Homogeneous Wall Research Articles

Thermal entry flow of power-law fluid through ducts with homogeneous slippery wall(s) in the presence of viscous dissipation

This article investigates the Graetz problem for an inelastic power-law fluid by incorporating the effects of homogeneous slippery surface(s). The energy equation with viscous dissipation term is handled by employing the separation of variable method supplemented with the Matlab based algorithm Bvp4c for both kinds of thermal conditions, namely isothermal and isoflux conditions. The graphical results of average temperature and local Nusselt number are displayed and discussed in the forms of main effect brought by the emerging parameters such as slip length, power-law index and Brinkman number. The analysis predicts that interplay among the fluid characteristics, wall properties and dissipation effect can lead to an increase in the overall convective heat transfer and therefore, this analysis is potentially useful in the manufacturing of several bio-fluidic and micro-fluidic devices.

Using Latent Energy of Water-ice Phase Change to Reduce Energy Losses in Buildings in Cold Climate

Energy efficiency in buildings is a very important challenge that has to be faced in order to achieve the aims set by the new EU directive on Building energy efficiency encouraging nearly zero energy buildings. Unfortunately in countries with cold climate it is very hard to achieve this goal. The thickness of insulation needed to reach low energy consumption in cold climate is very big and in many cases it is not economically feasible. There is a need for new solutions for increasing building energy efficiency. In this paper a new solution for increasing building energy efficiency is proposed. It is proposed to use the latent energy of water-ice phase change to reduce heat conduction losses through building envelope. The latent energy is recovered by using low potential heat source. In this paper the validity of the proposed new solution is tested on a one dimensional scale – homogeneous infinite wall. The presented methodology is chosen to calculate systems operational efficiency throughout the whole year.

A web application for analysis of heat transfer through building walls and calculation of optimal insulation thickness

Controlling heat transfer and managing heat flows in a building has become very important in recent years and is essential to ensure the thermal comfort of occupants, increase energy efficiency, and sustainable development. These measures reduce energy consumption in buildings, save resources and money and at the same time reduce pollution and CO2 emissions into the atmosphere, as the severity of the climate increases. The paper describes the analytical method used to analyse the one-dimensional, steady-state heat transfer through homogeneous walls and composite walls of buildings (wall structure may contain different construction materials, air spaces, insulation, etc.). The web application allows users to analyse one-dimensional and steady-state heat transfer through the building walls and calculate the heat flux density, total heat flux, overall heat transfer coefficient of the building wall, thermal resistance, temperature profile through the wall, the specific thermal resistances and the temperatures at the interface between wall layers. The user can analyse the one-dimensional, steady-state heat transfer through homogeneous and multilayer walls of buildings, being able to analyse a wall composed of a single layer, or one with a maximum of seven layers. The application allows the user, after defining the cross section’s geometry, materials properties, and boundary conditions, to determine the optimal insulation thickness, depending on its placement, on the inner or outer wall surface.

Stationarity and homogeneity assumptions in wavenumber-frequency representation of turbulent boundary layer wall pressure.

The utility of the wavenumber-frequency spectrum for description and interpretation of wall pressure fluctuations beneath turbulent boundary layers has been amply demonstrated over the past decades. This representation is widely used in modelling the flow-induced noise due to boundary layers developing on vehicle surfaces. A recurring issue concerns the underlying assumptions of stationary and homogeneous wall pressure fields. Even on a flat plate, the turbulent boundary layer thickening violates the homogeneous assumption. A numerical experiment of a spatially evolving turbulent boundary layer on a flat plate provides detailed wall-pressure data to assess the stationarity and homogeneity assumptions in the computation of wavenumber-frequency spectra. High-order statistics, stationarity tests developed for random time series and modern signal processing tools, such as the empirical mode decomposition, are applied. In particular, it is shown that the nonhomogeneity due to the space-varying nature of the turbulent sources does not change the characteristics of the wavenumber-frequency representation of the wall pressure field.

