The Design of an Experimental Model for the 3D Characterization of Airflow in Counterflow Cooling Towers

Abstract

The complexities and inherent 3D nature of airflow within cooling towers is often neglected in cooling tower analysis, and studies that attempt to investigate such air flow patterns are generally invalidated with regard to the 3D flows they attempt to simulate. This work outlines the design and construction of a lab-scale cooling tower model intended to collect airflow data in 3D for the purpose of investigating the complex flows generated by different features and components, both individually and collectively. Further, this lab-scale model is also capable of thermal and static pressure loss measurements traditionally utilized in 0D and 1D characterization of fill and other cooling tower components. The data presented in this work focuses on the model’s 3D airflow capabilities. A manually positioned pitot tube was used to measure the velocity and static pressure in 25-point arrays at a variety of cross-sections throughout the model cooling tower. These velocity and pressure maps were measured and plotted for the case of an empty tower including no fill, drift eliminator, nozzle, or water. Similar maps were plotted for the case of a full tower including fill, drift eliminator, and nozzle, but no water. In this same dry full-tower configuration, a 25-point pitot tube traverse was also performed across the two inlet faces to reveal the normal velocity and pressure profiles for the inflowing air. Traverse measurements of velocity and pressure were used to measure the static pressure drop across the fill for a variety of air flow rates and fill heights. Relationships for fill losses were established, but varied from those reported by the manufacturer. Similar tests performed with the fill further away from the inlet yielded different pressure drop results across the fill, indicating that the interaction of various airflow-altering components is significant when the components are in close proximity. The static pressure drop across the drift eliminator was also measured, both in standard full-tower configuration and in an arrangement with fill above and below the drift eliminator so as to prevent the local recirculation evident above it in other configurations. Pressure drop measurements throughout the tower were collected under wet conditions using a static tap method rather than the pitot traverse, yielding a similar disagreement with manufacturer data as observed for the dry case. Velocity and pressure maps were plotted above the drift eliminator, illustrating the velocity profile in the plenum chamber.