Read time: 10 minutes
Target audience: Thermal Researchers/ EV Automobile Engineers/ Thermal-Fluid Industry/ Aero Industry
Written by: Dr. Tabish Wahidi
Joule heating, also referred as Ohmic or resistive heating, occurs when an electric current flows through a conductive material. Common applications include electricity conduction, heat generation, and current regulation in power electronics. Accurately modeling Joule heating is crucial for electric and hybrid electric vehicle (xEV) components and other systems involving electrical sources and conductive materials. TAITherm’s Joule heating model simulates localized heating by applying a current or voltage source to specific shell or solid elements.
Heat generation in Joule heating depends on electrical resistance and current, with resistance influenced by resistivity, cross-sectional area, and length. Complex geometries like bus bars and connectors often have variable cross-sections, while resistivity varies with temperature, necessitating a temperature-dependent Multiphysics approach. Components of xEV where Joule heating is relevant include battery cell tabs, bus bars, wiring harnesses, fast charger connections, electronic circuits like inverters, electric motor rotor windings, radiative heaters for thermal comfort, and positive temperature coefficient heaters for HVAC systems. Other applications include exhaust catalyst heaters, windshield resistive elements for de-fogging and de-icing, heated clothing (vests, socks, gloves), heated seats, and general heating elements. Understanding the physic of Joule heating and its modeling is very critical for the effective design of a system.
TAITherm provides a 3D Multiphysics solution that accounts for temperature-dependent heat rates, accommodating complex geometries and varying thicknesses.
TAITherm uses electrical conductivity (the inverse of resistivity) to characterize electrical conduction, independent of part shapes and sizes. This allows users to define complex geometries without simplifying assumptions. The Joule heating model requires a single geometry, generating electrical nodes analogous to thermal nodes, using voltage for calculations. Heat is computed based on voltage differences and material conductivity at specific temperatures, with thermal node temperatures providing input.
This integrated approach simplifies model setup across thermal and electrical domains, supporting multiple connected parts through a continuous mesh of shell and solid elements. Contact resistance can be specified for localized heating, and multiple electrical sources and sinks can be defined for realistic circuit simulations. TAITherm’s Joule heating model integrates with other electrical models like batteries, motors, and power electronics, with thermal and electrical properties defined as scalars or curves. Electrical boundary conditions, non-conductive insulation layers, and temperature limits for parameter interpolation/extrapolation enhance model accuracy and convergence.
The Joule heating model has been validated through various geometries and electrical sources, including case studies on battery pack bus bars, inverters, heated seats, exhaust catalyst heaters, and fast charger cables. Both steady-state and transient simulations were conducted under diverse thermal and electrical conditions.
A case study of a heated seat as shown in Fig.1 is illustrates the joule heating modeling approach. The electrical setup involves applying a current curve to the seat heater geometry, with each heater having positive and negative terminals and at least one lead. The transient model runs for 4 minutes, starting at 5°C and heating up over time. The heat applied to the seat coils is generated by the Joule heating module, with imposed heat applied during periods of non-zero current.
The transient temperature behaviour of the model is shown below in Fig. 2. A highlighted case study involves a heated seat model operating over 4 minutes, starting at 5°C and heating via Joule heating in the seater coils.
An oscillating current prevents excessive heating, with heat applied during current flow and absent when current is zero (as shown in Fig. 3). This model allows designers to easily adjust boundary conditions and explore different seat designs.
TAITherm joule heating has potential integration with TAITherm’s Human Thermal Module (HTM) for comfort predictions. With HTM, comfort and sensation predictions can be done for more effective seat design.
TAITherm’s Joule heating model is versatile, capable of modeling nearly any electrical connector and accommodating 3D geometries with varying cross-sections and shapes. Tool is validated under numerous conditions, including different element types, mesh densities, and current/voltage sources, it integrates with other TAITherm electrification models for comprehensive thermal analysis. The Multiphysics approach can be combined with other electrification models in TAITherm for comprehensive thermal analysis, especially when temperature-dependent heat rates are critical. Leveraging TAITherm’s usability and speed, the Joule heating model can be integrated into full-vehicle simulations under a wide range of conditions.
To understand more about joule heating, read below blog: https://blog.thermoanalytics.com/blog/modeling-joule-heating-in-taitherm