Module 5-Heat Transfer

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Heat Transfer Created by: Marlon Flores Sacedon Physics section, DMPS June 2011

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Taking 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 you’re 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? conductor insulator The three mechanisms of heat transfer are conduction, convection, and radiation.

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Three Mechanisms of Heat Transfer Heat transfer occurs within a body or between two bodies in contact. Conduction

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Three Mechanisms of Heat Transfer Heat transfer depends on motion of mass from one region of space to another. ConVECtion

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Three Mechanisms of Heat Transfer Heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies. RADIAtion

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Conduction 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 grdient (K/m)

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Example 1: A Styrofoam cooler (Fig. 1) has total wall area (including the lid) of 0.80 m 2 and wall thickness 2.0 cm. It is filled with ice, water, and cans of Omni-Cola, all at 0 o C. What is the rate of heat flow into the cooler if the temperature of the outside wall is 30 o C? How much ice melts in 3 hours?

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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 100 o C by placing it in contact with steam, and the free end of the copper bar is kept at 0 o C 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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