Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento Cientfíico e Tecnológico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de Nvíel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)

Influence of stiffness on CHF for horizontal tubes under LPLF conditions

Studies reported in the past on critical heat flux (CHF) are mostly limited to vertical flow, large channel diameter, high pressure and high mass flux. Since horizontal flow is commonly encountered in boiler tubes, refrigerating equipments and nuclear reactor fuel channels (PHWR), there is a need to understand horizontal flow CHF, generate sufficient experimental database and to develop reliable predictive method. Few studies are reported on the effect of upstream flow restrictions on flow instabilities and CHF. The present work investigates the effect of upstream flow restriction on CHF in horizontal flow at near atmospheric pressure conditions. In the present study, stiffness is defined as the ratio of upstream flow restriction pressure drop to the test section pressure drop. The classification of a flow boiling system as soft or stiff on the basis of quantification of the stiffness is attempted. Experimental data shows an increase in the CHF with the increase in the stiffness for a given initial mass flux. A correlation for the prediction of CHF under various stiffness conditions is developed. A correlation is suggested to predict the mass flux at CHF as a function of stiffness and initial mass flux. Modeling and transient analysis of the stiffness effect on CHF is carried out using the thermal hydraulic system code RELAP5. The predicted phenomena are in agreement with the experimental observations. (C) 2014 Elsevier B.V. All rights reserved

Development, validation and application of multi-point kinetics model in RELAP5 for analysis of asymmetric nuclear transients

Point kinetics approach in system code RELAP5 limits its use for many of the reactivity induced transients, which involve asymmetric core behaviour. Development of fully coupled 3D core kinetics code with system thermal-hydraulics is the ultimate requirement in this regard; however coupling and validation of 3D kinetics module with system code is cumbersome and it also requires access to source code. An intermediate approach with multi-point kinetics is appropriate and relatively easy to implement for analysis of several asymmetric transients for large cores. Multi-point kinetics formulation is based on dividing the entire core into several regions and solving ODEs describing kinetics in each region. These regions are interconnected by spatial coupling coefficients which are estimated from diffusion theory approximation. This model offers an advantage that associated ordinary differential equations (ODEs) governing multi-point kinetics formulation can be solved using numerical methods to the desired level of accuracy and thus allows formulation based on user defined control variables, i.e., without disturbing the source code and hence also avoiding associated coupling issues. Euler's method has been used in the present formulation to solve several coupled ODEs internally at each time step. The results have been verified against inbuilt point-kinetics models of RELAP5 and validated against 3D kinetics code TRIKIN. The model was used to identify the critical break in RIH of a typical large PHWR core. The neutronic asymmetry produced in the core due to the system induced transient was effectively handled by the multi-point kinetics model overcoming the limitation of in-built point kinetics model of RELAP5 and standalone 3D core kinetics codes. (C) 2016 Elsevier B.V. All rights reserved

Implementation and validation of the condensation model for containment hydrogen distribution studies

This paper aims at the implementation details of a condensation model in the CFD code FLUENT and its validation so that it can be used in performing the containment hydrogen distribution studies. In such studies, computational fluid dynamics simulations are necessary for obtaining accurate predictions. While steam condensation plays an important role, commercial CFD codes such as FLUENT do not have an in-built condensation model. Therefore, a condensation model was developed and implemented in the FLUENT code through user defined functions (UDFs) for the sink terms in the mass, momentum, energy and species balance equations together with associated turbulence quantities viz., kinetic energy and dissipation rate. The implemented model was validated against the ISP-47 test of TOSQAN facility using the standard wall functions and enhanced wall treatment approaches. The best suitable grid size and the turbulence model for the low density gas (He) distribution studies are brought out in this paper. (C) 2014 Elsevier B.V. All rights reserved

Failure probability evaluation of passive system using fuzzy Monte Carlo simulation

