Effect of Friction on Dense Suspension Flows of Hard Particles

We use numerical simulations to study the effect of particle friction on suspension flows of non-Brownian hard particles. By systematically varying the microscopic friction coefficient $\mu_p$ and the viscous number $J$, we build a phase diagram that identifies three regimes of flow: Frictionless, Frictional Sliding, and Rolling. Using energy balance in flow, we predict relations between kinetic observables, confirmed by numerical simulations. For realistic friction coefficient and small viscous numbers (below $J\sim 10^{-3}$) we show that the dominating dissipative mechanism is sliding of frictional contacts, and we characterize asymptotic behaviors as jamming is approached. Outside this regime, our observations support that flow belongs to the universality class of frictionless particles. We discuss recent experiments in the context of our phase diagram.Comment: 8 page

By-products from production of Formaldehyde for Haldor Topsoe

Formaldehyde is an important chemical which is used as an intermediate and for the production of urea-formaldehyde, which is used in the production of plywood. The purpose of this report is to investigate to how impurities in methanol, that is the raw material in formaldehyde production, will affect the production. This report have mainly looked at how the impurities affect the by-products. This project is done in collaboration with Haldor Topsøe A/S (HT). To be able to study the production an experimental set-up had to be made. It was executed in the attempt to be as close to an HT formaldehyde plant as possible. The different impurities were added one by one and then a mixture of the components were made. The production stream were analyzed by a mass spectrometer (MS). In all experiment the different impurities were added one-by-one. The impurities that were used were: ethanol, higher alcohols (1-butanol and 2-propanole), methyl formate (MF) and acetone. In all the experimental cases an increase in dimethyl ether (DME) concentration could be seen and for nearly all impurities an increase in dimetoxy methane (DMM) was also detected. The same results could be seen for the mixture, in which all the impurities were added. This means that the different impurities does not seem to react with one another. DME and DMM will not be a problem since DME already exist as a by-product today, and DMM would most likely react back to methanol and formaldehyde in the acidic environment which exist in the absorption tower.Formaldehyd är en viktig kemikalie och en byggsten i kemiindustrin. Det dyraste vid produktionen är råvaran metanol, om rå-metanol används blir processen billigare. Projektet tittar främst på bildningen av biprodukter. Denna populärvetenskapliga sammanfattning är baserad på ett examensarbete där frågeställningen var att ta reda på om rå-metanol, en metanol som kommer direkt ifrån tillverkningen, skulle kunna användas för att producera formaldehyd. Formaldehyd är en viktig kemikalie som bland annat används vid framställningen av plywood och som byggsten för att producera andra kemikalier. Rå-metanolen innehåller olika föroreningar i olika mängd, framförallt innehåller den etanol samt andra högre alkoholer. Experimenten som gjorts har främst tittat på vilka biprodukter som har skapats från de olika orenheterna som finns i rå-metanol. Rapporten kom fram till att det främst fanns två biprodukter som, i alla fallen, ökade mest. Ämnena heter dimetyleter (DME) och dimetoxymetan (DMM). Ingen av dessa biprodukter skulle kunna komma att vara något problem i den processanläggning som används vid produktionen av formaldehyd. Från mixen som gjordes av alla orenheten sågs samma biprodukter (DME samt DMM) öka mest. Inga andra biprodukter kunde ses ha bildats. Detta är intressant då det medför att orenheterna förmodligen inte reagerar med varandra och skulle inte komma att störa processen. Den första biprodukten, DME, finns redan i produktionen idag som en biprodukt och borde därför inte påverka processen nämnvärt. Den andra, DMM, kommer förmodligen att reagera tillbaka till metanol och formaldehyd när produkten löses i vatten. Det som kan diskuteras är hur biprodukterna skulle påverkas då mer metanol omvandlas till formaldehyd, då detta var ett problem som existerade i projektet. Om mer metanol reagerar till formaldehyd kommer miljön att bli mer sur och resultera i att bilden av biprodukterna ser annorlunda ut. Det som bland annat gör det intressant att ta reda på om oren metanol skulle kunna användas för produktionen av formaldehyd är vad det skulle resultera i. Att mindre energi skulle behöva används vid produktionen av metanol på grund utav att reningssteg kan försummas. Vilket i sin tur resulterar till att pengar vid formaldehyd-produktionen skulle sparas, då metanolen står för stora delar av den rörliga kostanden för produktionen. Det finns fortfarande en hel del att göra på detta projekt innan det kommer att kunna appliceras i en process. Men om framtida studier inte hittar något som skulle kunna komplicera processen, ska det förhoppningsvis gå att använda rå-metanolen vid produktion av formaldehyd. Utifrån detta projekt ser framtiden ljus ut, dock är det en bra bit kvar innan detta kan säkerställas. Som nämnt ovan kan bilden av vilka biprodukter som tillverkas se annorlunda ut då en högre omsättning av metanolen reagerar till formaldehyd

