Experimental evaluation of a hybrid solar dryer with flexible open sorption thermal energy storage unit on demand for burdock root drying

Abstract

Solar drying represents an attractive way to implement an efficient and green development strategy. The viability of open sorption thermal energy storage (OSTES) can compensate for the inherent shortcomings of intermittency and instability of solar energy for ensuring the continuity of the drying process. Nevertheless, the existing solar-powered OSTES technologies only allow a batch mode while being severely restricted by sunlight's availability, thereby heavily limiting the flexibility in managing OSTES on demand. Herein, a novel proof-of-concept that a standalone solar dryer integrated with a reversible solid-gas OSTES unit is presented. Using in situ electrothermal heating (in situ ETH) could rapidly release adsorbed water of activated carbon fibers (ACFs) in an energy-efficient manner to achieve a charging process with faster kinetics. Applying electrical power by a photovoltaic (PV) module, particularly during sunlight-absent or insufficient time, allowed multiple OSTES cycles to proceed. Moreover, ACFs cylindrical cartridges can be flexibly interconnected in either series or parallel, forming universal assemblies with well-controlled in situ ETH capacity. The mass storage density of ACFs with a water sorption capacity of 570 mg/g is 0.24 kW·h·kg-1. The desorption efficiencies of ACFs are higher than 90%, corresponding to 0.057 kW·h maximum energy consumption. The resulting prototype can diminish the fluctuation of air humidity along the night and provide a relatively steady and lower air humidity for the drying chamber. The energy-exergy and environment analysis of the drying section for both setups are estimated, respectively.