The Role of Vorticity on Induction Ratio in Active Chilled Beam Systems

• Vorticity-based analysis to understand the physics of flows in chilled beams • Induction ratio (IR) is insensitive to inlet velocity under fixed nozzle geometry • Reducing nozzle radius increases IR by enhancing vorticity generation at the nozzle • Increasing nozzle distance increases IR by delaying interference of adjacent jets Active chilled beam (ACB) systems offer significant energy efficiency advantages in building HVAC applications, but their performance optimization has been limited by empirical design approaches. These approaches ignore the underlying physics and cannot explain how various design parameters affect induction performance. To address this research gap, a parametric study of nozzle geometry is performed to understand the physical mechanism of induction potential in ACB systems. Using validated computational fluid dynamics simulations, a comprehensive analysis was conducted to identify the fluid dynamic processes governing geometry-performance relationships. The investigation reveals that ACB induction performance is governed by two distinct physical mechanisms operating at different stages of jet development. The first mechanism involves enhanced vorticity generation at the nozzle outlet, where smaller nozzle radii (2.0-8.0 mm) concentrate momentum flux to create intense shear layers, resulting in performance improvements up to 464%. The second mechanism operates through delayed jet interaction, where larger nozzle spacing (20.1-78.9 mm) preserves individual jet entrainment by preventing premature interference, yielding performance enhancements of 131%. In contrast, nozzle length (8-44 mm) exhibits minimal influence on induction performance, with only 7.4% variation, affecting neither vorticity generation intensity nor jet interaction distance. Detailed vorticity field analysis quantitatively validates these mechanisms. The performance gain from reducing nozzle radius is driven by the peak normalized vorticity generated at the nozzle. The performance gain from increasing nozzle spacing is driven by the jet interaction distance downstream. The mechanistic understanding provides physics-based design principles for developing more effective ACB systems, complementing traditional empirical optimization.