Ansys FreeFlow and EnSight: Visualizing Heat Transfer in a Stirred Tank

Hello and welcome to this session on setting up a free flow simulation involving heat transfer between the SPH elements, the fluid, and basically the wall around the fluid that's represented by the SPH elements.

Here we have imported modules for the SPH, so the modules are basically, and I can show all the ones that are available, so imported the boundary interaction statistics, density, HTC module, very important for modeling heat transfer, and the mass flow rate module.

For physics we have gravity in the negative z direction and we have basically the default fluid which is representing water and that's what we use here so relatively straightforward and then we also have a motion frame so this motion frame is for the impeller and let me hide the SPH elements here it's for the impeller in the shaft we also have baffles.

We also have a specific configuration allowing us to model water as it's being added into our domain and partially filling the tank and mixed by the action of the impeller. So basically we incorporated the motion frame, we linked the motion frame here to the impeller and to the shaft.

and I can show how the frame is configured so we have relative position for the frame motion as well as basically rotation setup for it. So it's basically set to rotation with a fixed angular velocity of 20 radians per second for this simulation.

And it runs through the whole course of the iteration of the simulation. We have a 10 second simulation as set up in the solver. So if we continue going down through the data tree, we can see the geometries that have been imported. To do that, if you go right into the tank, we have a wall.

Let me increase this a bit. So we have a wall here on the tank and then we have these different tabs for transform, mass, nothing really to change here once you import the geometry. and then for thermal you can specify either as adiabatic, so no heat transfer, or you can prescribe a temperature.

Here I prescribed a temperature of 0°C or 273 Kelvin.

So basically that means the walls of the tank are going to have a constant temperature and they will be able to exchange heat with the incoming fluid, that's water, So here we have the mass flow rate of water, 4 tons per hour, and it is added at 90 degrees C, and you can change the units to whatever unit you prefer.

The time is added from the beginning, from time 0 to 4 seconds, and then we stop after that and let the impeller mix the contents of the tank, the water. We will see how the temperature evolves over time for the fluid phase.

So that's basically it, so we don't have any volumetric inlets for this case, we only have inlet coming from the inlet surface.

And I also implemented some user processes like for the water surface for example which we will see the results Yeah, so basically that is it for the basic setup for the simulation.

If I run this for a while and I will enable the view of the SPH elements, you can actually visualize the water coming in.

For the SPH elements, I have a stride of 10, so I'm not really showing all the elements, there are more elements, but I made the nodes relatively large so that we can see them individually a little bit better.

As water pours in, it is colored by temperature, you can also color by velocity or other variables. I want to see how the temperature of the fluid elements change over time. Ansys FreeFlow has a lot of useful post-processing capabilities for plotting as well.

One of them, for example, is the temperature here. You can plot the temperature of the SPH elements.

If you want to use the count fraction in percent, you can visualize what elements have the most predominant temperature You can also visualize the time evolution for temperature, so I click these ones You won't see much because it's recalculating them here, generating the statistics curves, but we can also in the meantime try to visualize other plots.

So this is at exactly 10 seconds of simulation, so this is time specific. So let me uncheck these ones.

and then what we see here is the velocity distribution versus radial distance so I created a custom property called radial distance which is basically the distance from the center of the domain for each SPH element and then I plotted the velocity profile for these points so you can see how the velocity changes so we have a high So basically showing how much velocity each element has and how much temperature each element has.

So these are useful cross plots showing the relationship between the two, if there is any. So you can definitely see that there is some high velocity particles that have a relatively high temperature. whereas usually lower velocity particles can have high and also some low temperature as well.

So it can be a bit complicated to judge by just looking without doing more complex analysis as well So I have another cross plot here that I want to visualize which is the temperature versus the Z coordinate So the Z coordinate is the vertical coordinate So what I basically looking at is how the temperature varies as you change your depth throughout your domain So basically we can see that at lower depths close to the bottom we can have quite low temperatures and as you go up you tend to have generally higher temperatures.

So there's more colder particles near the bottom and we can actually visualize that here in our in the 3D view. We can actually see that there's a lot of like bluish elements indicating it's cooler here in the bottom which might indicate as well that mixing is not that great possibly.

We could try to improve the geometry or speed up the rotation speed of the impeller or do something else to try to prevent like cold spots, areas where mixing doesn't seem to be that great.

For Turbulent Viscosity, we can see that the mixing is quite intense in the first 4 seconds and then it kind of drops afterwards. The Turbulent Viscosity axis is here, the secondary on the left side.

Here I'm just showing the variance of different properties like velocity of the particles and temperature. They seem to follow similar trends indicating that the temperature is tied with the velocity of your fluid overall, with the variance especially.

So, basically these are some of the useful tools that we can use to understand better, and there are more of course, useful tools that we can use in Ansys FreeFlow for both pre-processing and post-processing.

in cases where we have heat transfer between the walls of a domain of a geometry and the SPH elements. So if you want to do more advanced and maybe more realistic views of the fluid and integrate other parameters maybe, One of the useful tools that Ansys has is the Ansys EnSight.

So I'll open the model in Ansys EnSight. I've already opened it. So to do that you have to go into your simulation file that was generated from FreeFlow and there is a .rocky20 file that you can open up and that will you'll be able to manipulate the SPH elements and look at different properties.

Here, for example, I have the SPH elements enabled and if you're not familiar with Ansys, I would highly recommend going through tutorials on it. So the SPH elements here are colored by temperature and there's a lot of different controls.

I'm going to edit, you can see for instance basically the SPH as it's imported from FreeFlow and I can also create some very useful what is called ISO volumes as well. I will disable this and I will, to make it easier to visualize, I will disable the tank.

And then you can see here that I'm coloring everything by turbulent viscosity. So this is a view of basically the turbulent viscosity.

And we can see that areas close to the impeller have a relatively high value I can disable the legend to make it easier to visualize Turbulent viscosity is higher near the impeller, we can also visualize velocity as well So we can see velocity higher near the impeller as well, and temperature profile.

So this temperature is around at 5 seconds. If I go further and let it calculate, we can see that the temperature has changed. So we have cooler temperatures near the bottom of the domain, and warmer temperatures surrounding. So, with FreeFlow we can do all kinds of visualizations.

So here I can change the color to either a variable or I can make it constant. So for instance, I can set the color to say kind of a light blue to make it look more realistic like water or maybe change the transparency.

So to do that I could go into edit and if I click on advanced we have the general options here. There are a lot of different options, like the opacity to make it either more transparent or less transparent. I can change that and it will automatically change because I'm not delaying updates.

And here for node, the key thing to make this kind of visualization for liquid is to display the SPH as a screen surface. We can display as spheres, but the screen surface kind of builds a surface based on the SPH elements and gives it a more realistic water-like, fluid-like view.

So if we also increase the scale by the size, we can either make it a function of a variable or not, we can vary that scale to, we can basically make it even smoother.

And one thing that is also useful here is when you create the ISO volume, you can basically use a variable to constrain where you want your ISO volume to be. So basically I chose a neighbor account which for the SPH is related to like how many neighbors each element has around it.

So here I want to pick elements that are close together, not the elements that are far apart. You can export an animation here and you can select how many frames you want. So for here I'm starting from basically frame 200 but I can actually start from frame 0 likewise.

And go back where I have no fluid yet in my tank. This provides a lot of useful tools to actually visualize your fluid flow in a more realistic way, especially for animations, especially if you're doing a presentation or something like that. It's fairly helpful.

So yeah, so these are some of the tools for pre-processing, post-processing for Ansys FreeFlow with Ansys EnSight. Please contact us at https://ozeninc.com/contact for more information.