Enhancing pipe chilldown with axial grooves filled with silicone sealant

•A method to enhance the flow boiling heat transfer of liquid nitrogen using a surface texture composed of longitudinal grooves filled with a low thermal conductivity sealant is proposed and evaluated in this study.•The proposed method was validated through pool boiling and flow boiling experiments.•The results showed that the proposed method significantly improved the boiling heat transfer and shortened the chilldown time.•The proposed method reduced the consumption of liquid nitrogen to cool the pipe and was valid for tank pressures of 50, 100, and 150 kPa. This study proposes a method to accelerate the chilldown process in pipes using liquid nitrogen flow. Axial grooves were machined along the inner surface of the pipe and then filled with silicone sealant. This approach achieves a shorter chilldown time compared to previously proposed methods. Initial experiments involving pool boiling in liquid nitrogen were conducted to determine the optimal groove width and the ratio of groove-to-sealant area. The shortest chilldown time in pool boiling was achieved when the groove pitch was close to the capillary length. The effect of the copper-to-silicone sealant area ratio on the chilldown process was minimal. The shortest chilldown time was achieved with a surface that had a 2 mm pitch and a copper-to-silicone sealant area ratio of 0.25. The chilldown time was 1/4.4 of that of the bare surface. Pipes with different pitch and groove widths were tested in a flow chilldown experiment. Using the surface texture, the chilldown time of a stainless-steel pipe with an outer diameter of 1/2″ and a length of 120 mm from room temperature to the saturation temperature was reduced to a maximum of 1/3.6. The shortest cooling time is obtained at a groove pitch of 2 mm. In addition to the shorter cooling time, the amount of liquid nitrogen required for chilldown was also reduced.