Beräkning av arbetsmediemängd i värmepumpar och kylmaskiner
Examensarbete för masterexamen
The refrigerant charge is of great importance for the performance of heat pumps and chillers as it e.g. sets the level of liquid in the condenser. When simulating the running of heat pumps and chillers the refrigerant charge needs to be taken into account. Since many contemporary refrigerants are inflammable, refrigerant charge is a key parameter when analysing the safety of a plant and should be predicted when designing a heat pump/chiller. The purpose of this diploma work has been to develop refrigerant charge calculations (distribution of refrigerant as well as total quantity) for heat pumps and chillers. The new refrigerant charge calculation routines have been added to a module-based FORTRAN program for heat pump or refrigeration steady-state calculations. The program has been developed by researchers at Heat and Power Technology, Department of Chemical Engineering and Environmental Sciences, Chalmers University of Technology. The refrigerant charge routines use the program's existing routines as far as possible to make use of future updates of the main routines as well as for practical reasons. During the course of this diploma work, the following tasks have been carried out: • A routine has been created to compile and present refrigerant charge results from the different modules/units of the program. • Refrigerant charge calculation routines have been added to the modules modelling the five most common parts of a heat pump/ refrigeration system. • The heat transfer calculations in the liquid layer at the bottom of the condenser has been improved and the user is given better feedback when running the program. • Debugging and documentation Calculations with the program show that the amount of refrigerant in condensers dominate in systems where there are no other large liquid phase accumulations, e. g. suction gas heat exchangers or buffer tanks. It also shows that the amount of subcooling of the condenser outlet refrigerant stream is decisive for the amount of refrigerant in the condenser and that more subcooling increase the amount. The amount of refrigerant in an evaporator is affected in a reversed way by the amount of super heating of its refrigerant out stream. Preliminary calculations with the program indicate that when simulating changes in operating conditions the relative change in refrigerant amount is less than the relative change in the parameters altered. Thorough studies on how the amount and distribution of refrigerant are affected by changes in operating conditions are not done in this diploma work.
Kemiteknik , Chemical Engineering