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Want the facts on heat transfer? No sweat. Plus a free student handout from McGraw Hill’s AccessScience

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Heat Transfer Article by: Margaret Wooldridge, Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan. Ralph H. Luebbers, Formerly, Department of Chemical Engineering, University of Missouri, Columbia, Missouri. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource containing exclusive articles written by expert scientists and engineers; biographies of well-known scientific figures; science news, videos, and animations; and much, much more. Instructors can use AccessScience to guide students on their research project journeys, to help students understand scientific concepts, to support distance learning efforts, in flipped classroom approaches, and in countless other ways. Ward's World and AccessScience have partnered to offer educators a no-obligation, free trial subscription to AccessScience. Request your free trial today to discover how valuable AccessScience can be for you and your students! Get your free trial now. Heat transfer is a form of energy transfer and can occur by conduction, convection, and/or radiation. Heat transfer occurs any time there is a temperature difference between two objects and occurs in the direction of decreasing tempera- ture, meaning from a hot object to a cold object. Although the mechanisms and laws governing the three modes of heat transfer are quite different, they can co-occur in commonplace processes such as boiling a pot of water over an open flame (Fig. 1). This article provides introductory information on heat transfer and on important industrial devices called heat exchangers. Conduction Heat conduction involves the transfer of heat from one mole- cule to an adjacent molecule as an inelastic collision in the case of fluids, as oscillations in solid nonconductors of electricity, and as motions of electrons in conducting solids such as metals. (Note that the term "fluids" includes both liquid and gas phase materials.) For example, heat is transferred by conduction from a hot cooking utensil to your hand, from a soldering iron to the solder, and from the roof of your house + ward ' s science Content • Conduction • Convection • Radiation • Design considerations • Heat exchangers Fig. 1: Water boiling on a stove offers an example of all three modes of heat transfer occurring at the same time. Heat conducts through the metal fixture of the stove into the bottom of the pot of water. Heat also radiates from the flame of the gas burner to the bottom of the pot. Convection transfers the heat from the bottom of the pot to the water. (Credit: Ryerson Clark/Getty Images) Key Concepts • The transfer of heat can occur in three ways: conduction, convection, and radiation. • Heat transfer occurs between states of matter whenever a temperature difference exists and heat transfer occurs only in the direction of decreasing temperature, meaning from a hot object to a cold object. • Although the mechanisms and laws governing the three modes of heat transfer are quite different, all three modes can occur during a single process. • An important industrial device for enabling heat transfer between fluids is called a heat exchanger.

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