Characteristics of low reynolds number steady air jet impingement heat transfer over vertical flat surfaces

Abstract

In this paper, heat transfer characteristics of single-slot steady-impinging air jets on a 25.4 mm × 25.4 mm vertical surface were experimentally investigated. The experiments were conducted with four different nozzles (length × width: 4 mm × 1 mm, 8 mm × 1 mm, 12 mm × 1 mm, and 15 mm × 1 mm). The parameters varied in the testing were Reynolds number (Re) (100 - 2,000) and dimensionless nozzle-to-plate spacing (H/Dh = 5, 10, 15, and 20). Correlations for average Nusselt numbers (Nu) were developed that accurately predict experimental data. The heat transfer coefficient over a vertical surface increases with increasing Re. For a small nozzle-to-plate spacing (H/Dh = 5), the average Nu correlation is not only a function of Re but also a function of nozzle length. For large nozzle-to-plate spacing (H/Dh ≥ 10) and nozzle length larger than 8 mm, the heat transfer coefficient is insensitive to H/Dh and nozzle length. A subset of this data was then compared to synthetic jet data in a separate study.