The figure shows the cross section of wall made of wood of thickness La and brick of thickness La (=0.2 La). Two more layers are sandwiched between wood and brick with identical thickness and thermal conductivities. The thermal conductivity of the wood is k, and that of brick is ka (=5.0 ka). The face area A of the wall is unknown. Energy transfer through the wall is steady. The only known temperatures are T1 = 55°C, T2 = 30°C and Ts = -10°C. Apply the concept of steady-state heat transfer through conduction on the wall, and determine the interface temperature T4?

The figure shows the cross section of wall made of wood of thickness La and brick of thickness La (=0.2 La). Two more layers are sandwiched between wood and brick with identical thickness and thermal conductivities. The thermal conductivity of the wood is k, and that of brick is ka (=5.0 ka). The face area A of the wall is unknown. Energy transfer through the wall is steady. The only known temperatures are T1 = 55°C, T2 = 30°C and Ts = -10°C. Apply the concept of steady-state heat transfer through conduction on the wall, and determine the interface temperature T4?

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.37P: 1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm...

See similar textbooks

Similar questions

As a designer working for a major electric appliance manufacturer, you are required to estimate the amount of fiberglass insulation packing (k = 0.035 W/m K) that is needed for a kitchen oven shown in the figure below. The fiberglass layer is to be sandwiched between a 2-mm-thick aluminum cladding plate on the outside and a 5-mm-thick stainless steel plate on the inside that forms the core of the oven. The insulation thickness is such that the outside cladding temperature does not exceed 40C when the temperature at the inside surface of the oven is 300C. Also, the air temperature in the kitchen varies from 15Cto33C, and the average heat transfer coefficient between the outer surface of the oven and air is estimated to be 12.0W/m2K. Determine the thickness of the fiberglass insulation that is required for these conditions. What would be the outer surface temperature when the inside surface of the oven is at 475C?
1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.
1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
The compartment below is used as a freezer of refrigerator compartment. Inner wall is at -15 C and outer wall is at 25 C. Insulator with a thermal conductivity of 0.035 W/(mK) is used to prevent the heat losses from the compartment. The shape is in square form with a side of 1.2 m and unit width into the page. Determine the thickness of the insulator if the compartment heat load is 700 W? a)5 cm b)none c)4.2 cm d)2.4 mm e)9.6 mm
A manufacturer of loose-fill cellulose insulating material provides a table showing the relationship between the thickness of the material and its R-value. The manufacturer’s data is shown in the accompanying table. R -value (m2 ⋅K/W) Thickness (mm) R -40 275 R -32 225 R -24 162 R- 19 132 R -13 88 Calculate the thermal conductivity of the insulating material. Also, determine how thick the insulation should be to provide R-values of a. R-30 b. R-20 11.9
A glass window with an area of 0.625 m² is installed in the wooden outside wall of a room. The wall dimensions are 25 x 3.05 m. The wood has a k of 0.151W/m.K and is 3.05 cm thick. The glass has a k of 0.692W/m.K and is 5.0 mm thick. The temperature of the inside room is 27°C and outside air temperature is 268K. (1)What is the heat loss through wooden wall and glass window q(W) ? (2) What are the total heat loss?
In the figure below, it is known that the thermal conductivity of k1 = 0.06 W/mK, k3 = 0.04 W/mK, and k4 = 0.12 W/mK. The thickness of the layers is L1 = 1.50 cm, L3 = 2.8 cm, and L4 = 3.50 cm. Known temperatures T1 = 30°C, T12 = 25°C, and T4 = -10°C. Energy transfer through walls is constant. How much is T34?
The heat conducts through the shape below. The temperature of the right face is 93 °C, while the left face is at 23 °C. If the top and bottom faces are completely insulated, and the thermal conductivity of the material decreases with decreasing temperature. * Assume that the thermal conductivity is 100 at 23, decreased to 10 at 93. A) Sketch the temperature profile inside the plate. B) If both sides of the plate in the above problem is exposed to air: Left side (h = 20 W/m2K, TL = 20 °C) and right side (h = 90 W/m2K). Calculate the temperature of the air on the right side.
A wall has an overall U value of 0.25 W/m^2K. It includes a layer ofinsulation 50 mm thick. The conductivity of the insulation is 0.035 W/mK.It is decided that the thickness of the insulation should be increased sothat the U value is reduced to 0.20 W/m^2K. What is the new thickness ofinsulation required? answer = 85mm
A wall is constructed using bricks made of 3 different materials (A, B, C) as shown in the figure (all dimensions are in cm). The depth of the wall is ( w = 20 ), The pattern repeats itself every 20 cm distance in the vertical direction. Thermal conductivities of the materials are given as kA=0.5W/mK, kB=1 and kC=0.35. Inside and outside temperatures are 20 oC and 45 oC, respectively. Considering only convection inside (h=10 W/m2K) and both convection (h=25 W/m2K) and radiation (h=20 W/m2K) outside: w (m) = ? (a) Draw the thermal resistance network (b) Total thermal resistance (c) Total heat transfer rate from the repeated section (d) Temperature Tx
5. A 10-in nominal pipe (outside diameter = 10.75in) is covered with a composite pipe insulation consisting of 2.0 in of insulation I placed next to the pipe and 1.5 in of insulation II placed upon insulation I. Assume that the inner and outer surface temperatures of the composite insulation are 900F and 150F respectively, and that the thermal conductivity of material I is 0.05 BTU/hr-ft-F and for material II is 0.039 BTU/hr-ft-F. What is the individual thermal resistance of insulation I?
Consider a composite wall of overall height H = 30 mm and thickness L = 40 mm. Section A hasthickness LA = 15 mm and thermal conductivity of 3 W/(m·K). Sections B and C each have heightHB = 15 mm and thickness LB = 25 mm. The thermal conductivity is 1 W/(m·K) in section B and 2W/(m·K) in section C. The temperatures of the left and right faces of the composite wall are T1 =60°C and T2 = 30°C, respectively. The top and bottom of the wall are insulated. A) Draw a thermal circuit based on heat flux for the composite wall shown above.Assume that the temperature is uniform “vertically” in material A. Indicate thetemperatures, thermal resistances, and heat flux in the circuit diagram. Show theequations for the thermal resistances in the circuits. Do NOT need to perform anycalculations in this part.B. Draw a thermal circuit based on heat flux for the composite wall shown above.Assume that the temperature is NOT uniform “vertically” in material A and heat onlyflows along horizontal direction.…