An analytical procedure for calculating the performance of a two-phase flow screw-type expander is presented. Predicted results are compared with experimental measurements made with a recently developed prototype expander. This expander was designed for investigating the applicability of this type of machine as the expansion device in refrigeration or heat pump cycles with the objective of taking advantage of the power-producing capability of the expanding fluid. It has two rotors each with a diameter of 81.6 mm and a length of 135 mm, and was operated with Freon-12 entering at a pressure of 1.588 MPa (230.4 psia) and subcooling of between 2 and 12 K. Maximum power generated was 10 kW at a rotor speed of 3000 rpm. The internal (machine) efficiency is predicted to increase from about 30 to 70 percent as the rotor speed increases from 500 to 3000 rpm. Experimental results over this same speed range increase from 30 to 60 percent. The lower experimental values at the higher rotor speeds are attributed primarily to frictional losses not included in the analysis. Estimates of the performance of machines with larger diameter rotors yielded internal efficiencies reaching 80 percent and increases in power output proportional to the square of the rotor diameter.

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In order to estimate the total power output fluctuation of a high-penetration photovoltaic power generation system by using data from a limited number of points, the smoothing effect around individual observation points should be taken into account. Based on the transfer hypothesis, this study proposes a low-pass filter (LPF) to estimate the spatial average irradiance fluctuation characteristics taking the smoothing effect around the observation point into account. First, by using the irradiance data observed at 18 points in the Nobi plain, we confirmed that the fluctuation characteristics of the spatial average irradiance can be estimated by using the characteristics of the single point irradiance when the radius of the equivalent circular area is smaller than 30 km. Then, by formulating the relation between the area size and the fluctuation cycle from which the random fluctuation factor begins to increase, we developed a LPF to take the smoothing effect around the observation point into account. Finally, we demonstrated that the spatial average fluctuation characteristics can be estimated successfully for various area sizes within a radius of 20 km by applying a dedicated LPF according to the area size. C⃝ 2014 Wiley Periodicals, Inc. Electron Comm Jpn, 97(11): 1-9, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com).