Development of design model for a rectifier in GAX absorption heat pump systems

This paper develops a model for design of a rectifier in generator-absorber heat exchanger (GAX) heat pump systems with an ammonia-water solution pair. The objectives of this paper are to provide further understanding of the rectification process in ammonia-water systems and serve as a design tool for the rectifier using a stable computation method. Simultaneous heat and mass transfer analysis is performed for the rectification process. Three different geometric configurations of the rectifier, namely, vertical fluted tube, confined cross flow with fluted tube, and coiled smooth tube, are considered in this paper. The effects of the temperature difference between interface and bulk vapor and heat transfer coefficients in each region on the rectifier size are investigated. The importance of the composition of rectifying vapor, z, is studied. The results show that the temperature difference between the interface and the bulk vapor region should be minimized to obtain a rectifier of small size and a high coefficient of performance (COP). During the rectification process, the composition of rectifying vapor should be lower than the liquid concentration, i.e., z < x₁. The heat transfer coefficient in the vapor region has a much more dominant effect on the rectifier size than that in the liquid and the coolant regions. Mass transfer has a more significant effect on the rectifier size than heat transfer.