### All posts by Walter Frei

## Modeling a Coil Heat Exchanger

##### Walter Frei | August 21, 2014

Coil heat exchangers are simple and easy to manufacture. Here, we consider an axially wound coil of copper carrying hot water that heats air inside of a circular duct. Since the geometry is almost invariant about the centerline, the model is solved in the 2D axisymmetric plane. Additional expressions are added to compute the temperature drop between turns of the coil, which greatly simplifies the modeling.

Read more##### Walter Frei | July 14, 2014

Whenever modeling magnetic fields in steady-state, transient, or frequency domain with the AC/DC Module, we want to reduce the size of the model as much as possible to minimize the computational resources and time needed to solve the model. Today, we will introduce the three types of symmetry boundary conditions that you can exploit in your modeling and show how to use them.

Read more##### Walter Frei | June 27, 2014

When using COMSOL Multiphysics on a Floating Network License, it is possible to use the Client-Server mode of operation to access remote computing resources for solving large models, while still using the graphics card on a local machine to display graphics. This can have some significant advantages, so let’s look at Client-Server mode in more detail.

Read more##### Walter Frei | April 30, 2014

We all know that COMSOL Multiphysics can take partial derivatives. After all, it solves partial differential equations via the finite element method. Did you know that you can also solve integrals? That alone shouldn’t be very surprising, since solving finite element problems requires that you integrate functions. The COMSOL software architecture allows you to do a bit more than just evaluate an integral; you can also solve problems where you don’t know the limits of the integral! Here’s how.

Read more##### Walter Frei | April 14, 2014

One of the questions we get asked all the time is: “Can I use COMSOL Multiphysics for solving my fluid-structure interactions problems?” Of course the answer is yes, so let’s talk a little about the various fluid-structure interaction (FSI) modeling techniques. Along the way, we will introduce the add-on modules you will need for these various types of analyses.

Read more##### Walter Frei | April 9, 2014

In a previous posting, we looked at computing and controlling the volume of a cavity filled with an incompressible fluid, which solved for the static deformation of a fluid-filled rubber seal. In that example, we did not explicitly model the fluid, but added an equation to solve for the pressure, assuming incompressibility of the fluid. Here, we will extend this approach and include the hydrostatic pressure of the fluid in the deforming container.

Read more##### Walter Frei | March 25, 2014

It is well-known that you can use the RF Module to compute the impedance of lossless transmission line structures, such as coaxial cables of uniform cross section. But did you know that you can also compute an effective impedance for waveguides with non-uniform cross section? Let’s find out how!

Read more##### Walter Frei | February 17, 2014

COMSOL’s Optimization Module is a powerful tool for improving the performance of your devices and systems. Here, we will look at optimizing the power applied to two heaters in a flow channel with the objective of heating up the fluid as much as possible as it passes through the channel, while constraining the peak temperature at the heaters themselves. One application of this technique is improving the efficiency of thermal processes.

Read more##### Walter Frei | February 11, 2014

When solving a thermal processing problem, such as the heating or cooling of a part, it is desirable to change the heating, or cooling, based upon the computed solution. That is, we may want to include a feedback loop into our model. In this article, we will set up a feedback loop using a component coupling to turn a heat load on or off depending upon the temperature of the part being heated.

Read more##### Walter Frei | February 3, 2014

There are various ways of handling interactions between fluids and solids in COMSOL. You can, for example, explicitly model the fluid using the full Navier-Stokes equations for the pressure and fluid velocity fields. Although that can be a very accurate approach, itâ€™s much more expensive than is needed for certain types of Fluid-Structure Interaction (FSI) problems. Here, we’ll introduce a method for modeling enclosed volumes containing incompressible fluids, under the additional assumption that the momentum and energy transfer via the […]

Read more##### Walter Frei | January 17, 2014

We often want to model an electromagnetic wave (light, microwaves) incident upon periodic structures, such as diffraction gratings, metamaterials, or frequency selective surfaces. This can be done using the RF or Wave Optics modules from the COMSOL product suite. Both modules provide Floquet periodic boundary conditions and periodic ports and compute the reflected and transmitted diffraction orders as a function of incident angles and wavelength. This blog post introduces the concepts behind this type of analysis and walks through the […]

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