Within the family of jet devices, the thermopressor occupies a unique niche as a two-phase system based on direct contact cooling. Its performance is strongly dependent on geometric parameters, which govern the energy needed to overcome frictional effects and local hydraulic losses in the convergent–divergent sections. In this work, representative thermopressor configurations were analyzed for several cone half-angles of the convergent part (α = 30°, 35°, 40°, 45°, 50°) and different diffuser divergence angles (β = 5°, 6°, 8°, 10°, 12°). The results indicated that the most favorable geometry corresponds to α = 30° for the convergent section and β = 5° for the diffuser. Under these conditions, the pressure losses are minimized (ΔPloss = 3.0–9.5%), which provides the greatest pressure gain due to thermogasdynamic compression during liquid injection and subsequent evaporation in the mixing chamber. These findings may serve as design guidelines for developing low-capacity thermopressors intended for air-cooling applications in power generation systems.