COOLING WATER DISCHARGE INTO THE IMPOUNDMENT RESERVOIR VIENNA-FREUDENAU: EVALUATING DIFFUSER PERFORMANCE AND CORMIX-BASED MIXING SIMULATION

In the wake of the construction of the River Danube hydropower plant Vienna-Freundenau the cooling water discharge of the Donaustadt thermal power plant was redesigned, with the associated mixing simulations performed by means of CORMIX, the CORnell MIXing zone expert system. Particular attention had to be paid to an ecologically sensitive zone in the receiving Freudenau impoundment reservoir, comprising the fish pass of the Freudenau hydropower plant, which was (and is) located on the same (left) bank of the River Danube as the Donaustadt thermal power station. To achieve a reliably high initial dilution of the cooling water, a unidirectional multiport diffuser was chosen to be installed, a decision which consequently resulted in the first construction of a cooling water diffuser in Austria. This diffuser now discharges up to 20 m/s of cooling water into an impounded reach of the River Danube with a water depth of some 11 m. Injection is co-flowing in plan view and oriented 45 ° upwards. The diffuser comprises two feeder pipes with 16 nozzles each, giving a total of 32 discharge ports, equally spaced at a hydraulically effective distance of 2 m (with 62 m, therefore, between first and last discharge port centreline). CORMIX-based mixin