Assessing the heat-transfer performance, operational strategies and sucrose losses of falling-film and rising-film evaporators

Efficient operation of the evaporator station is the key to achieve high juice-processing rates and low steam consumption; however, the efficient design of the evaporator also plays important roles. An efficient design should provide a high heat-transfer coefficient (HTC) over an extended period, adequate mixing of the juice in the heating elements, and short residence time of juice in the evaporator. Falling-film and rising-film are the two evaporator types (both tubular and plate type) used in the sugar industry. This paper presents heat-transfer coefficients and operational strategies of falling-film tubular evaporators and compares them to the heat-transfer coefficients and operational strategies of Robert-type (rising-film tubular) evaporators available from other investigations. The assessment includes the heat-transfer performance, strategies for effective operation, residence times, and the extent of sucrose degradation in falling-film and rising-film tubular evaporators. Key words Falling-film evaporator, Robert-type evaporator, heat-transfer coefficient, residence time, sucrose degradation