In the present work a critical analysis about the
liquefaction technology research for medium and small scale
systems and transport ones is presented. In particular small
scale liquefaction systems are investigated. The thermal-fluid
dynamics of the liquid hydrogen flowing inside the transport pipelines is studied and the physical phenomena associated
with fluid flow and conductive-convective heat transfer are
discussed. Open issues such as external thermal load, boil-off and pumping power are discussed too.