When the flow rate or the cooling capacity of the supply air is much lower than the sensible cooling load, the discharge air cannot sustain the downward unidirectional motion due to upward resistance of the buoyant plume from the heat sources located near the floor. In these situations irrespective of the supply airflow rate,the downward air jet can maintain the unidirectional flow up to 55 percent of the distance, and then it spreads sideward as it realizes downstream obstructions such as equipment, workbench, people, and other similar objects located on the floor. Under isothermal conditions when the cooling capacity of the supply air is much higher than the sensible cooling load in the space, such as in cleanrooms with high air change rates, the supply air flow rate (discharge velocity) has a little impact on the directionality of the laminar flow. This study provided valuable insights into the dynamics of laminar flows which can be helpful to architects and HVAC engineers. We performed a CFD study to systematically analyze the impact of supply airflow rate (discharge velocity) on the dynamics of unidirectional airflow under isothermal and non-isothermal conditions. In such situation Computational Fluid Dynamics (CFD) can help predict and optimize the performance of laminar diffusers. There are no easy means to quantify the directionality of laminar flows and entrainment from the surrounding air. Ideally the unidirectional flow should sustain downward motion of the supply air without significant recirculation, mixing, and entrainment from the surrounding air. Laminar flow is required to deliver clean air to a “critical zone” where high level of cleanliness is required. Whereas non-unidirectional, mixing air flows are referred as “turbulent flow”. These air supply outlets (diffusers) are designed to provide unidirectional flow–often referred as “laminar” flow in the HVAC industry. Laminar diffusers are often employed in cleanrooms, hospital operating rooms, laboratories, and similar other spaces where high level of cleanliness is desired.
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