Constant flow rate charging characteristics of a full-scale stratified chilled water storage tank with double-ring slotted pipe diffusers

Temperature distributions formed during charging of a 14 m (46 ft) water depth, 7 m (23 ft) radius stratified chilled water storage tank with double ring octagonal slotted pipe diffusers were recorded and analyzed. Prior to the beginning of each test, the tank was fully discharged and at a relatively uniform temperature. To the extent possible, inlet flow rate and temperature were held constant during each test. Six tests were performed for flow rates varying from 50% to 95% of design. Thermal performance was quantified using thermocline thickness, half-cycle figure of merit (FoM1/2) and equivalent lost tank height (ELH). The thermal performance for all tested charge flow rates was good by current standards (FoM1/2 > 90%, ELH < 1 m in all but one case). Thermocline thickness for low and medium flow rates was relatively small, on the order of 1 m (3 ft). Erroneously large thermocline thickness measurements were obtained in the high flow rate case because of the effect of inlet temperature variation combined with the definition used. Significant bulk temperature increase observed below the thermocline in all cases was most likely due to large-scale convection cells driven by the inlet flow. Efforts to improve the performance of diffusers should focus on suppressing this circulation.