Modeling Of Heat Transfer Phenomena Research Articles

Identification of Heat Transfer Parameters for Gravity Sand Casting Simulations

Gravity sand casting simulations require accurate modelling of heat transfer phenomena to reliably evaluate the expected quality of the produced parts. Average model parameters can be easily retrieved from a validated database. However, these parameters are highly dependent on the specific sand used and the actual forming process in the foundry. Furthermore, the heat transfer from the solidifying alloy to the mould surfaces is not precisely known, so simulation models usually use typical values for overall heat transfer coefficients. Most research works investigate individual parameters, whereas heat transfer phenomena largely arise from their interaction together. Therefore, the present work describes a combined experimental and computational method based on genetic algorithm techniques for determining the most important parameters for heat transfer in a sand mould. The experiments examine both virgin and reused sand, as these are alternatively used in the foundry for mould forming. The density, thermal conductivity, and specific heat capacity of the different sands are identified, along with heat transfer coefficients. The counterproof simulations demonstrate that the standard parameters are quite reliable for virgin sand. However, in the case of reused sand, the identified parameters lead to more reliable results.

Physics-Informed Machine Learning for Surrogate Modeling of Heat Transfer Phenomena

Abstract In this paper, we propose a sparse modeling method for automatically creating a surrogate model for nonlinear time-variant systems from a very small number of time series data with nonconstant time steps. We developed three machine learning methods, namely, (1) a data preprocessing method for considering the correlation between errors, (2) a sequential thresholded non-negative least-squares method based on term size criteria, and (3) a solution space search method involving similarity model classification—to apply sparse identification of nonlinear dynamical systems, as first proposed in 2016, to temperature prediction simulations. The proposed method has the potential for wide application to fields where the concept of equivalent circuits can be applied. The effectiveness of the proposed method was verified using time series data obtained by thermofluid analysis of a power module. Two types of cooling systems were verified: forced air cooling and natural air cooling. The model created from the thermofluid analysis results with fewer than the number of input parameters, predicted multiple test data, including extrapolation, with a mean error of less than 1 K. Because the proposed method can be applied using a very small number of data, has a high extrapolation accuracy, and is easy to interpret, it is expected not only that design parameter can be fine-tuned and actual loads can be taken into account, but also that condition-based maintenance can be realized through real-time simulation.

Thermal finite element analysis of complex heat sinks using open source tools and high-performance computing

The modeling of heat transfer phenomena in thermal systems has been extensively explored in industry and academia by using the finite element method (FEM) with commercial software. However, when the thermal problem introduces complexities in geometry and physics, the availability of licenses for high-performance computing could represent a limitation to achieving results in a reasonable time. Hence, finite element analysis (FEA) using open-source software (OSS) becomes a prominent candidate in this case. Therefore, multiple open-source tools are integrated into this work to solve the heat transfer equation, including conduction, convection, and radiation. Several geometrically complex heat sinks commonly used in the electronics industry are considered application examples. The performance of parallel computing is assessed in terms of processing time. The finite element solution engine is built by implementing the energy balance equations in their weak formulation in Firedrake, using its solver PETSc, the mesh generator GMSH and the post-processor Paraview, thus creating a fully OSS-based Python framework. Finally, the results are verified with commercial software for different case studies, and its potential to be extended to other fields of engineering is evident.

