Numerical simulations of the agitation generated by coarse-grained bubbles moving at large Reynolds number

We present a numerical method for simulating the flow induced by bubbles rising at large Reynolds number. This method is useful to simulate configurations of large dimensions involving a great number of bubbles. The action that each bubble exerts on the liquid is modelled as a volume source of momentum distributed over a few mesh-grid elements. The flow in the vicinity of the bubbles is thus not finely resolved. The bubbles are treated as Lagrangian particles that move under the influence of the hydrodynamic force exerted by the liquid. The determination of this force on a given bubble requires knowledge of the liquid flow that is undisturbed by this bubble. A model is developed to accurately estimate this disturbance for large-Reynolds-number objects and get rid of any spurious self-induced effect. Thanks to that, a homogeneous swarm of rising bubbles is simulated. Comparisons with experiments show a good agreement with the flow scales larger than the bubbles, which turn out to be controlled by the interactions between bubble wakes and rather independent of unresolved smaller scales. This method can be used to study the coupling between bubble-induced agitation and large-scale motions, such as those produced in industrial bubble columns.

Validation of EFFTRAN for efficiency transfer to distant geometries and volume sources

The efficiency transfer procedure from a geometry where a volume source was placed directly on the endcap of a germanium detector to three different distant geometries was carried out using the EFFTRAN code. One of these distant geometries included absorbers consisting of poly(methyl methacrylate). The efficiency transfer to this geometry therefore had to be realized as a two-stage transfer, since a direct efficiency transfer is not possible using EFFTRAN in such a case. Efficiency transfer to all three distant geometries yielded results which can be considered as fit-for-purpose in e.g. most of the applications of gamma ray spectrometry.

Slavic-root verbs in CP: loanwords and problematic cases

Although being a comparatively small-volume source, the Catechism of Merkelis Petkevičius (CP) discloses the complexity of analysing Lithuanian loan verbs and Slavic-root hybrids. Conducting research on loanwords from the Slavic languages, the main focus is usually laid on nominal words. The key rule applied while analysing the verbs of Slavic origin is based on the compliance between the distinguished suffixes in the analysed words and the suffixes characteristic of the Slavic languages. However, Slavic-root loanwords are also found, the suffixes of which do not have any equivalents in the Slavic languages. Traditionally such verbs are assigned to hybrids but they may be of two types. The Slavic-root verbs were selected from CP, which contributed to revealing the problems encountered while analysing them. The majority of Slavic-root verbs in the CP are attributed to regular loanwords, which are also reflected in the adjacent text in Polish. Several words fall under the category of problematic Slavic-root verbs. The suggested division of hybrids into derivational and adaptational ones is determined by several principles. The hybrid, when a Slavic-root verb does not have precise suffix equivalents and due to the objective reasons cannot be seen as a loanword (there is no word in the Lithuanian language, which can serve as a derivational base word), is regarded to be an adaptational one, i.e., its morphological component that formally complies with the suffix, underwent changes in the process of integration but modifications in the meaning are rarely identified in such cases (liecavoti, -avoja, -vojo CP 217,23). Derivational hybrids are the verbs, which have a word of common root in the recipient language and the derivational link can be envisaged between them (prarakauti, -auja, -avo CP 160,17, pasnykauti, -auja, -avo CP 88,25). Such hybrids are more frequently based on the meanings of base word and this may lead to some differences in the meanings of respective root verbs in the Slavic languages.

Experimental validation of corrections factors for γ–γ and γ–X coincidence summing of 133Ba, 152Eu, and 125Sb in volume sources

True coincidence summing correction factors for 133Ba, 152Eu and 125Sb were determined experimentally for a small volume source and compared with correction factors obtained with three softwares (EFFTRAN-X, GESPECOR and VGSL). The radionuclides investigated have a relatively challenging decay scheme and their spectra are known to suffer from losses due to summation (γ–γ, γ–X and X–X) when measured at close distances on a HPGe detector sensitive to low energy photons. This study shows that the softwares were in good agreement with each other and the experimental data and the calculated activity was consistent with the activity in the volume source.

Assessment of optimal location for a centralized biogas upgrading facility

Since the 1990s, the volume of biogas produced in the world has been increasing. Biomethane (upgraded biogas) is a more versatile renewable fuel. Biogas transportation from production sites to upgrading facilities induces a scale advantage and an efficiency increase. Therefore, exploration of costs and energy use of biogas transportation using dedicated infrastructure is needed. A mathematical model to determine the optimum location for a certain biogas upgrading plant has been presented. It was developed to describe a local biogas grid that is used to collect biogas from several digesters and to deliver it to a central upgrading point. The model minimizes operational and maintenance costs per volumetric unit of biogas. The results indicate that cooperation between biogas producers in collecting biogas by means of a star layout reduces the cost of biomethane production (investment costs by 22.4–24.8% and operating and maintenance costs by 1.7–10.9%) relative to using a decentralized method. Merging smaller digesters into a smaller number of larger biogas upgrading plants reduces the biomethane production costs for the same biogas volume source.