Analys av off-design prestanda för ett absorptionskylsystem

Sammanfattning

This master thesis project at KTH is performed in the Mechanical and Aerospace Engineering

department at University of Florida (UF). The thesis is a small part of a gas turbine research

project where a vapour absorption refrigeration system (VARS) and a high pressure regenerative

turbine engine (HPRTE) are integrated together. The main objective is to build a computer

model of the VARS. The computer model is supposed to be used to analyse the off-design

performance of the VARS and should also be easy to integrate as a subroutine in a more complex

system model. To model the VARS some knowledge of the absorbent/refrigerant mixture had to

be well known, in this case a mixture of ammonia and water. The thermodynamics of the

different components is also studied and discussed in the report. The VARS consists of four heat

exchangers that rejects/absorbs heat to/from external sources; the evaporator, generator,

condenser and absorber. There are two internal heat exchangers used to increase the performance

of the VARS and to reduce the heat load on the other heat exchangers. A pump and some

throttling valves keep the pressure difference needed in the system to accomplish evaporation

and condensation in the heat exchangers. The most advanced component is the rectifier, a mass

and heat exchanger that purifies the ammonia-water mixture into almost pure ammonia. The

computer model built in this thesis is included in Appendix E and has been used in parametric

calculations to plot charts. The results presented and discussed in the report are related to

external parameters that are of interest and that have influence on the VARS performance. The

experimental test data from test runs in the Energy and Gas Dynamics Systems Laboratory at UF

is also compared with the model calculations. At the time of this thesis the VARS used in the

experimental setup at UF is operating at approximately half of its capacity and is capable of

much more. The most important conclusion drawn from the model calculations is that the

temperature of the coolant entering the condenser is very sensitive on the VARS performance

and should be kept close to design conditions.