Numerical and experimental study of steady and unsteady mixed convection flow in a cubical open cavity with the bottom wall heated
- Autores: Gorg Abdelmassih Bassit Megalaa
- Directores de la Tesis: Antonio Vernet Peña (dir. tes.), Jordi Pallarès Curto (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2016
- Idioma: español
- Tribunal Calificador de la Tesis: Francesc Xavier Grau Vidal (presid.), Roberto Castilla López (secret.), Pedro Javier Gámez Montero (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX hdl.handle.net hdl.handle.net
- Resumen
Mixed convection from open cavities have received considerable attention due its importance in many engineering applications. Cooling of electronic components is one of the most used applications at small scales for the flow over an open cavity. It is simple in design and has a cheap maintenance cost.
The main objective of this work is to study the mixed convective flow and three dimensional instabilities, focusing on the effect of the buoyancy forces on the flow topology for an incompressible laminar inflow in an open cavity with a bottom wall heated. The ranges of Reynolds and Richardson numbers considered (100≤Re≤1500 and 0.1≤ Ri≤10) correspond to the usual operating conditions of some processes associated with the cooling of electronic components. The effect of Ri on the flow stability and the analysis of the flow topology and its time evolution when the flow is unsteady are the main parts of this work.
Isothermal configuration was also proposed in the same range of Reynolds number in order to detect the impacts of the mixed convection on the flow structure. The Isothermal configuration proposes the walls for the cavity and the channel are adiabatic.
The 3DINAMICS finite volume parallel code has been used in this work. Air-flow and water-flow were considered separately as working fluids. The dependence of the physical properties with temperature was numerically analyzed and for the conditions considered the assumption of constant physical properties is acceptable.
Experimental study was achieved to validate the numerical results. Particle Image Velocimetry (PIV) is used for experimentally measuring the two in-plane velocity components in the cavity. Water flow is used for both proposed configurations. A good agreement has been found between experimental and numerical results especially for the heated wall configuration.
The flow is always steady at the isothermal configuration at Re≤1500. For the heated wall configuration, three flow patterns have been found in this range of Re and Ri, which are: steady, periodic and turbulent flow. For small Ri≤0.1, the buoyancy is weak for the whole range of Re≤1500.The flow is smooth and steady state while conduction heat transfer is dominant within the cavity. An unsteady periodic flow is found at Re=100 and Ri=10. Alternate flow ejections from the cavity to the channel occur near the lateral walls while the flow enters the cavity from the channel through the central part of the cavity.
The turbulent regime is observed for Re≥500 and Ri≥1. In these conditions the natural convection dominates the heat transfer mechanism within the cavity. A conditional sampling technique was used to analyze the mean flow history of the unsteady flows for Re=1500. The results show four mean flow structures, which are periodically repeatable. The most probable structure consists in two symmetrically distributed flow ejections, from the cavity to the channel, near the lateral walls and a flow inrush at the center of the cavity. The other three structures have a similar probability of occurrence. One consists in a central flow ejection from the cavity and two symmetrically distributed flow inrushes. The other two structures have a single mean lateral flow ejection near a lateral wall.
Nusselt number increases with Ri for each value of Re. The computed Nusselt numbers for both working fluids (air and water) are in general agreement with a previously reported correlation, valid for two dimensional cavities of different aspects ratios.
