Homogeneous Wall Research Articles

Renovation of Multi-Apartment Building in Latvia

Residential buildings in Latvia are one of the essential heat consumers during the heating season. The majority of Latvian as well as European residential buildings were constructed within the period from 1965 to 1990. The average heat transfer coefficient of typical homogeneous single layer external wall of Latvian multi apartment building as well as all buildings constructed in USSR is 0.80 till 1.20W/(m2∙K) [1,2]. Paper presents study on multi apartment buildings renovation specifics in Latvia and its influence in total energy consumption.

Modelling of tokamak glow discharge cleaning II: comparison with experiment and application to ITER

The primary function of the ITER glow discharge cleaning (GDC) system will be the preparation of in-vessel component surfaces prior to the machine start-up. It may also contribute to tritium removal in the nuclear phase. In GDC, conditioning efficiency is strongly dependent on the homogeneity of the flux of ions impinging onto wall surfaces. In order to assess the wall particle flux distribution in ITER, a novel 2D multi-fluid model, described in a companion paper, has recently been developed and is benchmarked here against both experimental glow discharge data obtained in a small laboratory chamber with cylindrical geometry and from two large toroidal devices: the JET tokamak and the RFX reverse field pinch. In the laboratory plasma, simulated and measured plasma electron density and temperature are in a good agreement in the negative glow region, while discrepancies exist in the anode glow, where the fluid description of the model is inaccurate due to long mean free paths of electrons. Calculated and measured ion flux distribution profiles in RFX are found in good agreement, whereas in JET comparison it is more difficult, due to the complex geometry of the first wall which leads to local inhomogeneities in the measured flux. Simulations of H2-GDC for ITER with one or two anodes indicate fairly homogeneous plasma parameters and wall ion flux in the negative glow at 0.5 Pa, a commonly used gas pressure for GDC in existing fusion devices. Although the axisymmetric geometry in the model does not allow all seven ITER anodes to be powered simultaneously in the simulations, the results can be extrapolated to the full system and predict ion current densities on wall surfaces close to the simple expectation of total anode current divided by wall surface area (0.21 A m−2), which is relevant to GDC in JET and other machines.

Order selection of thermal models by frequency analysis of measurements for building energy efficiency estimation

Experimental identification of the dynamic models of heat transfer in walls is needed for optimal control and characterization of building energy performance. These models use the heat equation in time domain which can be put in matrix form and then, through state-space representation, transformed in a transfer function which is of infinite order. However, the model acts as a low-pass filter and needs to respond only to the frequency spectrum present in the measured inputs. Then, the order of the transfer function can be determined by using the frequency spectrum of the measured inputs and the accuracy of the sensors. The main idea is that from two models of different orders, the one with a lower order can be used in building parameter identification, when the difference between the outputs is negligible or lower than the output measurement error. A homogeneous light wall is used as an example for a detailed study and examples of homogeneous building elements with very high and very low time constants are given. The first order model is compared with a very high order model (hundreds of states) which can be considered almost continuous in space.

Role of cardiovascular echo in patients with Takayasu arteritis.

Takayasu arteritis is an important differential diagnosis in young female patients presenting with fever, fatigue, hypertension, and/or neck pain. Aortic arch branch vessels are frequently affected and the carotid artery can have diffuse, homogeneous wall thickening, known as the 'macaroni sign'. The descending aorta can be stenotic with 'pseudo-coarctation'. Cardiovascular echo plays an important role in the screening and characterization of arterial lesions in patients with Takayasu arteritis.

THE IMPACT OF CLIMATE PARAMETERS ON THE SURFACE OF BUILDINGS’ WALLS

The durability of surface layers of enclosures (outside walls of buildings) is highly influenced by stresses occurring in the plane of contact between finishing materials and that of the enclosure. Damage to external walls depends on a high moisture content, which in turn depends on high water absorption during driving rains. One example of such damage is damage due to direct water penetration in homogeneous walls. The other negative effects of a high moisture content are impaired heat insulation and accelerated degradation. This article investigates the external layer of walls and the durability of different paints. In case of bi-laminar system “paint film-the wall being painted” two opposite processes take place: the water flow rate from the outside towards the wall, and the water vapor flow rate of the wall to the outside. The optimum selection of paint is necessary. An investigation of the durability of wall surface paints in a climatic chamber is instructive only after intermediate investigations and measurements of the substrates’ physical and mechanical properties that aid in predetermining durability. The influence of moisture deformations upon degradation of coatings depends on the porosity of surface materials being coated, and on the origin and macrostructure of the coating.

