Vertical Enclosure Research Articles

Entropy generation analysis of MHD nanofluid in a corrugated vertical walls enclosure with a rectangular baffle using the Brinkmann-Forchheimer model

Entropy generation analysis of MHD nanofluid in a corrugated vertical walls enclosure with a rectangular baffle using the Brinkmann-Forchheimer model

Numerical simulation of natural convection in a rectangular enclosure filled with porous medium saturated with magnetic nanofluid using Buongiorno's two‐component model

AbstractMotivated by studying emerging nanofluid‐based magnetic fuel cells and hybrid direct absorber solar collectors, a numerical study is presented for buoyancy‐driven flow in a vertical enclosure containing a porous medium saturated with magnetized nanofluid flow under a transverse static magnetic field. The enclosure features adiabatic side walls and vertical heat slits, ensuring consistent cold temperatures on the lower and upper bounded walls. The side walls of the regime are insulated, and the hot slits are centrally located on these walls. The finite difference method (FDM) is applied to employ the transformed dimensionless vorticity–stream function (VSF) formulation of the transport equations. The impact of pertinent parameters on isotherm, streamline, iso‐concentration, and average Nusselt and Sherwood numbers are visualized with contour plots and graphs. Increasing Darcy number values tend to amplify the isotherm magnitudes. Higher Hartmann (magnetic) number values, on the other hand, lead to a reduction in local Nusselt number profiles but do not significantly modify the local Sherwood number. The porous medium permeability, as simulated via the Darcy number, has a strong impact on streamlines, thermal contours, and iso‐concentrations. A reduction in Darcy's number suppresses local Nusselt and Sherwood numbers, whereas an elevation in Rayleigh's number enhances them. Increasing the Buongiorno nanoscale Brownian motion parameter enhances local Nusselt and Sherwood numbers at both cold walls of the enclosure. The simulations provide a deeper insight into enclosure flows involving electrically conducting nanofluids in advanced processing systems for nanomaterials and hybrid fuel cells utilizing electromagnetic and liquid fuel technologies.

Sensitivity of an electrical impedance-based sensor for the liquid fraction estimation during melting and solidification inside a vertical rectangular enclosure

Monitoring the liquid fraction in latent thermal energy storages (LTESs) can enable the implementation of smart control strategies for improved performance and increased utilization of renewable energy sources. However, measuring the liquid fraction is challenging because solid-liquid phase change processes occur at nearly constant temperature. The present study explores an electrical impedance-based sensing technique that could become a non-intrusive and accurate alternative to determine the liquid fraction. The study examines the melting and solidification of a phase change material (PCM) inside a vertical rectangular enclosure with an isothermal wall. Two sets of electrodes are located on each of the side walls of the enclosure. Initially, numerical simulations of melting and solidification are performed to generate physically meaningful solid and liquid phase distributions. Then, these phase distributions are used as input for electrical simulations to estimate the response to changes in the liquid fraction of the electrical impedance between electrode pairs in in-line, front-facing and crosswise configurations. Also, the effect of the contrast ratios between the electrical conductivity of the solid and liquid phase on the sensitivity is assessed. The front-facing electrodes are found to have the best performance across a large range of conductivity ratios. The in-line electrodes perform the lowest because the sensitivity drastically decreases as a layer of the more conductive phase starts forming on the wall where the electrodes are located. An improvement in the performance of in-line electrodes is observed when the conductivity ratio is decreased.

