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Applications of heat transfer ppt

boiling heat transfer ppt and advanced heat transfer ppt and heat and mass transfer powerpoint slides
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Dr.TomHunt,United States,Teacher
Published Date:22-07-2017
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A Short Course on Heat Transfer Intended as a repetition from previous courses by Björn Palm, Royal Institute of Technology, Stockholm Course Contents, based on Holman’s book Heat Transfer Chapter 1: Introduction Chapter 2: Steady-State Conduction - One Dimension Chapter 3: Steady-State Conduction - Multiple Dimensions Chapter 4: Unsteady-State Conduction Chapter 5: Principles of Convection Chapter 6: Empirical and Practical Relations for Forced-Convection Heat Transfer Chapter 7: Natural Convection Systems Chapter 8: Radiation Heat Transfer Chapter 9: Condensation and Boiling Heat Transfer Chapter 10: Heat Exchangers (Chapter 11: Mass Transfer) 2 Part 1 Introduction 3 Introduction What is heat? Heat is energy transfer caused by temperature difference 4 The four laws of thermodynamics: • Zeroth law: If two bodies both are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other, and they then are said to have the same temperature. 5 • First law: (Energy principle) Energy cannot be generated or destroyed, only converted to different forms. (”Energy consumption” is the transfer of ”prime” energy to thermal energy in the surrounding) 6 • Second law: Heat cannot by itself pass from one body to another body with higher temperature. (Entropy disorder strives to a maximum in a closed system. Shows the direction of time.) 7 • 8 Third law: The entropy of a pure, crystalline material takes its lowest value at absolute zero temperature, where it is 0. (There is a lowest limit to the temperature, 0K = -273.15°C. World record: 0.00000017 K = 170 nanokelvin) 9 Three modes of heat transfer: • Conduction Through solid bodies and ”still” fluids hot cold • Convection Through moving fluids (also boiling and condensation) • Radiation Between surfaces, through gas or vacuum hot cold 10 What do we know about conduction? 11 Conduction, thermal conductivity, Fourier´s law: Fourier’s law: q = -k⋅A⋅δT/δx where, q = heat flow (W) 2 A = area perpendicular to heat flow (m ) δT/δx = temperature gradient in the direction of heat flow(°C/m) k = thermal conductivity (W/(m °C)) Fourier´s law is the defining equation for the thermal conductivity. 12 Conduction, thermal conductivity, Fourier´s law: For one-dimensional heat transfer (a plane wall,) with constant thermal conductivity, Fourier´s law is simplified to q = k⋅A⋅ΔT/δ where ΔT = temperature difference (°C) δ = distance or thickness (m). 13 fig. 1 Temp δT/δx0 x Hot Cold q0 14 Fig. 2 Heat transfer through a plane wall T1 ΔT T2 δ 15 Table 1 Material Thermal conductivity (20°), (W/m⋅°C) Diamond, type IIa 2600 Copper 386 Iron, wrought, 0.5% C 60 Stainless steel, 18/8 16.3 Brick 0.69 Water 0.6 Pine wood, 0.15/0.33 (cross/along fibres) Cork 0.045 Glass wool 0.038 Mineral wool 0.04 Polyurethane 0.02 Air 0.026 Argon gas 0.018 16 Example to solve: Conduction: Calculate the heat flow per square meter (heat flux) through a mineral wool insulation, 5 cm thick, if the temperatures on the two surfaces are 30 and 200°C, respectively. 17 Heat transfer by convection, Newton’s law of cooling Convection is a general term for heat transfer through a moving fluid. 18 Fig 3, Different types of convection heat transfer Boiling Forced convection Diffusion, mass transfer Condensation 19 What do we know about convection? 20