Implementation, demonstration and validation of a user-defined wall-function for direct precipitation fouling in ANSYS Fluent

In a previous paper (Johnsen et al., 2015) and presentation (Johnsen et al., 2016), we developed and demonstrated a generic modelling framework for the modelling of direct precipitation fouling from multi-component fluid mixtures that become super-saturated at the wall. The modelling concept involves the 1-dimensional transport of the fluid species through the turbulent boundary layer close to the wall. The governing equations include the Reynolds-averaged (RANS) advection-diffusion equations for each fluid species, and the axial momentum and energy equations for the fluid mixture. The driving force for the diffusive transport is the local gradient in the species' chemical potential. Adsorption mechanisms are not modelled per se, but the time-scale of adsorption is reflected in the choice of Dirichlet boundary conditions for the depositing species, at the fluid-solid interface. In this paper, the modelling framework is implemented as a user-defined function (UDF) for the CFD software ANSYS Fluent, to act as a wall boundary condition for mass-transfer to the wall. The subgrid, 1-dimensional formulation of the model reduces the computational cost associated with resolving the fine length-scales at which the boundary-layer mass transfer is determined, and allows for efficient modelling of industry-scale heat exchangers suffering from fouling. The current paper describes the modelling framework, and demonstrates and validates its applicability in a simplified 2D heat exchanger geometry (experimental and detailed CFD modelling data by P\"a\"akk\"onen et al. (2012, 2016)). By tuning the diffusivity, only, good agreement with the experimental data and the detailed CFD model was obtained, in terms of area-averaged deposition rates.Comment: 12th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, SINTEF, Trondheim, NORWAY, May 30th - June 1st, 2017, 9 pages, 9 figure

”Työhön Punalipun puolesta!”:Punalippu-lehti työläislapsuuden ihanteen luojana 1923–1930

Tiivistelmä. Tutkielma käsittelee työläislapsen ihanteen rakentamista Punalippu-lehdessä vuosina 1923 ja 1925–1930. Tutkielmassa tarkastellaan ihanteelliseksi esitettyä lapsuutta kertomuksien ja annettujen esikuvien avulla. Tarkastelussa on myös ihanteen muutos ja sukupuolen vaikutus ihanteeseen. Punalippu oli laitavasemmiston lastenlehti, jonka tarkoitus oli saattaa lapset omaan aatepiiriin ja taistella koulujen porvarillista maailmaa vastaan. Lapsista, lehden lukijoista, oli tarkoitus tulla tulevaisuuden luokkataistelijoita. Tutkielman pääasiallisena metodina on ollut lähiluku. Lähiluvun avulla on ollut mahdollista tarkastella lähemmin työläislapsen ihannetta, ihanteen muutosta ja sen sukupuolittuneisuutta. Tutkielmassa osoitetaan, että työläislapsen ihanteessa oli monia aikanaan laajasti lapsuuteen miellettyjä ihanteita, kuten työteliäisyys sekä kiinnostus ajan ilmiöihin ja yhteiskuntaan. Myös koulutuksen arvostus oli selkeä teema työläislapsen ihanteessa, mutta porvarillisesta ihanteesta poiketen koulutus ymmärrettiin mahdollisuudeksi saada oppia myöhempään luokkataisteluun. Lehti korosti lasten osallisuutta taistelussa aatteen puolesta esimerkiksi levittämällä Punalippu-lehteä. Isänmaallisuus ja uskonto olivat teemoja, joista lehden luomassa ihanteessa haluttiin päästä eroon. Lukijoiden annettiin ymmärtää, että uskonto oli porvarien keino hallita hankalina pitämiään työläisiä. Isänmaata ei myöskään lehden mukaan työläisillä ollut. Aineistosta voidaan kuitenkin huomata, että sosialismi ja työväenliike ilmenivät lehden retoriikassa varsin samalla tavoin kuin isänmaa porvarillisessa retoriikassa. Tutkielma osoittaa, että lapsuus oli 1920-luvulla monella tapaa poliittista ja lapset huomioitiin osana aatetta eikä heitä haluttu jättää koulun vääräksi määritellyn arvomaailman piiriin. Työläislapsen ihanne erosi porvarillisesta ihanteesta aatteellisissa ja arvoihin liittyneissä kysymyksissä, mutta yhtäläisyyksiä oli luonteenpiirteisiin liittyvissä seikoissa. Työläispojat esitettiin neuvokkaina, rohkeina ja reippaina, mikä vastasi aikakauden ihannekuvaa porvaristoon kuuluvista pojista. Työläistytön ihanne muuttui tarkasteluajanjaksolla poikaihannetta enemmän. Tyttöihanne muuttui alun neuvokkaasta ja toimeliaasta tytöstä enemmän sivusta seuraavaksi aatteelliseksi kertojaksi

