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

Abstract

A thin film scraped surface evaporator (TFSSE), similar to that of Luwa's model was developed for concentration of fruit juices and pulps. The main body of the evaporator was 1.4 m high and 0.22 m in diameter. The TFSSE was evaluated for the effect of steam temperature, rotor speed and feed flow rate on water evaporation rate and overall heat transfer coefficient with water 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 °C −1 and 14.7–30.7 kg h −1, respectively. For tomato pulp, overall heat transfer coefficient, evaporation rate and final concentration (from 5.9% TS initial concentration) were varied between 625.6–910.9 W m −2 °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 temperature 65–80°C and rotor speed 355 rev min −1. The optimum process parameters for the concentration of tomato pulp at 355 rev min −1 rotor speed were found to be 40.3 kg h −1 feed flow rate and 73°C steam temperature. The optimum process parameters could give 840 W m −2 °C −1 overall heat transfer coefficient, 27 kg h −1 evaporation rate and 18% total solids. At 75°C steam temperature and 45.86 kg h −1 feed rate, the ascorbic acid and colour of tomato pulp were marginally affected.