Heat transfer modeling of shrimp in tunnel type individual quick freezing system

AbstractCryogenic freezers are commonly used for quick freezing of high‐value food products at a lower temperature. These freezers offer improved overall product quality and reduced dehydration and drip losses. An accurate prediction of heat transfer during the food freezing process is useful in deciding proper production, design, handling procedure, and amount of cryogen required. In this study, computational fluid dynamics (CFD) was used for numerical modeling of heat transfer phenomena in a freezing system during individual quick freezing (IQF) of shrimp. The residence time of shrimp in the developed IQF tunnel freezer was determined using modified Plank's equation and verified by experimentations. Modeling was done in two zones of the freezer: (i) Precooling zone containing cold liquid nitrogen (LN2) vapors that were utilized for precooling of incoming shrimp and (ii) freezing zone where LN2 was sprayed on shrimp before exiting freezer. Simulations of heat transfer in shrimp were performed using the Ansys CFD software at seven different locations of the IQF tunnel freezer. Results revealed that the core temperature of shrimp decreased from 304.5 K to 263 K as it passes through the freezer. In general, as compared to other segments of shrimp, core temperature of shrimp was the highest while the top portion was minimal. Dynamics of velocity distribution, thermal profile, and spray modeling results of cryogen in the freezer supported simulation model of shrimp. Overall, numerical modeling results are consistent (≤5% variation) with experimental values.Practical ApplicationsThe cryogenic freezer is widely preferred to obtain a superior quality of frozen food products owing to minimal defects (cracking and break down), drip loss, and freezing time compared to traditional mechanical freezers. The inefficient utilization of cryogen and handling issues results in a higher cost of food products frozen with IQF technology. Thus, an insight into heat transfer phenomena in cryogenic freezers may lead to improvement in the design, efficient utilization of cryogen, reduction of freezing time, and improvement in overall product quality. In conclusion, these would aid in reducing the cost of the technology.

Detailed Model of a Thermoelectric Generator Performance

Abstract The paper deals with mathematical modeling of heat transfer phenomena occurring in a system containing thermoelectric elements. The main focus was on creating a useful computational tool for designing, validating, testing, controlling, and regulating the energy harvesting system with a thermoelectric cell. The model widely described in the literature, assuming a constant temperature level on both sides of the cell, has been modified to take into account the thermal resistance of heat exchangers that are inseparable parts of nearly every device of this kind. The results and conclusions from the solutions of equations forming a formalized record of the proposed method, the assumed approach to modeling, used physical phenomena and sensitivity analysis of the impact of the tested parameters on the system operation was presented. The calculations were made for the data of a selected thermoelectric generating cell available on the market.

Numerical modelling of skin tumour tissue with temperature-dependent properties for dynamic thermography

Dynamic thermography has been clinically proven to be a valuable diagnostic technique for skin tumour detection as well as for other medical applications, and shows many advantages over static thermography. Numerical modelling of heat transfer phenomena in biological tissue during dynamic thermography can aid the technique by improving process parameters or by estimating unknown tissue parameters based on measurement data. This paper presents a new non-linear numerical model of multilayer skin tissue containing a skin tumour together with thermoregulation response of the tissue during the cooling-rewarming process of dynamic thermography. The thermoregulation response is modelled by temperature-dependent blood perfusion rate and metabolic heat generation. The aim is to describe bioheat transfer more realistically. The model is based on the Pennes bioheat equation and solved numerically using a subdomain BEM approach treating the problem as axisymmetrical. The paper includes computational tests for Clark II and Clark IV tumours, comparing the models using constant and temperature-dependent properties which showed noticeable differences and highlighted the importance of using a local thermoregulation model. Results also show the advantage of using dynamic thermography for skin tumour screening and detection at an early stage. One of the contributions of this paper is a complete sensitivity analysis of 56 model parameters based on the gradient of the surface temperature difference between tumour and healthy skin. The analysis shows that size of the tumour, blood perfusion rate, thermoregulation coefficient of the tumour, body core temperature and density and specific heat of the skin layers in which the tumour is embedded are important for modelling the problem, and so have to be determined more accurately to reflect realistic skin response of the investigated tissue, while metabolic heat generation and its thermoregulation are not.

