Heat transfer to immiscible liquid mixtures in a spiral plate heat exchanger

Abstract

Spiral plate heat exchangers have evinced significant interest owing to their compact size, large heat transfer surface area per unit volume, high heat transfer rates, less fouling, operational flexibility and ease of maintenance. Multiphase flow involving liquid-liquid systems is encountered in an increasing number of important applications such as petroleum and petrochemicals, metal processing and other industries. There is a strong need for understanding fluid flow behavior and heat transfer to liquid-liquid two-phase mixtures in heat exchangers. Liquid-gas and liquid-vapor flows have been studied extensively, but there have been fewer studies on liquid-liquid two-phase mixtures. There are even fewer studies on heat transfer to liquid-liquid mixtures. This gap is proposed to be partially bridged by the present work. In this work, liquid-liquid two-phase heat transfer studies were conducted in a spiral plate heat exchanger with water octane, kerosene, dodecane, diesel, and nitrobenzene in different mass fractions as the cold fluid and water as the hot fluid. Heat transfer coefficients of the two-phase liquids were found to be strongly dependent on the composition of the liquid mixture and exhibited abrupt transitions as a function of compositions. Two approaches were examined for predicting two-phase heat transfer coefficients. The first approach involved developing predictive empirical correlations for Nusselt Number from experimental data by linear regression. When the effect of temperature was included by measuring contact angles at average temperature of the cold fluids, significant improvement was seen, with highest errors of the order of 35%. The possible causes of these errors were identified. While the former approach gives better results, it requires specific experiments with liquid-liquid mixtures. The latter approach, if improved, has the advantage of generality, and better captures the physics of heat transfer in liquid-liquid mixtures. Both these approaches may be useful in designing spiral