We will use the correlation of Bolles and Fair (1982), for which HTUs are defined in the same way as here. The Bolles-Fair correlation is based on the previous correlation of Cornell et al., (1960a, b) and a data bank of 545 observations and includes distillation, absorption, and stripping. This model and variations on it remain in common use (Wang et al., 2005).
The correlation for HG is
where ψ is a packing parameter that is given in Figure 16-5 (Bolles and Fair, 1982) for common packings, and other special terms are defined in Table 16-2. Viscosity, density, surface tension, and diffusivities ...