Experimental investigation on heat transfer characteristics in the LNG intermediate fluid vaporizer

A supercritical nitrogen regasification system is designed and established to simulate and experimentally study the flow and heat transfer characteristics of the liquefied natural gas (LNG) intermediate fluid vaporizer (IFV), in which nitrogen is vaporized by the intermediate fluid condensed outside the tube. With the drastic temperature and wall subcooling variations along the tube, the influences of the condensation parameters on the regasification performance of the supercritical cryogenic fluid are analyzed. The condensation saturation temperature of the intermediate fluids is in the range of −17∼-2 °C, with the maximum wall subcooling of 60 °C. Compared with the propane and R134a systems, the system with propylene as the intermediate fluid shows the highest regasification capacity. It is found that the influence of supercritical nitrogen flowrate on nitrogen temperature rise is mainly shown near the tube inlet, while that of the saturation temperature (Tsat) is displayed in the rear section of the tube. Furthermore, a low-finned tube is applied to improve the regasification performance, especially for the temperature rise rate near the tube inlet. The enhancement ratio of the low-finned tube increases with the increase of wall subcooling and changes with the saturation temperature, reaching a peak at around Tsat = −10 °C. In addition, a new semi-empirical correlation is developed for the heat transfer of supercritical nitrogen inside the tubes. It agrees well with the experimental data, with 94 % of the predictions within 20 % error.