The Rotating Drum Latent Heat Exchanger as an efficient and fully controllable heat exchanger for Latent Heat Thermal Energy Storage

Kurzfassung

Thermal energy can be stored in latent heat thermal energy storages with high exergetic efficiency at a constant temperature level during the phase change of a storage material from solid to liquid. While discharging, Phase Change Material (PCM) solidifies at the heat transfer surface limiting the heat transfer due to the low thermal conductivity of commercially available PCMs. The presented rotating drum latent heat exchanger keeps the solid PCM layer at a constant thickness below 0.1 mm to maximize the heat flux. Here, a tempered rotating drum is partially immersed into liquid PCM which solidifies at the drums outer surface and is scraped off every rotation. An experimental test rig using decanoic acid as PCM is used to validate available theoretical data of a quasi-stationary analytical approach and a 1-D numerical scheme. Results are showing a heat flux density of up to 25 kW/m2 at a temperature difference of 10 K related to the active heat transfer surface. Doubling the temperature difference increases the heat transfer by a factor of 1.5 - 1.8 due to nonlinear effects. In addition, liquid PCM is adhering at the surface released out of the liquid PCM. Thus, the active heat transfer surface can be enlarged to the entire drums surface depending on the rotational speed. The storage density can be enlarged by overheating the liquid storage material to use the sensible heat as well. Furthermore, the heat flux is constant and fully controllable by adjusting the rotational speed and the solidified PCM can be stored separately from the liquid phase, resulting in a complete independence of thermal power and storage capacity. The presentation will show the latest experimental and theoretical results of the working test rig