Heat transfer enhancement in a cylindrical tube by a turbulator with slits generating multi-longitudinal vortices.

Abstract

This study analyses the effect of number of slits on a diverging conical ring insert when symmetrically cut out on the curved surface to generate multi longitudinal vortices in an incompressible fluid flow on a cylindrical tube. This is a passive augmentation technique aimed at achieving heat transfer enhancement. The insert disrupts flow creating a mixture between core and near wall fluid into a swirl flow with a pressure drop and friction characteristic generating higher heat transfer enhancement than that attained by either laminar or turbulent fluid flows achieved in a tube of equal diameter using other augmentation techniques. In this research work hot water is used as the test fluid in a simulation to establish the pressure drop and temperature variation along a tube of inner diameter 0.05 m and 8 m long with a diverging conical ring insert placed at a fixed distance from the entrance where uniform fluid velocity is attained to avoid the pipe entrance effect. Using a conical ring insert with inlet diameter of 0.036 m and an outlet diameter of 0.05 m giving a pitch ratio of 0.72, when the fluid flows into the pipe inlet region at a pressure P0=110,000 Pa and temperature T0 = 370 K. Analysis of the results shows a positive coefficient of heat transfer and thermal performance factor when comparing an insert with no slit and those with one, two and three slits. The highest rate of heat transfer enhancement is 423.38 attained when two multi – longitudinal vortex pairs are formed by a diverging conical ring insert with two slits on opposite sides of the curved surface. Comparison is done of simulated multi longitudinal vortices generated and analytical vortices that can provide perfect synergy of temperature field and the fluid velocity vector to provide maximum heat transfer enhancement. Also governing equations of the fluid flow are non- dimensionalized then discretized to determine pressure and temperature profiles at various Reynolds number with the fluid considered to be a laminar flows.