Sparger Tests in PPOOLEX on the Behaviour of Thermocline
Markku Puustinen, Lauri Pyy, Jani Laine, Antti Räsänen,
This report summarizes the results of the two sparger pipe tests (SPA-T8R and SPA-T9) carried out in the PPOOLEX facility at LUT in 2016. Steam was blown through the vertical DN65 sparger type blowdown pipe to the condensation pool filled with sub-cooled water. Two different flow conditions were tested. Flow was either through all the 32 injection holes at the sparger head or just through eight holes in the bottom row.
The main objective of the tests was to obtain data for the development of the EMS and EHS models to be implemented in GOTHIC code by KTH. KTH plans to extend the models to cover also situations where steam injection into the pool is via a sparger pipe. The test parameters were selected by KTH on the basis of pre-test simulations and analysis of the results of the earlier sparger tests in PPOOLEX. Particularly the behaviour of the thermocline between the cold and warm water volumes was of interest. For this purpose also PIV measurements were tried during the tests.
In SPA-T8R, where flow was via 32 injection holes, the thermocline seemed to be around the elevation of 670 mm at the end of the stratification phase just as predicted by the pre-test simulations. The thermocline moved downwards as the erosion process progressed. The prevailing mixing mechanism during the final mixing phase was also erosion rather than internal circulation.
In SPA-T9, where flow was via eight injection holes, the thermocline was at first at a higher elevation than in SPA-T8R. It then started to shift downwards as the flow rate was increased in small steps. Complete mixing of the pool was achieved with the steam mass flow rate of 85 g/s. Erosion was again the prevailing mechanism in the mixing process.
The few sequences with recognized flow patterns from the PIV measurements indicate that some kind of swirls could exist at the elevation of the thermocline. The flow direction just under the thermocline can also be opposite to that just above the thermocline. The somewhat chaotic nature of the investigated phenomenon creates problems when measuring with a slow-speed PIV system and therefore definitive conclusions on the detailed behaviour of the thermocline can’t be made.
These tests in PPOOLEX verified that mixing of a thermally stratified water pool can happen through an erosion process instead of internal circulation if suitable flow conditions prevail.