Al-Gebory Layth
Department of Materials Engineering, University of Technology, Iraq. Department of Mechanical Engineering and CEEE, Özyeğin University, Çekmeköy 34794, Istanbul, Turkey.
Nanotechnology. 2020 Apr 9;31(26):265404. doi: 10.1088/1361-6528/ab81c5. Epub 2020 Mar 20.
Nanofluids (Nfs) are considered as an effective working media in different thermal processes. Over the years, much attention has been paid to the problem of nanoparticle stability in base fluids in an unconfined area of research, especially in the field of thermal applications. There is still concern about the stability of nanoparticles and their effects on the transport properties and thermal performance in thermal systems. In the present paper, the transport properties and thermal behavior of ethylene glycol-water/[Formula: see text] binary Nfs are investigated in two sections, considering the effect of particle stability and size growth. The first section covering the experimental work, which includes the preparation and characterization of the Nfs where different percentages of base fluids at different pH values are used for this purpose. The characterization of the Nfs explains the effect of the zeta potential on the particle size distribution and the hydrodynamic diameter of suspended particles. The second section involves the theoretical study, where the transport properties and thermal behavior of the Nfs are estimated taking into consideration the effect of the particle stability and size growth. It is found that the binary Nfs that contain different types of base fluids show different stability behavior at different pH values at the same particle concentration. Ethylene glycol-water/[Formula: see text] binary Nfs at pH = 9 contain a low hydrodynamic diameter of suspended particles, and Nfs have good stability behavior. On the other hand, the Nfs at pH = 2 contain the maximum size of the particle hydrodynamic diameter. The Nfs that include 25% water + 75% ethylene glycol show a better stability behavior in comparison with other types of Nfs that included 75% water + 25% ethylene glycol. Particle size growth shows a significant effect on the transport properties (thermal conductivity and viscosity) as well as the particle-fluid interaction Nusselt number, Biot number, and convection heat transfer coefficient.
纳米流体（Nfs）被认为是不同热过程中的有效工作介质。多年来，在无限制的研究领域中，基础流体中纳米颗粒的稳定性问题受到了广泛关注，尤其是在热应用领域。纳米颗粒的稳定性及其对热系统中传输特性和热性能的影响仍然令人担忧。在本文中，考虑颗粒稳定性和尺寸增长的影响，分两个部分研究了乙二醇 - 水/[化学式：见原文]二元纳米流体的传输特性和热行为。第一部分涵盖实验工作，包括纳米流体的制备和表征，为此使用了不同pH值的不同百分比的基础流体。纳米流体的表征解释了zeta电位对颗粒尺寸分布和悬浮颗粒流体动力学直径的影响。第二部分涉及理论研究，其中在考虑颗粒稳定性和尺寸增长影响的情况下估计纳米流体的传输特性和热行为。研究发现，含有不同类型基础流体的二元纳米流体在相同颗粒浓度下于不同pH值时表现出不同的稳定性行为。pH = 9时的乙二醇 - 水/[化学式：见原文]二元纳米流体中悬浮颗粒的流体动力学直径较小，且纳米流体具有良好的稳定性行为。另一方面，pH = 2时的纳米流体中颗粒流体动力学直径最大。与包含75%水 + 25%乙二醇的其他类型纳米流体相比，包含25%水 + 75%乙二醇的纳米流体表现出更好的稳定性行为。颗粒尺寸增长对传输特性（热导率和粘度）以及颗粒 - 流体相互作用努塞尔数、毕渥数和对流换热系数有显著影响。
