Analytical predictions of cryogen storage in open and closed tanks

Abstract

• Storage dynamics of cryogen in a closed tank subjected to external heat leak. • An analytical model predicts the rise in pressure and vapour space temperature. • Comparison of characteristics of storing cryogen in a closed and open tank. • Parametric study relating the effects of heat leak rate and initial ullage volume. • Storage of cryogens in cylindrical and spherical tanks in open and closed states. The manuscript elaborates a new analytical approach illustrating the dynamic pressure and temperature variations of stored cryogen in a closed tank subjected to external heat input (also known as ‘ self-pressurization ’). The proposed method follows a proven formalism adopted for predicting the evaporation of cryogenic liquid in an open tank (often termed isobaric storing). While the new mathematical model for ‘self-pressurization’ has been validated with other researchers’ available experimental data, the ‘ open ’ storage performance analyses are verified with the in-house test results. The parametric studies involving external heat ingress, ullage space, and the geometrical tank shapes (spherical and cylindrical) reveal the essential features of storing (considering liquid hydrogen as the cryogen), highlighting the similarities and dissimilarities of the two storage options. Although the expressions for the ullage space temperatures of a ‘ closed ’ and ‘ open ’ tank are similar, the actual variations differ in two fundamentally dissimilar storage systems. The average temperature rise of the ullage space vapour in a closed tank reaches a maximum before falling in contrast to a monotonic increase of the same in an open tank. Under identical circumstances, storage performance in the spherical tank, both open and closed, is better than a cylindrical one.