Study on the similarity criterions for trans-critical flow and heat transfer of methane and nitrogen in PCHE

With the increasing use of liquefied natural gas (LNG), the printed circuit heat exchangers (PCHE) for LNG vaporizer has attracted more attention. Due to the flammable and explosive characteristics of natural gas, nitrogen was usually replacing natural gas for experiments. In this work, the similarity criterions of nitrogen and natural gas trans-critical flow and heat transfer were studied with numerical simulation. Firstly, the similarity analysis of the physical properties of methane and nitrogen was carried out, and the boundary conditions for similar conditions were selected. Then, the similar characteristics of the two working fluids were analyzed and the results showed that the local heat transfer coefficient and pressure drop along the channel of methane and nitrogen have a high consistency under the similar conditions. On this basis, the correlation of Nusselt number and Fanning friction factor was established based on nitrogen data, and parameters of methane were calculated and verified. The results showed that the calculating error of the Nusselt number and Fanning friction factor were less than 7 % and 10 % respectively. Finally, the similarity criterions of flow and heat transfer was established, which can provide guidance for nitrogen replace natural gas for trans-critical flow and heat transfer experiment.