Results in Engineering (Mar 2022)
Novel designs of LVGs conformations and introduction of Batch Heated and Channeled Pipe for increasing heat transfer efficiency in pipes
Abstract
The struggle for energy efficient systems is and will increasingly become the most prevalent element in every field of human activity, as new directives for green energy and minimization of energy waste are binding all new relevant projects, either operational or under development. A crucial part of this effort is rested upon the installations used for heat transfer and especially the pipes. In this paper we contribute towards this effort by proposing novel conformations for the interior of straight pipes of orthogonal cross section. Three conformations are presented and studied, for the case of a pipe having heated walls. The first two are using Longitudinal Vortex Generators (LVG) placed, not on a heated surface but inside the flow field, aiming at creating currents which will redirect the flow locally from the central regions of the pipe towards its walls. The third one is based on a completely different approach and it is named Batch Heated and Channeled Pipe (BHCP). Under this approach, one part of the fluid is separated in one small part of the pipe next to its walls so as to rise its temperature as high as possible, before being redirected towards pipe's core. Air was used as the working fluid. Models were designed in CATIA and simulated using ANSYS-Fluent computational package. Various turbulent flow conditions were considered, ranging from Re numbers starting at 5k and finishing at 20k. The efficiency of each conformation was examined based upon bulk temperature at the outlet, Nu number for various Re numbers, pressure losses caused by conformations presence as well as their effect on flow downstream of the conformation. For conformations performance evaluation was used additionally one of the best theoretical instruments for depicting and analyzing the flow and thermal fields' characteristics, specially modified for 3D flows, the Field Synergy Principle (FSP). The results reveal that the BHCP gives an extraordinary increase of the heat transfer efficiency, reaching the staggering 260% increase of mean Nusselt number. Unfortunately this comes with a very high pressure loss penalty which needs further attention. Nevertheless, this outcome regarding BHCP performance leads to the conclusion that the idea upon which this model is based is very promising and so further attempts would be considered in the direction of lowering the elevated pressure losses recorded, without neglecting any further potential improvements of the already elevated Nusselt Number.
