Transient Thermal Analysis

Transient thermal analysis determines temperatures and other thermal quantities which vary over time. In many instances, the temperatures from a transient thermal analysis are utilized as remarks for a structural analysis, which is used for thermal stress evaluations. The temperature distribution’s variation over time is useful in many practical applications such as with a quenching analysis for heat treatment or with cooling of electronic packages.

Several heat transfer applications such as electronic package design, heat treatment problems, nozzles, fluid-structure interaction problems, pressure vessels, engine blocks, etc. involve transient thermal analysis.

A transient thermal assessment can be either linear or nonlinear. Temperature dependent material properties such as thermal conductivity, specific heat or density, or radiation effects or temperature dependent convection coefficients can produce in nonlinear analysis which requires a reiterative procedure to reach accurate solutions. Most materials’ thermal properties vary with temperature and hence the analysis generally is nonlinear.

Specific heat, density and thermal conductivity need to be defined for transient thermal assessments. Thermal conductivity can be either isotropic or orthotropic. All properties need to be constant or temperature-dependent.

In a thermal analysis, any joints or springs are normally ignored and only contact is valid.

With contact, the initial status is retained all through the thermal assessment. Heat conduction is set to an adequately high-enough value across a closed contact face to form ideal contact with minimal thermal resistance. If needed, imperfect contact can be modeled by inputting a thermal conductance value manually.

If the temperature from this analysis is desired to be utilized in a consequent structural analysis, the mesh needs to be identical. Therefore you can make sure right from the beginning that the mesh is good enough for a structural analysis.

The basic controls for a transient thermal analysis are:

(a) to indicate the end time of the transient analysis,

(b) to control the time step size, and

(c) to create multiple steps when required.

The rate of loading is usually vital in transient thermal analysis when the material properties seem to be varying rapidly with temperature. Multiple steps are required if the solution settings are needed to be changed.

Output Controls let you identify the time points during which results can be available for post-processing. A transient analysis needs calculating solutions at numerous time points in the load history. However, you can throttle the amount of output by demanding results only at defined time points.

Temperature, convection, radiation, heat flow, heat flux, internal heat generation, imported temperature and imported convection coefficient are various kinds of loads supported in transient thermal analysis. The temperature results can also be used from a steady-state analysis of a similar model for the initial temperature distribution. The initial temperature is accepted as the starting temperature value for the model excepting instances where temperatures are specified explicitly.

Once a solution is accessible you can animate the results or contour the results to evaluate the response of the structure. Analysis data management settings let you save specific solution files for use in other analysis from a transient thermal analysis.