The development of a new, optimised fuel is a process in which various necessary fuel properties have to be taken into account. For an inclusion of candidates not synthesised yet into the design process, a fully predictive model relying on nothing but the molecular structure is mandatory for each relevant property. One of the most important aspects for the design of a fuel is its lubricity. In this study, the predictive method conductor-like screening model for realistic solvation (COSMO-RS) for the calculation of thermodynamic mixture properties is adopted for deriving a quantitative structure-property relationship for the lubricity of fuel components. COSMO-RS calculates molecular descriptors (sigma moments) based on quantum chemical calculations. These descriptors are adapted to describe the underlying phenomena causing the film formation ability and lubricity of the fuel. The lubricity is assessed via high-frequency reciprocating rig measurements taken from literature. The molecular descriptors and experimental data are evaluated via statistical methods in order to find the most influential molecular descriptors. ABBREVIATIONS BP-RI-DFT Becke-Perdew resolution of identity density functional theory COSMO conductor-like screening model COSMO-RS conductor-like screening model for realistic solvation HFRR high-frequency reciprocating rig HOMO highest occupied molecular orbital LUMO lowest unoccupied molecular orbital RMSECV root-mean-square error of leave-one-out cross validation SSCD surface screening charge distribution
In this paper, analytical equations for the central film thickness in slender elliptic contacts are investigated. A comparison of state-of-the-art formulas with simulation results of a multilevel elastohydrodynamic lubrication solver is conducted and shows considerable deviation. Therefore, a new film thickness formula for slender elliptic contacts with variable ellipticity is derived. It incorporates asymptotic solutions, which results in validity over a large parameter domain. It captures the behaviour of increasing film thickness with increasing load for specific very slender contacts. The new formula proves to be significantly more accurate than current equations. Experimental studies and discussions on minimum film thickness will be presented in a subsequent publication.
Within the present investigation, a miniature viscous disk pump (VDP) is utilized to characterize and quantify non-Newtonian fluid elastic turbulence effects, relative to Newtonian flow behavior. Such deviations from Newtonian behavior are induced by adding polyacrylamide to purified water. The VDP consists of a 10.16 mm diameter disk that rotates above a C-shaped channel with inner and outer radii of 1.19 mm, and 2.38 mm, respectively. A channel depth of 230 μm is employed. Fluid inlet and outlet ports are located at the ends of the C-shaped channel. Within the present study, experimental data are given for rotational speeds of 1200–3500 rpm, pressure rises of 0 to 700 Pa, and flow rates up to approximately 0.00000007 m3/sec. As such, the overall intent is enhancement of fundamental understanding of the associated physical processes associated with elastic turbulence, as it is induced in liquids by polymers subject to stretching and constriction by flow strain. Different amounts of flow strain are induced by changing the rotational speed of the disc. As rotational speed increases, overall magnitudes of flow strain increase, and the polymer strings become locally more agitated. The result is growth in the local elastic stress, and development of the Weissenberg instability as the Weissenberg number increases. Overall consequences include increased mixing, increased transport levels, and larger static pressure rise magnitudes. Also considered are changes to effective viscosity from the presence of elastic turbulence.
Within the present investigation, a miniature viscous disk pump (VDP) is utilized to characterize and quantify non-Newtonian fluid elastic turbulence effects, relative to Newtonian flow behavior. Such deviations from Newtonian behavior are induced by adding polyacrylamide to purified water. The VDP consists of a 10.16 mm diameter disk that rotates above a C-shaped channel with inner and outer radii of 1.19 mm and 2.38 mm, respectively. A channel depth of 230 μm is employed. Fluid inlet and outlet ports are located at the ends of the C-shaped channel. Experimental data are given for rotational speeds of 126 1/s, 188 1/s, 262 1/s, and 366 1/s, pressure rises as high as 700 Pa, and flow rates up to approximately 0.00000005 m3/s. Reynolds number ranges from 2.9 to 6.5 for the non-Newtonian polyacrylamide solution flows and from 51.6 to 149.8 for the Newtonian pure water flows. To characterize deviations due to non-Newtonian elastic turbulence phenomena, two new parameters are introduced, PrR and HCR, where HCR is the ratio of head coefficient (HC) for the polyacrylamide solution and head coefficient for the water solution, and PrR is the ratio of pump power for the polyacrylamide solution and pump power for the water solution. Relative to Newtonian, pure water flows, the polyacrylamide solution flows give pump head coefficient data, dimensional pressure rise data, slip coefficients (SCs), specific speed (SS) values, and dimensional power data, which show significant variations and differences as they vary with flow coefficient (FC) or dimensional volumetric flow rate. Also important are different ranges of specific speed (SS) for the pure water and polyacrylamide solutions, and a lower range of SC or slip coefficient values for the polyacrylamide solution flows, compared to the pure water flows. These variations are due to increased elastic turbulence losses, which occur as viscosity magnitudes increase and the elastic polymers are excited by mechanical stress, which causes them to extend, deform, stretch, and intertwine.
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