Transient Three-dimensional Heat Transfer Model Research Articles

Heat transfer in phase change materials for integrated batteries and power electronics systems

An integrated batteries and power electronics system has great potential in improving the compactness, flexibility and multifunctionality in electrical vehicles. However, it needs to overcome thermal management challenges due to different operation temperatures of batteries and power electronics. To tackle this issue, this paper presents the first systematic study on the heat transfer characteristics in phase change materials (PCMs) based thermal management system sandwiched between two significantly different constant heat sources, through an experimentally validated transient three-dimensional heat transfer model. All key parameters of PCMs affecting the system are identified through a new dimensionless formulation, including the ratio of horizontal and vertical thermal conductivity kxy and kz, the aspect ratio (ratio of thickness and length), and Jakob number Ja (ratio of sensible heat and latent heat). Modelling results show that the system operation duration τd increases monotonically with the increase of kxy. However, increasing kz is not always benificial for τd and there is an optimal value for kz when keeping kxy unchanged. In addition, the increase of PCMs thickness can prolong τd monotonically. The reduction of Ja, e.g. increasing latent heat, is always beneficial for τd.

Numerical study on the air-cooled thermal management of Lithium-ion battery pack for electrical vehicles

A Lithium-ion battery is one of the most common batteries being widely used as the power source in Electric Vehicle (EV) due to its high energy density, power density, long life span and environment friendly. Due to the high power requirement of EV, thousands of cylindrical Lithium-ion battery cells are typically connected in parallel and/or series forming a battery pack. This significantly generates enormous heat through the internal resistance effect and exothermic reactions inside the battery during the charge or discharge process. If the fetal heat cannot be dissipated sufficiently, the battery cells may encounter capacity fade, thermal runaway and instability issues. Thus, efficient thermal management of the Lithium-ion battery pack is essential to restrain high temperature and non-uniformity of temperature in the battery pack. This issue remains a challenge, although much research has been conducted on this topic. In this work, the air cooling thermal management system is numerically investigated due to lower manufacturing cost, simple layout requirements and higher reliability of the system. A transient three-dimensional heat transfer model of the cylindrical Lithium-ion battery pack is developed to study the effect of the inlet velocity, discharge rate and cell arrangement structure on the cooling performance. The proposed system is designed to minimize the maximum cell temperature and the cell temperature uniformity. The simulated results can be further applied as a reference in designing the structures of the battery pack and planning the cooling strategies.

Online Modelling of Heat Transfer, Solidification and Microstructure in Continuous Casting of Steel

Advanced numerical simulation models for continuous casting of steel were developed in Finland by Casim Consulting and Aalto University in cooperation with the University of Oulu and the steel industry. The aim was to develop models that are scientifically rigorous, but also computationally fast enough to be used in online applications. The models developed are a transient three-dimensional heat transfer model, CastManager, and a solidification and microstructure model, IDS. The computing time of these models are short, and they are integrated together in one online concept. This concept is installed in the automation systems of four slab casters in Finland. Testing and validation work is in progress. The system simulates the important heat transfer, solidification and microstructural phenomena in continuous casting online. The future aim is that this information will be used for online quality control and for optimizing the process conditions to avoid formation of defects. Many quality indices have already been developed. A steady state version of the CastManager tool has also been developed, called Tempsimu.

An alternative approach to thermal analysis using inverse problems in aluminum alloy welding

PurposeThe purpose of this article is the determination of the temperature fields in a weld region has always been an obstacle to the improvement of welding processes. As an alternative, the use of inverse problems to determine the heat flux during the welding process allows an analysis of these processes.Design/methodology/approachThis paper studies an alternative for the thermal analysis of the tungsten inert gas welding process on a 6,060 T5 aluminum alloy. For this purpose, a C++ code was developed, based on a transient three-dimensional heat transfer model. To estimate the amount of heat delivered to the plate, the specification function technique was used. Lab experiments were carried out to validate the methodology. A different experimental methodology is proposed to estimate the emissivity (radiation coefficient).FindingsThe maximum difference between experimental and numerical temperatures is lower than 5 per cent. The determined emissivity value for the aluminum 6,060 T5 presented a good agreement with literature values. The thermal fields were analyzed as function of the positive polarity. The specification function method proved to be an adequate tool for heat input estimation in welding analysis.Originality/valueThe proposed methodology proves to be a cheaper way to estimate the heat flux on the sample. The estimated power curves for the welding process are presented. The methodology to calculate the emissivity (radiation coefficient) was validated.

