Experimental study on ammonia/water mixture desorption heat transfer for vapor absorption-compression heat pump

• Experimental study on desorption heat transfer of ammonia-water mixtures in brazed plate heat exchangers. • Falling film desorber achieved heat load increases from 5 to 20 kW and thermal efficiency improvement from 66 % to 86 %. • Bubble mode desorber exhibited a vapor mass fraction range of 0.1–0.6 kg/kg and consistent thermal performance. • Key findings provide insights for optimizing desorber designs for high-temperature heat pump systems. • Results contribute to advancing efficient, compact solutions for industrial waste heat recovery. The aim of this study is to experimentally evaluate of brazed plate heat exchangers used as desorbers in absorption-compression heat pump systems, with a particular emphasis on recovering industrial waste heat applications. To reduce installation cost two vertical desorbers operating in different modes were experimentally investigated the overall heat transfer coefficient, using an ammonia-water mixture as the working fluid. To optimize the heat exchanger efficiency of plate type heat exchangers, an efficient design of desorber is an important factor in improving the performance of the system. The studied desorber system consists of two plate heat exchangers that are connected in series. The thermal performance of these units was analyzed under a constant heat source having an inlet temperature of 70 °C and a mass flux of 115 kg/m²⋅s. Experimental results revealed that, by varying the strong solution mass flux from 5 to 36 kg/m²⋅s, the following performance changes were observed in Desorber 1: heat load increased from 5 to 20 kW, the overall heat transfer coefficient improved from 1.1 to 1.7 kW/m²⋅K, and thermal efficiency increased from 66 % to 86 %. For Desorber 2, the heat load decreased from 17 kW to 14 kW, the heat transfer coefficient varied from 1.1 to 1.5 kW/m²⋅K, and thermal efficiency increased from 66 % to 80 %. Additionally, the vapor mass fraction at the outlet of Desorber 2 ranged from 0.1 to 0.6 kg/kg. The highest-pressure drop was recorded in Desorber 1. These results offer important insights for enhancing the design and functionality of desorber units in high-temperature heat pump systems, contributing to the development of more efficient and cost-effective solutions for industrial waste heat recovery.