Conjugate unsteady natural heat convection of air and non-Newtonian fluid in thick walled cylindrical enclosure partially filled with a porous media

A numerical study describes the conjugate unsteady natural heat convection of air on top of a non-Newtonian polymer-water solution characterized by a power-law model within a sealed vertical thick-walled cylindrical enclosure partially filled with a porous media in the lower section. Enzymes immobilized in an inorganic polymer, silica, used in synthesis processes constitute the porous media. Heating is by a constant high temperature at the bottom and at the vertical walls while the upper horizontal wall remains at the initial cold temperature. The Finite Volume Method allows the solution of the continuity, linear momentum and energy equations for a power law shear thinning fluid in a porous media with the Darcy-Brikman-Forchheimer model. The evolution of fluid mechanics of air and of the non-Newtonian fluid is described by the history of the streamlines. Transient heat transfer by conduction in the sealed tube walls and by natural convection of air and in the non-Newtonian fluid flow in the porous media is characterized by the evolution of isotherms. Experimental results are used to verify that the natural convective heat transfer conjugate computational model allows the prediction of temperature evolution in a thermal resistance challenge for free and immobilized enzymes. A difference of 1% is found between the experimental and the numerical results for the temperature history during the immobilized enzyme convective heating process. The applied numerical method has the capability of designing the enzyme temperature challenge test, by predicting the time needed to reach the uniform target temperature for biocatalyst processing, 500 s, in agreement with the experimental findings. The computational model contributes to the development of a technique to describe the kinetics of both immobilized and free enzyme during heating. This is a key issue for several industries, such as food modification, biofuel development, agroindustry and fishery waste valorization, that require enzymes operating at high temperature ranges in a reliable way for a long time.