Two-dimensional calculations for the novel axial turbo-vapor compressor

Abstract

Turbo-vapor compressors (TVCs) are critical for generating vacuum pressure in a novel combined cycle for electricity and freshwater production. This paper presents a new TVC design comprising a single axial compressor rotor directly driving a single axial turbine rotor, aiming to improve efficiency, increase allowable mass flow rate, and reduce cost and losses. A parametric study using ANSYS CFX investigates the effect of ax-ial and circumferential positioning of turbine blades relative to compressor blades. The optimal configuration is found at a 16-degree circumferential shift (the relative angular offset of turbine blades with respect to compressor blades around the rotation axis, mea-sured in degrees of rotation) relative to the centroid line and an axial shift of 21% of the compressor chord length. At this position, the work mismatch between compressor and turbine is reduced to 15 J/kg, corresponding to only 0.25% of turbine work. The corresponding compressor and turbine efficiencies reach 97.7% and 87.5%, respectively based upon profile losses only. This design offers a compact, high-flow-rate TVC with minimal work imbalance, advancing low-temperature thermal cycles for combined water and power generation. The novelty of the TVC lies in its distinct characteristics compared to conventional turbochargers: (1) it operates on steam as the working fluid, (2) maintains the same mass flow rate through both compressor and turbine, (3) features the same flow path, (4) shares the same hub diameter and is positioned on the same axis, and (5) operates at the same rotational speed. The operational principle involves starting the compressor with an external motor, after which the compressor creates vacuum in the evaporator to evaporate steam at 85 °C at lower than atmospheric pressure, instead of the conventional 100 °C at atmospheric pressure.