José A. Rabi

Pectin Extraction from Mango Peels in Batch Reactor: Dynamic One-Dimensional Modeling and Lattice Boltzmann Simulation

Abstract A dynamic one-dimensional model accounting for pectin generation from protopectin in the solid matrix of mango peels and its degradation in both interstitial and extra-particle (i.e. reactor-filling) acid solution is proposed. The model assumes that pectin diffusive transport occurs in the interstitial fluid while eventual diffusive, thermal and pH influences in the solid phase were lumped into the kinetic coefficient of protopectin-pectin conversion. First-order kinetic was assumed to pectin degradation. Differential equations were numerically solved by adapting an in-house simulator of bioprocesses via the lattice Boltzmann method (LBM). As part of the LBM method, particle distribution functions were assigned to the pectin concentration in interstitial and reactor-filling fluid as well as assigned to the protopectin concentration in the solid phase. Equilibrium distribution functions were adopted by considering stationary solid phase, diffusive transport in interstitial fluid, and no spatial dependence in the reactor-filling fluid. Model parameters were assessed by comparing numerically simulated extraction yield curves with existing experimental data of pectin extraction using a batch reactor under either conventional or microwave heating. While the expected behavior of extraction yield curves was fairly reproduced in LBM simulations, discrepancies with respect to the experimental data can be assigned to assumptions in this preliminary model (e.g. first-order degradation kinetic and/or lumping effects into the protopectin-to-pectin kinetic). Prospective influence of slab thickness on extraction yields was also examined in LBM simulations.

Human thermal comfort: an irreversibility-based approach emulating empirical clothed-body correlations and the conceptual energy balance equation

Exergetic analysis can provide useful information as it enables the identification of irreversible phenomena bringing about entropy generation and, therefore, exergy losses (also referred to as irreversibilities). As far as human thermal comfort is concerned, irreversibilities can be evaluated based on parameters related to both the occupant and his surroundings. As an attempt to suggest more insights for the exergetic analysis of thermal comfort, this paper calculates irreversibility rates for a sitting person wearing fairly light clothes and subjected to combinations of ambient air and mean radiant temperatures. The thermodynamic model framework relies on the so-called conceptual energy balance equation together with empirical correlations for invoked thermoregulatory heat transfer rates adapted for a clothed body. Results suggested that a minimum irreversibility rate may exist for particular combinations of the aforesaid surrounding temperatures. By separately considering the contribution of each thermoregulatory mechanism, the total irreversibility rate rendered itself more responsive to either convective or radiative clothing-influenced heat transfers, with exergy losses becoming lower if the body is able to transfer more heat (to the ambient) via convection.

Numerical methods to biosystems and food engineering students: Hands-on practices and cross-disciplinary integration

While virtualization has supported many engineering sectors, it remains underexplored in agroindustrial engineering. Accordingly, hands‐on activities in numerical methods have been proposed to food and biosystems engineering students at a didactic computational laboratory. As those learning‐by‐doing tasks refer to agroindustrial problems, integration with forthcoming disciplines has been achieved and pedagogical ethos has indeed been promoted.

Development of in-house lattice-Boltzmann simulator of bioreactors for wastewater treatment: basic concepts and initial results

While computational modelling has increasingly supported wastewater bioreactor engineering, novel numerical techniques have been developed such as the lattice-Boltzmann method (LBM). With vinasse treatment as case study, this work is a first step towards a comprehensive LBM simulator of a continuous-flow anaerobic packed-bed reactor. Extensions from typical models comprise one-dimensional (besides time) dependence, species transport via convection and diffusion, and imposition of either Dirichlet or Danckwerts condition at inlet. The LBM simulator proved to be operational when simulating the bioreactor at different hydraulic retention times (HRTs). Simulated profiles show that stepwise feeding concentrations are smoothed as they are transported towards the bioreactor exit while concentrations increase or decrease in response to generation or degradation kinetics. Good fitting was observed for concentrations of acetic acid (2.1 kg-COD/m3 for HRT = 24 h) and butyric acid (1.3 kg-COD/m3 for HRT = 16 h) at the exit whereas other concentrations were numerically simulated at proper order of magnitude.

Development of an in-House Lattice-Boltzmann Simulator Towards Bioreactors for Wastewater Treatment: Underlying Concepts

Lattice Boltzmann method (LBM) has become a powerful technique to simulate bioprocesses in porous media. Based on a relatively simple dynamic 1-D model, the present work is a first step towards a comprehensive LBM simulator of bioreactor for vinasse treatment, taken as case study. Species concentrations were LBM-simulated at appropriate order of magnitude.

Lattice Boltzmann Simulation of Transport Phenomena in Food and Bioprocesses: Fundamentals and Applications

As part of ongoing research on computational modelling of agroindustrial biosystems, lattice Boltzmann method (LBM) have been applied in order to numerically simulate transport phenomena in food and bioprocesses. This paper addresses LBM simulation of two different continuousflow processes in fixed-bed equipment whose models are quite similar, namely bioaffinity chromatography and extraction of biocompounds. Considering a dynamic onedimensional model framework for those processes, LBM was implemented in D1Q2 lattice and particle distribution functions were assigned to species (adsorbate or extract) concentrations in both fluid and solid phases. Equilibrium distribution functions were set by considering diffusiveconvective transport in the fluid phase whereas the solid phase remains stationary. LBM simulations were carried out in view of existing research work on bioseparation of lysozyme and extraction of essential oil from gorse. As the governing equation for species concentration in the solid phase lacked partial derivatives with respect to the spatial coordinate, the corresponding streaming step was suppressed in the LBM code. No loss of functionality was verified and the expected shapes of breakthrough as well as extraction yield curves were suitably reproduced in all LBM simulations.