Walls Of Enclosure Research Articles

Stereoscopic PIV measurements of near-wall flow in a tightly packed rod bundle with wire spacers

In this study, we experimentally investigated the flow field characteristics in the complex geometry of a tightly packed 61-rod bundle with wire spacers by employing matched-index-of-refraction (MIR) and stereoscopic particle image velocimetry (SPIV) techniques. SPIV measurements were performed on a cross-flow plane at Reynolds numbers of 500, 2500, and 6300, and the measurement area covered the interior and edge sub-channels that were located near the enclosure wall. The SPIV results showed that peaks of the velocity magnitude occurred in the edge sub-channel, indicating the wall effects on the flow symmetry in the cross-flow plane. Mean velocities at the central areas of the edge and interior sub-channels showed flat profiles for Re=500 and local peaks around 0.15<y/Drod<0.3, due to the wire’s presence and near-wall location of the edge sub-channel. The rms fluctuating profiles velocities showed that local maximal peaks linearly shifted from y/Drod=-0.44 to −0.36 and −0.28 as Re increased. Taylor’s hypothesis was applied to the SPIV velocity vector fields for reconstructing quasi-instantaneous three-dimensional (3D) vortical structures in the wire-wrapped rod bundle. The visualization of 3D vorticity iso-surfaces showed that vortical structures were generated from shear layers of neighboring rods and traveled in the streamwise direction. Finally, proper orthogonal decomposition (POD) analysis was applied to SPIV velocity snapshots taken at the edge and interior sub-channels to extract the most statistically dominant flow structures. The POD velocity decomposition revealed coherent structures with sizes and shapes comparable to instantaneous vortical structures identified by iso-surfaces. Energy fractions of the first POD modes were found to reduce from 46% and 31% to 26% and 18% when Reynolds numbers increased from Re=500 to 6300, respectively. On the other hand, kinetic energy levels of low-order POD modes (modes 2, 3, 4, etc.) increased when the Reynolds number increased.

Energy saving opportunities in the refrigerated transport sector through Phase Change Materials (PCMs) application

Transportation of food products at controlled temperature is a critical task in the transport sector. In fact, whilst there is a need of ensuring both food quality and safety to the global population, its impact in terms of energy consumption and related CO2 emissions into the atmosphere is becoming increasingly evident. In this regard, Thermal Energy Storage (TES) using Phase Change Materials (PCMs) can be considered as a potential way of reducing the cooling load, energy consumption and related greenhouse gas emissions in refrigerated transport sector. In this paper two different PCM applications are investigated. Specifically, in the first study a PCM (35 °C melting temperature) layer was added to the external side of a refrigerated enclosure wall with the aim of managing the cooling peak (shifting and reducing) and reducing the daily energy rate. Outdoor experimental results showed that the added PCM layer helps to reduce (between 5.55% and 8.57%) and delay (between 4.30 h and 3.30 h) the peak load of incoming heat compared to the reference one. In the second study, the energy performance of a refrigerated chamber with an air heat exchanger containing PCM (5°C melting temperature) was investigated. The study purpose was to reduce the cooling energy consumption during steady state operating conditions and the rate of temperature increase throughout the course of a power failure event. Test results showed that using a PCM air heat exchanger addition, up to 16% of energy can be saved.

Free Convection in a Porous Square Enclosure with Localized Sinusoidally Varying Temperature Profile on the Bottom Wall

This current study focuses on the simulation of free convection in square cavity filled with a porous medium considered homogenous, isotropic and saturated by a Newtonian fluid obeying the law of Darcy and the hypothesis of Boussinesq. The lower horizontal wall of the enclosure is subjected to a localized temperature varying sinusoidally with the space while the upper horizontal wall and rest of the bottom walls are insulated. The vertical walls are kept cold isotherm. In order to generalize the results, all governing equations are put into dimensionless form, discretized by the Finite Difference Method and solved by the relaxed Gauss Seidel (SUR) Algorithm. A code has been proposed in FORTRAN 95, in order to solve numerically the equations of the problem. The study parameters are the Rayleigh-Darcy number (Ra) and the amplitude (Ar) of the hot wall temperature. The effects of the Rayleigh-Darcy number, amplitude and length of source heating on the dynamic and thermal fields are investigated. On the other hand, the effects of the amplitude on the horizontal velocity distribution and the mean horizontal temperature distribution(y=0.5) were presented and discussed. It emerges from this study that the increasing of the amplitude and Rayleigh-Darcy number intensify the flow and the global heat transfer in our physical domain.

