阻流板对轴向搭接螺旋折流板换热器流动和传热性能的影响

Impact of Block Plates on the Flow and Heat Transfer Performance of Middle-axial-overlap Helical Baffle Heat Exchangers

对倾斜角为36°的X型缺口是否采用阻流板堵死的4种轴向搭接螺旋折流板换热器的流动和传热性能进行数值模拟研究,其中4种方案均采用三分螺旋折流板,正三角形布管且螺距近似相同,分别为无阻流板(36°MO)、最外侧一条缺口堵死(36°MOB1)、外侧缺口堵死(36°MOB2)和内外缺口全堵死(36°MOBA)。构建子午切片M1,正六边形切片H2和H3,采用速度矢量叠加速度或压力云图的方式全方位阐释壳侧流场特性。结果表明,在分别穿过X型缺口外、内三角区的正六边形切片H2和H3上所显示的相邻折流板之间的泄漏情况4种方案有明显不同;同时这4种方案的每个螺旋周期内都出现二次流,其中36°MOB2方案二次流强度最大;虽然阻流板阻挡面积越多的方案其传热系数越高,但流动阻力也越大,从壳侧综合性能ho/Δpo来说,36°MOB1方案和36°MOB2方案分列前两名,而36°MO方案最低;与36°MO方案相比,36°MOB1、36°MOB2和36°MOBA方案的壳侧传热系数ho和壳侧综合性能ho/Δpo的平均值分别高36.76%、38.59%、41.13%和19.88%、10.14%、9.30%。由于36°MOB1方案的综合性能指标较高且阻流板在管束最外侧,制造工艺可行,所以其应用价值较好。

The flow and heat transfer performances are numerically simulated for four middle-axial-overlap trisection helical baffle heat exchangers with 36° baffle incline angle,approximate spiral pitch and equilateral triangle tube layout,including one scheme without block plates （36°MO）,one scheme with the outermost strip notches blocked （36°MOB1）,one scheme with outer triangle notches blocked （36°MOB2） and one scheme with all notches blocked （36°MOBA）.The meridian slices M1 and unfolded concentric hexagonal slices H2 and H3 are constructed to obtain the full-angular view of shell-side flow characteristics by using pressure or velocity contours plus velocity vectors.The results show that the leakage patterns of the four schemes on concentric hexagonal slices H2 and H3 located respectively in outer and inner triangles of X-notch are quite different; each baffle chamber contains secondary flow,but the secondary flow of 36°MOB2 scheme is the strongest.Both heat transfer coefficient and pressure drop increase with the increase in blocked area,but in term of shell-side comprehensive performance ho/△po,the 36°MOB 1 and 36°MOB2 schemes rank the first and second highest,while that of 36°MO scheme falls to the last.The average values of shell-side heat transfer coefficient ho and shell-side comprehensive performance ho/△po for 36°MOB 1,36°MOB2 and 36°MOBA schemes are 36.76％,38.59％,41.13％ and 19.88％,10.14％,9.30％ higher than those of 36°MO scheme.The 36°MOB1 scheme possesses strong application promise because of its better comprehensive performance and feasibility in installation of the outmost block plates on the tube bundle.