The effect of microchannel geometry variations on heat transfer and absorption rate of an ammonia-water constrained thin film bubble absorber are presented. Experiments are performed at an absolute pressure of four bar and at a fixed inlet mass concentration of ammonia of 15 percent. The mass flow rate of the inlet weak solution are varied from 10 g/min to 30 g/min, and that of ammonia gas are varied from 1 g/min to 3 g/min. Five geometries, including two smooth-bottom-walled channels of differing depths, and three channels with structured bottom walls are considered. For identical rates of vapor absorption, the overall heat transfer coefficient for the 400 μm smooth microchannel is significantly larger than of the 150 μm smooth channel as well as that of the cross-ribbed and angled-cross-ribbed structured channel. The streamwise-finned channel exhibit high overall heat transfer coefficients for vapor flow rates of up to 2 g/min.

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