Vicinity Of Wall Research Articles

The spontaneous emission rate determination of a molecule near a perfect conductive wall

In this paper, the formalism describing the spontaneous emission rate of an excited molecule (or atom) with definite transition electric dipole moment, in vicinity of a perfect conductive wall is developed. Separately, for molecules (or atoms) with the electric dipole moment parallel and perpendicular to the wall, the spontaneous emission rate of the molecule is calculated in two ways: (1) by using the explicit form of the vector potential operator in the Fermi' golden rule and taking the expectation value in vacuum state and (2) by considering the relation between the spontaneous emission rate and the vector potential Green function, and calculating the required Green function components of the space at the presence of a perfect conductive wall. The two methods yield the same expression for the spontaneous emission rate. The agreement of the results with some previous works is shown and the variations of the spontaneous emission rate for each dipole moment orientation are demonstrated.

Molecular dynamics simulation of water-based Ferro-nanofluid flow in the microchannel and nanochannel: Effects of number of layers and material of walls

Due to the increasing development of nanotechnology and its wide applications, the flow of a nanofluid in a duct is also optimal geometric construction of ducts in the fabrication and production of various ducts to increase efficiency in nanofluid behavior are essential. In this paper, by using the molecular dynamics (MD) simulation process, the effect of Fe3O4 nanoparticles on the behavior of water-based fluid is investigated. Physical parameters such as total temperature, potential energy, fluid, nanofluid density profiles, fluid velocity, nanofluid profiles, and fluid and nanofluid temperature profiles are reported. Also, the effect of the number of layers and wall material on fluid flow is investigated. Therefore, the channel wall material in the following simulations will be considered as platinum, copper, and iron. Over time, the temperature of atomic structures reaches 300 K, which indicates the temperature stability in the simulated atomic structures. The results show that by increasing the number of wall layers in nanochannels and similar microchannels, interactions between fluid particles and walls increase. As these interactions increase, the accumulation of fluid particles in the vicinity of the channel walls increases, which increases the density of the shelves adjacent to the channel walls. Also, by changing the microchannel material from copper to iron and platinum, the number of interactions between particles in the present structures increases. This increase in the number of interactions between the particles present in the microchannel wall and the base fluid causes the maximum density to be observed in the platinum microchannel.

Stochastic inference of surface-induced effects using Brownian motion

Brownian motion in confinement and at interfaces is a canonical situation, encountered from fundamental biophysics to nanoscale engineering. Using the Lorenz-Mie framework, we optically record the thermally-induced tridimensional trajectories of individual microparticles, within salty aqueous solutions, in the vicinity of a rigid wall, and in the presence of surface charges. We construct the time-dependent position and displacement probability density functions, and study the non-Gaussian character of the latter which is a direct signature of the hindered mobility near the wall. Based on these distributions, we implement a novel, robust and self-calibrated multifitting method, allowing for the thermal-noise-limited inference of diffusion coefficients spatially-resolved at the nanoscale, equilibrium potentials, and forces at the femtoNewton resolution.

Presence of Left Atrial Fibrosis May Contribute to Aberrant Hemodynamics and Increased Risk of Stroke in Atrial Fibrillation Patients.

