Compact and efficient generator for low grade solar and waste heat driven absorption systems

Abstract

Absorption heat pumps offer a significant energy saving opportunity because of their capability to utilize low grade heat from solar thermal collectors, combustion systems and numerous other industrial applications. Reducing the required source temperature, size, and cost can greatly enhance the market potential of these systems. Here, a new compact plate-and-frame generator design is introduced with an approximately 3 times higher desorption rate at a substantially lower mass flux compared to conventional generators at only a 10°C wall superheat temperature. The new design utilizes a new surface structure to produce a uniformly thin solution film and to continuously interrupt the concentration and thermal boundary layers. At low wall temperatures, the desorption rate increased linearly with temperature. The desorption rate then exponentially increased due to a transition from direct diffusion desorption mode to nucleate boiling. The transition temperature was a strong function of the solution flow rate. A comparison of the desorption rate in the direct diffusion desorption mode with predictions of the laminar flow theory suggested that increasing solution flow rates results in mixing within the solution film. The high desorption rate at low mass flux enables significant reduction in the generator size and cost.