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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 [Fi r s [1] , Lin e 11 . 2 —— No r m * PgE [1] , CHAPTER 1 Basic Concepts ALLAN D. KRAUS University of Akron Akron, Ohio 1.1 Heat transfer fundamentals 1.1.1 Introduction 1.1.2 Conduction heat transfer One-dimensional conduction One-dimensional conduction with internal heat generation 1.1.3 Spreading resistance 1.1.4 Interface–contact resistance 1.1.5 Lumped-capacity heating and cooling 1.1.6 Convective heat transfer Heat transfer coef±cient Dimensionless parameters Natural convection Forced convection 1.1.7 Phase-change heat transfer 1.1.8 Finned surfaces 1.1.9 Flow resistance 1.1.10 Radiative heat transfer 1.2 Coordinate systems 1.2.1 Rectangular (Cartesian) coordinate system 1.2.2 Cylindrical coordinate system 1.2.3 Spherical coordinate system 1.2.4 General curvilinear coordinates 1.3 Continuity equation 1.4 Momentum and the momentum theorem 1.5 Conservation of energy 1.6 Dimensional analysis 1.6.1 Friction loss in pipe flow 1.6.2 Summary of dimensionless groups 1.7 Units 1.7.1 SI system (Syst`eme International d’Unit´es) 1.7.2 English engineering system (U.S. customary system) 1.7.3 Conversion factors Nomenclature References 1
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2 BASIC CONCEPTS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 [2], Lin e 6.2 8 —— Nor m PgE n [2], 1.1 HEAT TRANSFER FUNDAMENTALS 1.1.1 Introduction Practitioners of the thermal arts and sciences generally deal with four basic thermal transport modes: conduction, convection, phase change, and radiation. The process by which heat diffuses through a solid or a stationary fluid is termed heat conduction. Situations in which heat transfer from a wetted surface is assisted by the motion of the fluid give rise to heat convection, and when the fluid undergoes a liquid–solid or liquid–vapor state transformation at or very near the wetted surface, attention is focused on this phase-change heat transfer. The exchange of heat between surfaces, or between a surface and a surrounding fluid, by long-wavelength electromagnetic radiation is termed thermal heat radiation. It is our intent in this section to describe briefly these modes of heat transfer, with emphasis on an important parameter known as the thermal resistance to heat transfer. Simple examples are given for illustration; detailed descriptions of the same topics are presented in specialized chapters. 1.1.2 Conduction Heat Transfer One-Dimensional Conduction Thermal diffusion through solids is governed by Fourier’s law, which in one-dimensional form is expressible as q =− kA dT dx ( W ) (1.1) where q is the heat current, k the thermal conductivity of the medium, A the cross- sectional area for heat flow, and dT/dx the temperature gradient, which, because it is negative, requires insertion of the minus sign in eq. (1.1) to assure a positive heat flow q . The temperature difference resulting from the steady-state diffusion of heat is thus related to the thermal conductivity of the material, the cross-sectional area A ,
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