Prediction Of Temperature Evolution Research Articles

Numerical investigation of artificial ground freezing–thawing processes in tunnel construction

Artificial ground freezing is a frequently used method for temporary support of the soil in geotechnical interventions, such as tunneling. Besides the time required to form a supporting frozen soil structure during freezing, the prediction of temperature evolution during the thawing process and the final thawing time are also relevant, since settlements induced by thawing of the frozen soil can pose a risk to sensitive structures in urban tunneling. The freezing and thawing process of soils depends strongly on the unfrozen liquid content. The unfrozen liquid content during the freezing and thawing cycles is known to have a pronounced hysteresis response, whose effect on the temperature distribution and groundwater flow, especially at the structural level has not been extensively studied. In this work, we present a thermo-hydraulic finite element model for freezing soils and incorporate the hysteresis behavior of soil. We aim to investigate the suitability of the presented numerical model for tunnel construction on the one hand, and quantify the extent of the influence of the hysteresis response of the unfrozen liquid content at the structural level on the other. To this end, the model is first validated with the help of experimental data from a soil test subjected to a freezing–thawing cycle and subsequently used to analyze three problems of artificial ground freezing in tunnel construction during the freezing phase or freezing–thawing phases. The results show a good agreement with the experimental measurements. We show that the computational model is capable of providing accurate prognosis of the temperature profile as well as broader metrics such as the thickness and shape of the frozen body for tunneling applications under hydrostatic and seepage flow conditions. The hysteresis response is shown to have a significant influence on the coupled thermo-hydraulic process, with thawing times differing depending on whether hysteresis is considered. It is concluded, that the inclusion of the hysteresis response is crucial for obtaining an accurate representation of the freezing process.

Anisotropic and homogeneous model of heat transfer for self-heating ignition of large ensembles of lithium-ion batteries during storage

Self-heating ignition is a fire hazard in warehouses when stacking large quantities of reactive materials for storage, including lithium-ion batteries. Due to the heavy costs and dangerous fire risks, the thermal behaviour of large-scale LIB ensembles is usually studied by numerical methods. The state-of-the-art self-heating models on LIBs are either too computationally expensive to be applied to the predictions of large LIB ensembles, or capable of large ensemble predictions but missing important heat transfer characteristics like insulation in packaging. Based on four-step kinetics from the literature (Solid electrolyte interphase decomposition, negative-electrolyte reaction, positive-electrolyte reaction, and electrolyte decomposition), we have developed a 3D anisotropic homogeneous (Ani-Hom) transient heat transfer model that can incorporate complex packaging and is numerically affordable for large ensemble predictions based on COMSOL Multiphysics. The effect of packaging insulation is considered by using weight-averaged thermophysical properties and directional thermal conductivities. Lithium Cobalt batteries (LCO) are used as a case study. This Ani-Hom model was verified by comparing a box-scale simulation against an isotropic heterogeneous (Iso-Het) model from the literature. Both the predictions of temperature evolution and the heat generation agreed to within 5%, while the computational time of the Ani-Hom model is one order of magnitude lower than the Iso-Het model. The Ani-Hom model is then applied to LIB ensembles in four possible storage sizes, ranging from a single cell to a rack with around 10 million cells, with different packing configurations and spacing between cells. The model predicts that the presence of packaging insulation promotes self-heating ignition. A rack of this LCO LIBs is predicted to self-ignite at an ambient temperature of 45℃, which indicates that LIBs in a warehouse are vulnerable to fire hazards in warm environments. The presence of defects or abuse will even lower this critical ambient temperature. This work provides insights into the effects of complex insulation and spacing on self-heating ignition of LIBs during storage and contributes to a better understanding which can help mitigate such fires.

Conjugate unsteady natural heat convection of air and non-Newtonian fluid in thick walled cylindrical enclosure partially filled with a porous media

A numerical study describes the conjugate unsteady natural heat convection of air on top of a non-Newtonian polymer-water solution characterized by a power-law model within a sealed vertical thick-walled cylindrical enclosure partially filled with a porous media in the lower section. Enzymes immobilized in an inorganic polymer, silica, used in synthesis processes constitute the porous media. Heating is by a constant high temperature at the bottom and at the vertical walls while the upper horizontal wall remains at the initial cold temperature. The Finite Volume Method allows the solution of the continuity, linear momentum and energy equations for a power law shear thinning fluid in a porous media with the Darcy-Brikman-Forchheimer model. The evolution of fluid mechanics of air and of the non-Newtonian fluid is described by the history of the streamlines. Transient heat transfer by conduction in the sealed tube walls and by natural convection of air and in the non-Newtonian fluid flow in the porous media is characterized by the evolution of isotherms. Experimental results are used to verify that the natural convective heat transfer conjugate computational model allows the prediction of temperature evolution in a thermal resistance challenge for free and immobilized enzymes. A difference of 1% is found between the experimental and the numerical results for the temperature history during the immobilized enzyme convective heating process. The applied numerical method has the capability of designing the enzyme temperature challenge test, by predicting the time needed to reach the uniform target temperature for biocatalyst processing, 500 s, in agreement with the experimental findings. The computational model contributes to the development of a technique to describe the kinetics of both immobilized and free enzyme during heating. This is a key issue for several industries, such as food modification, biofuel development, agroindustry and fishery waste valorization, that require enzymes operating at high temperature ranges in a reliable way for a long time.