Modeling and Thermal Analysis of a CCP Collector System Based on Fractal Architecture: Receiver Proposal

Solar concentrator technology has been researches in different fields in order to enhancement efficiency and energy storage of these systems. Some changes in fluid and numerous components of the collectors has been proposed in recent years. In this context, this paper present results associates to the modeling and thermal analysis of a concentrating system based on parabolic through collector with receiver piper, designed with fractal geometry with the aim of improve system heat transfer. Founded on thermal modeling of heat transfer phenomena as radiation, convection and conduction, physical and mathematical relations between fractal geometrical parameters and transfer heat coefficient were established to find the influence of a chaotic structure on thermal behavior. Proposed designs were simulated through Solid works ® Flow Simulation tool. Was possible obtain maximum temperatures in air with fractal and cylindrical pipes of de 89°C, 86°C y 81°C respectively. The gap between fractal geometry results and cylindrical geometry is 10°C around.

Thermal impedance measurement of integrated inductors on bulk silicon substrate

The article presents the results of transient thermal measurements of a coil integrated in a silicon chip. Based on those measurements and using numerical procedures, thermal impedance, time constant distribution and structure functions were obtained. Next, using simple physical models of heat transfer phenomena, the 3 major time constants of the device under test were calculated, compared with measurement results and explained physically.

Efficient Estimation Of Volumetric Heat Source In Fusion Welding Process Simulation

Mathematical models of heat transfer phenomena in fusion welding process can provide important physical insight on the mechanism of weld pool development, and compute temperature field and final weld dimensions fairly reliably in several welding systems. In particular, the conduction heat transfer based numerical models are relatively simpler and computationally inexpensive in comparison to the comprehensive heat transfer and fluid flow models although the later can undertake greater physical attributes in weld pool. One significant requirement of the conduction heat transfer based models is the predetermination of a volumetric source term to account for the heat input from the welding heat source. We present here two efficient approaches to define the volumetric heat source term which do not require a-priori information of the final weld joint dimensions, which has always remained a difficult task. The first approach involves an intrinsic mapping of the heat source geometry with the numerically computed melt pool dimensions within the framework of modeling calculations in an iterative manner and is validated for the prediction of final weld dimensions in autogenous gas tungsten arc welds with butt joint geometry. The other approach involves an analytical estimation of the volumetric source term as function of only the welding conditions and the initial weld joint geometry and is examined successfully for the prediction of weld pool dimensions and thermal cycles in tandem submerged arc welds with typical groove joint geometry.

Temperature Estimation in the Combustion Chamber of an Internal Combustion Engine

The mathematical model of heat transfer phenomena is considered at the combustion chamber wall in an internal combustion (IC) engine. The mathematical model of proposed phenomena is established with respect to the crank angle. An inverse heat conduction problem is derived at the cylinder wall, and this problem is investigated numerically using Alifanov's regularization method. This problem studied as an optimization problem in which a squared residual functional is minimized with the conjugate gradient method. To show the ability of the proposed method, some test problems are considered.

Modelling of Heat Transfer Phenomena for Vertical and Horizontal Configurations of In-Pool Condensers and Comparison with Experimental Findings

Decay Heat Removal (DHR) is a fundamental safety function which is often accomplished in the advanced LWRs relying on natural phenomena. A typical passive DHR system is the two-phase flow, natural circulation, closed loop system, where heat is removed by means of a steam generator or heat exchanger, a condenser, and a pool. Different condenser tube arrangements have been developed for applications to the next generation NPPs. The two most used configurations, namely, horizontal and vertical tube condensers, are thoroughly investigated in this paper. Several thermal-hydraulic features were explored, being the analysis mainly devoted to the description of the best-estimate correlations and models for heat transfer coefficient prediction. In spite of a more critical behaviour concerning thermal expansion issues, vertical tube condensers offer remarkably better thermal-hydraulic performances. An experimental validation of the vertical tube correlations is provided by PERSEO facility (SIET labs, Piacenza), showing a fairly good agreement.

Human Thermal Model Expressing Local Characteristics of Each Segment

We discussed the present research trends of mathematical models of heat transfer phenomena within human body. In addition we introduced our mathematical model expressing local characteristics of each segment including a subroutine of calculation of physiological thermoregulatory responses. By using this computer program several simulations under various combinations of thermal environmental conditions and working levels were performed. The calculated results were agreed with the measured results and suggested the validity of the present mathematical model to evaluate human responses.

