Simulation of a rotating drum heat exchanger for latent heat storage using a quasistationary analytical approach and a numerical transient finite difference scheme

Kurzfassung

With the concept of the rotating drum heat exchanger, latent heat can be released with a high and constant surface specific heat flux. Phase change material (PCM) solidifies on the outer surface of a drum, which is steadily removed by a fixed scraper during rotation. Two novel calculation approaches for determining the heat transfer and the layer thickness for a rotating drum heat exchanger are developed and validated with existing experimental data. This includes the identification of correlations for the thickness of the adhering liquid layer after the surface emerges from the liquid PCM and the local surface coefficient of heat transfer on the outside of a partially immersed rotating drum. While a calculation approach based on the quasistationary simplification underestimates the experimentally measured heat transfer for rotational speeds above 4 min^-1 by 31% on average, a detailed transient numerical simulation based on a time-varying finite difference scheme reproduces the experimentally measured heat transfer with an accuracy of 8% on average. By applying the transient numerical simulation to a rotating drum heat exchanger using sodium nitrate as the PCM, a surface specific heat transfer based on the entire drum surface of up to 400 kW*m^-2 can be assumed, showing the high potential of the rotating drum heat exchanger for industrial and power plant applications.