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An investigation was conducted of the performance of thermally stratified vertical cylindrical tanks equipped with diffusers and containing either heated or chilled water, with emphasis on the latter. Tests were performed in a scale model tank equipped with radial diffusers and in a prototype 35,300 gal (133 m3 ) concrete tank equipped alternately with radial diffusers and an octagonal array of linear diffusers. Part I presents the results obtained from the scale model tank, and this part presents the results obtained from the prototype tank. Tests were performed on the prototype tank using two sizes of radial diffuser and an octagonal array of linear diffusers for a nominal temperature range from 40°F to 60°F( 4.4°C to 15.6°C) i.e., chilled water storage for space cooling. Tests were also performed with the smaller radial diffuser for the range from 100°F to 120°F(38°C to 49°C), corresponding to space heating applications.

The three diffusers all produced satisfactory stratification and tank thermal performance with an inlet Froude number of about unity, but stratification and performance improved from the smaller to the larger radial diffuser and again from the larger radial diffuser to the octagonal diffuser. It is hypothesized that this is due to successively lower values of the inlet Reynolds number produced by the latter two diffusers. Oscillation of the outlet temperature during discharging of a cool tank and charging of a warm tank was observed with the smaller radial diffuser, and incipient oscillations were apparently observed with the larger radial diffuser, but there was no evidence of oscillations with the octagonal diffuser. The performance of a heated tank with the smaller radial diffuser was about the same as for a cooled tank with the same diffuser.

Citation: Symposium, ASHRAE Transactions, vol. 95, pt. 1, Chicago 1989