Performance evaluation of a thin film scraped surface evaporator for concentration of tomato pulp

A thin film scraped surface evaporator (TFSSE), similar to that of Luwa's m odel was developed for concentration of fruit juices and pulps. The main bo dy of the evaporator was 1.4 m high and 0.22 m in diameter. The TFSSE was e valuated for the effect of steam temperature, rotor speed and feed flow rat e on water evaporation rate and overall heat transfer coefficient with wate r and tomato pulp as feed liquids. For water as the feed, the overall heat transfer coefficient and evaporation rate ranged within 476.9-939 W m(-2) d egrees C-1 and 14.7-30.7 kg h(-1), respectively. For tomato pulp, overall h eat transfer coefficient, evaporation rate and final concentration (from 5. 9% TS initial concentration) were varied between 625.6-910.9 W m(-2) degree s C-1, 13.22-33.72 kg h(-1) and 8.02-19.21% TS, respectively. The range of operating parameters were: feed flow rate 40.8-51.0 kg h(-1), steam tempera ture 65-80 degrees C and rotor speed 355 rev min(-1). The optimum process p arameters for the concentration of tomato pulp at 355 rev min(-1) rotor spe ed were found to be 40.3 kg h(-1) feed flow rate and 73 degrees C steam tem perature. The optimum process parameters could give 840 W m(-2)C(-1) overal l heat transfer coefficient, 27 kg h(-1) evaporation rate and 18% total sol ids. At 75 degrees C steam temperature and 45.86 kg h(-1) feed rate, the as corbic acid and colour of tomato pulp were marginally affected. (C) 2000 Pu blished by Elsevier Science Ltd. All rights reserved.