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Combined heat and moisture transportation in an enclosure has been numerically investigated, which could benefit the sustainable building energy conservations and electronic cooling designs. An adiabatic and impermeable partition of finite thickness is considered, placed in the enclosure following an ordered arrangement. Effects of length and location of the partition, buoyancy ratio and thermal Rayleigh number on convective heat and moisture transfer rates in the enclosure are discussed. Firstly, this situation of the partition placed in the horizontal wall is studied, where inhibition effect of partition is observed. It is seen that the location of partition put relatively weaker influences on the heat and mass transfer in the regime of thermal-driven flow, when its length exceeds the critical value. Additionally, inhibition effect is more pronounced as the partition is fixed in center of vertical wall. Furthermore, local heat and mass transfer rates could be suppressed when the buoyancy ratio becomes negative. Finally, thermal Rayleigh number greatly affects the transport structures of fluid, heat and moisture, whatever aiding flow or opposing flow situations. Heat and mass transfer potentials could be promoted with increasing thermal Rayleigh numbers. Present work could be adopted to optimize the enclosure flows simultaneously with heat and moisture transport. [ABSTRACT FROM AUTHOR]

A comprehensive investigation and review about the free vent boundary conditions are conducted regarding of natural convections inside an open cavity with one side horizontal opening, aiming to abandon the extended computational domain through imposing suitable pressure and momentum boundary conditions on the free ventilated ports. The main differences among Type A , Type C and Type D BCs are the definitions and assumptions on the free port boundary pressures. The physical governing equations for the present investigation are solved numerically for a wide range of thermal Rayleigh number and enclosure aspect ratio to identify the applicability of the four categories of free port boundary conditions. The simulation results show that, with the flow intensity increasing in the region near free opening, Type D BCs , Type C BCs and Type A BCs would take turns being the most effective and suitable BCs to achieve the flow solutions approaching to the reference ones. Regarding of the computational stability, authors-proposed free vent port boundary conditions ( Type D BCs ) achieve the best performance. In addition, it is found that enclosure ventilation rate is a more suitable and convincing criterion than heat transfer rate to validate the accuracy of the numerical methods. [ABSTRACT FROM AUTHOR]

Thermal buoyancy-driven natural convection in partial enclosures with multiple free openings is investigated regarding the coupling of the pressure correction algorithm with inner-loop iterations of the pressure correction equation. Unexpected steady flow phenomena, i.e., nonunique steady flow states, are observed when different inner-loop iterations m and relaxation factorsαof the pressure correction equation are implemented, after the appropriate assumptions on the free opening boundary conditions are made. Numerical experiments and benchmark exercises confirm that definitions on the free openings could be too weak to ensure global similarity to the results of extended domain methodology. Furthermore, inner-loop iteration m and relaxation factorαcould have similar effects on the nonunique steady flow results. As thermal Rayleigh number is relatively low, a linear relationship could be established among inner-loop iteration m, relaxation factorα, and mass exchange rate,MER. In addition, harmonic arrangements on the iteration residuals of the momentum equation and the pressure correction equation could accelerate convergence of the whole pressure correction algorithm. [ABSTRACT FROM AUTHOR]

Abstract: Combined natural convective heat and moisture transports in a moist-air-filled enclosure with four free vent ports are numerically investigated. Four situations of ambient air states, hot and humid (I), hot and arid (II), cold and arid (III), and cold and humid (IV), are taken into consideration. Convective transports of semi-enclosed air, heat and moisture are respectively analyzed using the contours of streamfunction, heatfunction and massfunction, in addition to the isotherms and iso-concentrations. Overall convective heat transfer rate (Nu) and moisture transfer rate (Sh) of the internal concentrated heat and moisture source have been correlated with the thermal Rayleigh number respectively within the domain of the heat transfer driven flows and that of moisture transfer driven flows. When different initial convective flow conditions were imposed in the cases (I) and (IV), dual steady flow states of semi-enclosed heat and moisture convection are observed, and heat and moisture transport potentials can be enhanced or inhibited depending on the flow solution branches. These results can be adopted to guide the design of natural ventilation in the humid regions. [Copyright &y& Elsevier]

