Development of performance analysis method and test loop for falling film evaporator of oil-free high temperature heat pump system

In the industrial sector, the introduction of high-temperature heat pumps which can provide process heat above 150 oC is necessary for carbon emission reduction. Since R134a, the most commonly used refrigerant in industrial heat pumps, is not suitable for such a high temperature, a transition of refrigerant is required. In this study, R1336mzz(Z) with GWP less than 10 was selected as the alternative refrigerant, and a falling film evaporator was developed to reduce refrigerant charge. A falling film evaporator can significantly reduce the total charge amount compared to a traditional flooded type. However, to minimize the risk of evaporator performance decrease due to dry-out, the heat exchanger design must embrace wide operation range, mitigating dry-out risks. Analysis of refrigerant charge was performed for the design evaporator conditions for 160oC steam production, revealing a 65.8% reduction in refrigerant quantity compared to flooded type. To ensure the accuracy of performance analysis, a test loop for falling film evaporation was designed and constructed with 10 kW capacity. The evaporation test range was designed as 70-90 oC, allowing experimentation with refrigerants such as R-245fa in the HFC series and alternative refrigerants like R-1336mzz(Z).