Regarding the effectiveness, Figure shows the results of Peigné et al. for different NTU values, obtained by varying the length of the heat exchanger between 1 m and 30 m, as well as our results for 𝐿 = 1.5 m and 𝐿 = 10 m -in which the 𝑈's used by Peigné et al. are knowncalculated by Eq. ( ) and the solution of Peigné et al. For this case, the NTU is defined as NTU = 2𝜋𝐿 (