{"id":17392,"date":"2020-07-23T10:40:31","date_gmt":"2020-07-23T14:40:31","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/simcenter\/?p=17392"},"modified":"2026-03-26T06:12:22","modified_gmt":"2026-03-26T10:12:22","slug":"simple-thermostatic-control-in-simcenter-flotherm-xt","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/simcenter\/simple-thermostatic-control-in-simcenter-flotherm-xt\/","title":{"rendered":"Simple Thermostatic Control in Simcenter Flotherm XT"},"content":{"rendered":"\n

Transient CFD modelling is increasingly used in today’s consumer electronics design. It allows an engineer to model in-use scenarios and develop a thermal design that provides reliability but also good user experience. For wearable products, reliability based on junction temperature is unlikely to be the reason to throttle performance. As John Wilson explains in Thermal challenges for wearable devices<\/a>, an external touch temperature is likely your limit. To see how the system changes with time as the thermal power of devices are changed or as fans are switched on and off some kind of thermostatic control is required. <\/p>\n\n\n\n

A full transient CFD analysis is often computationally expensive and takes too long for development life cycles. Simple thermostatic controls that can stop the simulation when it reaches certain criteria and then restart under new conditions are useful. In Simcenter Flotherm XT 2020.1 the new Halt on Goal feature allows you to set up this type of simple thermostatic control for your CFD simulation. <\/p>\n\n\n\n

How to Use Halt on Goal Functionality as a Simple Thermostatic Control<\/h2>\n\n\n\n

The halt on goal functionality allows you to stop a transient model when a specified goal meets certain criteria. Halt on goal settings are available within a parametric study and can be changed for different scenarios. <\/p>\n\n\n\n

To represent a simple thermostatic control, you can set up a parametric study with a series of scenarios. Each scenario can have different halt on goal criteria and different model settings to throttle power or fans. Then you can initialise each solution from the end of the previous scenario.  <\/p>\n\n\n\n

Example<\/strong><\/h3>\n\n\n\n

Here\u2019s a simple example of how to set this up in Simcenter Flotherm XT using the application example Epic PC Thermostatic Control.<\/a><\/p>\n\n\n\n

It demonstrates a fan switching on and off based on the junction temperature of a critical package. <\/p>\n\n\n\n

Set up the base case first<\/strong><\/h4>\n\n\n\n

Halt On Goal is only available for transient models, so I set that up first. The intention is for the solution to stop early so I\u2019m not too worried about the Total Transient Time. <\/p>\n\n\n\n

I do need to make sure that my time steps are small enough to capture the changes in the solution. Particularly at the start of each solve when the rate of change is likely to be highest. I like to use increasing time step sizes for this purpose. <\/p>\n\n\n\n

\"Transient
Specifying transient setup in Simcenter Flotherm XT 2020.1<\/figcaption><\/figure><\/div>\n\n\n\n

Initially, the fan will be off. I want the fan to be available to switch on in later scenarios though, so I use the derating factor. I set the derating factor close to zero for the fan off condition.<\/p>\n\n\n\n

\"Flow
Specifying the flow device setup in Simcenter Flotherm XT<\/figcaption><\/figure><\/div>\n\n\n\n

Then I can set up my halt on goal criteria. First I select the goal I want to base my stop criteria on.<\/p>\n\n\n\n