20120140505003 2-3

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print),

ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 17-29 © IAEME

17

EXPERIMENTAL AND THEORETICAL ANALYSIS OF HEAT AND

MOISTURE TRANSFER DURING CONVECTIVE DRYING OF WOOD

1Ahmed Khouya,

2Abdeslam Draoui

1Assistant professor, Department of Industrial & Electrical Engineering,

National School of Applied Sciences, Tangier, Morocco 2Professor, Dept. of physics, Faculty of Science and Technology, Tangier, Morocco

ABSTRACT

The main purpose of this paper was to investigate an experimental and theoretical analysis of

heat and moisture transport behavior in wood during convective drying process. A convective drying

cell was used to follow the measurements of the water content of samples subject to hot air flow in

longitudinal and transverse moisture transfer of wood. The effects of drying conditions such as

drying air temperature, air velocity and ambient relative humidity on the drying characteristics of

wood has been investigated. The constants drying and diffusion coefficients of the drying model,

which control the drying rate of wood, were determined from fitting the model against the

experimental drying curves. Results showed that, drying kinetic behaviour of the longitudinal

diffusion is very significant than the transverse one. The moisture content increased with increase in

drying air temperature and air velocity but decreased with time. From the curves of moisture flow

evolution versus moisture ratio, convective heat and mass transfer coefficients have been evaluated

and compared with values obtained from the literature and existing correlations.

Keywords: Convective Heat Transfer, Diffusion Coefficients, Drying, Mass Transfer Coefficients,

Wood.

I. INTRODUCTION

Convective drying process as well as other drying method is used in order to preserve wood

and food product for longer periods by releasing free water molecular presented in the bound cell of

products. Drying process in term of modelling and simulation are based on the analysis of drying rate

function. This function consists of three drying periods: Constant drying rate period, first period and

second falling rate period. Constant drying rate is defined as the period of drying where moisture

removal occurs at the surface by evaporation and the internal moisture transfer is sufficient enough

to maintain the saturated surface, thus the evaporation rate remains constant. In the first falling-rate

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH

IN ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 5, Issue 5, May (2014), pp. 17-29 © IAEME: www.iaeme.com/ijaret.asp Journal Impact Factor (2014): 7.8273 (Calculated by GISI) www.jifactor.com

IJARET

© I A E M E



18

period, the drying rate decreases as the moisture content decreases due to the additional internal

resistance for moisture transfer. The second falling-rate period begins when the partial pressure of

water throughout the material is below the saturation level.

Experimental and theoretical investigations have been conducted to determine the diffusion

coefficients during drying of wood [1], [2], [3]. Mouchot et al., [1] carried out an experimental study

to estimate the diffusion coefficient of Beech wood in unsteady-state conditions. The diffusion

coefficients of water are deduced from the diffusion coefficients of an inert solute (helium) measured

in a diffusion cell, type Wicke and Kallenbach at temperature of 30 °C. They showed that the

diffusion coefficient in the radial direction is larger than the diffusion coefficient in the tangential

direction. Agoua and al., [2] performed an experimental and theoretical approach to estimate the

diffusion coefficient of wood in unsteady-state conditions. The results found that the analytical

solution of diffusion equation taken into account the resistance to mass transfer at surface give more

satisfactory for determining diffusion coefficients of wood. Joseph and al., [3] Have been performed

an experimental study to determine the diffusion coefficients of wood in the radial, tangential and

longitudinal direction. Results found that the longitudinal diffusion coefficient is larger than the

transversal diffusion coefficient and radial coefficient is larger than the tangential one. Joseph and

al., found that the longitudinal diffusion results in the migration of the water content through fibres,

as for the transverse diffusion, it results in the progressive crossing of vessels cellular cavities.

Many investigations on heat and mass transfer coefficients during drying have been devoted

since several decades [4], [5], [6], [7], [8]. Tremblay and al., [4] performed an experimental and

theoretical investigation to determine heat and mass transfer coefficients of wood during drying.

