Abstract

Thermosyphons are among the most efficient passive heat transfer devices known nowadays. Due to heat and mass transfer limitations of working fluids, much effort is invested in developing a new generation of enhanced fluids, such as nanofluids. Previous studies reported improved thermal capacity when water was replaced by nanofluid. The interplay between nanoparticles and the evaporator surface is crucial here. However, the details of the deposition mechanism and its impact on boiling are still not known. This paper focusses on determining how the boiling process in the thermosyphon affects the inner wall of the evaporator and the nanofluid itself, and how it influences the thermal performance. For that purpose, we conducted the experimental study on a thermosyphon filled with silica nanofluid and then analyzed the samples of evaporator surface and silica nanofluid under a scanning electron microscope. Silica deposited into a porous layer during boiling, which enabled capillary wicking. This in turn decreased the overheating of the evaporator wall. Moreover, silica nanofluid increased heat transfer efficiency and transferred more thermal energy at low heat loads. After opening the thermosyphon, the deposited layer dried and split up. Based on two methods of crack pattern analysis, the mean thickness of the layer was estimated.

摘要

热虹吸管是当今已知的最有效的被动传热装置之一。由于工作流体的传热和传质限制，在开发新一代增强流体（例如纳米流体）方面投入了大量精力。先前的研究报告称，当水被纳米流体取代时，热容量会有所提高。纳米颗粒和蒸发器表面之间的相互作用在这里至关重要。然而，沉积机制的细节及其对沸腾的影响仍然未知。本文重点研究热虹吸管中的沸腾过程如何影响蒸发器内壁和纳米流体本身，以及它如何影响热性能。为了这个目的，我们对填充有二氧化硅纳米流体的热虹吸管进行了实验研究，然后在扫描电子显微镜下分析了蒸发器表面和二氧化硅纳米流体的样品。二氧化硅在沸腾过程中沉积在多孔层中，从而实现毛细管芯吸。这反过来又减少了蒸发器壁的过热。此外，二氧化硅纳米流体提高了传热效率，并在低热负荷下传递了更多的热能。打开热虹吸管后，沉积层干燥并分裂。基于裂纹模式分析的两种方法，估计层的平均厚度。二氧化硅纳米流体提高了传热效率，并在低热负荷下传递了更多的热能。打开热虹吸管后，沉积层干燥并分裂。基于裂纹模式分析的两种方法，估计层的平均厚度。二氧化硅纳米流体提高了传热效率，并在低热负荷下传递了更多的热能。打开热虹吸管后，沉积层干燥并分裂。基于裂纹模式分析的两种方法，估计层的平均厚度。