Investigating double-diffusive natural convection in a sloped dual-layered homogenous porous-fluid square cavity

This article investigates natural convection with double-diffusive properties numerically in a vertical bi-layered square enclosure. The cavity has two parts: one part is an isotropic and homogeneous porous along the wall, and an adjacent part is an aqueous fluid. Adiabatic, impermeable horizontal walls and constant and uniform temperatures and concentrations on other walls are maintained. To solve the governing equations, the finite element method (FEM) employed and predicted results shows the impact of typical elements of convection on double diffusion, namely the porosity thickness, cavity rotation angle, and thermal conductivity ratio. Different Darcy and Rayleigh numbers effects on heat transfer conditions were investigated, and the Nusselt number in the border of two layers was obtained. The expected results, presented as temperature field (isothermal lines) and velocity behavior in X and Y directions, show the different effects of the aforementioned parameters on double diffusion convective heat transfer. Also results show that with the increase in the thickness of the porous layer, the Nusselt number decreases, but at a thickness higher than 0.8, we will see an increase in the Nusselt number. Increasing the thermal conductivity ratio in values less than one leads to a decrease in the average Nusselt number, and by increasing that parameter from 1 to 10, the Nusselt values increase. A higher rotational angle of the cavity reduces the thermosolutal convective heat transfer, and increasing the Rayleigh and Darcy numbers, increases Nusselt. These results confirm that the findings obtained from the Finite Element Method (FEM), which is the main idea of this research, are in good agreement with previous studies that have been done with other numerical methods.

Finite Element Analysis for Magneto-Convection Heat Transfer Performance in Vertical Wavy Surface Enclosure: Fin Size Impact

Finite Element Analysis for Magneto-Convection Heat Transfer Performance in Vertical Wavy Surface Enclosure: Fin Size Impact

Light-thermal environment of vertical translucent enclosure structures under solar radiation and method of internal shading adjustment

Building energy consumption accounts for about one-third of global energy consumption, primarily air-conditioning and lighting. The indoor light-thermal environment is closely related to building energy consumption, and internal shading is an effective adjustment method. To understand the method of adjusting indoor light-thermal environment and energy consumption by internal shading and its adjusting effect, this paper establishes the theory of indoor light-thermal environment as well as the simulation and analysis method. A process for analyzing the light-thermal environment of a room with internal shading was established by calculating and fitting the direct solar radiation, scattered radiation, and indoor daylight illuminance. Secondly, with the goal of building energy saving, the “Internal Shading Light-Thermal Ratio” evaluation method is proposed to evaluate the adjustment effect of curtains. The results of the study show that the building energy consumption saved in the room exhibits a sequentially increasing tendency when the surface reflectivity of the curtains is from 10 % to 100 %, respectively. Thin and thick curtains positively contribute to the light-thermal environment improvement by reducing the office's daylight illuminance by about 58.5 % and 90.8 %, respectively, and the indoor solar heat gain by about 42 % and 79.9 %. Meanwhile, the thin curtains had the best adjustment effect at 17:00. In contrast, the rooms with thick curtains had the best adjustment effect at 18:00. In addition, thin curtains meet the requirements for comfort in a light-thermal environment and are more energy-efficient than the room with thick curtains. Compared to the office without curtains, the building energy consumption of the office with thin curtains decreased by 538 Wh, while the office with thick curtains increased by 357 Wh.

Mixed convection of two layers with radiative electro-magnetohydrodynamics nanofluid flow in vertical enclosure

Mixed convection flow of two layers nanofluid in a vertical enclosure is studied. The channel consists of two regions. Region I is electrically conducting while Region II is electrically non-conducting. Region I is filled with base fluid water with copper oxides nanoparticles and Region II is filled with base fluid kerosene oil with iron oxides. The simultaneous effects of electro-magnetohydrodynamics and Grashof number are also taken into account. The governing flow problem consists of nonlinear coupled differential equations which is tackled using analytical technique. Analytical results have been obtained by the homotopy analysis method (HAM). The results for the leading parameters, such as the Hartmann numbers, Grashof numbers, ratio of viscosities, width ratio, volume fraction of nanoparticles, and the ratio of thermal conductivities for three different electric field scenarios under heat generation/absorption were examined. It is found that the effect of the negative electric load parameter assists the flow while the effect of the positive electric load parameter opposes the flow as compared to the case when the electric load parameter is zero. All outcomes for significant parameters on velocity and temperature are discussed graphically.