Atrial fibrillation (AF) patients are at high risk of stroke, with the left atrial appendage (LAA) found to be the most common site of clot formation. Presence of left atrial (LA) fibrosis has also been associated with higher stroke risk. However, the mechanisms for increased stroke risk in patients with atrial fibrotic remodeling are poorly understood. We sought to explore these mechanisms using fluid dynamic analysis and to test the hypothesis that the presence of LA fibrosis leads to aberrant hemodynamics in the LA, contributing to increased stroke risk in AF patients. We retrospectively collected late-gadolinium-enhanced MRI (LGE-MRI) images of eight AF patients (four persistent and four paroxysmal) and reconstructed their 3D LA surfaces. Personalized computational fluid dynamic simulations were performed, and hemodynamics at the LA wall were quantified by wall shear stress (WSS, friction of blood), oscillatory shear index (OSI, temporal directional change of WSS), endothelial cell activation potential (ECAP, ratio of OSI and WSS), and relative residence time (RRT, residence time of blood near the LA wall). For each case, these hemodynamic metrics were compared between fibrotic and non-fibrotic portions of the wall. Our results showed that WSS was lower, and OSI, ECAP, and RRT was higher in the fibrotic region as compared to the non-fibrotic region, with ECAP (p = 0.001) and RRT (p = 0.002) having significant differences. Case-wise analysis showed that these differences in hemodynamics were statistically significant for seven cases. Furthermore, patients with higher fibrotic burden were exposed to larger regions of high ECAP, which represents regions of low WSS and high OSI. Consistently, high ECAP in the vicinity of the fibrotic wall suggest that local blood flow was slow and oscillating that represents aberrant hemodynamic conditions, thus enabling prothrombotic conditions for circulating blood. AF patients with high LA fibrotic burden had more prothrombotic regions, providing more sites for potential clot formation, thus increasing their risk of stroke.

Influence of aortic valve tilt angle on flow patterns in the ascending aorta

Transcatheter aortic valve implantation (TAVI) has become the alternative procedure to high-risk patients who are diagnosed with aortic valve stenosis. Differently from the traditional open-chest surgical procedure, a small variation on the prosthetic aortic valve deployment angle is expected with the TAVI procedure. The hemodynamic patterns of the blood flow in the ascending aorta are related to the development of many cardiovascular diseases. There are, however, few data available in the literature correlating the aortic valve tilt angle to hemodynamic effects. In this work, a 3D printed aorta model made of a transparent silicon resin was produced, based on the anatomy of a specific patient submitted to a TAVI procedure. The stereoscopic Particle Image Velocimetry technique was employed to measure three-component velocity fields at closely spaced cross-sectional planes, along the ascending aorta. The measurements were performed for a constant flow rate corresponding to the peak of the systolic phase of the cardiac cycle. Averaged velocity fields and turbulent quantities were determined for both, the base case, with no valve tilt, and for cases with an inclination of 4° and 8°, oriented at the four anatomical directions of the human body reference system, namely anterior, posterior, right and left. The results revealed the dominant flow patterns in the ascending aorta formed by a jet-like inlet flow impinging on the curved aorta right wall, inducing a significant eccentricity on the axial velocity profile. Regions of reverse flow were identified and linked to the abrupt area change associated with the typical reduced inlet diameter of TAVI implants. The impinging flow and wall curvature effects established circulation patterns defining a helical flow structure. The influence of the inlet flow orientation on the flow turbulent characteristics was assessed by the spatial evolution of the turbulent kinetic energy (TKE), Reynolds and viscous stresses. The maximum values of TKE were found around the inlet jet boundaries and concentrated in the neighborhood of the right aorta wall where the eccentric axial flow prevailed. Spatial distributions of the maximum Reynolds stresses were similar to the TKE distributions and presented maximum stresses typically one order of magnitude higher than the maximum average viscous shear stresses. Maximum average viscous stress distributions were revealed at the jet-like flow boundaries and in the vicinity of the right wall, displaying moderate stress levels that, according to the literature, can be sufficient to produce cell damage and platelet activation. The complex nature of the flow field was revealed by streamlines obtained from the measured flow fields, allowing the identification of the influence of the inlet flow orientation and tilt angle on the position of the stagnation point on the aorta right wall, as well as the angle of incidence of the jet-like flow on the wall. A simple model based on momentum balance was used to estimate the pressure increment on the wall due to flow impingement. The model captured the influence of the inlet flow orientation, indicating that pressure increases of the order of 40% in relation to the base case condition were obtained for the 8°, left inlet flow orientation.

