Search

Electrolysis of water for hydrogen-production has enormous potential. This study proposes a semi-closed Rankine cycle for efficiently utilizing direct hydrogen combustion via thermal power conversion. Unlike traditional closed Rankine cycles, combustion occurs inside the combustion chamber with hydrogen and pure oxygen, followed by a mixed heat exchange with the mainstream working fluid, water. The heat absorption process of the semi-closed Rankine cycle occurs within the working fluid and exhibits characteristics of both open and closed cycles. Thus, this cycle can combine the advantages of desirable parameters and isothermal heat rejection of the Rankine cycle. Applying the semi-closed Rankine cycle to hydrogen fuel utilization yields a higher energy efficiency, especially when coupled with a supercritical compression regeneration process. The main steam parameters were 620 °C/30 MPa, the cycle's average heat absorption temperature reached 561 °C, and its energy efficiency was 59.35%. When the main steam parameters were increased to 1200 °C/30 MPa, the average heat absorption temperature rose to 1021 °C and its energy efficiency was 68.27%, demonstrating a significant efficiency advantage. The newly proposed semi-closed Rankine cycle based on direct combustion of hydrogen fuel provides a novel and feasible path for exploring the efficient utilization of hydrogen. • The semi-closed Rankine cycle is proposed, which is suitable for direct combustion of hydrogen fuel. • The direct combustion characteristic significantly increases the main steam temperature of the cycle. • Supercritical compression regeneration process significantly increases the cycle's energy efficiency. • The cycle achieves efficient utilization of hydrogen in the thermal power conversion field. [ABSTRACT FROM AUTHOR]

The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO2 Brayton cycle. In the numerical simulation of the compressor, the rapid changes in the thermophysical properties of the CO2 near the critical point make it difficult to capture the condensation phenomenon. This paper investigates the influence of fluid physical properties on the condensation phenomenon. Firstly, the differences in the physical properties of CO2 in the SRK EOS (equation of state), PR EOS, and SW EOS are compared. Then, the simulation of nozzles and compressors were carried out and discussed. Results show that the condensation positions predicted by the three EOSs are basically the same. Compared with SW EOS, the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is 5.7% and 11.5%, and that of total pressure ratio is 0.3% and 3.8%, respectively. The results show that PR EOS can be considered for numerical simulation in engineering practice. Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently, it has considerable accuracy and numerical stability. [ABSTRACT FROM AUTHOR]