Phenomena and Modeling of Container Pressurization Due to Thermal Decomposition of Polyurethane Foams PDF Download
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Author:
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Languages : en
Pages : 21
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Author:
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Category :
Languages : en
Pages : 21
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Author:
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Category :
Languages : en
Pages : 1
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Category :
Languages : en
Pages : 27
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In this study, polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. It can be advantageous to surround objects of interest, such as electronics, with foams in a hermetically sealed container in order to protect them from hostile environments or from accidents such as fire. In fire environments, gas pressure from thermal decomposition of foams can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of polymeric methylene diisocyanate (PMDI)-polyether-polyol based polyurethane foam is presented and compared to experimental results to assess the validity of a 3-D finite element model of the heat transfer and degradation processes. In this series of experiments, 320 kg/m3 PMDI foam in a 0.2 L sealed steel container is heated to 1,073 K at a rate of 150 K/min. The experiment ends when the can breaches due to the buildup of pressure. The temperature at key location is monitored as well as the internal pressure of the can. Both experimental uncertainty and computational uncertainty are examined and compared. The mean value method (MV) and Latin hypercube sampling (LHS) approach are used to propagate the uncertainty through the model. The results of the both the MV method and the LHS approach show that while the model generally can predict the temperature at given locations in the system, it is less successful at predicting the pressure response. Also, these two approaches for propagating uncertainty agree with each other, the importance of each input parameter on the simulation results is also investigated, showing that for the temperature response the conductivity of the steel container and the effective conductivity of the foam, are the most important parameters. For the pressure response, the activation energy, effective conductivity, and specific heat are most important. The comparison to experiments and the identification of the drivers of uncertainty allow for targeted development of the computational model and for definition of the experiments necessary to improve accuracy.
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Category :
Languages : en
Pages : 91
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Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, gas pressure from thermal decomposition of polymers can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of PMDI-based polyurethane foam is presented to assess the validity of the computational model. Both experimental measurement uncertainty and model prediction uncertainty are examined and compared. Both the mean value method and Latin hypercube sampling approach are used to propagate the uncertainty through the model. In addition to comparing computational and experimental results, the importance of each input parameter on the simulation result is also investigated. These results show that further development in the physics model of the foam and appropriate associated material testing are necessary to improve model accuracy.
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Languages : en
Pages : 20
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Author: Sarah Nicole Scott
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Category :
Languages : en
Pages : 118
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Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. It can be advantageous to surround objects of interest, such as electronics, with foams in a hermetically sealed container to protect the electronics from hostile environments, such as a crash that produces a fire. However, in fire environments, gas pressure from thermal decomposition of foams can cause mechanical failure of the sealed system. In this work, a detailed study of thermally decomposing polymeric methylene diisocyanate (PMDI)-polyether-polyol based polyurethane foam in a sealed container is presented. Both experimental and computational work is discussed. Validation experiments, called Foam in a Can (FIC) are presented. In these experiments, 320 kg/m3 PMDI foam in a 0.2 L sealed steel container is heated to 1073 K at a rate of 150 K/min and 50 K/min. FIC is tested in two orientations, upright and inverted. The experiment ends when the can breaches due to the buildup of pressure from the decomposing foam. The temperature at key locations is monitored as well as the internal pressure of the can. When the foams decompose, organic products are produced. These products can be in the gas, liquid, or solid phase. These experiments show that the results are orientation dependent: the inverted cans pressurize, and thus breach faster than the upright. There are many reasons for this, among them: buoyancy driven flows, the movement of liquid products to the heated surface, and erosive channeling that enhance the foam decomposition. The effort to model this problem begins with Erickson's No Flow model formulation. In this model, Arrhenius type reactions, derived from Thermogravimetric Analysis (TGA), control the reaction. A three-step reaction is used to decompose the PMDI RPU (rigid polyurethane foam) into CO2, organic gases, and char. Each of these materials has unique properties. The energy equation is used to solve for temperature through the domain. Though gas is created in the reaction mechanism, it does not advect, rather, its properties are taken into account when calculating the material properties, such as the effective conductivity. The pressure is calculated using the ideal gas law. A rigorous uncertainty quantification (UQ) assessment, using the mean value method, along with an analysis of sensitivities, is presented for this model. The model is also compared to experiments. In general, the model works well for predicting temperature, however, due to the lack of gas advection and presence of a liquid phase, the model does not predict pressure well. Porous Media Model is then added to allow for the advection of gases through the foam region, using Darcy's law to calculate the velocity. Continuity, species, and enthalpy equations are solved for the condensed and gas phases. The same reaction mechanism as in the No Flow model is used, as well as material properties. A mesh resolution study, as well as a calibration of parameters is conducted, and the model is compared to experimental results. This model, due to the advection of gases, produces gravity dependent results that compare well to experiment. However, there were several properties that had to be calibrated, and replacing these calibrated parameters with physically derived values is desired. To that end, Vapor Liquid Equilibrium (VLE) equations are added to the Porous Media model. These equations predict the vapor/liquid split of the organic decomposition products based on temperature and pressure. UQ for the parameters in the model as well as a sensitivity study is presented, in addition to comparison to experiment. The addition of the VLE improved temperature and pressure prediction, both qualitatively and quantitatively.
Author: Kevin J. Dowding
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Category :
Languages : en
Pages : 176
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Author: Richard Guy Hills
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Category :
Languages : en
Pages : 190
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A case study is reported to document the details of a validation process to assess the accuracy of a mathematical model to represent experiments involving thermal decomposition of polyurethane foam. The focus of the report is to work through a validation process. The process addresses the following activities. The intended application of mathematical model is discussed to better understand the pertinent parameter space. The parameter space of the validation experiments is mapped to the application parameter space. The mathematical models, computer code to solve the models and its (code) verification are presented. Experimental data from two activities are used to validate mathematical models. The first experiment assesses the chemistry model alone and the second experiment assesses the model of coupled chemistry, conduction, and enclosure radiation. The model results of both experimental activities are summarized and uncertainty of the model to represent each experimental activity is estimated. The comparison between the experiment data and model results is quantified with various metrics. After addressing these activities, an assessment of the process for the case study is given. Weaknesses in the process are discussed and lessons learned are summarized.
Author: W. D. Woolley
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Category :
Languages : en
Pages : 19
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Author: W. D. Woolley
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Category : Plastic foams
Languages : en
Pages : 43
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