Experimental study of heat transfer and pressure drop in mechanically-assisted heat exchangers with active scrapers

Abstract

A mechanically assisted heat exchanger has been studied. The reciprocating movement of the active insert device, located inside a round tube, generates macroscopic displacements of the flow, increasing heat transfer. At the same time, the inner tube wall scraping avoids fouling. Pressure drop and heat transfer characteristics have been experimentally studied, in order to characterize the thermo-hydraulic behaviour of the dynamic insert device, using propylene-glycol as working fluid. Experimental results for Fanning friction factor and Nusselt number as functions of flow and dimensionless geometric parameters have been presented. Friction factor increases up to two times at higher Reynolds numbers for different scraping frequencies. Nusselt number increases up to four times at low Reynolds numbers, for different scraping frequencies. At high Reynolds number, no influence of the scraping frequency is shown.