Trinh Vu, Xu Jiajun
Department of Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA.
Nanoscale Res Lett. 2017 Dec;12(1):216. doi: 10.1186/s11671-017-1984-1. Epub 2017 Mar 23.
This work experimentally studied the convective flow and heat transfer characteristics of a novel nanostructured heat transfer fluid: "ethanol/polyalphaolefin nanoemulsion" flowing through 12 circular minichannels of 1-mm diameter each. Ethanol/polyalphaolefin nanoemulsion is a thermodynamically stable system formed by dispersing ethanol into a mixture of "polyalphaolefin (PAO)" and surfactants. In this study, ethanol/PAO nanoemulsion is used as the working fluid to study the effect of ethanol nanodroplets on its convective flow and heat transfer characteristics. In addition, the effect of flow regime on its heat transfer is examined. It is found that using ethanol/PAO nanoemulsion fluids can improve convective heat transfer compared to that of pure PAO under both single- and two-phase flow regimes. For single-phase flow, there is no significant difference in Nusselt number between ethanol/PAO nanoemulsion and pure PAO in laminar flow regime. However, when entering transition flow regime, the ethanol/PAO nanoemulsion fluid showed a substantial increase in Nusselt number. Meanwhile, there is an increase in pressure drop and early onset of the laminar-turbulent transitional region for the ethanol/PAO nanoemulsion compared to pure PAO. The heat transfer coefficient of ethanol/PAO nanoemulsion can be further enhanced when the ethanol nanodroplets undergo phase change, which is hypothesized that such an effect is likely related to the enhanced interfacial thermal transport between the nanodroplets and base fluid under elevated temperature and the latent heat of phase changeable nanodroplets inside nanoemulsion. Further studies are needed to fully explore the convective heat transfer properties of nanoemulsion fluids.
本研究通过实验研究了一种新型纳米结构传热流体“乙醇/聚α-烯烃纳米乳液”在12个直径均为1毫米的圆形微通道中的对流流动和传热特性。乙醇/聚α-烯烃纳米乳液是通过将乙醇分散到“聚α-烯烃（PAO）”和表面活性剂的混合物中形成的热力学稳定体系。在本研究中，乙醇/PAO纳米乳液用作工作流体，以研究乙醇纳米液滴对其对流流动和传热特性的影响。此外，还考察了流型对其传热的影响。研究发现，在单相和两相流型下，与纯PAO相比，使用乙醇/PAO纳米乳液流体可改善对流换热。对于单相流，在层流状态下，乙醇/PAO纳米乳液和纯PAO的努塞尔数没有显著差异。然而，当进入过渡流状态时，乙醇/PAO纳米乳液流体的努塞尔数大幅增加。同时，与纯PAO相比，乙醇/PAO纳米乳液的压降增加，层流-湍流过渡区域提前出现。当乙醇纳米液滴发生相变时，乙醇/PAO纳米乳液的传热系数可进一步提高，据推测，这种效应可能与高温下纳米液滴与基液之间增强的界面热传输以及纳米乳液内部可相变纳米液滴的相变潜热有关。需要进一步研究以充分探索纳米乳液流体的对流换热特性。
