Concept explainers
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
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Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- 1.77 Explain each in your own words. (a) What is the mode of heat transfer through a large steel plate that has its surfaces at specified temperatures? (b) What are the modes when the temperature on one surface of the steel plate is not specified, but the surface is exposed to a fluid at a specified temperature?arrow_forwardWhat is the rate of heat transfer, temperature gradient, and the direction of the heat transfer through a piece of Celotex 3 ft by 8 ft by 1 in. in thickness, if the temp of one surface is 80°F and of the other side is 60°F? - thermal conductivity of Celotex in AES = 0.028.arrow_forwardSolving Thermal Properties Related Problems Estimate the thermal diffusivity of butter at 20°C.arrow_forward
- 1.)An aluminum tank with a volume of 1000 liters is filled with gasoline. Both are at a temperature of 12°C. The tank is transported to a place where the temperature is 37° and, due to the difference between the volumetric expansion coefficients of the metal and the liquid, the ebb of the tank. Assuming the tank expands like a massive volume of aluminum, how many liters of gasoline overflow from the tank? Data: βaluminum=7*10-5/ºC and βgas=9.5*10-4/ºCarrow_forwardA nuclear power station is situated in Coal Valley, which is a roughly rectangular valley that is 5 km long, 2 km wide, and 200 m deep. You have been asked to evaluate the effects of a worst-case scenario where the reactor housing fails, and radiation is released to the atmosphere. In your evaluation, you determine that 120 kg of Iodine-131 (a radioisotope that causes thyroid gland and liver damage) could be released into the atmosphere. Assuming the release of Iodine-131 was very rapid and all of it was uniformly distributed through the valley’s atmosphere with none escaping the valley, what would the concentration of Iodine-131 be in the valley’s air? Your answer should be expressed in units of ppm(v), and you may assume an atmospheric pressure of 1.0 atm and a temperature of 20oC. 2. Assuming the Iodine-131 concentration you calculated in part (a) is the initial concentration in the valley, you now want to determine the time it will take for the concentration to decrease to…arrow_forward2 inch OD during a visit to a plastic sheet factory 60 m long section of a horizontal steam pipe passes from one end to the other without insulation is observed. While the temperature of the ambient air and its surfaces is 20 °C, the temperature measurements at several points are the average of the exposed surfaces of the steam pipe. indicates that the temperature is 160 °C. It is seen that the outer surface of the pipe is oxidized and The emissivity can be taken as 0.59. According to this; a) Calculate the heat loss in the steam pipe. b) The steam used is produced in a gas furnace operating with an efficiency of 59%. Factory 105500 It pays $1.10 per kJ of natural gas. If it is assumed that the factory works all year (365 days), for this facility Calculate the annual cost of heat losses in the steam pipe.arrow_forward
- 1. Residual oil, with a heating value of 18,480 BTU/bm, is used as a fuel in a power plant which produces 947,870 BTU/s of electricity. The overall efficiency of the power plant is 52 Determine the: a. Heat input, in BTUs b. Daily fuel consumption, in lbm C. Dimensions of the cylindrical storage (assuming length is equal to the diameter), in ft. d. Heat rejected the environment, in BTU/s. The density of the oil is 62 ID/ft.arrow_forwardA temperature difference of 85 •C is impressed across a fiberglass layer of 13 cm thickness. The thermal conductivity of the fiberglass is 0.035 W/m • -C. Compute the heat transferred through the material in kcal per hour per unit square meter area.arrow_forwardIf a heat transfer coefficient of 2.84 W l(m2 • K) exists on each of the two inside faces of two sheets of 6.35-mm-thick glass separated by an air gap, calculate the gap that can be used such that the rate of heat transfer by conduction through the air gap equals the rate of heat transfer by convection. What is the rate of heat transfer if this gap is exceeded. The thermal conductivity of air of 0.0242 WI (m . K). Solve for temperature of 20°C and 12°C on the outside surfaces of the glass. Would the calculated gap change in value for different values of the surface temperatures? Would there be any advantage to increasing the gap beyond this calculated value?arrow_forward
- Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. How do you connect it with thermodynamics and why is it necessary for us, mechanical engineers, to study it? Essay around 300 wordsarrow_forwardA father and son conducted the following simple experiment on a hot dog which measured 12.5 cm in length and 2.2 cm in diameter. They inserted one food thermometer into the midpoint of the hot dog and another one was placed just under the skin of the hot dog. The temperatures of the thermometers were monitored until both thermometers read 20°C, which is the ambient temperature. The hot dog was then placed in 94°C boiling water and after exactly 2 min they recorded the center temperature and the skin temperature of the hot dog to be 59°C and 88°C, respectively. Assuming the following properties for the hot dog: r = 980 kg/m3 and cp = 3900 J/kg·K and using transient temperature charts, determine (a) the thermal diffusivity of the hot dog, (b) the thermal conductivity of the hot dog, and (c) the convection heat transfer coefficient.arrow_forwardThe boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is -196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and 196°C. The tank is exposed to 22°C ambient air with a heat transfer coefficient of 22 W/m2 · °C. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air in kg/sec. Answer in…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning