EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesPROPERTIES OF PURE SUBSTANCES

Pure Substance Phase of a Pure Substance Phase-Change Processes of Pure Substances Property Diagrams for Phase-Change Processes Property Tables

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.1 Pure Substance

A substance that has a fixed chemical compositione.g. water, nitrogen, helium and carbon dioxide

A mixture of two or more phases of a pure substance is still a pure substance as long as the chemical composition of all phase is the same.

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.2 Phase of A Pure Substance

There are 3 principal phases- solid, liquid and gas

The molecules in a solid are arranged in a 3 dimensional pattern (lattice) that is repeated throughout, because of the small distances between molecules in a solid, the attractive forces of molecules on each other are large and keep the molecules at fixed positions.

The molecular spacing in the liquid phase is not much different from solid, except the molecules are no longer at fixed positions relative to each other and they can rotate and translate freely.

In the gas phase, the molecules are far apart from each other and a molecular order is nonexistent. Gas molecules move about at random, continually colliding with each other.

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.3 Phase-Change Processes of A Pure SubstanceThere are many practical situation where 2 phases of a pure substance coexist in equilibrium. Water exists as a mixture of liquid and vapor in the boiler and the condenser of steam power plant. The refrigerant turns from liquid to vapor in the freezer of a refrigerator.

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesCompressed Liquid and Saturated LiquidConsider a piston-cylinder device containing liquid water at 20oC and 1 atm pressure. Under these condition, water exist in liquid phase (compressed liquid / sub cooled liquid) meaning that is not about to vaporize. As the temperature rises, the liquid water expands slightly and specific volume increases. To accommodate this expansion, the piston move slightly. The pressure in the cylinder remains constant. Water is still a compressed liquid at this state since it has not started to vaporized

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesAs more heat is transfer, the temperature keep rising until it reaches 100oC. At these point water is still liquid but any heat addition will cause some of the liquid to vaporize. A phase change process from liquid to vapor is about to take place and called a saturated liquid

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesOnce boiling starts, the temperature stop rising until the liquid is completely vaporized. The only change we will observe is a large increase in the volume and a steady decline in the liquid level as a results of more liquid turning to vapor. Midways about the vaporization line, the cylinder contains equal amounts of liquid and vapor.Saturated Vapor and Superheated Vapor

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesAs we continue transferring heat, the vaporization process continues until the last drop of liquid is vaporized. At this point, the entire cylinder is filled with vapor that is on the borderline of liquid phase. Any heat loss from these vapor will cause some of the vapor condense (phase change from vapor to liquid). A vapor that is to condense is called saturated vapor.

A substance at between state 2 and 4 is referred to as a saturated liquid-vapor mixture

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesOnce the phase change is completed, the further transfer oh heat results in an increase in both the temperature and the specific volume. At state 5, the temperature of the vapor e.g. 300oC, if we transfer some heat from the vapor, the temperature may drop, but no condensation will take place as long the temperature remains above 100oC. A vapor is no about to condense (not a saturated vapor) is called superheated vapor

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesSaturation Temperature and Saturation Pressure

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.4 Property Diagrams for Phase-Change ProcessesThe T-v Diagram

Liquid starts boiling at much higher temperature at higher pressure The specific volume of the saturated liquid is larger and the specific volume of saturated vapor is smaller than the corresponding values at 1 atm As the pressure increased, the saturation line continues shrink and it become a point (critical point) it is define as the point at which the saturated liquid and saturated vapor states are identical

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances At pressure above the critical pressure, there is not a distinct phase-change process. The specific volume of the substance continually increases and at all time there is only one phase present The saturated liquid states can be connected by a line called saturated liquid line and saturated vapor states can be connected by another line call saturated vapor line

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances All the compressed liquid states are located in the region to the left of the saturated liquid line (compressed liquid region) All the superheated vapor states are located to the right of saturated vapor line (superheated vapor region) All the states that involve both phase in equilibrium are located under dome (wet region)

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesThe P-v Diagram

The general shape of the diagram for pure substances is very much like T-v but T = constant lines

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesThe P-T Diagram

This diagram is often called the phase diagram since all 3 phases are separated from each other by 3 lines. The sublimation line separates the solid and vapor regions, the vaporization line separates the liquid and vapor region and the melting line separates solid and liquid regions.

