Transferência de Energia e de Massa Energy and Mass Transfer Lecture 1: Introduction to the subject and to the course

Objectives of the Course To introduce the processes responsible for Energy and Mass Transfer, To introduce calculation methods, To assess some case studies representative of the main engineering cases.

Expected Achievements Assimilation of new concepts, Consolidation of former knowledge acquired in former courses: Physics, Fluid Mechanics, Thermodynamics, Mathematics, Informatics/programing

Course Program Basic concepts Heat and Mass diffusion Detailed Program (web Page) Introduction. Physical Origins and rate equations. The conservation of energy. Introduction to conduction. The thermal properties of matter. The heat diffusion equation. Boundary and initial conditions. One dimensional conduction. The plane wall and radial systems. Conduction with thermal energy generation. Two dimensional steady state conduction. The method of separation of variables. Finite difference equations. Finite difference solutions. Transient conduction. The lumped capacitance method. Time constant. The semi-infinite solid. Finite difference methods. The explicit method. The implicit method. Introduction to convection. Boundary Layer. Laminar and turbulent flows. Boundary Layer equations. The normalized boundary layer equations. Free and Forced convection. Convection correlations. Radiation. Fundamental concepts. Radiation intensity. Black body, Plank's law, Wien's law, Stefan Boltz-man's law. Absortivity, reflectivity and transmissivity. Kirchoff's law. The gray surface. Radiation exchange between surfaces. Multi-mode heat transfer. Diffusion mass transfer. Conservation of species. Mass diffusion in stationary conditions. Sensible and latent heat. Basic concepts Heat and Mass diffusion Heat and Mass convection Radiation Integration of processes.

Learning Assessment Two tests: 4th April and another at the last lecture (2nd June). Any of them can be repeated at the same date/hour of the 1st exam; Or final exam (two dates); (70%, minimum 10 marks) A numerical simulation exercise; (30%) Home work at the end of each chapter (+ 1 mark, if all delivered)

Bibliography Fundamentals of Heat and Mass Transfer - 7th edition: Incropera, F. P., D. P. DeWitt 2002

Energy Transfer/Transformation Is Radiation synonymous of heat? Almost….

A energy transfer in the atmosphere Why are clouds important in the atmosphere? Why do we need heat to evaporate Water? How do we get in back in condensation? Why is latent heat so big? (2500kJ/kg) Energy transfer is a physical process!

Is CO2 cycle associated to Energy transfer? Carbon oxidation releases energy. Photosynthesis fixes energy. Energy transfer in earth requires the consideration of Carbon and Water cycles. How to minimize urban thermal islands? Biology makes the difference between Energy Transfer and Energy transformation less clear..

Atmospheric Circulation and Energy Transfer Atmospheric circulation is the most effective energy transfer mechanism on earth. It carries heat from warmer to colder regions. Aeolian and hydric energies are a product of that transfer.

Ocean circulation is another mechanism for energy transport. Ocean circulation is mostly driven by solar energy (directly or indirectly through atmospheric forcing) The conveyer belt carries energy, oxygen and nutrients.

Green House Effect http://www.windows2univers e.org/earth/climate/greenhou se_effect_gases.html

The Engineering scale…

Our Course scale…

Heat, Energy, Mass Heat vs Energy: units (Calorie or Joule?) 1 cal is the energy necessary to increase the temperature of 1g of Water by 1k: Cp of Water (at 300k) = 4.179 kJ/kg/k => 1cal=4.18 J 250ml of orange juice have 200Kcal. If I use the stairs in a building, how many floors should I (weight 80kg) walk up to spend this energy? Considering 3 m height per floor, I will increase my potential energy by Ep=mgh=80*9.8*3=2.4E3 J/floor. A bottle is 200kcal=200*1000*4.179=8.3*10E5J/bottle N=300 floors… Something seems to be wrong…

Is Exercise the best strategy to loose weight? If mammals spend most of energy to keep temperature, the best way to consume more energy is to eliminate isolation… The problem is that body gets mad when temperature lowers… So, if controlling the output is not so much effective, the best is to cut on input, i.e. to go for diet…

Energy Transfer vs Mass Transfer What forms of energy transfer do not have mass transfer associated? Heat/radiation? Mechanical Energy? (Pressure, kinetic, potential) Internal Energy? Chemical Energy? Electrical Energy? …. Heat Conduction and Radiation are the only forms of Energy that are not associated to Mass Transfer (apart from Electrical Energy). This is why “Energy and Mass transfer” is often taken as synonymous of “Heat and Mass transfer”

Summary of the Lecture The Course Organization The importance of Energy and Mass Transfer at global and Engineering scale. The close linkage between Mass and Energy Transfer Heat Conduction and radiation as the only energy transport processes not associated to mas transfer. This is why the course will start with heat conduction.

Next Lecture Subject Basic concepts of Heat Transfer