밀폐사이클을 적용한 LNG 연료탱크의 단열 특성연구

Abstract

Recently the LNG(liquefied natural gas) public buses and LNG-fueled container trucks have been introduced to prevent the air pollution in metropolitan areas. As the LNG temperature in fuel tank is as low as -162℃, the thermal and structural effects of tank components need to be studied in order to keep liquid phase as long as possible by reducing heat leakage from outside ambient. The LNG for buses is stored in horizontal tank that is insulated with Mylar sheet and high vacuum between annular space of double-walled tanks. As the stored cryogenic liquid evaporates over 6.0% daily by the present insulation system, more efficient storage tank, that can reduce the evaporation rate, might be newly required.

This research invented new triple tanks, that has middle tank having closed-cycle insulation filled with R134a refrigerant which evaporated by absorbing intake heat from ambient prior to LNG evaporation.

The heat transfer rate and temperature distribution of tank body and support system were evaluated by FLUENT, and the thermal stress and strain were analysed using ANSYS. The results showed that the rate of heat transfer from outer vessel to inner one was reduced significantly compared with the common double tank having super insulation only.

By the experimental evaluation, it showed that the evaporation rate of liquid nitrogen was 2.54% per day, whereas the national approval law for LNG fuel tank regulated the evaporation rate of 6.0% or below.

New developed tank could be highly efficient LNG storage tank for vehicles and would help LNG fuel system safe.