Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
1
3
2009
NATURAL CONVECTION IN A NONUNIFORMLY HEATED CHANNEL WITH APPLICATION TO PHOTOVOLTAIC FACADES
231-258
Stephanie
Giroux-Julien
Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, F-69621,
Villeurbanne, France
Christophe
Menezo
Universite de Lyon, CNRS, France ; Chaire INSA-EDF Habitats et Innovations Energetiques, CETHIL, UMR5008, F-69621, Villeurbanne, France; University Savoie Mont-Blanc, LOCIE UMR CNRS 5271, Campus Scientifique Savoie Technolac − F- 73376, Le Bourget-du-Lac, France
Jeremie
Vareilles
Centre de Thermique de Lyon UMR 5008, (CETHIL, CNRS/INSA Lyon/UCBL), Lyon, France
Hervé
Pabiou
Univ Lyon, CNRS, INSA-Lyon, Universite Claude Bernard Lyon 1, CETHIL UMR5008, F-69621, Villeurbanne, France
Marco
Fossa
Dime, Universita di Genova, Via Opera Pia 15a, 16145 Genova, Italy
Eddie
Leonardi
Computational Fluid Dynamics Research Laboratory, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia 2052
This paper investigates an active component of the building envelope: a photovoltaic-thermal double-skin facade. This element consists of a vertical open air channel bound by two parallel walls: one is made of photovoltaic panels and one is the main frame of the building. Integrating this system in a building facade is not an easy matter because the electrical output is strongly dependent on the operating temperature of the photovoltaic component. The aim of this study is to promote better cooling of the photovoltaic facade working on its typical geometrical arrangement. This consists of an alternation of photovoltaic cells (localized heat sources) and semitransparent window panes (unheated zones). Fundamentally, the flow of natural convection that develops within the vertical channel appears to be subjected to boundary-localized thermally active areas and adiabatic areas, evenly distributed throughout the height. This requires investigations of parametric variations of magnitude and space frequency of the heated areas as well as intermediate spacing. Two complementary experimental apparatuses were developed, namely, at CETHIL and at the CFD Research Laboratory UNSW in collaboration with the DIPTEM. Experiments were conducted on both. For these experiments, Grashof numbers, based on the channel width and the convective heat flux, are about 1010. The results obtained constitute an important database, which allows characterization of convective heat transfer. Some of the results concern the dynamic boundary conditions that are required for the numerical investigation. The present study compares (on a common operating range) both experimental and numerical investigations focusing on the CETHIL experiments.
A NUMERICAL METHOD FOR THREE-DIMENSIONAL PARABOLIC FLOW AND HEAT TRANSFER IN STRAIGHT DUCTS OF IRREGULAR CROSS SECTION
259-288
Nirmalakanth
Jesuthasan
Heat Transfer Laboratory, Department of Mechanical Engineering, McGill University, Montreal, Quebec H3 A 2K6, Canada
Bantwal Rabi
Baliga
Heat Transfer Laboratory, Department of Mechanical Engineering, McGill University, 817 Sherbrooke St. W., Montreal, QC H3A 2K6, Canada
In the proposed method, a step-by-step marching procedure in the axial direction is used to solve the problems of interest from the inlet to the exit planes of the ducts. In each step or slice, the following formulation is used: the slice is first discretized into six-node prism-shaped elements of triangular cross section, and then each set of corresponding upstream and downstream nodes are associated with prism-shaped control volumes of polygonal cross section. The dependent variables are stored at the same nodes (colocated) and interpolated using equal-order element-based functions. Algebraic approximations to integral mass, momentum, and energy conservation equations for each of the prism-shaped control volumes are then derived using the aforementioned interpolation functions, and the resulting discretized equations are solved using an adaptation of a sequential iterative variable adjustment scheme. This formulation provides the following novel capabilities compared to those of earlier numerical methods for the solution of three-dimensional parabolic problems: it is applicable to ducts of irregular- and regular-shaped cross section; and for any axial step size, the solution is independent of the sequence in which the dependent variables are solved. A novel automatic axial step-size selection procedure is also proposed for problems in which the dependent variables vary monotonically in the axial direction. The validity of the proposed method is established by applying it to developing laminar forced convection in a straight duct of square cross section and comparing the results to those available in the literature.
