Years ago there was a large EPRI study done on cooling tower fill. The two-part report can be obtained online but is rather expensive. While several parties are listed in the report, I personally performed all of the fill calculations, including the ones attributed to the other contractors. You can get some of the subsequent reports for free (e.g., one on the Lewis number). Did you want fill coefficients or need to perform specific calculations? I can give you several software packages and even put together an Excel spreadsheet if you're interested.