Abstract: Simultaneous transport of heat and moisture by conjugate natural convection in a partial enclosure with a solid wall is investigated numerically. Moist air motions are driven by the external temperature and concentration differences imposed across enclosures with different ambient moisture conditions. The Prandtl number and Schmidt number used are 0.7 and 0.6, respectively. The fluid, heat and moisture transports through the cavity and solid wall are, respectively, analyzed using the streamlines, heatlines and masslines, and the heat and mass transfer potentials are also explained by the variations of overall Nusselt and Sherwood numbers. The numerical simulations presented here span a wide range of the main parameters (heat and mass diffusion coefficient ratios, solid wall thickness and thermal Rayleigh numbers) in the domain of aiding and opposing buoyancy-driven flows. It is shown that the heat transfer potential, mass transfer potential, and volume flow rate can be promoted or inhibited, depending strongly on the wall materials and size, thermal and moisture Rayleigh numbers. [Copyright &y& Elsevier]

Abstract: A numerical implementation of estimating boundary heat fluxes in enclosures is proposed in the present work. Particularly, the flow field is dynamically coupled with the heat convection in the fluid and the heat conduction in the solid domain. An iterative conjugate gradient method is applied such that the gradient of the cost function is introduced when the appropriate sensitivity and adjoint problems are defined. In this approach, no a priori information is needed about the unknown function to be determined. Numerical solutions are obtained for the case of a square enclosure centrally-inserted with a solid block and subjected to an unknown heat flux on one side and to known conditions on the remaining sides. Fluid and heat transports are visualized by the streamlines and heatlines respectively, which are evidently affected by the thermal Rayleigh number, solid body size and thermal conductivity of solid phase, and the functional form of the imposed heat flux. The accuracy of the heat flux profile estimations is shown to depend strongly on the thermal Rayleigh number, body size and relative thermal conductivity of the solid material. Effects of functional form of the unknowns, sensors number and position, and measurement errors on the accuracy of estimation are also investigated. The present work is significant for the flow control simultaneously involving the heat conduction and convection. [Copyright &y& Elsevier]

For energy efficient ventilation and low carbon design, solar chimney has been extensively applied on buildings. In the present work, three representative solar chimneys were introduced, i.e., Model 1 with top-horizontal outlet, Model 2 with upper-vertical outlet and Model 3 with middle-vertical outlet. Updraft ventilation from the built enclosure to the outlet and heat transfer from the absorber to the fluid by heat convection were numerically and theoretically investigated, and their limitations and correlations with governing parameters were also discussed. Streamlines and heatlines were used to visualize transport paths of air and heat respectively. Reverse flow could not be observed in the solar chimney channels of Model 2 and Model 3; Therefore, total volume flow rate induced by the solar chimneys Model 2 and Model 3 and convection heat transfer rate of the absorber increases positively with thermal Rayleigh numbers (Ra). Model 2 chimney produces greater thermal buoyancy than that by Model 3, and its air flow rate is higher than that of Model 3. Generally, volume flow rate induced in Model 1 is higher than those of Model 2 and Model 3 as Ra is no more than 2.5 × 106, and simultaneously, convection heat transfer rate Nusselt number (Nu) is also greater than those of Model 2 and Model 3. When Ra exceeded 2.5 × 106, reverse air flow was intensified further, Nu of Model 1 started to decline. The three models with discrete heat sources could induce more air from indoor than that respective model without discrete heat sources. The maximum increment rate is obtained by the Model 1 solar chimney with discrete heat sources, then Model 2 and the least done by Model 3. Their power relationships between Nu and Ra , V*and Ra are regressed respectively. The dependence of volume flow rate on broad thermal Rayleigh numbers covering all the three flow regimes showed that there were linear correlations between discrete numerical volume flow rates and the scaling predictions, except in Model 1 for high Ra (exceeding critical value 9.0 × 105), where volume flow rate was remarkably reduced due to reverse air flow. This research could provide useful theoretical information for applying small sized vertical solar chimneys attached to the building sidewall to effectively reduce built energy consumption. [ABSTRACT FROM AUTHOR]

