螺旋折流板换热器壳程流动特性

摘要

可视化实验研究了透明螺旋折流板换热器的壳程速度分布特征，重点研究了轴向速度的分布规律及对应的机理。结果表明，轴向速度按照折流板的螺旋周期呈周期性变化，不同流量下同一测点的轴向速度分布规律相似。轴向速度在换热器壳程周边区域分布比较均匀，沿轴向变化幅度较小，流动相对稳定，湍流度较低。由于受三角区漏流的影响，管束中心区域轴向流速急剧增大，沿轴向变化幅度较大，稳定性差，湍流强度较高。中心区域轴向速度平均值明显高于外围区域，离换热器中心越近，轴向速度越大。随着壳程流量的增大，中心区域轴向速度的增幅高于外围区域。管束中心处轴向速度波动剧烈，壳程流量较小时，中心处轴向流速平均值最大，随着流量的增加，湍流度增大，流体返混现象明显，中心处轴向流速平均值逐渐减小。%Experimental study was explored with the ultrasonic Doppler velocimeter on the shell side fluid flow characteristics in helical baffled heat exchanger made from acrylic glass. Emphasis was on the axial velocity distribution characteristics. Results indicate that the axial velocity is uniformly distributed in the circumferential region of the shell side. Benefiting from the leakage flow in the triangular region, the corresponding axial velocity in the central region is rapidly increased. With the increase of mass flow rate, the variation magnitude of axial velocity in the central region is much larger than that in the circumferential region. An obvious fluctuation of axial velocity on the shell side of the helical baffled heat exchanger is also an important phenomenon. The mean velocity in the central region increases with the mass flow rate, but this feature is absent when the corresponding turbulent flow is dominant and backmixing flow occurs.