compressor, sorption, hybrid, watersteam, lithiumbromide
In various applications the use of sorption chillers and heat pumps is limited by the available temperature level of the driving heat source or the heat sink for export of reject heat. These constraints can be overcome by integrating an efficient high-speed transonic turbo-compressor into the internal cycle of a thermally driven water/lithium bromide absorption heat pump. The operation in a hybrid heat pump with the refrigerant water implies specific challenges for the design of the compressor: Saturation pressures in the sub-atmospheric range, low vapor density, high volume flows and a targeted pressure ratio of 3 result in high impeller tip speed up to 660 m/s and transonic flow phenomena in the flow channel of impeller and diffusor. Here the authors present a theoretical design study based on a 3D-simulation of a centrifugal compressor, targeted at the given operating conditions for a hybrid heat pump. Key figures are investigated to figure out the relationship between impeller tip speed, compressor pressure ratio and operating range of the compressor meeting the requirements, wide stable operating range between surge and choke line and appropriate pressure ratio. The optimization of the impeller geometry comprises both fluid dynamic behavior and structural stability.