Thermodynamics and Energy Balance for Engineers

Identify the differences between work and heat as energy transfer across a system boundary, and apply the sign convention to derive the first law and the energy balance.

Explore expansion and contraction work in a closed piston-cylinder system, deriving the work expression as negative integral of pressure with respect to volume while noting reversibility and energy losses.

Compare reversible and non-reversible contraction and expansion work for an isothermal ideal gas, showing how external pressure differs from system pressure and how this affects calculated work.

Compare reversible and irreversible isothermal expansion of a gas in a piston cylinder, showing how external pressure governs work; reversible expansion yields more work than irreversible due to real losses.

Examine shaft work as energy transferred to or from a fluid without changing the control volume, with pumps, turbines, and agitators as examples, and its role in energy balance calculations.

Explore flow work, or flow energy, the energy a fluid adds or removes as it enters or leaves an open system, using pressure, area, and velocity.

Explore heat flow as the transfer of thermal energy driven by temperature differences, illustrated by blocks reaching thermal equilibrium and the zeroth law, with Q used in energy balance.

Develop the closed system energy balance by accounting for heat and work interactions (expansion and contraction work, shaft work, flow work) under the conservation of energy, with mass constant.

Explore units in energy balance by analyzing internal, kinetic, and potential energy terms, distinguishing intensive versus extensive properties, and showing all terms reduce to joules in SI units.

Apply the closed system energy balance to two blocks by defining boundaries, analyzing heat transfer, and tracking internal energy changes. Note signs and when solid expansion work may be neglected.

Explore open system steady state energy balance, deriving the general enthalpy-based energy balance with inlet and outlet flows, heat, and shaft work, plus key delta enthalpy concepts.

Compute shaft work for a liquid pump using open-system energy balance and steam-table enthalpies, then compare with a constant-volume approximation for saturated water from 20°C to 10 and 100 MPa.

apply shaft work approximation for liquids in a steady open-system pump to estimate reversible shaft work as Δp·v with constant specific volume, and compare to enthalpy-based results.

Explore the complete energy balance for unsteady open systems, including energy accumulation and the general equation with mass, heat, shaft work, and expansion work, plus transient vs unsteady state nuances.

Explore how internal energy and enthalpy relate to temperature and pressure, and learn to calculate them from measurable properties using constant volume and constant pressure heat capacities.

Relate Cp and Cv to changes in internal energy and enthalpy for ideal gases, and note limits for real gases and liquids without phase-change effects.

Learn to calculate enthalpy change for an ideal gas during nitrogen compression from 5 to 10 bar, with 20°C to 50°C, using cp delta t and noting pressure independence.

Analyze adiabatic compression of nitrogen in a closed piston cylinder, raising temperature from 25 Celsius to 300°C and calculating work from the internal energy change, 5716 joules per mole.

Identify enthalpy and internal energy changes during phase transitions, such as vaporization and condensation, and apply Clausius-Clapeyron or Kessler Lee correlations when data are unavailable.

Estimate the enthalpy of vaporization of water at 100° C and 1 atm using the Lee Kessler and Clausius-Clapeyron methods, comparing results (39.4 vs 41.4 kJ/mol) to ~40.65 kJ/mol.

Learn how reference states define baselines for internal energy and enthalpy, and how energy changes drive calculations in energy balances.

Specify a reference state by temperature, pressure, composition, and set enthalpy or internal energy to zero; compare phase-change pathways from 120°C vapor to 50°C liquid.

Explore how reference states affect energy balances and enthalpy changes by solving the heating of acetone from liquid at 20°C to vapor at 90°C, showing cancellation of reference enthalpies.

Explore how reference states affect energy balance calculations for acetone, including enthalpy of vaporization, condensation, heating steps, and ideal gas approximations.

Compare enthalpy and internal energy changes with kinetic and potential energy changes through open-system energy balance, using two examples that show when velocity and height terms are significant or negligible.

Analyze the energy balance for adiabatic reversible expansion of an ideal gas in a closed system. Derive the final temperature using separation of variables with constant volume heat capacity.

Explore continuous adiabatic reversible compression of an ideal gas in a steady-state open system, deriving outlet temperature and compressor power via energy balance and enthalpy change.

Analyze isothermal, reversible compression of air as an ideal gas, apply energy balance to equate shaft work and heat removal, and determine a 0.48 kW compressor power.