Drying Technology: An International Journal Empirical ...

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Empirical Equation for Limit of Hygroscopicity a

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Branko Kolin , Gradimir Danon & Tatjana Stevanovic Janezic

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Branko Kolin. Gradimir Danon. Tatjana Stevanovic Janezic Faculty of Forestry. Univenity of Belgrade , Belgrade., Kneza Viseslava 1, 11030, Yugoslavia Published online: 02 Aug 2007.

To cite this article: Branko Kolin , Gradimir Danon & Tatjana Stevanovic Janezic (1995) Empirical Equation for Limit of Hygroscopicity, Drying Technology: An International Journal, 13:8-9, 2133-2139 To link to this article: http://dx.doi.org/10.1080/07373939508917069

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DRYING TECHNOLOGY. 13(8&9). 2133-2139 (1995)

TECHNICAL NOTE

Downloaded by [The University of Manchester Library] at 13:09 23 January 2015

EMPIRICAL EQUATION FOR LIMIT OF HYGROSCOPICITY

Branko Kolin. Gradimir Danon. Tatjana S t e v m v i c Janezic Faculty of Forestry. Univenity of Belgrade 11030 Belgrade, Kneza Viseslava 1. Yugoslavia

KEY WORDS bmlt of hygmscoptoly, finer saluratlon po~lit. parallel to grain, thermal treatmert chemical composition

compression Strenght

ABSTRACT

In this paper we are pnmoting the pmperlies related to \Imd aMtcfny and d e m i d mmpcsition as the faciu of influence to limit of h y g m p i d t y of (LH). The vrood samples of the most imwrtant domestic vrmd species: oak Ouercus mbur. beech Fagus sytvatica. fir Abies alba and spwce Picea abies were selected lor this investigation. For determining LH in our investigations we have applied the method of compression strength parallel to grain. The results of expenmental measurements w r e stallst cally analyzed and !le emplncal equalton lor LH depenaance upon the s~gnlllcant (~nfluentlal) lactom temperature. cellullse content and vrood density in oven dry slate is defined

INTRODUCTION

Limit ol hygmsmpicity (LH) or fiber saturation point (FSP) is of interest for the artificial drying specialist and vrwd scientist because mas( problems during drying arise i n this

Copyright 0 1995 by Msrccl Dckkcr, Ins.

KOLIN. DANON. AND STEVANOVlC lANEZlC

2134

wwd moisture region. The limit of hygmsmpicity is the important point beyond which the s e l l i n g and shrinkage phenomena occur, causing certain strains in wwd stlucture vrhich could, i n some cases, lead to the drying degrade. When compiling kiln drying schedules, as well as for the most of the calculations, limit of


hygmswpicity (or fiber saturation point) is taken as a constant, mthin the limits behreen 28 and 30%. The influences of the differences in wwd densities, temperature, chemical composition and other factors are not being taken as influencing the limit of hygroscopicity (LH). The influences of particular facton upon the LH are, h o e v e r , considered in some papers. Vorreiter 119631 is examining the influence of m d density upon the LH, for the temperature of 20

'c.

Bramhall [I9791 proposed the empirical relation representing

dependence of the LH on temperature, but for Douglas fir only, i n the follomng form:

Similar type of research [ I ] on five Central Europeans industlial wwd species Kolin (1985) obtained the follouing equation of the LH dependence on temperature:

In the same research the dependence of the LH upon the vaod density at constant temperatures (among 20 and 90 'c) is evaluated. The aim of the present investigation is to determine general empillcal equation based on the results of the previous researches [Kolin 1985. 1990. Kolin. Stevanovic. 19941 vrhich w u l d represent the LH dependence on temperature, nood density and vaod cellulose content through a simplified mathematical model as was done in paper [Bramhail. 19791. This paper outlines the empirical delivation of such simplified equation, and compares LHs calculated by this equation, uith measured LHs for commercial domestic wwd species. MATERIALS AND METHODS

For determining LH in our investigations e v.

have applied the method of compression

slrength parallel to grain. The wwd samples of the most important domestic wwd

LIMIT OF HYGROSCOPICITY

2135

species: oak Quenus mbur, beech Fagus sylvatica, fir Abies alba and spruce Picea abies were selected for this investigation. The wmpression strength parallel to grain measurements have been performed for several moisture contents in hygmscopic area, and on uccd samples in water-saturated


state. The other details about the applied methods of measurements are described in our previous paper [Koiin. Stevanovic. 19941.

RESULTS AND DISCUSSION

The results of CSPG measurements were statistically analyzed in wder to define the regression model adequate to the obtained experimental data for the hygroscopic area that proved to be polynomial, i.e.. linear for the beyond hygroscopicarea. The dependence of compression strength on uccd moisture content is taken to be linear regression equation in the hygroscopic area, as this is a n a m m hygroscopicity area. although the dependence of the wmpression strength on uccd moisture mntent is a WNe, as it is notified previously. This is illustrated in Figure 1, in M i c h the area around the limit of hygroscopicity is emphasized. The least squares method applied on the obtained expenmema data f a hygrosoopc area yielded the fdloning f a m of pdymmial regream and f a the beyond hygmscopicarea: u=a+bt+c*u

~Nlmm'l

Mere: a, b, c t

-

u-

-

pdymmial meffidents r\ood temperature [OC]: vaod moisture m t e m [%I.

