Numerical Simulation of Bubble Coalescence using a Volume of Fluid (VOF) Model

This paper presents a Volume Tracking model developed with the specific objective of studying the time – dependent behavior of multiple, “large” gas bubbles rising in an initially quiescent liquid. The model, based on the Volume – Of – Fluid concept, employs an advanced interface tracking scheme known as Youngs’ VOF to advance the gas – liquid interface through the Eulerian mesh. Additionally, the model solves the incompressible Navier – Stokes equations to obtain the flow field. Results obtained for four different cases will be discussed: the formation and rise of a skirted bubble and of a spherical cap bubble, the coalescence of two identical gas bubbles and the behavior of two gas bubbles emanating from two adjacent orifices. It could be concluded that the Volume Tracking model is able to track the motion of a gas – liquid interface, subject to appreciable changes in its topology, embedded in a flow field with significant vorticity

Computational fluid dynamics applied to gas-liquid contactors.

In this paper a `hierarchy of models¿ is discussed to study the fluid dynamic behaviour of gas-liquid bubble columns. This `hierarchy of models¿ consists of a Eulerian-Eulerian two fluid model, a Eulerian-Lagrangian discrete bubble model and a Volume Tracking or Marker Particle model. These models will be briefly reviewed and their advantages and disadvantages will be highlighted. In addition, a mixed Eulerian-Lagrangian model and a volume tracking model, both developed at Twente University, will be discussed. Some selected results obtained with these models will be presented with emphasis on the results obtained with the volume tracking model. Finally, a brief discussion on advanced experimental techniques, which reflect the recent progress in experimental fluid dynamics, will be presente

Dynamic simulation of gas-liquid two-phase flow: effect of column aspect ratio on the flow structure.

In this paper an Eulerian/Lagrangian model, describing the hydrodynamics of a gas-liquid bubble column, is presented. The model resolves the time dependent, two-dimensional motion of small, spherical gas bubbles in a liquid using the equation of motion. The model incorporates all relevant forces acting on a bubble as it rises through the liquid, and additionally accounts for direct bubble-bubble interactions. The liquid-phase hydrodynamics are described using the volume-averaged Navier-Stokes equations. This model is used to study the hydrodynamic behaviour of bubble columns with aspect ratios ranging from 1.0 to 11.4. In addition to these theoretical results, experimental observations are presented of the flow structure in a pseudo-two-dimensional bubble column with different aspect ratios. A clear transition in the gas-liquid flow pattern could be observed, both experimentally and theoretically, from the well-known `cooling tower¿ mode of circulation (L/D = 1.0) to the staggered vortices mode of circulation (L/D 2.0). The computational results clearly showed the presence of vortical structures in the liquid phase at aspect ratios exceeding 2.0. These vortical structures in the liquid phase were studied experimentally using neutrally buoyant tracer particles and streak photography. The experimentally observed vortical structures are shown to resemble the computed structures

Dynamic simulation of dispersed gas-liquid two-phase flow using a discrete bubble model.

In this paper a detailed hydrodynamic model for gas-liquid two-phase flow will be presented. The model is based on a mixed Eulerian-Lagrangian approach and describes the time-dependent two-dimensional motion of small, spherical gas bubbles in a bubble column operating in the homogeneous regime. The motion of these bubbles is calculated from a force balance for each individual bubble, accounting for all relevant forces acting on them. Contributions from liquid-phase pressure gradient, drag, virtual mass, liquid-phase vorticity and gravity are considered, whereas direct bubble-bubble interactions are accounted for via an interaction model resembling the collision model developed by Hoomans et al. (1996) to model gas-fluidized beds. The liquid-phase hydrodynamics are described using the volume-averaged, unsteady, Navier-Stokes equations. A preliminary model validation has been performed by comparing the computational results with experimental observations published previously in literature by various authors. The model is shown to predict correctly the motion of a bubble plume in a pseudo-two-dimensional bubble column operated at different superficial gas velocities, provided that a detailed description of the bubble dynamics is incorporated in the model. The effect of bubble column aspect ratio on the hydrodynamic behaviour of the column has also been investigated. Our model predicts the effect of aspect ratio on the flow structure in the bubble column. The importance of the various forces acting on the bubbles will also be discussed and it will be shown that the added mass force and the lift force cannot be neglected in bubble column simulation. Finally, the model has been used to study the start-up behaviour of a two-dimensional bubble column. It will be shown that the history of the gas-liquid two-phase flow significantly affects the flow structure ultimately obtained in a bubble column. This finding has, to our knowledge, not been reported before in literature

