Figure 7.15 Calculated Efficiency for Monochromatic Cells Coupled to Laser Light Tuned to the Cell Material Bandgap, and Assuming an Input Power of 500 MW/cm2. [Chubb,92] The gyroreactor proposed prototype presented in is shown on Figure 7.16. [Bailly du Bois, 1991] This engine uses xenon with 0.3 % of helium as a working fluid. It can produce 20 kW if a radiation flux of 40 W/cm2 is considered. With a higher radiation flux (136 W/cm2) the same reactor can generate 50 kW. In each case the rotation speeds are different (20 000 RPM and 50 000 RPM). The following parameters give additional information about the engine. * Radiated surface * Rotor's weight * Distance between the lateral faces of the rotor * Maximum distance from the axes (outer shell) * Pressure operation * Maximum temperature Liquid Droplet Radiator Radiators are a dominant percentage of the mass of large solar dynamic power systems. The current technology which is the heat pipe radiator has a specific mass of 5 kg/m2. To reduce the mass, a few concepts such as moving belt, dust radiators and liquid droplet radiator (LDR) have been proposed. One of the most promising is the LDR which can be up to 10 times lighter. This concept is shown schematically in Figure 7.17. This radiator has two main components; the droplet generator and the collector. The heat is radiated in space through the surface of billions of droplet traveling in between those two parts. Droplets' diameter size range from 60 to 1000 pm. For the design, the main parameters are the droplet diameter, velocity, the type of the working fluid and the distance between the droplet. The mass of the system was found to be quit sensitive to the fluid density, fluid specific heat and emissivity. In addition, LDRs have a lower rejection
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