Towards a single-phase mixed formulation of refractory castables and structural concrete at high temperatures. (June 2021)

• Record Type: Journal Article
• Authors: Moreira, M.H.; Ausas, R.F.; Dal Pont, S.; Pelissari, P.I.; Luz, A.P.; Pandolfelli, V.C.
• Is Part Of: International journal of heat and mass transfer. Volume 171(2021)
• Publication Date: 2021-06
• Subjects: Thermohygro model -- FEM -- Porous materials -- High temperature -- Sorption isotherms -- Refractory castable; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2021.121064
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Unprecedented numerical convergence study of widely used finite element model for concrete and refractory castable at high temperature. It was shown that the strategy of the numerical implementation of the sorption isotherm does not change dramatically the convergence order (both in time and space). Sensitivity analysis of the input parameters that helps the end users to decide which properties must be carefully characterized or not. Such analysis showed that the permeability is the most important quantity, followed by the thermal conductivity. A new mixed-element formulation is proposed and validated, providing a framework for extreme cases with high heating rates and strong discontinuities on the mesoscale domains properties. Abstract: Structural materials are broadly used in applications such as nuclear vessels, high-temperature processes, and civil construction. Usually, during their placing and lifespan, they may present free or chemically bonded liquid phases in their structure, demanding careful attention when exposed to high heating rates. Their behavior in such conditions is a challenging problem as it comprises numerous highly nonlinear properties (not easily measured via experimental tests), strongly coupled equations and unreliable experimental benchmarks. Nonetheless, such simulations are of great interest. This work aims to provide a numerical study, checking whether its solution indeed converges and yields reliable results. Additionally, as the model needs several input parameters, this work conducts a sensitivity analysis and also assesses its applicability to more complex scenarios, as such issues remain open in the literature. In order to do that, a simple model that can be easily adapted for mixed formulations and complex geometries was proposed. It was found out that when considering unidimensional models the choices regarding the interpolation of the sorption isotherms are not essential to the numerical stability of the system. Besides that, the permeability and thermal conductivity of the material are the most important parameters that affect the simulation results of pressure, temperature and evaporable water content profiles. Finally, the 2D mesoscale simulation of concrete with polymeric fibers (based on the mixed formulation of the problem) yielded results that agreed with experimental observations. Thus, the model proposed herein can provide a solid base for future works and also important insights towards simpler methodologies.