Present work numerically and theoretically investigates the fluid flow and heat transfer in an inclined solar chimney induced by thermal buoyancy within a range of thermal Rayleigh numbers (Ra) and chimney inclination angles (α). Transport paths of fluid and heat were visualized by streamlines and heatlines, respectively. Backflow could be observed in the solar chimney when Ra increases beyond a certain value, and it directly paralyses the ventilation of the chimney. Numerical results further demonstrate that the larger the inclination angle α is, the smaller the corresponding critical Ra number of the reverse flow occurs at the glass side is. The larger the inclination angle α is, the greater Nusselt (Nu) value of the absorber wall is, while its increment rate decreases gradually with the increase of the inclination angle α, when thermal Ra is maintained. As α varies from 30° to 90°, corresponding critical Ra for reversal flows gradually decreases; furthermore, these critical values obtained by the theoretical solutions were higher than those from simulation. Volume flow rates increase positively with Ra when α is no more than 30°; however, they increase initially and then decline with Ra when α is no less than 45°. In order to enhance ventilation performance, a solar chimney flush attached with discrete heating sources on the glazing wall is proposed. The numerical results indicated that modified inclined solar chimney with discrete heating sources could enhancing its ventilation performance by preventing reverse flow occurring in the channel. Our investigations also showed that the optimal inclination angle for maximum volume flow rate heavily depends on Ra. This research could provide necessary technical support and guidance for solar energy utilization and building energy conservation through air channel in building envelopes. • Thermal buoyancy driven natural convection occurred in the inclined solar chimney. • Reverse flows observed at the outlet strengthen with increasing inclination angle. • Optimal inclination angle for maximum volume flow rate heavily depends upon Ra. • Heat transfer rates and volume flow rates were influenced by discrete heating sources. • Solar chimney with discrete heat sources could improve ventilation performance. [ABSTRACT FROM AUTHOR]

An objective-oriented optimization procedure consisting of a simplified conjugated gradient methodology and a two-dimensional fluid and thermal energy transfer model is implemented to discover optimal morphologies of local heating elements. Direct heat transfer problem and inverse optimization problem are subsequently investigated. Full simulation shows that thermal Rayleigh number, enclosure inclination, heating strength ratio and size ratio of local heating sources have significant effects on the natural convection heat transfer in the inclined enclosure, asymptotically modeling like solar energy collectors or electronic boxes. The fluid flow and energy transfer inside the enclosure are analyzed in some representative situations, by the simultaneous use of streamlines, isotherms and heatlines. Inverse natural convection solutions on the maximization of global conductance are addressed, concerning on the effects of thermal Rayleigh number, inclination angle, heater strength ratio and heater length ratio. Mathematical correlations have been proposed by the multiple linear regressions to identify the role of governing parameters on maximizing global conductance and optimal morphologies of the discrete heat sources, concerning on the unique global heating flux. Present numerical methodology and inverse procedures could benefit free cooling of electronic components and effective solar collection elements. [ABSTRACT FROM AUTHOR]

Inverse conjugate natural convection problem with multiple unknown heating fluxes is examined in this study by conjugate gradient method based on temperature measurements inside the enclosure. The direct problem, as well as the auxiliary problems, required for the solution of the inverse problem with the CGM is formulated in terms of the Cartesian coordinates. Particularly, the pressure-based SIMPLE algorithm is adopted to solve the continuum direct, sensitivity and adjoint problems in unification. Some parameters affect the fluid and heat transport significantly, which have been vividly analyzed by streamlines and heatlines, respectively. The effect of thermal Rayleigh number, body size, thermal conductivity of solid-to-fluid, number of blocks, heat flux profiles, measurement errors and the number of sensors on the inverse solution accuracy are respectively addressed. Inverse solutions obtained with simulated temperature measurements reveal that extremely accurate estimations could be obtained for the unknown heat flux functions with the present inverse problem approach. This research could be significant for the design of electronic cooling and enclosed air environment. [ABSTRACT FROM AUTHOR]

