、厚径比δ/di和入口雷诺数Re0有关。在模拟范围内,ξ先随ui/u的增大而减小,到达一个临界值后,ξ不再随ui/u的增大而变化;δ/di对ξ影响不太明显;当Re0属于湍流范围时,ξ随Re0的变化不太明显,但是总体随Re0的增大而减小。

CFD simulation of variable mass flow inside circular distributor

The circular distributor plays an important role in uniform distribution of the coolant in the shell side of multitubular fixed bed reactor.Computational fluid dynamics(CFD) method was employed to simulate the variable mass flow in the circular distributor.Firstly,the distributions of velocity and static pressure in the circular distributor were simulated,and then the relations between perforation resistance coefficient and distributor structure as well as inlet flow condition were studied.The results indicate that the apparent velocity gradient and pressure gradient exist in the circular channel.The velocity decreases and the static pressure increases along with the flow direction.The holes along the flow direction should be opened smaller in order to enhance the perforation pressure and to make sure that the coolant can be uniformly distributed.Moreover,the study shows that the perforation resistance coefficient ξ essentially has a clear relationship with the ratio ui/u of the velocity through the hole to the velocity along the axis direction in the main channel,the ratio δ/di of hole thickness to hole diameter and entrance Reynolds number Re0.In the simulation range ξ firstly decreases with the increase of ui/u,and ξ keeps a constant after reaching a critical value;the relationship between ξ and δ/di is not obvious;when the inlet fluid belongs to turbulent range,the relationship between ξ and Re0 is not obvious,but ξ decreases with the increase of Re0.