Análise da convecção em cavidade com o topo deslizante preenchida com meio poroso heterogêneo

Abstract

The study of convection in porous media is relevant to a variety of engineering applications in the energy, pharmaceutical, food and petroleum industry. In this work, the convection heat transfer in a lid-driven square porous cavity subjected to a gravitational stable condition is numerically simulated. Such condition is achieved because the enclosure top surface temperature is higher than the base and gravity acts downwards. The sidewalls are adiabatic. As buoyancy is not capable of promoting the fluid flow, a constant velocity is prescribed at the top surface. The porous media is modeled in micro scale with the solid constituent being envisioned as identical, uniformly distributed and heat conductive square solid blocks. The balance equations are applied at the blocks surfaces, requiring equal temperature and heat flux in both domains. The main objective is to evaluate the influence of the flow parameters, in the 1000 <= Re <= 2500 and 100000 <= Gr <= 10000000 , the volume fluid fraction, 0,19 <= φ <=1 ,and the number of blocks, 1 <= N <=. A numerical solution is sought through the Finite Volume Method using the QUICK scheme for the treatment of the advection terms and the SIMPLE algorithm for the pressure – velocity coupling. In general, the insertion of the solid obstructions is intensified either reducing the volume fraction (keeping N constant). It is observed two patterns for the heat transfer: convective and conductive-dominant. The latter is related with the occurrence of stagnant fluid near the enclosure base due to the hampering action of the buoyant forces. Curiously, for convective predominant situations, holding N constant and decreasing φ , might results in heat transfer augmentation. However, for low values of φ, the hindrance effects are so severe that the average Nusselt decays. Additionally, for constant φ , the convection is mitigated with increasing N because of the channeling effect imposed over the flow by the channels between the blocks. On the other hand, for conductive-dominant configurations, the blocks introduction disfavor the convection. Although, if φ is low or the number of blocks is high, the fluid is forced to envelop the blocks due to the squeezing effect. Such effect benefits the heat transfer, but it is mostly observed for N = 1. Once for N > 1, the channeling effect cloaks the squeezing and maintain flow stagnation in the cavity base adjacencies.