Effect of circulation flowrate and coolant temperature on progressive freeze concentration of roselle extract

Abstract

In this research, progressive freeze concentration (PFC) has been applied in concentrating roselle extract. The aim of this research is to investigate the effect of two operating parameters which are the circulation flow rate and coolant temperature on the average freezing rate and average concentration efficiency of roselle extract. The process has been improved in this research as an automated PFC system was implemented to assist in concentrating the roselle extract. Analyses of the results illustrated that with a decrease in coolant temperature and increase in circulation flow rate, the average freezing rate showed an increment in trend. It has been found that average concentration efficiency increased as coolant temperature increased but decreased as circulation flow rate increased. From the analysis, it can be concluded that the highest average freezing rate for the effect of coolant temperature and circulation flow rate is 0.0112 min-1 and 0.25 min-1 at coolant temperature of -14°C and circulation flow rate of 3000 mL/min respectively. As for the average concentration efficiency, the highest value for the effect of coolant temperature and circulation flow rate has been recorded as 0.91 (at -6°C) and 1.02 (at 2200 mL/min) respectively.