RICERCA ITALIANA     

Enhancement of the thermal and fluid-dynamic performance of internal flow systems in mixed convection regime

Università degli Studi di Bologna

Abstract

The purpose of this research program is to deepen the knowledge of both basic and applied topics of mixed convection heat transfer. More precisely, the aims are to analyse some aspects of the mathematical-physics models of mixed convection and to provide novel results for technological applications. Mixed convection processes are important in a very broad field of technical applications, such as: thermal control of electronic devices, safety systems in nuclear plants, fuel-cells, thermal and photovoltaic solar energy conversion systems, heat treatments of materials (welding, hot rolling, drawing, extrusion, casting), Chemical Vapour Deposition (CVD). The combined development of basic studies on the mathematical-physics models and of useful information for industrial application is a typical feature of research on mixed convection. In fact, the study of a mixed convection process requires the combined control of different physical phenomena and features of the system under exam, which, altogether, define the specific elements of the thermal and fluid-dynamical process. Among these phenomena and features of the system, one can quote: the geometry of the duct in which the fluid flows, the thermal boundary conditions at the duct walls, the relative motion of the duct walls, the flow stability, the rheological behaviour of the fluid, the effect of viscous dissipation, the presence of a porous medium saturated by the fluid. Very often, the analysis of a mixed-convection process in >>>

Principal Investigator

Antonio BARLETTA Università degli Studi di BOLOGNA

Research Objectives

An essential step in the design of several technological devices of great interest for industry is given by the study and the optimization of mixed convection processes in ducts or partially open cavities. This occurs, for instance, in the design of heat exchangers, of fuel cells, of devices for the cooling of electronic circuits, of devices for the processing of polymers or for the production of thin films through the method of Chemical Vapour Deposition (CVD). To optimize the thermal and fluid-dynamic performance of apparatuses, the research-development performed by companies in these areas employs either design correlations already available or numerical simulations by computational codes based on mathematical physics models well established in the scientific literature. For mixed convection phenomena with severe effects of buoyancy forces, this investigation method cannot lead to satisfactory results if it is not coupled to a deeper research activity. In fact, the design correlations available in the literature are not so abundant. Moreover, the mathematical physics issue to be investigated is rather complicated, since the simultaneous solution of the mass, momentum and energy local balance equations is needed. Two fundamental problems arise.
A first problem is given by the need to control the reliability and the accuracy of numerical solutions by means of benchmark analytical solutions or experimental data, referring to simpler cases similar to those under exam >>>

Timescale

24 months

National and international background

Several technological applications are strictly connected to mixed convection flows. Smoke control in safety systems of buildings and tunnels, thermal control of electronic components, safety system of nuclear plants, fuel cells, active and passive solar systems and classical and hybrid photovoltaic systems represent only some examples of applications of mixed-convection heat transfer. Moreover, mixed convection is extremely important in the heat treatments of materials (such as welding, hot rolling, drawing, extrusion, casting) and in the Chemical Vapour Deposition (CVD) for surface covering [1-2].
Nowadays, the correlations available in the literature [3-7] are widely used to determine the thermal and fluid-dynamical performance of mixed-convection-based control systems both in the industrial field and in the civil one. However, these correlations, obtained theoretically or experimentally, often rely on mathematical-physics models not completely satisfactory. In the field of internal mixed-convection flow, for instance, the mathematical models usually employed are based on the Boussinesq approximation with an arbitrary choice of the reference temperature of the fluid and, thus, they do not appear to be sufficiently reliable. For these reasons, it is important to improve the basic knowledge on mixed convection, in order to develop new methods to optimize the fluid-dynamical performance of heat exchangers and thermal control devices.
In the literature, a >>>