Given a conduction time of 60 seconds, what is the ratio of the total heat flow in configuration (1) to the total heat flow in configuration (II)?
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- 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.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.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.)
- Suppose you stand with one foot on ceramic flooring and one foot on a wool carpet, making contact over an area of 80.0 cm2 with each foot. Both the ceramic and the carpet are 2.00 cm thick and ale 10.0 on their bottom sides. At what rate must heat transfer occur from each foot to keep the top of the ceramic and carpet at 33.0 ?An aluminum rod 0.500 m in length and with a cross sectional area of 2.50 cm2 is inserted into a thermally insulated vessel containing liquid helium at 4.20 K. The rod is initially at 3(H) K. (a) If one-halt of the rod is inserted into the helium, how many liters of helium boil off by the time the inserted half cools to 4.20 K? Assume the upper half does not yet cool, (b) If the circular surface of the upper end of the rod is maintained at 300 K. what is the approximate boil-off rate of liquid helium in liters per second after the lower half has reached 4.20 K? (Aluminum has thermal conductivity of 3 100 YV/m K at 4.20 K; ignore its temperature variation. The density of liquid helium is 125 kg/m3.)What mass of water at 25.0C must be allowed to conic to thermal equilibrium with a 1.85-kg cube of aluminum initially at 1.50 102C to lower the temperature of the aluminum to 65.0C? Assume any water turned to steam subsequently recondenses.
- 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.A high-end gas stove usually has at least one burner rated at 14 000 Btu/h. (a) If you place a 0.25-kg aluminum pot containing 2.0 liters of water at 20.C on this burner, how long will it take to bring the water to a boil, assuming all the heat from the burner goes into the pot? (b) Once boiling begins how much time is required to boil all the water out of the pot?To help prevent frost damage, 4.00 kg of water at 0 is sprayed onto a fruit tree. (a) How much heat transfer occurs as the water freezes? (b) How much would the temperature of the 200-kg tree decrease if this amount of heat transferred from the tree? Take the specific heat to be 3.35k J/kg. , and assume that no phase change occurs in the tree.
- A bilayer polymer swab (1.2 m long, 1.4 m wide, 5 cm thick) is placed on a hot plate,?which keeps the side of the slab touching the hot plate at 105 deg C. The thermal conductivity of layer 1 (2cm thick) is 0.44 W/ m-K and the thermal conductivity of Layer 2 ( 3cm thick) is 0.67 W/m-K. If the air surrounding the slab is 27 degree C and the convective heat transfer coefficient between the top of the slab and the air is 19W/m^2-K. What is the rate of heat transfer from the side of the slab touching the hot plate to air?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 bloodIn a production facility, 1.2-in-thick, 2-ft *2-ft square brass plates (r = 532.5 lbm/ft3 and cp =0.091 Btu/lbmF) that are initially at a uniform temperatureof 75F are heated by passing them through an ovenat 1300F at a rate of 450 per minute. If the plates remain in the oven until their average temperature rises to 1000F,determine (a) the rate of heat transfer to the plates in thefurnace and (b) the rate of entropy generation associatedwith this heat transfer process.