The reconstruction of time domain through-wall imaging for a metallic cylinder

Shape reconstruction from scattered electromagnetic fields is considered for two-dimensional through-wall imaging (TWI). The finite-difference time-domain method is applied to calculate the scattered E fields for forward scattering. Inverse scattering problems are transformed into optimisation problems based on the scattered E fields. A dynamic differential evolution (DDE) stochastic searching algorithm for shape reconstruction of a two-dimensional conducting target hidden behind a homogeneous building wall is demonstrated using simulated backscattered fields. The DDE is a population-based optimisation approach that aims to minimise the objective function between mimic measurements and computer-simulated data. Thus, the shape of a metallic cylinder can be obtained by minimising the objective function. Simulations show that DDE can successfully reconstruct TWI for a metallic cylinder. In addition, the effect of Gaussian noise on the reconstruction is investigated.

Humidity Conditions of Homogeneous Wall from Gas-Concrete Blocks with Finishing Plaster Compounds

In this article the single-layer homogeneous enclosure structure are considered. In this work calculation of vapor permeability of walls from gas-concrete blocks is made. The calculation of resistance to vapor permeability for rough walls and for walls with an external plaster covering is made. Calculation is executed in the context of St. Petersburg climatic conditions for external walls of residential buildings.

Fabrication of iron oxide nanotube arrays by electrochemical anodization

Highly ordered iron oxide nanotubes with smooth and homogeneous wall were electrochemically synthesized by potentiostatic anodization of iron foil in an ethylene glycol based electrolyte containing NH4F and deionized water at 60°C. A model was proposed to explain the formation mechanism. The effects of anodization conditions, such as potential, H2O concentration, NH4F concentration, temperature and thermal treatment, on morphology and structural features of the oxide layer were thoroughly investigated. It is shown that the current transient curve can be used as a tool to approximately predict the morphology and the formation of nanotube during the anodization of iron.

Thermal characterization of homogeneous walls using inverse method

Abstract Current environmental concerns have promoted efforts to reduce the consumption of energy. In moving towards improving existing buildings, the study of the thermal behaviour of a wall is not easy because its actual thermophysical properties are not well-known. These parameters are nevertheless fundamental for the economic optimisation of building refurbishment or for the verification of their performance in situ. It is thus important to be able to characterize existing building walls. The objective of our study was to develop a method to thermally characterize a wall adapted to in situ applications based on an active approach. The principle of identification consists of thermally examining an access surface by applying a heat flux and studying the response in terms of the temperature recorded by infrared thermography on the opposite surface. Based on signals of flux and of temperatures measured at the edges of the wall, the thermophysical properties (thermal conductivity and volumetric heat) of the wall are estimated by inverse method. The method was applied first to a homogeneous gypsum-tile panel in laboratory. The results were compared to reference values obtained from a classical procedure. Then, the method has been implemented in situ on a homogeneous reinforced concrete shell.

Combined multi-nozzle deposition and freeze casting process to superimpose two porous networks for hierarchical three-dimensional microenvironment

An engineered three-dimensional scaffold with hierarchical porosity and multiple niche microenvironments is produced using a combined multi-nozzle deposition–freeze casting technique. In this paper we present a process to fabricate a scaffold with improved interconnectivity and hierarchical porosity. The scaffold is produced using a two-stage manufacturing process which superimposes a printed porous alginate (Alg) network and a directionally frozen ceramic–polymer matrix. The combination of two processes, multi-nozzle deposition and freeze casting, provides engineering control of the microenvironment of the scaffolds over several length scales; including the addition of lateral porosity and the ratio of polymer to ceramic microstructures. The printed polymer scaffold is submerged in a ceramic–polymer slurry and subsequently, both structures are directionally frozen (freeze cast), superimposing and patterning both microenvironments into a single hierarchical architecture. An optional additional sintering step removes the organic material and densifies the ceramic phase to produce a well-defined network of open pores and a homogenous cell wall material composition. The techniques presented in this contribution address processing challenges, such as structure definition, reproducibility and fine adjustments of unique length scales, which one typically encounters when fabricating topological channels between longitudinal and transverse porous networks.

