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A wall with a thickness
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Chapter 1 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- 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?arrow_forward1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.arrow_forward1.37 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.arrow_forward
- 1.2 The weight of the insulation in a spacecraft may be more important than the space required. Show analytically that the lightest insulation for a plane wall with a specified thermal resistance is the insulation that has the smallest product of density times thermal conductivity.arrow_forward1.10 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.arrow_forwardA plane wall of thickness 2L has internal heat sources whose strength varies according to qG=qocos(ax) Where qo is the heat generated per unit volume at the center of the wall (x=0) and a is a constant. If both sides of the wall are maintained at a constant temperature of Tw, derive an expression for the total heat loss from the wall per unit surface area.arrow_forward
- Determine k, thermal conductivity of a wall if q = 1000 kcal/m2 -hr at thickness, k = 33 mm and ∆t = 30°C.arrow_forwardA wall is made from an inhomogeneous (nonuniform) material for which the thermal conductivity varies through the thickness according to k = ax + b, where a and b are constants. The heat flux q"q" is known to be constant. Determine expressions for the temperature gradient and the temperature distribution when the surface at x = 0 is at temperature T1. Use the following values a = 11 W/K b = 25 W/m-K k = 11x + 25 W/m-K q"q" = 104 W/m^2 T1 = 60 Carrow_forwardQ1/The thermal conductivity 14.4w/m.k for the block of stainless steel shown below is well insulated on the front and back surfaces, and the temperature in the block varies linearly in both the x- and y directions, Find: The heat fluxes and heat flows in the x- and y-directions. 5 cm 15°C 10°C -5 cm - 10 cm 5°C 0°C Q2-Consider a two layer composite wall of copper and Teflon as shown below. The copper has a thickness of 10cm but the thickness of the Teflon is to be determined. The temperature on the left boundary is equal to 200 C and on the right boundary 25C. Determine the thickness of the Teflon layer so that the heat flux is equal to 200W/m2. L2 T = 200C Te = 25 C L1 = 01m TA T3 %3D - 007 = 5 coper télon Tcarrow_forward
- A slab of thickness L = 0.1 m and of thermal conductivity k = 1 W/mK has the temperature distribution as T(x) = ax2 + bx + c. The boundary conditions; insulation at at x = L and a 100 W/m2 constant heat flux at x = 0. What is the temperature at the insulated surface if c = 5 °C?arrow_forwardQ1/ A thick wall consists two layers of Gypsum, insulation and brick as shown in figure below. The ambient temperature is 20 °C and heat transfer coefficient is 5 W/m2. K in the left side. The surface temperature of right side is 45 °C. find the heat losses per meter length. What will happen if the insulation's thickness * .increases by 25% Gypsum k = 0.04W/m. K T = 45 °C h=5 W/m'. K T. = 20 °C 5 cm Insulation k = 0.04W/m. K Brick k = 0.69 W/m. Karrow_forwardähäi 100 Q1: Consider a long resistance wire of radius r1 = 0.3 cm and thermal conductivity kwire = %3D 17 W/m•°C in which heat is generated uniformly as a result of resistance heating at a constant rate of q = 100 W/cm3 (see Figure below). The wire is embedded in a 1-cm- thick layer of ceramic whose thermal conductivity is kceramic =1 W/m.°C. If the center temperature of the resistance wire is measured to be Tc= 705°C, determine the temperatures at the surface of ceramic and the interface of the wire and the ceramic layer under steady conditions.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning