THERMODYNAMICS

THERMODYNAMICSTHERMODYNAMICSCONTENTS:

Definition of TermsProperties of Working SubstanceWork, Heat and PowerLaws of ThermodynamicsIdeal GasesProcesses Involving Ideal GasesPure SubstanceProcesses Involving Pure SubstanceThe Carnot CycleThermodynamics the study of heat and work and those properties of substance that bear a relation to heat and work.Definition of Terms:Surroundings all matter and space outside to a system.Isolated System is a physical system that does not interact or exchange energy with its surroundings.Control Volume the focused volume is in space from which the substance flows. (Ex. Turbine, pumps, heater, etc.)Control Surface the surface that surrounds the control volume.Phase quantity of matter having same chemical composition or homogeneous.Property a quantity which serves to describe a substance.Two Types of Thermodynamic PropertiesIntensive Property a property which does not depend on the mass of the substance such as temperature, pressure, density, stress and velocity.

Extensive Property a property which depends on the mass of the substance such as volume, momentum and energy.Working Substance - a substance to which heat can be extracted.PROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCEPROPERTIES OF A WORKING SUBSTANCE6. Internal Energy, u, kJ/kg

Internal Energy heat energy due to the movement of the molecules within the substance brought about its temperature.

Internal Energy is zero if temperature is constantPROPERTIES OF A WORKING SUBSTANCE15PROPERTIES OF A WORKING SUBSTANCE8. Enthalpy, h, kJ/kg

Enthalpy the total heat and heat content of a substance which is equal to the sum of the internal energy of a body and the product of pressure and specific volume.

Enthalpy = Internal Energy + Flow Work

h = u = PvPROPERTIES OF A WORKING SUBSTANCEWORK, HEAT AND POWERWORK the quantity of energy transferred from one system to another. Units of work are, ft-lb, J or kJ.

Work = Force x Distance, ft-lb, kN-m or kJ

W = F x L = PvWORK, HEAT AND POWERWORK, HEAT AND POWERWORK, HEAT AND POWERCONVERSION UNITS OF HEAT:

1Btu = 778 ft lb1 kcal = 4.187 kJ= 252 cal (0.252 kcal)1 N m = 1 J= 1.055 kJ1000 J = 1 kJWORK, HEAT AND POWERLAWS OF THERMODYNAMICSFIRST LAW OF THERMODYNAMICS

Total Energy Entering a System = Total Energy Leaving a System

FIRST LAW OF THERMODYNAMICSB. SECOND LAW OF THERMODYNAMICSKelvin Planck statement applied to the heat engine:

It is impossible to construct a heat engine which operates in a cycle and receives a given amount of heat from a high temperature body and does an equal amount of work.SECOND LAW OF THERMODYNAMICSClausius statement applied to the heat pump:

It is impossible to construct a heat pump that operates without an input work.

The most efficient operating cycle is the Carnot Cycle.C.THIRD LAW OF THERMODYNAMICSThe entropy of a substance of absolute zero temperature is zero.D. ZEROTHs LAWIf two bodies has the same temperature as a third body they have the same temperature with each other.IDEAL GASESBASIC PROPERTIES OF AN IDEAL GAS:PROPERTIES OF AIR:PROCESS INVOLVING IDEAL GASESPROCESS INVOLVING IDEAL GASESPROCESS INVOLVING IDEAL GASESCONSTANT PRESSURE (Charles Law)CONSTANT VOLUME (Charles Law)CONSTANT TEMPERATURE (Boyles Law)CONSTANT ENTROPYPOLYTROPIC PROCESSPARTICULAR VALUES OF n:Particular Values:Process:n = 0Constant Pressure or isobaricn = 1Constant Temperature or isothermaln = kConstant entropy or isentropic (adiabatic)n > 1Polytropic processn = Constant volume or isochoric or isometricMIXTURES INVOLVING IDEAL GASESConsider a mixture of three gases, a, b, and c, at a pressure P and a temperature T, and having a volume V.A. MASS OR GRAVIMETRIC ANALYSIS:B. VOLUMETRIC OR MOLAL ANALYSIS:C. DALTONs LAW OF PARTIAL PRESSURED. SPECIFIC HEAT OF THE MIXTURE:PURE SUBSTANCE is a working substance that has a homogenous and invariable chemical composition even though there is a change of phase.PHASES OF A PURE SUBSTANCESolid the state of matter that does not depend on the shape of its container.

Subcooled liquid liquid whose temperature is lower than the saturation temperature at the given pressure.

Saturated liquid liquid water at its boiling temperature and at standard temperature.PHASES OF A PURE SUBSTANCE4. Liquid-vapor Mixture substance made up of liquid and vapor portion or a two-phase liquid-vapor system.

