Evaluation of the performance of a hybrid electro- thermophilic silver cyprinid dryer

Abstract

Bulk fish production continues to suffer losses from poor preservation and more specifically inadequate drying in many rural communities. Mechanized dehydration is preferred over the traditional open-air sun drying, but it is energy intensive and costly. Minimizing energy losses and enhancing process efficiency remain key priorities for dryer design. In this study, the energy saving potential of integrating compostable insulations in the dryer walls was evaluated under the assumption that supplementing process heat with energy from thermophilic decomposition of the biodegradable materials could enhance efficiency. The influence of thermophilic energy on drying processes remains undocumented. Therefore, the main objective of this study was to evaluate the performance of a hybrid electro-thermophilic Silver Cyprinid fish dryer and more specifically: to characterize the batch-drying of silver cyprinid, establish appropriate models for the drying kinetics, and assess the energy saving potential of the integrated thermophilic energy vis-a-viz the pure electric system. A dryer with a total load capacity of ten trays each having a capacity of 800g was used. Fresh Silver Cyprinid fish samples were exposed to both pure electric and hybrid electro-thermophilic drying at temperature settings of 40 o C and 60 o C, each exposed to both low (1.4 m/s) and high (2.8 m/s) air velocities—the samples were also subjected to one, five and ten-tray experiments. Drying curves were determined gravimetrically and Graph Expert TM software applied to model the drying kinetics. Analysis of the results showed drying entirely in the falling rate period with drying times ranging between 8 and 20 hrs for a moisture content reduction from 85.37 to 8.57 %wb, across all experiments. Air velocity, temperature and tray settings had substantive impact for complete drying of the sample in both pure electric drying and hybrid electro-thermophilic drying. Lower drying times and higher drying rates were experienced at lower tray settings. A number of mathematical drying models (Newton, Page, Henderson & Babis, Logarithm, Lewis, and Diffusion model) were investigated and the Lewis model was superior with highest value of coefficient of determination (R 2 ) of 0.988213 and lowest values of standard error of estimate (SEE) of 0.001913. The specific energy consumption SEC, at the 5-tray setting, was 8.05 kJ/kg of water removed for pure electric drying compared to 7.54 kJ/kg of water removed for the hybrid electro-thermophilic drying, representing an energy saving of close to 24%. The results demonstrated the untapped potential of integrating beneficial thermophilic bacteria into walls to enhance the performance and lower costs in food drying systems. In this study thermophilic energy was applied only to one side of the dryer. Further research is recommended on commercial applicability of the prototype and to establish the influence of integrating this energy into all the walls of the dryer. Use of different compostable materials, besides the cow manure and shredded maize stover applied in this study, should also be investigated.