35 Ton LAr Impurity Distribution Measurements and CFD simulation Erik Voirin – Fermilab – Thermal and Fluids Engineering Group / Engineering Analysis Group Thanks to Terry Tope, Alan Hahn, and Stephen Pordes for measurements and other Information Important to this study. Erik Voirin1 35 Ton Impurity/Lifetime Measurements and CFD Simulation

Scope of Measurements and CFD Simulation: There are 4 purity monitors in one corner of the 35 TON LAr cryostat which measure electron lifetime, which is inversely proportional to impurity levels. The lifetime measurement at the top and the bottom have always shown a difference in purity levels. In March of 2016, a power outage occurred, which stopped the pumps and purification, and during this time, a homogeneous lifetime profile could be seen, as the top and bottom purity monitors read the same value, and lifetime decreased together. This can be seen in slide 4, where the tag name “35T_PRM_Lifetime_1.F_CV” was the bottom purity monitor, and “35T_PRM_Lifetime_4.F_CV” is the top purity monitor. When the pumps and purification was restarted around 10:00 am, the vertical gradient in purity levels could be seen again, with higher electron lifetime, and more pure liquid on the bottom of the cryostat. See Slide 5 for data after the pumps were restarted, note there are 4 purity monitors plotted here, #1 through #4 being in order of elevation, #1 near the bottom up to #4 being near the top. Since no gradient was seen with purification off, it was apparent the cryostat did indeed have a real, and large vertical gradient in purity. Since we are conducting Computational Fluid Dynamics (CFD) simulations of the future LBNF cryostat, and making conceptual design decisions based on these simulations, we conducted a similar simulation of the 35 TON cryostat to compare to the measurements and validate the model. Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 2

Geometry of 35 Ton Cryostat Erik Voirin3 35 Ton Impurity/Lifetime Measurements and CFD Simulation 4 purity monitors in this corner (Geometry Not in CFD model)

Pumps and Purification Off Same Electron Lifetime at Top and Bottom. Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 4

Pumps and Purification Restarted. Vertical gradient develops in electron lifetime/purity Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 5

Liquid Surface of Cryostat (Saturation Temp = psia) (Average Impurity Flux from Liquid Surface of nanogram/m^2/sec of water) Erik Voirin6 35 Ton Impurity/Lifetime Measurements and CFD Simulation 4 purity monitors in this corner (Geometry Not in CFD model)

Wall Heat Flux Through Insulation ( 15 W/m^2) Erik Voirin7 35 Ton Impurity/Lifetime Measurements and CFD Simulation

Cryostat with APA and CPAs, Pumps, Pump Piping, Field Cage Frame, Electronics Boxes. Pump 1 Body has 255W of Heat Flow. Erik Voirin8 35 Ton Impurity/Lifetime Measurements and CFD Simulation

Field Cage: PCB with slots cut into it. (¼” slot every 2”) Erik Voirin9 35 Ton Impurity/Lifetime Measurements and CFD Simulation

Field Cage: 12.5% Open Slots Erik Voirin10 35 Ton Impurity/Lifetime Measurements and CFD Simulation

Inlet Pipe and Inlet Flow Path ( 9.5 gpm Pure Slightly above Saturation Temp: K, which is colder than bulk argon due to phase separator at the top) Erik Voirin11 35 Ton Impurity/Lifetime Measurements and CFD Simulation Pump Suction Pump Discharge Pipe with Phase Separator on Top

Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 12

Electron Lifetime vs Impurity levels Electron Lifetime inversely related to impurity levels: – Known for Oxygen, estimated for water. Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 13

CFD Results: Electron Lifetime and Velocity Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 14

CFD Results: Electron Lifetime and Velocity Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 15

Comparison of Measurements to CFD Model. Impressive overall agreement with measured lifetime values. Purity Monitor geometries are not in CFD model, 5” diameter cylinders with porous mesh on sides. These could influence the Impurity distribution near the top as the Vertical pump pipe does, which shows a sharp gradient near at the top purity monitor. Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 16 Purity Monitors span up to 2 feet in elevation, but give a single value for electron lifetime.

Discussion of Results / Lessons Learned Phase separator cools inlet flow to approach saturation temperature, which is below the “bulk temperature” of the argon. This cooler, more dense layer of argon tends to stay at the bottom, and not mix well with the rest of the argon. Back pressure control at the phase separator could allow us to flow in warmer argon, which would then mix well with the bulk. Erik Voirin17 35 Ton Impurity/Lifetime Measurements and CFD Simulation Pump Suction Pump Discharge Pipe with Phase Separator on Top, LAr flows down, and impinges on cryostat floor.

5.3x at much Impurity Flow during Deterioration: 11.5 ng/sec Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 18

Impurity Flow During Power Outage With 11.5 ng/sec water impurity flow into LAr, we would only be able to achieve 1ms lifetime. During power outage, boil off gas (with a lot of contaminants) is condensed straight back into liquid without filtering. This shows we normally absorb 19% of all contaminants released in the ullage. – The other 81% exit out gas outlets and purge ports. – This is a very reasonable fraction of absorbed contaminants based on previous ullage space CFD models. Erik Voirin 35 Ton Impurity/Lifetime Measurements and CFD Simulation 19