During a picnic on a hot summer day, the only available drinks were those at the ambient temperature of 90°F. In an effort to cool a 1 2-fluid-oz drink in a can, which is 5 in high and has a diameter of 2.5 in. a person grabs the can and starts shaking it in the iced page 311 water of the chest at 32°F. The temperature of the drink can be assumed to be uniform at all times, and the heat transfer coefficient between the iced water and the aluminum can is 30 Bta1rfi2°F. Using the properties of water for the drink, estimate how long it vi11 take for the canned drink to cool to 40°F. Solve this problem using lumped system analysis. Is the lumped system analysis applicable to this problem? Why?
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- Consider a 0.8-m-high and 1.5-m-wide double-pane window consisting of two 4-mm-thick layers of glass (?= 0.78 W/m · °C) separated by a 10-mm-wide space filled with STAGNANT ARGON GAS (?= 0.016 W/m · °C). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 20°C while the temperature of the outdoors is 10°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be ℎ1= 10 W/m2 · °C and ℎ2= 40 W/m2 · °C, which includes the effects of radiation.arrow_forwardwhat are the different modes of heat transfer? Explain transfer of heat by convection process?arrow_forwardThe vertical 0.8-m-high, 2-m-wide double-pane window consists of two sheets of glass separated by a 2-cm air gap at atmospheric pressure. If the glass surface temperatures across the air gap are measured to be 12°C and 2°C, determine the rate of heat transfer through the window.arrow_forward
- Hi, can you help me to answer this question using the first law of thermodynamics formula to explain this event? On a hot summer day, a student turns his fan on when he leaves his room in themorning. When he returns in the evening will the room be warmer or cooler than theneighborouing rooms ? Explain your answer using the first law of thermodynamics.Assume ALL doors and windows are kept closed.arrow_forwardWhat are the mechanisms of heat transfer? How are they distinguished from each other?arrow_forwardThere is a cylindical piece of nickel, that is 5 cm in diameter and 10 cm in length, that is initially at 20 degrees Celcius before being dropped into a hot fluid that is at 190 degrees Celcius. Determine the amount of heat gained by the cylinder until its temperature rises to 80 degrees Celcius. Show details in calculations and specify values retrieved from property tables.arrow_forward
- A 10-m-long section of a 6-cm-diameter horizontal hot-water pipe passes through a large room whose temperature is 27°C. If the temperature and the emissivity of the outer surface of the pipe are 73°C and 0.8, respectively, determine the rate of heat loss from the pipe by (a) natural convection and (b) radiation.arrow_forwardA 40-cm-long, 800-W electric resistance heating element with diameter 0.5 cm and surface temperature 120°C is immersed in 75 kg of water initially at 20°C. Determine how long it will take for this heater to raise the water temperature to 80°C. Also, determine the convection heat transfer coefficients at the beginning and at the end of the heating process.arrow_forwardConsider a 1.2-m-high and 2-m-wide double-pane window consisting of two 0.0023-m-thick layers of glass (k = 0.78 W/m·K) separated by a 12-mm-wide vacuum space. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1 = 10 W/m2·K and h2 = 25 W/m2·K, and disregard any heat transfer by radiation. Assume that the space between the two glass layers is evacuated.Determine the steady rate of heat transfer (in W) through the glass window. The room is maintained at 24°C while the temperature of the outdoors is –5°C. (Radiation in outer side of the double-pane window should be disregarded but in the inner part, the only mechanism of heat transfer in vacuum is by radiation. Emissivity for glass is around 1, and the temperature of inner surfaces of the double-pane window should be assumed to be 5 and 15 'C.)arrow_forward
- A person puts a few apples into the freezer at 15°C cool them quickly for guestswho are about to arrive. Initially, the apples are at a uniform temperature of 20°C,and the heat transfer coefficient on the surfaces is 8 W/m2·K. Treating the apples as9-cm-diameter spheres and taking their properties to be 840 kg/m3, Cp 3.81 kJ/kg·K, k = 0.418 W/m·K, and α =10-7 m2/s, determine the center and surface temperatures of the apples in 1 h. Also, determine the amount of heat transfer from each apple. Solve this problem using analytical one-term approximation method (notthe Heisler charts). Answer: Center: 11.2 ℃, Surface: 2.7 ℃, heat transfer: 17.2 kJarrow_forwardConsider a person who is trying to keep cool on a hot summer day by turning a fan on and exposing his entire body to air flow. The air temperature is 85°F and the fan is blowing air at a velocity of 6 ft/s. If the person is doing light work and generating sensible heat at a rate of 300 Btu/h, determine the average temperature of the outer surface (skin or clothing) of the person. The average human body can be treated as a 1-ft-diameter cylinder with an exposed surface area of 18 ft2. Disregard any heat transfer by radiation. What would your answer be if the air velocity were doubled? Evaluate the air properties at 100°F.arrow_forwardexplain why summer is warmer than winter. Specifically, how can summer be warmer than winter if Earth is farther away from the Sun at that time?arrow_forward
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