Coupled heat transfer analysis of U-type tube module of LNG ambient air vaporizer under dry conditions

Liquefied natural gas (LNG) ambient air vaporizer (AAV) utilizes renewable aerothermal energy from ambient air to regasify LNG, which is usually chosen as the first choice in gas stations. Its gasification efficiency depends on the heat transfer performance of U-type finned tube which is composed of multiple straight finned tubes connected in series by U-bends. This paper developed a two-way coupled heat transfer model of AAV U-type module considering the conjugated interaction between different fluid domains and the phase interactions during the vaporization process of LNG. Experiments were conducted to validate the numerical model, and the results are in good agreement. The coupled heat transfer analysis indicates that mutually interference of the heat transfer process between two adjacent finned tubes in a U-type tube module occurs and gets more obvious as closer to the entrance of LNG. The heat flux of the inner tube surface decreases along the flow direction of LNG on the whole, yet there exists an obvious drop on the inner surface of the U-bend due to lack of fins. Besides, the heat transfer performance of the vertical straight finned tube is superior to U-type tube, and the difference is more obvious with higher LNG velocity.