Heat Transfer

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  • Heat Transfer
    • Conduction
    • Convection
      • propagation of thermal energy between adjacent ions/molecules/ions
      • transfer thermal energy between a solid surface and the adjacent fluid by bulk movement of the fluid
      • forced convection - mechanical input (fan, pump) or wind
      • natural convection - buoyancy forces
    • Radiation
      • thermal energy emitted in the form of electromagnetic
      • at moderate temperatures radiation is not significant compared to conduction or convection
    • Temperature Driving Force
      • if two adjacent region have a temperature difference, heat will flow from the hot to cold to establish thermal equilbibrium
    • Heat Exchanger
      • devices that enable the transfer of heat between two fluids e.g. car radiator, power plant condensor
      • larger heat transfer coefficient, more rapid heat transfer (larger Qdot) or smaller A for given Qdot
        • Qdot = driving force/resistance
          • devices that enable the transfer of heat between two fluids e.g. car radiator, power plant condensor
      • Double Pipe Heat Exchanger - one pipe set inside another, concentric pipe heat exhcanger
        • co-current - same direction
        • counter-current - opposing direction - possible to get Tco greater than Tho
        • T1 = temperature difference between hold and cold at one end of the heat exchanger
        • T2 = temperature difference between hold and cold streams at the other end of the heat exchanger
        • assume that the fluid undergoing a phase change will remain at constant teperature as the energy transfered will be associated with the latent heat Hfg

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