A importância da utilização do cateter central de inserção periférica

O cateter venoso central de inserção periférica PICC é um cateter que se insere em uma veia periférica e progride para veia cava superior ou inferior adquirindo características de um cateter central. É um dispositivo que possui diversas versões, com um, dois ou três lumens, é flexível, radiopaco, de paredes lisas e homogêneas, feito de silicone ou poliuretano. Tal dispositivo beneficia no tratamento ao neonato que requer cuidados prolongados. O presente estudo visa analisar a importância da utilização do Cateter Central de Inserção Periférica – PICC no cuidado a neonatos enfermos, bem como analisar a função da equipe de enfermagem na inserção e manutenção dessa técnica. A metodologia utilizada foi pesquisa bibliográfica com análise de artigos científicos, teses e outras publicações de enfermagem encontrados em bases de dados relacionadas com o tema. Os resultados encontrados a partir dos estudos revisados mostraram que PICC é um dispositivo advindo das novas tecnologias que proporcionam um melhor tratamento aos recém-nascidos que precisam de tratamento prolongado. O enfermeiro e a equipe de enfermagem devem sempre está se atualizando e capacitando para prestar um atendimento humanizado e de qualidade.

Effect of process parameters on micro flexible deep drawing of stainless steel 304 cups utilizing floating ring: Simulation and experiments

Due to its simplicity, versatility of process and feasibility of prototyping, using flexible tools in sheet forming seems appropriate for producing cups at microscales. This article presents a novel micro deep drawing technique in which a cooperation of a floating ring, as a primary rigid die, with a rubber pad, as a main flexible die, is employed for forming micro-cups. The function of the floating ring is to overcome minor wrinkles that commonly occur at flange portion, while the flexible die is to complete the forming stroke. The influence of initial sheet thickness, drawing ratio, punch corner radius and rubber height is studied through simulations and experiments. Furthermore, three size scales are adopted to investigate the possibility of using the proposed technique under different process dimensions. The code ABAQUS/Standard is utilized to build the finite element models and thereafter micro-forming experiments are carried out to verify the numerical results. For this purpose, a special setup is developed to be compatible with simulation models. The results show that the formed cups are characterized by very accurate dimensions, high surface quality, homogeneous wall thickness distribution in terms of maximum thinning and thickening and relatively large aspect ratio.

Place actuelle de l'imagerie non invasive des artères de gros calibre dans l'artérite à cellules géantes: du diagnostic au suivi

Large vessel involvement in giant cell arteritis has long been described, although its right frequency and potential prognostic value have only been highlighted for two decades. Large vessel involvement not only is associated with a high incidence of late aortic aneurysms, but also might cause greater resistance to glucocorticoids and longer treatment duration, as well as worse late cardiovascular outcomes. These data were brought to our attention, thanks to substantial progress recently made in large vessel imaging. This relies on four single, often complementary, approaches of varying availability: colour Doppler ultrasound, contrast-enhanced computed tomography with angiography and, magnetic resonance imaging, which all demonstrate homogeneous circumferential wall thickening and describe structural changes; 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET/CT), which depicts wall inflammation and assesses many vascular territories in the same examination. In addition, integrated head-and-neck PET/CT can accurately and reliably diagnose cranial arteritis. All four procedures exhibit high diagnostic performance for a large vessel arteritis diagnosis so that the choice is left to the physician, depending on local practices and accessibility; the most important is to carry out the chosen modality without delay to avoid false or equivocal results, due to early vascular oedema changes as a result of high dose glucocorticoid treatment. Yet, ultrasound study of the superficial cranial and subclavian/axillary arteries remains a first line assessment aimed at strengthening and expediting the clinical diagnosis as well as raising suspicion of large-vessel involvement. In treated patients, vascular imaging results are poorly correlated with clinical-biological controlled disease so that it is strongly recommended not to renew imaging studies unless a large vessel relapse or complication is suspected. On the other hand, a structural monitoring of aorta following giant cell arteritis is mandatory, but uncertainties remain regarding the best procedural approach, timing of first control and spacing between controls. Individuals at greater risk of developing aortic complication, e.g. those with classic risk factors for aneurysm and/or visualised aortitis, should be monitored more closely.

In-Situ Determination of Buildings’ Thermo- Physical Characteristics: Method Development, Experimentation, and Computation

In-Situ Determination of Buildings’ Thermo- Physical Characteristics: Method Development, Experimentation, and Computation

IgG4 Related Peri-aortitis: A Case Diagnosed in Combined Military Hospital, Dhaka

