The advance builds on past NIST research designed to optimize mixtures of chiller refrigerants with lubricants. The researchers discovered that some lubricants, when injected in small amounts, can significantly enhance evaporator heat transfer, increasing the efficiency of chillers. When they studied the process more closely they found the most efficient heat transfer occurred when the added oil's surface tension, viscosity, composition and chemical characteristics complemented those of the chiller's base lubricant.
In a recent paper* describing the method, Kedzierski describes how the right additive forms a very thin covering on an evaporator surface, which produces enhanced bubbling during boiling. The improved conversion of the refrigerant molecules into vapor molecules increases the chiller's cooling capacity similar to a heat pump.