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Prof. Marlon Flores Sacedon
Heat Transfer Prof. Marlon Flores Sacedon Department of Mathematics and Physics College of Arts and Sciences Visayas State University, Visca Baybay City, Leyte, Phiippines
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First long exam Date: Aug 23, 2017 Time: 5:00-7:00 PM Venue: EB-105
Coverage: from start to heat transfer No. of Items: 60 pts. Bring the following: Calculator, 5 sheets of yellow, ballpen, etc.
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How do we describe the difference between these two materials?
conductor insulator Talking about conductors and insulators, materials that permit or prevent heat transfer between bodies. In the kitchen you use a metal or glass pot for good heat transfer from the stove to whatever youβre cooking, but your refrigerator is insulated with a material that prevents heat from flowing into the food inside the refrigerator. How do we describe the difference between these two materials? The answer is heat transfer.
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Heat transfer is the exchange of thermal energy between physical systems. The rate of heat transfer is dependent on the temperatures of the systems and the properties of the intervening medium through which the heat is transferred.
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Three Mechanisms of Heat Transfer
Conduction Heat transfer occurs within a body or between two bodies in contact. Conduction is the process by which heat energy is transmitted through collisions between neighboring molecules.
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Three Mechanisms of Heat Transfer
ConVECtion is the transfer of heat from one place to another by the movement of fluids. Convection is usually the dominant form of heat transfer(convection) in liquids and gases.
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Three Mechanisms of Heat Transfer
RADIAtion Heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies.
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Conduction Steady-state heat flow due to conduction in a uniform rod.
Where: H = heat current (W or watt) k = thermal conductivity (W/m.K) TH & Tc = hot and cold temperature (oC) A = area of conductor (m2) L = length of conductor (m) (TH - Tc)/L = temperature gradient (K/m)
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Example 1: A Styrofoam cooler (Right Figure) has total wall area (including the lid) of 0.80 m2 and wall thickness 2.0 cm. It is filled with ice, water, and cans of Omni-Cola, all at 0oC. What is the rate of heat flow into the cooler if the temperature of the outside wall is 30oC? How much ice melts in 3 hours? π»= 0.027π/πβπΎ π π πͺ βπ π πͺ π =32.4 π=32.4 π½/π π=π πΏ π π= π πΏ π = π½/π 10,800 π 3.34π₯ π½/ππ =1.0 ππ
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Example 2. A steel bar 10.0 cm long is welded end to end to a copper bar 20.0 cm long. Each bar has a square cross section, 2.00 cm on a side. The free end of the steel bar is kept at 100oC by placing it in contact with steam, and the free end of the copper bar is kept at 0oC by placing it in contact with ice. Both bars are perfectly insulated on their sides. Find the steady-state temperature at the junction of the two bars and the total rate of heat flow through the bars.
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Assignment
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Assignment
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Assignment
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Answers to odd numbers
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eNd
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