Simulated conical diffuser performance charts for organic working fluids

The pressure recovery performance of conical diffusers has been extensively investigated in past experimental research, utilizing air as the working fluid. However, since organic Rankine cycles are receiving more and more attention due to their energy recovery capability, the investigation of conical diffuser performance using different organic working fluids is of particular interest. Therefore, this work focuses on the numerical investigation of conical diffuser performance using the working fluids methanol (γ≈1.14), air ideal gas (γ=1.4), and n-hexane (γ≈1.04). First, the numerical model is validated against experimental data. Afterwards, the diffuser opening angle and inflow Mach number are varied systematically, while guaranteeing Reynolds number similarity between the working fluids. The numerical results lead to the creation of performance charts, which are then compared to evaluate the influence of the working fluid and the Mach number on conical diffuser performance. The performance charts also provide a valuable tool for the design of organic Rankine cycle diffusers. Finally, for the first time, a physics-based correction methodology is developed to correct air performance data to arbitrary working fluids based on their isentropic exponent, inlet Mach number, and compressibility factor.