G. S. Barozzi

Physical and numerical modelling of a solar chimney-based ventilation system for buildings

Abstract This paper describes an experimental and numerical study to analyse the thermal performance of a bio-climatic building prototype in Nigeria. The roof performs as a solar chimney, generating an air flow through the living space of the building to provide cooling. Experimental tests on a 1:12 small-scale model of the prototype are outlined, and the results, bith qualitative and quatitative, are used to validate a two-dimensional flow simulation model, in which the steady state conservation equations of mass, momentum and thermal energy are solved using a finite volume formulation. The experimental and numerical results, expressed in terms of temperature and velocity fields, for two different window geometries are critically evaluated and compared with good agreement.

A Comprehensive Review of Natural Convection in Triangular Enclosures

Natural convection in triangular enclosures is an important problem. It displays well thegeneric attributes of this class of convection, with its dependence on enclosure geometry,orientation and thermal boundary conditions. It is particularly rich in its variety of flowregimes and thermal fields as well as having significant practical application. In this pa-per, a comprehensive view of the research area is sought by critically examining the ex-perimental and numerical approaches adopted in studies of this problem in the literature.Different thermal boundary conditions for the evolution of the flow regimes and thermalfields are considered. Effects of changes in pitch angle and the Rayleigh number on theflow and thermal fields are examined in detail. Although most of the past studies are inthe laminar regime, the review extends up to the recent studies of the low turbulent re-gime. Finally, areas of further research are highlighted. [DOI: 10.1115/1.4004290]Keywords: buoyancy-induced flows, flow fields, triangular enclosures

Experimental investigation of coupled conduction and laminar convection in a circular tube

Abstract Wall heat conduction effects on laminar flow heat transfer are experimentally investigated. The steady flow of water through a uniformly heated copper pipe is considered in the experiment, which covers a range of Reynolds numbers from 500 to 1900. The thermal behaviour of the test section is simulated numerically and the influence of conduction along the pipe wall is therefore accounted for in the reduction of the data. Fully developed flow results satisfactorily compare with predictions by a theoretical method previously developed by the authors [ Heat Technol . 2 ,72 (1984)]. Results are also reported for the case where the velocity profile is partially developed at the inlet of the heat transfer section. The combined effects on heat transfer of flow development and of wall axial heat conduction are discussed.

Laminar heat transfer to blood flowing in a circular duct

Abstract Entrance-region heat transfer to blood steadily flowing in a pipe is studied. It is assumed that the non-Newtonian behaviour of blood can be expressed both by the Casson equation and the more complex law suggested by Merrill and Pelletier [ J. Appl. Physiol. 23 , 179–182 (1967)]. The possible presence of a thin cell-free plasma layer at the wall is accounted for. The velocity distribution is determined analytically and a solution of the energy equation is obtained by a finite-difference method, for the two cases: (a) the uniform wall temperature, and (b) the uniform wall heat flux. Results are presented for the yield number Y ( = 2 Rτ y / σu m ) = 1, 5, 10 and 20 and the non-dimensional marginal layer thickness D ( = σ / R ) = 0,0.0002, 0.01 and 0.1.

A FAST CARTESIAN SCHEME FOR UNSTEADY HEAT DIFFUSION ON IRREGULAR DOMAINS

A numerical integration method is presented for the treatment of transient heat conduction problems. A Cartesian formulation is developed that is suitable for the treatment of irregular domains under general boundary conditions. The qualities of the scheme are demonstrated, in terms of both accuracy and computational efficiency, by comparison with analytical and numerical solutions. Results for the basic two-dimensional annular geometry show that the method has nearly second-order accuracy in space and time, at least in simple cases. Finally, a complex multiconnected domain is considered, to test the method performance under more severe conditions, including the presence of multiple length scales. The numerical experiment demonstrates that the numerical scheme is efficient, stable, and convergent.

Convective Heat Transfer Coefficients in the Circulation

Convective heat transfer in the vessels of the circulatory system is investigated numerically. In the modeling, account is taken of the non-Newtonian rheological properties of blood and the presence of a cell-depleted plasma layer at the vessel wall. The latter is found to produce a remarkable enhancement of the heat transfer rate in the small vessels, while the effects due to the rheological behavior of blood are comparatively low. A comparison with experimental data available in the open literature is finally attempted.

Non-Newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm

Three models of different stent designs implanted in a cerebral aneurysm, originating from the Virtual Intracranial Stenting Challenge’07, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the CFD simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified by other groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating WSS, to understand dynamic flow effects, and to discriminate more effectively between stent designs.

Combined convection and wall conduction effects in laminar pipe flow: numerical predictions and experimental validation under uniform wall heating

Laminar combined convection in horizontal circular ducts is investigated both numerically and experimentally, under uniform wall heating. A series of experiments for the heating of water in a long horizontal copper tube are simulated numerically in order to assess the reliability of the theoretical results. Peripheral and axial wall conduction effects, inherently present in the experiments, are accounted for in the numerical model. The cross validation of experimental and numerical data allows significant conclusions to be reached on conjugate conduction and convection with buoyancy effects in horizontal duct flows. Buoyancy is considered for values of the modified Rayleigh number,Raqo, up to 5·106; the forced convection contribution is considered for two values of the entry Reynolds number,Reo=500 and 1000.ZusammenfassungEs wird der Wärmeübergang bei laminarer Mischkonvektion in gleichmäßig beheizten waagrechten Rohren numerisch und experimentell untersucht. Einige experimentelle Befunde für gleichförmige Beheizung von Wasser in einem langen Kupferrohr werden mit den Ergebnissen eines numerischen Modells verglichen, um dessen Zuverlässigkeit zu eruieren. Die Einflüsse der Wärmeleitung in Umfangs-und Axialrichtung des Rohrmantels fanden darin Berücksichtigung. Der Vergleich der experimentellen und numerischen Ergebnisse liefert konkrete Hinweise, unter welchen Bedingungen der Auftrieb und die Konvektion, für Wandwärmeleitung Einfluß auf den konvektiven Wärmeübergang in horizontalen Rohren nehmen. Die Stärke des Auftriebs wird durch Rayleigh-Zahlen bis 5·106 repräsentiert, die der Zwangskonvektion durch zwei Werte der Reynolds-Zahl am Eintritt, 500 und 1000.

Sharp entry and transition effects for laminar combined convection of water in vertical tubes

Abstract In previous work the authors showed a sharp entry to have a definite effect on laminar forced convection to water in a vertical circular tube. The study has been extended to situations of strong aiding natural convection, and new experimental data and numerical predictions are reported. The expected entry effect is confirmed, but it is found to be less marked in a strong combined convection field than in the previous forced convection study. The experimental data also include evidence of transition from laminar flow, and a possible criterion of transition is investigated, based on the axial location of minimum local Nusselt number. This is experimental and predictive data for this criterion are compared with the experimental correlation of Lawrence and Chato based on a criterion of temperature fluctuations

Shading effect of eggcrate devices on vertical windows of arbitrary orientation

Abstract A combination of horizontal and vertical elements forming an eggcrate-type shading system is often used in the architectural design of building facades. An analytical-numerical method is presented to estimate the shading effect of such a structure on vertical windows of arbitrary azimuthal orientation. The effect of reflections from aggregate walls is accounted for in the analysis. Daily and monthly average solar radiation data are presented for shaded windows in Venice (45.40° northen latitude). The effects of the window geometry and the eggcrate projection are discussed.