Diagnóstico dos principais problemas no cultivo de hortaliças no Estado do Amazonas.

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Como previnir o tombamento em mudas de hortaliças.

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The challenging modelling of kLa in a periodic constricted small-scale tube

An extensive use in chemistry, biological and pharmaceutical laboratories is envisaged for a novel continuous screening reactor based on the oscillatory flow technology (Harvey, 2001). The basic unit of this reactor was recently presented by Harvey et al. (2003) and Reis et al. (2004) and consists in a 4.4 mm internal diameter and 350 mm long jacketed glass small-scale tube provided with smooth periodic constrictions, SPCs (Figure 1). Prediction of fluid mixing and residence time within this tube were successfully achieved with CFDs (Harvey et al. (2003) and Reis et al. (2004)), but modelling of oxygen mass-transfer coefficient forecast as a very challenging task. Physical properties, sparger and column configuration, agitation/oscillation intensity, superficial gas velocity, all affects kLa, controlling the properties of gas-phase: bubble size, bubble velocity/residence time and gas hold-up. In all, the the overall volumetric mass transfer coefficient, kLa can be affected by the mass transfer coefficient, kL or by the interfacial area, a. Previous work with this novel reactor (Reis et al., in Proceedings of 16th CHISA, 2004) demonstrated improved oxygen mass transfer rates. The modelling of kLa requires a good understand of liquid and gas-phase behaviours. The application of oscillatory flow motion to the constricted tube induced significant modification in bubbles trajectories, resulting in complex liquid-bubble mixing pattern, and made breakage and coalescence of bubbles become regular events in each cavity. Those patterns switch with the increase of mixing intensity (either by increasing the oscillation frequency and/or amplitude) in several regimes (Figure 2), in the same way as in conventional oscillatory flow reactors (OFRs): initially, bubbles move upward, but with the increase of oscillation intensity bubbles start to move downwards in certain phases of the oscillation cycle. At intensive levels of oscillation, rising bubbles are trapped within each cell for several seconds thus staying in each cavity longer due to the motion of vortices as compared with a bubble column. It was found that bubble size and hold-up contribute to the measured mass transfer enhancement but is the combination of small bubbles with the tortuous routes for bubbles to travel that promotes enhanced mass transfer. Moreover, the small-scale of the tube associated with the 1.6 mm internal diameter of the constriction walls, makes the Taylor flow of gas bubbles contribution an important variable, requiring (or not) to be considered in kLa modelling. This question is bringing into discussion

Process intensification using a meso-scale oscillatory flow reactor

Meso-technologies are currently triggering a paradigm change in the design of chemical and biochemical processes. Mass and heat transfer rates can readily be maximised in smaller, sustainable, cheaper and safer plants, whilst virtually reducing the design of (bio) process unit operations to the intrinsic kinetics of the system. A novel meso-scale reactor running with oscillatory flow mixing was recently developed in the University of Minho in collaboration with the University of Cambridge, UK. The oscillatory meso-reactor (OMR) has shown an outstanding performance for gas-liquid contacting [1] and particles suspension, and a fine control of the residence time distribution due to a superior combination of the internal reactor geometry (OMR is composed of 5 mm internal diameter tube provided with smooth periodic constrictions) and a well-proved mixing technology (i.e. oscillatory flow). Proof-of-concept experiments were carried out demonstrating the potential of the OMR in the bioprocess intensification. The time scale for the production of -decalactone by Yarrowia lipolytica in a gas-liquid-liquid system was halved and the yield of biomass on glucose nearly doubled for the aerobic growth of Saccharomyces cerevisiae in comparison with parallel trials in an aerated stirred tank fermentor [2]. The OMR is currently finding potential applications in the kg-per-day production of valueadded pharmaceutical and biopharmaceuticals. Commercial computational fluid dynamics tools have shown capable of predicting the flow patterns within the OMR, thus being valuable tools in the design of unit operations based on this new technology