The use of non-linear inverse problem and enthalpy method in GTAW process of aluminum

This work presents an alternative approach for the thermal analysis of the GTA (Gas Tungsten Arc) welding process on a 6065 T5 aluminum alloy. For this purpose, a C++ code was developed, based on a transient three-dimensional heat transfer model with phase change and mobile heat source. The thermal model took into account the dependence of thermal properties on temperature and heat losses by convection and radiation. The convection heat transfer coefficient and the emissivity were also considered variables with the temperature. To estimate the amount of heat delivered to the plate, the BFGS (Broydon–Fletcher–Goldfarb–Shanno) technique was used. Moreover, an analysis of the duration time of the electrode in positive (t+) and negative (t−) polarities was carried out. The methodology was validated by accomplishing lab controlled experiments. The aluminum samples lay on four conical head screws and submitted to a heat flux on one surface by the GTAW process torch. The torch displaces along the sample, thus simulating a real process. The numerical results presented low deviation when compared to the experimental results, which in turn, confirm the validation of the methodology for the study of the welding process presented.

Transient Three-Dimensional Heat Transfer Model of a Solar Thermochemical Reactor for H2O and CO2 Splitting Via Nonstoichiometric Ceria Redox Cycling

A transient three-dimensional heat transfer model is developed for a 3 kWth solar thermochemical reactor for H2O and CO2 splitting via two-step nonstoichiometric ceria cycling. The reactor consists of a windowed solar receiver cavity, counter-rotating reactive and inert cylinders, and insulated reactor walls. The counter-rotating cylinders allow for continuous fuel production and heat recovery. The model is developed to solve energy conservation equations accounting for conduction, convection, and radiation heat transfer modes, and chemical reactions. Radiative heat transfer is analyzed using a combination of the Monte Carlo ray-tracing method, the net radiation method, and the Rosseland diffusion approximation. Steady-state temperatures, heat fluxes, and nonstoichiometry are reported. A temperature swing of up to 401 K, heat recovery effectiveness of up to 95%, and solar-to-fuel efficiency of up to 5% are predicted in parametric studies.

Development of Artificial Neural Network based heat convection algorithm for thermal simulation of large rectangular cross-sectional area Earth-to-Air Heat Exchangers

An Earth-to-Air Heat Exchanger (ETAHE) is a low energy cooling and heating building component. It uses the ground's thermal storage to dampen ambient air temperature oscillations by delivering the air through a horizontally buried duct. To reduce airflow resistance, some hybrid ventilated buildings have recently adopted large cross-sectional area ducts. This paper describes the development of an Artificial Neural Network based Heat Convection (ANN-HC) algorithm to predict local average Nusselt Numbers along the duct surfaces. Furthermore, the ANN-HC algorithm is integrated with a transient three-dimensional heat transfer model based on finite element analysis of heat conduction in the ground domain surrounding the ETAHE to establish a new thermal modeling method for ETAHEs. A case study is presented to demonstrate the working principle of the new method. It is shown that the method can very well simulate the interactions between an ETAHE and its environment.

A transient three-dimensional heat transfer model of the human body

The objective of this work is to develop an improved model of the human thermal system. The features included are important to solve real problems: 3D heat conduction, the use of elliptical cylinders to adequately approximate body geometry, the careful representation of tissues and important organs, and the flexibility of the computational implementation. Focus is on the passive system, which is composed by 15 cylindrical elements and it includes heat transfer between large arteries and veins. The results of thermal neutrality and transient simulations are in excellent agreement with experimental data, indicating that the model represents adequately the behavior of the human thermal system.

A Multi-Purpose Test Chamber for the Assessment of Building Envelope Thermal Performance

Full-scale field measurements under actual weather conditions are considered a realistic approach for the measurement of energy consumption and the assessment of building envelope performance. In this paper, a description of a simply constructed outdoor test chamber is presented; and the requirements for temperature, solar radiation, wind speed, and wind direction measurements are outlined. A simple experimental procedure for evaluating window energy consumption is described. Other aspects such as instrumentation, equipment, data measurements and recording are also addressed. Some of the field measurements obtained were compared with results from a transient three-dimensional heat transfer model and a good agreement was found.

Importance of skin temperature in the regulation of sweating.

Human sweating regulation at rest, evaluating thermal inputs effects on thermoregulatory center and internal hypothalamic and skin temperatures