Effect of Tank Orientation and Fill Level on the Thermal Response of Bi-Lobed Type C Tanks for Liquefied CO₂ Transport

Bi-lobed Type C pressure vessels are an attractive cargo-containment option for the marine transport of liquefied carbon dioxide (LCO₂) because they combine the high design pressure of cylindrical Type C tanks with an improved utilization of the prismatic hold volume. Although the structural and sloshing behaviors of such tanks have received considerable attention, their thermal response (heat ingress, boil-off and self-pressurization) has not been thoroughly examined. Furthermore, the influence of tank orientation (vertical versus horizontal) remains unresolved even for conventional cylinders. In this study a bi-lobed Type C tank, derived from a validated single-lobe design through the Senjanović proportioning rule, is analyzed using a two-node lumped-parameter thermal network built in Thermal Desktop 24.2/SINDA/FLUINT, with CO₂ properties supplied by the Span–Wagner equation of state through REFPROP 9.1. The model was verified against the NASA multipurpose hydrogen test bed (MHTB) liquid-hydrogen self-pressurization experiment and against a liquid-CO₂ cargo-tank measurement. Vertical bi-lobed tank (VBT) and horizontal bi-lobed tank (HBT) orientations were then compared at four fill levels ranging from 20% to 90%. The results demonstrate that orientation significantly alters cumulative heat ingress, pressure rise and vapor temperature, with the effect being strongly amplified at low fill levels. The pressure rise is shown to be governed by the onset of boiling, the timing of which is determined by how quickly each orientation warms the liquid to saturation.