Refrigerant charge estimation methods for brazed plate heat exchangers

Brazed plate heat exchangers (BPHE) are commonly used as condensers and evaporators. The required charge is low but cannot be calculated accurately yet because of an often unknown charge distribution. Four different methods for the investigation of refrigerant charge and distribution were examined on BPHEs with propane and will be discussed: The total charge has been detected using quick closing valves, the filling level differs significantly for different operation conditions. A sight glass was used to detect the charge stored inside the ports visually with the result of a strong dependency on the flow regime entering the BPHE. An ultrasonic damping diagnosis was applied on a BPHE yielding in different damping factors. A single channel light transmittance method was applied on a condenser and shows signal differences for different operation conditions. Due to signal differences in two-phase flows all methods seem to be suitable for void fraction evaluation on BPHEs.