Jafarimoghaddam Amin, Aberoumand Sadegh
Aerospace Engineering Department, K. N. Toosi University of Technology, Tehran, I.R. Iran.
Independent Researcher, Tehran, Iran.
PLoS One. 2017 Jul 28;12(7):e0180883. doi: 10.1371/journal.pone.0180883. eCollection 2017.
The present study aims to experimentally investigate heat transfer performance of rectangular and semicircular tubes in the presence of Ag / water nanofluids. The nanoparticles of Ag (silver) were used in seven different volume concentrations of 0.03%, 0.07%, 0.1%, 0.2%, 0.4%, 1% and 2%. The experiment was conducted in relatively low Reynolds numbers of 301 to 740. A heater with the power of 200 W was used to keep the outer surface of the tubes under a constant heat flux condition. In addition, the rectangular tube has been designed within the same length as the semicircular one and also within the same hydraulic diameter. Moreover, the average nanoparticles size was 20 nm. The outcome results of the present empirical work indicate that, for all the examined Reynolds numbers, the semicircular tube has higher convective heat transfer coefficient for all the utilized volume concentrations of Ag nanoparticles. The possible reasons behind this advantage are discussed through the present work mainly by taking the boundary effect on Brownian motions into account. Coming to this point that the conventional design for cooling system of photovoltaic cells is a heat sink with the rectangular graves, it is discussed that using a semicircular design may have the advantage over the rectangular one in convective heat transfer coefficient enhancement and hence a better cooling performance for these solar cells.
本研究旨在通过实验研究在存在银/水纳米流体的情况下矩形管和半圆形管的传热性能。银（Ag）纳米颗粒以0.03%、0.07%、0.1%、0.2%、0.4%、1%和2%这七种不同的体积浓度使用。实验在相对较低的雷诺数301至740下进行。使用功率为200W的加热器使管的外表面保持在恒定热通量条件下。此外，矩形管的设计长度与半圆形管相同，且水力直径也相同。而且，纳米颗粒的平均尺寸为20nm。本实证研究的结果表明，对于所有考察的雷诺数，在所有使用的银纳米颗粒体积浓度下，半圆形管具有更高的对流换热系数。通过本研究主要考虑布朗运动的边界效应来讨论这种优势背后的可能原因。鉴于光伏电池冷却系统的传统设计是带有矩形槽的散热器，讨论了采用半圆形设计在提高对流换热系数方面可能比矩形设计具有优势，从而对这些太阳能电池具有更好的冷却性能。
