Simulation, Rheology and Efficiency of Polymer Enhanced Solutions April 5, 2017

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1 CCEFP INDUSTRY-UNIVERSITY SUMMIT of Polymer Enhanced Solutions April 5, 2017 Duval Johnson, Uma Shantini Ramasamy, Ashlie Martini, University of California Merced, Merced, CA Mercy Cheekolu, Pawan Panwar, Paul Michael Milwaukee School of Engineering Fluid Power Institute, Milwaukee, WI

2 Research Strategy Project Goal: Bridge the gap between fundamental behavior of polymer enhanced fluids and the performance of complex fluid power systems Hydraulic Efficiency Solution Rheology Molecular Structure 2

3 Test Fluids Two straight-grade fluids with Newtonian viscosity characteristics HM46-6 and HM46-7 Group III and Group II respectively Two multigrade fluids with non-newtonian viscosity characteristics HV46-5 and HV46-8 Same ratio of 4cSt and 8cSt Group III base oils Different polyalkylmethacrylate (PAMA) polymers Low shear stability and high shear stability Fluid ID HM46-6 HM46-7 HV46-5 HV46-8 Base Oil Group III Group II Group III Group III ZDDP antiwear package 1% 1% 1% 1% 8 cst Base Oil, wt% 99% 99% 32% 32% 4 cst Base Oil, wt% % 54% Polymethacrylate, wt% % 13% Polymethacrylate Mw, g/mol (ave) ,000 50,000 approximate additive and base oil ratios 3

4 Shear Stability ASTM D Standard Test Method for Sonic Shear Stability of Hydraulic Fluids 10.0% 16.2% formulators.dynavis.com Fluid ID Method HM46-6 HM46-7 HV46-5 HV46-8 Kin 40 C, cst D445 before shear Kin 40 C, cst D5621 after shear Kin 100 C, cst D445 before shear Kin 100 C, cst D5621 after shear Viscosity loss, % 100 C 0.4% 0.6% 16.2% 10.0% 4

5 Dynamometer Danfoss Series 45 Pump Modified ISO 4409 Axial piston pump Variable displacement 50⁰C and 80⁰C inlet temp Danfoss Series 90 Motor Modified ISO Axial piston motor 1000 to 4000 psi 1 to 1400 RPM Studied change in system flow losses over time Flow losses = internal leakage that is lost kinetic energy that doesn t produce work Flow losses = pump and motor case drains + pressure compensator + valves 35 Data sets 328 combinations of pressure, speed and temperature for each data set 11,480 measurements 5

6 Effect of Pressure Internal leakage is caused by pressure driven flow As pressure increases, internal leakage flow rates increase The straight grade oils exhibit higher internal leakage flows HM46-6 vs HV46-5 HM46-7 vs HV46-8 6

7 Mean Flow Losses When the machine is working hard, the system pressure is high At high pressures the multigrade oils losses were 4% to 5% lower Reducing flow losses improves machine productivity HM46-6 vs HV46-5 HM46-7 vs HV46-8 7

8 Effect of Operating Time Straight grade fluids were tested for 32 hours Multigrade fluids were tested for 200 to 300 hours Viscosity changes were observed but flow losses were fairly consistent HM46-6 vs HV46-5 HM46-7 vs HV46-8 System Leakage Flow Bar label = Kinematic Viscosity at 100C Mean of Qls/ gpm Operating time, Hours 8

9 Benchtop vs Dyno Shear Stability Operating time correlated with viscosity change in dynamometer test Sonic shear test correlated with rate of viscosity change in dynamometer Viscosity vs operating time HV46-8 and HV46-5 9

10 Flow Loss Correlation Flow losses showed a weak correlation with operating time Flow losses showed a weak correlation with viscosity Leakage flow vs operating time HV46-8 and HV46-5 Leakage flow vs viscosity HV46-8 and HV

11 Kinematic Viscosity 1. Fill the viscosity to the prescribed level 2. Immerse the tube in a constanttemperature bath 3. Equilibrate the fluid for 15 minutes 4. Draw the fluid up the tube via vacuum 5. Allow the fluid to flow back down by gravity 6. Record flow time from start to stop 7. Calculate viscosity in centistokes as the product of flow time and tube constant 8. Report results in cst or mm 2 /s 11

12 Dynamic Viscosity Low Shear Rate Viscosity Comparison Rotational Motion Strain or deformation ( ) is applied, while stress or force ( ) is measured. Kinematic Viscosity in C Dynamic Viscosity in C - 100/s 13 Fluid HM46-6 HM46-7 HV46-5 HV46-8 Test Oil Temperature Control. Shear rate = = v h Rotor Stator v h v=0 12

13 High Shear Viscometer Small Amount of Fluid Injected into Rotor/Stator Rotor is spun at high speeds and viscosity was measured Tests were performed at 60, 80 and 100 C Rotor/Stator The shear rate ranged from 500,000 and 6,000,000 1/s 13

