Thermal behaviors in heat exchanger channel with V-shaped ribs and grooves

Abstract

An experimental work has been conducted to explore the influence of the combined V-rib and chamfered-V-groove vortex generator (VG) on flow and heat transfer behaviors in a heat exchanger channel having a constant heat-flux on the top wall. Firstly, the V-shaped ribs were mounted on the plain top-wall with a view to creating multiple vortex flows inside. The investigated geometrical parameters were three relative rib pitches (RP = P/H = 1.0, 1.5 and 2.0) and relative rib heights (called “blockage ratio”, RB = e/H = 0.3, 0.4 and 0.5) at a single attack angle (α = 45°). Secondly, the ribs were again placed on the chamfered-V-grooved top-wall having three relative groove-pitches (RP = 1.0, 1.5 and 2.0) like the rib case but at a fixed groove width and depth. Air as the test fluid flowed through the heat exchanger channel for Reynolds number (Re) ranging from 5300 to 23,000. Influences of the newly designed heat exchanger surface on the Nusselt number (Nu) and friction factor (f) have been examined and compared with the flat surface data at similar test conditions. The experimental result reveals that the combined rib-groove with small RP and large RB yields the heat transfer and friction loss higher than the one with large RP and small RB. Nevertheless, thermal enhancement factor (TEF) obtained at a constant pumping power shows that the combined rib-groove case with PR = 1.5 and RB = 0.4 provides the highest value around 1.907. To explore the influence of the rib thickness on thermal performance, the rib thickness size was reduced to be a very thin rib, called the “baffle”. The study points that at PR = 1.5, the baffle-groove with RB = 0.3, 0.4 and 0.5 provide, respectively, TEF around 2.12, 2.14 and 2.11, indicating that the baffle-groove performs better than the rib-groove around 13%.