6 Single object rotation

QW-BHM module is a tool developed in order to address the needs of users working in the microwave power area and especially with microwave heating applications. Due to a wide variety of physical phenomena that may occur during heating, QW-BHM has been developed in a way, which makes it possible to use jointly with external applications. As explained previously, such external modules can account even for most complex physical effects. However, one important issue has been neglected up to this point – load rotation during heating.

In a typical domestic microwave oven a more uniform temperature distribution within the load is obtained through rotating of the load during heating. Such slow movement of the heated object may to a great extent affect the temperature field. In order to maintain high computational accuracy also in such scenarios, the QW-BHM module has a built-in mechanism accounting for this effect.

The load rotation mechanism lets the user simulate heating of arbitrarily shaped objects rotating around any point chosen on the XY plane. Thanks to this feature it takes just a few mouse clicks to prepare all the data necessary to perform simulation of such problems for specified heating time during which the object is being rotated with a given angular speed.

There are three basic assumptions behind the automatic rotation mechanism in QuickWave software:

1. Rotation is facilitated around a point in the xy-plane, or in other words, around an axis parallel to the z-axis.

2. The rotating part may comprise lossless or lossy dielectric materials (Dielectric isotropic or Dielectric anisotropic in QW-Editor). PEC and Metallic rotation is allowed, however the user should account for possible simulation instabilities, which may result from strong field singularities at the metal boundaries that are not appropriately included in the calculations if the metal edges are not snapped to mesh lines (the singularity corrections models are off). Rotation of dispersive media (Dielectric dispersive, Metamaterial, Ferrite) is not supported.

BHM iter.	Min temp	Max temp
1	-4.99	-4.22
2	-4.92	-3.57
3	-4.81	-2.93
4	-4.75	-2.44
5	-4.72	-2.43
6	-4.46	-2.43
7	-4.24	-2.28
8	-4.01	-2.26
9	-3.85	-2.23
10	-3.71	-2.10
11	-3.60	-2.02
12	-3.45	-1.98

Fig. 6 -1 Temperature in heat_rot_udo project, and final temperature pattern across the load (in -5÷0°C scale, in layer 8).

The first two assumptions are consistent with the physical situation of a domestic microwave oven, which operates in an approximately monochromatic regime and does not allow heating metal items. More details about the third assumption are given herein.

An object, in the QW-Editor sense, is a group of elements on which certain operations like shift or rotation can be performed together. Objects can be created in two ways:

- from UDO scripts, in which case all elements placed between OPENOBJECT(onam) and CLOSEOBJ commands belong to the object of name onam;

- in manual operation, in which case all elements defined between Draw-Object-Open and Draw-Object-Close commands belong to this object.

Two examples, prepared in the above two ways, are provided n the installation DVD. They are: heat/heat_rot_udo.pro and heat/heat_rot_man.pro, respectively. Their analysis with QuickWave is described in Rotation example, while Creating rotation examples and Converting elements to objects explain how a “static” heat.pro scenario can be converted to the two “rotating” ones.