Experimental investigation of turbulence level in enhanced heat exchangers with active insert devices

Abstract

This work presents a visualization study carried-out on a dynamic insert device. The flow pattern is obtained by employing the Particle Image Velocimetry (PIV) technique. The insert device is moved alternatively along a tube and consists of several circular elements with six circumferentially distributed holes on them, which are mounted on a shaft with a pitch of 5D. The whole is moved alternatively along the axial direction by a hydraulic cylinder. The increase of the turbulence level of the Flow will be analyzed and related to the heat transfer augmentation. By the use of Particle Image Velocimetry technique and water as test fluid, the 2-Dimensional pattern of the turbulent flow is obtained on the two symmetry planes of the device: hole center and between holes. The results permit to establish the flow pattern along the devices. In static conditions of the scraper, experiments are carried out at three different Reynolds ranging from 4000 to 6323. In dynamic conditions, the Reynolds number has been kept constant at 7400, while varying the velocity of the scrapper in relation of 0.5, 1 and 2 with the bulk velocity of the flow. Co current and counterflow directions of the scraping device have been analyzed, and results show the insert device movement on flow behavior.