Abstract
BackgroundThis study investigates the impact of jet impingement cooling with varying nozzle lengths on the heat transfer performance of smooth and conical pinned target surfaces under turbulent flow conditions. The study focuses on the Reynolds numbers (Re) of 13,000, 26,000, and 39,000, using the liquid crystal thermography (TLC) method to collect experimental data. The dimensionless conical pin heights (Hc/d = 0.00, 0.67, 1.00, 1.33) and target surface-nozzle distances (G/d = 1.0, 2.0, 3.0, 6.0) were analyzed to understand their effects on heat transfer. MethodsThe experimental setup involved measuring Nu numbers and pressure losses in models with elongated nozzles and conical pins. The study examined how the interaction between pin heights and nozzle lengths influences heat transfer in a channel-confined impinging jet flow. The analysis included evaluating heat transfer performance in different jet regions and assessing pressure loss coefficients for various configurations. Significant FindingsResults indicated that for smooth target surfaces, elongated nozzles increased heat transfer in the first two jet regions but decreased it in the last jet regions due to cross-flow effects. In contrast, conical pinned surfaces showed a significant increase in heat transfer, particularly in the stagnation and last jet regions, with lower G/d and higher Hc/d values. Conical pinned surfaces enhanced overall heat transfer by at least 5 % compared to smooth surfaces, with a maximum Nu number increase of 21.87 %. However, configurations with G/d < 2.0 and Hc/d ≤ 0.67 negatively impacted heat transfer. Pressure loss analysis revealed that using conical pins and extended jets together increased pressure loss, with a maximum drop of 5.67 kPa at Re = 39,000. The Thermal Performance Criterion (TPC) ranged from a minimum of 0.97 at Re = 26,000 (G/d = 1.0, Hc/d = 1.00) to a maximum of 1.18 at Re = 26,000 (G/d = 6.0, Hc/d = 1.33).
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