IgG4 related disease is a multi-organ immune-mediated condition which links many disorders previously regarded as isolated, a single-organ disease without any known underlying systemic condition. It may mimic anymalignant, infectious and inflammatory disorders. It was recognized as a unified entity only 10 years ago. Histopathology is the key to diagnosis. The three central pathology features of IgG4 related disease are lymphoplasmacytic infiltration, stroriform fibrosis, and obliterative arteritis. It is important to promptly diagnose IgG4 related disease because this disease commonly manifests as swelling of the affected organs, which must be differentiated from true neoplasms. Periaortitis or periarteritis is one of the clinical features of IgG4 related diseases. IgG4 related arterial lesions occur mainly in the aorta and its main branches and radiologically characterized by homogeneous arterial wall thickening corresponding to pathological features of IgG4 related sclerosing inflammation in the adventitia. There are 5 types of IgG4 related peri-aortitis, out of which Type 2 is most common. IgG4 related peri-aortitis generally respond to glucocorticoids in its inflammatory stage, but recurrent or refractory cases are common. Greater awareness of this disease is needed to ensure earlier diagnoses to prevent severe organ damage. A 38-year-old male was diagnosed as Type 2 IgG4 related periaortitis 2 years ago in CMH, Dhaka. He was treated with oral steroid and Azathioprine with a rewarding outcome.
 Journal of Armed Forces Medical College Bangladesh Vol.14 (2) 2018: 217-219

Detection of defects in building walls using modified OptD method for down-sampling of point clouds

ABSTRACT Terrestrial laser scanning is a simple and nondestructive method for the high-accuracy, three-dimensional mapping of buildings and structures. It yields a high-resolution point cloud, allowing for comprehensive and reliable diagnosis of the target building. However, there are difficulties in processing such large datasets. Commercial software typically reduces the datasets using random methods, resulting in the loss of useful information. Herein, we propose a modified optimum dataset (OptD) method for performing diagnostic measurements on buildings. The modified OptD method allows the retention of more points corresponding to areas of interest, such as those with cracks, cavities, and other surface imperfections, and removal of redundant information related to flat and homogeneous surface walls. We propose two approaches for reducing the size of the datasets while simultaneously detecting the imperfections in building walls. The first is to down-sample the datasets in the OXYZ coordinate system to improve the detection of defects corresponding to geometric changes (e.g. cracks and cavities). The second is to down-sample the datasets in the OXYI coordinate system (where I is the laser intensity) to improve the detection accuracy for defects corresponding to changes in the physicochemical properties of the surface (e.g. moisture content, weathering, salt blooming, and biodeterioration).

Hybrid Phase-Change Lattice Boltzmann Simulation of Vapor Condensation on Vertical Subcooled Walls

Abstract Saturated vapor condensation on homogenous and heterogeneous subcooled walls is presented in this study by adopting a hybrid phase-change multiple-relaxation-time Lattice Boltzmann model. The effects of wall wettability on the condensation process, including droplets' growth, coalescence and falling, and the influence of vapor flow to condensation are investigated. The results demonstrate that the heat fluxes around the triple-phase contact lines are higher than that in other cold areas in homogeneous subcooled walls, which actually indicates the fact that filmwise condensation is preventing the continuous condensation process. Furthermore, the dropwise condensation can be formed more easily on the heterogeneous surface with a mixed surface wettability. At last, the dynamic process of condensation of continuous vapor flow is also investigated by considering the homogenous and heterogeneous subcooled surfaces. The results show that the heterogeneous surface with mixed wettability does not significantly contribute to the formation, growth of droplets, when compared to the homogeneous surface. It is expected that this study can bring more attention to simulate condensation using multiphase LBM for complex geometries in heat transfer community.

Dual cocatalysts decorated three dimensionally ordered mesoporous g‐C3N4 with homogeneous wall thickness for enhanced photocatalytic performance

Making several components be more intimate interfacial contacts in the photocatalyst is an efficient strategy to improve the separation and transfer of photogenerated charge carries and enhance the photocatalytic performance in the visible light region. In this work, a promising photocatalyst was fabricated by loading of Au nanoparticles and Cd(0.58)Zn(0.42)S nanoparticles onto the three dimensionally ordered mesoporous g‐C3N4 material (Au/3DOM CN/Cd(0.58)Zn(0.42)S) via two‐step synthesis method to significantly intensify the transfer capability of charge. The results of characterization demonstrate that Au/3DOM CN/Cd(0.58)Zn(0.42)S photocatalyst possesses the intimate interfacial contacts of three components and homogeneous wall thickness of 3DOM g‐C3N4 framework, and these properties give Au/3DOM CN/Cd(0.58)Zn(0.42)S photocatalyst an ability that it can harvest a wider range of visible light and endow it superior photocatalytic activities for hydrogen evolution from water splitting and RhB degradation. Finally, a possible mechanism was proposed based on the photoelectrochemical measurement. This work would provide a new strategy to design and fabricate g‐C3N4‐based with 3DOM architecture materials with superior photocatalytic activity.

