The research paper published by IJSER journal is about Experimental Determination of Thermal diffusivity of Teak Wood as a Function of Water Content 1

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Experimental Determination of Thermal diffusivity of

Teak Wood as a Function of Water Content.

Malahimi ANJORIN, Aristide C. HOUNGAN, Christophe AWANTO, Alain ADOMOU, Antoine VIANOU

Abstract - The wood of teak is much used as building materials in Benin. The quest of comfort conditions in housing needs a better knowledge of thermal performance of the materials forming the walls of building structures. The goal of this study is to estimate the thermal diffusivity of teak as a function of water content using the regular state method. The analysis of the results shows that teak can be used as a good thermal insulating material which allows realizing thermal comfortable apartments in fair conditions.

Keywords: thermal diffusivity, thermal comfort, water content, building materials

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1 INTRODUCTION

HE wood lays over a great part of over planet. Actually it represents four hundred millions of ton oil equivalent as energy and gets advantage to be renewable [1]. In Benin for- ests take up a significant part of the territory and provides among other products some teak which is much used as con- struction material. The amount of removed wood yearly, can give a valuation about 5.2 millions of ton. More than 90% of that products are used firewood, the remainder as timber and building structures, furnishing and electricity networks pylons

[2].

The extensive development of housing trade in Benin and par-

ticularly the need to save energy while giving a thermal com-

fort, require a better knowledge of the thermal characteristics

to realize building walls. The use of climate adapted building

materials as teak, gives to the building cover, in addition to its

insulating rule, to regulate itself temperature and internal hy-

grometry (via walls inertia and wall breathing phenomena).

More over that contributes to minimize the energy consump-

tion of the building. As hygroscopic material, wood is used as

a natural regulator of dampness in houses. The goal of the

tal display dial. The temperature stabilization obtained in time is
± 0.1°C. The water is intensively stired with a helix integrated agitator to the system. Considering the volume of water to boil, a powerful pump 750W/ 220V associated at the same time with the agitator, that allows to distribute regularly the heat flow pro- duced by the serpentine and the thermostat.

The testing sample of the material is placed in the bath contain- ing water with a constant temperature Tf about 50°C. The tem- perature of the test tube is measured using some J (iron, constant- an) type thermocouple lower diameter, 1mm, oversheathed and insulated. Before measuring, all the thermocouples are first tested. The hole receiving the lead is made with an electric drill, diameter about 1mm, then, the couple setting in the central volume of the test tube, the opening is closed with waterproof glue. All those precautions minimize the intrusive effect of the lead. At the end of the measurement, the samples are cut out and the verticality of the lead at the measuring point is controlled a second thermocou- ple same type is used to record the temperature of thermostatic bath.

present study is to give an estimation of the thermal diffusive-

ness of teak as a function of water content using the method of

consistent system. This study presents the experimental device

and the principle of the method as well as the analysis and the

interpretation of results.

2 PRESENTATION OF THE EXPERIMENTAL DEVICE

The method of the thermal regular system imposes the use of an homogeneous thermostatic bath so that the thermoconvective exchange factor (coefficient) is enough higher to get Biot number above 100 [3]. The figure 1 shows the experimental measuring devices. It is composed of a regular metallic vase containing a thermostatic bath with size

P C

Pompe à eau

Centrale d’acquisition

Thermo- couple J

Thermo- cryostat

Agitateur motorisé

Bain thermostaté

540 mm high, 800 mm long and 795 mm wide given an useful
volume of 340 l. The vase is put into a box and insolated on the
base plate and its lateral sides with polystyrene 90 mm thick.
The heating of fluid in the vase is realized using compact thermo-
stat type LAUDA and serpentine heating at 1 kW / 220V drived by an electronic thermo regulator. The target temperature is set with an electron potentiometer and the reading is made on a digi-
FIGURE1 Measuring device of thermal diffusivity of building
materials.

2.1. SAMPLES PREPARATION

In order to measure the thermal diffusivity of building materials
for different water contents, small size test tubes are realized to make sure the uniformity of the dampness into their porous me-

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The research paper published by IJSER journal is about Experimental Determination of Thermal diffusivity of Teak Wood as a Function of Water Content 2

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dia. To obtain the required water contents, samples are placed

 u  h u

= 0 for x = ± ex

(2)
during many days either into steam room saturated with water
air dried or conditioned into climatic wall. The water contents are

x x hx

x = ± ex

controlled using twin samples and measuring at the end their anhydrous mass. The figure3 below shows the photo of samples

 u  h u = 0 for y = ± ey (3)

y y y

of teak used. The size and the water content of those samples are

 u  h u

z = ± e

recorded in table1.
The samples are cut into three perpendicular plans: transverse

z z

z = 0 pour z

(4)

into a plan remote and ical (R) and of wood. In to principal the disposi- o are made
Where u0 = T(x, y, z, t = 0) -Tf Tf surrounding temperature
At the end of essays u (x, y, z, ) = 0 The samples temperature tends towards Tf.
Considering the above equations, we can analytically determine at any point of the test tube, the thermal field in variable system. The solution of that problem is obtained bearing on the variables separation method and applying Von Neumann theorem (3). The reduced temperature solution (1) with boundary conditions (2-4) noted

u T  x, y, z, t  - T f

   (5)

u T T

0 0 - f

is given by

    