Experiments were carried out on Red pine at drying air temperature of 56 °C, relative humidity of 52

% and air velocity ranged from 1 to 5 m.s-1

. Heat and mass transfer coefficients were determined

from the constant drying period. They showed that the mass and heat transfer coefficients increase

with increasing air velocity. Nabhani and al., [5] carried out an experimental determination of

convective heat and mass transfer coefficients during drying of Red pine sapwood. They showed that

the heat and mass transfer coefficients are constant until the surface moisture content occurs 60%,

and that these coefficients increase with air temperature and air velocity. Yeo [6] estimated the mass

transfer coefficients of Maple, Oak and pine wood at 30 °C using a colorimetric technique. The mass

transfer coefficient calculated ranges from 1,81 x 10-6

to 5,69 x 10-6

m.s-1

. Comparatively few

investigations have been made to determine heat and mass transfer coefficients from the Nusselt

number and Sherwood formula [7]. Salin [7] mentioned that the use of the Lewis analogy is not

appropriate to estimate heat and mass transfer coefficients. Ananias and al., [8] have been used an

overall mass transfer coefficient to predict the drying curves of wood at low-temperature. They

showed that conventional drying curves of Canelo wood may be modelled by a constant mass

transfer coefficient.

A review of literature reveals very little empirical research about the drying kinetic

behaviours of Red pine. Since, the purpose of this paper is to present an experimental and theoretical

analysis of heat and moisture transfer during drying of wood. We analyse the effect of drying

conditions such as drying air temperature, air velocity and ambient relative humidity on moisture

diffusion, heat and mass transfer coefficients during convective drying process of Red pine.

I I . M A T E R I A L A N D M E T H O D

Experimental device The experimental setup is composed of an electric dryer heating element, humidifier and

probes to control temperature and relative humidity (Figure 1). A Software laboratory controls the air

climate conditions with the thermostat which measures the dry and wet bulb temperature in the drying

cell. Dry and wet bulb temperatures were measured using electrical resistance sensors. The dry bulb



19

temperature can be controlled between 20 to 70 °C, with a standard deviation of 0,5 °C. Ambient

relative humidity of the drying cell ranged from 20 to 80 %. The average standard deviation of the

relative humidity was 5 %. The climatic cell is equipped with a balance of 0,001 g precision.

The wood material used in this work was cut from Red pine (Pinus resinosa). The samples are

obtained in mixed heartwood/sapwood along the same longitudinal and transverse section. Table 1

provides some physico-mechanical data of Red pine.

Figure 1: Schematic representation of the drying cell

Table 1: Physical and mechanical properties of Red pine [9]

Density 504 kg/m3

Volumic shrinkage 14 %

Total tangential shrinkage 8,5 %

Total radial shrinkage 5 %

Rupture stress 47,5 MPa

Elasticity module 11305 MPa

In order to study both longitudinal moisture transfer and transverse moisture diffusion mode

of wood, a layer of marine varnish has been applied to block the moisture transfer on the other faces

of the sample and the hot air stream was set only along the longitudinal direction of specimen (or the

transverse direction). Table 2 reports the experimental tests performed to determine the effect of

drying conditions such as drying air temperature (T), air velocity (V) and ambient relative humidity

(RH), on the drying kinetic of wood. The samples are put into a drying cell in which the temperature

and relative humidity are controlled respectively by a thermostat and a hygrometer. Several tests of

the moisture diffusion were conducted on the cubic samples of dimensions 20 x 20 x 20 mm (Radial

x Tangential x Longitudinal). A water sorption analysis was used in order to estimate the moisture

migration and moisture flow of wood during drying. The amount of release water was determined by

weighing the sample during the drying process. The moisture content X (%) of the samples

is computed as follows:



20

s

st

M

MMX

−= (1)

Where Mt is the weight of sample at time t, and Ms is the dry solid weight.

The dry solid weight is obtained by drying the sample in a heated oven at temperature of 103

°C until constant weight. The equilibrium moisture content of the sample is occurs when the

moisture content of samples does not vary for a constant drying air temperature and relative

humidity.

