MASS TRANSFER PROPERTIES OF ACACIA MANGIUM PLANTATION WOOD

MASS TRANSFER PROPERTIES OF ACACIA MANGIUM PLANTATION WOOD 2 Ha Tien Manh1*, Adam L. Redman2, Chuong Pham Van3, Bui Duy Ngoc1 3 1 Research Institute of Forest Industries, Vietnamese Academy of Forest Sciences, Bac Tu Liem, Hanoi, 4 Vietnam. 5 2 Queensland Department of Agriculture and Fisheries, Horticulture and Forestry Science, Salisbury 6 Research Facility, Salisbury, Queensland, Australia. 7 3 Vietnam National University of Forestry, Xuan Mai, Chuong My, Hanoi, Vietnam. 8 *Corresponding author: hatienmanhfsiv@gmail.com 9 Received: June 02, 2020. 10 Accepted: September 20, 2021 11 Posted online: September 21, 2021 12 13 ABSTRACT 14 This study investigated the mass transfer properties (permeability and mass diffusivity) in the 15 longitudinal, radial and tangential directions of plantation-grown Acacia mangium in Vinh Phuc 16 province, northeast, Vietnam. These properties will be used to complement a conventional drying model 17 in the future. Measurements of gas and liquid permeability were performed using a Porometer 18 (POROLUXTM1000). Mass diffusivity was determined in a constant humidity and temperature chamber 19 using PVC-CHA vaporimeters. Results showed the gas permeability was significant higher than liquid 20 with the descending order of longitudinal, radial, and tangential directions. The permeability anisotropy 21 ratios from the longitudinal to transverse directions of Acacia mangium were much lower than other 22 published species. However, the obvious anisotropy ratios from radial to tangential for both permeability 23 and diffusivity, is one of concerns as they can exacerbate defects during drying. Besides, the high 24 permeability and diffusivity of Acacia mangium compared to some other species reported compounds 25 its relatively fast drying rate. 26


INTRODUCTION
the boards, a 70 mm long sawn section was removed and a pair of 23 mm diameter cylinders were cored 78 through the surface using a 28 mm hole-saw. Each core was cut into two equal thickness pieces using a 79 band-saw and was router planed to 10 mm thickness, to produce 20 tangential and 20 radial permeability of the diagram was cored through the surface using a 79 mm diameter hole-saw and was cut using a 87 band-saw to get 2 equal thickness, 74 mm diameter cylinders. Afterwards, these cylinders were router 88 planed to 8 mm thickness to produce 10 radial and 10 tangential (in thickness direction) samples for 89 determining transverse diffusivity. The side surfaces of all specimens were coated with two layers of 90 epoxy resin to guarantee the air tightness of the lateral surfaces during measurement. In order to create 91 a fresh flow through surface, these specimens were cleaned by air at pressure of 7 bar. The samples used 92 for gas permeability were equalized in a conditioning chamber at 65 % ± 2 % relative humidity and 20 93 ºC ± 0,1 ºC temperature to produce equilibrium conditions of 12 % moisture content. The diffusivity Maderas-Cienc Tecnol 24(2022):2, 1-20 Ahead of Print: Accepted Authors Version 5 samples were equalized in another conditional chamber at 75 % ± 2 % relative humidity and 35 ºC ± 0,1 95 ºC temperature to meet 14 % moisture content.

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In the present study, all measurements and calculations for all three directions permeability (longitudinal, radial 119 and tangential) were carried out automatically on a Porolux 1000 Porometer (IB-FT GmbH, Berlin, Germany) 120 ( Figure 2) with control software. Two types of medium for permeability determination were gas (atmospheric 121 air) and liquid (rain-water). For gas, atmospheric air pressure was increased to 4200 mbar. The gas permeability 122 was measured at a pressure difference within this range. For liquid, rain-water pressure was increased and

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As mentioned, before the experiment, wood samples were placed into the conditioning chamber to meet 160 14 % moisture content. (1) (2)  Gas and liquid permeability data for A. mangium in the longitudinal, radial, and tangential directions 211 were presented in Table 1. The results highlighted the major difference between gas and liquid figures.

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The gas permeability was 4, 23, and 74 times higher than the liquid permeability in the longitudinal, 213 radial, and tangential direction respectively. The difference between the gas and liquid permeability was 214 smallest in the longitudinal direction, but it was significant because the p-value was 5,67x10 -27 , much 215 less than 0,05. These highly significant differences can be attributed to air being approximately 50 times 216 less viscous than water at room temperature and the lower molecular size of air compared with water.

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Air is able to move through the small opening in wood tissue more easily than water. It is in agreement 218 with the results obtained by Taghiyari (2012). The results also showed the anisotropy ratios of both gas and liquid permeability. In previous studies,  Table 2. This suggests the high permeability of A. mangium compared to other species reported partly relating to its fast drying rate at above fibre saturation point.

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The gas permeability anisotropy ratios were more modest in A. mangium than other species reported.
247 This is probably due to the fact that the transverse pathways system (e.g. pits, rays) of A. mangium is 248 more open.

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The measured diffusion coefficients in the radial, tangential, and longitudinal directions for A. mangium 267 were presented in Table 3. The difference in the diffusivity between each pair of direction were highly 268 significant because p-values were all much less than 0,05. The highest p-value was 7,3x10 -4 . The 269 obtained diffusion coefficients were in the range of 10 -11 m 2 ꞏs -1 to 10 -9 m 2 ꞏs -1 in the order of tangential, 270 radial to longitudinal direction. The longitudinal to transverse anisotropy ratios of diffusivity which were 271 in tens were much more modest than those of permeability. The radial diffusivity was 2,57 times higher 272 than the tangential diffusivity. Similar to the permeability, the variation of ray, pit and cell wall capillary can be faster than that of these Australian hardwoods, but slower than that of these temperate hardwoods.

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Besides, the higher radial to tangential diffusivity anisotropy ratio of A. mangium compounds its 286 relatively easier drying defects at the late drying stage. To summarize, results from this study suggested that the permeability and diffusivity of A. mangium 291 were higher than other hardwoods published. By plotting permeability with diffusion coefficients, the 292 demarcation between A. mangium and other materials were observed (Figure 8). Except for two  Vietnam. The results highlighted that:

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-The gas permeability was significantly higher than liquid permeability in each direction. This 306 difference increased respectively from the longitudinal, radial, to tangential direction.
-The permeability anisotropy ratios from longitudinal to transverse direction were not as so high as 308 that of other species in previous reports. The radial to tangential anisotropy ratio was not significant 309 in gas permeability, but quite high in liquid permeability.

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-The measured mass losses over time in the transverse and longitudinal directions were plotted.

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There was an obvious distinction between groups of sloped curves. The big group was the water-312 vapour loss through the longitudinal direction and the small one was that of transverse directions.

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-The longitudinal to transverse anisotropy ratios of diffusivity were much slighter than 314 permeability. The difference between the radial and tangential diffusivity was significant, as same 315 as for liquid permeability. This could be a cause of appearance of drying defects.

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-By obvious demarcation on the mixed species graphs, the permeability and diffusivity in A. 317 mangium were higher than other published hardwoods, which indicated a fast drying rate.