The Relationship Between Critical Velocity Of Superfluid Helium And The Pipe

Fluid flow process is an interaction process between fluid and carrier (such as a pipe or metal lattice), the performance characteristics of fluid flow process(such as viscocity or superfluidity), has a relationship with the interaction characteristics between fluid and environment.And the change of flow characteristics associated with not onlv the fluid it’s own characteristics but also the change of interaction characteristcis between fluid and environment.Viscocity is determined by characteristics of fluid and carrier as well as thermodynamic factors.a process that a fluid turn into superfluid and loss it’s viscocity must also be the result of changes of all these factors.Landau superfluid theory and BCS superconductive theory are discussed by the fluid’s own elementary excitation energy spectrum,it predicated wether a fluid has superfluidity with Landau superfluid cretorion.However,these theories are based on the fluid’s own elementary excitation energy spectum.it can’t reflect all the characteristics of the carrier.So that these theories are hard to reflect the relationships between the change of fluid characeristics and all carrier factors,so they can’t study differences of superfluid with various carriers(such as the differences of superconductor with different components and structures)This article begains with analysis of energy conversion in interaction system.and then analyzes the factors influencing fluid characteristics in a fluid flow process.The result shows that the conversion of fluid’s kenetic energy has relationships with the physical characteristics of fluid and carrier.and thermodynamics factors.In condition of low excited state.it has relationships with characteristics of elementary excitation energy spectrum inside fluid and carrier or a combination of fluid and carrier.Therefore.this article explains the elementary excitation energy spectrum in Landau superfluid creterion as elementary excitation energy spectrum inside fluid and carrier or a system combinating fluid and carrier.At the end.this article discussed factors influencing suface state of carrier(capillary),and phenomenologically gave some forms of elementary excitation energy spectrum of the inner suface of capillary,which reflected the inner diameter of capillary. And discussed how it affects the critical velocity of superfluid.