Study Of The Dynamic Performance Of The Evaporator

Evaporator is one of the most important parts of cooling & heat pump systems.The real-time simulation of their dynamic characteristics, and thereafter theperformance prediction is crucial not only to design, operation but also to theiroptimization and control for the cooling & heat pump systems as a whole. Thepurpose of this paper is to develop a real-time simulation software of evaporator,which can simulate and predict dynamically the process due to changing of some inletparameters in evaporator reasonably.The evaporator used in the simulation has a counter current flow arrangement inco-axial tubes, which simply called counter current flow co-axial tube evaporator(CCFCTE). A dynamic distribution parameter model of the evaporator is proposedbased on the equations of mass-conservation, momentum-conservation andenergy-conservation with some logical assumptions in this paper. These governingequations are solved numerically combining with some selected heat transfercorrelations, pressure drop correlations and the physical property fitting equations ofthe refrigerant. The computation code programmed using Visual Basic has beenvalidated bycheckingthe error dependence on grid number, the equation discretenessand Tri-Diagonal Matrix Algorithm(TDMA) with a simple single phase model.The dynamic process in the evaporator by giving a step change of different inletparameters has been simulated using the simulation program. The distribution orchange of some brief parameters with time in both sides of refrigerant and water in theevaporator are obtained and analyzed.An experimental apparatus of a heat pump system was set up in order to comparethe simulation results with the experimental results in those dynamic processes bygiving a step change of inlet water flow rate. It shows that the numerical andexperimental results are in reasonable agreement, which indicates that the dynamicmathematic model used and the computer program built for a evaporator simulationarereliable.