Table 2: Experimental data conducted to determine the effect of drying conditions on heat and mass

transfer in longitudinal and transverse diffusion of Red pine

Test V (m.s-1

) T(°C) RH (%)

n° 1 1 30 50

n° 2 1 45 70

n° 3 1 60 50

n° 4 1 45 70

n° 5 1 45 35

n° 6 2 45 50

n° 7 0,5 45 50

II.2. Estimation of longitudinal and transverse diffusion coefficients of wood

The mathematical model of moisture diffusion is based on the following assumptions:

- The moisture transfer is in one dimensional;

- The problem considers a sample wood exposed to longitudinal (or transversal) hot flow during

convective drying;

- Moisture transfer is by diffusion only;

- The flow air is laminar;

- The initial moisture content of the sample is uniform,

- The shape of the materiel remains constant and shrinkage is negligible;

- There is a thermal equilibrium between the wood surface and air.

Moisture diffusion, in a slap of thickness e is written in the (ox) referential:

∂

∂

∂

∂=

∂

∂

x

XD

xt

Xm (2)

where X is the moisture content (kg water.kg dry solid-1

), t is the drying time, and Dm is the

longitudinal diffusion coefficient (m2/s) (or transversal diffusion coefficient).

The analytical solution of the equation (2) using appropriate boundary conditions [10]:

∑∞

=

−−

−=

−

−=

12

22

22

...)12(exp.

)12(

18)(

n

m

ei

e

e

tDn

nXX

XtXMR

π

π (3)

where X(t) is the average moisture content, Xe is the equilibrium moisture content and Xi the

initial moisture content of the sample (kg water.kg dry solid-1

).

In many cases the diffusion coefficients of wood estimated by using only the first term (n=1)

of the general solution. Thus (1) can be written as:



21

).exp(..

.exp.8

2

2

2tAK

e

tDMR m =

−= π

π (4)

where: 2

8

π=K ;

2

2 .e

DA mπ−= (5)

In order to apply the diffusion equation in our study, we assumed that the measurements of moisture

content X of the sample verified the following expression:

BAtMRLny ii +== )( (6)

where i is the numerous of moisture ratio measurement at time t.

The coefficients A and B are obtained using the simple linear regression method as follow:

∑ ∑

∑ ∑ ∑

= =

= = =

−

−

=N

i

N

i

ii

N

i

N

i

N

i

iiii

ttN

ytytN

A

1 1

22

1 1 1

)(

;

∑ ∑

∑ ∑ ∑∑

= =

= = ==

−

−

=N

i

N

i

ii

N

i

N

i

N

i

iiii

N

i

i

ttN

yttyt

B

1 1

22

1 1 11

2

)(

(7)

where N is the number of measurements during test.

The slope A provides measurement of diffusion coefficient for each experiment and is

calculated by substituting the experimental data into equation (5). The root mean square error

between the experimental and fitting results with the model is as follows:

∑ −×=N

cal XXN

RMSE1

2

exp

1 (8)

where Xcal and Xexp are respectively the theoretical and experimental moisture ratio of wood during

convective drying process.

II.2. Determination of heat and mass transfer coefficients

The moisture content of Red pine is measured by using the gravimetric method. This method

allows recording the mass M of the sample versus drying time. These data are converted to draw the

curve of the drying rate. The moisture flow F is calculated thanks to the experimental data obtained

from the drying rate evolution versus time and the transfer surface S between the steam water and

wood [9]:

−=

dt

dM

SF

1 (kg.m

-2.s

-1) (9)

where dt

dMis the drying rate (kg.s

-1) and S is the transfer surface (m

2)

The moisture ratio is: ei

e

XX

XXMR

−

−= (10)

Xe is the equilibrium moisture content and Xi is the initial moisture content.



22

Convective heat and mass transfer coefficients are required in any heat and moisture transfer

calculations. Convective heat transfer coefficient is often determined using empirical correlations

based on the measurements of different geometry and flows. Convective heat transfer between a

moving fluid and a surface transfer of materiel can be defined by the following relationship:

vst HFTThQ ∆=−= ∞ .)( (11)

where F is the mass flow (kg.m-2

.s-1

), Q is the heat flow (W.m-2

), ht is the convective heat transfer

coefficient (W.m-2

.°C-1

), Ts is the temperature at surface (°C), T_ is ambient air temperature (°C) and

∆Hv is the differential heat of sorption (J.kg-1

).

