Numerical investigation of non-newtonian flow and heat transfer in tubes of heat exchangers with reciprocating insert devices

Abstract

Non-Newtonian flow and heat transfer in tubes of heat exchangers with reciprocating insert devices have been numerically investigated. The heat exchanger is mechanically assisted by a reciprocating cylinder, which moves the scraping rods inserted in the tubes. An array of semi-circular elements is mounted on each rod, with a pitch p=5D. These elements fit the internal diameter of the tubes. During the reciprocating motion, they scrape the inner tube wall, avoiding fouling. Additionally, the movement of the inserted device generates macroscopic displacements of the flow, which continuously mix core regions with peripheral flow. A power law model with temperature dependent properties is implemented in FLUENT, for a Carboxymethil cellulose (CMC) solution in water with concentration of 2%. Flow pattern and pressure drop mechanisms are analyzed in static and dynamic conditions, and heat transfer enhancement features are discussed.