Frequent use of crossflow heat exchangers in industries-such as chemical, automotive and refrigeration-has created the need for more complex computational tools so that you can predict even better its thermal performance. Because of that, this work presents different methodologies for calculating effectiveness and other evaluation parameters of thermal performance of crossflow heat exchangers. In Chapter 3 was developed a methodology to simulate twelve configurations of crossflow heat exchangers and to calculate numerically data of thermal performance parameters by the method of effectiveness-number of transfer unit (-NTU) for simple and complex flow arrangements. The accuracy of simulated data has been confirmed by comparison with analytical theoretical relations from literature for crossflow heat exchangers with one to four rows, and for parallel and counter-crossflow arrangements with one to four passes on the in-tube fluid. Based on use of matrix method for calculating  effectiveness, it became possible obtaining theoretical relationships of effectiveness for heat exchangers of industrial use, for example, heat exchangers with Z format configuration. Finally, the methodology studied in Chapter 4 allows to obtain analytical relationships for twelve different general configurations including one-pass cross-flow arrangements with several tube rows (in-tube fluid circuits), and parallel and counter-crossflow arrangements with several passes of internal fluid and several tube rows (in-tube fluid circuits). In all cases, it has obtained quite accurate results in a wide range of values of NTU and C * variables. The proposed procedures are useful research tools for theoretical and experimental studies on the thermal performance of crossflow heat exchangers. Besides calculation of effectiveness, studied computational procedures make it possible to obtain the correction factor F of mean logarithmic temperature difference method, as well as performance parameters related to entropy generation and a new concept of heat exchanger efficiency.