Double-diffusive natural convection in a vertical enclosure containing various solid block arrays is numerically and analytically investigated in present work, where heat and species source and sink are simultaneously attached on the walls. Rayleigh number, buoyancy force ratio, number of inner solid blocks, solid thermal conductivity and mass diffusion coefficient have been varied to observe inherent flow structures and mechanism of thermal and mass transports, regarding of different levels of solid-to-fluid volume ratios. Correlations have been presented for different flow regimes, namely thermal buoyancy driven flow and solutal buoyancy driven flow. Simulation and correlation results demonstrate that influences of thermal conductivity and mass diffusion coefficient of the solid block arrays on average Nusselt and Sherwood numbers are not evident compared with that of Rayleigh number. Furthermore, there is a positive correlation between average Nusselt number and Sherwood number. In addition, under certain values of Rayleigh number, absolute values of buoyancy force ratio close to unity will cause multiple steady solutions in pure natural convection. This research could benefit the future thermal and species management for electronics and built environment. • Electronic cooling and pollutant transport are driven by the natural convection. • Multiple steady solutions of pure natural convection inside the enclosure were disclosed. • Thermal conductivity and mass diffusion coefficient of solid matrix were broadly tested. • Rayleigh number, buoyancy ratio, volume and number of solid blocks put effects on the convection. • Convective heat lines and mass lines were presented to identify the characteristics of transports. [ABSTRACT FROM AUTHOR]

This paper deals with thermosolutal convection in an inclined enclosure inserted with heat-generating porous blocks under the influence of magnetic field. The general Brinkman-extended Darcy model is adopted to formulate the fluid flow in the enclosure. An extensive series of numerical simulations is investigated in the range of parameters 0 ≤ Ha ≤ 150, 103 ≤ Ra ≤ 107, −10.0 ≤ N ≤ 10.0, 10−9 ≤ Da ≤ 10−1, 0.1 ≤ Kr ≤ 10 and −90° ≤ Φ ≤ 90°. Streamline, isotherms, isoconcentrations and masslines are produced to illustrate the fluid, heat and moisture flow structures. It is founded that overall Nusselt number is an increasing function of Ra , N , Da and Kr in the vertical enclosure, while decreasing with Ha. The permeability and thermal conductivity of porous blocks have no significant effect on moisture transfer rate. The Nusselt and Sherwood curves for different inclination angle are presented to be parabolic, and the maximum are near at Ф = −10° and 30°, respectively. In addition, correlations of the overall Nusselt and Sherwood numbers depending on thermal Rayleigh number, buoyancy ratio, Hartmann number and inclination angle have been obtained, which are beneficial to determine heat and moisture transfer rates in electrical devices. • Heat and moisture transfer processes occurred in cooling of multiple electronic devices • Disconnected porous blocks with internal energy generation are inserted in the enclosure. • Overall Nusselt number increases with Ra , N , Da and Kr , while decreases with Ha. • Permeability and thermal conductivity of porous blocks hardly influence the moisture transfer rate. • Correlations of the overall Nusselt and Sherwood numbers have been obtained. [ABSTRACT FROM AUTHOR]

The application of porous media for electronic cooling process, instead of solid one, generally strengthens heat conduction while weakens convection insignificantly at high Darcy number. In the present work, effects of morphology and topology of porous fins on the laminar natural convection heat transfer were investigated in a differentially heated enclosure. Volume averaged Darcy-Forchheimer model was applied to solve the transport process within the porous media while the Navier-Stokes equations were employed within pure fluid region. Relevant governing parameters, including thermal Rayleigh number, Darcy number, thermal conductivity of the porous matrix, designs of porous fins, are sensitively varied to identify their effects and roles on the natural convection flows. Depending on thousands of numerical data, the correlation has been developed for all designs of porous fins. Numerical results illustrate that the adding porous fins with excellent permeability and heat conduction contribute to the remarkable heat transfer enhancement while the adding fins, acting like solid ones and having poor heat conduction, could result in an increase of thermal resistance and the deterioration of heat transfer. Numerical results further show that there exists an optimal design of porous fins to achieve the best performance of heat transfer if some conditions were satisfied. Overall, this study could benefit the electronic cooling by the installation of porous-alike materials. • Electronic passive cooling is modeled by the natural convection in an enclosure. • Thermal conductivity and Darcy number of porous matrix were broadly tested. • Morphology and topology of porous fins on the natural flow were analyzed. • Porous fins flush mounted on the hot wall affect heat transfer rates significantly. • Porous fins maximize the heat transfer rate if some conditions were satisfied. [ABSTRACT FROM AUTHOR]