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The current work presents energy efficient hot air drying by controlling the relative humidity (RH) including step-down and continuous dehumidification of RH as to specify material based on Weibull and Bi-Di models. The drying characteristics of yam slices of different thickness (6, 1 2 ,18 mm) and longan were investigated using two RH control strategies. Results showed th a t continuous decrease of RH was energy efficient for longan, while the stepdown strategy was more energy efficient for 12 or 18 mm thick yam slices drying. In terms of drying kinetics, the step-down control strategy of RH is more energy efficient for those materials whose drying rate as well as sample's temperature curves display three distinct stages and sample thickness is relative large. In terms of β and Bi values in Weibull and Bi-Di models respectively, it is observed th a t the step-down control strategy of RH drying method is more efficient when the β value exceeds 1 and the Bi value was more than 0.1. The current investigation provided an assessment method for the convective hot air drying method by controlling RH to improve drying efficient and save energy consumption. [ABSTRACT FROM AUTHOR]

In the present work, the drying kinetics and evolution of sample's core temperature and moisture distribution of yam slices during convective hot-air-drying were investigated. In terms of drying kinetics, the effect of drying temperature (50, 55, 60, 65, 70°C), relative humidity (20, 30, 40, 50%), and sample thickness (5, 7, 9 mm) on drying characteristics of yam slices were studied. Results indicated that all the three factors had significant influence on the drying kinetics, whereas drying temperature gave the most significant effect, followed by relative humidity and sample thickness. Moisture-effective diffusivity and activation energy were calculated, and it was found that the diffusivity was in the range of 5.5454 x 10-10 - 1.0804 x 10-9m²/s and the activation energy was 29.528 kJ/mol. Heat and mass transfer models were developed based on the finite element method to calculate the core temperature and moisture distribution of yam slices during drying. Model validation exhibited good agreement between predicted and experimental data, which illustrated that the developed models could precisely predict the core temperature profile and moisture distribution of the sample. The current work provides further insights to understand the characteristics and mechanism of drying process of yam slices. [ABSTRACT FROM AUTHOR]