In-Situ Determination of Buildings’ Thermo- Physical Characteristics

In-Situ Determination of Buildings’ Thermo- Physical Characteristics

Combined effect of viscosity variation and non-Newtonian Rabinowitsch fluid in wide parallel rectangular-porous plate with squeeze-film characteristics

The present article carries out the study of viscosity variation of non-Newtonian fluid with the homogeneous porous wall on wide parallel rectangular-plate based on the Rabinowitsch fluid model. The non-linear modified Reynolds equation is derived for the lubrication of rectangular squeeze film bearing with viscosity variation and porous parameter. Using the Morgan–Cameron approximation, the nonlinear Reynolds-type equation for squeeze-film which governs the film pressure is solved within the fundamentals of small perturbation technique. The characteristic of the wide parallel rectangular-porous plate is numerically computed for different physical quantities such as film pressure, load carrying capacity and response time. Moreover, as limiting cases some of the results from the available literature are recovered also. Further, the findings reveal that the viscosity variation of non-Newtonian fluid and the presence of porous wall lead to reduction in the load capacity and the response time respectively. Here, the porous matrix consists of a system of capillaries of very small radii with the homogeneous porous wall. The impact of porosity is incorporated as a result it acts as self-lubrication on bearing surface. Also, the effect of viscosity variation is one of the most important characteristics of fluid which helps in the design of bearings for lubrication in engineering and industrial applications.

Patient specific characterization of artery and plaque material properties in peripheral artery disease

Patient-specific finite element (FE) modeling of atherosclerotic plaque is challenging, as there is limited information available clinically to characterize plaque components. This study proposes that for the limited data available in vivo, material properties of plaque and artery can be identified using inverse FE analysis and either a simple neo-Hookean constitutive model or assuming linear elasticity provides sufficient accuracy to capture the changes in vessel deformation, which is the available clinical metric. To test this, 10 human cadaveric femoral arteries were each pressurized ex vivo at 6 pressure levels, while intravascular ultrasound (IVUS) and virtual histology (VH) imaging were performed during controlled pull-back to determine vessel geometry and plaque structure. The VH images were then utilized to construct FE models with heterogeneous material properties corresponding to the vessel plaque components. The constitutive models were then fit to each plaque component by minimizing the difference between the experimental and the simulated geometry using the inverse FE method. Additionally, we further simplified the analysis by assuming the vessel wall had a homogeneous structure, i.e. lumping artery and plaque as one tissue. We found that for the heterogeneous wall structure, the simulated and experimental vessel geometries compared well when the fitted neo-Hookean parameters or elastic modulus, in the case of linear elasticity, were utilized. Furthermore, taking the median of these fitted parameters then inputting these as plaque component mechanical properties in the finite element simulation yielded differences between simulated and experimental geometries that were on average around 2% greater (1.30–5.55% error range to 2.33–11.71% error range). For the homogeneous wall structure the simulated and experimental wall geometries had an average difference of around 4% although when the difference was calculated using the median fitted value this difference was larger than for the heterogeneous fits. Finally, comparison to uniaxial tension data and to literature constitutive models also gave confidence to the suitability of this simplified approach for patient-specific arterial simulation based on data that may be acquired in the clinic.

Mathematical apparatus for determination of homogenous scalar medium thermal resistance

Introduction: the article suggests a method for determining a thermal resistance of small and large-sized areas (one-dimensional and multidimensional problems) of wall enclosure. The subject of the study is the thermal resistance of homogeneous scalar medium (homogeneous wall enclosure). The aim is the determination of thermal resistance of a wall structure for areas of arbitrary dimension (by the coordinates xi, where 1 ≤ i ≤ d and d is the area dimension) filled with a scalar (homogeneous and isotropic) heat-conducting medium.
 
 
 Materials and methods: the article used the following physical laws: Fourier law (the value of the heat flow when transferring heat through thermal conductivity) and continuity condition for the heat flow rate leading to the thermal conductivity equation.
 
 
 Results: this method extends the standard definition of thermal resistance. The research proved that the active thermal resistance does not increase with increasing of the area dimension (for example, when switching from a thin shell or plate to a rectangle with length and width of the same order of magnitude). That is the sense of geometric inclusion, i.e., increase of the dimension of an area filled with a homogeneous isotropic medium. Evident expressions are obtained for the determination of active, reactive, and total thermal resistance. It is proved that the total resistance is higher than the active resistance since the reactive resistance is positive, and the wall possesses an ability to suppress the temperature fluctuations and accumulate/give up the heat.
 