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesThe P-v-T Surface

All the point on the surface represent equilibrium states. All states along the path of a quasi-equilibrium process lie on the P-v-T surface since such a process must pass through equilibrium states. Chapter 2: End of first part

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.5 Property TablesEnthalpy A Combination Property

h = u +Pv(kJ/kg)Where:h enthalpyu specific internal energyv specific volumeTenaga disimpan yang jumlahnya sama dengan jumlah tenaga yang dipindahkan

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances1a. Saturated Liquid and Saturated Vapor Statesvf specific volume of saturated liquidvg specific volume of saturated vaporvfg difference between vg and vf

hfg enthalpy of vaporization

(the amount of energy needed to vaporize a unit mass of saturated liquid at a given temperature or pressure)

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-1

A rigid tank contains 50 kg of saturated liquid at 90oC. Determine the pressure in the tank (kPa) and the volume of the tank (m3).

P = P sat @ 90 deg C = ?

v = v f @ 90 deg C = ?

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-2

A piston-cylinder device contains 0.06m3 of saturated water vapor at 350 kPa pressure, Determine the temperature (oC) and the mass of the vapor inside the cylinder (kg).

T= T sat @ 350 kPa = ?

v = v g @ 350 kPa = ?

m = ?

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-3

A mass of 200 g of saturated liquid water is completely vaporized at a constant pressure of 100 kPa. Determine (a) the volume change (m3) and (b) the amount of energy transferred to the water (kJ)

vfg = ?

V = ?

mhfg = ?

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances1b. Saturated Liquid Vapor MixtureQuality, x as the ratio of the mass of vapor to the total mass of mixture

where

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesConsidering a tank contains a saturated liquid-vapor mixtureDividing by mt yeildsSince x = mg/mtWe obtain

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesChapter 2: End of second partThe analysis can be repeated for internal energy and enthalpy with the following results:

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-4 Pressure and volume of a saturated mixture

A rigid tank contain 10 kg of water at 90oC. If 8 kg of the water is in the liquid form and the rest in the vapor form, determine (a) the pressure in the tank and (b) the volume of the tank

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2. Superheated Vapor

In the region to the right of the saturated vapor line and at temperatures above the critical point temperature, a substance exists a superheated vapor

Superheated vapor is characterized by

Lower pressure (P < Psat at given T)Higher Temperature (T > Tsat at given P)Higher specific volume (v > vg at given P or T)Higher internal energy (u > ug at given P or T)Higher enthalpies (h > hg at given P or T)

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-7 Temperature of superheated vapor

Determine the temperature of water at a state of P = 0.5 MPa and h = 2890 kJ/kg

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances3. Compressed Liquid

In general, a compressed liquid is characterized by

Higher pressure (P > Psat at given T)Lower Temperature (T

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-8 Approximating Compressed Liquid as Saturated Liquid

Determine the internal energy of compressed liquid water at 80oC and 5 MPa, using a) data from the compressed table and b) saturated liquid data. What is the error involved in second case?

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-9 The use of steam table to determine properties

Determine the missing properties and the phase description in the following table for water

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances2.6 The Ideal Gas Equation of state

Any eq. that relates the pressure, temperature and specific volume of a substances is called an equation of state. Where the gas constant is R

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure SubstancesEXAMPLE 3-10 Mass of Air in a Room

Determine the mass of the air in a room whose dimensions are 4m x 5m x 6m at 100 kPa and 25oC

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances

EPT 201 THERMODYNAMICS Chapter 2: Properties of Pure Substances