A study of the influence of coflow on flame dynamics in impinging jet diffusion flames

Non-premixed impinging jet flames with different coflow conditions are performed using PIV technology combined with numerical simulation to investigate flame instability in the vicinity of wall. Results indicate that the increase of coflow velocity results in a more chaotic flow field and higher fuel efficiency, and the increase of coflow temperature leads to ignition advance and the increase of NO concentration. These can be attributed to the coupling effect of Kelvin-Helmholtz instability, convective instability and Rayleigh-Taylor instability. High coflow velocity is more likely to induce Kelvin-Helmholtz instability and convective instability, and the increase of coflow temperature enhances Rayleigh-Taylor instability and convective instability. Due to the impact effect in the vicinity of wall, the flame instability is more likely to be induced at high coflow velocity. Meanwhile, the increase of coflow temperature can inhibit flame wrinkles. The flame dynamics is affected by turbulent mixing, head-on collision, shear and convective behaviors in non-premixed flames.

Baffle jetting modelling

Horizontal flow in the lower part of the reactor pressure vessel was found responsible for the so-called baffle jets impinging in the direction almost perpendicular to the nuclear fuel rods axes. This flow may generate flow-induced vibrations of the fuel rods that can damage the rods.As opposed to the flow-induced vibrations in a purely cross-flow situation, as in the case of e.g. heat exchanger tubes, the flow direction in the bottom part of the core barrel is of a combined axial and cross flow nature. One of peculiarities of the baffle jet and fuel rods interaction is the vicinity of the solid walls of the core barrel; also, the velocity profile impacting onto the fuel rods is non-uniform.The present study aims to further investigate the nature of flow field in the geometry relevant to the baffle jetting in the pressurized water reactors (PWRs). A separate effect study is conducted in order to assess the ability of a number of turbulent models to predict the complicated flow field in the case of baffle jets. Conclusions were drawn for the models’ ability to predict both the time-average and the transient, spectral, characteristics of the flow.An experimental program PANACHET was employed in CEA, France, for the study of baffle jetting. Flow velocity was measured for the conditions mimicking the flow field in the bottom periphery part of the core barrel. The PANACHET experiments were simulated using the models validated in the separate effects study.

Generating Compressive Surface Residual Stresses Using Hydraulic Autofrettage Process With Heat Treatment

Abstract Recently, a method of inducing compressive residual stresses in the vicinity of the walls of a thermally autofrettaged cylinder was proposed. In the proposed method, the thermally autofrettaged cylinder was heated in such a manner that its outer wall attained a temperature more than the lower critical temperature and the inner wall was at a sufficiently lower temperature. When the cylinder was quenched, compressive residual stresses were induced in the vicinity of the cylinder walls. This article investigates the feasibility of the same procedure for a hydraulic-autofrettaged cylinder made of AISI 1080 steel. A finite element method (FEM)-based analysis is carried out using commercial package abaqus by incorporating microstructure and temperature-dependent material properties. The results indicate that the heat treatment design proposed for the thermally autofrettaged cylinder to induce compressive residual stresses at the outer wall can also be adapted for a hydraulic-autofrettaged cylinder. However, for cylinders subjected to high percentage of autofrettage, heating of the outer wall needs to be carried out well below the lower critical temperature. In fact, this is an advantage in terms of energy saving and can be implemented even for cylinders subjected to a low percentage of autofrettage.

Pore-scale effects during the transition from capillary- to viscosity-dominated flow dynamics within microfluidic porous-like domains