     A F

exp - n2 Fox  n2 Foy  n2 Foz 

(6)

i1 j1 k 1

ijk ijk

 ix jy

kz 

niη is the positive root of line 1 of transcendental equation

niη

L cotg n

iη =

η

R

2ey

with (  x, y, z )

If Biot number. Biη tends towards infinity, the suitable numbers have as values niη

2ez

π

n1 η =

2

π

, n 2 η = 3

2

π

, n3 η = 5

2

π

, ni η = (2i-1)

2

when the time is
FIGURE 2 : Samples photo.
superior to that of the regular system starting, the sery (6) be- comes convergent and can be replaced accurately better than 1% (3) by its first term:

2.2 EQUATION OF TRANSFER INTO MATERIAL

  A111F111 exp mt 

(7)

 n2 a

n2 a y

n2 a 

The heat transfer (equation in orthotropic environment as wood

m   1x x  1y

 1z z 

(8)

is  e2

e2 e2 

 x y z 

2u

2u

2u u

 

as linear equation  in the regular system field, we have:



x x

   

y

2  c t  0

ln   mt  Cte

The value m can be experimentally obtained by the relation
(9)
with u = T(x,y,z,t)-T
(1)

ln 1
 ln 2
ln u

1
 ln u
2
(10)

f m  

 t t  t
The figure3 shows the coordinates system for a wood plate.
The initial condition and the Fourier boundaries conditions are :

u (x, y, z, t = 0) = u0

t2 1 2 1

In practice, m is used equal to absolute value of the slope line determined by a linear regression from experimental point into regular state. The identification of diffusivity ax, ay, az needs three experimental recordings on the same type of sample of the ma-

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The research paper published by IJSER journal is about Experimental Determination of Thermal diffusivity of Teak Wood as a Function of Water Content 3

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terial but within characteristic sizes of the test tubes adequately chosen.
For example: in simple case using three test tubes with respec- tive sizes

3. RESULTS AND INTERPRETATION

The identification of the exploitable zone corresponding to regu-
lar state needs to define pertinent criteria. Theoritically, the linear
regression, concerns only the experimental points corresponding
to times defining a Fourier number above 0.23 (3) As Fourier

n1: 2e , 2e , 2e

ax  0,135 5 1 -

2 - 3 e2

number is a function of the caracteristic size and diffusiveness

 x y z



 m m m x



There-
that values are unknown the time tr assiociated to the apparition

n2 : 2ex , 2e' y  ey , 2ez

a y  0,135  2 -

1e2

(11)

m m y

 

of the regular system can be known exactly. The analysis of the

 n3 : 2ex , 2ey , 2e'z  ez

az  0,135 m - m e2

curve f(t) = Ln(∆T), allows to delimit the exploitable zone with a

  3 1 z

fore knowing m values representing the variation rate of tempera- ture logarithm during the regular system at any point of each test tube, we can deduce the diffusiveness in comparison with the principal directions by the relation (11).
below limit equal to 1°C so that the measurements not to be de-
pendent on parasites noise and on above limit equal to 22°C of
initial difference of the temperature (To- Tf) (3). Figure 4 shows
the sample temperature variations.

Table1: thermal diffusivity of teak (Tectona Grandis) with 50°C for various water contents to 22% (T0 - TF)

In the data processing we have considered pratically the record- ings of second half experimental time of acquisition, while taking care to eliminate values of ∆T below 1°C. (Figure 4 et 5).

Experimental points (dry teak)

Figure 4. Thermogram (f(t) = T) for a dry teak sample

Times

(T bath= 50°C) Figure 5. Thermogram (f(t) = Ln( ΔT )for a dry teak sample (T
bath= 50°C)

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1.5

1.0

0.5

0

160 180 200 220 240 260

Times (s)

FIGURE 6. linear regression after 160 seconds for dry teak (T
bath:= 50°C)

From that table we can deduce an average anisotropic rate varing from aL/aR = 1.9-5.2 ; aL /aT = 1.8-9.5 ; aR/ aT = 1.6-3.0. That differ- ences between anisotropic ratio show the influence of water con- tent on the heat transfert. The absolute incertainly values estimat- ed by a trust interval at 95% about the diffusiveness are summa- rized in table1. The figure 7 representing the longitudinal thermal diffusiveness as function of dampness ratio, shows about teak that longitudinal diffusiveness is higher than transversal one. We no- tice also on that curves so as transversal (radical and tangential) the thermal diffusiveness is not much over 2.10-7 m2/s. Also for the lower water content (0- 15%) the diffusivity obtained in short cut moves up to maximum. That result has been experimentally proved (4) for water contents between 0 and 10% for wood and other materials.

