ConclusionsThe different empirical correlations tested in this work givesimilar results, specially the Moisseytsev correlation and the corre-lation developed by Gnielinski. CFD simulations for the LTR and theprecooler demonstrate that the three correlations give good results,being the Gnielinski correlation the most approximated to the sim-ulations. Hesselgreaves et al. [12] deduced that Dittus–Boelter is notthe best correlation for compact heat exchangers, as it is confirmedin these simulations. The Moisseytsev correlation was obtainedfor a case where the CO2is at different conditions of pressureand temperature. However, the results obtained are approximated,although they could not very considered appropriate.The ratio of total heat load to volume of the PCHE is not con-stant but it depends on the fluids involved in the heat exchangerand the thermal approach. These ratios have been compared withreported values from other authors, finding a good agreement. Theexception is the LM heat exchanger, which is proposed as a newheat exchanger and is still in development.