We perform a numerical and experimental study of immiscible two-phase flows within predominantly 2D transparent PDMS microfluidic domains with disordered pillar-like obstacles, that effectively serve as artificial porous structures. Using a high sensitivity pressure sensor at the flow inlet, we capture experimentally the pressure dynamics under fixed flow rate conditions as the fluid–fluid interface advances within the porous domain, while also monitoring the corresponding phase distribution patterns using optical microscopy. Our experimental study covers 4 orders of magnitude with respect to the injection flow rate and highlights the characteristics of immiscible displacement processes during the transition from the capillarity-controlled interface displacement regime at lower flow rates, where the pores are invaded sequentially in the form of Haines jumps, to the viscosity-dominated regime, where multiple pores are invaded simultaneously. In the capillary regime, we recover a clear correlation between the recorded inlet pressure and the pore-throat diameter invaded by the interface that follows the Young–Laplace equation, while during the transition to the viscous regime such a correlation is no longer evident due to multiple pore-throats being invaded simultaneously (but also due to significant viscous pressure drop along the inlet and outlet channels, that effectively mask capillary effects). The performed experimental study serves for the validation of a robust Level-Set model capable of explicitly tracking interfacial dynamics at sub-pore scale resolutions under identical flow conditions. The numerical model is validated against both well-established theoretical flow models, that account for the effects of viscous and capillary forces on interfacial dynamics, and the experimental results obtained using the developed microfluidic setup over a wide range of capillary numbers. Our results show that the proposed numerical model recovers very well the experimentally observed flow dynamics in terms of phase distribution patterns and inlet pressures, but also the effects of viscous flow on the apparent (i.e. dynamic) contact angles in the vicinity of the pore walls. For the first time in the literature, this work clearly shows that the proposed numerical approach has an undoubtable strong potential to simulate multiphase flow in porous domains over a wide range of Capillary numbers.

Hydrodynamic Boundary Layers at Solid Wall—A Tool for Separation of Fine Solids

A theoretical study is performed about the hydrodynamic interaction of fine species entrapped in the boundary layer (BL) at solid wall (plate). The key starting point is the analysis of the disturbance introduced by solid spheres in the background fluid flow. For a neutrally buoyant entity, the type of interaction is determined by the size of the spheres as compared to the thickness of the BL region. The result is granulometric separation of the solids inside the BL domain at the wall. The most important result in view of potential applications concerns the so-called small particles Rp < L/ReL5/4 (ReL is the Reynolds number of the background flow and Rp is the radius of the entrapped sphere). In the case of non-neutrally buoyant particles, gravity interferes with the separation effect. Important factor in this case is the relative density of the solid species as compared to this of the fluid. In view of further practical uses, particles within the range of Δρ/ρ < Fr2/ReL1/2 (Fr is Froude number and Δρ/ρ is the relative density of the entrapped solids) are systematically studied. The trajectories inside the BL region of the captured species are calculated. The obtained data show that there are preferred regions along the wall where the fine solids are detained. The results are important for the assessment of the general efficiency of entrapment and segregation of fine species in the vicinity of solid walls and have high potential for further design of industrial separation processes.

Direct Numerical Simulation of Turbulent Heat Transfer with Slip and Temperature Jump

The fully developed turbulent flow and heat transfer in a plane channel at a nominal shear Reynolds number of 180 is studied via the direct numerical simulation technique. A linear velocity-slip boundary condition is assumed on one of the channel walls, whereas the classical no-slip condition is imposed on the other wall. The heat transfer at the slip wall is assumed to occur with and without temperature jump, whereas a classical first-kind temperature boundary condition is assumed on the no-slip wall. Various statistical quantities are shown and discussed. It is observed that the velocity fluctuations are attenuated in the proximity of the slip wall but they are amplified in the vicinity of the no-slip wall. The behavior is somewhat different for the temperature fluctuations. For the case without temperature jump, the temperature fluctuations are amplified near the slip wall, whereas they are attenuated close to the no-slip wall. For the case with temperature jump, the modifications of turbulent heat fluxes are more dramatic and they decrease by increasing the amount of wall slip. In general, the velocity slip condition will result in an enhanced heat transfer if no temperature jump is taken into account. This behavior is reversed when the temperature jump at the slip wall is taken into account. The budget of temperature variance is shown and discussed for the case with temperature jump.

