CFD ANALYSIS OF THE EFFECT OF HEATING COIL INSTALLATION ON HEAT AND

AIR FLOW DISTRIBUTION WITHIN COMPARTMENT WOOD DRYING KILN

Asst. Prof. Dr. Nirundorn Matan1

Marhaindra Gary Isworo2

1Department of Material and Science, School of Engineering and Resources, Walailak

University, Thailand

222 Thaiburi, Thasala District, Nakhon Si Thammarat, Thailand

mnirundo@wu.ac.th 2Department of Mechanical Engineering, Engineering Faculty, Sriwijaya University,

Indonesia

Jalan Palembang-Prabumulih Km.32 Indralaya, South Sumatra, Indonesia

ABSTRACT

Problem that exists in the timber industry in particularly process of water content reducing in

the wood using compartment kiln is about heating coil installation within the kiln. In this

research, the coil installation will be determined the best of coil installations by taking

samples from the factories by looking at the heat and airflow distribution uniformity within

the kiln. Method of This study is CFD (Computational Fluid Dynamic) analysis by software

Flovent 9.1. There are 3 variable coil positions, the coil placed horizontally (parallel to the

fluid flow of the fan), vertically (perpendicular to the fluid flow), and with slope of 57. This

research concluded that the position of the coils have uniform distribution of heat and air flow

is in the horizontal position or parallel to the direction of air flow.

Keywords: Compartment Kiln, Flovent CFD, Heating Coil

Introduction

The timber of living trees and freshly felled

logs contains a large amount of water, which

often constitutes over 50% of the woods'

weight. Water has a significant influence on

wood. Wood continually exchanges moisture

or water with surroundings, although the rate

of exchange is strongly affected by the

degree wood is sealed. Drying timber is one

method of adding value to sawn products

from the primary wood processing industries.

The lumber cannot be used to produce a high

quality finished product. Properly dried

lumber sells for a higher price and is much

easier to work than lumber that has not been

dried. When lumber is dried right, it

machines better, glues better, and finishes

better. Drying also improves the strength of

the lumber, kills infestations, hardens pitch,

preserves color, reduces weight and controls

shrinkage. Lumber that is not dried under

controlled conditions is prone to warping,

staining, and other degrade that diminishes

its selling price and workability.

Most of this water must be removed in order

To obtain satisfactory performance from

wood that is to be processed into consumer

and other types of useful products (Bousquet,

2000).

Figure 1. Compartment Kiln

(source: http://wnyhardwoods.wordpress.com)

Take the example of a truck load of oak.

Fresh cut oak weighs about 5,4 kg/m2. So a

truckload of 8 m2 so weighs about 43,2 kg.

Once you remove enough water to get the

oak down to a moisture content of 6% - 8%,

it weighs about 3.5 kg/m2. So that truckload

now weighs 28 kg. That means that to

completely dry a truckload of 8 m2 of oak,

you have to remove 15,2 kg of water. Thats why choosing the right drying system and

using the proper method are so important.

Conventional way of drying is most

frequently used way of drying wood because

the kilns are technically very simple, even for

large capacity kilns (over 100 m3 of timber).

They do not require extra maintenance and

electrical power consumption is reduced by

using wood wastes as fuel for boiler. There

are two types of convention kiln,

Compartment Kiln (figure 1) and Progressive

Kiln, which are different from the way to dry

the wood (Sucipto, 2009). In this research

defined to analyze Compartment Drying Kiln

and the energy source is constant temperature

from steam.

The airflow in the kiln chamber is very

important. The velocity of the air over the

wood affects the drying rate and provides

even drying. We should know air velocity

with the kiln manufacturer to be sure that the

air velocity in the kiln will be adequate for

the species and thickness of the lumber we

are drying and the type of kiln you are using.

The air velocity is depending on how we put

the coil installation. Now, in Thailand there

are many company using coil verticality and

another country using with different

direction. Generally, industries have not take

attention about coil installation. Then, this

research would be analyzed which one is the

best coil installation within the kiln.

Method

The modeling and simulation process starts

with the consideration of a series of

assumptions related to how the physical and

chemical phenomena occur within the pieces

of equipment, and then, they are inserted in a

series of fundamental equations (mass

balance, quantity of movement and energy,

conservation equations, etc.) The model is,

then, mathematically solved - simulation -

generating answers that are compared to the

data of the experiment, to its validation

(Islabo, 2010).

1) Software: Its not always possible to make experiments with systems or prototypes. In

these cases, the CFD analysis shows parts of

the systems or phenomena, which enable

assumptions to be materialized, tested situations. In this research using Software

Flovent 9.1 Copyright 1989-2010 Mentor

Graphics Corporation.

2) Subject Space: Dimensional kiln is 4.20m x 7.50m x 5.20m with wall thickness of 0.1

meter. There are 4 fan motors diameter 0.2

meter, 1.2 meter outer diameter, and

thickness of 0.1 meters as a fan maker of

fluid flow at a distance of 6.7 cm coil. This

kiln is illustrated by incorporating wood stick

by dimensions 0.1m x 1.3m x 0.038m.

Inside, there is a layer of wood stick that

juxtaposed as many as 29 stems. Each turn of

the pinned layer of wood stick 3 buffer rod

transverse to the wood stick by dimensions 3

x 2.54 cm x 2.74 cm, the distance of each

buffer as far as 0.65 m. Forming a space for

air to flow between the layers of wood stick

as high as 2.74 cm. Nested layers of wood

stick to 48 layers, so that the total dimension

lumber is 3m x 1.3m x 3.5m.

3) Coil Installation: Coil dimension is 7.5 meters long and radius 3.3 cm. This research

will be analyzed the airflow and the

temperature changes by coil K0067

(horizontally), K5767 (slope 57o), and K9067

(vertically) see figure 2. Distance of each coil

is the same, namely by 6.7 cm. The amount

of coil at K0067 is 5 pieces, K5767 is 11

pieces and K9067 is 9 pieces.

Figure 2. Coil Installation Variable

4) Boundary Condition:

Table 1. Boundary Condition of Kiln Design

No. Subject Material Construction

1 Wall Brick Wood 0,84 W/moK

2 Fan Axial Fan 8 m3/s

3 Fan Deck Brick wood Non-conducting

4 Wood Stack Wood

Blocks 30

oC

5 Template

Lumber

Wood

Blocks 30

oC

5 Coil Iron 90oC

6 Vent Hole 100% open

7 Buffle Aluminum 201 W/moK

5) Experiments: All of design (K0067, K5767, and K9067) will be run using

Flovent, then the result that will be taken are

temperature, x-velocity, and speed on each

wood stack space from bottom to top in

every lumber. After all of parameters has

been taken then researcher will analyze the

result and make some group of analyzing,

those are Top to Bottom (TB), Front to Rear

(FR), and Left to Right (LR). From these

group of analyses should be determined the

airflow distribution and thermal in every

wood stack space and combining and

analyzing all results and put the value into

the graphic then make the conclusion. We

can see which one the design that has

uniform distribution of airflow and thermal.

Results and Analyses

Based happened in the industry today, there

are some companies using closed kiln system

or otherwise kiln without ventilation.

However, in this research also made kiln

design with open ventilation system to keep

the pressure within the kiln. Based on the

results obtained that the vents open or closed

the temperature and velocity of fluid in the

system does not change significantly. It

means that company should open vents in

certain time to maintain the stability of the

pressure within the kiln. So in this research

selected kiln system with open ventilation

conditions.

Figure 3 showing the airflow distribution of

K0067 with color approximately the same,

only at one point. Figure 4 or K5767 is

colorful, it means the airflow distribution is

not uniform. And figure 5 showing the colors

are almost the same only some point

differences and darker than K0067. From

these figures can be seen if the air speed of

K9067 is the fastest airflow, but we dont know yet about the uniformity.

Figure 3. X-Velocity K0067

Figure 4. X-Velocity K5767

Figure 5. X-Velocity K9067

Figure 6 presents the pattern of air flow

distribution only at x-axis within the kiln,

where the blue color given to K0067 has a

shape that is almost like a horizontal straight

line. It is claimed that the kiln with

horizontally mounted coil installations have a

good uniformity of air flow from the top to

the bottom of the lumber.

Figure 6. X-Velocity Comparison

Uniformity of air velocity has not been able

to be a benchmark of good or not a kiln

system. Speed is uniform but the temperature

is not uniform can produce the products are

not uniform as well, and vice versa. So, it

should be noted also how the temperature

distribution in each wood stack space at the

same point as in the analysis of fluid

velocity. Figure 7 can be seen that each coil

has the same pattern, which is the highest

temperature is at the center of the lumber.

