[논문]대단면 수심정각재 건조를 위한 포화-과열증기 연속 건조 공정의 이용가능성 평가

PARK, Yonggun; CHUNG, Hyunwoo; KIM, Hyunbin; YEO, Hwanmyeong

doi:10.5658/wood.2020.48.2.121

[국내논문] 대단면 수심정각재 건조를 위한 포화-과열증기 연속 건조 공정의 이용가능성 평가
Applicability of Continuous Process Using Saturated and Superheated Steam for Boxed Heart Square Timber Drying 원문보기

목재공학 = Journal of the Korean wood science and technology, v.48 no.2, 2020년, pp.121 - 135

PARK, Yonggun (Department of Forest Sciences, College of Agriculture & Life Sciences, Seoul National University) , CHUNG, Hyunwoo (Department of Forest Sciences, College of Agriculture & Life Sciences, Seoul National University) , KIM, Hyunbin (Department of Forest Sciences, College of Agriculture & Life Sciences, Seoul National University) , YEO, Hwanmyeong (Department of Forest Sciences, College of Agriculture & Life Sciences, Seoul National University)

초록
AI-Helper

본 연구에서는 대단면 목재의 건조를 위해 포화증기와 과열증기를 연속 적용하는 공정의 이용 가능성을 평가해보고자 하였다. 낙엽송 수심 정각재를 건조하는 동안 표면층, 내부층 및 중심층의 슬라이스 시험편을 통해 함수율 변화를 확인한 결과 포화증기 건조 중에는 표면층과 내부층 사이에서, 과열증기 건조 중에는 내부층과 중심층 사이에서 함수율 경사가 크게 발생하였다. 하지만 각 슬라이스 층간의 함수율 경사에도 불구하고, 표면 할렬은 발생하지 않았으며, 내부 할렬은 수나 미성숙재 부근에서만 발생하였다. 슬라이스의 탄성 변형률과 낙엽송의 접선 방향 탄성계수를 통해 건조 중인 낙엽송 정각재의 건조 응력의 최댓값은 1.30 MPa이었고, 건조 응력이 최대인 시점 온도와 함수율 조건에서 낙엽송의 접선 방향 인장강도는 5.21 MPa로 추산된다. 즉, 포화증기 및 과열증기를 연속 건조 공정에서 목재의 건조 응력이 접선 방향 인장강도를 초과하지 않았기 때문에 표면에서 할렬이 발생하지 않았다. 내부 할렬 발생 억제를 위한 과열증기 건조 조건 완화와 같은 추가 연구를 통해 포화-과열증기 연속 건조 공정이 대단면 목재 건조에 이용 가능할 것이라 기대된다.

Abstract ▼ AI-Helper

This study aims to evaluate applicability for the continuous drying process using saturated and superheated steam for large-square timber. During drying of the boxed heart square timber, changes in moisture content were examined through the slices of the surface, inner and core layers. The results showed that there was a large moisture content difference between the surface and inner layers during saturated steam drying and between the inner and core layers during superheated steam drying. However, despite the moisture content difference between the layers, no surface check occurred, and an internal check occurred only near the pith or juvenile parts of the wood. The maximum value of the drying stress of the dried larch boxed heart square timber, calculated from the elastic strain of the slice and the tangential elastic modulus of the larch, was 1.30 MPa. The tangential tensile strength of the larch was estimated at 5.21 MPa under temperature and moisture content conditions when drying stress was at a maximum. That is, in the continuous drying process, the saturated and superheated steam did not generate a check in the surface because the drying stress of the wood did not exceed the tangential tensile strength. In further studies, the superheated steam drying conditions will need to be relaxed to suppress the occurrence of internal checks. Such studies would make the continuous drying process using saturated and superheated steam available for the drying of large-square timber.

주제어

표/그림 (10)

그림 Fig. 1. Phase change of water with temperature change (Ro, 2008).
그림 Fig. 2. Equilibrium moisture content of wood versus relative humidity at some temperatures according to the Hailwood-Horrobin equation.
그림 Fig. 3. Preparation of the specimen for the continuous drying process using saturated and superheated steam.
그림 Fig. 4. Preparation of the specimens to measure average moisture content and to analyze drying stress in the square timber during the continuous drying process using saturated and superheated steam.
그림 Fig. 5. Dimensional changes of slice during the drying process (Han, 2014).
그림 Fig. 6. Specimen for tension test in tangential direction.
그림 Fig. 7. Changes in steam temperature, wood temperature, and steam pressure during the continuous drying process using saturated and superheated steam.
그림 Fig. 8. Changes in moisture content of the slice during the continuous drying process using saturated and superheated steam.
그림 Fig. 9. Cross-sectional images at the center of the timber during the continuous drying process using saturated and superheated steam.
그림 Fig. 10. Changes in elastic strain of slice during the continuous drying process using saturated and superheated steam.