Cylindrical heat conduction models for enclosed thermophones

The efficiency of enclosed thermophones is governed by the time-dependent heat transport between the heating element and the enclosure gas. Efficiency gains have been made by reducing the heat capacitance of the heating elements so that a maximum amount of energy is available for transport. However, efficiency is still limited when there is poor conduction into and out of the enclosure gas. An analytical model for the conduction in an enclosed thermophone with a heating element composed of a regularly spaced linear array of conducting fibers will be presented. The model considers interaction between the individual fibers and treats the enclosure wall as a heat sink. The conduction model will be incorporated into a device model which can calculate steady-state acoustic output. The results are compared against experimental data. In addition, the device model can be used to explore the optimal fiber spacing for enclosed thermophones with regularly spaced linear array heating elements. [Work funded by the Naval Research Laboratory.]

Dating Prehistoric Fortified Coastal Sites in the Balearic Islands

AbstractA special type of coastal settlement, promontory forts defended by inland-facing walls, appeared in the Balearic Islands in an imprecise time during the Bronze Age. A research project was initiated in 2011 to study one of these sites on each of the two major islands of the archipelago. The first one, Es Coll de Cala Morell (north Menorca), is a walled promontory with a relatively large plateau, with 13 horseshoe-shaped houses (navetes). The second, Sa Ferradura (east Mallorca), is a smaller coastal cape, with a different spatial planning, with only two large built-up areas, both attached to the enclosure wall. Two of the navetes have been excavated at Es Coll de Cala Morell, showing a domestic space with a central hearth in both cases. The occupation has been dated to around 1600–1200 cal BC. At Sa Ferradura seven hearths have been recorded in a large, open-air area. Their chronology falls within the interval of approximately 1200/1100–900 cal BC. From a chronological point of view, fortified settlements in coastal promontories are not, as was expected, a unitary phenomenon in Menorca and Mallorca and have to be related to different cultural periods.

Natural convection in a cold enclosure with four hot inner cylinders in a diamond array (Part-II: Effect of unequal horizontal and vertical distances of inner cylinders)

Two-dimensional numerical simulations were conducted to investigate the natural convection in an enclosure with four cylinders in a diamond array. The convection phenomena induced by the temperature difference between the hot surfaces of the cylinders and enclosure walls were investigated using different Rayleigh numbers (103≤Ra≤106) and distances between neighboring cylinders (0.3≤ε≤0.7). The immersed boundary method (IBM) was used to capture the virtual boundary of the cylinders. Detailed analysis results were obtained using a visualization technique, including the distribution of streamlines and isotherms. The heat transfer characteristics were also investigated with regard to the primary frequency and transition of the flow regime from steady state to unsteady state at a relatively high Rayleigh number of Ra=106.

Numerical Modeling of Natural Convection Heat Transfer in a Wavy Wall Enclosure Filled by a Cu-water Nanofluid with a Square Cooler

Numerical Modeling of Natural Convection Heat Transfer in a Wavy Wall Enclosure Filled by a Cu-water Nanofluid with a Square Cooler

PIV measurements of turbulent flows in a 61-pin wire-wrapped hexagonal fuel bundle

The current work experimentally investigates the flow characteristics in the near-wall region of the 61-pin wire-wrapped hexagon fuel bundle via the matched-index-of-refraction technique. Particle image velocimetry (PIV) measurements were taken in the region near the surfaces of the pins, wires and enclosure wall at the Reynolds number of 19,000. From the obtained PIV velocity vector fields, flow statistics such as mean velocity and root-mean-square fluctuating velocity profiles were computed. In addition, spatial-temporal cross-correlations of velocity-velocity and pressure-velocity were analyzed. A strong correlation between the wall fluctuating pressure signal and flow structures was observed. Finally, we applied the POD analysis to the vorticity snapshots obtained in the near-wall region to reveal the dominant flow structures. It was found that the large-scale structures were elongated and aligned with the mean flow direction.