14 High Shear Viscosity Results The viscosities of the Newtonian fluids were independent of the shear rate The viscosities of the Non-Newtonian fluids decreased as the shear rate increases The high shear rate viscosity plateau is evident at 80 and 100 C 60 C, cp Scatterplot of Vis, cp vs Shear 60 C Shear rate, 1/s Results include rows where T = 60. Fluid HM46-6 HM46-7 HV46-5 HV46-8 Scatterplot of Vis, cp vs Shear 80 C Scatterplot of Vis, cp vs Shear C Viscosity at 80 C, cp Fluid HM46-6 HM46-7 HV46-5 HV46-8 C, cp Fluid HM46-6 HM46-7 HV46-5 HV Shear rate, 1/s Shear rate, 1/s Results include rows where T = 80. Results include rows where T =

15 High Shear Viscosity vs Hours Shear rate 1,000,000 1/s Viscosity measurements exhibit a decreasing trend over time at 60 and 80 C The viscosity measurements do not exhibit the same trend at 100 C 1,000,000/s & 60 C, cp Scatterplot of Vis, 60 C vs Hrs Operating time, hours 300 Fluid HM46-6 HM46-7 HV46-5 HV46-8 Results include rows where 'Nom Shear Rate' = And T=60. Scatterplot of Vis, 80 C vs Hrs Scatterplot of Vis, 100 C vs Hrs 1,000,000/s & 80 C, cp Fluid HM46-6 HM46-7 HV46-5 HV46-8 1,000,000/s & 100 C, cp Fluid HM46-6 HM46-7 HV46-5 HV Operating time, hours Operating time, hours Results include rows where 'Nom Shear Rate' = And T=80. Results include rows where 'Nom Shear Rate' = And T=

16 16 Oscillatory Viscosity μ = σ γሶ σ = σ 0 cos(ωt) γ = γ 0 cos(ωt δ) ω = 2πf G = Storage Modulus = σ 0 γ 0 cos(δ) G " = Loss Modulus = σ 0 γ 0 sin(δ) G = Complex Shear Modulus = σ 0 γ 0 cos δ + σ 0 γ 0 jsin(δ) μ = Complex Viscosity = σ 0 jγ 0 ω ejδ = G jω 16

17 17 Constant Strain, Variable Frequency Increase of storage modulus as angular velocity increases Decrease of loss modulus as angular velocity increases 17

18 Molecular Simulations 2 cst (PAO) Polyalphaolefin Polyisobutylene (PIB) Each model system contains base fluid molecules and one or more polymer molecules The periodic boundary conditions (black lines in figure to the left) mean that we are effectively modeling a much larger system 18

19 Model Validation Viscosity is measured directly for comparable fluids to provide reference data for validation Blending Viscosity Measurement H PAO2 19

20 Viscosity (cp) Viscosity (cp) Direct Comparison Comparisons between experiments and simulations at 40C and 100C were reasonable, suggesting our methods are sound 10 wt.% PIB 20 wt.% PIB C 100 C C Rheometer MD-1 Polymer Rheometer MD-1 Polymer MD-2 Polymer MD-2 Polymer 20

21 Viscosity (cst) Viscosity Trends 2 nm Viscosity increases with PIB MW at the same concentration (10 wt.%) For the 1,346 MW PIB, viscosity also increases with concentration, as expected 21

22 Thickener or VI Improver? A polymer can be a thickener (same viscosity increase at all T) or a VI improver (enhanced viscosity at high T only) VI improvement can occur via several mechanisms, each of which can be explicitly tested using the simulation: Coil Expansion Aggregation/Association Solubility 22

23 Count VII Mechanism Tests Coil Expansion 40C R g 100C Temperature (C) Mean Rg (Angstrom) ± ± 1.5 Radius Aggregation # Contact Atoms 100 C Viscosity (cp)

24 VII Mechanism Tests Solubility Temperature (C) Δδ δ = solubility parameter E = cohesive energy V = molar volume Summary of Simulations: We developed molecular models of polymer-enhanced fluids Models were validated by comparison to experiments for select cases and by their ability to reproduce expected trends The simulations provide a tool with which to test thickener and VI improver mechanisms 24

25 Summary Polymer additives (VI improvers) reduced flow losses The relationship between permanent viscosity loss and leakage flow was investigated The correlation between permanent polymer shear thinning and flow losses was weak It is hypothesized that the combined permanent and temporary polymer shear thinning affect flow losses High shear rate viscosity measurements at 100 C captured temporary and permanent viscosity loss The viscoelastic properties of the fluid were investigated using an oscillatory viscometer Molecular dynamics simulation techniques have been developed to discern the functional mode of polymers 25

26 Acknowledgements National Fluid Power Association Pascal Society Donors of the American Chemical Society Petroleum Research Fund (# ND6) UC Merced BEST Travel Support Thank you for your kind attention! 26