[22] models, can be found. This section extends previous studies to limit solutions of a TTHE-HL model. These limit solutions represent classical results from the heat exchanger literature, thus demonstrating the consistency of the present solution and adding significant theoretical content to the work. Two methods will be used to obtain the limit solutions: the traditional method, which uses limit operations and other mathematical techniques (see ), and the use of analogies with TTHE-HL, which is the focus of this work. Using both methods allows for a better understanding of the underlying physics and the analogies used.