The main objective of this article is to present a new and practical correlation associating the effectiveness (epsilon) with its number of transfer unit (NTU) and vice versa of the humidification process. This correlation is featured by its simplicity in use and has non-iterative procedure to implement as the traditional published correlations in the literature. The new correlation can predict the thermal performance/design of the humidifier at different Lewis numbers (both unit and non-unit) with a reasonable accuracy. General integral equation, which is similar to that of Merkel equation, is developed and used in the present humidifier simulation model. The validity of the new correlations was tested against the available experimental and numerical data reported in literature for an industrial air humidifier. In addition, the comparison was conducted with the traditional numerical model at different Lewis numbers. The simulated results of the present correlation show a good agreement with those obtained from the experimental work within 10% accuracy. The main benefits of this new correlation are: (1) its simplicity to be implemented through simple calculations of input parameters and (2) it provides helpful guidelines for developing of humidification-dehumidification HDH desalination cycle simulation program. (C) 2016 Elsevier B.V. All rights reserved.