Similarly, mass transfer coefficient hm (kg2.m

-2.s

-1.J

-1) can be described by the following equation:

)( ∞−= ψψ smhF (12)

where �ψs is the surface water potential (J.kg-1

) and ψ� is the water potential of air-water vapour

mixture (J.kg-1

).

III. RESULTS AND DISCUSSION

Figure 2 shows the effect of drying air temperature on wood behaviour during convective

drying in longitudinal and transverse diffusion. The initial moisture content is equal to 0,7 kg

water.kg dry solid-1

. The ambient relative humidity of drying cell during this test has 50 % with an

air velocity of 1 m.s-1

. The wood samples subjected to drying process are small, mainly, to reduce the

drying time and to reaches rapidly the equilibrium moisture content. The convective hot air caused

evaporation of water in the surface of wood, leads to decreases moisture content and drying time, till

it reached equilibrium water content with the surrounding air. Results showed that the longitudinal

diffusion is larger than transverse one, probably because of the longitudinal contribution of the fibres

in the transport of water [3]. The sample micro-topography obtained with the scanning electron

microscope (figure 3); explain the difference between the longitudinal and the transverse diffusion of

water. The drying kinetic curves show the falling drying rate period controlled by diffusion process

that governs the moisture movement in the bound wood cell. This results show that the drying time

decreased with air temperature, because the drying force between the vapour pressure of air and

surface saturated pressure increased as the drying air temperature increased. In fact, the increase of

the energy supply rate to the product and moisture migration throughout the wood is accelerated. The

drying time was reduced substantially with an increase of drying air temperature from 30 °C to 60

°C. For drying air temperature of 60 °C, only 8 hours were needed to reach the equilibrium moisture

content. For 45 °C, the equilibrium moisture content moisture was obtained after 24 hours of drying.

However, for an air temperature of 30 °C, 24 hours were still sufficient and the drying is completed

when the thermal equilibrium between wood surface and surrounding air is established.

The effect of ambient relative humidity on drying kinetic of Red pine is shown in Figure 4. It

can be noticed that the drying rate decreased as the ambient relative humidity increased from 50 to

70 %. This effect is considered less important than that of the drying air temperature. Figure 5 shows

that the air velocity, affects the drying rate of wood because the surface water potential depend on

the convective heat and mass transfer coefficients which decreased as the air velocity decreased [4].

It is showed that there is an acceleration of the drying process due to the increase of the air velocity

from 0,5 to 2 m.s-1

. This effect is considered, in general, lower than the influence of drying air

temperature.



23

Figure 2: Average moisture content versus time: effect of drying air temperature

a) b)

Figure 3: Longitudinal a) and transverse b) micro-topography of Red pine

Figure 4: Average moisture content versus time: effect of ambient relative humidity.



24

Figure 5: Average moisture content versus time: effect of air velocities.

Fitting the moisture ratio model has been done with the experimental data of drying at 30, 45

and 60 °C, ambient relative humidity of 35, 50 and 70 % and three level air velocities 0,5, 1 and 2

m.s-1

. Several experiments fitted the drying model in the form of changes in water content versus

time. From equation 6, a plot of ln(MR) versus drying time for various drying air temperature gives a

straight line with intercept =B, and slope =A (Figure 6). It is noted that the slope of straight line

increased as the air temperature increased and the drying times also become shorter as the drying air

temperature is increased.

Table 3 show the diffusion coefficients, drying constants A and B which are deduced after

fitting our model with the experimental results with a root mean square error (RMSE) not exceeding

0,2. The drying constant A was evaluated to estimate the diffusion coefficients using the equation

(5). The drying constant A of the moisture ratio model was calculated from the slopes of drying

curves as shown in figure 6. The drying constant A ranged from – 0,129 to – 0,65 h-1

. Air velocity

and ambient relative humidity also affected the slope of ln(MR) versus drying time; the slop A was

found higher in the high values of air velocity and relative humidity is low. As discussed previously,

the drying times also become shorter as the air flow rate is increased.

