1. A very long piece of wood (5 m of length) with a 20 cm x 20 cm cross section is to be thermally treated in a large industrial kiln (Figure 1). This heat treatment is a chemical-free alternative that protects wood against rot, provide dimensional stability, and repel water and insects. At the end of the treatment, the piece of lumber is at a uniform temperature of 210°C and has to be cooled by dry air at 24.8°C. The average properties of the wood after the thermal process have been measured at p = 435 kg m³, k = 0.115 Wm1°C and Cp = 2380 J kg 1°C-1. The convective heat transfer coefficient between all surfaces of the wood is constant and uniform at h = 16 Wm 2°C 1. After 400 minutes of cooling, calculate: a. The maximum temperatures in the piece of wood. Clearly state/show the location of the maximum temperature. b. The minimum temperatures in the piece of wood. Clearly state/show the location of the minimum temperature. c. Obtain mass average temperature of the piece of wood after 400 minutes. d. Calculate the distance d from the origin to the point where the temperature is equal to 69.5°C on the line that joins the center of the cross section of the lumber to the middle point of an edge (Figure 1). 20 cm 20 cm h. T 5 m ||jd = ? (0,0) (a) Lumber dimensions (b) Cross section for Part d. Figure 1: Schematics of the lumber
1. A very long piece of wood (5 m of length) with a 20 cm x 20 cm cross section is to be thermally treated in a large industrial kiln (Figure 1). This heat treatment is a chemical-free alternative that protects wood against rot, provide dimensional stability, and repel water and insects. At the end of the treatment, the piece of lumber is at a uniform temperature of 210°C and has to be cooled by dry air at 24.8°C. The average properties of the wood after the thermal process have been measured at p = 435 kg m³, k = 0.115 Wm1°C and Cp = 2380 J kg 1°C-1. The convective heat transfer coefficient between all surfaces of the wood is constant and uniform at h = 16 Wm 2°C 1. After 400 minutes of cooling, calculate: a. The maximum temperatures in the piece of wood. Clearly state/show the location of the maximum temperature. b. The minimum temperatures in the piece of wood. Clearly state/show the location of the minimum temperature. c. Obtain mass average temperature of the piece of wood after 400 minutes. d. Calculate the distance d from the origin to the point where the temperature is equal to 69.5°C on the line that joins the center of the cross section of the lumber to the middle point of an edge (Figure 1). 20 cm 20 cm h. T 5 m ||jd = ? (0,0) (a) Lumber dimensions (b) Cross section for Part d. Figure 1: Schematics of the lumber
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter3: Transient Heat Conduction
Section: Chapter Questions
Problem 3.25P
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Question
Heat transfer question. Use one term approximation. Answers must be the following for each part:
a. 120.6 ◦C
b. 26.1 ◦C
c. 69.5 ◦C
d. 0.075 m
Transcribed Image Text:1. A very long piece of wood (5 m of length) with a 20 cm x 20 cm cross section is to be thermally treated in
a large industrial kiln (Figure 1). This heat treatment is a chemical-free alternative that protects wood
against rot, provide dimensional stability, and repel water and insects. At the end of the treatment, the
piece of lumber is at a uniform temperature of 210°C and has to be cooled by dry air at 24.8°C. The
average properties of the wood after the thermal process have been measured at p = 435 kg m³, k =
0.115 Wm1°C and Cp = 2380 J kg 1°C-1. The convective heat transfer coefficient between all
surfaces of the wood is constant and uniform at h = 16 Wm 2°C 1. After 400 minutes of cooling,
calculate:
a. The maximum temperatures in the piece of wood. Clearly state/show the location of the maximum
temperature.
b. The minimum temperatures in the piece of wood. Clearly state/show the location of the minimum
temperature.
c. Obtain mass average temperature of the piece of wood after 400 minutes.
d. Calculate the distance d from the origin to the point where the temperature is equal to 69.5°C
on the line that joins the center of the cross section of the lumber to the middle point of an edge
(Figure 1).
20 cm
20 cm
h. T
5 m
||jd = ?
(0,0)
(a) Lumber dimensions
(b) Cross section for Part d.
Figure 1: Schematics of the lumber
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