MODELLING TWO-PHASE FLOWS IN RENEWABLE POWER GENERATION SYSTEMS
Improving the heat transfer predictions in renewable energy systems such as organic Rankine cycle (ORC) systems and solar powered systems is key to making these systems more efficient and less expensive. To this end, a model detailing the forced convective annular flow with phase change in a tube is presented. This dynamic model is defined by a set of partial differential and algebraic equations (PDAEs) accounting for the vaporisation of a liquid working fluid into the vapour phase, and the liquid droplets entrainment and deposition phenomena observed in annular flows. The model is validated against air-water experimental data from various sources. The entrainment
and deposition phenomena are effectively captured as the model is shown to predict the entrained fraction of liquid
droplets in the gas phase to within 12% of experimentally obtained values while the dryout lengths (which determine the onset of the critical heat flux) are predicted to within 5%. The mechanistic nature of the model makes it suitable to be deployed in larger renewable energy system models and/or to be used in optimisation studies, while overcoming the dependence on often inaccurate heat transfer coefficient correlations and leading to more precise estimates of sizes and costs of evaporators and condensers.