Flow distribution characteristics of parallel narrow rectangular channels under deformation conditions -Part I: An experimental study

Abstract

Plate-type fuel assembly has been a promising option for core miniaturization applications. The parallel coolant channels, characterized by narrow rectangular with a large aspect ratio, may generate flow distribution deviation due to structural deformation. This study is dedicated to a comprehensive investigation of flow distribution characteristics accompanied by fluid boiling at high-pressure conditions in parallel twin narrow rectangular channels. The study will be presented in two parts: Part I of this paper comprises experimental methodology and flow distribution results. The experimental setup includes an integrated parallel channels geometry designed to improve pressure-bearing capabilities. Additionally, experiments are conducted on severe channel deformation modes, such as swelling and bending, by modifying the shape and dimensions of the ceramics within the test apparatus.Based on the experimental data, including pressure difference, wall and main fluid temperatures, the flow and heat transfer performance between twin channels is analyzed. Results shows that a significant deviation in flow distribution occurs in the swelling channel. Then methods involving thermal balance and pressure difference are employed to ascertain the mass flow rate of each distinct channel. The research reveals that the impact range of flow distribution is categorized into single-phase and two-phase control regions. The corresponding flow deviation of swelling channel surges from 5% to approximately 30%, significantly exceeding the design threshold specified for plate-type fuel assembly. Regarding the bending channel, the overall deviation consistently remains within 3%. Even when the fluid transitions into two-phase region, the flow deviation does not enlarge further. Moreover, a lower mass flux and higher heat flux aggravate the uneven flow distribution, while an increase in system pressure alleviates the flow deviation. Furthermore, Part II of this investigation introduces a numerical model derived from the experimental data, and the flow distribution characteristics under various channel deformations are examined through model calculations.