Air mixing criteria for ceiling slot-ventilated agricultural enclosures

Yu, Hsin
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The use of a scale-model is an effective technique to predict the performance of ventilation in full-scale prototypes. Many criteria have been proposed to simulate the behavior of airflow between scale-model and prototype. Because of the inconsistent results of past proposed similarity criteria, more validation work is needed to clarify the conflicts;Dimensional analysis using both the Buckingham Pi method and manipulating the governing differential equations was used to theoretically establish similarity parameters. Only partial similarity was reached since conflicts exist between proposed similarity parameters;Experiments of two scale models were conducted to study airflow similarity in ceiling slot-ventilated agricultural enclosures using different similarity criteria. The evaluation of similarity between scale-model and prototype included validation of penetration distance, airflow pattern, airspeed field, and temperature field using methods that included smoke visualization, airspeed field measurement, and temperature field measurement;The studies focused on the Reynolds number (Re) and inlet jet momentum ratio (Rm) as the similitude criteria for isothermal airflow, and Archimedes number (Ar) for nonisothermal airflow. The experimental results offer better agreement using Rm than using Re as the similitude criterion for isothermal airflow. Ar is an appropriate similitude criterion when the nonisothermal airflow pattern exhibits two-circulation airflow behavior. After the airflow is increased resulting in a single-circulation airflow, Rm associated with a similar heat load becomes the better similitude criteria;Future studies including improvement of the evaluation method, more complete investigation of the enclosure, variation of scale dimension and configuration layout, and better control of the experimental environment are recommended.

Agricultural and biosystems engineering, Agricultural engineering