733 research outputs found
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 and the viscous number , 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 ) 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 TopsĂže 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 Ă€r en viktig kemikalie och en byggsten i kemiindustrin. Det dyraste vid produktionen Ă€r rĂ„varan metanol, om rĂ„-metanol anvĂ€nds blir processen billigare. Projektet tittar frĂ€mst pĂ„ bildningen av biprodukter. Denna populĂ€rvetenskapliga sammanfattning Ă€r baserad pĂ„ ett examensarbete dĂ€r frĂ„gestĂ€llningen var att ta reda pĂ„ om rĂ„-metanol, en metanol som kommer direkt ifrĂ„n tillverkningen, skulle kunna anvĂ€ndas för att producera formaldehyd. Formaldehyd Ă€r en viktig kemikalie som bland annat anvĂ€nds vid framstĂ€llningen av plywood och som byggsten för att producera andra kemikalier. RĂ„-metanolen innehĂ„ller olika föroreningar i olika mĂ€ngd, framförallt innehĂ„ller den etanol samt andra högre alkoholer. Experimenten som gjorts har frĂ€mst tittat pĂ„ vilka biprodukter som har skapats frĂ„n de olika orenheterna som finns i rĂ„-metanol. Rapporten kom fram till att det frĂ€mst fanns tvĂ„ biprodukter som, i alla fallen, ökade mest. Ămnena heter dimetyleter (DME) och dimetoxymetan (DMM). Ingen av dessa biprodukter skulle kunna komma att vara nĂ„got problem i den processanlĂ€ggning som anvĂ€nds vid produktionen av formaldehyd. FrĂ„n mixen som gjordes av alla orenheten sĂ„gs samma biprodukter (DME samt DMM) öka mest. Inga andra biprodukter kunde ses ha bildats. Detta Ă€r intressant dĂ„ 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 dĂ€rför inte pĂ„verka processen nĂ€mnvĂ€rt. Den andra, DMM, kommer förmodligen att reagera tillbaka till metanol och formaldehyd nĂ€r produkten löses i vatten. Det som kan diskuteras Ă€r hur biprodukterna skulle pĂ„verkas dĂ„ mer metanol omvandlas till formaldehyd, dĂ„ 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 pĂ„ om oren metanol skulle kunna anvĂ€ndas för produktionen av formaldehyd Ă€r vad det skulle resultera i. Att mindre energi skulle behöva anvĂ€nds vid produktionen av metanol pĂ„ grund utav att reningssteg kan försummas. Vilket i sin tur resulterar till att pengar vid formaldehyd-produktionen skulle sparas, dĂ„ metanolen stĂ„r för stora delar av den rörliga kostanden för produktionen. Det finns fortfarande en hel del att göra pĂ„ detta projekt innan det kommer att kunna appliceras i en process. Men om framtida studier inte hittar nĂ„got som skulle kunna komplicera processen, ska det förhoppningsvis gĂ„ att anvĂ€nda rĂ„-metanolen vid produktion av formaldehyd. UtifrĂ„n detta projekt ser framtiden ljus ut, dock Ă€r det en bra bit kvar innan detta kan sĂ€kerstĂ€llas. Som nĂ€mnt ovan kan bilden av vilka biprodukter som tillverkas se annorlunda ut dĂ„ en högre omsĂ€ttning 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 -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 -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
Pride, Prejudice and Pigeonholing - a study of multiculturalism in a Swedish setting
The following essay deals with the issue of immigration. Within the field of immigration the focus concerns demos, multiculturalism and identity. Moreover, Sweden acts as the focal point due to its state proclaimed positive multicultural attitude, and more specifically RosengÄrd, a suburb to the city of Malmö. Due to the state's positive attitude towards multiculturalism, the implications in implementation are multifaceted. The questions derive from the problem of how to institutionally design a society with room for multiple cultures within one demos. The answer is contingent upon the factors of how these different cultures collectively identify themselves, and what components induce a certain pattern of identification. It is all dependent on the normatively set aim to produce trust and an effective society with multiculturalism as a positive factor. With the ongoing debate of the situation in segregated areas, the primary interest lies in identifying why some, especially youths, in immigrant dense areas, according to the general discourse, demonstrate a deviating behaviour. The results show that the process of individual identification takes a toll through especially media's stereotyping of, in this case, a specific subur
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