Ejection and breakup behaviors of a novel direct contact thermal storage using ejection PCM

To solve the blocking issue of direct contact thermal storage and further improve the heat exchange efficiency, a novel method that ejecting the molten phase change material (PCM) into the heat transfer fluid (HTF) was proposed in this paper. The experiments were carried out to understand the ejection and breakup behaviors of PCM and investigate the feasibility of this concept. Two properties about ejection and breakup, i.e. jet breakup length (L-P) and angle (beta), were discussed. The relationship between operation parameters, including ejection velocity, nozzle size, ejection temperature, and particle diameters were quantificationally analyzed. The results shown that there exist four obvious stages of ejection and breakup behaviors: i) 0-40 mm: an approximate horizontal liquid column with smooth surface; ii) 40-110 mm: a slight curvulate liquid column with unstable and fluctuate surface; iii) 110-210 mm: peel-off and superficial breakage; iv) From 210 mm: deposition of PCM droplets. The two properties L-P and beta shows negative and positive correlation with ejection velocity, respectively. The L-P varies from 72.2 mm to 30.2 mm, the beta varies from 17.5 degrees to 21.0 degrees. However, the correlation between above two properties and nozzle size and also ejection temperature is on the contrary. The diameter of most PCM particle is in the range of 0-8 mm. The higher ejection velocity, smaller nozzle size, and lower ejection temperature results in smaller particle diameters in breakup processes. Compared with the traditional direct contact thermal storage, the novel method can not only solve the blocking issue but also dramatically enlarge heat transfer area by dispersing molten PCM, which can provide an insight of development of new direct contact thermal storage.

Automated summary

A novel method of ejecting molten PCM into HTF was proposed to solve the blocking issue and improve heat exchange efficiency. Four stages of ejection and breakup behaviors were observed, and the relationship between operation parameters and particle diameters was quantificationally analyzed. Higher ejection velocity, smaller nozzle size, and lower ejection temperature lead to smaller particle diameters during breakup processes.