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Unformatted text preview: Introduction ME309 1 ME309 Heat and Mass Transfer Lecture 1. Introduction Introduction ME309 2 Topics Heat (energy) transfer and temperature Heat transfer modes Conduction heat transfer Steady 1D cartesian, cylindrical, spherical Transient 0D1D Boundary conditions: flux, temperature, generalized flux Convection heat transfer Forced Natural Thermal Radiation Condensation and boiling Types of boiling Drop and film condensation Mass transfer Diffusion Conservation of species Types of boundary conditions Introduction ME309 3 Mathematical background Emphasis on physical meaning of equations and assumptions Differential equations Ordinary: lumped analysis Partial: conduction Only new(?) MATH, gradient (slope) = z f y f x f f y x z f z x y f z y x f yz xz xy z y x f + = + = + = + + = 3 2 3 2 3 2 ) , , ( Introduction ME309 4 What is Heat Transfer What happens when we place a cold object on top of a hot stove? What happens when you put a hot object into a cold bucket of water? Introduction ME309 5 Where do you see heat transfer? Heating and cooling of spaces and objects Electric heaters, Space heaters, Hot coffee on your desk,? Thermal processes Cooking, electric generation, material processing, ? Natural phenomena Sun, climate, volcanoes, ocean depths, ? Machines Automotive engines, steam engines, Rankine engines, ? Mechatronic systems Motors, fans, heat sinks,? Biological systems ? Introduction ME309 6 Introduction Thermodynamics: Energy transfer between a system and its surroundings. A system interacts with its surroundings by exchanging work and heat Q W : Rate of work at constant pressure dU Q W dt U Internal energy dV W p dt = + = p v At constant volume: At constant pressure: enthalpy T: temperature c : constant pressure specific heat of the object c : constant volume specific heat v p dU dT Q mc dt dt dV dU dH dT Q p mc dt dt dt dt H pV U = = = + = = = + of the object Introduction ME309 7 What is temperature? ( Statistical view ) Average mechanical energy of motion on the molecular scale Kinetic energy of gases Rotational and dilational energy of molecules in fluids and amorph solids Lattice vibration in solids ( Thermodynamics general view) Units of temperature Kelvin, [K] (with respect to absolute zero) Other convenient (cultural) units, o C, o F, ....
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 Spring '09
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