Optimization of Plate Frame Evaporator for a Standard Vapor Compression Cycle
Vapor compression chillers are the primary cooling technology for large building applications. Chillers have a large up front capital cost, with the heat exchangers accounting for the majority of the cost. Heat exchanger cost is a function of size, and, therefore, a reduction in heat exchanger size can be correlated to a reduction in chiller capital cost. This investigation focuses on the optimization of the evaporator in a vapor compression chiller. To reduce the size and cost of the system, this study utilizes plate and frame heat exchangers in the chiller design, rather than traditional shell and tube. A heat exchanger model was integrated into a simple vapor compression cycle model to determine the relationship between core volume and refrigerant side pressure drop, in an effort to determine the minimum required volume for the evaporator. The model was run in both parallel and counter flow configurations. The heat exchanger model used in this investigation was developed and validated in a previous study for a liquid-coupled evaporator in an experimental vapor compression system. This model accounted for variable fluid properties, and complex geometries within the evaporator core. The minimum volume was achieved by varying the ratio between core length and number of channels, for a fixed evaporator heat duty and outlet condition. This allowed for the inlet condition to float, and be defined by the pressure drop through the core. It was found that there was an optimum relationship between evaporator pressure drop and core volume, and that the parallel flow arrangement resulted in a smaller volume than the counter flow arrangement.