Com paring psychrom eter and hum idity sensor Com paring psychrom - - PowerPoint PPT Presentation

Com paring psychrom eter and hum idity sensor Com paring psychrom eter and hum idity sensor during conventional kiln drying especially at low during conventional kiln drying especially at low tem perature and low relative hum idity tem perature and low relative hum idity

W ood EDG Sem inar W ood EDG Sem inar I m provem ent of W ood Drying Quality by Conventional and I m provem ent of W ood Drying Quality by Conventional and Advanced Drying Techniques Advanced Drying Techniques

Bled, Slovenia 2 3 .0 4 .2 0 0 9

• Dr. Christian Hansm ann

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Conventional kiln drying experiments

Laboratory Drying Kiln Air velocity up to 10 m/s Sample capacity : 160 x 85 x 85 cm Climate : up to 130 °C; up to 100 % RH Prepared for steaming; Fit for high temperature drying Control system up-to-date, industrial standard High Pressure Spraying

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Starting situation

• Revealing problems to reach the desired EMC (2%)
• Amount of water in fresh air low enough
• Electronic sensors show lower EMC

Reason for differences?

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Comparing EMC readings

EMC according to psychrometer and electronic humidity- temperature transmitter

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Elevated temperatures

Less differences between psychrometer and electronic humidity- tempreature transmitters Problems with temperature measurements by means of the two PT- 1000 sensors?

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Comparing temperature readings

Temperature readings during continuous heating

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Conclusions

• A general shift exists between dry- and wet bulb thermometers
• Systematic errors other than the thermometers could be excluded
• Shift is approximately constant over a wider range, but a distinct

sensor drift above 85°C can be observed

• The observed shift is not the reason for the different EMC readings

and does not lead to too severe drying schemes (the opposite is true)

• Another reason has to be identified – next experiments will analyse

the influence of the tissue-finish

• The observed problems would lead to an overestimation of the EMC

in the drying chamber and consequently lead to very severe drying conditions drying quality can be negatively affected

• Control system must be adjusted to the drying technique

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Thank You for Your attention

Contact: Kompetenzzentrum Holz GmbH St.-Peter-Straße 25 A-4021 Linz Tel.: +43 (0)732 6911-4596 Fax: +43 (0)732 6911-4086 E-Mail: zentrale@kplus-wood.at Homepage: www.wood-kplus.at

Financial support by Mühlböck-Holztrocknungsanlagen GmbH (Eberschwang, Austria) is gratefully acknowledged