High concentration NH3/H2O is suitable for Kalina cycles used for the recovery of low grade heat. Plate heat exchangers (PHEs) are compact and reduce the charge of working fluid. This work investigates the absorption of NH3/H2O in a PHE, which has a weight concentration of 96%. Being different from normal absorption systems, the concentration difference between vapor and liquid is small, and apparent heat transfer coefficients (HTCs) are used to interpret the phase change process, which assumes that the vapor and liquid are in equilibrium state. The apparent HTCs and frictional pressure drop of NH3/H2O are presented and are compared with those of NH3. The mass transfer resistance has noticeable influences on heat transfer depending on the flow patterns, while the influence on frictional pressure drop is minor.@en