A rectangular-wave-honeycomb composite adsorbent with sorption thermal energy storage for continuous solar drying of mushroom

Solar drying is an energy-efficient and environmentally friendly method. However, during periods without sunlight, the lack of energy input to the dryer causes it to cease drying, leading to challenges such as water vapor condensation and product rehydration. To address this, our study proposed a continuous solar dryer (CSD) that integrated conventional solar drying with sorption thermal energy storage (STES), characterized by internal circulation dehumidification at night. The inclusion of adsorption beds within the dryer removed water vapor inside the drying chamber and released sorption heat to supply energy for continuous drying. A series of composite adsorbents was prepared based on an activated carbon fiber (ACF) matrix through impregnation and spraying methods. Among these, ACF-calcium alginate-1/1 (ACF-CA-1/1) was identified as the optimal adsorbent for system-scale preparation and then used for drying mushrooms. Experimental results showed that ACF-CA-1/1 exhibited an adsorption capacity of 0.45 g/g at 20 ℃ and 80 % relative humidity (RH), with an energy storage density of 676.7 J/g. During nighttime drying from 21:00 to 9:00, the adsorption beds facilitated a reduction of 2.64 kg water from 10 kg mushrooms, resulting in a moisture ratio decrease of 29.53 %. The average RH within the drying chamber with STES was 61.37 % and 45.46 % on the first and second nights, respectively. Furthermore, the overall energy efficiency and specific moisture extraction rate of the dryer with STES were 15.50 % and 6.9 × 10 −5 kg/kJ, respectively. Those of the dryer without STES were 14.23 % and 6.3 × 10 −5 kg/kJ for the same factors, respectively. Notably, solar drying with STES achieved a 30.74 % decrease in RH of drying chamber, an 8-hour reduction in drying time, and a 1.27 % increase in energy efficiency compared to solar drying without STES. Herein, the CSD effectively overcame the rehydration problem of agricultural products at night, offering a promising solution to the intermittent nature of solar drying.