An efficient thermal evolution model for cryoablation with arbitrary multi-cryoprobe configuration

Cryoablation has been demonstrated powerful in treating of a variety of diseases, especially for the tumor ablation, which destroys the target tissue through the controlled freezing of cryoprobe. The prediction of temperature evolution during cryoablation is of great importance for developing and improving clinical procedure. This paper presented an efficient thermal model to characterize the freezing effect of cryoprobe with arbitrary layout including its size, orientation and number. The key step of the presented model is to establish a boundary heat source method to implicitly characterize the heat transfer from cryoprobe with fixed temperature or convective heat transfer boundary condition, which is furthermore incorporated to a fast parallel alternating direction explicit (PADE) finite difference method for computation acceleration. A novel dynamical and conformal computational region is designed through the shortest distance definition to balance the thermal effect of tissue and computational efficiency. The detailed test cases including a real head tissue demonstrated that the current model can accurately predict the temperature field evolution induced by arbitrary multi-cryoprobe configuration, and achieve significant computational ability due to allowable large time step (100-fold compared with the explicit finite difference method), compact computational region (at least reducing 40% number of voxels) and high parallel efficiency (speedup ratio about 8 for 12 threads) for complex tissue structure.

Application of infrared thermography in the characterization of voids and honeycomb in concrete structure

Purpose – The purpose of this paper is mainly the quantitative and the qualitative analysis of a reinforced concrete slab containing two types of delaminations: voids and honeycomb, with different sizes and depths. Design/methodology/approach – In this paper the paper adopts the infra-red thermography as a sounding method. It is used as a tool to estimate the change in temperature or thermal contrast induced by the presence of a defect in specimen besides using numerical simulation based on FEM to develop the prediction of temperature development in concrete structure. Findings – This study shows that the numerical methods can be used to evaluate and validate the experimental results. The coupling of the simulation and the experimentation can be of a great utility because it allows predicting the results before beginning the experimentation. Originality/value – The paper finds that the use of FEM in the prediction of temperature evolution in concrete, and the validation of the numerical simulation with the results obtained by the experimental measurements have a key importance in the study of civil engineering structure.

Response of NSTX liquid lithium divertor to high heat loads

Samples of the NSTX Liquid Lithium Divertor (LLD) with and without an evaporative Li coating were directly exposed to a neutral beam ex-situ at a power of ∼1.5MW/m2 for 1–3s. Measurements of front face and bulk sample temperature were obtained. Predictions of temperature evolution were derived from a 1D heat flux model. No macroscopic damage occurred when the “bare” sample was exposed to the beam but microscopic changes to the surface were observed. The Li-coated sample developed a lithium hydroxide (LiOH) coating, which did not change even when the front face temperature exceeded the pure Li melting point. These results are consistent with the lack of damage to the LLD surface and imply that heating alone may not expose pure liquid Li if the melting point of surface impurities is not exceeded. This suggests that flow and heat are needed for future PFCs requiring a liquid Li surface.

Prediction of temperature evolution during the extrusion of 7075 aluminium alloy at various ram speeds by means of 3D FEM simulation

In the present work, an attempt was made to predict the temperature evolution during the extrusion of 7075 aluminium alloy by means of 3D FEM computer simulation. Results show that ram speed has a significant influence on the temperature distribution in the billet, which continuously changes throughout the process, as a result of complex heat generation and heat loss. The thermal effect results in characteristic variation of extrusion pressure. At a higher ram speed, the decrease of extrusion pressure is faster during the steady-state extrusion, due to more heat generation, less heat loss and thus more steeply decreased flow stress, as the process proceeds. The temperature inhomogeneity on the cross-section of the workpiece entering the die bearing is more pronounced when ram speed is higher. While going through the die, the extrudate undergoes a process of temperature redistribution and the temperature becomes more homogeneously distributed at the die exit. The present simulation does not render support to the general statement that the corner of the extrudate is hotter than the flat surfaces. Incipient melting is predicted to occur after a half of the billet is extruded at a ram speed as low as 1 mm/s corresponding to an extrusion speed of 0.48 m/min, if the billet contains the phases with low melting points. However, if the billet of the same alloy is in an improved metallurgical condition, no melting-related defects would be expected to occur to the extrudate running at a speed eight times faster. The results also confirm the linear relationship between the increase of the maximum temperature and logarithmic ram speed during the steady-state extrusion.

Prediction of temperature evolution by FEM during multi-pass hot flatrolling of aluminium alloys

In rolling, deformation is applied by a series of passes, which arenecessarily separated by holding periods between passes. The formation of thetemperature profile therefore has a complex history. Accurate information onthe time variation of temperature is essential for predicting microstructuraldevelopment during hot working conditions and for the design of anacceptable rolling pass schedule. In the present paper, the finite-elementmethod is employed to compute temperature changes under both laboratoryand industrial breakdown rolling conditions. The calculated results are thencompared with temperature records extracted from the literature. Thedifference between laboratory and industrial rolling is discussed. By usinginverse analysis methods, appropriate heat transfer coefficients can beascertained.