CFD Analysis of LAr Flow in 35 ton prototype, ProtoDUNE, & LBNF cryostats Gregory Michna Stephen Gent Aaron Propst Department of Mechanical Engineering South Dakota State University November 10, 2017
Project Goals • Study impurity levels within a LAr cryostat using Computational Fluid Dynamics (CFD) simulation methods. • Explore effect on impurity levels by changing: – LAr circulation flow rate and inlet temperature – LAr inlet and outlet locations – Internal electronics heat load • Desire a uniform and stable distribution of impurities 11/10/2017 Liquid Argon Flow CFD Simulations 2
Methods • Simulate LAr motion due to natural convection (buoyancy) with Boussinesq model. – Fluid body force equation: � � � � � � � ��� � � � � thermal expansion coefficient, � ��� � average temperature • Simulate impurity levels with a passive scalar. – Passive scalar is carried (convected and diffused) by LAr similar to colored dye in water. – One ‐ way coupling: “passive” scalar does not affect the LAr motion. • Simplify cryostat FC and APA geometry using porous regions. 11/10/2017 Liquid Argon Flow CFD Simulations 3
Impurity Level Quantification • Method 1: Electron Lifetime ����� ��∗�� ��� ���� – τ �������� �� � ����� ���� ∗���������� ����� �� � ∗�� ��� ����� – Useful when exact value of the impurity surface flux is known. – Can compare to experimental electron lifetime measurements from 35 Ton cryostat. 11/10/2017 Liquid Argon Flow CFD Simulations 4
Impurity Level Quantification • Method 2: Normalized Percent Difference – Impurity level scaled such that the average level within the field cage is 1 (or 100%). – Levels expressed as +/ ‐ % above or below 100%. – Useful when exact value of the impurity surface flux is unknown. – Easier to compare impurity levels between simulations. 11/10/2017 Liquid Argon Flow CFD Simulations 5
Simulations to Date ProtoDUNE 35 Ton • 35 Ton • V1 Design – Full and symmetric models • V2 Design – Symmetric only • Latest Design Top View of Latest Design – Full and symmetric – Various operating conditions � � �. � � • ProtoDUNE � � �. � � Removed in Symmetric Models 11/10/2017 Liquid Argon Flow CFD Simulations 6
35 Ton Simulation • Red: heat enters through wall • Blue: constant temperature, constant impurity flux • Yellow: field cage is a 23% porous wall • 9.5 GPM LAr flow rate • Constant inlet temperature: 87.808 K 11/10/2017 Liquid Argon Flow CFD Simulations 7
35 Ton Simulation Impurity Distribution Fermilab Results (Erik Voirin, Fermilab) 11/10/2017 Liquid Argon Flow CFD Simulations 8
35 Ton Simulation 4 purity monitors in this corner (Geometry Not accounted for in CFD model) (Erik Voirin, Fermilab) 11/10/2017 Liquid Argon Flow CFD Simulations 9
35 Ton Simulation 6000 5500 5000 SDSU Simulation Electron LIfetime [ μ s] Fermilab Simulation ‐ Probe 1 4500 Fermilab Simulation ‐ Probe 2 Fermilab Simulation ‐ Probe 3 4000 Experimental 3500 3000 2500 0 0.5 1 1.5 2 2.5 Elevation from Cryostat Floor [m] 11/10/2017 Liquid Argon Flow CFD Simulations 10
35 Ton Simulation • Simulation agrees with experimental data. • Can apply same CFD methods to other designs. 11/10/2017 Liquid Argon Flow CFD Simulations 11
LBNF Cryostat ‐ Geometry APA CPA APA CPA APA • APA – approx. 80% open Field Cage • CPA – impermeable • Field Cage – 23% open Field Cage 11/10/2017 Liquid Argon Flow CFD Simulations 12
LBNF Cryostat ‐ Geometry Cross Section from Side View Field Cage Field Cage Field Cage Field Cage 11/10/2017 Liquid Argon Flow CFD Simulations 13
LBNF Cryostat – Boundary Conditions • Top Wall (LAr surface): V1 Full V1 Sym. Latest Sym. – LAr Saturation Temperature: 88.348 K Inlet Flow Rate 4 Pumps 4 (2) Pumps 1 (0.5) pump – Passive Scalar Flux: 1 # of Inlets 1 1 (0.5) 12 (6) • Remaining Exterior Walls: # of Outlets 4 4 (2) 7 (7) – Heat Flux: 7.2 W/m^2 • Electronics Surfaces: Single Pump = 103 GPM – Total Heat Source: 23,700 W • Inlet Temperature: – Maintained at 0.4418 K above outlet temperature to account for pump work – Flow rate in table on the right • APA and FC Planes: – Treated as Porous Region, see next slide Electronics Surfaces in pink 11/10/2017 Liquid Argon Flow CFD Simulations 14
Representing APA Plane with Porous Region The APA planes consisted of 10 layers: • Plane 1 : Vertical wires (150 micron diameter at a 5 ‐ mm pitch) • Plane 2 : +60° wires • Plane 3 : ‐ 60° wires • Plane 4 : Vertical wires • Plane 5 : Mesh 80% open (90° wires of 0.528 ‐ mm dia. and 5 ‐ mm pitch) 1 • Planes 6 ‐ 10 : Symmetry of planes 1 ‐ 2 3 4 5 5, with a 75 mm space between planes 5 and 6. 11/10/2017 Liquid Argon Flow CFD Simulations 15
