The thermal analysis performance of evaporative fluid coolers (EFCs) is improved by replacing plain tubes by twisted oblong tubes. Results of the system are assessed by a rapid design algorithm (RDA) and compared to conventional plain-tube EFCs and other traditional algorithms including the effectiveness number of transfer units (e-NTU). Based on the RDA, a relationship between heat transfer coefficients, pressure drops, heat transfer area, and mass transfer coefficient is derived. Using the maximum allowable pressure drops in this algorithm, the minimum required heat transfer area can be determined. The algorithm is validated by comparing the plain-tube EFC design with twisted-tube design. The RDA-designed EFCs with twisted tubes provide higher efficiency compared with the traditional designs with plain tubes in such that the new design needs a lower heat transfer area for a given heat load.