A microchannel flow with presence of micro-post arrays on channel top wall

A microchannel flow is considered and the influence of the micro-post arrays and air trapped on velocity and temperature increase of the working fluid is examined experimentally and numerically incorporating 3-D simulations. The channel bottom plate is considered to be smooth and hydrophilic, which moves with a constant velocity, while channel top wall is stationary and it has staggered arrangement of micro-post arrays with hydrophobic wetting state. An experiment is carried out to validate velocity and temperature predictions while setting simulation conditions in line with the experiments. It is found that the flow field in top channel wall vicinity is influenced by the micro-post arrays; hence, wavy flow field is generated in this region. Flow circulation in the trapped air in between the micro-post arrays influences the heat transfer rates. The Nusselt number reduces slightly with increasing pitch size of the micro-post arrays. In addition, increasing the microchannel height lowers the Nusselt number. The pressure drop between the channel inlet and exit is influenced significantly by the micro-post arrays. Increasing pitch size of the micro-post arrays reduces the pressure drop; however, further increase of the pitch size beyond 12 μm does not alter the pressure drop across the microchannel.

Large-Eddy Simulation of Flame Dynamics During the Ignition of a Swirling Injector Unit and Comparison With Experiments

Abstract During the ignition of a swirled single-injector combustor, two phases have been identified experimentally. In the first, the flame penetrates the injection unit, while in the second, the flame lifts off after a substantial delay before stabilizing at a distance from the injector. This transient phenomenon is investigated using Large Eddy Simulations based on an Euler–Lagrange description of the liquid spray, an energy deposition model to mimic ignition, and the thickened flame combustion model. It is shown that the initial penetration of the flame in the injector unit is linked with the positive pressure excursion induced by the rapid volumetric expansion of burnt gases. This sudden expansion is itself due to the fast increase in heat release rate that occurs during the initiation of the process. The corresponding positive and negative pressure disturbances induce a rapid reduction of the mass flow rate through the injector, followed by an acceleration of the flow and a return to the nominal value. It is also shown that the flame root disappears after another delay, which results in the flame edge lifting and stabilization at a distance from the injector exhaust corresponding to steady operation of the device. The relatively long delay time before this liftoff takes place is found to correspond to the residence time of the cooled burnt gases in the vicinity of the chamber walls, which are ultimately entrained by the internal recirculation zone and quench the lower flame foot.

Liquid Transport Through Nanoscale Porous Media with Strong Wettability

It is important to investigate interfacial effects on liquid transport characteristics through nanopores with strong wettability due to potential applications in several fields. The structural and transport properties of wetted liquid argon through nanochannels were investigated via molecular dynamics (MD) simulations. A mathematical model for liquid flow in nanoporous media was established based on the constant negative slip length by combining MD simulations with fractal theory for complex media. The results show that the strong liquid–solid attraction allows the liquid to be adsorbed onto the solid walls. In addition, compared with the bulk diffusion coefficient in the center of the nanochannel, the coefficient parallel to the interface near the solid walls is largely reduced, indicating the liquid molecules are strongly bound to the solid walls. Furthermore, negative slip can exist in the vicinity of solid walls with strong wettabilities. The variations in negative slip length with the external driving force can be characterized by two regimes. In steady negative slip regime, the negative slip length remains constant. As the driving force continues to increase, the transition negative slip regime exists, where the negative slip length decreases linearly with the driving force until the slip length becomes zero. The presence of a negative slip length reduces the liquid flow rate compared with no slip or a positive slip length due to the reduced effective cross section for fluid transport. Moreover, the increased fractal dimensions about the capillary radius result in an enhanced liquid flow rate, while that about the tortuosity reduces the liquid flow rate.

Transitions of power-law fluids in two-dimensional lid-driven cavity flow using lattice Boltzmann method

