“…Flight data recorded for the CMET during a flight in Mexico City [1] measured ambient relative humidities between 0-75%. An injection of water into the cathode inlet can be accounted for by adding the enthalpy input term, H w,in , H w,in =ṁ v,ca,in C p,lw (T ca,in − T o ) + h f g,Tca,in , (25) to the change in enthalpy in the cathode, ∆H w,ca from (19), whereṁ v,ca,in =ṁ a,ca,in M w φ ca,in p sat,Tca,in M a (p ca,in − φ ca,in p sat,Tca,in ,…”