Experimental Analysis of Watertightness Performance of Interfaces between Masonry and Steel Structures Subjected to Accelerated Aging

Steel buildings often experience failure at the interfaces between their vertical exterior enclosure systems (VEESs) and structural elements. This phenomenon generates various pathological manifestations in steel buildings, resulting in the precocious decay of the structure and the diminishment of its service life. The treatment of these interfaces is essential for ensuring their proper performance and watertightness, and to protect the durability of the steel structure. This paper proposes a method for treating common interface joints between masonry and steel structures with the application of an EPDM (ethylene propylene diene monomer) elastomer membrane. The main goal of this building technique is to ensure the durability and watertightness of the interface’s joints when they are subjected to aging triggered by heat exposure and thermal shock. The experimental models tested consisted of a steel frame and a conventional masonry vertical enclosure system with ceramic blocks plastered with cement mortar. The models were subjected to ten cycles of heat exposure and thermal shock for the purpose of simulating accelerated aging, followed by a watertightness experiment that simulated the action of both rain and wind pressure. The interfaces between masonry and the steel structure proposed in this study allowed adequate differential movements between the parts, without damage to joints and masonry. Only small cracks were observed in the outer test region of all of the interfaces tested. In the regions of the joints treated with the EPDM membrane, no alterations were visible to the naked eye. During the cycles of the heat exposure and thermal shock test, the maximum relative horizontal displacements observed in the joints were 0.743 mm for vertical joints and 0.230 mm for horizontal joints, indicating the accurate reproduction of the behavior expected from an untied interface. The results obtained in the previously mentioned watertightness test showed that no humidity stains were found on the inner face of any of the specimens, even after the continuous application of a pneumatic pressure of 400 Pa for eight hours. Therefore, the results indicated satisfactory performance in terms of durability and watertightness in all evaluated cases, indicating that the application of an EPDM membrane can be effective in preventing water leaks in the interfaces between masonry and steel elements, thus contributing to ensuring the steel structure’s durability.

Behaviour, Furnishing and Vertical Space Use of Captive Callimico (Callimico goeldii): Implications for Welfare.

Provision of optimal captive care should be supported by species-specific evidence. Callimico (Callimico goeldii) is a small South American callitrichid primate. This study sought to address gaps in species-specific knowledge and captive management research by examining differences in callimico behaviour across multiple collections, investigating vertical enclosure use and a possible association between specific behaviours and vertical zones. Observational research was conducted at five European Association of Zoos and Aquaria (EAZA) organisations, in exhibits that were visually divided into four vertical zones. Instantaneous scan sampling was used to record behaviour and location of callimico over a six-day period at each collection, exceeding 160 observational hours. Significant differences were observed in foraging between collections and were much lower than the recommendations in Best Practice Guidelines, although near-wild levels were recorded in one enclosure. At an average height of 2 m, callimico utilized a similar vertical space across very different enclosures, regardless of overall available height, reflective of their natural ecology. The association between whole food items and increased foraging time, horizontal branches and locomotion and deep substrate and diversity of behaviours, offers further species-specific evidence of how the callimico use their captive environment. Our findings complement current EAZA guidelines to support species appropriate care for callimico and makes specific recommendations for further research.

CO2 storage in porous media unsteady thermosolutal natural convection -Application in deep saline aquifer reservoirs

In this paper, the storage of CO2 is investigated numerically under supercritical conditions in deep saline aquifer reservoirs. The simulations were performed on a non-deformable, saturated porous material inside a vertical enclosure that was assumed to be impermeable and insulated on three sides. The porous medium is homogeneous and isotropic with constant thermo-physical properties except for the fluid density, which varies according to Boussinesq approximations. A dynamic model assumes that flow is two-dimensional and obeys Darcy's motion law. The thermal equilibrium assumption (LTE) is also considered. The set of conservation equations and the appropriate initial and boundary conditions have been resolved numerically by the classical finite volume method. Spatio-temporal variations of different state variables such as pressure, velocity, temperature, and concentration were numerically simulated and plotted versus controlling parameters, particularly the thermal and solutal Rayleigh numbers, RaT and RaS; the Lewis number, Le; and the reservoir's aspect ratio, A. According to regulating factors, and physical and geological qualities, we could predict the behavior of CO2 that would be stored in a geologic reservoir that is thought to be porous media. We could also estimate the time and direction of CO2 mass transfer based on the abovementioned factors. Great attention was paid to examining the sensitivity of fluid flow, heat, and mass transfer rates according to the reservoir form and the operating conditions.

