CHAPTER 1 Introduction To Thermodynamics ERT 206/4 Thermodynamics Miss. Rahimah Bt. Othman Email:...

CHAPTER 1Introduction To

Thermodynamics

ERT 206/4ERT 206/4ThermodynamicsThermodynamics

Miss. Rahimah Bt. Othman

Email: rahimah@unimap.edu.my

COURSE OUTCOME 1 CO1)

1.Chapter 1: Introduction to Thermodynamics

Identify and analyze scope, dimensions and units, measure of amount or size, force, temperature, pressure, work, energy and heat.

2. Chapter 2: The First Law and Other Basic Concepts

3. Chapter 3: Volumetric properties of pure fluids

4. Chapter 4: Heat effects

5. Chapter 5: Second law of thermodynamics

6. Chapter 6: Thermodynamics properties of fluids

* Thermodynamics Definition.(from the Greek θέρμη therme, meaning "heat“ and δύναμις, dynamis, meaning "power")

- is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure.

THERMODYNAMICS: Definition

THERMO =

DYNAMICS =

HEAT AND TEMPERATURE

MOTION

* Initially, thermodynamics is the study of the flow of heat to produce mechanical energy that could be used for locomotive; - after that is used for steam engines, turbines, pumps, air conditioners etc.

* Because such equipment also used in chemical/ bioprocess plant, it is also important for those engineers to learn the fundamental of such equipment.

THERMODYNAMICS: Definition

- The production of chemicals, polymers, pharmaceuticals and other biological materials, and oil and gas processing, all involve chemical or biochemical reaction that produce a mixture of reaction product.

(e.g:Production of acetic acid from ethanol using Acetobacter aceti bacteria)

1.These must be separated from the mixture and purified to result in product of societal, commercial, or medicinal value.

•These is the area where thermodynamics plays a central role in bioprocess eng.

•Separation processes, e.g. distillation are designed based on information from thermodynamics

OHHCOCHOOHHC 223252

THERMODYNAMICS: Example

- Dimension is recognize through our sensory perceptions and not definable without the definition of arbitrary scales of measure, divided into specific units of size.

- The units have been set by international agreement, and are codified as the International System of Units (SI).

• Note: See Table 1.1 for Prefixes (eg: deca, hecto, kilo, etc.) of SI units. (eg: 1 cm = 10-2 m, 1 kg = 103 g)

• Three measures of amount or size are in common use: Mass, m ; Number of moles, n ; Total volume, Vt

• Mass, m divided by the molar mass M (molecular weight) to yield number of moles;

Total volume, divided by the mass or number of moles of the system to yield specific or molar volume.

M

mn Mnmor

mVV t

nVV t

m

VV

t

n

VV

t

• Specific volume:

• Molar volume: or

or

SI unitSI unit Metric engineering Metric engineering system unitssystem units

Newton (N) Kilogram force (kgf)

F = ma mag

Fc

1

21c

2

c

s f kg m kg .80665 9 g

ms 9.80665 x kg 1 x g

1 kgf 1

* Note : The kilogram force is equivalent to 9.80665 N

An astronaut weighs 730 N in Houston, Texas, where the local acceleration of gravity is g = 9.792 ms-2. What are the astronaut’s mass and weight on the moon, where g = 1.67 ms-2.

212

55.74792.9

730sNm

ms

N

g

Fm

Solution

With a = g, Newton’s law is : F = mg. Hence;

Because the newton N has the unit kg m s-2,

kgm 55.74

This mass of the astronaut is independent f location, but weight depends on the local acceleration of gravity. Thus on the moon the astronaut’s weight is;

N 124.5 kgms 124.5 )F(or

ms 1.667 x kg 74.55)()( 2-

2

moon

moonmgmoonF

• Temperature is commonly measured with liquid-in-glass thermometers, wherein the liquid expands when heated.

• The pressure P exerted by a fluid on a surface is defined as the normal force exerted by the fluid per unit area of the surface.

SI unitSI unit Metric engineering system unitsMetric engineering system units

Pascal (Pa) Kilogram force per square centimeter (kgf cm-2)

• The primary standard for pressure measurement is the dead-weight gauge in which a known force is balanced by a fluid pressure acting on a known area.

ghA

gAh

A

mg

A

FP

A

mg

A

FP

A dead-weight gauge with a 1 cm diameter piston is used to measure pressures very accurately. In a particular instance a mass of 6.14 kg (including piston and pan) brings it into balance. If the local acceleration of gravity is 8.82 ms-2, what is the gauge pressure being measured? If the barometric pressure is 748 Torr, what is the absolute pressure?

Solution

The force exerted by gravity on the piston, pan and weights is

22

Ncm77.76)1)()(4/1(

295.60 pressure Gauge

N 295.60)82.9)(14.6(

A

F

mgF

The absolute pressure is therefore;

kPa 4.867 or

Ncm 74.86)013332.0)(748(77.76 2

P

P

At 27oC (300.15 K) the reading on a manometer filled with mercury is 60.5 cm. The local acceleration of gravity is 9.784 ms-2. To what pressure does this height of mercury correspond?

Solution

Recall the equation in the preceding text, P = hρg. At 27 oC (300.15 K) the density of mercury is 13.53 g cm-3. Then,

bar 0.8009 kPa 80.09 Ncm 8.009 cmkgms 8.009or

cmgms 8,009ms 9.784 x gcm 13.53 x cm 60.5 222

2223

P

P

• Work, W is performed whenever a force acts through a distance.

t

t

V

V

t

t

t

PdVW

PdVdW

A

VPAddW

FdldW

2

1

* Note: The minus sign ‘-’ the volume change is positive, and the minus sign is required to make the work negative.

THANK YOU

TUTORIAL 1 - QUESTIONS

Problems : 1.3, 1.4, 1.11, 1.14, 1.22

Reference Book:

Smith, J.M., Van Ness, H.C. and Abbort, M.M., Introduction to Chemical Engineering Thermodynamics, Seventh Edition, McGraw-Hill, 2005.