The following PhD thesis has been carried out in the Institute for Energy Engineering of Universitat Politècnica de València and during a stay at at the National Institute of Standards and Technology (NIST). The main objective of this thesis is to develop a high accuracy model for microchannel heat exchangers (MCHX), which has to be useful for designing purposes in terms of computational cost.
In the author’s opinion, there are some drawbacks when existing models are applied to some recent designs of heat exchanger such as serpentine and parallel tubes MCHXs. Thus, the first stage of thesis identifies the phenomena that have the largest effect on the accuracy of a MCHX model. It was also evaluated the degree of accomplishment of some classical assumptions and approaches. To this end, the high accuracy model Fin2D was developed as a tool to carry out the mentioned research.
Fin2D model is a useful tool to analyze phenomena that takes place but requires a large computational cost; not being feasible for design purposes. Therefore, based on the knowledge acquired with Fin2D, a new model was developed: Fin1Dx3 model. This model only accounts for the most important phenomena preserving nearly the same accuracy as Fin2D but with a reduction of one order of magnitude in the required simulation time. It introduces a novel discretization and a unique numerical scheme for modeling the air-side heat transfer. This novel approach allows modeling consistently existing phenomena with great accuracy and with much less simplifying assumptions than current models of literature. Furthermore, it achieves a reasonable computational cost for the objective set. The thesis includes the experimental validation of this model for both a condenser and a gas cooler.
With the aim to present Fin1Dx3 model as a suitable design tool for MCHX, it has been compared in terms of accuracy and computational cost against Fin2D model, simplifications of the Fin1Dx3 model and other representative models from literature.
Finally, as application of the proposed model for design purposes a set of numerical studies were carried out. The studies are about the influence of some design parameters on the MCHX’s performance. The importance of these studies is that they cannot be carried out by a model that do not take into account the phenomena modeled by Fin1Dx3.