Phase change heat transfer processes of high performance applied to solar energy recovery

Abstract

Solar irradiation is a source of renewable energy and its use depends on the conversion of solar irradiation into heat and/or electricity. In the last two decades, the economic and environmental importance of incorporating solar energy to the energy matrix of most of countries have drastically increased. To convert solar irradiation to usable forms of energy, heat exchangers are necessary either to make use of the heat generated in the solar receptor or to the thermal management of photovoltaic cells. The concentrated solar irradiation absorbed by solar receptors can imply on the need of dissipating heat flux higher than 150W/cm2, corresponding to 1500 times the solar irradiation at the Earth's Surface. The maintenance of such high heat fluxes under safe conditions characterized by restrict temperature ranges is a recurring subject of research in the field of thermal sciences and has emerged as a major challenge for engineers and researchers. In this context, the present research proposal has the main goals of investigating the fundamental aspects and developing high-performance devices based on phase-change heat transfer processes applied to the use of solar energy. The specific objectives of this project are the following: (i) development and experimental evaluation of heat radiation absorbers based on flow boiling through microchannel array. The development of these devices will incorporate solutions proposed based on analyses of experimental results from IR-thermography for flow boiling inside single- and microchannel array heat absorbers, and of computational results from simulations using the Thermal Lattice Boltzmann Methods (TLBM); (ii) development of innovative additive/3-D manufacturing processes and application of them to the manufacture of high-performance heat radiation absorbers and all the instruments necessary to their study using the infrastructure of Laboratory of Research on Devices (LPD) of Department of Applied Physics (DFA) and Multi-user Lab (LAMULT) both of the "Gleb Wataghin" Institute of Physic and the Center for Semiconductor Components (CCS) at UNICAMP; (iii) development of instrumentation and control techniques applied to heat transfer with phase change in pulsating heat pipes. These devices present the potential of being used as high performance fins. In the present project, their development will be focused on their application as heat transfer mediums in the vapor absorber and in the vapor generator of absorption refrigeration systems, thus reducing the volume of these devices and improving their thermal efficiencies; (iv) experimental study of falling film absorption process of ammonia-water mixtures focusing on the development of a vapor absorber. From ecological and economical points of view, absorption air-conditioning and refrigeration systems combined with power generators having solar irradiation as energy source are extremely attractive, considering the use of the remaining heat of a process of photovoltaic generation or of a heat engine operating according to the Stirling, Ericsson or Organic Rankine cycles (ORC). Finally, it is worth noting that this project involves the investigation of topics at the edge of knowledge that are strategic for the development of the state of São Paulo and of Brazil, combining renewable energy source and complex micro-manufacturing techniques. Moreover, the proposal comprises challenges involving fundamental and theoretical aspects summed to the high potential of developing of new technologies and new products with immediate application. (AU)