Daylighting performance assessment of traditional skywell dwellings: A case study in Fujian, China

China's rural revitalization strategy has aroused people's attention toward the preservation and renewal of traditional dwellings. Characterized by small courtyards and small top openings, traditional skywell dwellings in southern China are facing prominent daylight environment problems. However, only few studies have evaluated the visual comfort in skywell dwellings under daylight conditions using incomprehensive methods. To fill this gap, this paper systematically assessed the daylighting performance of skywell dwellings in Xingxian Village from 2D reference planes and 3D spatial interfaces. An accurate daylighting simulation model of skywell dwellings was established and validated with field measurements. ClimateStudio was used to analyze the performance metrics from the aspects of daylight quantity, daylight uniformity, and glare. Results identify insufficient daylight quantity indoors as the severest problem in skywell dwellings, which require artificial lighting throughout almost the entire daytime. Seasonal glare and inferior daylight uniformity were also observed in semi-outdoor areas. The effects of top, horizontal, and vertical spatial interfaces on the daylight environment were further investigated, and results highlight the influence of roof slope and opening setting on indoor lighting, the decay mechanism of daylight quantity on horizontal substrate interfaces, and the mismatch between daylight distribution and the positions of doors and windows on vertical enclosure interfaces. The changes in building orientation and seasons were also found to have limited effects on daylighting performance. These results can guide architects specializing in dwelling renovation, so as to improve the visual comfort of buildings and save up on living and energy costs due to artificial lighting.

Experimental and numerical evaluation of phase-change material performance in a vertical cylindrical capsule for thermal energy storage

• Laboratory study of melting in a vertical cylinder heated from the bottom/side. • Directly visualized experimental results of convective and close-contact melting. • Original in-house numerical model encompassing all basic physical phenomena. • Melting patterns in a vertical cylindrical enclosure under realistic conditions. • Conclusions relevant for latent heat thermal energy storage units design. Thermal energy storage (TES) is considered vital for the advancement of renewable energy solutions. Latent heat thermal energy storage (LHTES) captures the thermal energy via a solid-liquid phase transition that occurs in phase-change materials (PCM). The PCM is usually encapsulated in some way. In this study, we consider PCM melting in a vertical cylindrical enclosure, that is a prototype of a capsule used in a future storage system. Moreover, we achieve the highly desirable close-contact melting (CCM), which speeds up the charging process significantly. First, different types of experiments are conducted to elucidate the melting behavior in an original experimental device that allows different types of melting in such configuration, demonstrating the prominent role of close-contact melting. The device main features are transparency of the melting chamber, separate heating methods for the periphery and the bottom of the chamber, and axisymmetric melting. To further investigate the heat transfer modes in the system, an in-house numerical model for combined convective and close-contact melting in an axisymmetric cylindrical geometry is validated with the experimental results. Then, this original model is used to simulate a vertical cylindrical shell in a practical configuration, namely, when an enclosure is exposed to fluid flow normal to its bottom. The results clearly illustrate the importance of close-contact melting for the overall melting process under practical conditions. The conclusions from this work would aid the design of LHTES installations which involve macro-encapsulated PCM.

