Characterization of heat transfer and pressure drop in condensation processes within mini-channel tubes with last generation of refrigerant fluids

Resumen

Heat exchanger developments are driven by energetic efficiency increase and emission reduction. To reach the standards new system are required based on mini-channels. Mini-channels can be described as tubes with one or more ports extruded in aluminium with hydraulic diameter are in the range of 0.2 to 3 mm. Its use in refrigeration systems for some years ago is a reality thanks to the human ability to made micro-scale systems. Some heat exchanger enterprises have some models developed specially for their use in automotive sector, cooling sector, and industrial refrigeration without having a deep knowledge of how these reduced geometries affect the most important parameters such as pressure drop and the heat transfer coefficient. To respond to this objective, an exhaustive literature review of the last two decades has been performed to determinate the state of the research. Between all the publications, several models have been selected to check the predicting capacities of them because most of them were developed for single port mini-channel tubes. Experimental measurements of heat transfer coefficient and frictional pressure drop were recorded in an experimental installation built on purpose at the Technical University of Cartagena. Multiple variables are recorded in this installation in order to calculate local heat transfer coefficient in two-phase condensing flow within mini-channels. Both pressure drop and heat transfer coefficient experimental measurements are compared to the previously mentioned models. Most of them capture the trend correctly but others fail predicting experimental data. These differences can be explained by the experimental parameters considered during the models development. In some cases the models found in the literature were developed specific conditions, consequently their predicting capacities are restricted. As main contributions, this thesis provides new modelling tools for mini-channels condensing pressure drop and heat transfer coefficient calculation. A comparison of a recently developed refrigerant is also given in this thesis. http://repositorio.bib.upct.es/dspace/