Passive systems have become an inherent feature of the advanced reactors. The main reason being the passive systems are, theoretically, more reliable than the active ones. Nevertheless the passive system may fail to fulfill its mission not only because of a consequence of classical mechanical failure of component (passive or active) of the passive system, but also due to the deviation from expected behavior due to physical phenomena mainly related to thermal hydraulic or due to different boundary or initial conditions. In this paper the methodology used for performing the passive system reliability analysis has been discussed. A case study on passive decay heat removal system (PDHRS) of large sized pressurized heavy water reactor (PHWR) has been discussed. Thermal hydraulic analysis have been carried out by using RELAP5 code to generate the response surface (from various ranges of identified key parameter values), keeping the criterion as clad surface temperature exceeding certain critical value. Some uncertainties, due to incomplete information, cannot be handled satisfactorily in the probability theory and the fuzzy set theory is more appropriate. In this study the random variables are considered as fuzzy numbers and the fuzzy set theory is employed. In addition, the Monte Carlo simulation technique is utilized to evaluate the probability of failure of system. (C) 2011 Elsevier B.V. All rights reserved

Hougaard process stochastic model to predict wall thickness in Flow Accelerated Corrosion

Nuclear Power Plants (NPPs) operate at very high temperature and high fluid mass flow rate which are favourable for Flow Accelerated Corrosion (FAC) resulting in wall thickness reduction in pipes, bends and other geometries. The prediction of progressive reduction in pipe wall thickness is required for safety of operating NPP. In this paper, Hougaard process stochastic model is proposed for prediction of wall thickness reduction in pipes between two consecutive in-service-inspections. The probability distribution function (PDF) for the Hougaard process is computationally unstable near the origin. Hence, its saddle point approximation was used along with method of maximum likelihood (MLE) to derive the mathematical expressions for the three parameters with generally given time interval between in-service-inspection and corresponding changes in wall thickness. The gamma process model fit and linear fit to data have also been carried out. The predictions of change in pipe wall thickness from probabilistic model are validated by using (a) Experimental data for FAC for 58 bend pipe and (b) NPP feeder pipe data on FAC. The results compare well with the experimental and field data used in analysis. (C) 2018 Elsevier Ltd. All rights reserved

Measurement of Steady-State CHF in Horizontal Channels for Low-Pressure, Low-Flow Conditions

Experimental investigations on critical heat flux (CHF) are mostly on vertical channels involving high mass fluxes and high system pressures. Reported studies on CHF in horizontal flow channels under low-pressure, low-flow (LPLF) conditions are limited. Understanding CHF is essential in the design and operation of heat exchangers and heat-generating devices including fuel channels of nuclear reactors. The present work investigates CHF in horizontal tubes for low steady flow at atmospheric pressure conditions. Appearance of a "red hot" spot on the test section is considered to be the occurrence of critical heat flux condition in this study. Present data could not be predicted using the reported method of applying a correction factor for the vertical lookup table data. A correlation using the experimental data is developed incorporating the fluid-to-fluid modeling parameters for the prediction of CHF in horizontal channels under LPLF conditions. Numerical study using thermal hydraulic system code RELAP5 suggests liquid film dryout as the mechanism of CHF occurrence in the present investigations

Steam drum process dynamics and level control of a pressure tube BWR

The Advanced Heavy Water Reactor (AHWR) is a pressure tube type light water cooled heavy water moderated Boding Water Reactor (BWR) with natural circulation at all power levels It has parallel inter connected loops with 452 boding channels in the Main Heat Transport (MHT) system configuration These multiple (four) interconnected loops influence the Steam Drum (SD) level control adversely Such a behavior has not been reported in the open literature The M HT configuration has been chosen based on comprehensive overall design requirements and certain Postulated Initiated Events (PIEs) This does not allow the partitioning of the Common Reactor Inlet Header (CRIH If partitioning of the CRIH into four segments is allowed then, it will make each loop independent Then the SD level control problems subside as the unaccounted interaction among the loops is eliminated It has also been observed that the open loop response is stable, non-oscillatory and non diverging for a step change in the feed flow rates A conventional individual 3 element SD level controller cannot account for the highly coupled and interacting behaviors, of the four loops and SD levels To overcome these interactions It is proposed to inter connect all the four steam drums in the liquid and vapor regions respectively The influence of the interconnect configuration and the level controller are studied in detail to find a robust solution The response obtained for unsymmetrical core power disturbances shows that the SD levels do not diverge and quickly settle to the set points assigned with SD interconnect The proposed scheme also works well for most of the PIEs considere