New natural convection heat transfer correlations in enclosures for building performance simulation

ABSTRACTThis paper presents new correlations to calculate natural convection heat transfer coefficients (CHTC) in enclosures for building performance simulation. Current work related to the development of correlations is not oriented to building enclosures, and the influence of high numbers of Rayleigh (Ra) and aspect ratio on the CHTC has not been studied in detail. In this work, two new correlations have been developed for a vertical wall, one in laminar regime (Ra < 107) and another one in turbulent regime (107<Ra<1011). Moreover, two new correlations have been developed for floor and ceiling, one in laminar regime (Ra < 106) and another one in turbulent regime (Ra > 106). All correlations have been developed as function of the aspect ratio (H/L) and Ra numbers calculated from the enclosure average air temperature and wall surface temperature. By contrast, in previous works the Ra numbers have been calculated from the temperature difference of opposite walls. Computer Fluid Dynamics (CFD) simulations for different aspect ratios (H/L = 0.5–1–2) and Ra numbers (103–1011) have been carried out in order to obtain these correlations. The SIMPLE algorithm has been used for the solution of the Navier–Stokes equations and the realizable turbulence k- model with an enhanced wall-function treatment has been used. The correlations developed follow the expected trend for the low number of Ra in comparison with the expressions developed by other authors. For a high number of Ra, our correlations improve the previous correlations, because it is a function of the aspect ratio of the enclosure and the average air temperature of the enclosure. This approach is simple to implement in the construction of thermal simulation programs with low computational cost.

MHD natural convective Ag-water nanofluid flow in an enclosure having internal heat generation with centre heater and bottom heat source

Numerical study on MHD natural convection inside enclosure filled with Ag-water with centre heater is conducted. The vertical walls of enclosure are maintained at temperature Tc whereas its top wall is insulated and bottom wall is considered with constant heat source. The governing equations are solved numerically by finite volume method and SIMPLE algorithm. The effects of heater length, Rayleigh number, Hartmann number and heat generation parameter are investigated. Results are presented with streamlines, isotherms, variation of average Nusselt number and mid height velocity profile. It is found that high heat transfer is obtained for the vertical heater and Hartmann number is a good control parameter for suppressing heat transfer. Moreover, the fluid flow, thermal fields and rate of heat transfer are strongly depending on heater length and heat generation parameter. Also, increasing solid volume fraction of nanoparticles cause better enhancement of heat transfer inside enclosure.

Natural convection over circular cylinders in a porous enclosure filled with a nanofluid under thermo-diffusion effects

Abstract In this study, we solved numerically the double-diffusive natural convection over circular cylinders in a non-Darcy porous enclosure filled with nanofluids using a simple algorithm in a finite volume method. Here, the inner circular cylinders are maintained at a hot temperature Th, and concentration Ch. The enclosure vertical side walls are maintained at a cool temperature Tc, and concentration Cc, and the horizontal walls are assumed to be adiabatic. The nanofluids on the outer enclosure walls and inner cylinders are passively controlled. We investigated the effects of the circular cylinders locations and sizes on the heat and mass transfer and fluid flow. The effects of Rayleigh number, Darcy parameter, Soret number with modified Dufour number and nanoparticles parameters in heat and mass transfer and fluid flow have been studied with graphical illustrations. It is found that, the size and formation of cells inside the enclosure strongly depend on the Rayleigh number with Darcy parameter, and sizes and locations of the inner circular cylinders. The current numerical results are well validated with a reasonable agreement.

Mixed convection in a partially heated triangular cavity filled with nanofluid having a partially flexible wall and internal heat generation

Abstract Numerical study of mixed convection in a partially heated nanofluid-filled lid driven cavity with internal heat generation and having a partial flexible wall was performed. The bottom wall of the triangular enclosure is moving with constant speed and left vertical wall is partially heated. The inclined wall of the cavity is cooled and partially flexible. The governing equations are solved with Galerkin weighted residual finite element method. The effects of Richardson number (between 0.05 and 50), internal Rayleigh number (between 10 4 and 10 8 ), size and elastic modulus of the partial flexible wall and nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer were numerically investigated. It was observed that the local and averaged heat transfer reduce as the value of the Richardson number and internal Rayleigh number increase. As the value of the elastic modulus of the inclined wall and nanoparticle volume fraction increase, local and average heat transfer enhance. The discrepancy between the averaged Nusselt number increase for different sizes for the lower values of elastic modulus of the flexible wall. When heat transfer process is effective adding nanoparticles to the base fluid is advantageous.

