1,721,022 research outputs found
A Numerical Study of Turbulent Mixed Convection in a Smooth Horizontal Pipe
No full textThis paper presents a numerical study aimed at identifying a suitable turbulence model to describe the fully developed turbulent mixed convention of air in smooth horizontal pipes. The flow characteristics considered here are relevant to those typically observed in ventilated hollow core slab (VHCS) applications and, because of this, the adopted geometry and boundary conditions are represented by the Reynolds number and Richardson number of about 23,000 and 1.04, respectively. Empirical expressions available in the literature are used as reference to evaluate the accuracy of different turbulence models in predicting the dimensionless velocity (u+) and temperature (T+) profiles as well as the Nusselt number (Nu). Among the turbulence models considered, the standard and realizable k-ε models provide the best overall predictions of u+, T+, and Nu in the fully developed flow, and the former is recommended for the modeling of VHCS systems as it gives slightly better estimates of the Nu values
A numerical study on the thermal performance of night ventilated hollow core slabs cast with micro-encapsulated PCM concrete
No full textThis paper presents a numerical procedure for predicting the thermal performance of ventilated hollow core slabs (VHCS). The proposed approach is validated against experimental measurements available in the literature and then applied to study the effects of incorporating micro-encapsulated phase change materials (mPCM) in VHCSs for the cooling of office buildings. In particular, the impact of mPCM content, mPCM type (i.e. phase change temperature) and hollow core ventilation rates uin on the slab's cooling potential is evaluated under two ideal room temperature cases. The first case reflects the behaviour of a high thermal mass building in which the high thermal mass enforces room temperature variations to be negligible. The second case imitates a low thermal mass building in which the room temperature is significantly affected by external temperature variations. It is assumed that the temperature responses within typical offices would fall between these two scenarios. The results indicate that, with the VHCS placed in a high thermal mass building, the use of the mPCM with a phase changing temperature of 20 °C (denoted by mPCM20) improves the cooling potential of the slab, regardless of the mPCM content (up to 20% incorporation) and the ventilation rate (up to uin = 5 m/s). However in the low thermal mass building case, the best performing mPCM type depends on the ventilation rate (i.e. mPCM20 when uin ≤ 2 m/s, and mPCM19 – the mPCM with a phase changing temperature of 19 °C when uin = 5 m/s) and is independent of the mPCM content
Flow Field around Swimming Mosquito Larvae
Get PDFUnlike most natural swimmers, larvae of mosquitoes swim tail first where the posterior end of the
body leads the anterior end. To achieve this mosquito larvae display a high amplitude, side-to-side
flexural motion of their body. Their body size and swimming speed also put them in an intermediate
Reynolds number regime (1<Re<2000) where both inertial and viscous forces are likely dominant.
This study experimentally investigates the hydrodynamics of tail-first swimming in mosquito larvae
through Particle Image Velocimetry (PIV) analysis. Analysis of the velocity and vorticity field around
the larvae revealed the presence of jets and favourable pressure gradient near the head and tail of the
larvae at about mid-stroke which are likely responsible for the generation of thrust
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Enhancing natural convection in a cube using a strong magnetic field — Experimental heat transfer rate measurements and flow visualization
No full textThe effect of a strong magnetic field on the average heat transfer rate and flow profiles of joint gravitational and thermo-magnetic convection of a paramagnetic fluid in a cubic enclosure heated from below and cooled from above was experimentally investigated. The working fluid consisted of 80% mass glycerol aqueous solution with a concentration of 0.8 mol/kg gadolinium nitrate hexahydrate making it paramagnetic. The cubic enclosure of 32-mm sides was located in the 10-cm bore of a horizontally oriented 5-Tesla super-conducting magnet at a position where the magnetic force distribution was relatively uniform. Under this configuration, the magnetic field imposed in the horizontal direction acted perpendicularly to gravity. It was found that the heat transfer rate through the cube increased with the increase of the magnetic induction. Furthermore, steady and transient state flow visualizations were carried out with a 10-Tesla super-conducting magnet to show a change in the temperature field when magnet-thermo convection dominated. Visualization was made using thermo-chromic liquid crystal slurry added to the working fluid and illuminated in a vertical cross-section of the cube
Natural convection boundary-layer adjacent to an inclined flat plate subject to sudden and ramp heating
No full textThe natural convection thermal boundary-layer adjacent to an inclined flat plate subject to sudden heating and a temperature boundary condition which follows a ramp function up until a specified time and then remains constant is investigated. The development of the flow from start-up to a steady state has been described based on scaling analyses and verified by numerical simulations. Different flow regimes based on the Rayleigh number are discussed with numerical results for both boundary conditions. For ramp heating, the boundary-layer flow depends on the comparison of the time at which the ramp heating is completed and the time at which the boundary layer completes its growth. If the ramp time is long compared with the steady-state time, the layer reaches a quasi-steady mode in which the growth of the layer is governed solely by the thermal balance between convection and conduction. On the other hand, if the ramp is completed before the layer becomes steady; the subsequent growth is governed by the balance between buoyancy and inertia, as for the case of instantaneous heating
Natural convection in attic-shaped spaces subject to sudden and ramp heating boundary conditions
No full textIn this study, a discussion of the fluid dynamics in the attic space is reported, focusing on its transient response to sudden and linear changes of temperature along the two inclined walls. The transient behaviour of an attic space is relevant to our daily life. The instantaneous and
non-instantaneous (ramp) heating boundary condition is
applied on the sloping walls of the attic space. A theoretical understanding of the transient behaviour of the flow in the enclosure is performed through scaling analysis. A proper identification of the timescales, the velocity and the thickness relevant to the flow that develops inside the cavity makes it possible to predict theoretically the basic flow features that will survive once the thermal flow in the enclosure reaches a steady state. A time scale for the heating-up of the whole cavity together with the heat transfer scales through the inclined walls has also been obtained through scaling analysis. All scales are verified by the numerical simulations
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