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An Introduction to Thermal Physics
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- 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.arrow_forwardDuring heavy exercise, the body pumps 2.00 L of blood per minute to the surface, where it is cooled by 2.00C. What is the rate of heat transfer from this forced convection alone, assuming blood has the same specific heat as water and its density is 1050kg/m3 ?arrow_forwardConsider the latent heat of fusion and the latent heat of vaporization for H2O, 3.33 105 J/kg and 2.256 106 J/kg, respectively. How much heat is needed to a. melt 2.00 kg of ice and b. vaporize 2.00 kg of water? Assume the temperatures of the ice and steam are at the melting point and vaporization point, respectively. (a). UsingEq21.9, Q = mLF = (2.00 kg) (3.33l05 J/kg) = 6.66105 J (b).UsingEq21.10. Q = mLV = (2.00kg) (2.256106 J/kg) = 14.51106 Jarrow_forward
- In 1993, the U.S. government instituted a requirement that all room air conditioners sold in the United States must have an energy efficiency ratio (EER) of 10 or higher. The EER is defined as the ratio of the cooling capacity of the air conditioner, measured in British thermal units per hour, or Btu/h, to its electrical power requirement in watts. (a) Convert the EER of 10.0 to dimensionless form, using the conversion 1 Btu = 1 055 J. (b) What is the appropriate name for this dimensionless quantity? (c) In the 1970s, it was common to find room air conditioners with EERs of 5 or lower. State how the operating costs compare for 10 000-Btu/h air conditioners with EERs of 5.00 and 10.0. Assume each air conditioner operates for 1 500 h during the summer in a city where electricity costs 17.0 per kWh.arrow_forwardA 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?arrow_forward(a) What is the rate of heat conduction through the 3.00-cm-thick fur of a large animal having a I .40-m surface area? Assume that the animal's skin temperature is 32.0 , that the air temperature is 5.00 , and that has the same thermal conductivity as air. (b) What food intake will the animal need in one day to replace this heat transfer?arrow_forward
- During heavy exercise, the body pumps 2.00 L of blood per minute to the surface, where it is cooled by 2.00ºC . What is the rate of heat transfer from this forced convection alone, assuming blood has the same specific heat as water and its density is 1050 kg/m? (answer in W)arrow_forwardConsider a flat-plate solar collector placed on the roof of a house. The temperatures at the inner and outer surfaces of the glass cover are measured to be 33°C and 31°C, respectively. The glass cover has a surface area of 2.5 m2, a thickness of 0.6 cm, and a thermal conductivity of 0.7 W/m·K. Heat is lost from the outer surface of the cover by convection and radiation with a convection heat transfer coefficient of 10 W/m2·K and an ambient temperature of 15°C. Determine the fraction of heat lost from the glass cover by radiation.arrow_forwardThe quantity of energy Q transferred by heat conduction through an insulating pad in time interval Δt is described by Q/Δt = κAΔT/d, where κ is the thermal conductivity of the material, A is the face area of the pad (perpendicular to the direction of heat flow), ΔT is the difference in temperature across the pad, and d is the thickness of the pad. In one trial to test material as lining for sleeping bags, 86.0 J of heat is transferred through a 3.40-cm-thick pad when the temperature on one side is 37.0°C and on the other side is 2.00°C. In a trial of the same duration with the same temperatures, how much heat will be transferred when more of the material is added to form a pad with the same face area and total thickness 8.41 cm?arrow_forward
- One way to keep the contents of a garage from becoming too cold on a night when a severe subfreezing temperature is forecast is to put a tub of water in the garage. If the mass of the water is 122 kg and its initial temperature is 24.2°C, how much energy must the water transfer to its surroundings in order to freeze completely? The specific heat of water is 4186 J/kg·K, and the latent heat of fusion is 333 kJ/kg.arrow_forward1) A wall is made up of four elements, as follows: ½” wood siding R = 1.0 ½” plywood sheathing R = 0.5 3 ½” fiberglass R = 11 ½” sheetrock R = 0.5 How many Btu per hour would be transferred through a 10 sq. foot section of the wall if the outside is 40ºF colder than the inside. In which direction (in or out) would the heat flow? (Units of R-value are ft2-hr-ºF/Btu) 2) (a) Calculate the hourly heating load of a house in which all exterior surfaces have a thermal resistance of R= 20 ft2hoF/Btu, the inside temperature is 70oF, and the outside temperature is 0oF. The dimensions of the house are 40ft x 40ft x 40ft. (b) calculate the calculation of the infiltration heat loss. Assume K-value of air exchanges per hour is 2. (HINT: Lecture 10, Slide 25 & 32-34) 3) An 80 kg man is standing on ice that can withstand 5000 Pa of pressure. a) If he is standing, having a total contact area from both feet of 0.1 m2. How much pressure is the applying, and will he fall through the…arrow_forward
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