There is a predominance of studies in literature involving flow boiling of refrigerants at low pressures, characteristics of refrigeration and air conditioning applications. Due to the growing interest in organic Rankine cycles (ORCs), as well as in circulating fluidized bed boilers and supercritical water reactors, studies on high pressures have intensified in recent years. Fluids thermophysical properties show significant variations at high pressures, especially near the critical pressure. Latent heat and liquid density in this region present a more accentuated decrement than in lower pressures, resulting in a unique boiling heat transfer behavior. However, only a few scholars have discussed the heat transfer phenomenon at high pressures, and even less at near-critical pressures. Most of the studies found in literature were carried out in conventional-diameter channels using refrigerants with significant global warming potential (GWP). Furthermore, although both horizontal and vertical flows have been explored, the studies have not dealt with intermediate inclinations. In this context, the present proposal deals with the study of the high-pressure flow boiling of R245fa and R1233zd(E) in a 2 mm diameter tube with different inclinations. Both fluids have potential for application in ORCs, with the second having almost null GWP. The study will be carried out on an experimental bench located at the Centre d'Énergétique et de Thermique de Lyon and the effect of mass velocity, heat flux, inclination and inlet subcooling on the heat transfer coefficient, pressure drop and critical heat flux will be evaluated. The results will be compared with prediction methods and, if necessary, new prediction methods will be proposed.
News published in Agência FAPESP Newsletter about the scholarship: