A preliminary investigation comparing the use of biochar powder coatings to standard materials for heat and mass transfer surfaces in evaporative coolers

Recently, evaporative cooling systems have gained importance thanks to the study and development of the Maisotsenko cycle, which adopt an innovative indirect evaporative cooling strategy. This technology allows lowering the theoretical outlet temperature limit to the dew point temperature of the inlet air, thus increasing its wet bulb effectiveness, giving a second chance to the diffusion of indirect evaporative coolers (IEC) often penalized by poor performance in relation to their higher complexity and cost. The Maisotsenko cycle improves the performance of the IECs by pre-cooling the working flow. This is achieved by diverting a portion of air from the primary channel at its outlet and reintroducing it, cooler, into the wet secondary channel. To obtain the best performance the Maisotsenko cycle requires special attention to the wet channel where water evaporation occurs. Many studies have tested different materials and coatings to absorb and distribute water as evenly as possible over the entire heat and mass exchange surface. The most common choices are waterproof aluminum walls and coatings made of organic fibers or fabrics. However, this study aims to investigate a coating made of biochar powder glued onto an aluminum sheet by means of a layer of epoxy resin. Biochar is a high carbon content material and is produced through thermochemical process of biomass. It is characterized by high stability, porosity, and a large specific surface area. Although traditionally used as a soil amendment in agriculture, it is now being investigated for various other applications. In this work, the promising results of initial tests to assess the feasibility of using biochar in evaporative cooling are presented.