Numerical investigation on Rayleigh-Bénard convection of cyclohexane-oxygen mixture near its maximum density in a rectangular container

Abstract

The oxidation of cyclohexane is an important route in the chemical industries for producing cyclohexanol, cyclohexanone, plasticizers, surfactants and so on. However, it will be in danger of explosion once the concentration of cyclohexane in the mixture exceeds the explosion limit. Therefore, it is necessary to research the temperature distribution and flow characteristics in Rayleigh-Bénard (RB) convection of cyclohexane/oxygen mixture to avoid the potential hazard of deflagration. In this paper, a set of three-dimensional simulations were performed to understand RB flow characteristics of cyclohexane/oxygen mixture near the maximum density in a rectangular container with an aspect ratio of 2. Rayleigh (Ra) number ranges from 2 × 103 to 6 × 105. Results show that the density inversion has a notable influence on RB convection of cyclohexane/oxygen mixture. The critical Rayleigh numbers for the onset of stable flow and for the oscillatory flow show an upward tendency with increasing density inversion parameter (Θm). When Θm is small, the flow occurs in the whole cavity. When Θm is large, the fluid layer near the top wall is static in the region. Multiple flow states and their evolutions are obtained at various Θm. The heat transfer ability is enhanced with increasing Ra, while it weakens with increasing Θm.