Determine the Mass Transfer Characteristic of Thermal Drying and Osmotic Dehydration of Pumpkin and Bitter Leaf
The experiment was carried out and three osmotic solutions were prepared, “hypertonic solution 60% concentrated, hypotonic solution 40% concentrated and isotonic solution 50% concentrated” and oven drying was also carried in the course of the experiment, the effect of sodium chloride (osmotic agent) concentration, temperature and immersion time on overall mass transfer coefficient, effective diffusivity, drying rate weight loss and shrinkage ratio on oven drying and osmotic dehydration of Pumpkin and bitter leaf. Results showed that both pumpkin and bitter leaf had a highest mass transfer coefficient in oven drying at highest temperature of 80oc, for pumpkin leaf 0.149(m/min), bitter leaf was 0.149(m/min), the results were also obtain for osmotic dehydration at 80Oc at highest concentration (Hypertonic solution) had the highest mass transfer coefficient, for pumpkin leaf was 0.015(m/min) for bitter leaf was obtained to 0.032(m/min). For osmotic dehydration, both samples weight loss percent (WL%) for hypertonic solution at 800C for 90mins had the highest weight loss percent, but the shrinkage ratio decrease with increase in time.The mass transfer during oven drying of pumpkin and bitter leaf was described using Fickian equation of diffusion with drying taking place in the falling rate period, the effective moisture diffusivity value showed temperature dependence on both samples. Effective diffusivity values were also determined for oven drying at different temperature, and the values increases as the temperature increases, for pumpkin and bitter leaf at 600C, 700C and 800C, the effective diffusivities were 1.0E-09, 1.87106E-09 and 2.1843E-09m2/min and 8.52966E-10, 1.00015E-9 and 2.45308E-08m2/min.