温度成層型水蓄熱槽の鉛直流出入ディフューザにおける空気混入限界の検討

摘要

Synopsis : A water thermal energy storage (TES) system is used to cut down heating and cooling cost during daytime. In the temperature-stratified water TES tank, a diffuser was used as an inlet/outlet for mixing restraint of water in tank. The upper diffuser in the water tank sucks water near the surface in the storage mode of chilled water, and may entrain air near the water surface. In addition, water could not flow through the pipe system smoothly under air-mixing condition. This study aimed to show a limit condition of air mixing of inlet/outlet diffuser in the water TES tank and to design a procedure on the safe side. A theoretical study was conducted using a dam hydraulics theory. The prediction accuracy of a theoretical limit condition derived from the dam theory was verified through unsteady two- and three-dimensional analysis of computational fluid dynamics. It was found that the theoretical limit condition was predicted with good precision.%温度成層型水蓄熱槽の運転において水面近くに設置されたディフューザでの空気混入を防ぐことは非常に重要な課題である。本研究では，蓄熱運転時に吸い込み側となる水面付近に設置されたディフューザにおける空気混入発生条件を理論的に導出し，二次元及び三次元の混相流CFD解析を用いて理論予測式の検証を行った。その解析結果を元に，実際に鉛直流出入ディフューザを有する温度成層型水蓄熱槽を設計する際のディフューザ設置水深と流量の関係についての検討を行った。これらの結果，理論的に求めた空気混入限界がある程度の精度を持つことが示され，安全側で設計を行う際の条件が明らかになった。