HeatWave Thermal Analysis
There are many, many sources of moisture variation on operating paper machines, whether tissue, fine paper, or liner board machines. These variations can be present in both the cross-machine and machine-direction. PROdry Technology has developed a proprietary analysis package to analyze the sheet and dryer temperature for periodicity and to identify the frequency of all variation components. (Please see "News" on HeatWave.) This technology, which is analogous to a mechanical vibration analysis, reveals subtle details of the thermal patterns which are extremely helpful in diagnosing the source(s) of thermal variation on the machine.

The use of PROdry's HeatWave analysis is illustrated in Example 5. The Precision Infrared Image (PIR) shows a complete revolution of the Yankee dryer while making paper at 4000 feet/minute. The dryer is a smooth-bore dryer with four internal condensate pickup locations. Several thermal features stand out on this dryer, including a pair of cold/wet streaks near the center and a hot region at the back/center of the dryer.

To perform the HeatWave analysis, PROdry engineers first obtained several thousand lines of thermal data at high frequency, then processed them to produce the Thermal Frequency Spectrum (TFS) shown. The dominant peak of the spectrum occurs at four times the Yankee dryer rotation frequency, or 5.65 Hz. The sideband frequency that separates this peak from the others around it is the Yankee rotation frequency itself. This implies that the condensate removal system geometry is responsible for a major part of the thermal variation in the sheet. However, a peak which is only slightly lower appears in the TFS at a frequency of 51.88 Hz, much higher than normally seen in Yankees. This peak, the spoiler-bar pass frequency, can be related directly to the spacing of the spoiler bars installed inside the smooth-bore dryer.

This example serves to illustrate the high sensitivity of the HeatWave analysis to subtle thermal variations on the paper machine. In addition to pinpointing causes of such variation, the Thermal Frequency Spectrum defines a unique thermal "fingerprint" which is characteristic of the machine. The TFS can be highly valuable as a baseline measurement to be used for comparison during later analyses.

Example 5: PIR line scan and Thermal Frequency Spectrum of smooth-bore Yankee dryer. ("Ironbow" palette).
Click each to enlarge

© 2007 PROdry Technology, Inc. Site last updated 3/7/07