Figure 6: ln(MR) versus drying time: effect of drying air temperature



25

The longitudinal diffusion coefficient is larger than the transverse diffusion coefficient. The

diffusion coefficients was found higher in the high drying air temperature, because the heat sorption

of bound cell increased as the drying air temperature increased. It was also observed that the

diffusion coefficients range from 1,44 x 10-9

to 7,2 x 10-9

m2.s

-1 under the above drying conditions.

The result has shown that the logarithmic of drying model has strong linear relationship with drying

time. This study confirms the reliability of the simple regression linear method used to estimate the

diffusion coefficient because the values of these coefficients are in good agreement with results

given by Mouchot [1] and Agoua [2] for wood.

Table 3: Constants drying fitting of moisture ratio model and diffusion coefficients of Red pine

Transfer mode T (°C) RH

(%)

V

(m.s-1

) A (h

-1) B

Dm x 10-9

(m2.s

-1)

RMSE

Longitudinal

diffusion

30 50 1 – 0,165 0,14 1,84 0,052

45 50 1 – 0,21 0,02 2,35 0,065

60 50 1 – 0,65 0,1 7,2 0,15

45 70 1 – 0,137 – 0,009 1,53 0,024

45 35 1 – 0,284 – 0,394 3,18 0,17

45 50 0,5 – 0,138 – 0,087 1,54 0,035

45 50 2 – 0,357 – 0,436 4 0,065

Transverse

diffusion

30 50 1 – 0,146 0,22 1,63 0,081

45 50 1 – 0,182 0,164 2,03 0,053

60 50 1 – 0,45 0,45 5,04 0,083

45 70 1 – 0,129 0,08 1,44 0,057

45 35 1 – 0,258 – 0,167 2,88 0,18

45 50 0,5 – 0,13 0,003 1,45 0,028

45 50 2 – 0,344 – 0,082 3,85 0,02

Figures 7 and 8 show the profile of moisture flow versus drying time in longitudinal and

transverse moisture diffusion of Red pine. The moisture flow is calculated from the experimental

data of water content using the equation (9). For each sample the transfer surface is S = 400 mm².

The moisture flow curves were found higher in the high drying air temperature and low ambient

relative humidity. In fact, high drying air temperature and low relative humidity allowing to favorite

the driving force for the water evaporates into the air and get more power for drying.



26

Figure 7: Moisture flow versus moisture ratio of longitudinal diffusion

Figure 8: Moisture flow versus moisture ratio of transversal diffusion

When the air velocity was increased, the moisture flow and water evaporation inside the

materiel were considerable. This phenomenon is because of applying more flow rate to the wood

product and increasing in moisture migration and reduces the drying time. These results provide that

the drying air temperature is the main factor affecting the drying rate and reduce the drying time

during the convective drying process of wood.

Table 4 indicates heat and mass transfer coefficients deduced from the maximum moisture

flow data. The difference in water potential between the surface and the surrounding air is used to

determine the convective heat and mass transfer coefficients by substituting the experimental data of

moisture flow into equations (11) and (12).



27

Table 4: Heat and mass transfer coefficients calculated on the basis of the moisture flow

Transfer mode T (°C) RH (%) V

(m.s-1

)

ht

(W.m-2

.°C-1

)

hm x 10-10

(kg2.m

-2.s

-1.J

-1)

Longitudinal diffusion

30 50 1 4,59 1,83

45 50 1 10,52 5,18

60 50 1 18,06 10,48

45 70 1 10,19 4,35

45 35 1 11,35 8,2

45 50 0,5 6,82 2,86

45 50 2 17,59 8,66

Transverse diffusion

30 50 1 4,45 1,78

45 50 1 7,03 3,46

60 50 1 13,2 7,66

45 70 1 8,38 2,78

45 35 1 9,26 4,77

45 50 0,5 5,35 2,63

45 50 2 10,79 5,31

For similar operating conditions, these values are different and depend on the longitudinal

and transverse moisture diffusion of wood. These values range from 4,45 to 18,04 W.m-2

.°C- 1

for

heat transfer coefficient and from 1,78 x 10-10

to 10,48 x 10-10

Kg2.m

-2.s

-1.J

-1 for mass transfer

coefficient. Both coefficients increase as drying air temperature and air velocity increased.

