Abstract

This study investigates the thermal and hydrodynamic effects of incorporating nanomaterials to the continuous and gas-liquid Taylor flows in mini scale tubes. Aluminum Oxide nanopowder was dispersed in distilled water to produce three nanofluid concentrations: 1, 2 and 4 wt% using a two-step method. Heat transfer enhancement in miniscale tubes ($\sim$1.5 mm) was assessed using Nusselt number and dimensionless mean wall heat flux. The experiments were conducted under laminar developing flow with isothermal boundary condition. In addition, nanofluid experiments covered: thermal conductivity measurements, scanning electronic microscopy, and performance efficiency analysis. The thermal and hydrodynamic effects of incorporating nanoparticles to the base fluid were evaluated using performance efficiency analysis which considers friction factor and Nusselt number. The results demonstrated that heat transfer enhancement is associated with the nanoparticles concentration when compared with Graetz theory. Total enhancement in segmented nanofluid flows was observed to be a combination of the individual contributions of internal circulations within the liquid slugs and the interaction between the nanoparticles. Overall, the present study highlights the potential of heat transfer enhancement within mini/micro tubes using segmented nanofluid flows.

摘要

本研究调查了将纳米材料加入到微型管中的连续气液泰勒流中的热和流体动力学效应。使用两步法将氧化铝纳米粉末分散在蒸馏水中以产生三种纳米流体浓度：1、2 和 4 wt%。微型管中的传热增强 ($～$1.5 mm) 使用努塞尔数和无量纲平均壁热通量进行评估。实验是在等温边界条件下的层流发展下进行的。此外，纳米流体实验还包括：热导率测量、扫描电子显微镜和性能效率分析。使用考虑摩擦系数和努塞尔数的性能效率分析来评估将纳米粒子结合到基础流体中的热和流体动力学效应。结果表明，与 Graetz 理论相比，传热增强与纳米颗粒浓度有关。观察到分段纳米流体流动的总体增强是液塞内内部循环的单独贡献和纳米颗粒之间的相互作用的组合。总体而言，本研究强调了使用分段纳米流体流在微型/微型管内增强传热的潜力。