Vpliv notranjega in zunanjega snovnega upora na kinetiko konvekcijskega sušenja lesa : doktorska disertacija

Straže, Aleš (author), Gorišek, Željko (mentor), Bučar, Bojan (comentor)

Kinetika konvekcijskega sušenja bukovega lesa (Fagus sylvatica L.) je bila raziskana pri stacionarnem postopku sušenja ter v adaptivnih sušilnih pogojih. Uporabili smo radialno orientirane preizkušance, debeline od 6 mm do 24 mm, s tračno žagano in s skobljano sušilno površino. Stacionarno konvekcijsko sušenje lesa smo izvedli v laboratorijskem sušilnem kanalu pri konstantni temperaturi in relativni zračni vlažnosti (T = 30 °C, f = 85%), z variiranjem hitrosti zraka (v) od 0,6 m/s do 7,6 m/s. Med sušenjem smo v zaporednih časovnih intervalih gravimetrično določali povprečno lesno vlažnost (u), vlažnostni gradient in masni tok vode v okolico. V drugem delu raziskave se je kinetika konvekcijskega sušenja lesa uravnavala s trenutno doseženim masnim tokom vode z iterativnim prilagajanjem sušilnega potenciala v zaprto-zančnem računalniškem algoritmu. Sušilna hitrost se je splošno povečevala s hitrostjo gibanja zraka ob površini lesa ter zmanjševala z večanjem debeline preizkušancev. Pri majhnih hitrostih zraka ter manjših debelinah preizkušancev je bila sušilna hitrost pri izločanju proste vode pri preizkušancih s skobljano površino, večja kot pri vzporednih, z žagano površino, kar je posledica razlik v snovni prestopnosti. Povečanje začetne sušilne hitrosti (v > 2,5 m/s) je pri preizkušancih večjih debelin povzročilo neposredno sušenje s padajočo sušilno hitrostjo, ob prevladujočem notranjem snovnem uporu. Adaptivno sušenje je bilo v splošnem hitrejše v primerjavi s konvekcijskim sušenjem pri konstantnih sušilnih pogojih. Pri visoki lesni vlažnosti in izločanju proste vode smo optimalni sušilni potencial dosegli z iterativnim prilagajanjem zračne vlažnosti in hitrosti zraka. Pri sušenju pod točko nasičenja lesnih vlaken in naraščanju notranjega snovnega upora dosežemo optimalni sušilni potencial s kombinacijo zračne vlažnosti in temperature sušenja.

• Language: Slovenian
• Keywords: les, sušenje, postopki, kinetika
• Work type: Dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: BF - Biotechnical Faculty
• Place of publishing: Ljubljana
• Publisher: [A. Straže]
• Year: 2010
• Number of pages: XV, 114 f., [10] f. pril.
• PID: 20.500.12556/RUL-491
• UDC: 674.047.3(043.3)
• COBISS.SI-ID: 1793673
• Publication date in RUL: 11.07.2014

STRAŽE, Aleš, 2010, Vpliv notranjega in zunanjega snovnega upora na kinetiko konvekcijskega sušenja lesa : doktorska disertacija [online]. Doctoral dissertation. Ljubljana : A. Straže. [Accessed 14 May 2025]. Retrieved from: http://www.digitalna-knjiznica.bf.uni-lj.si/dd_straze_ales.pdf

Secondary language

• Language: English

Abstract

Drying kinetics of convectional drying of beechwood (Fagus sylvatica L.) was researched at common stationary drying and at adaptive kiln drying process. We used radially oriented specimens of thickness from 6 mm to 24 mm, having sawn and planed drying surface. Firstly, a series of convectional drying processes were carried out in the laboratory tunnel drier at constant drying conditions of 30 °C, at relative humidity of 85%, varying air velocity (v) from 0.6 m/s to 7.6 m/s. During the drying, moisture content (u) and water mass flow were gravimetrically determined at successive time intervals. In the second part of the research, the real water mass flow and the iteratively adaptive drying potential were used at the computer controlled convective drying. Drying rate generally increased with the air velocity and decreased with the increasing thickness of wood. Low air velocities caused also initially higher drying rate at specimens with planed surface comparing to sawn one, due to differences of the surface mass transfer coefficient. Increasing of the air velocity (v > 2.5 m/s) caused irreversible reduction of initial water mass flow and transition to the period of falling drying rate, where the internal water mass resistance predominates. Too high initial drying rate, especially at greater material thicknesses caused high initial moisture content gradient and significantly prolonged the drying process in continuation. Adaptive drying was generally faster in comparison to convective drying at constant climatic conditions. In the first drying period, at the removal of free water, the optimized drying potential was reached with the iterative variation of the air humidity and the air velocity. Combination of the air humidity and the temperature was successful to optimize the drying potential at the moisture content bellow fibre saturation, where higher internal mass transfer resistance existed.