Comparison of mass and heat transfer properties of kelp when dried by radiation or conduction using a novel superheated steam system with built-in heat recovery unit

Abstract

Kelp is an aquatic product that must be dried after harvest to prevent spoilage. This study tested a novel system for drying kelp. It utilized superheated steam for heating and could recover the latent heat of the exhausted steam, for further drying of the product. The system was tested in four drying modes, including single-face radiation drying mode (SRDM), double-face radiation drying mode (DRDM), single-face conduction drying mode (SCDM), and combined conduction and radiation drying mode (CCRDM). A one-dimensional semi-empirical mathematical model was used to predict the change in the moisture content and temperature of kelp during drying in each of the four drying modes. The drying characteristics of standardized kelp samples in each drying mode were investigated and the efficiency of heat recovery was assessed and compared. The change in moisture content and surface temperature of kelp during drying in each of the four drying modes was also predicted. The results showed that the drying characteristic of the kelp differed significantly depending on the drying mode. The CCRDM was determined as the optimal drying method and exhibited the best drying characteristics, including the highest kelp surface temperature, shortest drying time, and fastest drying rate. Compared to SRDM, DRDM and SCDM, CCRDM recovered, 83.3, 79.5, and 4.5% more energy from the system, and was the most energy efficient among 4 operation modes. Compared with changes in moisture, the changes in the surface temperature of kelp were more accurately predicted during drying.