Nanostructured Architectures on the Heater Surface at Nanofluids Boiling and Their Role in the Intensification of Heat Transfer

Bondarenko B.I,Komysh D.V,Khovavko A.I,Moraru V.N,Sydorenko S.V

doi:10.13189/nn.2016.040102

Abstract

A major problem of modern science and industry is intensification of a heat transfer. One of the most promising ways for its solution is use of nanofluids as heat carrier and coolant that is capable to operate at high specific heat fluxes. In the course of nanofluids boiling porous sediments of nanoparticles are formed on the heating surfaces and provide a stable nucleate boiling mode. Whereas the specific heat fluxes grow up to 300-400% compared with water there is observed a significant increase of heat transfer coefficients, which is probably associated with the increase of porosity, roughness and wettability of heating surface. In order to clarify this question we studied the process of nanostructures formation in the course of different nanofluids boiling on the surface of Ni/Cr- heater. The morphology and topography of artificial coatings were studied and the results were compared with the values of the basic boiling parameters: specific heat flux and heat transfer coefficient. The conclusions based on experimental results are: maximum values of the specific heat flux and the heat transfer coefficient refer for nanofluids consisting of a mixture of nanoparticles with anisometric shape. While boiling process in on they are able to create nanostructures with the most developed surface roughness and porosity. Most likely, this is due to the highest density of nucleation sites and the area of heat transfer surface formed in these nanostructures.

Highlights

Called “nanofluids” (NFs) are the new generations of heat transfer medium, containing the colloidal dispersion of nanoparticles (NPs) in usual liquids [1]
We investigated the phenomenon of intensification of heat transfer by forming a porous layer of nanoparticles deposited on the heating surface at nanofluids boiling
We have found that the particles deposition and formation of nanostructures on the heating surface has been observed already in the pre-crisis area of the nucleate boiling of NFs, which dramatically changes the shape boiling curve and increases heat transfer coefficient

Summary

Introduction

Called “nanofluids” (NFs) are the new generations of heat transfer medium, containing the colloidal dispersion of nanoparticles (NPs) in usual liquids (water, ethylene glycol, oils, etc.) [1] Due to their increased heat conductivity and abnormally high heat exchange at NFs boiling they are promising for cooling of different power equipment (nuclear reactors, etc). The value of q at boiling of water-based NFs may increase by 300-400% compared to pure water and to achieve the value of 3-4·106 W/m2, and the heat transfer coefficient (a) may exceed 45000 W/m2K [1] It was found [2] that forming of the porous layer on the heater surface can delay or eliminate the phenomenon of the boiling crisis, which may lead to burnout and breakdown of equipment. It is assumed that all these positive effects are associated with alteration of the nature of heat transfer surface (wettability and roughness) and that a namely the porous structure and properties of deposited layer greatly determine the thermal parameters which characterize heat transfer at NFs boiling

Methods

Results

Conclusion