Direct-coupled desorption for small capacity ammonia-water absorption systems

•Direct-coupled, gas driven desorption of ammonia-water mixtures.•Heat and mass transfer model for direct-coupled desorption.•Implementation of diabatic distillation process at compact scales.•Experimental validation of design and heat and mass transfer model. An investigation of direct gas-coupled desorption for small capacity ammonia-water absorption is presented. Some applications favor or require the use of direct-coupling of the heat source for desorption; therefore, a systematic treatment of this topic is needed for the optimal design of small-capacity absorption systems. Gas-coupled desorption is accomplished through diabatic distillation, and an optimal gas side geometry is established. Gas side optimization considers pressure drop minimization as well as geometric constraints such as column diameter and number of gas tubes. A heat and mass transfer model is developed and validated with experiments. Excellent internal vapor purification is achieved and the results agree well with the heat transfer and pressure drop predictions. These results demonstrate the applicability of direct-coupled desorption to small-capacity ammonia-water absorption systems. A comparative assessment with indirect-coupled desorption components is also made.