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# Fluid flow and thermal analysis in induced draft cooling towers

• Author / Creator
Prashanth Karupothula
• Cooling towers are heat rejection devices that utilize ambient air to cool hot water. The ambient air is drawn into the tower and brought into direct contact with hot water and where the heat and vapour get transferred. Fluid flow distribution in the tower can result in better thermal performance. However, the complex nature of airflow in the tower is often neglected in cooling tower analysis that has relied chiefly on simplified 1D models using semi-empirical equations. 2D numerical models were proposed, but these models use semi-empirical equations to simplify the evaporative process in the fill. A detailed analysis of the fluid flow in the tower and the effect of the fill on the fluid flow is studied. The current study is aimed at understanding the fluid flow distribution in the tower for different fill arrangements.\\\\ \\noindent A numerical model developed in an in-house open-source software, namely Fuel Cell Simulation Toolbox (OpenFCST), is used to solve the Reynolds Averaged Navier-Stokes (RANS) equations with an algebraic turbulence model for closure. Simulations were performed considering the domain on a fill testing facility built in the ESDLab. The fluid flow distribution was obtained for an empty tower both in 2D and 3D. The obtained pressure drop in the empty cooling tower was compared against experimental data. Ansys software was utilized to estimate the fluid flow distribution with the $k-\\epsilon$ turbulence model. The algebraic turbulence model shows a good agreement with the experimental data. \\\\ \\noindent The fill in the tower is considered as a porous media using the Darcy-Forchheimer equation. The fill permeability value is estimated based on the available experimental data, which is then utilized to estimate the pressure drop in the tower. Parametric studies were performed with different fill heights and locations to assess their effect on the fluid flow distribution in the tower. The obtained fluid flow distribution is utilized to estimate the heat and mass transfer distribution inside the cooling tower. The fill location in the tower does not affect the overall pressure drop in the tower.\\\\ \\noindent The advection-diffusion equations were employed to solve for heat and mass distribution in the tower. Transfer coefficients estimated based on the test facility predict the temperature and mass fraction in the ESDLab cooling tower. The outlet air temperature and mass fraction increase with fill height and decrease with air flowrate in the ESDLab cooling tower.\\\\ \\noindent The current numerical model is used to estimate the fluid flow and temperature and mass fraction distribution in an industrial-scale cooling tower and a cross-flow cooling tower. The industrial-scale cooling tower has similar observations as that of the ESDLab test facility, except the inlet effects are lower due to the tower's larger dimension. \\\\

• Subjects / Keywords
Fall 2021
• Type of Item
Thesis
• Degree
Master of Science
• DOI
https://doi.org/10.7939/r3-wwr7-8320