The potential HVAC&R applications of nanofluids

Starting from their discovery (Choi and Eastman, 1995), several studies have been published on nanofluids in the literature. In particular, their promising enhanced thermal, rheological and tribological properties have been deeply considered, often supplying contradictory results. Strong enhancements in thermal conductivity and heat transfer coefficients are not always found, depending on the nanoparticles dispersed in the base fluid, their concentration, the method of preparation, the suspension stability and the presence of dispersants. For this reason, it should be fundamental to have a good characterization of the considered nanofluid before any experiments on it. In the last years, several applications have been proposed for nanofluids in the heating, ventilating, air conditioning and refrigeration (HVAC&R) field. They should be applied both as primary or secondary fluids, obtaining better plants performances. In the first case, nanoparticles are directly dispersed in the refrigerants. In the second case, they should by employed as thermal vectors in commercial refrigeration, chiller or solar panels. They should be used also as nanolubricants, improving thermal dissipation, anti-wear and extreme pressure properties as compressors lubricants. In this paper, the results obtained in the last years by the laboratory of nanofluids at the Istituto per le Tecnologie della Costruzione are presented, together with the last studied HVAC&R applications published in the literature.