Study of the conductive heat flux from concrete to liquid nitrogen by solving an inverse heat conduction problem

The conductive heat flux from concrete to liquefied natural gas (LNG) is important to evaluate the hazards of LNG spills. In this paper, experiments are conducted to investigate the conductive heat flux from concrete to liquid nitrogen (LN2), which was used as a safe cryogenic analogue to LNG. During experiments, LN2 was spilled onto a concrete block instantly and thermocouples were embedded inside the concrete at different depths to monitor the temperature data during LN2 vaporization. The solution procedure for inverse heat conduction problems is employed to reconstruct the dynamic heat flux profile at concrete surface, using the measured temperature data and concrete thermal properties as inputs. The results indicated that the perfect thermal contact model (PTCM) well matches the calculated heat flux at later stage of spill. While at initial stage the heat flux values are restricted by the vapor cushion caused by vigorous boiling of LN2, which is also responsible for the error distribution trend in data fitting by PTCM. Evaporation rate of LNG is evaluated based on present heat flux results and it is found to be lower than when LNG spilled on water. The results in this paper provide insights for the applicability of PTCM in predicting conductive heat flux from concrete to cryogenic liquids. The results are also expected to improve the source term model involved in hazard evaluation of LNG spills.