Lightnin静态混合器内纳米流体湍流传热特性分析

Analysis of turbulent heat transfer characteristics of nanofluids in theLightnin static mixer

静态混合器作为一种高效传热传质连续流强化设备,在化工过程强化技术中具有明显技术特色。由于缺乏纳米流体的物性对Lightnin静态混合器(LSM)内传热特性影响的研究,一定程度上制约了LSM强化传热应用的进一步推广。本文采用混合多相流模型和SST k-ω湍流模型,在Re=8000~28000和恒热流密度条件下,从熵产以及速度场与温度场的协同性等方面分析纳米颗粒的体积分数、种类及粒径大小对LSM内传热特性的影响。结果表明,随着Cu纳米颗粒体积分数的增加,纳米流体的综合传热性能及温度场与速度场的协同性能逐渐增强,总熵产率和Be数逐渐减小,体积分数为0.5%~2.0%的Cu-H_(2)O的纳米流体在Re=8000~28000范围内的综合传热性能系数(PEC)分别达到2.16~2.25、3.16~3.25、3.94~4.15及4.64~5.16。Cu-H_(2)O、Al_(2)O_(3)-H_(2)O及CuO-H_(2)O这3种纳米流体相比,Cu-H_(2)O纳米流体的强化传热性能要远好于其他两种纳米流体,Al_(2)O_(3)-H_(2)O及CuO-H_(2)O纳米流体的平均PEC分别是Cu-H_(2)O纳米流体的0.47倍和0.46倍。随着Cu纳米颗粒粒径的增加,纳米流体的综合传热性能和温度场与速度场的协同性能逐渐减弱,总熵产率和Be数逐渐增加。

The static mixer is a kind of highly efficient and online heat and mass transfer enhancedequipment and has excellent characteristics in the chemical process intensification. The lack of researchabout the effects of physical properties of nanofluids on the heat transfer characteristics in the Lightninstatic mixer (LSM) restricts a further industrial application of LSM in the field of enhancing heat transfer.The effects of volume fraction, particle type and size of nanoparticles on the heat transfer in LSM werenumerically evaluated under the conditions of Re=8000—28000 and constant heat flux using the SST k-ωturbulence model and multiphase mixture model. With the increasing of volume fraction of Cu-H_(2)O nanofluids, the comprehensive heat transfer performance (PEC) and synergy between velocity field andtemperature field of nanofluids are gradually enhanced while the total entropy production rate and Begradually decrease. The PEC values of Cu-H_(2)O nanofluids with volume fractions from 0.5% to 2.0% couldbe obtained up to 2.16—2.25, 3.16—3.25, 3.94—4.15 and 4.64—5.16 at Re=8000—28000, respectively.The enhanced heat transfer performance of Cu-H_(2)O nanofluids is much better than that in the Al_(2)O_(3)-H_(2)Oand CuO-H_(2)O nanofluids. The average PEC of Al_(2)O_(3)-H_(2)O and CuO-H_(2)O are 0.47 and 0.46 times of CuH_(2)O nanofluids, respectively. With the increasing particle size of Cu-H_(2)O nanofluid, the comprehensiveheat transfer performance and synergistic performance of the nanofluids are gradually weakened while thetotal entropy production rate and Be gradually increase.