Adsorption heat transformer with zeolite-water working pair has been proposed to directly generate high-temperature superheated steam from unsaturated hot water. A concept of direct-contact method between adsorbent and working fluid is adopted in order to enhance heat transfer inside the packed bed with porous adsorbent. Steam generation process is modeled to investigate dynamic behavior by combining mass

heat and momentum governing equations. Three-phase calculations of zeolite

water and gas are performed in zeolite-water and zeolite-gas regions connected by a moving water-gas interface. Two typical packed bed with different particle distributions are presented for numerical discussions:fine-coarse bed (F-C bed) and coarse-fine bed (C-F bed). Overall mass of generated steam are the same for the two kinds of beds. In F-C bed steam generation rate is faster but generation time is shorter. Time ratio of steam generation to water input is 58.8% in F-C bed. Superheated steam at 249℃ with gross temperature lift of 139℃ is achieved for both beds. All of the steam is generated at the maximum value for F-C bed

while only one-third of that could be obtained at the peak for C-F bed. Mass ratio of generated steam from the outlet to the moving water-gas interface is larger for F-C bed. It's thus concluded F-C bed is more effective for steam generation with a considerable temperature lift.