# A Review on Two-Phase Volumetric Expanders and Their Applications
## 5 Two-Phase Twin Screw Expander
### Literature Review of Two-Phase Twin Screw Expander
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\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42. In 2007, [PERSON] et al. [50] experimentally investigated a two-phase twin screw expander with \"N\" profiles in a TFC using R124 as working fluid. The quality at the expander inlet was 0.95. The expander produced electric power of 22 kW with an isentropic efficiency of 0.74. In 2014, [PERSON] et al. [51] studied a twin-screw expander in a wet vapor Rankine cycle using water. They performed the multi-variate geometrical optimization of the machine in order to maximize the output power. Experimental tests were conducted on the optimized geometry at different pressure difference values. They showed that the maximum isentropic efficiency was equal to 0.78 at nominal conditions. In 2016, [PERSON] et al. [52] elaborated a simulation model of a TFC operating with two-phase twin screw expander and water. It was assumed that sufficient heat transfer between the vapor and liquid phases existed to reach a stable state within a time step. The simulations showed good agreement with the experimental data, even though deviations on the power output and pressure-volume diagram took place, especially at low revolution velocities. In 2018, [PERSON] et al. [53] experimentally investigated a water injected twin-screw expander suitable for TFC. In particular, the auxiliary liquid (water) was aimed at minimizing the internal leakages within the expander and at lubricating moving machine parts. The last investigation related to the application of the two-phase twin-screw expanders in the power cycles was carried out in 2020 by [PERSON] et al. [54]. They elaborated a numerical model of a TFC with R245 fa as the working fluid. The expander had a variable built-in volume ratio thanks to a sliding valve in the casing that opened an additional suction port. The simulation showed that when lowering the built-in volume ratio from 5.06 to 2.63, the volumetric efficiency increased from 0.53 to 0.77, whereas the isentropic efficiency decreased from 0.82 to 0.63 due to the under-expansion. An additional application of the two-phase twin-screw expanders was investigated between the 1980s and early 2000s in the vapor compression refrigeration cycle, as suggested in [48] by [PERSON] et al. to improve the COP. [PERSON] et al. [30] carried out a numerical study on a high-temperature heat pump composed of two coupled cycles operating at two temperature levels with different working fluids. The cycle at lower temperature operated between 40 \({}^{\circ}\)C and 105 \({}^{\circ}\)C using ammonia, while the other one was between 105 \({}^{\circ}\)C and 180 \({}^{\circ}\)C by employing water steam. In both cycles, twin screw expanders replaced the throttling valves and drove twin screw compressors. [PERSON] et al. [55] empirically investigated the cycle using R113 and implemented the expander with built-in volume ratio of 2.85 and overall volume ratio of 12.3. The operating conditions were an inlet pressure of 8.45 bar, inlet temperature of 126 \({}^{\circ}\)C, outlet pressure of 3.76 bar, and an outlet temperature of 93 \({}^{\circ}\)C. The maximum measured isentropic efficiency was 0.76. Moreover, [PERSON] et al. [56] carried out a theoretical study on the \"Expressor\", comprising a two-phase twin screw expander driving a single-phase twin screw compressor. The maximum calculated isentropic efficiency of the expander in the expressor working with R134a was 0.72. Empirical tests performed by [PERSON] et al. [57] showed that the expander (with a built-in volume ratio of 1.85) in the expressor had an isentropic efficiency of 0.66 when working with R113. It was also demonstrated that the rotor forces created by the compression and expansion processes can be partially balanced in order to eliminate the axial forces and reduce the radial bearing forces [58].