As discussed previously, several types of researches have been conducted in order to determine heat

and mass transfer coefficients during drying of wood, the difference between these works is the main

driving force used in different version of diffusion models such as moisture potential, water potential

or pressure vapour. The main driving force used in different version of diffusion model is reported in

table 5. Our results are in good agreement with results of Tremblay [4], and Nabhani [5], using the

water potential as driving force. These results demonstrate the feasibility and accuracy of the

approach using the water potential to estimate convective heat and mass transfer coefficients during

drying of wood.

Table 5: Heat and mass transfer coefficients given by some authors for wood

Authors Method Air conditions hm ht

Tremblay [4]

Water potential T =56 °C,

V =1 to 5 m.s-1

1 to 14 x 10-10

Kg2.m-2.s-1.J-1

5 to 45

W.m-2.°C-1

Dimensionless

parameters

T =56 °C,

V=1 to 5 m.s-1

8,6 to 13,8 x 10-10

Kg2.m-2.s-1.J-1 23 to 34

W.m-2.°C-1

Nabhani [5]

Water potential T =30 to 90 C,

V =2 to 5 m.s-1

7 to 20 x 10-10

Kg2.m-2.s-1.J-1

13 to 25

W.m-2.°C-1

Dimensionless

parameters

T =30 to 90 °C,

V =2 to 5 m.s-1 0,008 to 0,025 m.s

-1

4 to 18

W.m-2.°C-1

Ananias [8] Moisture

content

T =40 to 70 °C,

V =2,5 m.s-1 0,012 to 0,021 m.s

-1

26 to 44

W.m-2.°C-1

Thomas [11] Moisture

potential T =110 °C

2,5 x 10-6

kg2.m

-2.s

-1.°M

-1 22,5 W.m-2

.°C-1

Sutherland [12] Vapour density T =90 °C,

V =3 m.s-1

0,02 m.s

-1 20,9 W.m

-2.°C

-1



28

IV. CONCLUSIONS

Experimental and theoretical analysis of heat and moisture transfer during convective drying

of Red pine has been investigated. The curves of moisture content versus drying time shows only the

falling drying rate period and that the longitudinal moisture transfer removes water faster than the

transverse mode. The results has shown that drying time is affected by drying air temperature, air

velocity and ambient relative humidity and that the drying air temperature is the main factor in

controlling the product drying rate. The plot of ln (MR) versus drying time for various drying

conditions gives a straight line relationship with time. The diffusion coefficients have been

determined from the values of the slop A and the longitudinal moisture diffusion coefficient is larger

than the transverse one. From the measurements of moisture flow evolution during drying, heat and

mass transfer coefficients have been determined and compared to results from the literature to

demonstrate the efficiency analysis of the method used to estimate heat and moisture movement

during convective drying of Red pine. However, this method for the estimation of the diffusion

coefficient only assumes a constant diffusion coefficient in longitudinal and transverse direction

throughout the whole drying process. For this further reason, more comprehensive drying conditions,

energy efficiency and design of drying model should be considered to determine the need

for further diagnostic research on drying efficiency of Red pine. Moreover, the influence of drying

method and various sizes of specimen can be studied using this theoretical approach.

REFERENCES

[1] N. Mouchot, A. Wehrer, V. Bucur, A. Zoulalian, Détermination indirecte des coefficients de

diffusion de la vapeur d’eau dans les directions tangentielle et radiale du bois de hêtre, Ann.

For. Sci. 57, 2000, 793 – 801.

