High-Porosity Metal Foams: Potentials, Applications, and Formulations

This chapter is aimed as a concise review, but well-focused on the potentials of what is known as “High-porosity metal foams,” and hence, the practical applications where such promising media have been/can be employed successfully, particularly in the field of managing, recovering, dissipating, or enhancing heat transfer. Furthermore, an extensive comparison is conducted between the formulations presented so far for the geometrical and thermal characteristics concerning the heat and fluid flow in open-cell metal foams

Numerical simulation of film cooling effectiveness in a rotating blade at high blowing ratios

The film-cooling performance in a low-speed rotor blade of a 1-1/2 turbine stage has been examined using LES approach. Two rows of film holes were positioned on the rotor blade surface, one on the pressure surface and the other one the suction surface, with axial locations of 24.2% and 22.6% of the chord length, respectively. Each row has three cylindrical film-cooling holes with a diameter (D) of 4 mm and a tangential injection angle of 28o on the pressure side and 36o on the suction side. The Reynolds number, based on the mainstream velocity of the turbine outlet and axial length of the turbine, was fixed at Re=1.92×105, the coolant-to-mainstream density ratio (DR) was about 2.0, and the speed of the rotor blade was taken to be 1800 rpm. Several blowing ratios (BR) in the range of 1.0–5.0 were investigated. The effects of blowing ratio, rotation, and curved surfaces were analysed to investigate the effects of the stator–rotor interaction on the film-cooling characteristics. The commercial CFD code STAR-CCM+ was used to run the simulations using the WALE subgrid-scale model for modelling the turbulence. The solutions were obtained by solving the incompressible, 3D Navier–Stokes equations under the rotating coordinates system with the energy equation, and the pressure–velocity coupling was achieved by using the well-known SIMPLE algorithm. The results show that on the pressure side, the film coverage and film-cooling effectiveness increase with increasing BR. A lower BR results in stronger film deflection. The film injection with higher BR produces better film attachment. The film deflects centripetally due to the effect of rotation. On the suction side, the trend of film coverage and film-cooling effectiveness is parabola as the blowing ratio rising and a centripetal deflection of the film is observed. The deflection of the film path could be amplified by decreasing the BR.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

A POROUS MEDIA APPROACH FOR NUMERICAL OPTIMISATION OF THERMAL WHEEL

The experimental investigations of rotating heat exchangers are usually too costly and provide limited understanding for the phenomena of heat and fluid flow within them; hence, a less expensive and more comprehensive method is required to investigate what can affect their overall performance. In the current study, a porous media concept is presented as an alternative way to numerically analyse the fluid flow and heat transport through a rotary thermal regenerator. An aluminum core formed of multi-packed square passages is simulated as a porous medium of an orthotropic porosity in order to allow the counter-flowing streams to flow in a way similar to that inside the regenerator core. The geometric properties of the core were transformed into the conventional porous media parameters such as the permeability and inertial coefficient based on empirical equations; so, the core has been dealt with as a porous medium of known features. Fluid and solid phases are assumed to be in a local thermal non-equilibrium state with each other. A commercial CFD code "STAR CCM+" was used to solve the current problem numerically, where heat is allowed to be exchanged between the two phases and tracked by creating a heat exchanger interface in the core region. The results are presented by means of overall thermal effectiveness, pressure drop, and coefficient of performance COP. Using porous media approach has been found to be sufficient to simulate the current problem, where the currently computed data were found to deviate by up to 2.7% only from the corresponding analytical and experimental data. The data obtained reveal an obvious impact of the core geometrical parameters on both the heat restored and pressure loss; and hence, the overall efficiency of the regenerator system