Surface-Current Measurements as Data for Electromagnetic Imaging Within Metallic Enclosures

A 3-D microwave imaging method within metallic enclosures is investigated and improved. This method uses the components of the surface-current vector at receiver points on the enclosure wall as data. At the metallic wall, the normal component of the magnetic field as well as the tangential components of the electric field is negligible, whereas the vectorial surface current, which is directly related to the tangential components of the magnetic field, is dominant. After presenting the results of a numerical investigation based on synthetic data, the method is validated using an experimental system comprised of 24 co-resident shielded, coaxial half-loop antennas, distributed in four layers, within a cylindrical metallic enclosure. These antennas are used in receiver–transmitter pairs to introduce an electromagnetic field into the chamber and collect the magnetic field at the receiver points. The measured data are used as input to a multiplicatively regularized finite-element contrast source inversion algorithm. Due to their relatively small size and minimal protrusion into the chamber, these antennas minimally perturb the field distribution inside the chamber and thereby allow the use of a simple numerical inversion model, which does not need to account for the passive antennas. These attributes are especially useful for large computationally intensive industrial applications. The experimental system described herein is a laboratory-scale prototype for a stored-grain imaging application where metallic silos are utilized.

Acoustic modeling of a three-dimensional rectangular opened enclosure coupled with a semi-infinite exterior field at the baffled opening.

A modeling method is proposed for the acoustic analysis of a three-dimensional (3D) rectangular opened enclosure coupled with a semi-infinite exterior field by a rectangular opening of arbitrary size, and with general wall impedance. In contrast to existing modeling methods that solve the differential equations, the energy principle in combination with a 3D modified Fourier cosine series is employed in the present method for the modeling of this system. Under this theoretical framework, the effect of an opening in the wall of a rectangular enclosure is taken into account via the work done by the sound pressure acting on the opening between the finite enclosure and exterior domain. The sound pressure inside the opened enclosure is expressed as the combination of a 3D trigonometric cosine series and one supplementary 2D expansion introduced to ensure uniform convergence of the solution over the entire solution domain including opening boundary. The acoustic responses of the opened enclosure are obtained based on the energy expressions for the enclosure system. The effectiveness and reliability of the current method are checked against the results obtained by the boundary element method and experimental results, and excellent agreement is achieved. The effects of sizes and positions of the opening and wall impedance on the acoustic behaviors of opened enclosure system are investigated.

Natural convection heat transfer in an inclined square enclosure filled with a porous medium saturated by nanofluid using Buongiorno’s mathematical model

This paper presents numerical study of nanofluid free convection in a porous enclosure. Two vertical walls are maintained at constant but different temperatures. (Th>Tc), while the remaining walls are insulated Two-phase Buongiorno nanofluid model is employed in this work considering Brownian diffusion and thermophoresis effects. Governing equations are solved using a Simple-based finite volume method. Two different nanofluids are considered in this study, i.e. Al2O3/water and Cu/water. Numerical simulations are conducted for different porous Rayleigh numbers (Rap=102, 103 and 104), porosities (ɛ=0.5, 0.7 and 0.9), particle volume fractions (0⩽φAve⩽0.04) and inclination angle of enclosure ranging from 0° to 60°. Numerical results indicate that porosity plays an important role on the heat transfer rate especially at high porous Rayleigh numbers. Compared to Al2O3, Cu nanoparticles show more uniform distribution inside the enclosure. Numerical results demonstrate that there is mass boundary layer adjacent to enclosure walls and its thickness decreases by reducing porosity or increasing porous Rayleigh number.

Lattice Boltzmann Pore Scale Simulation of Natural Convection in a Differentially Heated Enclosure Filled with a Detached or Attached Bidisperse Porous Medium

In this research, pore scale simulation of natural convection in a differentially heated enclosure filled with a conducting bidisperse porous medium is investigated using the thermal lattice Boltzmann method. For the first time, the effect of connection of the bidisperse porous medium to the enclosure walls is studied by considering the attached geometry in addition to the detached one. Effect of most relevant parameters on the streamlines and isotherms as well as hot wall average Nusselt number is studied for two of the bidisperse porous medium configurations. It is observed that effect of geometrical and thermo-physical parameters of the bidisperse porous medium on the heat transfer characteristics is more complicated for the attached configuration. To assess the validity of the local thermal equilibrium condition in the micro-porous media, the pore scale results are used to compute the percentage of the local thermal non-equilibrium for two of the bidisperse porous medium configurations. It is concluded that for the detached configuration, the local thermal equilibrium condition is confirmed in the entire micro-porous media for the ranges of the parameters studied here. However, for the attached geometry, it is shown that departure from the local thermal equilibrium condition is observed for the higher values of the Rayleigh number, micro-porous porosity, solid–fluid thermal conductivity ratio, and the smaller values of the macro-pores volume fraction.

