PERFORMANCE AND CHARACTERISTICS OF COMPRESSOR/EXPANDER COMBINATION FOR CO2 CYCLE

Since the air cooled CO2 refrigeration cycle has a large throttling loss, an expander can improve the performance of the CO2 refrigeration cycle by recovering the throttling loss. One way to utilize the recovered work is to drive an additional compressor by the expander. In such a case, it is effective to use an intercooler between a first-stage compressor and a second-stage compressor, which reduces the compression work of the second-stage compressor. A compressor/expander combination, in which the second-stage compressor is driven by the expander autonomously, is designed so that it is operated at a balance point of mass flow rate and shaft torque between the compressor and the expander. There are two balance points, however, and it is expected that the combined machine will be operated at the different condition from the original design point. The compressor performance was measured individually and it was expressed by a function of pressure increase by the compressor and rotational speed. The performance was used to calculate the balance point of the prototype compressor/expander combination. Although the performance of the combined expander is too low to drive the compressor, it ran autonomously with compressing the gas under the special experiment in which an additional flow is supplied to the expander. The operating point can be estimated using the performance maps of the compressor and the expander.