Microwave heating of liquid foods in laminar flow through a circular tube has been modeled. In particular, skim milk as a Newtonian fluid and apple sauce and tomato sauce as non-Newtonian fluids have been considered. The temperature profiles have been obtained solving the motion and energy equations in transient regime and Maxwell's equations in the frequency domain. Numerical resolution of Finite Element Method has been implemented in Comsol Multiphysics. The generation term due to the microwave heating has been evaluated according both to Lambert's law and Poynting theorem. Finally, a comparison between the two methods has been made in order to check to what extent the results obtained with the simpler Lambert's law approximation are comparable with those deriving from the exact solution of Maxwell equations. Dielectric properties are considered to be temperature dependent.
KeywordsContinuous Microwave Heating, Lambert's Law, Maxwell Equations, Poynting Theorem, Non-Newtonian Fluids, FEM polarizes the molecules of dielectric materials and creates dipole moments that cause these molecules to rotate. The resulting molecular friction causes heat
In this work, the enzymatic hydrolysis reaction of sucrose through invertase under unsteady-state conditions has been investigated. The aim is to evaluate the inhibition phenomena influence on the reaction rate and, then, on the concentration and temperature profiles by simulating the process in a tubular reactor, varying the enzyme concentration and the reactant mixture velocity. The transport phenomena considered during the enzymatic hydrolysis process have been described by means of unsteady-state momentum, mass and energy balance equations, taking into account molecular and convective transport and generation terms. Interpretation and discussion of the results obtained by FEM resolution of PDEs involved allow to understand the relevance of the operating parameters.
Enzymatic synthesis of ethyl hexanoate from hexanoic acid and ethanol in a solvent-free system, carried out at optimum conditions, has been modeled. The process follows a Ping-Pong Bi-Bi reaction rate and it is endothermic, so microwave heating is provided to prevent its shutdown. The mathematical model has been numerically solved with the FEM method. Results show that microwave heating can be successfully used to carry out this kind of reaction.
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