Wednesday, 6 August 2014

How effective is your insulation?

As an applications engineer, I’m often asked by customers to give advice on how to test designs using SOLIDWORKS. One of the most recent examples that demonstrates how quick and easy SOLIDWORKS makes this process related to testing how effective a layer of insulating material for an oven was.

The customer designs and manufactures insulation components to be used in industrial ovens and wanted to assess how effective those components were ate shielding the outer surfaces of the oven from the temperatures achieved within.

SOLIDWORKS Simulation Professional gives you the ability to run a Thermal analysis which can be carried out under a large range of conditions and on complex model geometry. But without the lengthy operation of setting up and running an analysis on a complex fully accurate model, here’s a tip on running that all important first test to see if the components and the material properties meet some basic criteria.
Firstly, simplify the study by only including what you have to for the moment.

I have done this by only including what I am interested in with regards to heat transferring from the inside of the oven to the outside face. This leaves me with as sandwich of materials representing the internal wall of the oven, the layer of insulating material and then the outside skin of the oven.

By reducing the information that you are including in any simulation study, you will in turn reduce the complexity of the study and therefore the time taken to mesh and run the study. Also, with less geometry to consider, the mesh used to describe your study can be made from smaller elements.

The next step after generating a suitable model for your study is to create the study (or mathematical model) itself.

If you haven’t already, make sure that your SOLIDWORKS Simulation add-in is turned on by going to Tools – Add-ins.

SOLIDWORKS Simulation is fully integrated into the user interface enabling you to dynamically move between modelling and simulation without skipping a beat.

On the Simulation tab on the command manager simply choose to create a new study and select the type of study that you would like to perform. Depending on the level of Simulation package that you have, only the study types available to you will be shown at this point. For this example, I would like to perform a Thermal study.

 A study tree is generated in the feature tree / property manager area of the user interface and this allows you to keep track of and modify your study. To speed things up even further, most functionality for controlling and running your study can now be accessed by right-clicking the relevant item in the study tree.

 All of my materials have been transferred over from my SOLIDWORKS model including the customer material properties that I have added for my insulation material. Also because my basic layers of material are all coincident, they will automatically have a bonded connection defined in the study.

For this particular study, I would like to test the oven when it is running at a temperature of 210 degrees Celsius over the period of an hour and it will probably take a few minutes to heat up. SOLIDWORKS Simulation Professional gives you the option to change the properties of the study to make it transient and to specify both the overall time and the increments to be tested by right clicking the study and choosing properties.

I've chosen to run the study for 3600 seconds at 60 second increments.
Now what I need to do is apply the variables to my study. By right-clicking the Thermal Loads section of the study tree, I get the options to add Temperature, Convection, Heat Flux & Power, or Radiation values.

To start, I would like to define what temperature the components are at the moment. To do this, I’ll create a temperature load as an initial value for all solid bodies of 25 degrees Celsius.

 I’ll then represent the heat on the inside of the oven by adding a Temperature load to the face that represents the inside of the oven and setting it at 210 degrees Celsius. But as I said, it will take time for the oven to achieve this, so I’ll click the edit button in the Variation with Time section of the properties.

Here I can set the time that the temperature source takes to reach particular values. I’ll set this to reach full temperature at 300 seconds (5 minutes).

One last thing before I run the study, I’ll specify that the outer face of the oven is subject to convection into the surrounding atmosphere. This is applied as a Thermal Load onto the outside face.

I’ll select the correct face and then add my Convection Coefficient and Bulk Ambient Temperature. A Coefficient of 5-25 W/m^2.K will represent natural convection into the surrounding atmosphere (i.e. no assistance). So a value of 20 should represent a well-ventilated area. You can also switch unit settings if it is easier for you, but 298.15 Kelvin works out at 25 degrees Celsius.
At this point you can specify any mesh size that you would like. But for this study I will simply use the default mesh size that SOLIDWORKS Simulation generates based upon the physical geometry. To save myself a couple of clicks, I can use the default mesh and run the study at the same time by right clicking the top of the study tree and selecting Run.

Due to the simplified model geometry and using lightning fast solvers, this study takes no time at all to solve.

I can analyse these results using a range of tools including Probe which is accessed through right-clicking the result plot. This enables me to analyse the results on just the face representing the outside of the oven and I can see that the temperature is reasonably low compared to the inside of the oven and I can check this information against my design requirements.

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