The composite insulation shown, which was described in Chapter 1 (Problem 1.86e), is being considered as a ceiling material. It is proposed that the outer and inner slabs be made from low-density particle board of thicknesses L 1 = L 3 = 12.5 mm and that the honeycomb core be constructed from a high-density particle board. The square cells of the core are to have length L 2 = 50 mm , width W = 10 mm , and wall thickness t = 2 mm . The emissivity of both particle boards is approximately 0.85, and the honeycomb cells are tilled with air at 1-atm pressure. To assess the effectiveness of the insulation, its total thermal resistance must be evaluated under representative operating conditions for which the bottom (inner) surface temperature is T s , i = 25 ° C and the top (outer) surface temperature is T s , i = − 10 ° C . To assess the effect of free convection in the air space, assume a cell temperature difference of 20°C and evaluate air properties at 7.5°C. To assess the effect of radiation across the air space, assume inner surface temperatures of the outer and inner slabs to be −5 and 15°C, respectively.
The composite insulation shown, which was described in Chapter 1 (Problem 1.86e), is being considered as a ceiling material. It is proposed that the outer and inner slabs be made from low-density particle board of thicknesses L 1 = L 3 = 12.5 mm and that the honeycomb core be constructed from a high-density particle board. The square cells of the core are to have length L 2 = 50 mm , width W = 10 mm , and wall thickness t = 2 mm . The emissivity of both particle boards is approximately 0.85, and the honeycomb cells are tilled with air at 1-atm pressure. To assess the effectiveness of the insulation, its total thermal resistance must be evaluated under representative operating conditions for which the bottom (inner) surface temperature is T s , i = 25 ° C and the top (outer) surface temperature is T s , i = − 10 ° C . To assess the effect of free convection in the air space, assume a cell temperature difference of 20°C and evaluate air properties at 7.5°C. To assess the effect of radiation across the air space, assume inner surface temperatures of the outer and inner slabs to be −5 and 15°C, respectively.
Solution Summary: The diagram shows the kinematic properties of air at the ambient temperature of stackrel, i=25°C.
The composite insulation shown, which was described in Chapter 1 (Problem 1.86e), is being considered as a ceiling material. It is proposed that the outer and inner slabs be made from low-density particle board of thicknesses
L
1
=
L
3
=
12.5
mm
and that the honeycomb core be constructed from a high-density particle board. The square cells of the core are to have length
L
2
=
50
mm
, width
W
=
10
mm
, and wall thickness
t
=
2
mm
. The emissivity of both particle boards is approximately 0.85, and the honeycomb cells are tilled with air at 1-atm pressure. To assess the effectiveness of the insulation, its total thermal resistance must be evaluated under representative operating conditions for which the bottom (inner) surface temperature is
T
s
,
i
=
25
°
C
and the top (outer) surface temperature is
T
s
,
i
=
−
10
°
C
. To assess the effect of free convection in the air space, assume a cell temperature difference of 20°C and evaluate air properties at 7.5°C. To assess the effect of radiation across the air space, assume inner surface temperatures of the outer and inner slabs to be −5 and 15°C, respectively.
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Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning