This question requires the use of the conduction charts given in the appendix at the end of this paper. A wooden sphere of diameter 5 cm is initially at a uniform temperature of 21 °C. Its surface temperature is suddenly raised to 83 °C. The thermal conductivity and thermal diffusivity of the wood are 0.15 W/m K and 0.82 x 10-7 m²/s, respectively. a) Calculate the temperature 2 cm beneath the surface of the sphere 30 min after the sudden increase in temperature.

This question requires the use of the conduction charts given in the appendix at the end of this paper. A wooden sphere of diameter 5 cm is initially at a uniform temperature of 21 °C. Its surface temperature is suddenly raised to 83 °C. The thermal conductivity and thermal diffusivity of the wood are 0.15 W/m K and 0.82 x 10-7 m²/s, respectively. a) Calculate the temperature 2 cm beneath the surface of the sphere 30 min after the sudden increase in temperature.

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 1.77P: 1.77 Explain each in your own words. (a) What is the mode of heat transfer through a large steel...

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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?
1.3 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.
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.
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Wearing layers of clothing in cold weather is often recommended because dead-air spaces between the layers keep the body warm. The explanation for this is that the heat loss from the body is less. Compare the rate of heat loss for a single 2-cm-thick layer of wool [k=0.04W/(mK)] with three 0.67-cm layers separated by 1.5 mm air gaps. The thermal conductivity of air is 0.024 W(mK).
show schematic drawings, conversions, units and box in your final answers A furnace wall is made up of three layer of thickness 200 mm, 100 mm, and 125 mm with thermal conductivity of 1.65 W/m-K, k2, and 9.2 W/m-K respectively. The inside is exposed to gases at 1200°C with a convection coefficient of 25 W/m²-K and the inside surface temperature is at 1000°C, the outside air temperature is at 30°C with convection coefficient of 12 W/m²-K. Calculate: a. the unknown thermal conductivity; b. the outside surface temperature and mid-plane temperatures in °F.
1. A beverage cooler is in the shape of a cube, 42 cm on each inside edge. Its 3.0-cm thick wall are made up of plastic (kr = 0.050 W/mK). When the outside temperature is 20°C, how much ice will melt each hour? Tice is 0°C. 2. One of the possible mechanisms of heat transfer in human body is conduction through body fat. Suppose that heat travels through 0.03 m of fat in reaching the skin, which has a total surface area of 1.7 m² and a temperature of 34°C. Find the amount of heat that reaches the skin in half an hour, if the temperature at the body, interior is maintained at the normal value 37°C ? Thermal conductivity of body fat is k = 0.2 J/sm°C. 3. The air in a room is at 25°C and outside temperature is 0°C. The window of the room has an area of 2m² and thickness 2mm. Calculate the rate of loss of heat by conduction through window ? Thermal conductivity for glass is 1 Wm¯'degree!.
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GChoose the right answer 1. The temperature profile for steady hest conduction through a plane wall of constant thermal conductivity is a. logarithmic b. parabolic 2. A brick wall (k-0.75 W/mK ) transmits $02 of heat loss through another wall (k-0.25 W/mK, x-100 mm). If the temperature difference across both walls is the same, the thickness of the brick wall would be a.150 mm c. linear 6T b. 240 mm c. 300 mm d. 375 mm 3. The maximum temperature at the center of the solid sphere of radius R having heat generation q (W/m') is given by g'R +9R b. T, + 4k T+9R 6k d. T+9R 8k a. 2k C. 4. The internal thermal resistance of a solid can be ignored if the Biot number is less than a. 1 b. 0.5 c. 0.1 d. Fourier number 5. The ratio of heat transfer of a fin to the heat transfer without fin is referred to as a. fin resistance b. fin efficieney efin effectiveness d. fin conductance.