Shin Sekiya

Development of a Scroll Expander for the CO2 Refrigeration Cycle

In this study, a scroll expander was developed to recover the throttling loss in CO2 cycles. In cycles with an intercooler, the expander drives the second-stage compressor using the energy recovered from the expansion process. To carry out this function, a back-to-back scroll mechanism was applied to the expansion and subcompression processes. A prototype of the expander/subcompressor was designed by calculating the gas pressure in the chambers and estimating the gas forces. The prototype was built and tested. According to the experimental results of the prototype device, the subcompressor increased the pressure by 1.30 MPa (188.5 psi), while the pressure drop between the inlet and outlet of the expander was 3.19 MPa (462.7 psi). Based on the gas state at the expander inlet, the volumetric efficiency was about 104%.

Stability analysis of a forced-flow cooled superconducting coil: numerical simulation of multiple stability

Abstract The stability of a forced-flow cooled superconducting coil is investigated by use of numerical simulation. A numerical code to integrate the simultaneous partial differential equation system composed of the 1D hydrodynamic equations and the 1D thermal conduction equation has been developed. By using the code, stability margins are evaluated as functions of coolant mass flow rate, operation current and imposed magnetic field. The results of computations show that the stability margin is multivalued with respect to these operation parameters, as expected from the experimental results. It is also shown that the appearance of the first unstable regime is closely related to the existence of the stagnant region located on the upstream side of the heated zone and that the second stable regime appears because the heat transfer is appreciably enhanced by the induced fast backflow due to the thermal expansion of coolant.