For the TTHE of this case study -with the modifications described previously -, Figure shows the effectiveness for different ambient air conditions. Figure (B) shows the effectiveness for a hypothetical co-current flow, under the same boundary conditions and capacity rates as in Figure (A). In each case, the effectiveness of a TTHE-A is also shown (see e.g. ) -note that, due to the previous considerations, the results in Fig. (A) cannot be directly compared to those of Peigné et al. . Also, in this case, for NTU greater than about 2.5, the correlation for natural convection used by Peigné et al. is outside the range of validity and, therefore, the results should be considered as an extrapolation.