Cooling storage performance of a novel phase change material nano-emulsion for room air-conditioning in a self-designed pilot thermal storage unit

Abstract

The dynamic stability of phase change material (PCM) emulsions is a crucial factor for their practical applications. So far most previous studies on PCM emulsions have been focused on the static stability in the laboratory and cooling performance in small scale systems, but few or none on the dynamic stability and cooling performance in pilot- or larger-scale systems. This study was to evaluate the dynamic stability or service life and cooling storage performance of a novel PCM nano-emulsion for room air-conditioning application in a self-designed, pilot-scale latent heat thermal energy storage unit. The pilot unit was constructed with a chiller, a storage tank, three sets of ceiling panels, circulation pumps and flow control valves in a pipeline. The PCM nano-emulsion remained stable through 45 repeated charging and discharging cycles over a period of 70 days in the pilot unit and could be well regenerated for even longer period of operation. The PCM nano-emulsion retained a stable cooling capacity, e.g. with a discharging rate of 199.6 W in the 1st-5th cycles and 196.9 W in the 35th-40th cycles at a given flow rate. The droplet size increased to a maximum of ∼180 nm but was still small compared with many of the previously published ranges. Therefore, it is expected that the novel PCM nano-emulsion can have a long service life. Moreover, its volumetric thermal storage capacity was about 1.45 times higher than water in the range of 5.5–20 °C, with the highest average charging rate of about 1.4 kW during the phase transition process, and a high efficiency of ∼85% in the cooling energy release with no limitation by fast discharging flow rate, which make it favourable for practical situations.