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Nanofluids stability effect on a thermosyphon thermal performance
International Journal of Thermal Sciences ( IF 4.5 ) Pub Date : 2020-07-01 , DOI: 10.1016/j.ijthermalsci.2020.106347
Karen Cacua , Robison Buitrago-Sierra , Elizabeth Pabón , Anderson Gallego , Camilo Zapata , Bernardo Herrera

Abstract Nanofluids stability on rest is important to characterize the nanofluids thermophysical properties before being used on different thermal systems. However, this stability can be modified during devices operation because of different thermal loads, fluid movements and phase changes. Particularly, in Two Phase Closed-Thermosyphon (TPCT), nanoparticle deposition on the evaporator surface is one of the most important issues that affects their thermal performance, this deposition indicates a lost in the nanofluids stability during operation and also a modification in their thermophysical properties. In addition, surfactants are commonly employed to improve nanoparticles dispersion and nanofluids stability and its effect on the TPCT thermal performance has been little studied. Surfactant presence modifies the surface tension of the base fluid, affecting the boiling heat transfer in the TPCT evaporator, which contributes also with the thermal performance variations. In this study, the stability of Al2O3-water nanofluids was evaluated on rest exploiting different surfactants. After that, nanofluids with high and low stability were used as working fluid in a thermosyphon in order to evaluate the effect of stability and the presence of surfactant on the TPCT thermal performance. Stability after several operation cycles was also studied and results show that the nanofluid with Sodium Dodecylbenzene Sulfonate SDBS at critical micelle concentration as surfactant was stable after several operation cycles. On the contrary, nanoparticles were completed sedimented after operation for nanofluids without surfactant and with Cetyl Trimethyl Ammonium Bromide CTAB. Decrease in the thermal resistance was up to 24% for the different nanofluids (stable and unstable) and surfactant solutions in comparison with water, but no effects of nanofluid stability on rest in the final thermal performance were not found. Moreover, interesting phenomena during operation were observed such as a dry path with water and high bubble formation with surfactant presence.

中文翻译:

纳米流体稳定性对热虹吸热性能的影响

摘要 纳米流体在静止状态下的稳定性对于表征纳米流体在用于不同热系统之前的热物理性质很重要。然而,由于不同的热负荷、流体运动和相变,这种稳定性可以在设备运行期间改变。特别是,在两相闭式热虹吸管 (TPCT) 中,蒸发器表面上的纳米颗粒沉积是影响其热性能的最重要问题之一,这种沉积表明纳米流体在运行过程中失去了稳定性,同时也改变了它们的热物理性能. 此外,表面活性剂通常用于改善纳米颗粒的分散性和纳米流体的稳定性,其对 TPCT 热性能的影响很少被研究。表面活性剂的存在改变了基液的表面张力,影响 TPCT 蒸发器中的沸腾传热,这也与热性能变化有关。在这项研究中,利用不同的表面活性剂评估了 Al2O3-水纳米流体的稳定性。之后,将具有高稳定性和低稳定性的纳米流体用作热虹吸管中的工作流体,以评估稳定性和表面活性剂的存在对 TPCT 热性能的影响。还研究了几次操作循环后的稳定性,结果表明,以临界胶束浓度的十二烷基苯磺酸钠 SDBS 作为表面活性剂的纳米流体在多次操作循环后是稳定的。相反,在没有表面活性剂和十六烷基三甲基溴化铵CTAB的纳米流体操作后,纳米粒子完全沉淀。与水相比,不同纳米流体(稳定和不稳定)和表面活性剂溶液的热阻降低高达 24%,但未发现纳米流体稳定性对最终热性能的静止影响。此外,在操作过程中观察到了有趣的现象,例如有水的干燥路径和存在表面活性剂的高气泡形成。
更新日期:2020-07-01
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