11 August, 2020

Given the rising power-density of devices—from laptops and servers to phones and household appliances—electronics designers are under more pressure than ever to design cost-effective products that can efficiently dissipate heat. Steady-state thermal analysis is important for designing electronics that have a fixed power dissipation to ensure the system can reach the desired thermal equilibrium during standard operation or when modelling a fixed worst case power dissipation.

In this blog, we’ll define steady-state thermal analysis and illustrate a few examples of how it’s used in the electronics thermal simulation industry to design devices that run efficiently.

Steady-state thermal analysis is evaluating the thermal equilibrium of a system in which the temperature remains constant over time. In other words, steady-state thermal analysis involves assessing the equilibrium state of a system subject to constant heat loads and environmental conditions. The simplest form of steady-state analysis is linear steady-state analysis in which input parameters, such as material properties, are prescribed independent variables.

Real systems exhibit non-linear steady state behavior. Non-linear steady state analysis is where input parameters are inter-dependent. In such cases, a solver must iterate to find a steady-state solution to the governing equations that satisfies the input parameters. Examples of systems with non-linear characteristics include those with temperature-dependent thermal conductivity, radiation, or natural convection.

For many simulations, steady-state thermal analysis can be used to design and evaluate systems, even throughout the final stages of the design process. For example, steady-state thermal analysis can be used when simulating a server’s thermal state, which typically remains constant over time. Steady state thermal analysis is also beneficial when used to guide early design and prototyping efforts with quick feedback for simple models. It facilitates design decisions for typical operating conditions and acts as a baseline for transient analysis of controls and failure analysis.

**1. Prototyping and early design**

A simple model of a heat sink can be used to evaluate off-the-shelf components to decide on a heat sink that best meets the design criteria. In such a scenario, the heat sink can be placed in a full system model or flow data can be extracted from simulation or testing results to give approximate boundary conditions. For this situation, a simple steady-state analysis with prescribed boundary conditions is sufficient to compare heat sinks. The flow rate and component power are assumed to be constant. Although it is always good practice to verify design decisions with full system models and physical testing, a simple steady-state thermal analysis can provide a good starting point.

*Figure 1. A simple steady-state analysis of a heat sink*

**2. Evaluating standard operating conditions**

Another application of steady-state thermal analysis is evaluating system performance under typical operating conditions. This could be considered as a ‘Pro-Forma’ analysis, with operating conditions associated with the typical use case and normal operation. From this, design decisions can be made, and system performance predicted. Alternate design decisions can be explored and compared using 6SigmaET’s PAC manager and optimization tool to guide the design towards a system with maximum operational efficiency.

*Figure 2. Evaluate system performance under typical operating conditions*

**3. Precursor to transient analysis**

Steady-state thermal analysis can also be used as a precursor to transient thermal analysis. For example, one could be interested in a cooling failure analysis. In such an analysis, we want to see the effects of a failure in some portion of the cooling capacity of the system. Take the system below for example. Say we wanted to evaluate the system response to a failure of the top fan tray. We would first need to simulate the steady-state behavior of the system at normal operating conditions. Then, we can turn off the fan tray and run a transient simulation to evaluate the thermal response of the system following the failure. This may also involve various control systems, including fan controllers and power throttling, which can be modeled in 6SigmaET.

*Figure 3. Simulate the steady-state behavior of a system at normal operating conditions prior to transient analysis*

Steady-state analysis is the fundamental tool used to evaluate the thermal behavior of electronics systems. It can be used to guide design decisions from concept to final design. 6SigmaET is a leading electronics thermal simulation tool with the capability to evaluate electronics systems using both steady-state and transient thermal analysis.

To find out more about our steady-state thermal analysis related features, and how 6SigmaET can benefit your business, get in touch with our team here. Check out our most recent installment in our Thermal Focus Series here: Thermal Challenges and Trends in the LED Industry.

*Blog written by: Joseph Warner, Applications Engineer*

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