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Forms of Energy

• Economic Importance

  • Understanding energy conversion and losses is crucial.

  • Define work and heat using standard conventions.

Outline of Topics

• Laws of Thermodynamics

• Units for Energy

• Sources and Forms of Energy

• System and Surroundings

• State and Equilibrium

Common Applications in Design Process

• Energy required in process systems includes:

  • Heating utility (e.g., boilers, heaters)

  • Cooling utility (e.g., condensers, refrigeration)

  • Heats of reactions

  • Fluid motive devices (e.g., pumps, compressors, turbines)

  • Chemical energy stored in crude oil

  • Phase change from liquid to vapor through heat transfer

  • Separation of oil components using thermal energy.

Thermodynamics

• This science explains energy flow between forms, deals with heat and work, and predicts process directions and transformations.

  • First Law of Thermodynamics: Energy is conserved; can change form but not destroyed.

  • Second Law: Entropy is generated easily but cannot be destroyed; appears in different forms.

Units for Energy

• Joule (J): SI unit (1 J = 1 kg∙m²/s²)

• Calorie (cal): Raises temperature of 1 g of water by 1°C (1 cal = 4.184 J)

• Nutritional Calorie (Cal): 1 Cal = 1 kcal = 1000 cal

• British Thermal Unit (Btu): Raises temperature of 1 lbm of water by 1°F (1 Btu = 1055 J)

• Centrigade Heat Unit (Chu): Energy to raise 1 lbm of water by 1°C under standard atmosphere.

Sources of Energy

• Renewable: Continuous sources; cleaner (e.g., sun, wind).

• Non-renewable: Ex: coal, crude oil, natural gas, uranium.

Forms of Energy

• Kinetic Energy

  • Related to the motion (KE = 1/2 mv²).

• Potential Energy

  • Gravitational PE (PE = mgz).

  • Elastic PE due to deformation (PE = 1/2 kx²).

• Internal Energy (U)

  • Related to molecule motion, position, and bonding.

• Work (W)

  • Energy flowing in response to a force, includes:

    • Expansion/Contraction Work (dW = - PdV)

    • Shaft Work (no volume change)

    • Flow Work (Pout * Vout - Pin * Vin)

• Heat (Q)

  • Energy from temperature difference (flows from high to low).

System and Surroundings

• System: Part of the universe studied.

• Surroundings: Everything outside the system.

• Boundary: Separates the system from surroundings; either real or imaginary.

Kinds of Systems

• Open System: Exchange of energy and matter.

• Closed System: Exchange of energy only.

• Isolated System: No exchange of energy or matter.

Properties of a System

• Intensive Properties: Independent of quantity (e.g., temperature, pressure).

• Extensive Properties: Proportional to quantity (e.g., volume, entropy, internal energy).

State and Equilibrium

• State: Describes conditions of a system.

• Equilibrium: No unbalanced potentials exist.

  • Types: Thermal, mechanical, chemical.

• Zeroth Law of Thermodynamics: Equilibrium established with a third object.

Heat, Work, and Internal Energy

• First Law of Thermodynamics: Total energy remains constant with energy transfer between system and surroundings.

• Energy equation: ∆Esys = Q + W.

• Analyzing changes in energy with different energy types.

Example Problems and Calculations

• Analyze energy changes in various scenarios and calculate using thermodynamic laws, units, etc.

  • Enthalpy Calculations: Use standard enthalpy changes in chemical reactions.