Analytical Model for Heat Transfer Phenomena in Cup-Cast Method

Cup-cast method is a new method deals with semi-solid slurry preparation recently developed by the authors. In this method, suspension of globular solid particles in molten metal is prepared by controlling the nucleation and growth of solid-particles through the simplest and quickest techniques. In this method, heat transfer phenomenon plays an important role in governing the shape, size, and fraction of solid particles. In the current study, a heat transfer model was proposed and applied to Al-A356 alloy semi-solid slurry preparation. The heat transfer model was based on heat balance consideration between cup and slurry and it was in a good agreement with experimental results.

Estimation of the atmospheric corrosion on metal containers in industrial waste disposal

Solid industrial waste are often stored in metal containers filled with concrete, and placed in well-aerated warehouses. Depending on meteorological conditions, atmospheric corrosion can induce severe material damages to the metal casing, and this damage has to be predicted to achieve safe storage. This work provides a first estimation of the corrosivity of the local atmosphere adjacent to the walls of the container through a realistic modeling of heat transfer phenomena which was developed for this purpose. Subsequent simulations of condensation/evaporation of the water vapor in the atmosphere were carried out. Atmospheric corrosion rates and material losses are easily deduced. For handling realistic data and comparison, two different meteorological contexts were chosen: (1) an oceanic and damp atmosphere and (2) a drier storage location. Some conclusions were also made for the storage configuration in order to reduce the extent of corrosion phenomena.

Modeling of Heat Transfer Phenomena with Air Existing in Fusing Region

Modeling of Heat Transfer Phenomena with Air Existing in Fusing Region

Mathematical Modelling of Heat Transfer Phenomena in Continuous Casting of Steel.

A steady-state three-dimensional heat flow model based on the concept of artificial effective thermal conductivity has been developed. On the basis of available literature information, boundary conditions to the governing heat flow equation have been applied, and the equation was solved via the control-volume based finite difference procedure. The model is sufficiently general and can be applied to various geometrical shapes of relevance to continuous casting of steel. Sensitivity of the predicted results to various numerical approximation including grid configurations, as well as to other modelling parameters such as axial conduction, mushy zone modelling procedure, choice of value of Keff have been extensively studied. It has been shown that assumptions and numerical procedures influence the computed results significantly. Finally, numerical predictions have been compared with three sets of experimental measurements reported in literature on shell thickness in industrial casters. In contrast to some earlier claims, these indicated only poor to moderate agreement between model predictions and experimental results.

MODELIZATION OF HEAT TREATMENT BY CO2 POWER LASER WITH MULTIMODAL BEAM

Based on classical solutions of the heat equation, we developed an efficient three dimensional analytical model of heat transfer phenomena. It allows to calculate the temperature fields during multiple passes surface treatment of pieces of various shapes, in particular at the beginning and at the end of a pass, were the assumption of stationary conditions can't be made. The model can also be used to evaluate the consequences of beam temporal instabilities on treatments. We found a good agreement between theoretical and experimental results. In some cases however finite difference method can not be avoided : as an example we model temperature measurements by thermocouples in the HAZ.

Adiabatic-isothermal mixed boundary conditions in heat transfer

Mixed boundary conditions of the adiabatic-isothermal type often arise in the mathematical modeling of heat transfer phenomena. Under certain circumstances, the mixed condition gives rise to singular behavior which cannot be adequately treated by numerical means alone. The numerical procedure must be supplemented by an asymptotic analysis for the local behavior near the singularity. In the special case of a mixed boundary condition on a straight boundary, the strength of the singularity is given in terms of a path-independent integral, the value of which can be determined from the numerical solution for the far-field behavior. Implications of overlooking the singular behavior due to the mixed boundary condition are discussed.