Numerical and Experimental Investigation of the Centrifugal Solar Particle Receiver

Kurzfassung

Particle solar receivers promise economical and operational advantages compared to molten salt based solar receivers. The Centrifugal Solar Particle Receiver (CentRec) is a promising design because it allows active control on particle residence time and particle outlet temperature. Particles moving as a thin film in an inclined rotating drum under centrifugal and gravity forces are heated by concentrated sunlight. In the present work, the main objective is to develop a numerical thermal model and evaluate the thermal performance of the CentRec. To do so, particles are modeled as discrete phase instead of continuum to better reflect the particle interactions, and resulting effects of these interactions, e.g. mixing, on the thermal performance. The Discrete Element Method (DEM) tool LIGGGHTS is used to simulate the particle motion. The developed simulation model is validated with a set of experiments conducted. A scaling approach is developed to scale-down the particle film characteristics in CentRec because of huge computational power requirement of large-scale receivers. An optical system consisting of diffuse lamps, GoPro cameras etc. is developed to record the particle motion in CentRec. A tracer recognition and tracking algorithm is developed to detect the particles’ velocity and the film thickness for various combinations of particle mass flow rate and receiver rotation speed. A separate thermal model is developed in MATLAB, which uses the particle positions calculated with the DEM simulation. All heat transfer mechanisms being effective in CentRec are developed, validated and embedded to the main thermal code. A novel radiation penetration model and a novel reflection model are developed to distribute the solar irradiation to the individual particles. Moreover, long-range and short-range thermal radiation models are considered separately to calculate the emissive heat exchange between large surfaces and between individual particle pairs, respectively. All radiation models are based on some approximations to reduce the computational burden significantly. Besides, a particle scale conduction model from literature is modified for the current application. Supplementary submodels, namely convection and conduction loss models, are also developed and integrated to the thermal model. The complete thermal model is applied to several CentRec sizes to measure the thermal performance. A considerable effect of the particle mass flow rate on the receiver thermal efficiency is found. Convection loss is the main thermal loss mechanism for the considered receiver sizes. The thermal losses are quantified for various combinations of operational parameters and receiver sizes. The findings are to be used for further scaling-up the CentRec technology.