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  • 1.
    Gamero, Rafael
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Internal mass transfer during isothermal drying of a porous solid containing multicomponent liquid mixture2005In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 23, no 9-11, p. 1939-1951Article in journal (Refereed)
    Abstract [en]

    Internal mass transfer in a porous solid partially saturated with multicomponent liquids has been experimentally and theoretically studied. Isothermal drying experiments were performed using a jacketed wind tunnel where the transient composition profiles and total liquid content of a cylindrical sample were determined. Sand samples wetted with the ternary liquid mixtures watermethanol-ethanol and 2-propanol-methanol-ethanol were dried at two different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both gas and liquid phase was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids where weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained provided that axial dispersion is included in the model.

  • 2.
    Luna, Fabio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Birgersson, Erik E.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Martinez, Joaquin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Diffusion equation applied to isothermal drying of a multicomponent liquid film2005In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 23, no 11-sep, p. 1953-1975Article in journal (Refereed)
    Abstract [en]

    Liquid-side-controlled drying by convection of a multicomponent liquid film is studied. Interactive diffusion in liquid phase is considered the main mechanism for mass transfer. Assuming an isothermal drying process and a constant matrix of multicomponent diffusion coefficients, an analytical solution of the diffusion equation is developed. The equations are decoupled by a similarity transformation and solved by the method of variable separation. The solution is applied to the drying of ternary mixtures, one of them containing a component of negligible volatility. The variation of diffusion coefficients along the process trajectory was taken into account by a piecewise application of the solution in time intervals with averaged coefficients from previous time steps. Despite the simplifications made, the analytical solution gives a god insight into the selectivity of the drying process and is computationally fast. The limitations of the analytical solution and the prospect of applying the solution to the description of a nonisothermal process are discussed. It would introduce an important computational economy since the rigorous treatment of multicomponent drying leads to partial differential equations with variable coefficients, which can only be solved by time-consuming iterative procedures.

  • 3.
    Luna, Fabio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Stability of the Dynamical System describing Isothermal Gas-Phase-Controlled Drying of Ternary Mixtures1998In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 16, no 9-10, p. 1807-1825Article in journal (Refereed)
    Abstract [en]

    A stability analysis of the ordinary differential equations describing the process of convective gas-phase-controlled evaporation during drying of ternary mixtures was performed. The case considered was that of a gas flowing parallel to the surface of a flat solid, wetted with a liquid mixture, during drying at constant gas conditions. If evaporation is isothermal, the solutions of a system of ODEs are the trajectories in the phase plane represented by a triangular diagram of compositions. Analysis of the ternary mixture showed that the predicted ternary dynamic azeotropes were unstable nodes and composition trajectories moved away from them. On the other hand, some of the binary azeotropes could be stable nodes. Nodes represented by pure components could be either stable or unstable. Loading the gas with one of the components might give rise to additional critical points and might reverse or change the stability of the previous ones. The present stability analysis permits the prediction of the trajectories and final state in a gas-phase-controlled drying process. It is of great importance due to the critical influence of the composition of the remaining moisture on the quality and properties of the final product.

  • 4.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Closed-cycle drying of solids1996In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 14, no 5, p. 1041-1062Article in journal (Refereed)
    Abstract [en]

    The influence of the recovery system and other system parameters upon drying selectivity was studied in a closed-cycle dryer. A continuously-worked unit consisting of a single stage dryer and a ondenser was simulated. In the dryer, a thin solid wetted with a liquid mixture was dryed in contact with an inert gas flowing either parallelly or as an impinging jet Partial recycle of the exhaust gas was allowed. Two recovery systems were studied, a scrubber condenser and an indirect condenser. Both drying and condensation were described by a mathematical model considering a s-phase-controlled process. The inlet liquid composition in the scrubber condenser has the greatest influence on drying selectivity. Degree of vapour recovery, recycle ratio and other operational parameters ffect selectivity and equipment dimensions in a variable extent. The combined use of these variables constitutes a powerful method to control selectivity. The present models may be useful to aid the optimization of the system with regard to product quality in gas-phase-conirolled processes.

  • 5.
    Picado, Apolinar
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Mathematical Modeling of a Continuous Vibrating Fluidized Bed Dryer for Grain2012In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 30, no 13, p. 1469-1481Article in journal (Refereed)
    Abstract [en]

    A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results.

  • 6.
    Tórrez, Norvin
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), PO Box 5595, Managua, Nicaragua.
    Gustafsson, M.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Schreil, A.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Modelling and Simulation of Crossflow Moving Bed Grain Dryers1998In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 16, no 9-10, p. 1999-2015Article in journal (Refereed)
    Abstract [en]

    The drying of grain in dryers of a crossflow moving bed type was theoretically and experimentally studied. Two different dryer configurations were analyzed, a dryer with central air distribution and another with multiple air duels. Experimental information was obtained in pilot-size dryers. A mathematical model to simulate the process was developed. Hindered drying was accounted for by using the concept of relative drying rate. An adjustable factor, specific to the dryers, was used to account for the uncertainties of the contact area and the transfer coefficients encountered in the literature. Agreement between experimental results and simulations was fairly good. Simulations showed that distance between inlet air and outlet devices, air to solid flow ratio and dryer height to cross section ratio have great influence on the process. The mathematical model may be a useful tool for process exploration and optimization of this type of dryers.

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