Physical characteristics of frost formation in semi-closed cycle turbine engines

The power, water extraction, and refrigeration (PoWER) system generates electric power, potable water and refrigeration effects simultaneously, and is composed of a micro-turbine and vapor absorption refrigeration system, which typically uses ammonia, heat exchangers, and a turbocharger. In order to improve the efficiency and the electric output power of the micro-turbine portion of the PoWER system, attempts have previously been made to reduce the inlet temperature of the compressor. However, it was problematic to drive it below the freezing point since frost or ice forms from the humidity in re-circulated air. As a result, the ice accretion that attaches on the bell mouth or guide vane might increase the pressure drop, leading to performance loss. Furthermore, large sections that break from the ice accretion may cause damage to the compressor blades. In this paper experiments have been conducted under the same environmental conditions as the PoWER system in order to observe the physical characteristic of the frost formation on cylindrical tubes. The results show the thickness of the frost formation for different air velocities (3, 5, 7 m/s) and surface temperatures (−9.8, −16.6, −24.4°C) with respect to time.