Research PaperHeat transfer scaling analysis of the single-phase natural circulation flow system

- A set of system-level and local heat transfer similarity numbers were proposed.
- The proposed dimensionless numbers can be applied to analyze the heat transfer similarity.
- Three set of scaling criteria for the design of reduced-size thermal systems were proposed.
- The tube inner diameter was found to be related to the length scaling ratio by diR=l¯R0.75.

In this study, the heating power in the heat source or the core decay power is proposed as the reference parameter for the scaling analyses. From the scaling analyses assuming quasi-steady state flow, three system-level dimensionless numbers for the thermal heat transfer were obtained: the dimensionless power rate number, the dimensionless HX heat transfer number, and the dimensionless heat loss number. Based on the three local heat transfer processes, the dimensionless HX heat transfer number is further broken down into three dimensionless local heat transfer numbers: the dimensionless HX tube internal convective heat transfer number, the dimensionless HX tube conductive heat transfer number, and the dimensionless HX tube external convective heat transfer number, with each representing local heat transfer similarity. Analogically, three dimensionless local heat loss numbers were also derived. With the obtained dimensionless numbers, the scaling criteria for exact HX heat transfer similarity were derived. It was found the tube inner diameter should be scaled down in terms of the tube length scaling ratio for exact heat transfer similarity. In addition, three sets of scaling criteria for a full-pressure model, the new scaling criteria (general), the new scaling criteria (ideal), and the new scaling criteria (practical), were proposed.