Experimental quantification of heat haze errors in stereo-DIC displacements: Application to thermoplastics thermoforming temperature range

Stereo digital image correlation (Stereo-DIC) is recurrent in photo-mechanics to measure kinematic fields which can be of high interest for instrumenting open-mould forming processes. Nevertheless, in the presence of pre-heating operations, as observed in the context of thermoforming processes, natural convective heat flows risk emerging and causing optical distortions in the recorded images. Consequently, this alters the precision of the measured full-fields of displacements. To address these challenges, this study proposes an experimental approach with two distinctive features. Firstly, it focuses on regenerating the heat haze effect at a laboratory scale within a partially opened vertical enclosure and without utilizing any filtering air flows. Secondly, the study quantifies the spatial and temporal variations of errors through statistical analyses of the differences between measurements obtained from quasi-static speckle translations and known imposed displacements. Experimental results indicate that the main cause of displacement errors is related to the 3D nature of the hot air turbulence caused by the natural convection phenomenon. This observation is supported by the detection of feather-shaped heat flows causing optical out-of-plane surface deviations. Furthermore, the study validates the possibility of obtaining time-dependent corrective functions for bias errors, which characterize the performance of the calibrated Stereo-DIC system in the presence of heat haze. Despite the limitation of extensive measurements required by the proposed approach, this study contributes to addressing the heat haze effect and constitutes a step towards extending the use of stereo-DIC for in-situ instrumentation of short-duration thermomechanical tests in the presence of heat haze.

Study of heat transfer and the nanofluid flow inside a rectangular enclosure with five rectangular baffles in the middle affected by a magnetic field

This article simulates free and forced convection (FCN) in a two-dimensional rectangular enclosure. In the center of the cage are five rectangular heat sources with high temperatures. The two side walls are insulated, and the top (moving) and bottom walls are maintained at a low temperature. In the presence of a magnetic field (MFD) along the length of the enclosure, which is saturated with copper/water nanofluid, the enclosure is affected. The study examines the impact of the Richardson number (Ri) ranging from 0.1 to 100 and Hartmann number (Ha) changing from 0 to 40 on average Nusselt number (NUA). Lattice Boltzmann method (LBM) and FORTRAN software are employed for numerical simulations. The results of this study demonstrate that an increment in the Ha enhances the Nusselt number (Nu) at the Ri of 0.1. At other Ri, enhancing the Ha reduces the NUA. The maximum NUA is 6.89 for the Ha of 40 and the Ri of 0.1. The enhancement in the Ri and the reduction of FCN strength reduce the NUA. The horizontal enclosure has the maximum Nu, which is equal to 3.10, and the vertical enclosure has the minimum NUA.

COMPARATIVE NUMERICAL STUDY OF NATURAL CONVECTION IN SQUARE AND TRIANGULAR CAVITY

This paper is based on the numerical investigation of natural convection of two vertical enclosure of square and triangular cavity with air filled. The vertical cavity consist of adiabatic and hot and cold wall with wide range of Rayleigh number from 103 to 106 with aspect ratio from 1 to 10 at the interval of 2.5. Flow patterns and isotherm plots were used to display the results, and for every case, local and mean Nusselt values were also produced. The results show that an increase in Rayleigh numbers greatly increases heat transfer, natural convection intensity, and average Nusselt number at a particular aspect ratio. Keyword: ANN (average Nusselt number), AR (aspect ratio), LNN (local Nusselt number), Nu (Nusselt number), Pr (Prandtl number), Ra (Rayleigh number).

Natural convection flow on a bent wavy vertical enclosure filled with power-law nanofluid simulated by Element Free Galerkin method

The present paper contains a study of heat transfer and flow of a power-law nanofluid in bent vertical wavy walls enclosure. The system of governing equations has been solved by mesh free method (EFGM) with a parallel scheme. The results are found in terms of heat transfer rate at the hot wall, isotherms and streamlines under the influence of Aspect ratio, Rayleigh number, Prandtl number, power-law index and wave amplitude. It is observed that the average Nusselt number improves with enhancing the Prandtl number, Rayleigh number and aspect ratio but it decrements with enhancing the power-law index and surface waviness. A parallel implementation scheme gives better efficiency as compared to the sequential scheme. Such problems have direct application in electronic devices, food processing industries, and biomedical applications.

