įor the equalization of flows, sluice gates are used. Unequal flow distribution among the chambers of a settling basin causes its malfunctioning. To equalize the flows, three solutions with (i) fix, (ii) fix in a range of flows, and (iii) variable positions of the sluice gates are analyzed. The local flow resistances in the analytical model are determined by the CFD model combined with RA. Afterward, the analytical model, which consists of a system of three pressure drop equations for three parallel and partly imaginary streams, is formed. Initially, the CFD model of the side-weir intake was developed and validated. The first four are not because of the weir design, and the fifth because of the three-dimensional flow character. From the previous list, only the sixth methodology is applicable. The additional models and RA are intended to speed up the solution finding. To find their positions, the following methodologies are considered: (1) measurements combined with trial-and-error method (TAE), (2) measurements with regression analysis (RA), (3) CFD model combined with TAE, (4) CFD model with RA, (5) CFD model supported by a one-dimensional flow model, and (6) CFD model with an analytical model. To equalize the flows, sluice gates are used. Unequal flow distribution between the chambers of a three-chamber settling basin causes its malfunction and endangers the turbines of a small hydropower plant. The difference between the NPV's for two optimal solutions for the analyzed period of 12 years, which is the period of validity for incentive measures for power production from renewable resources in the Republic of Serbia, is less than 0.02%. The optimal is steel pipeline with the inner diameters of 1800 mm. The net present value (NPV), which was calculated as the ratio between the profit from electricity selling and the penstock investment, was used as the selection criterion for optimal diameter. Steel, polyester (fiberglass), polyvinyl, and wood were the analyzed pipeline materials. Based on the known pipeline routing and probability of the river flowrates, friction factors for different pipe materials, total pressure drop, and total electricity production were calculated. One of these turbines is used for low flowrates during which maximal gauge static pressure in the penstock rises from 3.776 bar to 7.23 bar. During these flowrates the existing turbine in the SHPP Belci has low efficiency, which is improved by bypassing SHPP Belci and implementing two turbines in the SHPP Kašići. The SHPP should be functioning as the second plant in a cascade system when the above SHPP Belci has extremely low flowrates, below 17% of the nominal. The SHPP has nominal flowrate of 5.65 m 3 /s, the head 37.76 m and the total pipeline length 3000 m. The goal of the paper is to find the optimal diameter and pipeline material for a small hydropower plant (SHPP) Kašići on the Jošanica river.
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