Flow throttling in surge tanks using porous structures

Well-designed local loss throttles at inlet of pressurized and open surge tanks are beneficial in terms of reducing tank size and faster dampening of pressure oscillation. This research investigates porous structures experimentally as a possibility to increase the head loss at surge tanks throttle. Both scenarios of valve closure from upstream and downstream of the pipeline are considered to model pump trip and load rejection in hydropower plants. Performance of porous structure is examined and compared with the case of using simple and differential orifice throttles. Layered porous media is also studied to examine feasibility of achieving variable throttling effect for inflow and outflow from the surge tank. Results confirm considerable advantages of porous throttling over customary orifice throttling for faster transient dampening. This is due to lower head loss coefficient of porous throttle in high velocity flow and higher head loss coefficient in low velocity flow in comparison with the orifice throttle. In a layered porous structure, flow from smaller to larger spheres showed to have an average of 15% lower head loss than the flow from larger to smaller spheres. The Reynolds similarity of the porous spheres is also shown to be governing parameter in up and downscaling of the modeling results in practice.