NH₃ condensation within plate heat exchangers

Abstract

Energy shortage and energy related environmental problems are urgent issues to be addressed in the coming years. Low-grade heat is utilized to drive energy conversion cycle and to produce electricity, which is a renewable and sustainable approach to energy supply. These thermodynamic cycles for energy conversion require eco-friendly working fluids and highly efficient heat transfer processes. NH3 is a natural refrigerant with superior thermal properties such as large latent heat and high thermal conductivity. However, the application of NH3 is restrained due to safety issues. Plate heat exchangers have the potential to be used in the thermal facility of NH3 for the recovery of low-grade heat. These compact structures are able to transfer large heat loads with reduced charge of working fluid, thereby mitigating the safety risk. For instance, the Organic Rankine Cycles of NH3 equipped with plate heat exchangers have smaller sizes compared with the plants filledwith other refrigerants. Furthermore, plate heat exchangers have the advantage of design flexibility and easy maintenance for highly efficient heat transfer, bringing aboutwide utilization in refrigeration, pharmacy and chemical engineering. In this thesis, NH3 condensation is experimentally and theoretically investigated in plate heat exchangers. The main aim is to provide design methods of compact plate condensers used in the thermal facility of NH3, which are not available in open literature. The experiments ofNH3 condensation have been reported, but no design method is provided. The heat transfer and frictional pressure drop correlations of hydrofluorocarbons (HFCs), hydrocarbons (HCs) and hydrofluoroolefins (HFOs) are assessed making use of an experimental database. Most suitable correlations are recommended.