CE530Mechanical Systems for BuildingsBasic Concepts of ThermodynamicsGraciano Emmanuelito E. Dela Cruz III,RMESchool of Mechanical EngineeringMapua Institute of Technology

THERMODYNAMICSMerriam Webster: physics that deals with the mechanical actions or relations of heat.A science that includes the study of energy transformations and the relationships among the physical properties of substances which are affected by these transformations.

THERMODYNAMICS: ENGINEERING APPROACHMechanical Engineers (arguably the fathers of the field) are often interested in converting heat (such as from a chemical fuel) into work (shaft work, electricity).

Chemical Engineers differentiate themselves through a focus on phase equilibria and reaction equilibria.

THERMODYNAMICS: ENGINEERING APPROACHChemists use thermodynamics to evaluate driving forces (a.k.a chemical potential) for reactions or phase-change processes.

Metallurgists and geologists are interested in solid phase equilibria.

WHAT ABOUT CIVIL ENGINEERS!?!A Civil engineer provided one of the most useful power cycle used in the world

William John Macquorn Rankine

THERMODYNAMICSThermodynamics is the science that is devoted to understanding energy in all its forms, such as mechanical, electrical, and how energy changes forms.Thermodynamics is derived from the Greek words therme, meaning heat, and dynamis, meaning strength, particularly applied to motion.Heat strength

So what is Engineering thermodynamics?Engineering Thermodynamics is a branch of thermodynamics in which emphasis is placed on the engineering analysis and design of processes, devices, and systems involving the beneficial utilization of energy and material.

TWO METHODS OF STUDY (view points)Microscopic or statistical thermodynamics this is based on statistical behavior of large groups of individual particles.

Macroscopic or Classical thermodynamics concern with the overall effect of the individual molecular interactions. The macroscopic level is the level on which we live.

Dimensions and UnitsDimensions are names that characterize quantities. Examples include length, time, force, mass, electric charge and temperature.Units are those arbitrary magnitudes and names assigned to dimensions which are adopted as standards for measurements. Examples are feet, miles, centimeters.

Systems of unitsThe Systeme Internationale (international system) also known as the SI units.

United States Customary System of Units (USCS) , engineering units or English units.

English UnitsHorse power from mine pony.

King Henry IYard descended from standards as the length from the thumb to the nose of Henry I of England.

SubstancesSubstance may be solid, liquid, vapor, or a mixture which is performing the energy transformation.

Pure substance Mechanical mixtureIdeal gas or perfect gas

THERMODYNAMIC SYSTEMSThermodynamic System is a three-dimensional region of space or an amount of matter, bounded by a arbitrary surface.Open system is a system for which mass as well as energy may cross the selected boundaries.Closed system or control mass is a system for which no mass crosses the boundary.Isolated system when neither mass nor energy crosses the boundary.

Parts of a systemBoundary may be real or imaginary, may be at rest or in motion, and may change its size or shape.Surroundings, or the environment the region physical space that lies outside the arbitrarily selected boundaries of the system.Any thermodynamic analysis begins with a selection of the system, its boundary, and its surroundings.

Parts of the system

PropertiesA property is a characteristic quality of the entire system and depends not o how the system changes state but only on the final system state.Extensive property depends on the size or extent of the system: Volume, energy.Intensive property independent of the size of the system.e.g. temperature and pressure.Specific property overall system is divided by the mass

Phase and statePhase is a quantity of matter that is homogeneous throughout in physical structure and chemical composition.

The state of a system is the condition of the system described by the values of its properties.

Processes and cyclesA process is a change of a system from one equilibrium state to another.A system is in thermodynamic equilibrium if it is not capable of a finite, spontaneous change to another state without a finite change in the state of its environment.The path of a process refers to the specific series of states through which the system passes.A thermodynamic cycle is a collection of two or more processes for which the initial and final states are the same.

Thermodynamic processesQuasi-static or quasi-equilibrium process- a process which proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.Reversible process- process that can be reversed without leaving any trace on the surroundingsIrreversible or real process- includes friction, unrestrained expansion, mixing of two fluids, heat transfer across finite temperature difference, electric resistance, inelastic deformation of solids and chemical reactions.

Point and path functionsPoint function or state functions: all properties are state functions, since the change in the value of a property depends solely on the property values at the initial and final states, and not on the path of the process.Path or process functions: quantities whose values depend on the path of the process.

Density, specific volume, specific gravityDensity is defined as the mass per unit volume.Specific gravity (SG or RD) of a substance: is the ratio of its density to that of water at a specified temperature, such as 4 or 20C or 60F.Specific volume: the volume per unit massSpecific weight: the weight per unit volume

PressurePressure is defined as the normal force per unit area acting on the boundary of the system.Absolute pressure: measured relative to absolute zero pressure.Atmospheric pressureGage pressure: pressure difference between the absolute pressure and atmospheric pressure.Vacuum: negative gage pressure

temperatureA property of an object which determines the direction of heat flow when the object is placed in thermal contact with another object. Absolute temperature, Kelvin and RankineArbitrary temperature, Celsius and Fahrenheit

Study units and dimensionsThank you.