[2] E. Agoua, S. Zohoun, P. Perré, A double climatic chamber used to measure the diffusion

coefficient of water in wood in unsteady-state conditions: determination of the best fitting

method by numerical simulation, International Journal of Heat and Mass Transfer. 44(11),

2001, 3731 – 3744.

[3] A.M. Josef, W.T. Claude, Experimental determination of the diffusion coefficients of wood

in isothermal conditions, Heat Mass transfer, 41(11), 2005, 977 – 987.

[4] C. Tremblay, A. Cloutier, Y. Fortin, Experimental determination of the convective heat and

mass transfer coefficients for wood drying, Wood Sci Technol, 34(3), 2000, 253 –276.

[5] M. Nabhani, C. Tremblay, Y. Fortin, Experimental determination of convective heat and

mass transfer coefficients during wood drying, 8th Intl. IUFRO Wood Drying Conf., 2003,

225 – 230.

[6] H. Yeo, W.B. Smith, R.B. Hanna, Mass transfer in wood evaluated with a colorimetric

technique and numerical analysis, Wood and Fiber Science, 34(4), 2002, 657 – 665.

[7] J.G. Salin, Prediction of heat and mass transfer coefficients for individual boards and board

surface, Proceedings of the 5th Intern. IUFRO Wood Conf., Aug. 13-17, Quebec, 1996,

49 – 58.

[8] R.A. Ananias, B William, A Mara, S Carlos, B.K Roger, Using an Overall Mass Transfer

Coefficient for Prediction of Drying of Chilean Coigüe, Wood Fiber Sci, 41(4), 2009,

426 – 432.

[9] A. Khouya, A. Draoui, Détermination des courbes caractéristiques de séchage de trois

espèces de bois, Revue des Energies Renouvelables, 12(1), 2009, 87 – 98.

[10] J. Crank, the Mathematics of Diffusion, Clarendon Press, London, UK, 2nd edition, 1975.



29

[11] H. Thomas, R.W. Lewis, K Morgan, A fully nonlinear analysis of heat and mass transfer

problems in porous bodies, International Journal for Numerical Methods in Engineering,

15(9), 1980, 1381 – 1393.

[12] J.W. Sutherland, I.W. Turner, R.L. Northway, A theoretical and experimental investigation of

the convective drying of Australian Pinus radiate timber, Proceeding of the 3th IUFRO

International Wood Drying Conference, Aug. 18-21, Vienna, Austria, 1992, 145 – 155.

[13] Singh, L.P., Choudhry V. and Upadhyay, R. K., “Drying Characteristics of a Hygroscopic

Material in a Fabricated Natural Convective Solar Cabinet Drier”, International Journal of

Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2012, pp. 299-305,

ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.

[14] Yogesh Dhote And S.B. Thombre, “A Review on Natural Convection Heat Transfer Through

Inclined Parallel Plates”, International Journal of Advanced Research in Engineering &

Technology (IJARET), Volume 4, Issue 7, 2013, pp. 170 - 175, ISSN Print: 0976-6480,

ISSN Online: 0976-6499.

[15] Dr P.Ravinder Reddy, Dr K.Srihari, Dr S. Raji Reddy, “Combined Heat and Mass Transfer in

MHD Three-Dimensional Porous Flow with Periodic Permeability & Heat Absorption”

International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2,

2012, pp. 573 - 593, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.

[16] Dr. Sundarammal Kesavan, M. Vidhya and Dr. A. Govindarajan, “Unsteady MHD Free

Convective Flow in a Rotating Porous Medium with Mass Transfer”, International Journal of

Mechanical Engineering & Technology (IJMET), Volume 2, Issue 2, 2011, pp. 99 - 110,

ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.

[17] S.K. Dhakad, Pankaj Sonkusare, Pravin Kumar Singh and Dr. Lokesh Bajpai, “Prediction of

Friction Factor and Non Dimensions Numbers in Force Convection Heat Transfer Analysis of

Insulated Cylindrical Pipe”, International Journal of Mechanical Engineering & Technology

(IJMET), Volume 4, Issue 4, 2013, pp. 259 - 265, ISSN Print: 0976 – 6340, ISSN Online:

0976 – 6359.