Micro-porous surfaces for enhanced boiling with enhanced mechanical stability

Abstract

Consulta en la Biblioteca ETSI Industriales (8129)

[EN] Enhanced boiling has been object of intense research to tackle problems such as energy wasting or energy conversion systems with low efficiency. Nanotechnology and Nanoscience have been employed by scientists to enhance boiling during last couple of decades. Since boiling is a vigorous process that can erodes enhanced surfaces in heat exchangers or heat pump equipments, new surfaces with high mechanical properties are required. The main objective of this research work is to fabricate nanostructured micro-porous (NMp) surfaces by using electrodeposition technique under certain conditions with dynamic gas bubbles as template, with enhanced mechanical stability through postprocessing. As the porous structure (dendritically ordered copper branches) is formed during the evolution of the dynamic bubbles, it is suited for applications where bubbles are required, like boiling. However, since boiling is a vigorous process, such NMp surface structures require better mechanical stability in order to be used in boiling. In this thesis, different routes such as extra low-current deposition, adding additive, alloying Cu with other metals, etc. have been used to enhance the mechanical stability of the NMp structures. Blowing tests using compressed air under certain parameters directly to the surfaces have been employed to evaluate the mechanical stability of such porous surfaces. As a consequence, new NMp surfaces with enhanced mechanical stability have been obtained, with a %weight remaining after the blowing test more than 90% on some routes. Boiling tests have also been conducted using the widely used chlorofluorocarbon (R134a) as refrigerant, where the heat transfer coefficient (HTC) of such NMp surfaces with enhanced mechanical stability was improved more than 19 times compared to a reference surface at a heat flux of 1 W/cm2. Thus, the mechanical stability of NMp surfaces has been greatly improved without compensating the excellent boiling performance in air conditioning and refrigeration applications.