New integral-mean temperature difference model for thermal design and simulation of parallel three-fluid heat exchanger

As we know, the mean temperature difference approach perfectly solves the problem of thermal design of a two-fluid heat exchanger. However, so far, the equivalent method has not been found for that of three-fluid heat exchanger. In this paper, a mean temperature difference method called IMTD (integral-mean temperature difference) is developed in detail for a parallel stream three-fluid heat exchanger with two communications. It includes the derivation of IMTD formulae, the illustration of design and simulation procedures of IMTD thermal model, the corresponding exemplary calculations and discussion, and the validation of IMTD thermal model. The research shows that the derived IMTD formulae and accelerated method proposed in the present IMTD model significantly improve the design process in the past analytical models. It realizes a fast convergence which is usually within 10 steps for all parallel stream flow arrangements. Moreover, the present model has the same accuracy as past exact analytical models and simultaneously can be comparable to past approximate analytical models in simplicity.

► The formulae equivalent to the two-fluid’s LMTD is derived for three-fluid exchanger. ► New integral-mean temperature difference model is developed for three-fluid heat exchanger. ► New model realizes fast convergence in the design procedure that is usually within 10 steps.