AI 본문요약
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제안 방법

Therefore, after larch timbers with similar initial moisture content were dried under the same conditions until the set time, drying stress was measured. As for the measurement time point, four measurement time points (6 hours, 12 hours, 18 hours, 24 hours after the start of drying) were set in 6-hour units in the saturated steam drying section of 24 hours. In the 42 hour superheated steam drying section, there were five measurement points set, including 4 time points (10 hours, 34 hours, 44 hours, 54 hours, 64 hours after the start of drying) in 10-hour units for 40 hours and a time point at the end of superheated steam (66 hours after the start of drying).
In this study, to evaluate the applicability of the continuous drying process using saturated and superheated steam for large-square timber, larch boxed heart square timber was put under saturated steam of 100°C at 0.1 MPa for 24 hours and superheated steam of 220°C at 0.5 MPa for 42 hours, and under 12 hours of cooling.
In this study, we tried to evaluate the possibility of drying large-square timber without occurring checks using the drying method in which saturated steam and superheated steam were continuously applied. Saturated steam is in an equilibrium with no apparent change because the number of molecules evaporating equals the number of gas molecules entering a liquid or solid form (Fig.
5 MPa for 42 hours, and under 12 hours of cooling. The slice method was applied to quantitatively evaluate the drying stress that occurred in the wood during the drying process, and slices with a thickness of 3 mm were prepared in the surface, inner and core layers. The moisture content in the surface layer dropped below 10% within 12 hours after the start of drying, and the moisture content of the inner layer tended to decrease gradually.

이론/모형

2. Equilibrium moisture content of wood versus relative humidity at some temperatures according to the Hailwood-Horrobin equation.
In order to measure the tangential tensile strength and the modulus of elasticity, rectangular slices with width of 3 cm (radial direction), thickness of 2 cm (longitudinal direction), length of 15 cm (tangential direction) were manufactured according to ｢method of tension test for wood｣ in Korean standard (KS F 2207). Then, as shown in Fig.

성능/효과

5 (Han, 2014), and to calculate these five deformations dimensions of the slice were measured in following five states: the initial length in green state (L₀), the length of the wood shrunk due to decreased moisture content during drying (= widthwise length of specimen B immediately after cutting from the timber in drying, L₁), the length (L₂) of the slice with a thickness of 3 mm momentarily changed immediately after cutting from the specimen B, the length (L₃) changed as the stress was relaxed over time with no change in moisture content, and the length (L₄) of the slice in which the maximum shrinkage without drying stress is applied. In this study, in order to calculate elastic strain for measuring the drying stress, only the widthwise length (L₁) of the specimen B immediately after cutting from the square timber in drying and the widthwise length (L₂) of the slice with a thickness of 3 mm momentarily changed immediately after cutting from the specimen B were measured. In addition, the elastic strain (ε_e) was calculated according to Eq.
The tangential tensile strength of the larch measured with the tension test was 6.51 MPa, the tensile modulus of elasticity was 304.72 MPa, and the moisture content was about 11.74% (± 0.20%).

후속연구

Therefore, because the drying stress of the surface layer did not exceed the tangential tensile strength of the larch wood, no surface checks occurred. However, further studies are needed to study for the determination of the conditions under which no checks occur even in the pith or juvenile parts during the superheated steam drying. It is expected then that the continuous drying process using saturated and superheated steam will allow for drying of larger size of the square timber.
Most domestic large-square timber is very likely to contain pith or juvenile parts in the interior. Therefore, further studies are needed to study for the determination of the conditions under which no checks occur even in the pith or juvenile parts during the superheated steam drying.

참고문헌 (29)

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상세보기

표제어: PCR

동의어: Packet Collision Rate

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용어 설명: PCR은 세균 특이성이 있는 primer를 이용하여 적은 수의 세균이 있을지라도 쉽게 검출할 수 있는 유용한 방법이며, 이를 이용하여 구강 내 치면세균막이나 타액에서 직접 세균을 검출할 수 있게 되었다[8].

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