Estimate the rate at which heat can be conducted from theinterior of the body to the surface. As a model, assume thatthe thickness of tissue is 4.0 cm, that the skin is at 34°Cand the interior at 37°C, and that the surface area is 1.5m2Compare this to the measured value of about 230 W thatmust be dissipated by a person working lightly. This clearlyshows the necessity of convective cooling by the blood

Estimate the rate at which heat can be conducted from theinterior of the body to the surface. As a model, assume thatthe thickness of tissue is 4.0 cm, that the skin is at 34°Cand the interior at 37°C, and that the surface area is 1.5m2Compare this to the measured value of about 230 W thatmust be dissipated by a person working lightly. This clearlyshows the necessity of convective cooling by the blood

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter1: Temperature And Heat

Section: Chapter Questions

Problem 100P: One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a...

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For the human body, what is the rate of heat transfer by conduction through the body's tissue with the following conditions: the tissue thickness is 3.00 cm, the difference in temperature is 2.00 , and the skin area is 1.50 m2. How does this compare with the average heat transfer rate to the body resulting from an energy intake of about 2400 kcal per day? (No exercise is included.)
One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a house. Suppose a single-story cubical house already had 15 cm of fiberglass insulation in the attic and in all the exterior surfaces. If you added an extra 8.0 cm of fiberglass to the attic, by what percentage would the heating cost of the house drop? Take the house to have dimensions 10 m by 15 m by 3.0 m. Ignore air infiltration and heat loss through windows and doors, and assume that the interior is uniformly at one temperature and the exterior is uniformly at another.
Check Your Understanding How does the rate of heat transfer by conduction change when all spatial dimensions are doubled?
An astronaut performing an extra-vehicular activity (space walk) shaded from the Sun is wearing a spacesuit that can be approximated as perfectly white ( e=0 ) except for a 5 cm × 8 cm patch in the form of the astronaut's national flag. The patch has emissivity 0.300. The spacesuit under the patch is 0.500 cm thick, with a thermal conductivity k 0.0600 W/m , and its inner surface is at a temperature of 20.0 . What is the temperature of the patch, and what is the rate of heat loss through it? Assume the patch is so thin that its outer surface is at the same temperature as the outer surface of the spacesuit under it. Also assume the temperature of outer space is 0 K. You will get an equation that is very hand to solve in closed form, so can solve it numerically with a graphing calculator, with software, or even by trial and error with a calculator.
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Compare the rate of heat conduction through a 13.0-cm-thick wall that has an area of 10.0 m2 and a thermal conductivity that of glass wool with the rate of heat conduction through a 0.750-cm-thick window that has an area of 2.00 m2, assuming the same temperature difference across each.
The thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m K and 0.020 W/m K, respectively, while other tissues inside the body have conductivities of about 0.50 W/m K. Assume that between the core region of the body and the skin sin face lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. (b) Find the rate of energy loss when the core temperature is 37C and the exterior temperature is 0C. Assume that both a protective layer of clothing and an insulating layer of unmoving air a absent, and a body area of 2.0 m2.
Why don't we operate ocean liners by extracting heat from the ocean or operate airplanes by extracting heat from the atmosphere?
Does adding heat to a system always increase its internal energy?
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Repeat the preceding problem, assuming the water is in a glass beaker with a mass of 0.200 kg, which in tum is in a calorimeter. The beaker is initially at the same temperature as the water. Before doing the problem, should the answer be higher or lower than the preceding answer? Comparing the mass and specific heat of the beaker to those of the water, do you think the beaker will make much difference?
A sealed room has a volume of 24 m3. It's filled with air, which may be assumed to be diatomic, at a temperature of 24 and a pressure of 9.83104 Pa. A 1.00-kg block of ice at its melting point is placed in the room. Assume the walls of the room transfer no heat. What is the equilibrium temperature?