Tulkkien työmuistista ja toiminnanohjauksesta

Peer reviewe

EVALUATION OF HEAT TRANSFER BOUNDARY CONDITIONS FOR CFD MODELING OF A 3D PLATE HEAT EXCHANGER GEOMETRY

In this paper fluid flow and heat transfer are modeled in a corrugated 3D plate heat exchanger geometry with a commercial computational fluid dynamics (CFD) program, Fluent 6.1.22 (Fluent Inc., Lebanon), in order to find out the most realistic heat transfer boundary conditions for a plate heat exchanger. The built-in boundary conditions of Fluent available for this case are Heat flux, Convection and Constant wall temperature. The CFD models are verified with correlations and experimental data obtained by a flat plate test equipment of which parameters can be calculated analytically. Deficiencies are found in all the built-in heat transfer boundary conditions. Heat transfer modeling with CFD in a corrugated plate heat exchanger is problematic because of the assumptions that have to be made when defining the boundary conditions in the complex geometry. The values of the computational parameters have spatial variations and can not be defined explicitly. However, when compared to the experimental correlations in the literature, the Convection boundary condition gives the most realistic results in the case of corrugated plate heat exchanger

Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst

The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. A predicted optical outburst was observed in late 2006/early 2007. We here present the radio-to-optical WEBT light curves during the outburst, together with UV data acquired by Swift in the same period. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of 5 mag led to the outburst peak in February 19-21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some shutdown mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin.Comment: 9 pages, 7 figures, in press for Astronomy and Astrophysic

WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase. Detection of the little and big blue bumps

The blazar 3C 454.3 underwent an unprecedented optical outburst in spring 2005. This was first followed by a mm and then by a cm radio outburst, which peaked in February 2006. We report on follow-up observations by the WEBT to study the multiwavelength emission in the post-outburst phase. XMM-Newton observations on July and December 2006 added information on the X-ray and UV fluxes. The source was in a faint state. The radio flux at the higher frequencies showed a fast decreasing trend, which represents the tail of the big radio outburst. It was followed by a quiescent state, common at all radio frequencies. In contrast, moderate activity characterized the NIR and optical light curves, with a progressive increase of the variability amplitude with increasing wavelength. We ascribe this redder-when-brighter behaviour to the presence of a "little blue bump" due to line emission from the broad line region, which is clearly visible in the source SED during faint states. Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV, suggesting the existence of a "big blue bump" due to thermal emission from the accretion disc. The X-ray spectra are well fitted with a power-law model with photoelectric absorption, possibly larger than the Galactic one. However, the comparison with previous X-ray observations would imply that the amount of absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum presents a curvature, which may depend on the X-ray brightness. In this case, two scenarios are possible.Comment: 9 pages, 7 figures, accepted for publication in A&

Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution

The larger number of models of asteroid shapes and their rotational states derived by the lightcurve inversion give us better insight into both the nature of individual objects and the whole asteroid population. With a larger statistical sample we can study the physical properties of asteroid populations, such as main-belt asteroids or individual asteroid families, in more detail. Shape models can also be used in combination with other types of observational data (IR, adaptive optics images, stellar occultations), e.g., to determine sizes and thermal properties. We use all available photometric data of asteroids to derive their physical models by the lightcurve inversion method and compare the observed pole latitude distributions of all asteroids with known convex shape models with the simulated pole latitude distributions. We used classical dense photometric lightcurves from several sources and sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff, Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the lightcurve inversion method to determine asteroid convex models and their rotational states. We also extended a simple dynamical model for the spin evolution of asteroids used in our previous paper. We present 119 new asteroid models derived from combined dense and sparse-in-time photometry. We discuss the reliability of asteroid shape models derived only from Catalina Sky Survey data (IAU code 703) and present 20 such models. By using different values for a scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in the dynamical model for the spin evolution and by comparing synthetics and observed pole-latitude distributions, we were able to constrain the typical values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201