Bowel wall thickening at CT: simplifying the diagnosis

ObjectiveIn this article we present a simplified algorithm-based approach to the thickening of the small and large bowel wall detected on routine computed tomography (CT) of the abdomen.BackgroundThickening of the small or large bowel wall may be caused by neoplastic, inflammatory, infectious, or ischaemic conditions. First, distinction should be made between focal and segmental or diffuse wall thickening. In cases of focal thickening further analysis of the wall symmetry and perienteric anomalies allows distinguishing between neoplasms and inflammatory conditions. In cases of segmental or diffuse thickening, the pattern of attenuation in light of clinical findings helps narrowing the differential diagnosis.ConclusionFocal bowel wall thickening may be caused by tumours or inflammatory conditions. Bowel tumours may appear as either regular and symmetric or irregular or asymmetric thickening. When fat stranding is disproportionately more severe than the degree of wall thickening, inflammatory conditions are more likely. With the exception of lymphoma, segmental or diffuse wall thickening is usually caused by benign conditions, such as ischaemic, infectious and inflammatory diseases.Key points• Thickening of the bowel wall may be focal (<5 cm) and segmental or diffuse (6-40 cm or >40 cm) in extension.• Focal, irregular and asymmetrical thickening of the bowel wall suggests a malignancy.• Perienteric fat stranding disproportionally more severe than the degree of wall thickening suggests an inflammatory condition.• Regular, symmetric and homogeneous wall thickening is more frequently due to benign conditions, but can also be caused by neoplasms such as well-differentiated adenocarcinoma and lymphoma.• Segmental or diffuse bowel wall thickening is usually caused by ischaemic, inflammatory or infectious conditions and the attenuation pattern is helpful in narrowing the differential diagnosis.

Mathematical modeling of radiofrequency ablation for varicose veins.

We present a three-dimensional mathematical model for the study of radiofrequency ablation (RFA) with blood flow for varicose vein. The model designed to analyze temperature distribution heated by radiofrequency energy and cooled by blood flow includes a cylindrically symmetric blood vessel with a homogeneous vein wall. The simulated blood velocity conditions are U = 0, 1, 2.5, 5, 10, 20, and 40 mm/s. The lower the blood velocity, the higher the temperature in the vein wall and the greater the tissue damage. The region that is influenced by temperature in the case of the stagnant flow occupies approximately 28.5% of the whole geometry, while the region that is influenced by temperature in the case of continuously moving electrode against the flow direction is about 50%. The generated RF energy induces a temperature rise of the blood in the lumen and leads to an occlusion of the blood vessel. The result of the study demonstrated that higher blood velocity led to smaller thermal region and lower ablation efficiency. Since the peak temperature along the venous wall depends on the blood velocity and pullback velocity, the temperature distribution in the model influences ablation efficiency. The vein wall absorbs more energy in the low pullback velocity than in the high one.

Pollen tube growth through nucellus into embryo sac of Spinacia - an ultrastructural investigation

The micropylar parts of nucellus and embryo sac were studied in relation to pollen tube growth and its entrance into the embryo sac. The initially homogeneous walls of the cells of the conductive nucellar tissue disintegrate at the middle lamellae region. Pollen tubes pierce the nucellar cuticle and continue their growth into the nucellus intercellularly. Subsequently they can follow various pathways to reach the FA of the degenerated synergid. The penetration into this synergid, and the discharge of the tube contents are described and discussed.