Energy and life cost analysis of a wet wall solar still with various pump working conditions

In this study, a basin type solar still is investigated whose enclosure walls are soaked with a periodic injection. The equipment was tested under the climatic conditions in Semnan, Iran. Two enclosures were manufactured for this purpose. One of them enjoyed a pump to soak the enclosure walls, while the other one was a conventional system with no such pump. In active chamber, effects of pump's working and off durations were investigated before being compared with those of a passive one. The results showed that the efficiency could be enhanced 7% and the rate of output fresh water could be increased ∼75% with the wet walls. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 532–538, 2017

Detecting Slope and Urban Potential Unstable Areas by Means of Multi-Platform Remote Sensing Techniques: The Volterra (Italy) Case Study

Volterra (Central Italy) is a town of great historical interest, due to its vast and well-preserved cultural heritage, including a 2.6 km long Etruscan-medieval wall enclosure representing one of the most important elements. Volterra is located on a clayey hilltop prone to landsliding, soil erosion, therefore the town is subject to structural deterioration. During 2014, two impressive collapses occurred on the wall enclosure in the southwestern urban sector. Following these events, a monitoring campaign was carried out by means of remote sensing techniques, such as space-borne (PS-InSAR) and ground-based (GB-InSAR) radar interferometry, in order to analyze the displacements occurring both in the urban area and the surrounding slopes, and therefore to detect possible critical sectors with respect to instability phenomena. Infrared thermography (IRT) was also applied with the aim of detecting possible criticalities on the wall-enclosure, with special regards to moisture and seepage areas. PS-InSAR data allowed a stability back-monitoring on the area, revealing 19 active clusters displaying ground velocity higher than 10 mm/year in the period 2011–2015. The GB-InSAR system detected an acceleration up to 1.7 mm/h in near-real time as the March 2014 failure precursor. The IRT technique, employed on a double survey campaign, in both dry and rainy conditions, permitted to acquire 65 thermograms covering 23 sectors of the town wall, highlighting four thermal anomalies. The outcomes of this work demonstrate the usefulness of different remote sensing technologies for deriving information in risk prevention and management, and the importance of choosing the appropriate technology depending on the target, time sampling and investigation scale. In this paper, the use of a multi-platform remote sensing system permitted technical support of the local authorities and conservators, providing a comprehensive overview of the Volterra site, its cultural heritage and landscape, both in near-real time and back-analysis and at different scales of investigation.

Numerical simulation of three-dimensional natural convection in a cubic enclosure induced by an isothermally-heated circular cylinder at different inclinations

This study numerically examines three-dimensional natural convection of air induced by temperature difference between a cold outer cubic enclosure and a hot inner cylinder. Simulations have been carried out for Rayleigh numbers ranging from 103 to 107 and a titled angle of the enclosure varying from 0° to 90°. The developed mathematical model is governed by the coupled equations of continuity, momentum and energy and is solved by finite volume method. The effects of cylinder inclination and Rayleigh number on fluid flow and heat transfer are presented. The distribution of isocontours of temperature, components of velocity and streamtraces eventually reaches a steady state for Rayleigh numbers ranging from 103 to 107 for titled inclination of 90°. However, for the remaining inclinations, Rayleigh numbers must be in the range 103–106 to avoid unsteady state which is manifested by the subdivision of the area, containing the maximum local heat transfer rate, into three parts for a Rayleigh number equal to 107 and an inclination of 90°. We mention that instability study is not included in the present paper which is solely devoted to three dimensional calculations. Results indicate also that optimal average heat transfer rate is obtained for Rayleigh number set to 106 and an inclination of 90° for both cases of the inner cylinder and lateral walls of cubical enclosure.

Energy Remediation Combining Insulation Materials Based on Calcium Silicate and Expanded Polymers

Energy rehabilitation of buildings using airtight insulating materials based on expanded polystyrene is often accompanied by the formation of moisture problems in the enclosure wall footing. Moisture progress in the rehabilitated structure is simulated using modern moisture transient models in Delphin software. Combinations of the developed plate thermal insulating materials based on calcium silicate and the conventional thermal insulation panels based on expanded polymer have been designed to address the moisture problems. This article describes the function of this solution during the reconstruction of a house built from full clay bricks with malfunctioning waterproofing in the lower house construction.