The Merkel equation revisited: A novel method to compute the packed height of a cooling tower

In this work, a new methodology of analysis and computation is presented which simplifies calculation of the packed height in a counter current cooling tower, especially for design and cost optimization studies. An algorithm is presented with an implementation in MATLAB to compute the thermodynamic minimum air flow rate for the desired cooling. Combining the Merkel equation and a standard empirical mass transfer correlation, the packed height is shown to be independent of the water flow rate and tower diameter, and dependent only on the excess air flow. The relationship is unique for a given cooling range of water and inlet air wet bulb temperature. A simple power law regression is used to approximate this relationship and results are presented for Vertical Corrugated Packing.

► A relationship between packed height and excess air flow rate is derived.
► The relationship is independent of tower diameter and water flow rate.
► It is well approximated by a power law curve for industrially relevant cases.
► An algorithm to compute the thermodynamic minimum air flow rate is detailed.
► Computation of the packed height is simplified especially for design-optimization.