Studying transitions from laminar to turbulence of non-Newtonian fluids can provide a theoretical basis to further mediate their dynamic properties. Compared with Newtonian fluids, transitions of non-Newtonian fluids turning are less focused, thus being lack of good predictions of the critical Reynolds number (<i>Re</i>) corresponding to the first Hopf bifurcation. In this study, we employ the lattice Boltzmann method as the core solver to simulate two-dimensional lid-driven flows of a typical non-Newtonian fluid modeled by the power rheology law. Results show that the critical <i>Re</i> of shear-thinning (5496) and shear-thickening fluids (11546) are distinct from that of Newtonian fluids (7835). Moreover, when <i>Re</i> is slightly larger than the critical one, temporal variations of velocity components at the monitor point all show a periodic trend. Before transition of the flow filed, the velocity components show a horizontal straight line, and after transition , the velocity components fluctuate greatly and irregularly. Through fast Fourier transform for the velocity components, it is noted that the velocity has a dominant frequency and a harmonic frequency when <i>Re</i> is marginally larger than the critical one. Besides, the velocity is steady before transition of flow filed, so it appears as a point on the frequency spectrum. As the flow filed turns to be turbulent, the frequency spectrum of the velocity component appears multispectral. Different from a single point in the velocity phase diagram before transition, the velocity phase diagram after transition forms a smooth and closed curve, whose area is also increasing as <i>Re</i> increases. The center point of the curve moves along a certain direction, while movement directions of different center points are different. Proper orthogonal decompositions for the velocity and vorticity field reveal that the first two modes, in all types of fluids, are the dominant modes when <i>Re</i> is close to the critical one, with energy, occupying more than 95% the whole energy. In addition, for one type of fluid, the dominant modes at different <i>Re</i> values have similar structures. Results of the first and second modes of velocity field show that the modal peak is mainly distributed in vicinity of the cavity wall.

Dynamic permeability of fluids in rectangular and square microchannels: Shift and coupling of viscoelastic bidimensional resonances

Pulsatile dynamics of Newtonian and Maxwellian fluids is exactly solved by theoretical analytical means when confined within rectangular microchannels subject to oscillatory driving forces. The analytical solution exhibits a complex behavior caused by the fluid dynamics along the smallest and the secondary confinement dimensions. For Newtonian fluids, the maximum and average flow velocities within the microchannel differ considerably from the ones predicted by simplified one-dimensional models when fluids are subject to moderate and high driving force frequencies. This is caused by the stagnation of flow velocity in the vicinity of the channel walls at the secondary confinement dimension. For Maxwellian fluids, the secondary confinement incorporates flow resonances that are coupled to the ones caused by the smallest confinement, leading to a shift of the main resonance and the arising of resonances when bidimensional vibration modes are excited. These effects depend on the aspect ratio between channel width and height and on the magnitude of the driving force frequency, compared to the characteristic viscous frequency of the microchannel. The theoretical results are compared with recent experimental results in the literature in pulsatile microfluidics for hyaluronic acid solutions with viscoelastic properties, as well as for water. In both cases, an agreement is found between theoretical and experimental results.

Developing flow of Newtonian fluids over superhydrophobic transverse grooves in circular tube

In this paper, the effects of dimensionless gas area fraction (δ) and normalized groove-rib periodic spacing (Λ) on developing flow for Newtonian fluid past circular tube having alternating superhydrophobic transverse grooves were numerically investigated. Fluid flow at Re ranging from 0.001 to 10 over various superhydrophobic microstructures scales (0.05 < Λ < 1, 0 <δ < 1) were studied. Numerical results show that the presence of superhydrophobic transverse grooves would consistently yield a longer hydrodynamic entrance length (Lh) as compared to that of smooth surface. This is principally owing to the flow redistribution with higher flow rate that is permitted in the vicinity of the superhydrophobic wall. However, the scale of the superhydrophobic transverse grooves yield non-monotonic trend on hydrodynamic entrance length, with reduced delaying effect at higher Λ. Despite the Lh alteration, Lh arising from the presence of superhydrophobic transverse grooves in tube of diameter D, at low Re (i.e., Re < 1), is still bounded within tube length of D.

