Influence of Different Surface Treatments on the Heat Flux From Solids to Liquid Nitrogen

In this work, a quasi-stationary procedure has been applied to analyze the heat flux from copper samples to liquid nitrogen (LN₂). The purpose is to quantify the influence of the surface treatment on the heat flux. Copper samples with different surface roughness as well as copper samples whose surface had been previously laminated with commercially available Kapton (lamination or self-adhesive tape) have been tested. The experimental procedure consisted in cooling down the copper samples in a liquid nitrogen bath from room temperature to 77.3 K (boiling temperature of LN₂ at atmospheric pressure). During the cool-down, the temperature has been measured and recorded. From the measured temperature data, the heat flux and the boiling curve were calculated for each copper sample. According to the experimental results, the surface roughness does not have a general influence on the cooling behavior. Regarding the laminated samples, results show a significant change in the boiling curve. In this case the cooling capability in LN₂ is therefore enhanced. This behavior is due to the low thermal-conductivity of the lamination material. Indeed, that leads to a small temperature difference between the lamination and the coolant.