Author(s): Giacomo Pellegrini

Abstract: A Tesla turbine sometimes called a boundary-layer turbine or bladeless turbine is a rotary machine in which the working fluid transfers momentum to a set of closely spaced smooth discs through viscous shear rather than through aerodynamic lift on bladed vanes ^[1]. Because the rotor carries no blades, it is inherently tolerant of liquid droplets and particulate matter in the expanding fluid, a property that makes it attractive for organic Rankine cycle (ORC) applications where the expander inlet may contain a significant liquid fraction ^{[2, 3]}. This research presents the design, construction and experimental testing of a bench-scale Tesla-turbine expander intended to recover low-grade waste heat in the 80–120 °C temperature range using R245fa as the working fluid in a two-phase expansion process. The turbine rotor consisted of eight stainless-steel discs (outer diameter 100 mm, thickness 0.8 mm, inter-disc gap 0.5 mm) mounted on a precision shaft and enclosed in a volute casing machined from aluminium. Steady-state tests were conducted at five inlet pressures (3.0–7.0 bar gauge) and three rotational speeds (1500, 3000 and 4500 rpm) while the inlet vapour quality ranged from 0.82 to 0.97. The maximum shaft power output was 187 W at 6.0 bar and 3000 rpm, corresponding to an isentropic efficiency of 44.4%. At 7.0 bar the efficiency declined slightly to 43.1%, suggesting that windage and disc-friction losses begin to outweigh the enthalpy gain at higher pressures for this rotor geometry. A correlation matrix across the operating variables showed a strong positive relationship between inlet pressure and shaft power (r = 0.94) but a weaker and non-monotonic relationship between pressure and isentropic efficiency (r = 0.72). These results confirm that a simple, low-cost Tesla turbine can serve as a viable expander for small-scale ORC systems targeting industrial waste heat below 120 °C, particularly where the working fluid enters the expander with appreciable liquid content that would damage a conventional bladed machine.

DOI: https://www.doi.org/10.22271/27078043.2026.v7.i2a.136

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