Replacing control valves in the inlet lines of oil transmission stations with hydropower plants can be a logical solution to convert energy losses into useful power. In this regard, this paper carried out an experimental and numerical investigation to study the feasibility of applying a pump as turbine in a hydropower system and its performance on the oil transmission lines. An experimental platform, comprising a tank, hydropower, centrifugal pump, electromotor, and measuring instruments, was constructed. An external gear pump was employed regarding the high working pressure of the system, maximally 80 bar, as an actuator of the centrifugal pump. By comparing the efficiency of the electropump with the hydropower-driven pump, it was observed that maximum efficiency, approximately 20.6%, occurred when the pump reached its best efficiency point. Furthermore, based on experiments on hydropower-driven pump under different inlet pressures, an optimal point was observed for the system. This issue enhanced the system's efficiency by 19% as the flow rate increased by 1.9 L/s in the inlet pressure of 80 bar. According to the results, as the flow rate increases, there is a descending trend in outlet pressure. Besides this, there is an optimum condition for the maximum efficiency of hydropower plants and this crucial point should be determined by experimental or numerical studies to reach maximum performance. Furthermore, extracted values of power from the computational fluid dynamics model were compared with the experiments with less than 8% error in most cases. Therefore, a correlation was introduced for the prediction of power based on effective parameters of outlet pressure and volumetric flow rate for the off-design condition in each inlet pressure with roughly 2% error.

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