TREND OF HEAT DEVELOPMENT OF PARALLEL AND TRANSVERSE WOOD PLACING IN OPEN FIREPLACE

8/13/2019 TREND OF HEAT DEVELOPMENT OF PARALLEL AND TRANSVERSE WOOD PLACING IN OPEN FIREPLACE

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TREND OF HEAT DEVELOPMENT OF PARALLEL AND

TRANSVERSE WOOD PLACING IN OPEN FIREPLACE

Open fireplace is most rudimentary form of human exploitation of the fire for purpose of

regulating basic physiological needs . All the necessary components of such fireplace can be

found or produced in nature , which makes it indispensable in survival situations . The big

disadvantage of the open fireplace is very low efficiency. Soderstrom (1982 ) states that open

fireplaces in houses have efficiency of 15-25 %, which means that the only 15-25 % of the

total wood heat potential is exploited. One should consider that the open fireplaces in houses

is certainly more economical than those in nature because the walls and chimney absorb and

radiate around 5-15 % of the total heat potential ( Soderstrom , 1982). Control over the open

fireplace can be achieved by modulating the relationship between wood mass / wood surface ,

and changing the total amount of exposed wood in the fire . Unlike wood stove where ispossible to control air flow , that is not possible in open fireplace.

In the chart below we can see the difference in the burnabiiity between pieces of wood that

are gradually split into thinner pieces (Tresemer, 1981).


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Modularity in terms of exposed fuel can be achieved by two distinctive forms of placing wood

in fireplace : PARALLEL AND TRANSVERSE WOOD PLACING.

In order to examine differences in the trend of heat development between these two forms , a

colleague and I conducted an experiment .

I will not go into detail. We were used willow logs, one meter in length, that are sorted into

two identical groups by size and weight.

Group comprised 6 different log categories by diameter ( measured at both ends , then the

average value is taken )

6 categories diameter : 5.5 , 6 , 6.5 , 7 , 7.5 , 8 cm

Two groups are formed, each with 4x5.5cm(log diameter) , 10x6cm , 10x6.5 , 4x7cm , 2x8cm

and 8x7.5cm, making a total of two sets with 19 logs , every group weighing 37kg .

Moisture content of wood was 10~11 % .

Air temperature during the measurement was between 0 and 0.5 C, humidity 83 % ,

experiment began at 00:30 and finished at 07:30 .

It was used 12 digital thermometer , placed at a heights of 50cm, on the four sides of world

and distances of 80, 160and 240cm from the center of the fireplace.

At the center of the fireplace it was stuck a piece of thick wire in the ground that served as a

landmark for adding wood and placing thermometers .

It was used an identical quantity of firewood for fire ingnition.

After 10 min of burning, placing of logs started. The first method was tranverse placing.

Wood is added so that approximately the first third of log was in the fire , and when

unburned piece broke, it was added back into the fire.

The dynamics of the adding logs was identical in both methods of placing :

After 5 min 5x5.5cm , 3x6.5cm 30min , 55min 2x6.5 and 2x7cm , 3x7.5cm 80min ,

105min 1x7.5 and 1x8cm .

Interval of thermometer reading was 5min .

Direction of the log longitudinal axis in a parallel placing was east-west .

Transverse placing method burned 205min, and parallel 160min. Experiment stops when

all burned down and when flame was not visible .


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Chart 1. Average temperatures

Chart 2. North


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Chart 3. West

Chart 4. South


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Chart 5. East

The highest recorded temperature:

transverse: 62 C

parallel: 56.7 C

Average values:

80 transverse = 28.65 C

160 transverse = 7.30 C (25.47% of 28.65)

240 transverse = 2.79 C (9.73% of 28.65)

80 parallel = 26.23 C

160 parallel = 6.72 C (25.61% of 26.23)

240 parallel = 2.50 C (9.53% of 26.23)

It is known that the spreading of sound, light, strength of gravity, and thermal radiation

follows the inverse square law, which specifically meant if at 80 cm from a fireplace getting

temp of 28C then when double that distance, you get only one quarter of that amount of heat

that is 25 %, at twice that distance from you (240cm) you will get only 1/9 or 11% of heat, as

the above results prove ..


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Illustration below nicely explain inverse square law.

The results indicate significant differences between these two ways of placing logs, although

the transverse created a higher temperature, I think that this distribution of thermometers

failed to include specific geometry of thermal expansion in the parallel placing. Parallel

method consumes a lot more fuel (almost entire logs are burning), but produces moderate /

lower temp dispersed over a larger area. Anyone who has tried to sleep beside burning logs

1.5-2 meters length, will know the advantages of this fireplace.

Transverse method emited higher temperature, and because only a small portion of the logs

are exposed (Approx.1 / 3), wood is slowly consumed, the flames of this fireplace are higher

and brighter, which is ideal for creating light, signaling, boiling water ...

References:

Soderstrom, N. (1982) Heating Your Home with Wood. New York: Harper & Row

Tresemer, D. (1981). Splitting Firewood. Brattleboro, Vermont: Green River Tools


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TREND OF HEAT DEVELOPMENT OF PARALLEL AND TRANSVERSE WOOD PLACING IN OPEN FIREPLACE

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