Abstract
In this paper, detailed flow patterns and heat transfer characteristics of a jet impingement system with extended jet holes are experimentally and numerically studied. The jet holes in the jet plate present an inline array of 16 × 5 rows in the streamwise (i.e., the crossflow direction) and spanwise directions, where the streamwise and spanwise distances between adjacent holes, which are normalized by the jet hole diameter (xn/d and yn/d), are 8 and 5, respectively. The jets impinge onto a smooth target plate with a normalized distance (zn/d) of 3.5 apart from the jet plate. The jet holes are extended by inserting stainless tubes throughout the jet holes and the extended lengths are varied in a range of 1.0d–2.5d, depending on the jet position in the streamwise direction. The experimental data is obtained by using the transient thermochromic liquid crystal (TLC) technique for wide operating jet Reynolds numbers of (1.0 × 104)–(3.0 × 104). The numerical simulations are well-validated using the experimental data and provide further insight into the flow physics within the jet impingement system. Comparisons with a traditional baseline jet impingement scheme show that the extended jet holes generate much higher local heat transfer levels and provide more uniform heat transfer distributions over the target plate, resulting in the highest improvement of approximately 36% in the Nusselt number. Although the extended jet hole configuration requires a higher pumping power to drive the flow through the impingement system, the gain of heat transfer prevails over the penalty of flow losses. At the same pumping power consumption, the extended jet hole design also has more than 10% higher heat transfer than the baseline scheme.
Highlights
Jet impingement cooling is an effective internally enhanced heat transfer technique, which is widely employed at the backsides of a combustor liner and in leading-edge, mid-chord, and endwall regions of turbine vanes and blades in gas turbine engines to thermally protect the hardware from the erosion of hot gases
An experimental and numerical combined study of flow and heat transfer characteristics within an extended jet impingement configuration was conducted in this paper, aiming at improving the jet impingement heat transfer performance under strong crossflow conditions
The experimental measurements were performed by using the transient liquid crystal (TLC) technique for a range of jet Reynolds numbers from 1.0 × 104 to 3.0 × 104, and corresponding numerical simulations were undertaken to provide complementary information of flow physics
Summary
Jet impingement cooling is an effective internally enhanced heat transfer technique, which is widely employed at the backsides of a combustor liner and in leading-edge, mid-chord, and endwall regions of turbine vanes and blades in gas turbine engines to thermally protect the hardware from the erosion of hot gases. The study of Liucià et al [8] showed that the crossflow was increased with the hole number, leading to a rapid drop of heat transfer in the further downstream regions of the target surface, but a slight impact in upstream regions. Gao and Ekkad [16] presented a detailed heat transfer distribution for a linearly stretched impingement jet array, in which the spacing between adjacent holes in both the streamwise and spanwise directions was increased for further downstream rows to reduce the crossflow effects. To balance the heat transfer improvement and pressure drop, Tepe et al [27,28] experimentally and numerically examined a novel impingement concept by extending the jet holes into the crossflow channel based on the work by Esposito et al [20,29]. Where N is the total number of jet holes and ∆p is the pressure drop through the jet impingement configuration from the inlet plenum to the exit of the impingement channel
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