Tangential direction Radial direction Longitudinal direction

FIGURE 7: Thermal diffusivity of teak as function of water con- tents
For water contents over 15% we notice a decrease of the thermal diffusivity. That can easily explained if the diffusiveness is inter- pretated as reducing power of a superficial thermal disturbance
within the material. In fact, during the wood humidification, the low water diffusiveness (about 1.44 10-7m2/s at 20°c) replace the air dry that the diffusivity (about 2.15 10-5m2/s) is very higher than its. Our results are compared with that’s of the two air dry woods oils (3). Very used in Benin, what stands out that longitu- dinal thermal diffusivity is about 3.21 10-7m2/s for versus 2.49 10-

7m2/s for Swietenia senegalensis Desc when in short cut, these values are 2.69 10-7 m2/s and 1.55 10-7 m2/s respectively. We notice that for a water content of 15,6% our results are lower than that’s of those wood oils

4. CONCLUSION

The thermal diffusiveness of teak is measure using the method of regular system. The one advantage of that method is the quick obtainable experimental results (an assay lasts less than 15 minutes). On the other hand, the method of regular system uses a particularly simple device to implement and lend itself well to highly automated measurement. We overall notice the decrease of thermal diffusiveness related to the dampness rate of wood and a greater value of diffusiveness in axial direction compared with transversal one

Nomenclature e: thickness, m t: time

x; y, z: space coordinates
u: temperature deviation k
ax ay az : thermal diffusivity depending on x, y, z, m2.s-1
Bi: Biot number

F i, j, k: order function i, j, k

Fo: Fourier number
hx, hy, hz: exchange coefficient depending on x, y, z,
W.m2.K-1
n1: appropriate value
T: temperature, °c
m: logarithm variation rate of T during regular system

REFERENCES

[1] A. Houngan, hygrothermic Characterization of local materials of Benin : conductivity and thermal diffusivity, isotherms of sorption and mass diffusivity, Thesis of the National School of the Agricultural engineering of National Forestry. Nancy-France (2008), p 232.
[2] S. Gboyahida, Characterization of the transfers of heat
and mass of three tropical Wood gasolines. Memory of Poly- technic D.E.A College of Abomey-Calavi (1997), p.80
[3] A. Vianou, A. Girardey, Exploitation of the regular-state
phenomenon in thermokinetics for the determination of the thermal properties of building materials, Publication High- Temperatures- High Press, 25(1993), 635- 641.
[4] D. Quenard, J P. Laurent, H. Sallée - Influence of water content and temperature on the thermal parameters of the plaster Rev. Gen. Therm n°291(1986), 137 – 144.

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 Malahimi Anjorin received a M.Sc. in Moscow and a Ph.D. degrees in Heat Transfer from INPL of Nancy (FRANCE)

He is currently Assistant Professor of Heat and Mass transfer, fluid mechanic at Polytechnic School of Abomey-Calavi – Uni- versity of Abomey-Calavi (BENIN). His principal research inter- ests are applied mechanics and Heat and Mass Transfer in building Material and Biomass energy in Laboratory of Ener- getics and Mechanics Applied (L.E.M.A)

e-mail : malahimianjorin1@yahoo.fr

 Comlan Aristide HOUNGAN received a M.Sc. in Benin and a Ph.D. degrees in Energetics and Environment from Agro Paris- Tech /ENGREF of Nancy (FRANCE)

He is currently Assistant Professor of Heat and Mass transfer,

fluid mechanic at the Technological Institute of Lokossa – Uni- versity of Abomey-Calavi. His principal research interests are applied mechanics and Heat and Mass Transfer in building Ma- terial in Laboratory of Energetics and Mechanics Applied (L.E.M.A).

e-mail : hounaris@yahoo.fr

 Christophe AWANTO received a M.Sc. in Paris XII and a

a ph.D. Degrees in Energetic from the Université d’Evry Val d’Essonne of France.

Assistant Professor of Heat and Mass transfer, fluid mechanic at Polytechnic School of Abomey-Calavi – University of Abomey- Calavi (BENIN). –. His principal research interests are applied Energetic in Laboratory of Energetics and Mechanics Applied (L.E.M.A).

e-mail : christophe.awanto@gmail.com

 Alain Adomou received a M.Sc. and a ph.D. degrees in Theo- retical Physics from the Russian People University of Moscow, Federation of Russia.

He is currently Assistant Professor of mechanical theory of con- tinua at the Technological Institute of Lokossa – University of Abomey-calavi. His principal research interests are applied me- chanics and theory of gravitation in Laboratory of Energetics and Mechanics Applied (L.E.M.A)

e-mail : denisadomou@yahoo.fr

 Antoine VIANOU received a ph.D. degrees in Heat transfer

from the Université d’Evry Val d’Essonne of France.

He is currently Professor of Heat and mass transfer at Polytech- nic School of Abomey-Calavi – University of Abomey-Calavi (BENIN). His principal research interests are applied mechanics and Heat and Mass Transfer in building Material in Laboratory of Energetics and Mechanics Applied (L.E.M.A)

e-mail:avianou@yahoo.fr

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