Three-Dimensional Synthetic Aperture Radar Imaging Through Multilayered Walls

Most of existing through-the-wall radar imaging (TWRI) algorithms deal with a single layer homogeneous wall in two-dimensional scenario. In this communication we present a generalized three-dimensional (3-D) beamforming algorithm for the focused imaging of targets behind multilayered building walls. The far field layered medium Green's function is incorporated in the 3-D beamformer for the compensation of the wall effect. 3-D polarimetric imaging is exploited in TWRI for enhanced target identification and feature extraction as well as wall effect mitigation. Numerical results show that the proposed 3-D beamformer provides high quality focused images in various wall-target scenarios.

New Designs of Molten-salt Tubular-receiver for Solar Power Tower

One of the main problems of solar power tower plants with molten salt as heat transfer fluid is the reliability and lifetime estimation of central receivers. The receivers must withstand high working temperatures, molten salt corrosion and important solar flux transients that lead to thermal stresses and fatigue. Therefore, it is necessary optimize the design of these receivers.The aim of this work is to study the thermal behavior of a new design of central receiver. This new external receiver is composed by several vertical panels formed by bayonet tubes. Each bayonet tube presents an inner tube and an outer tube concentric to the internal one. Both are joined in one side by a bayonet end-cap. The heat transfer fluid flows through the inner tube and the annular gap between the two tubes. In addition, the outer tube will be coated in its external surface by a material of high absorptivity of the solar radiation.In absence of experimental data of the receivers both concepts of external receiver, traditional and bayonet, have been characterized using simplified numerical simulations. The results obtained have been the salt, the film and the wall temperature evolutions and the thermal efficiencies. The advantages of the bayonet receiver over the traditional tubular receiver are: soften wall and film temperatures, lower thermal stresses due to a more homogeneous wall temperature, and lower corrosion rate, that allows use more economical materials to built the receiver tubes or even reduce the receiver surface increasing the thermal efficiency.

Setting up and validating a complex model for a simple homogeneous wall

The present paper describes modelling of the thermal dynamics of a real wall tested in dynamic outdoor weather conditions, to identify all the parameters needed for its characterisation. Specifically, the U value, absorptance and effective heat capacity are estimated for the wall using grey-box modelling based on statistical methods and known physical dynamic energy balance equations, related to the heat flux density through a simple and homogeneous wall. The experimental test was carried out in a hot-temperature climate for nine months. This study aims at proposing a dynamic method improving the regression averages method for estimation of parameters which describe the thermal behaviour of the wall. Solar irradiance and long-wave radiation balance terms are added in the heat balance equation besides modelling of wind speed effect to achieve a complete description of the relevant phenomena which affect the thermal dynamics of the wall. The method is applied using different frequency data samples looking for the best to study this wall. The U value obtained characterising the wall is consistent with the one given by the regression averages method.

The Paleozoic record of Thaumatoporella PIA, 1927?

From Palaeozoic (mainly Devonian) shallow-water carbonates, spherical to irregular shaped microfossils with thin, apparently homogeneous or perforate micritic walls are widely reported. They are classically referred either to unilocular parathuramminid foraminifera, algae incertae sedis or calcispheres (e.g., Bisphaera, Cribrosphaeroides, Uslonia, Vermiporella myna, Irregularina). Due to their morphology and microstructural features, they are here reassessed more accurately as belonging to Thaumatoporella PIA, a widespread Mesozoic-Early Cenozoic taxon of incertae sedis showing a remarkably high morphological variability. In analogy to Mesozoic thaumatoporellaceans, Bisphaera malevkensis BIRINA is interpreted as the cyst (= resting) stage of forms ascribed to different genera, i.e., Cribrosphaeroides, Uslonia and Vermiporella (here: Vermiporella myna WRAY). This new interpretation leads to taxonomic reassessment as Thaumatoporella malevkensis (BIRINA) nov. comb. As a consequence of our interpretation, the rather long Mesozoic to Early Cenozoic (Ladinian to Early Ypresian) record of thaumatoporellaceans is supposed to be significantly larger than formerly assumed, showing four periods of increased abundance in the Middle/Late Devonian, Late Permian (?), Early/Middle Jurassic and Late Cretaceous time windows.

