Experimental Determination of Heat Transfer Coefficient and Liquid Film Thickness in Concentration of Apple Juice, Using Falling Film Evaporator

Apple juice is a heat sensitive material. Vitamins, proteins, and other organic materials present in apple juice may be easily decomposed during heat processing. Therefore, evaporators with minimum residence time and maximum efficiency should be used for concentrating this material. Thus, long tubular type of falling film evaporator is a suitable device. In this work, the concentration of apple juice obtained from Uroumieh (North West region of Iran) up to 40 °BX in a pilot-plant with single effect of falling film evaporator has been investigated. The results show that liquid film of apple juice flows down in turbulent regime. Also, variations ofthe Nusselt number and thickness of liquid film versus Reynolds number have been presented. Comparison of obtained results with the results of Chun-Seban, Garwin-Kelly and Mudawware-El Masri, show that Nusseltnumbers in this case are very close to their results and the film thickness is less than the results of Brauer, Feind,and Takahama. These results mean that the heat transfer coefficients of the liquid film in evaporation of applejuice are greater than the evaporation of regular water.