Eksperimentalno i numeričko istraživanje termo-strujnih procesa u spiralnom naboranom toplotnom apsorberu koncentrisanog zračenja

Abstract

The utilization of modern paraboloidal concentrators for conversion of solar radiation into heat energy requires the development and implementation of compact and efficient heat absorbers. This research is directed toward innovative design solution that involves the development of heat absorber made of spirally coiled tubes with transverse circular corrugations. The main advantage of the considered design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. Investigation of the influence of hydraulic, physical and thermal conditions, as well as the geometry of the spirally coiled corrugated heat absorber, on the local intensity of heat transfer and pressure drop was conducted using modern experimental and numerical methods. Laboratory model of heat absorber was instrumented and mounted in the radiation field. Test section instrumentation included inlet fluid flow rate, pressure drop, inlet and exit fluid temperature and 35 type K thermocouples welded to the surface of the coil. The thermal analysis of experimentally obtained data included consideration of the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results showed significant enhancement of the heat transfer compared to spirally coilled smooth tubes, up to 240% in the turbulent flow regime. The influence of radiant field intensity and geometrical parameters of corrugations outside the experimental range were investigated using computational fluid dynamics techniques in terms of heat transfer and pressure drop. Finally, the reliable correlations for determining the intensity of convective heat transfer coefficient and pressure drop were obtained for different flow regimes, which are applicable in engineering practice.