射流冲击纳米流体对半圆形螺旋通道传热特性的影响

Effect of jet impingement nanofluid on heat transfer characteristics of semicircular spiral channels

为提高管式反应器外半圆形螺旋通道的换热效果,在传统螺旋通道壁面上设置了射流入口,采用三种纳米流体(CuO-H_(2)O、Al_(2)O_(3)-H_(2)O和TiO_(2)-H_(2)O)作为传热流体,基于Mixture混合模型探究了不同纳米流体在不同Re=10000~36000、不同射速比下对半圆形螺旋通道换热和流动特性的影响规律,并利用传热强化因子PECj0和PECj分别评价了半圆形螺旋通道增加射流前后的综合强化传热性能。研究结果表明:在射速比ε=0~5时,Al_(2)O_(3)-H_(2)O纳米流体的压降最大,CuO-H_(2)O纳米流体的压降最小。在ε=0时Al_(2)O_(3)-H_(2)O纳米流体的传热效果最好,其平均Nu数是H_(2)O的1.31倍。与ε=0相比,在ε=1~5工况下,螺旋通道平均Num最高提升了52.01%。随着射速比的增加湍动能越大,射流与主流混合效果越好。各射速比工况下射流冲击的影响范围为0°≤θj≤50°,在ε=3时,螺旋通道产生三涡结构。PECj0随Re先增加后降低,在Re=20173时取得最大值,PECj随射速比的增大而增大。综合对比,射流冲击Al_(2)O_(3)-H_(2)O纳米流体对螺旋通道传热提升效果最佳。

To improve the heat exchange effect of the semicircular spiral channel outside the tubular reactor,a jet inlet was set on the wall of the traditional spiral channel.Three kinds of nanofluids(CuO-H_(2)O,Al_(2)O_(3)-H_(2)O and TiO_(2)-H_(2)O)were used as heat transfer fluids,respectively.Based on Mixture mixing model,the influence of different nanofluids on the heat exchange and flow characteristics of the semi-circular spiral channel at different Re(10000—36000)and jet velocity ratios was investigated.The heat transfer enhancement factors PECj0 and PECj were used to evaluate the comprehensive heat transfer enhancement before and after increasing the jet flow in the semi-circular spiral channel.The results showed that at the jet speed ratioε=0—5,the pressure drop of Al_(2)O_(3)-H_(2)O nanofluids was highest,while that of CuO-H_(2)O nanofluids was lowest.Al_(2)O_(3)-H_(2)O nanofluids exhibited the best heat transfer performance atε=0,with the average Nu number 1.31 times that of H_(2)O.Compared toε=0,the average Num of the spiral channel increased by 52.01%atε=1—5.With the increased jet velocity ratio,the higher the turbulent kinetic energy,the better the mixing effect between jet fluid and main stream fluid.The influence range of jet fluid at each velocity ratio was 0°≤θj≤50°.Whenε=3,the spiral channel generates three vortex structures.PECj0 increased first and then decreased with the rising Re,reaching its maximum value at Re=20173,while PECj increased with the rising jet velocity ratio.Overall,the heat transfer enhancement effect of jet impinging on Al_(2)O_(3)-H_(2)O nanofluids in spiral channels was the best in this study.