Category: Transient Plane Source
Author(s): Bjorn Palm, Cke Melinder, Monika Ignatowicz, Willem Mazzotti
Keywords: Denaturing agents, Ethyl alcohol, Ground source heat pump, Secondary fluid, Thermal Conductivity, Transient Plane Source, Transient plane source (TPS) method
Abstract: Ethyl alcohol based secondary heat transfer fluids are typically used in ground source heat pumps (GSHPs) in Sweden because of their attractive thermophysical properties and low toxicity. Denaturing agents must be added to ethyl alcohol based secondary fluids, and in Europe, the most commonly used are: propyl alcohol, n-butyl alcohol, methyl ethyl ketone, and methyl isobutyl ketone. In Sweden, only propyl alcohol and n-butyl alcohol can be used because of their low toxicity compared to ketones. In this paper, the thermophysical properties of 20 wt-% solutions of the four commonly used denaturing agents with bases of ethyl alcohol water were analyzed and compared with two ethyl alcohol reference fluids. A Thermal Constants Analyser measured the thermal conductivity of the 10 ml samples using the Transient Plane Source (TPS) method. Results showed that the thermal conductivity of the samples increased as the temperature of the solutions moved toward 30 °C, but the ethyl alcohol and propyl alcohol solution (EA18 + PA1.6 + BA0.4) had the highest overall performance, and was the only sample that had a higher thermal conductivity than the reference fluids. The solutions with ketone denaturing agents had the lowest thermal conductivities in comparison to the reference fluids, and are the most toxic, which makes propyl alcohol the best choice as an effective denaturing agent.
Reference: 12th IEA Heat Pump Conference (2017) 000-000