Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
EXPERIMENTAL EVALUATION OF THERMAL INSTABILITIES DURING FLOW BOILING OF DI-WATER IN MICROCHANNELS HAVING THEIR SURFACES COVERED WITH NANOPARTICLES
Submission Author:
Tiago Augusto Moreira , SP
Co-Authors:
Francisco Julio do Nascimento, Gherhardt Ribatski, Tiago Augusto Moreira
Presenter: Tiago Augusto Moreira
doi://10.26678/ABCM.COBEM2017.COB17-2141
Abstract
The present paper concerns an experimental evaluation of the influence of nanoparticles deposition inherent to the boiling process of nanofluids on the thermal instabilities during flow boiling of DI-water inside a single microchannel with 1.1 mm ID and 200 mm long. Experiments were performed for a tube as commercially available and with its surface covered with Al2O3 nanoparticles (20-30 and 40-80 nm), and SiO2 (15 and 80 nm). The coating of the surfaces was performed by submitting to the test section through a boiling process of nanofluids with volumetric concentration of 0.1%. Thermal instabilities were characterized by the amplitude of the temperature oscillation of the test fluid at the channel inlet. In general, surfaces covered with nanoparticles smaller than 30 nm provides a reduction of the thermal instabilities. For larger nanoparticles, opposite behavior was noted and higher thermal instabilities were observed compared to flow boiling of DI-water on the original surface. An analysis of the surfaces was performed in order to evaluate the effect of deposition on the surface texture and, consequently, on the bubble nucleation density. As result, it was found that the deposition of nanoparticles smaller than 30 nm provides a reduction of the number of cavities with sizes within the range of dimensions corresponding to the active nucleation sites, relative to the surface as commercially evaluated. This behavior was associated to the reduction of thermal instability effects. An opposite trend was observed for nanoparticles lager than 40 nm.
Keywords
Flow boiling, Nanoluids, microchannels, Thermal instabilities