Coupled energy and mass transport for non-Newtonian nanofluid flow through non-parallel vertical enclosure

Several phenomena that occur in nature and engineering are expressed mathematically in large part by nonlinear differential equations. Therefore, heat and mass transport for buoyancy driven nanofluid flow through converging/diverging channel are modelled using non-Newtonian constitutive model in form of non-linear differential equations. It is worth mentioning that such models are frequently involved in blood flow through arteries and flow through nozzles, etc. Utilizing non-dimensionless transformations, leading partial differential equations are converted to a system of nonlinear ordinary differential equations. The Runge-Kutta Fehlberg algorithm with shooting technique is exercised to tackle reduced system numerically. The computed results for dimensionless velocity, temperature, nanoparticle concentration, skin-friction coefficient, local Nusselt and Sherwood numbers are presented for both buoyancy-assisting and opposing flow. Detailed analysis revealed that temperature field is higher at opening of flow in converging channel. Furthermore, with growing buoyancy force, the skin friction coefficient decreaseswhile local Nusselt number increases.

Investigations on effect of arrangement of fins on melting performance of vertical PCM enclosure (3D simulation using FVM methods)

Present investigation, effect of different forms of rectangular fins on melting performance of a vertical enclosure filled by with phase change material (PCM) was examined. Three individual fins were used instead of unit fin. The heat transfer surface was kept constant. The effect of location of fins as well as effect of length of fins and the distance of fins were considered as variant parameters. Firstly, placement of fins at lower half and upper half was examined. Secondly, effect of length of fins were examined. Finally, effect of vertical distance of fins was evaluated. Results presented that optimum melting efficiency was achieved when two of the three fins were placed in lower half. Through first step, case one, provided best performance which presented up to 23 percent improvement in overall melting time. At second step, case 10 had best performance and provided 30% improvement in melting time. Finally, at third step, case 13 had best melting performance. In this case, two of fins were positioned on lower half. lower and upper fins had the length of 40.5 and 10 mm. It is noteworthy that case 13 provided up 39% saved time for melting process in comparison with base case.

Sensitivity analysis of design parameters for melting process of lauric acid in the vertically and horizontally oriented rectangular thermal storage units

Widespread commercialization of PCM-based latent heat storage systems is limited by the low melting and solidification rates during the phase transition process. In this study, fins are used to enhance the phase change process. A parametric study is conducted to understand the effect of fins on the thermal performance of vertically- and horizontally-oriented rectangular storage tanks. Throughout simulations, the fin volume, and thereby the mass of PCM in the tank, were kept constant. It was observed that the horizontal enclosures can take advantage of the development of strong natural convection flow until near the end of the melting process, whereas with vertical counterparts the strength of the convection currents was diminished during the shrinkage stage. The results suggest that longer and thinner fins are more beneficial for enhancing the melting rate than shorter and thicker fins. It was concluded that for horizontal enclosures with fin lengths of 25 and 35 mm, increasing the number of fins does not necessarily shorten the melting time. The maximum melting time reduction compared to the 3-fin vertical enclosure with a fin length of 25 mm (chosen as our benchmark case) was 75.1% when nine 45-mm-long fins are used in a horizontal enclosure.

Investigation on effect of connection angle of “L” shaped fin on charging and discharging process of PCM in vertical enclosure

This study probes the effect of connection angle of “L” shaped fin on the melting and discharge process of a vertical PCM unit. The PCM enclosure had dimensions of 50 ×50 mm and the L shaped fin was located at middle of enclosure. The enclosure was heated and cooled by considering constant temperature at the vertical wall. The Lauric acid was considered as the phase change material. Seven different coincidence angles of 0°, 30 °, 60 °, 90 °, −30 °, −60 ° and −90 ° were considered in present investigation. Results indicated that L shaped fin with Teta = −30 ° could provide 14% reduction in the melting process. Furthermore, the case with Teta = 0° provided 45% enhancement in solidification time. The outcomes revealed that maximum charging rate was associated with case with Teta = −30 ° which had the value of 103.41 J/S and provided a 32% enhancement in comparison with the base case. Also, the best discharge rate for the solidification process was about 34.184 J/s which was related to case with Teta = 0° and presented a 2.23 times improvement in the average solidification rate.