The development of a nursing subset of patient problems to support interoperability

Since the emergence of electronic health records, nursing information is increasingly being recorded and stored digitally. Several studies have shown that a wide range of nursing information is not interoperable and cannot be re-used in different health contexts. Difficulties arise when nurses share information with others involved in the delivery of nursing care. The aim of this study is to develop a nursing subset of patient problems that are prevalent in nursing practice, based on the SNOMED CT terminology to assist in the exchange and comparability of nursing information. Explorative qualitative focus groups were used to collect data. Mixed focus groups were defined. Additionally, a nursing researcher and a nursing expert with knowledge of terminologies and a terminologist participated in each focus group. The participants, who work in a range of practical contexts, discussed and reviewed patient problems from various perspectives. Sixty-seven participants divided over seven focus groups selected and defined 119 patient problems. Each patient problem could be documented and coded with a current status or an at-risk status. Sixty-six percent of the patient problems included are covered by the definitions established by the International Classification of Nursing Practice, the reference terminology for nursing practice. For the remainder, definitions from either an official national guideline or a classification were used. Each of the 119 patient problems has a unique SNOMED CT identifier. To support the interoperability of nursing information, a national nursing subset of patient problems based on a terminology (SNOMED CT) has been developed. Using unambiguously defined patient problems is beneficial for clinical nursing practice, because nurses can then compare and exchange information from different settings. A key strength of this study is that nurses were extensively involved in the development process. Further research is required to link or associate nursing patient problems to concepts from a nursing classification with the same meaning

Quality of health care according to people with Down syndrome, their parents and support staff—A qualitative exploration

Background: People with Down syndrome (PDS) have complex healthcare needs. Little is known about the quality of health care for PDS, let alone how it is appraised by PDS and their caregivers. This study explores the perspectives of PDS, their parents and support staff regarding quality in health care for PDS. Method: The present authors conducted semi-structured interviews with 18 PDS and 15 parents, and focus groups with 35 support staff members (of PDS residing in assisted living facilities) in the Netherlands. Results: According to the participants, healthcare quality entails well-coordinated health care aligned with other support and care systems, a person-centred and holistic approach, including respect, trust and provider–patient communication adapted to the abilities of PDS. Conclusions: Our findings may be used to improve health care for PDS, and provide insight into how health care could match the specific needs of PDS

70-luvun vanhusten asuintalon purkuanalyysi

Raportissa esitetään pääpirteittään Lahden vanhusten asuntosäätiön Onnelanpolku-hankkeessa tehty vanhojen asuintalojen purkaminen uudisrakentamisen tieltä sekä purkamisessa huomioonotettavat seikat. Raportissa käydään läpi myös eri rakennusjätejakeita koskevat säädökset, varsinaisia purkutöitä koskevat säädökset ja  kaupungin järjestyssäännöt. Purkutyön kulku alkaa hankesuunnittelusta ja etenee rakennesuunnitteluun ja työvaihesuunnitteluun. Keskeisiä toimijoita ovat rakennuttaja, rakenne- ja purkusuunnittelija, päätoteuttaja ja urakoitsija tai urakoitsijat.  Selvityksessä esitellään eri toimijoiden välinen työn- ja vastuunjako