5. Saturated Vapor vapor or steam at standard atmospheric pressure and at its boiling temperature.

6. Superheated Vapor vapor whose temperature is higher than the saturation temperature at the given pressure. A superheated vapor absorbs more heat than is needed to vaporize.PHASES OF A PURE SUBSTANCESaturation Temperature - the temperature at which vaporization takes place at a given pressure, this pressure being called the saturation pressure for the given temperature.

Degrees Superheat difference between actual temperature and saturation temperature.

Compressed Liquid liquid whose pressure is higher than the saturation pressure at the given temperature.If the temperature is held constant and the pressure is increased beyond the saturation pressure.PHASES OF A PURE SUBSTANCEDegrees Subcooling difference between saturation temperature and actual temperature.

Critical Point is the condition of pressure and temperature at which a liquid and its vapor are indistinguishable. At the critical point the latent heat vaporization is zero.

Triple Point is the point in which the temperature and pressure at which three phases (gas, liquid and solid) of a substance may coexist in thermodynamic equilibrium.SATURATED LIQUID AND SATURATED VAPORExamples of saturation temperature at various pressures for three common pure substances:SATURATION TEMPERATUREPressureWaterAmmoniaFreon-1250 kpa81.33C-46.73C-45.19C101.325 kpa100C-33.52C-29.79C500kpa151.86C4.08C15.59CPROPERTIES OF SATURATED LIQUID AND SATURATED VAPORat various temperatures and pressures are found in tables (Table 1 and Table 2 for steam) with the following typical construction:MIXTUREPROPERTIES OF MIXTURETHE T-S DIAGRAM OF A PURE SUBSTANCEThe Mollier diagram (h-s) of steam is usually useful in determining the final enthalpy of steam after an isentropic process.

PROCESS INVOLVING PURE SUBSTANCES:BASIC FORMULAS:THE CARNOT CYCLESchematic Diagram of a heat engine:

THE T-S DIAGRAM:

PROCESS 1 2: ADIABATIC REVERSIBLE EXPANSION.This piston and cylinder are completely insulated so that no heat is gained or lost during this process. The piston continues to expand with increasing volume while doing work on the surrounding.PROCESS 2 3: ISOTHERMAL COMPRESSION.The piston compresses the substance with decreasing volume and heat is transferred at constant temperature to the low temperature reservoir.PROCESS 3 4: ADIABATIC REVERSIBLE COMPRESSION.This piston and cylinder are completely insulated in no heat is gained or lost during the process. The piston compresses the working substance and causing the temperature to rise.PROCESS 4 1: ISOTHERMAL EXPANSIONDuring this process, the piston expands with increasing volume and heat is transferred reversibly at constant temperature from the high-temperature reservoir.BASIC FORMULAS:BASIC WORKING CYCLES FOR VARIOUS APPLICATIONS:APPLICATIONBASIC WORKING CYCLESteam Power PlantRankine CycleGasoline Engine(Spark-Ignition)Otto CycleDiesel Engine(Combustion-Ignition)Diesel CycleGas TurbineBrayton CycleRefrigeration SystemRefrigeration CycleExample No. 1A Carnot engine receives 130 Btu of heat from a hot reservoir at 700F and rejects 49 Btu of heat. Calculate the temperature of the cold reservoir.-21.9 FC. -20.8 F-24.2 FD. -22.7 F

Example No. 2The maximum thermal efficiency possible for a power cycle operating between 1200 F and 225 F is:58%C. 57.54%58.73%D. 57.40%Example No. 3An ideal gas at 45 psig and 80F is heated in a closed container to 130 F. What is the final pressure?54 psiaC. 75 psia65 psiaD. 43 psia

Example No. 4A Carnot engine requires 35kJ/sec from the hot source. The engine produces 15 kw of power and the temperature of the sink is 26 C. What is the temperature of the hot source in C?245.57C. 250.18210.10D. 260.68Example No. 5An air bubble rises from the bottom of a well where the temperature is 25C, to the surface where the temperature is 27C. Find the percent increase in the volume of the bubble if the depth of the well is 5 m. Atmospheric pressure is 101,528 Pascals.49.3C. 56.741.3D. 38.6Example No. 6Steam enters a throttling calorimeter at a pressure of 1.03 MPa. The calorimeter downstream pressure and temperature are respectively 0.100 Mpa and 125C. What is the percentage moisture of the supply system?

Properties of steam:P, MPahfhfghg1.032010.72779.25Note: at 0.100 MPa and 125C, h = 2726.6 kJ/kg

2.62C. 3.155.21D. 1.98Example No. 9The enthalpy of air is increased by 139.586 kJ/kg in a compressor. The rate of air flow is 16.42 kg/min. The power input is 48.2 kw. Which of the following values most nearly equals the heat loss from the compressor in kw?-10.0C. +10.0-9.95D. +9.95