Konsantre güneş enerjisi alanında yüksek sıcaklıklı partikül akışlarını modellemedeki gelişmeler

Within the field of concentrating solar power (CSP), central receiver ("tower") type systems are capable of achieving temperatures reaching or exceeding 1000 ⁰C. To utilize this heat efficiently, a growing body of research points to the benefits of using solid, sand-like particles as a heat storage medium in CSP plants. Modeling capabilities for flowing groups of particles at high temperature are lacking in several aspects, and thermal radiation in particle groups has received relatively little attention in research. This thesis focuses on developing the modeling capabilities needed to simulate heat transfer in solid particle solar receivers and heat exchangers using the Discrete Element Method (DEM), where particle mechanics and heat transfer are modeled at the particle scale. Several original contributions are made in this thesis: A) a 3D Monte Carlo Ray Tracing code is developed for modeling radiation for gray, uniformly sized particles, B) an expression for the effective thermal conductivity due to radiation is derived from Monte Carlo simulations, C) the "Distance Based Approximation" (DBA) model for radiative heat transfer in particle groups is developed, which can be implemented directly into DEM codes, D) an open source heat transfer code is developed for dense granular flows, named Dense Particle Heat Transfer (DPHT), which uses the DBA radiation model and several previously proposed heat conduction models to form a code which is readily usable for particle-based heat exchange devices, and E) the DPHT code is used to model a solar receiver for preheating of lime particles for calcination. In addition to modeling, experimental work on dense granular flows is carried out under a high-flux solar simulator, with particle temperatures reaching 750 ⁰C. A close match is shown between experimental results and the newly developed DPHT heat transfer code.