Representing APA Plane with Porous Region • Motivation: Cells required to Outlet represent real APA geometry for APA Mesh Layers entire cryostat is vastly beyond computational resources. Symmetry on 3 sides • Mimic the flow resistance on the macro ‐ scale using porous regions. – Simulate only a small section of real APA plane geometry. Inlet – Find pressure drop across planes at several velocities in expected range. 11/10/2017 Liquid Argon Flow CFD Simulations 16
Representing APA Plane with Porous Region • Plot pressure vs. velocity. 1.2 • Determine quadratic trend line. 1 Pressure Drop [Pa] • Use coefficients as inertial ( � � ) and 0.8 viscous ( � ) flow resistance 0.6 coefficients. 0.4 • Divide coefficient by porous region y = 563.21x 2 + 5.9315x thickness. 0.2 R² = 0.9999 • Final APA resistance coefficients: 0 0 0.01 0.02 0.03 0.04 – Inertial: 11,300 kg/m^4 Velocity [m/s] Fermilab Simulation SDSU Simulation – Viscous: 119 kg/m^3 ‐ s Poly. (SDSU Simulation) 11/10/2017 Liquid Argon Flow CFD Simulations 17
Representing FC Plane with Porous Region • FC plane consist of 23% open, slot geometry, assumed 23 mm slot at 100 mm pitch. Symmetry on all • Used same method as APA plane four sides Outlet to find resistance coefficients. • Final resistance coefficients: 2.3 cm slot – Inertial: 411,000 kg/m^4 – Viscous: 247 kg/m^3 ‐ s Inlet 11/10/2017 Liquid Argon Flow CFD Simulations 18
LBNF V1: Impurity and Temperature at z = 30.5 m plane (pump discharge) 11/10/2017 Liquid Argon Flow CFD Simulations 19
LBNF V1: Impurity and Temperature at z = 0 m plane (center of cryostat) z = 0 m plane (center of cryostat) 11/10/2017 Liquid Argon Flow CFD Simulations 20
Simulations • Latest Configuration: – Symmetric: standard operating conditions, electronics turned off, and half LAr flow rate. – Running full model: Erik Voirin’s results showed significant asymmetry. Top View of Latest Configuration � � �. � � � ����� � � �. � � Removed in Symmetric � ������ Models 11/10/2017 Liquid Argon Flow CFD Simulations 21
Mesh Validation • Used two mesh types with varying levels of refinement. • Solutions have been in agreement. • Polyhedral mesh requires more iterations and time (about 30%) to solve the passive scalar for impurity distribution. • Currently using trimmed cell mesh (hexahedral, cubes of varying sizes). Trimmed Polyhedral 11/10/2017 Liquid Argon Flow CFD Simulations 22
Latest Design: Symmetric vs. Full Model • Simulating half the cryostat will cut calculation time in half. • Must determine if both full and symmetric models yield similar results. 11/10/2017 Liquid Argon Flow CFD Simulations 23
Sym. vs. Full: Temperature at Z = 5.17 m In Line with Inlet Full Symmetric 11/10/2017 Liquid Argon Flow CFD Simulations 24
Sym. vs. Full: Impurity at Z = 5.17 m In Line with Inlet Full Symmetric 11/10/2017 Liquid Argon Flow CFD Simulations 25
Sym. vs. Full: Temperature at X = 3 m Full Symmetric 11/10/2017 Liquid Argon Flow CFD Simulations 26
Sym. vs. Full: Impurity at X = 3 m Full Symmetric 11/10/2017 Liquid Argon Flow CFD Simulations 27
Electronics Turned Off • Heat flux on electronics changed from 23,700.0 W to 0.0 W. • No other changes. • Will compare impurity level minimum, maximum, and standard deviation after slides of images. 11/10/2017 Liquid Argon Flow CFD Simulations 28
Electronics Off: Temperature at Z = 5.17 m In Line with Inlet Electronics On Electronics Off 11/10/2017 Liquid Argon Flow CFD Simulations 29
Electronics Off: Impurity at Z = 5.17 m In Line with Inlet Electronics On Electronics Off 11/10/2017 Liquid Argon Flow CFD Simulations 30
Electronics Off: Temperature at X = 3 m Electronics On Electronics Off 11/10/2017 Liquid Argon Flow CFD Simulations 31
Electronics Off: Impurity at X = 3 m Electronics On Electronics Off 11/10/2017 Liquid Argon Flow CFD Simulations 32
Half Flow Rate • LAr inlet flow rate changed from 103 GPM to 51.5 GPM 11/10/2017 Liquid Argon Flow CFD Simulations 33
Half Flow Rate: Temperature at Z = 5.17 m In Line with Inlet Regular Flow Rate Half Flow Rate 11/10/2017 Liquid Argon Flow CFD Simulations 34
Half Flow Rate: Impurity at Z = 5.17 m In Line with Inlet Regular Flow Rate Half Flow Rate 11/10/2017 Liquid Argon Flow CFD Simulations 35
Recommend
More recommend
