Small-scale turbocompressors for wide-range operation with large tip-clearances for a two-stage heat pump concept

Two mechanically driven small-scale turbocompressors running on gas lubricated bear-ings have been theoretically designed for a 6.5 kW two-stage heat pump functioning under variable operating conditions. The novelty in the heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused heat from various secondary heat sources. Managing the heat pump operational deviations with the second-ary heat is difficult for the turbocompressors. The turbocompressors can potentially exceed their operating range defined by the surge, choke and maximum rotational speed margins. Furthermore, regulating the tip-leakage flow caused by large tip-clearances in small-scale turbomachinery is challenging. This paper will guide the readers through different stages of the design process of small-scale turbocompressors subjected to different operational and design constraints. The design review and the presented methodology will help the de-signers make suitable parameter selections for achieving high efficiency and wide compressor operating range.