Experimental Study on Low-Thermal Conductivity Coatings for Rapid Chill-Down of Stainless-Steel Plates in Liquid Nitrogen Pool

Abstract

In this study, the chill-down performance of a metal plate with various surface conditions, including a bare metal surface, a laser-treated surface, and a low-thermal-conductivity (low-k) coated surface, is examined. Among these, the low-k coated surface demonstrated superior chill-down performance, prompting further investigation into rapid chill-down technology utilizing low-k coatings. Additionally, a novel approach involving grid-patterned low-k coatings was proposed and systematically examined. A series of quenching experiments using liquid nitrogen (LN2) on stainless-steel plates were conducted under various surface conditions: bare stainless-steel, fully coated with a low-k material (ETFE), and partially coated with grid patterns. Specifically, surfaces with coating thicknesses ranging from 50 to 200 μm and grid pattern sizes of 2.5, 5, and 10 mm were analyzed to quantitatively assess the effects of low-k coating. Due to the rapid transition from the film boiling to the transition boiling regime, fully coated surfaces achieved a 52–58% reduction in chill-down time compared to bare surfaces. However, the low-k coating layer introduced additional thermal resistance, resulting in reduced thermal performance during the nucleate boiling regime. In contrast, partially coated surfaces with a grid pattern demonstrated superior thermal performance across all boiling regimes. Notably, when the grid pattern size matched the wavelength defined by the Taylor instability, the regime transition was effectively accelerated. Furthermore, as the pattern size approached the capillary length in the nucleate boiling regime, thermal performance significantly improved. Consequently, the chill-down time for the partially coated surface with a grid pattern size of d = 2.5 mm was reduced by 79 %, owing to faster regime transitions and enhanced performance throughout the process. Finally, compared to fully coated surfaces (~2.4), the grid-patterned coatings demonstrated a twofold improvement in coating effectiveness (~4.8). This study provides new guidelines for applying low-k coatings to enhance the chill-down performance of metal plates across all boiling regimes.