What lies between a free adiabatic expansion and a quasi-static one?
  An expression is found that relates the initial and final volumes and temperatures for any adiabatic process. It is given in terms of a parameter r that smoothly interpolates between a free adiabatic expansion (r = 0) and a quasi-static one (r = 1). The parameter has to be evaluated numerically, but an approximate expression is given. 
E. N. Miranda
physics.gen-ph