Molecular dynamics study on flow structure inside a thermal transpiration flow field

Thermal transpiration flow is a thermally driven flow from a cold part toward a hot part using a temperature gradient along a wall under a high Knudsen number condition. Many studies have used this type of flow as a pump for microtechnology. The flows adopted in these studies were, in most cases, in the slip or transitional regime. Accordingly, in this research, thermal transpiration flow through a two-dimensional channel with nanoscale clearance in the height direction was studied using the molecular dynamics method. The solid atoms composing the channel walls were explicitly considered. The center part of the nanochannel was controlled as a hot reservoir, whereas both ends of the nanochannel were kept cold. The temperatures of the channel wall atoms were also controlled based on their positions by linearly interpolating the temperature between the hot and cold reservoirs. Two Knudsen number conditions were adopted by changing the width of the computational cell. To study the mean velocity distribution inside the nanochannel, these simulations were performed for 10 ns. We successfully obtained a mean velocity distribution inside the nanochannel, showing the thermal transpiration flow in the vicinity of the channel wall using the pressure-driven counterflow at the center in the height direction even under the dense gas condition. The velocity profile across the nanochannel in the height direction indicated that thermal transpiration flow was induced in the adsorption layer of gas molecules on the channel wall under the dense gas condition.

DISTRIBUTION OF BLOOD COMPONENTS ALONG THE CROSS-SECTION OF THE VASCULAR DEPENDING ON THE CONCENTRATION OF ERYTHROCYTES

The dependence of the stationary distribution of blood components over the cross section of the cylindrical Poiseuille flow on the content of erythrocytes is described by the method of numerical simulation. A thermodynamic approach was used, in which dispersed phases are represented by a set of cellular components (erythrocytes, leukocytes, platelets), and blood plasma is considered as a low molecular weight dispersion medium. The simulation is based on the search for the minimum of the total energy of the system, including the chemical potentials and kinetic energy of all components. This state corresponds to the only solution describing the consistent distributions of all components of the multiphase flow over the section. Distributions of components were simulated, in which the content of leukocytes and platelets corresponds to the normal, for cases of normal, pathologically low (erythropenia) and high (erythrocytosis) content of erythrocytes. As an example, the Poiseuille flow in a vessel 1 mm in diameter with a shear rate of 10 s -1 is considered. According to the simulation results, the deviation of the number of erythrocytes from the norm leads to redistribution over the cross section of the flow of other components (leukocytes and platelets). The concentration of platelets and leukocytes has maximum values in the vicinity of the vessel walls with a low number of erythrocytes. When the number of red blood cells increases, maxima concentration of platelets and white blood cells are shifted to the center of the vessel and the proportion of red blood cells near the vessel walls increases

Application of thermal comfort assessment models to indoor areas near glazed walls – experimental evaluation

In this paper, some of the results of an experimental study are presented. Its purpose was to better understand the impact of glazing on thermal comfort of users of indoor spaces (living and working), especially in the areas near glazed walls. Glazed elements, such as windows and glazed doors, allow visual access to the outdoor environment and the entrance of natural light and solar heat gains but they are often the cause of unwanted heat losses and gains and are disturbing elements in obtaining thermal comfort, both in global terms and in what concerns local discomfort due to radiant asymmetries and/or air draughts. Furthermore, solar radiation directly affecting users in the vicinity of glazing can also cause discomfort. These disturbances are recognized by users, both on cold winter days and on hot summer days. To assess thermal comfort or thermal neutrality of a person in a particular indoor space, it is important to know their location within that space. Thus, in order to adequately assess thermal comfort in the areas near the glazing, the indoor thermal environment must be characterized for this specific location. In this study, two indoor spaces (a classroom and an office-room) of a school building were monitored at different periods of the year. The measurements of the environmental parameters were performed both in the center of the rooms and in the areas near the glazing. Five models of thermal comfort assessment were then applied to the results, in order to compare the comfort conditions between the two studied locations and to evaluate the applicability of these models to the areas close to glazed walls. It was observed there was clearly a greater variability of comfort conditions in the vicinity of the glazed walls when compared to the center of the rooms. The application of thermal comfort assessment models to the two studied rooms was able to reveal the differences between the two compared locations within each space. It was also possible to show the effect of incoming solar radiation and the influence of the geometry of the spaces and of the ratio between glazed area and floor area by comparing the results for both spaces. The assessment model proposed by LNEC (Portuguese National Laboratory of Civil Engineering) proved to be the most adapted to Portuguese users’ habits.