Nodiadau Astudio Thermodinameg

Thermodynamics Study Notes

• Heat Effects & Phase Transitions:

  • Latent heat describes energy changes during phase transitions (e.g., melting, vaporization).
  • Sensible heat refers to energy changes associated with changes in temperature.
  • Heat of combustion describes energy released during a combustion reaction.
  • Heat of formation refers to energy absorbed or released when a compound is formed from its elements.

• Critical Point & Equations of State:

  • At the critical point, the liquid and gas phases become indistinguishable, and a cubic equation of state has one real value among the three solutions.

• Cascade Refrigeration Systems:

  • A two-stage cascade system uses two cycles to achieve lower cooling temperatures.
  • The second cycle (cycle 2) operates closer to the desired cooling temperature.
  • This arrangement is useful for specific cooling applications.

• Energy in Transit:

  • Heat is considered a form of energy in transit.
  • Kinetic and potential energy, internal energy, are not considered energy in transit.

• Liquid Properties & Pressure:

  • Isothermal compressibility relates changes in volume to pressure at constant temperature.
  • Compresibility factor is helpful to relate ideal gas behavior.

• Carnot Cycle & Efficiency:

  • The Carnot cycle, an ideal thermodynamic cycle, has maximum efficiency for a given temperature range.
  • Expressed generally as a function of temperature.

• Compressor Efficiency:

  • Compressor efficiency is a measure of how efficiently the compressor converts input work into fluid flow work.
  • The efficiency is a ratio of ideal work to the actual work.

• Reversible Processes:

  • Reversible processes are those that can be reversed without leaving any effect on the surrounding system.
  • Frictionless processes and equilibrium states are characteristics of reversible processes.

• Two-Phase Region (Fluid):

  • The CEOS solution with the greatest value for a fluid in a two-phase region represents the vapor/vapor-like solution.

• Steam Power Plants:

  • Increased boiler pressure increases thermal efficiency in a steam power plant.
  • Refrigerant characteristics are crucial for condenser and evaporator operations.

• Refrigerant Specifications:

  • Essential refrigerant property is it has a higher vapor pressure than the atmospheric pressure, and lower vapor pressure at evaporator temperature.

• Carnot Refrigerator:

  • Coefficient of performance (COP) for a Carnot refrigerator is independent of the type of refrigerants.

• Isothermal & Isobaric Processes:

  • Adiabatic processes allow a measure of work.
  • Carnot cycle is used in an idealised closed system.
  • Mechanical reversible and isothermal process have zero change in internal energy.
  • Work is a change in energy between an open system and surroundings.

• State Functions:

  • State functions do not depend on the path taken to reach a particular state.
  • State functions depend only on present state independent of how or where they were achieved.

• Equations of State:

  • Equations of state describe the relationship between pressure, volume, temperature, and composition of a substance.
  • These models allow for predictions of the behavior of fluids and are very important in thermochemistry and chemical engineering.

• Internal Energy & Heat Transfer:

  • Internal energy of a substance is the sum of all microscopic energies within the substance.
  • Heat transfer is energy transfer between two objects at different temperatures from higher to lower. Internal energy isn't transferred.
  • For a closed system, the changes or variations of Q+W are related to the changes in internal energy of the system.

• Refrigerants & Montreal Protocol:

  • The Montreal Protocol is an international treaty to phase out refrigerants that harm the ozone layer.

• Critical Point: -The critical point is a state where the liquid and gas phases become indistinguishable.

• Flow Processes: -When the process is reversible, the heat transfer to the surroundings is zero and the heat energy is conserved.

• Refrigeration Effect:

  • Refrigeration effect per unit of work is described by a relation with temperature.

• Steam Power Plant Thermal Efficiency:

  • Higher condensing temperature leads to increased thermal efficiency.

• Entropy Change:

  • Entropy change during a process depends on the path followed.

• Heat Capacity:

  • Constant Pressure heat capacity (Cp) and constant volume heat capacity (Cv) are intrinsic physical properties of any substances.

• Carnot Efficiency:

  • Carnot efficiency depends only on the temperature levels and not on working substance.

• Phase Change Enthalpy:

  • Enthalpy of Vaporization is proportional to the slope InPsat vs 1/T.