Heat Transfer
- Created by: Emily L S Bloom
- Created on: 19-11-14 22:28
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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
- Qdot = driving force/resistance
- 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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