# A Review on Two-Phase Volumetric Expanders and Their Applications
## 4 Two-Phase Scroll Expander
### Literature Review of Two-Phase Scroll Expander
In 2008, [PERSON] et al. [35; 40] experimentally investigated a prototype of a two-phase scroll expander with an inlet volume of 2.8 cm\({}^{3}\) and a BVR of 2, which was lubricated by polyalkylene glycol (PAG) oil. The tests were conducted to investigate the influence of several parameters, i.e., inlet pressure (6.5-9.5 MPa), inlet temperature (20-45 \({}^{\circ}\)C), pressure ratio (1.5-2.6), rotational speed (2000-3500 min\({}^{-1}\)), and CO\({}_{2}\) mass flow rate (135-220 kg/h), on the prototype performances. The tests results demonstrated that the isentropic efficiency of the prototype had a maximum value equal to 0.83. In 2008, [PERSON] et al. [41] performed a numerical simulation of a two-phase scroll expander for directly driving the first stage compressor of a two-stage intercooled compressor. The assumed inlet volume and built-in volume ratio were 1.32 cc and 2.91, respectively. The assumed operating conditions were an inlet pressure of 10 MPa, inlet temperature of 35 \({}^{\circ}\)C, outlet pressure of 3.5 MPa, shaft speed of 3500 rpm and a shaft power of 0.440 kW. The calculated volumetric, isentropic, and mechanical efficiencies of the machine were 0.86, 0.86, and 0.63, respectively. The last investigation related to the application of the two-phase scroll expanders in the CO\({}_{2}\) vapor compression refrigeration cycles was carried out in 2010 by [PERSON] et al. [42]. In particular, they developed a prototype of a two-phase scroll expander for directly driving the second stage compressor of a two-stage intercooled compressor. The tests were conducted with inlet fluid in the subcooled liquid state and at the difference between inlet and outlet pressures of 1.69-4.16 MPa, with a shaft speed of 1800-3600 rpm. The experimental volumetric efficiency was 0.97-1.54 (the excess over 100% was due to the pressure loss at the inlet port and mutual, as well as close-range interference between the fixed and orbiting wraps). An additional application of the two-phase scroll expanders was investigated in the late 2000s, in particular in the wet vapor Rankine cycle using water as working fluid. In 2007, [PERSON] et al. [43] developed a prototype of the machine with a displacement volume of 68.83 m\({}^{3}\) and a double-sided configuration, i.e., two fixed spirals are placed on both sides of the orbiting spiral. Thus, the axial forces balance each other, and the thrust bearing is not required. The tests were conducted at an inlet pressure of 1.2-1.3 MPa, inlet temperature of 139-145 \({}^{\circ}\)C, outlet pressure of 0.11 MPa, shaft speed of 1000-1400 rpm, and a shaft power of 15 kW. The experimental maximum volumetric and maximum total efficiencies were 0.52 and 0.34, respectively. Moreover, the computer simulation showed that the volumetric and total efficiencies could be equal to 0.83 and 0.65, respectively, by the reducing the current clearance between orbiting and fixed spirals (i.e., 64 \(\upmu\)m) by half. In 2010, the ECR International developed two types of two-phase scroll expanders for a wet vapor Rankine cycle (with water as the working fluid) used for cogeneration. In particular, the thermal power is transferred in the condenser to a thermal fluid vector for building heating. The first type is the single-shaft configuration with maximum output power of 1.9 kW at 2800 rpm. The second type is the three-idler crank scroll expander with power of 2.5 kW in the range of 3000-3600 rpm [44]. The literature suggests that most studies about scroll machine were published between 2008-2010 and investigated CO\({}_{2}\) transcritical cycles for heat pump and refrigeration (Table 1). The total efficiency was in a wide range between 0.30-0.60 for a rotating speed ranging from 1000-4000 rpm.