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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
 serhatyeşilyurt
 Thermodynamics, Heat Transfer, Tsur

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