On-line monitoring of multi-phase flow in a novel oscillatory screening reactor using fibre optical probes

This paper demonstrates the effectiveness of using fibre optic micro-probes for the measurement of dispersion and mixing in continuous flow within a novel screening reactor operating under oscillatory flow conditions. The unsteady tracer injection technique was used at different oscillation conditions, with oscillation frequencies from 0 to 20 Hz and amplitudes from 0 to 3 mm (centre-to-peak). Application of optical micro-probes for on-line and real-time acquisition of experimental data allowed modelling and comparison with three different well-known non-ideal models (tanks-in-series, with no backflow; differential backmixing; stagewise backmixing) and with one two-parameter flow model (a plug flow and a stirred tank reactor in series). Model parameters were found by fitting the theoretical response with experimental data in both Laplace and time domains by different methods. An intermediate mixing behaviour (between plug flow and stirred tank reactor) was achieved in that range of oscillation frequencies and amplitudes. Dispersion was found to be dependent on the oscillation conditions (amplitude and frequencies) and related with the fluid backflow and with the breaking of flow symmetry. The discrete (stagewise) backmixing model was considered as the best model representing residence time behaviour in the small-scale tube

Proof-of-concept of a novel micro-bioreactor for fast development of industrial bioprocesses

The experimental performance of a novel micro-bioreactor envisaged for parallel screening and development of industrial bioprocesses has been tested in this work. The micro-bioreactor with an internal volume of 4.5mL is operated under oscillatory flow mixing (OFM), where a controllable mixing and mass transfer rates are achieved under batch or continuous laminar flow conditions. Several batch fermentations with a flocculent Saccharomyces cerevisiae strain were carried out at initial glucose concentrations (S0) range of ~5–20 g/L and compared to yeast growth kinetics in a stirred tank (ST) bioreactor. Aerobic fermentations were monitored ex situ in terms of pH, DO, glucose consumption, and biomass and ethanol production (wherever applicable). An average biomass production increase of 83% was obtained in the micro-bioreactor when compared with the ST, with less 93.6% air requirements. It also corresponded to a 214% increase on biomass production when compared with growth in a shaken flask (SF) at S0=20 g/L. Further anaerobic fermentations at the same initial glucose concentration ranges gave the opportunity to use state-ofthe-art fiber optics technology for on-line and real-time monitoring of this bioprocess. Time profiles of biomass concentration (measured as optical density (OD))were very similar in the ST bioreactor and in the micro-bioreactor, with a highly reproducible yeast growth in these two scale-down platforms.Fundação para a Ciência e a Tecnologia (FCT

Aseptic processing of a strawberry pulp in a continuous ohmic heater: numerical simulations and model validation

Continuous food-sterilization processes often involve the flow of liquids or solid-liquid mixtures, frequently highly viscous and with non-Newtonian behaviour, in pipes and reactors. Heat treatment of such flows is complex and it is necessary to guarantee that each part of the material is adequately processed, preventing overcooking as much as possible. The use of ohmic heating technology as an alternative heating method has regained interest for complex fluids or multiphase foods

Powering process intensification in an oscillatory flow meso-reactor

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CFD simulations of RTD of a strawberry pulp in a continuous ohmic heater

A pilot ohmic heater is to be tested for the continuous aseptic processing of strawberry pulps and jams. The hydrodynamics and the fluid residence time distribution (RTD) have been experimentally investigated for Newtonian and non-Newtonian fluids (water and an industrial strawberry pulp, respectively), for several inlet flow rates. The results were obtained using Computational Fluid Dynamics (CFD) with a user-defined function (UDF) description of the fluid phase (pulp). For all of the conditions tested the fluid phase is described using the laminar flow model. The results show that the RTD is affected by the inlet flow rate but not so significantly by the process temperature. Some shortcuts and dead zones were detected in the ohmic heater specially for Newtonian fluids. The heater behaves like a piston flow with longitudinal mixing