Distribution Map of Multi-Walled Carbon Nanotubes in a Refrigerant/Oil Mixture Within a 2.5 Ton Unitary Air-Conditioner

In recent years, nanoparticles have received considerable attention as a potential additive to heat transfer fluids (i.e. refrigerant) in order to increase the heat transfer capabilities of these fluids. The potential of carbon nanotubes (CNTs) to exit the compressor, migrate throughout a vapor compression air conditioning system, and possibly foul the components of such a system was experimentally investigated in this research. Six grams of CNTs were dispersed in the polyol ester oil used by a 2.5 ton (8.79 kW) unitary air conditioning system, which was continuously operated for 168 hours. After this time, the unit was shut down and dismantled in order to determine if and where the CNTs had migrated, and to discover any possible fouling. Of the six grams (92.6 grains) initially placed into the compressor, only approximately 2.5 grams (38.6 grains) were recovered from inside the compressor, leaving approximately 3.5 grams (54 grains) distributed throughout the system. A portion of the CNTs found in the system were in the process of flowing with the refrigerant, but the majority had become strongly adhered to the interior walls. The location of the heaviest fouling was found in the first 2-3 feet (0.61-0.91m) of each aluminum condenser circuit. The results indicate that the most conducive environment for CNTs to foul the interior tube walls is when the refrigerant is a superheated vapor. When the refrigerant was at or very close to 0% vapor quality, almost no fouling was observed. This work showed conclusively that CNTs will exit a scroll compressor and have high fouling potential when utilized in a standard vapor compression air conditioning system