Processing of a LLDPE/HDPE pressure vessel liner by rotomolding

Biaxial rotational molding is a low-pressure process that uses a polymer powder to produce large and/or complex-shaped hollow thermoplastic goods using low cost molds, being very suitable for prototype production. In the present work, liner prototypes (Φ 78 × 280 mm) made of linear low density (LLDPE) and high density polyethylene (HDPE) blends were produced aiming to later use them as compressed natural gas type IV cylinders. The LLDPE/HDPE blend composition and the process parameters (temperature/time cycle, and rotation speed) were varied to evaluate their effect on blend miscibility and liner final properties, such as density and crystallization behavior. Blend composition and process parameters were found vital for the production of a homogeneous wall and for the liner to reach adequate characteristics for the intended product.

Life under flow: A novel microfluidic device for the assessment of anti-biofilm technologies

In the current study, we have developed and fabricated a novel lab-on-a-chip device for the investigation of biofilm responses, such as attachment kinetics and initial biofilm formation, to different hydrodynamic conditions. The microfluidic flow channels are designed using computational fluid dynamic simulations so as to have a pre-defined, homogeneous wall shear stress in the channels, ranging from 0.03 to 4.30 Pa, which are relevant to in-service conditions on a ship hull, as well as other man-made marine platforms. Temporal variations of biofilm formation in the microfluidic device were assessed using time-lapse microscopy, nucleic acid staining, and confocal laser scanning microscopy (CLSM). Differences in attachment kinetics were observed with increasing shear stress, i.e., with increasing shear stress there appeared to be a delay in bacterial attachment, i.e., at 55, 120, 150, and 155 min for 0.03, 0.60, 2.15, and 4.30 Pa, respectively. CLSM confirmed marked variations in colony architecture, i.e.,: (i) lower shear stresses resulted in biofilms with distinctive morphologies mainly characterised by mushroom-like structures, interstitial channels, and internal voids, and (ii) for the higher shear stresses compact clusters with large interspaces between them were formed. The key advantage of the developed microfluidic device is the combination of three architectural features in one device, i.e., an open-system design, channel replication, and multiple fully developed shear stresses.

Computational modeling of vortex shedding in water cooling of 3D integrated electronics

This work aims at understanding the flow and heat transfer through a microcavity populated with micropins, representing a layer of a 3D integrated electronic chip stack with integrated cooling. The resulting vortex shedding behavior and its effect on the heat removal is analyzed in the Reynolds number (Re) range from 60 to 450. The lateral confinement, expressed as the ratio of diameter to lateral distance between two cylinders’ centers, is varied between 0.1 and 0.5; the longitudinal confinement (diameter to longitudinal distance between two cylinders’ centers) between 0.25 and 0.5; and vertical confinement (diameter to microcavity height ratio) between 0.1 and 0.5. For a single pin, as the lateral confinement is increased, the Strouhal number (St) and the shedding frequency increase by up to 100%. The thermal performance represented by the spatiotemporal averaged Nusselt number (Nu), based on the average pin surface and fluid temperatures, is also enhanced by over 30%. A direct relationship between Nu and the shedding frequency was found. For a row of pins, Nu in the vortex shedding regime was found to be up to 300% higher compared to the steady case. A decrease in the longitudinal confinement, tested with rows of pins (either with 50 or 25 pins) in the streamwise direction, led to an upstream migration of the vortex shedding location and in more homogeneous but higher wall temperatures. This coincided with a drastic reduction of pressure losses and a 30% Nu enhancement for the same pumping power. Finally, the vertical confinement is also investigated with 3D simulations around a single cylinder. With increasing Re and vertical confinement, the wake becomes strongly three-dimensional. For a given Re, the increase of vertical confinement naturally shows a suppression or even a complete elimination of the vortex shedding due to a strong end-wall effect. Our results shed light on the effects of confinement on vortex shedding and related heat transfer in the integrated cooling of 3D chip stacks.