Heat Transfer on Internal Surfaces of a Duct Subjected to Impingement of a Jet Array With Varying Jet Hole-Size and Spacing

Abstract

One significant issue concerning the impingement heat transfer with a jet array is related to the so-called “crossflow”, where a local jet performance is influenced by the convection of the confluence from the impingement of the jet/jets placed upstream. As a result, the heat transfer coefficient may vary along the streamwise direction and creates more or less nonuniform cooling over the component, which is undesirable from both the performance and durability standpoints. Described in this paper is an experimental investigation of the heat transfer coefficient on surfaces impinged by an array of six inline circular jets with their diameters increased monotically along the streamwise direction. The local heat transfer distributions on both the target surface and jet-issuing plate are measured using a transient liquid crystal technique. By varying the jet hole-size in a systematic manner, the actual distribution of jet flow rate and momentum within a jet array may be optimally metered and controlled against crossflow. The effects on the heat transfer coefficient distribution due to variations of jet-to-target distance and inter-jet spacing are investigated. The varying-diameter results are compared with those from a corresponding array of uniform jet diameter.

Influence of spanwise pitch on local heat transfer distribution for in-line arrays of circular jets with spent air flow in two opposite directions

“…The effect of streamwise pressure gradient on the local heat transfer distribution due to impingement of arrays of multiple jets with spent air exiting in one direction are investigated in Hebert et al [23]. The effect of increasing the jet hole diameters and their spacing in the streamwise direction on the local heat transfer distribution for one streamwise row of jets is studied in Uysal et al [24].…”

Narrow impingement channels: recent advancements and future directions

“…The most critical surface for a reliable thermal design of a narrow impingement channel is obviously the target plate since it is located closer to the external hot flow path, and hence, experiences the highest thermal loads. For this reason, although very nice comparisons for all channel interior walls have been obtained in the literature (Uysal et al, 2006;Llucià et al, 2015;Terzis et al, 2015Terzis et al, , 2014a, only the heat transfer characteristics of the target plate will be presented in detail. Figure 6 shows the local Nusselt number distributions at the target plate centerline at different Reynolds numbers for two different channel heights.…”

“…The minimization of Hartsel aerodynamic losses, however, dictates limited usage of external cooling in future turbine systems. For pure impingement studies, the improvements include the use of elongated-elliptical impingement holes (Chambers et al, 2010), varying jet diameters (Uysal et al, 2006;Miller et al, 2013;Terzis et al, 2015) as well as the use of divergent channel geometries (Terzis et al, 2016a). The majority of these modifications, however, can only marginally improve the mean heat transfer levels of the cooling channel, even with rib/pin roughened target plates (Miller et al, 2013;Rao, 2018), and therefore alternatives have to be considered.…”

Analysis of a Coupled Micro- and Triple- Impingement Cooling Configuration in the C3X Vane

“…Research by Uysal investigated the effects of impingement heat transfer with jet arrays relating to the "crossflow" or the convection influence of the upstream jet propagating downstream (Uysal, 2006). This was done by the author while varying the size and hole of the jet configuration.…”