Exo-reversible staging of coolers in series and in parallel

Serial and parallel staging of exo-reversible coolers are formulated, analyzed and compared. The parallel staging includes an extensive parameter which is the proportion of combined stages. This extensive free parameter affects the intensive factors of specific power and figure of merit. Serial staging reduces the 1st Law efficiency and parallel staging improves the 2nd Law efficiency. Comparison of a parallel with a serial staging under common cooling capacity and cooling range, shows that it is always possible to find a parallel arrangement of lower specific power and more compact. Some results are demonstrated on staging of Joule-Thomson cryocoolers (below and above the Joule-Thomson inversion temperature).