Desenvolvimento de materiais intermediários com grafite para intensificar a transferência de calor em sistemas de refrigeração

Abstract

This work aims to develop and experimentally evaluate the thermophysical properties of composite materials in order to apply them as intermediate materials for thermal energy storage in refrigeration systems operating with hydrocarbon refrigerant fluid, specifically in a refrigeration system of liquids. For this, a conductivity meter was used to analyze the properties, an experimental bench was developed for the analysis of heat transfer in these materials and an evaporator was designed to operate with the help of the intermediate material. With the obtained results, it was observed that the addition of graphite in hydrated lime, gypsum and cement composites increased the thermophysical properties, especially the thermal conductivity, which developed by 134 %, 106 % and 16 %, respectively. This increment influenced the efficiency of the heat transfer process and allowed for faster temperature variations. Furthermore, the influence of the amount of water used in the manufacture of the materials was noted, since as drying occurs, voids appear due to water loss. Therefore, the greater the number of pores, the lower the thermal conductivity and diffusivity and the less efficient the heat transfer processes become. Finally, the application of the evaporator containing intermediate material, with graphite, in a refrigeration system of liquids made it possible to replace the refrigerant R-22 with R-290, with reduced load and similar capacity. The discharge temperature of the propane in the compressor was much lower than that observed for the HCFC. And when comparing the average values of active power, the system with the help of the new material obtained a reduction of 40 %, having a direct influence on the electric energy economy consumed by the equipment.