Transition from viscous to inertial regime in dense suspensions

Non-Brownian suspensions present a transition from Newtonian behavior in the zero-shear limit to a shear thickening behaviour at a large shear rate, none of which is clearly understood so far. Here, we carry out numerical simulations of such an athermal dense suspension under shear, at an imposed confining pressure. This set-up is conceptually identical to the recent experiments of Boyer and co-workers [Phys. Rev. Lett. 107,188301 (2011)]. Varying the interstitial fluid viscosities, we recover the Newtonian and Bagnoldian regimes and show that they correspond to a dissipation dominated by viscous and contact forces respectively. We show that the two rheological regimes can be unified as a function of a single dimensionless number, by adding the contributions to the dissipation at a given volume fraction.Comment: 4 pages, 3 figure

A historical study of the theatre of the Mother Lode during the Gold Rush period

Many events of the gold rush have been adequately narrated in numerous books and articles. The succeeding pages in this thesis will recall, historically by topic, important incidents of one phase of that period never before treated as a separate study that phase is the theatre of the Mother Lode region. The argonauts of the Mother Lode wanted to be entertained and could pay for it. Many preferred the saloon and gamboling hall, but the theatre did not languish because of this, and in fact, developed in some instances directly out of the saloons and fandango halls. It was the purpose of this study (1) to present the history of the theatre of the Mother Lode during that portion of the gold rush period of the decade 1851-1861; (2) to show who some of the notable thespians were; (3) to describe the modes of transportation used; (4) to give historical accounts of the buildings used for, or built for, theatres; (5) to review some of the plays and performances offered; and (6) to show the influence of the audiences\u27 reactions to the bill of theatrical fare

Extended μ(J)\mu(J)-rheology for dense suspensions at oscillatory shear flows

Recent studies have highlighted that oscillatory and time-dependent shear flows might help increase flowability of dense suspensions. While most focus has been on cross-flows we here study a simple two-dimensional suspensions where we apply simultaneously oscillatory and stationary shear along the same direction. We first show that the viscosities in this set-up significantly decrease with an increasing magnitude of the oscillations, contrary to previous claims. The decrease can be attributed to the large decrease in the number of contacts and an altered microstructure as the magnitude of the oscillation is increased. As a sub-result we find both an extension to the $\mu(J)$-rheology, a constitutive relationship between the shear stresses and the shear rate, valid for pure oscillatory flows and with a higher shear-jammed packing fraction for suspensions composed of frictional particles compared to steady-shear conditions.Comment: 5 pages, 5 figure

Classical van der Waals interactions between spherical bodies of dipolar fluid

The van der Waals interaction free energy Aint between two spherical bodies of Stockmayer fluid across a vacuum is calculated using molecular simulations and classical perturbation theory. The results are decomposed into their electrostatic and Lennard-Jones parts, and the former is shown to agree excellently with predictions from dielectric continuum theory. Aint is decomposed into its energetic and entropic contributions and the results are compared with analytical predictions. Finally, we expand the electrostatic part of Aint in a multipole expansion, and show that the surprisingly good agreement between the molecular and continuum descriptions is likely due to a cancellation of errors coming from the neglect of the discrete nature of the fluid within the dielectric description

Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows

Dry, wet, dense, and dilute granular flows have been previously considered fundamentally different and thus described by distinct, and in many cases incompatible, rheologies. We carry out extensive simulations of granular flows, including wet and dry conditions, various geometries and driving mechanisms (boundary driven, fluid driven, and gravity driven), many of which are not captured by standard rheology models. For all simulated conditions, except for fluid-driven and gravity-driven flows close to the flow threshold, we find that the Mohr-Coulomb friction coefficient $\mu$ scales with the square root of the local P\'eclet number $\mathrm{Pe}$ provided that the particle diameter exceeds the particle mean free path. With decreasing $\mathrm{Pe}$ and granular temperature gradient $M$, this general scaling breaks down, leading to a yield condition with a variable yield stress ratio characterized by $M$