Analys av off-design prestanda för ett absorptionskylsystem
This master thesis project at KTH is performed in the Mechanical and Aerospace Engineeringdepartment at University of Florida (UF). The thesis is a small part of a gas turbine researchproject where a vapour absorption refrigeration system (VARS) and a high pressure regenerativeturbine engine (HPRTE) are integrated together. The main objective is to build a computermodel of the VARS. The computer model is supposed to be used to analyse the off-designperformance of the VARS and should also be easy to integrate as a subroutine in a more complexsystem model. To model the VARS some knowledge of the absorbent/refrigerant mixture had tobe well known, in this case a mixture of ammonia and water. The thermodynamics of thedifferent components is also studied and discussed in the report. The VARS consists of four heatexchangers that rejects/absorbs heat to/from external sources; the evaporator, generator,condenser and absorber. There are two internal heat exchangers used to increase the performanceof the VARS and to reduce the heat load on the other heat exchangers. A pump and somethrottling valves keep the pressure difference needed in the system to accomplish evaporationand condensation in the heat exchangers. The most advanced component is the rectifier, a massand heat exchanger that purifies the ammonia-water mixture into almost pure ammonia. Thecomputer model built in this thesis is included in Appendix E and has been used in parametriccalculations to plot charts. The results presented and discussed in the report are related toexternal parameters that are of interest and that have influence on the VARS performance. Theexperimental test data from test runs in the Energy and Gas Dynamics Systems Laboratory at UFis also compared with the model calculations. At the time of this thesis the VARS used in theexperimental setup at UF is operating at approximately half of its capacity and is capable ofmuch more. The most important conclusion drawn from the model calculations is that thetemperature of the coolant entering the condenser is very sensitive on the VARS performanceand should be kept close to design conditions.