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A computer program was developed for an ammonia-water-based generator absorber heat exchange (GAX) component that simulates the simultaneous heat and mass transfer for coexisting liquid film absorption and flow boiling desorption. Key input parameters were identified and used to simulate the variations of heat and mass transfer coefficients, total amounts of heat and mass transferred, temperature and concentration driving forces, and the temperatures of different phases. The simulated temperature profiles were found to match well with experimentally obtained profiles for different vapour and liquid flow rates. The simulated values of the absorption-side vapour-phase flow rates were found to approach zero near the end of the GAX component, showing another close match with the experimental boundary condition. The simulations of the coupled heat and mass transfer processes are useful for detecting the presence of pinch points, appropriate sizing of equipment, realistic estimation of the coefficient of performance (COP) and the efficiency, and determining the individual phase flow rates. The insight developed from these simulations enhances the understanding of the heat and mass exchanger behaviour and thus contributes to a reliable and efficient design. The simulation program is of a general nature, applicable to the design of dephlegmators and other heat and mass exchangers beyond those involved in GAX heat pumps.

KEYWORDS: year 1997, Components, calculating, validating, computer programs, ammonia, water, absorption heat pumps, heat flow, fluid flow, heat transfer coefficient, temperature, content, temperature distribution

Citation: Symposium, ASHRAE Trans. 1997, vol.103, part 1