ON THE USE OF DNS TO ANALYZE HEAT AND MASS TRANSFERS IN A DROPLET-LADEN TURBULENT JET
289-308
Zakaria
Bouali
UMR 6614 CNRS CORIA, Rouen University, bp 12−Site universitaire du Madrillet, 76801 St Etienne du Rouvray, France
Bruno
Delhom
CORIA, University of Rouen, France
Karine
Truffin
Institut Français du Pétrole - R102 1&4 avenue Bois Préau 92852 Rueil Malmaison, France
Hicham
Meftah
CORIA, University of Rouen, France; Ibn Zohr University, GEMS Laboratory, ENSA, B.P 1136, Agadir-Morocco
Julien
Reveillon
CORIA UMR 6614, University of Rouen, Technopole du Madrillet, BP 12, 76801 Saint-Etienne-du-Rouvray Cedex, France
Nowadays, it is fundamental to decrease fuel consumption and pollution generated by cars by improving engine efficiency. The characterization, the prediction, and the control of the physical phenomena interacting within the combustion chamber are necessary if one wants to improve the current systems and to develop new technologies. This is why it is important to understand and control the whole of the physical processes taking place from the liquid injection and atomization down to combustion phenomena and gas exhaust. In direct-injection engines, modeling the evaporation of the liquid fuel is a very difficult phase. Experimental results have shown that the droplet presence amplifies the temperature fluctuations and modifies the mixing between the vapor of fuel and the oxidizer. If, up to now, the effects of evaporation on the equivalence ratio and the velocity fluctuations have been taken into account in engines modeling, temperature exchanges between the spray and the gas phase have not been clearly evaluated. These fluctuations, however, could play a considerable role in the process of self-ignition and then pollutant formation. The main objective of this work is to carry out direct numerical simulation (DNS) of an evaporating gasoline spray in order to estimate the effects of the droplets on the energy field and to study temperature and enthalpy fluctuations. We focus mainly on the vaporization sources terms found in the balance equation of the variance of the sensible enthalpy. DNS is a useful tool that allows exactly solving the Navier-Stokes equations by considering all the characteristic scales of the flow. When two-phase flows are considered, only a DNS of the carrier phase is carried out, whereas a Lagrangian model is necessary to describe the liquid phase. The droplets are considered as local sources of vapor, momentum, and energy; a two-way coupling is considered.
CONVECTION SUPPRESSION IN A TRIANGULAR-SHAPED ENCLOSURE
309-321
Timothy
Anderson
Mike
Duke
Department of Engineering, University of Waikato, Hamilton, New Zealand 3240
James
Carson
Department of Engineering, University of Waikato, Hamilton, New Zealand 3240
The use of convection suppression devices has been widely discussed in the literature as a means of reducing natural convection heat loss from the front surface of glazed solar collectors. In this study, the use of baffles in an attic-shaped enclosure was examined as a possible low-cost means of suppressing heat loss by natural convection from the rear surface of a roof-integrated solar collector. To determine the effect of baffles in the attic-shaped enclosure, a three-dimensional triangular cross-sectioned enclosure with a vertical aspect ratio of 0.5 and a horizontal aspect ratio of 3.3 was modeled. The flow patterns and heat transfer in the enclosure were determined for Grashof Numbers in the range of 106−107 using a commercially available finite volume CFD solver. It was found that the use of a single adiabatic baffle mounted vertically downward from the apex, and extending the length of the enclosure, would alter the flow such that the heat transfer due to natural convection was reduced as the length of the baffle was increased.
THREE-DIMENSIONAL NUMERICAL LAMINAR CONVECTION HEAT TRANSFER AROUND LATERAL PERFORATED FINS
323-340
Mahmood A.
Yaghoubi
School of Mechanical Engineering, Shiraz University, P. O. Box 71348-51154, Shiraz, Iran; Academy of Science, I.R. Iran
Mohammad Reza
Shaeri
Advanced Cooling Technologies, Inc., 1046 New Holland Avenue, Lancaster, PA 17601, USA
Khosrow
Jafarpur
School of Mechanical Engineering, Shiraz University, Shiraz, Iran
Three-dimensional laminar steady fluid flow and conjugate heat transfer from an array of rectangular solid and perforated fins are presented numerically. Perforations with window square cross section in various numbers and dimensions are arranged in the lateral surface of fins. Due to perforations, the flow may become unsteady sooner than solid fins; hence, the computation performed for the range of Reynolds numbers 100 to 250. For analysis, a FORTRAN code base on the SIMPLE algorithm with staggered grid is developed. Also, the second-order upwind technique is used to calculate convective terms in momentum and energy equations. Results show that by utilizing perforated fins, considerable fin weight reduction is achieved without any penalty for heat transfer rate.
CONJUGATE NATURAL CONVECTION IN AN ENCLOSURE WITH LOCAL HEAT SOURCES
341-360
Mikhail A.
Sheremet
Department of Theoretical Mechanics, Tomsk State University, 634050, Tomsk, Russia; Institute of Power Engineering, Tomsk Polytechnic University, 634050, Tomsk, Russia
Genii V.
Kuznetsov
National Research Tomsk Polytechnic University, Institute of Power Engineering, Tomsk,
634050, Russia
The development of unsteady conjugate natural convection in an enclosure has been numerically studied. The decision region is common in many applications, such as environmental control (e.g., room), applied chemistry (e.g., storage reservoir), and electronics (e.g., cabinets). The enclosure considered has thick walls, two heat sources, and a zone with an elevated heat transfer intensity. The heat sources are isothermal. The governing unsteady, three-dimensional heat transfer equations, written in dimensionless terms of the vorticity vector, vector potential functions, and temperature, have been solved using an implicit finite-difference method. The conjugate heat transfer in the enclosure is investigated by means of a continuum model, which treats the fluid and solid constituents individually. The solution has the following parameters: the Grashof number Gr and the Prandtl number Pr. Results have been obtained for a Prandtl number of 0.702 and Grashof number ranged from 104 to 107.