Improved Nu number correlations for gas flow in monolith reactors using temperature-dependent fluid properties

Abstract

This paper reports an investigation of heat and mass transfer coupled with fluid flow inside monolith honeycomb substrates. Many important aspects of multiscale models of a monolith are investigated. Three common geometrical representations of monolith channels are tested, and their advantages and disadvantages are analysed. A detailed computational model and a large set of computational experiments, covering a broad range of substrate void fractions, channel Reynolds numbers and heating rates is used. Results assuming constant and temperature-dependent fluid properties are reported and compared. At a high heating rate, assuming constant fluid properties leads to a significant error in the estimation of Nusselt and Sherwood numbers in the entry region. At a constant wall temperature and a high heating rate, there is a minimum in the Nusselt curve that classical models are not able to describe. Hence, a novel correlation that shows excellent agreement with channel data is presented together with a methodology to fit it. Additionally, empirical models to estimate the placement and value of the minimum Nusselt are proposed. These results contribute significantly to the improvement of lumped parameter multiscale models of monolith catalytic reactors.