Selection of Heat Transfer Promoters for Heat Exchanger Retrofit

Abstract

From the thermal point of view, the main operational problems conventional heat exchangers of the tubular type face are the prevalence of the laminar sublayer on the surface immediately adjacent to the heat transfer surface that is responsible for low heat transfer coefficients. A passive means of disrupting this layer is using mechanical inserts known as turbulence promoters. The search for new geometries with better thermohydraulic performance has increased the number of designs available in the open literature. In sight of the large number of different options available for use in design, the selection of the right type of insert for a given application is the focus of this paper and introduces an alternative approach for the selection of turbulence promoters based on the thermal and hydraulic lengths. The approach allows for a quick comparison of the thermo-hydraulic performance in design and retrofit. It considers the effect of the magnitude of the heat transfer coefficient of the opposing stream as well as the effect of viscosity on the selection. Some turbulence promoters out of the many that have been published are used to demonstrate the methodology. This work confirms that the two conditions that result in a greater impact of the turbulence promoter on the overall heat transfer coefficient are when the tube-side presents the higher thermal resistance and when a highly viscous fluid flows through the tubes.