RegresSioncwfflcients f a the above equfilons are presented in @Me 1 F a the beyond hygrosoopc area the fdlming equation is adopted:

and the regression wefflcients and mrrelatiw are p-esented in table 2


KOLIN, DANON, AND STEVANOVlC JANEZlC

0

8

16

24

32

moisture content (%) FIGURE 1 DEPENDENCE OF COMPRESSION STRENGTH PARALLEL TO GRAIN ON WOOD MOISTURE CONTENT I = Cons1 (1 Hygroscopic area -nontlnear correlation. 2. Hygmscopic area linear correlation. 3 Beyond hygroscopic area -linear comlationl

-

TABLE 1 Regression coeffidents for hygroscopic area



TABLE 2 Coefflaents of regression for beyond hygroscopic area

The basic premise of d y s i s is lhat lhe LH f a m e (selmed) nmd species is lhe linear flndim of temperature, as f d l m :

H = a + b t [%I The limit of hygmswpialy

KBS

(3)

determined by mathematid sduiim of the system of

equatiw (1) and (2) (see 60. 1). It is possible to wnclude fmm the data presented in table 3 that the LH dependence on temperature is linear for the examined wxd speaes. Different values of LHs muld be explained pimanly by the differences in umd densities and pehaps also by the differences in anatomy and in chemical compositions of the examined rmd species. We have generalizedlhe LH equatim nilhcul taking into axuml lhese f a d m of influence m t h e L H , a - d t y s l a 6 5 6 c d ~ w e h e d % i n e d ~ m m r r h x0.75(?=060). m Taking into mthe readts of a n previous irwes(igatiom [Kdin.1985. Kdin. Stevanovic. 19941, vre have in(mdtKed as lhe important f a d m of influence lhe cellldose content and the \md density in wen dry slate. The cellldase contents and vmd densities are presented in

table 4, m e data f a p b e wxd densities are taken fmm as paper [Kdin. 1 4 . ard the data f a c e l l ~ d m contents from paper [Kdin. Slevanovic, 19941. lrnpmved regressim equatim f a m m p r w i m Sren@h in hyemswpic area. vhich is laking into aomunt the influences of temperatwe (1 - OC), umd moisture mntent (u cellulose content (cell - %) ard density in wen dry slate (p. - g / unj is as f d l m :

nw

- %).

KOLIN. DANON, AND STEVANOVIC JANEZIC TABLE 3


Regression coefficients for calculating the LH dependence upon temperature

TABLE 4

Cellulose w e n t and w e n dry dewily af seleaed domestic umd spedes

M i l e forthe beyond hygroscopic area the improved equation is:

o

-

40.204 - 0.113. t - 0.607 .cell+ 20.579

[~lmm~]

(5)

Sdving the system of equations (4) ard (5) on u, general empirid equation f a Ule limit of hygmscopiaty dependence on temperature

("c),cellulose w e n t

(%) and vmd density

(glcm3)is obtained:

CONCLUSIONS

By linearimion of the temperatwe dependence d LH MI substantially different rendts from

those obwned lmm the equation presented in paper [Kdin. 19851. The infiuence 01vmd density upon the

w in temperature range 20... w OC

is quantified sn

t M Ule vmd specjes nith smaller density in oven d r l state e ~ i b i t shigher W that is in a x d a n c e nith the cudusions of the research presented in paper plareiter. 19631.


2139

We are pomotlng in this paper as the f a a a of inlluerce on the LH the pmperties related to

nmd m o m y ard demical mmpositim. As the maja wad h y g m p i a t y oxddhnci is designated cellulose. The LH is increasing nith wad cellulose m e n t iraease, as can be seen lmm the equation (6). The obtained empirical equatim is vmple ard suffidently


accurate to apply la differern w a d spedes, temperatwes ard celldose amnerns.

REFERENCES Bramhall. G. (1979), Mathematical Modell for Lumber Drying II. The Modell. Wccd Sdence.

-

vd. 12 (1). p. 22 31 Kdin. 8. (1985). Li%cajtemperature na pitisnu cvrstaz~i granimu higroskopmsl drveta. (doldaska disertadja),Summki fakultet. Beograd. (Temperature effedupon the m m p w i o n slrengUl ard the limit of h y g m p i d t y of wad. Ph.D. thesis. Fmdty of Fareslry of the Uriverslty of Belgrade)

Kdin.B.. Ranisavljev D.. (1990) Uticaj temperature i trajanja temperatumog tretmana na sorpciona svojstva drveta. (Effed of temperature and duration of thermal treatment upon the suplion behaviw of wad). Sumarstvo (6). p. 49-53 Kdin. 8. Stevanavic Janezic. T. (1994). Effed of thema Veflmern u

p Lhe limit of

hyQrmoopiatyof seleded domestic wad species, The First IntemalkxLd Conference on the Development of VIncaj Saerce ITedlrdogy 8 Faestry (Canfererce Proceedings). Missenden Abbey, Kdin B.. Vujosevic, V. (1990) Uticaj temperature i tram@temperaturog tretmana na g h m u higrmkopnrm drveta (Effed of temperature ard dmalim of thermal treatment upon Vle limit of h i g m p i a l y of wad). Sumamo (5). p. 17-20 Vweiter. L. (1963) FaseMngungsfeudrte und h W t e Waueraulnahme der Hazer, Hdzfaschung, (5). p. 139 -146