 
 Conclusions: the appearance of an additional wall dimension (comparable length-to-thickness ratio) does not increase its active resistance. In the general case, the total thermal resistance exceeds the active thermal resistance no more than four times. Geometric inclusions must be considered in the calculation of wall enclosures that are variant from one-dimensional bodies.

Application of infrared thermography for in-situ determination of building envelope thermal properties

Thermal resistance of building envelope systems plays an important role in the building energy evaluation, design, and retrofit efforts; in-situ determination of the thermal resistance is highly desired for obtaining a realistic building energy performance picture. The conventional heat flow meter method for measuring thermal resistance requires a considerable number of sensor installations and also an appropriate definition of the homogeneous wall area. Therefore, a simpler and more practical measurement method is needed. Recent studies indicate that the infrared thermography method has the potential to be used as a quantitative technique for thermal resistance measurement. However, there are limitations in the previously developed infrared thermography method that may lead to difficulties in practical application. In the study reported in this paper, an innovative infrared thermography model is proposed and its effectiveness is validated by comparison with the heat flow meter method. A convective heat transfer coefficient model is also proposed, which can particularly be used for low-rise residential buildings. A recommended testing procedure is then given at the end of the paper for appropriate use of the proposed measurement method.

A pseudospectral approach applicable for time integration of linearized N‐S operator that removes pole singularity and physically spurious eigenmodes

SummaryThis paper addresses a modified singularity removal technique for the eigenvalue or optimal mode problems in pipe flow using a pseudospectral method. The current approach results in the linear stability operator to be devoid of any unstable physically spurious modes, and thus, it provides higher numerical stability during time‐based integration. The correctness of the numerical operator is established by calculating the known eigenvalues of pipe Poiseuille flow. Subsequently, the optimal modes are determined with Farrell's approach and compared with the existing literature. The usefulness of this approach is further demonstrated in the time‐based numerical integration of the linearized Navier‐Stokes operator for the adjoint method–based optimal mode determination. The numerical scheme is implemented with the radial velocity‐radial vorticity formulation. Even number of Chebyshev‐Lobatto grid points are distributed over the domain r∈[−1,1] omitting the centerline, which also efficiently provides higher resolution near the wall boundary. The boundary conditions are imposed with homogeneous wall boundary conditions, whereas the analytic nature of a proper set of base functions enforces correct centerline conditions. The resulting redundancy introduced in the process is eliminated with the proper usage of parity.

Practical aspects of heat conduction simulation in household heating optimization tasks

Mathematical model selection for simulation heat conduction processes in household heating optimization task is considered. The essence of the matter is that the heat transfer dynamics properties are very diversified, so simulation procedure formulae and parameters should be properly selected to avoid excessive modeling errors with reasonable calculation time being held. The typical state-space model and analytical formulae for step response of the heat conduction across a homogeneous wall are presented and compared in terms of modeling errors. Formal and numerical problems of heat losses simulation are discussed. Semi-analytical step-response formulae for multilayer walls are derived and their accuracy is compared with effects of simulation based on the state-space model. Some recommendations for time and space discetization parameters are given.

Stokes-layer formation under absence of moving parts—A novel oscillatory plasma actuator design for turbulent drag reduction

A novel plasma actuator concept is proposed to mimic the effect of spanwise wall oscillations without mechanically moving parts, where four groups of electrodes and three independently operated high-voltage power supplies maintain a pulsatile dielectric barrier discharge (DBD) array. Time-resolved planar velocity fields are obtained with high-speed particle image velocimetry (PIV) in proximity of the discharge zones for quiescent ambient conditions. Resulting flow topologies and wall-normal velocity profiles indicate the Stokes-layer-like flow formation, which is elevated above the wall due to the no-slip condition. The underlying body forces are derived from the PIV data to provide further insight into cause-effect relations between pulsatile discharge and oscillatory flow. The momentum transfer domain is found to be only interrupted with the width of the exposed electrode, which is an important step toward homogeneous virtual wall oscillations. A comparison with earlier studies by Gatti et al. [“Experimental assessment of spanwise-oscillating dielectric electroactive surfaces for turbulent drag reduction in an air channel flow,” Exp. Fluids 56, 110 (2015)] leads to the hypothesis that DBD-based turbulent drag reduction might be a competing alternative to conventional active and passive shear-layer formation strategies, where the adjustability of both oscillation frequency and velocity amplitude might cover a wide range of Reynolds numbers.