However, the average temperature is highest

become to K9067 and the lowest is K0067.

Although the K5767 has the highest number

of coil is 11 coils but the temperature is

under of K9067.

Figure 7. Temperature Comparison

Based on the results obtained could not be

determined conclusion yet, because the

K0067 has a uniform speed of the airflow but

the temperature is very low (low efficiency).

K9067 is a highest efficiency but the airflow

is not uniform. Based on the hypothesis of

the researcher, main cause why K0067 is

low temperature due to the amount of coils is

only 5 coils, while the K9067 is 9 coils. To

have a kiln with high temperature and a

uniform distribution of air flow, K0067 need

4 coils to be added without changing the flow

rate of the air.

Figure 8. K0067 with 5 coils

Figure 9. K0067' with 9 coils

In figure 8, kiln has 5 coils horizontally and

Figure 7 can be seen that kiln is added 4 coils

to raise the temperature of the coil and names

become to be K0067'. At K0067 design made 2 lines parallel with the coil distance is

1 cm to prevent air flow velocity changes. To

fulfill the total coil then there is a vacancy on

the inside of, the reason why researcher

select this point is based on researched

before. That was almost the same result as

before when the vacancy is at the outside of.

Figure 10 presents changes that happened

due addition the number of coil on K0067.

Purple line is the temperature for K0067'

while the green line is the K9067.

0

0.5

1

1.5

2

2.5

3

3.5

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6

Air

Sp

ee

d (

m/s

)

Altitude (m)

X-Velocity (Bottom to Top)

K0067 K5767 K9067

30.8

31

31.2

31.4

31.6

31.8

32

32.2

32.4

32.6

32.8

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6

The

mp

era

ture

(oC

)

Altitude (m)

Temperature (Bottom to Top)

K0067 K5767 K9067

Temperature value of K0067' is a little bit

higher than the K9067. In another hand

K0067' velocity of air flow that occurs has a

pattern similar to the K0067.

Figure 10 Temperature Comparison

From the figure above we can make the

conclusion of the best coil installation is

K0067. It has good uniformity of air flow

distribution and the thermal efficiency also

good. Let see figure 11 shows the color of

temperature within the kiln, the color is dark

yellow and approximately the temperature at

the points are the same 32,4oC.

Figure 11 Visualization of Thermal DIstribution K0067'

Conclusions

The coil amount of compartment kiln with

coil direction 57o by dimension 1,3 meter

from fan deck to the roof and 0,8 meter from

wall to the wood stack is 11 coils, this design

is the greatest number of coil but for

temperature and air flow distribution are

worst than the others.

Compartment kiln with coil direction 90o by

the same dimension has 9 coils, temperature

efficiency of this system is 36% otherwise

the temperature is better than 57o

of coil

direction, but air flow distribution is not

good.

Compartment kiln with coil direction 0o by

the same dimension has 5 coils and modified

to be 9 coils with 2 row coil (5 coils above, 4

coils below), at this design the air flow is

uniform from top to bottom of wood stack

and the temperature efficiency is 36% as

same as coil direction 90o.

References

Bousquet, Dan. 2000. Lumber Drying: An

Overwiew of Current Processes. University

of Vermont Extension, Burlington.

Gebhart, B. 1973. Natural Convection Flows

and Stability: Advances in Heat Transfer.

Volume 9. Academic Press.

Islabo, G. I.; Pinto, J.C.; Junior, A.D. 2010. Technological Trends in CFD Applications.

Journal of Technology Management &

Innovation. Volume 5. Universidad Alberto

Hurtado: 77.

Mike Papkes Portable Sawmilling & Specialty Hardwoods. 2010. Second Dried

Load. http://wnyhardwoods.wordpress.com.

[Accessed: October 20, 2013].

Mills, A.F. 1999. Heat Transfer. Prentice-

Hall, New Jersey.

Sucipto, T.S. 2009. Pengeringan Kayu

Secara Umum. Ph.D. Thesis, Universitas

Sumatera Selatan, Medan, Indonesia.

30.8

31

31.2

31.4

31.6

31.8

32

32.2

32.4

32.6

32.8

33

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6

The

mp

era

ture

(oC

)

Altitude (m)

Temperature (Bottom to Top)

K0067' K0067 K9067 K5767