Abstract
This paper describes three-dimensional, transient heat conduction in a rectangular piece of wood with crossgrain, and in an orthotropic wooden cylinder. Computerized solutions of a generalized, nonlinear heat equation are derived by discretizing the space and the time domains, using explicit and implicit finite-difference techniques. A simplified example of linear heat conduction in cylindrical coordinates illustrates how to apply the finite-difference solutions. The accuracy of the solutions for this special case is evaluated via comparing them with a well-known exact solution.
Zusammenfassung
Der Verlauf des dreidimensionalen Wärmeübergangs innerhalb eines Holzquaders mit quer verlaufender Faserrichtung und in einem orthotropen Holzzylinder werden beschrieben. Numerische Lösungen der allgemeinen, nicht-linearen Wärmegleichung werden abgeleitet durch Unterteilen in Raum-und Zeitintervalle mit Hilfe der expliziten und impliziten Finite-Differenz-Methode. Ein vereinfachtes Beispiel einer linearen Wärmeleitung in Zylinder-Koordinaten beleuchtet die Anwendungsmöglichkeiten dieses Lösungsansatzes. Die Genauigkeit der Lösungen für diesen Spezialfall wird durch Vergleich mit der bekannten exakten Lösung abgeschätzt.
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Abbreviations
- A :
-
axial direction
- a :
-
coordinate in the axial direction (m)
- C :
-
circumferential direction
- c :
-
coordinate in the cirumferential direction (m)
- c.. :
-
directional cosine
- Cp :
-
specific heat at constant pressure (J/kg · °C)
- D :
-
distance between mesh points (m)
- d :
-
ordinary differential operator
- Fo :
-
Fourier number
- {G} :
-
gradient of temperature
- J :
-
Bessel function
- [K] :
-
thermal conductivity tensor
- k :
-
thermal conductivity (W/m · °C)
- kcr :
-
“critical” thermal conductivity (W/m · °C) in the stability criterion
- [I] :
-
identity matrix
- L :
-
length (m)
- [M] :
-
matrix of directional cosines
- MC :
-
moisture content based on dry mass (percent)
- Q :
-
heat flux (W/m2)
- R :
-
radial direction
- r :
-
coordinate in the radial direction (m)
- SG :
-
specific gravity based on dry mass and green volume (−)
- T :
-
temperature (°C)
- V :
-
volume (m3)
- X :
-
X-axis
- x :
-
coordinate in theX-direction (m)
- Y :
-
Y-axis
- Y :
-
coordinate in theY-direction (m)
- Z :
-
Z-axis
- z :
-
coordinate in theZ-direction (m)
- δ:
-
interval (−)
- α:
-
diffusivity coefficient in radial direction (m2/s)
- β:
-
fiber grain angle (rad)
- Γ:
-
growth ring angle (rad)
- ŗ:
-
time (s)
- Ω:
-
0,0.5, 1
- δ:
-
partial differential operator
- φ:
-
angle in cylindrical coordinates (rad)
- θ:
-
density (kg/m3)
- a :
-
axial direction
- avg:
-
average
- c :
-
circumferential direction
- e :
-
exterior
- i :
-
nodal point 0, 1, 2, 3… inY-orC-direction
- m :
-
nodal point 0, 1, 2, 3… inX-orR-direction
- max:
-
maximum
- min:
-
minimum
- n :
-
nodal point 0, 1, 2, 3… inZ-orA-direction
- r :
-
radial direction
- t :
-
total
- x :
-
X-direction
- y :
-
Y-direction
- z :
-
Z-direction
- o :
-
initial
- ∞:
-
ambient
- p :
-
time level 0, 1, 2, 3…
- T :
-
transpose
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Khattabi, A., Steinhagen, P. Analysis of transient nonlinear heat conduction in wood using finite-difference solutions. Holz als Roh-und Werkstoff 51, 272–278 (1993). https://doi.org/10.1007/BF02629373
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DOI: https://doi.org/10.1007/BF02629373