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

Conventional kiln drying experiments Laboratory Drying Kiln Air velocity up to 10 m/s Sample capacity : 160 x 85 x 85 cm High Pressure Spraying Climate : up to 130 °C; up to 100 % RH Prepared for steaming; Fit for high temperature drying 2 Control system up-to-date, industrial standard

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? 3

Comparing EMC readings EMC according to psychrometer and electronic humidity- temperature transmitter 4

Elevated temperatures Less differences between psychrometer and electronic humidity- tempreature transmitters Problems with temperature measurements by means of the two PT- 1000 sensors? 5

Comparing temperature readings Temperature readings during continuous heating 6

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 7

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