Study on the influence of injection frequency by exhaust area regulation on gas wave refrigeration and performance optimization

The gas wave refrigerator (GWR) utilizes gas waves within a wave rotor to achieve separation of hot and cold gas. This study investigates the impact of injection frequencies on the performance of the GWR mechanism under different exhaust area configurations. In fixed-geometry refrigeration wave rotors, processing capability and energy density distribution are critical to system performance. Multi-cycle injection, surpassing single-cycle methods, offers a promising route to optimize GWR. The results indicate that, when the expansion ratio (α) is below 2, higher injection frequency significantly enhances exhaust efficiency. The frequent opening and closing of the ports dissipate compression waves to limit heating of expanded gas, mitigating exhaust temperature rise at the exhaust end due to thermal conduction. The experiments demonstrate that increasing the single-frequency injection to dual-cycle injection yields lower temperatures in both the deep expansion zone and the exhaust end, resulting in a 7.1 % enhancement in refrigeration efficiency (ηexp). However, excessive injection frequency decreases the effective exhaust area, causing higher exhaust velocities and increased losses. In this study, increasing frequencies from four to five reduced ηexp by 58 %. When α exceeds 2, higher injection frequency causes greater pressure wave distortion, leading to a larger drop in ηexp. When low flow rates make higher injection frequency unsuitable, reducing exhaust area enables single-cycle injection to match multi-cycle performance. Moderate exhaust area reduction improves exhaust efficiency, increasing ηexp by 2.7 %. However, excessive narrowing induces strong compression wave oscillations, decreasing ηexp by up to 14.5 %, replicating multi-frequency effects with a single frequency harms performance.