CHE 3473Chemical Engineering Thermodynamics

Room A-235, SECM, W, F, 9:30-10:20 AM

Lecture 2Force, Temperature, Pressure

Thermodynamics is important and maybe interesting (agreed?!)

From the previous lecture

Exam data & time- M1, Oct. 2 (Fr)- M2, Oct. 28 (We) - M3, Nov. 23 (Mo)- Final, Dec. 15 (Tu), 8:00 10:00 am, A-235

7:00 9:00 pm, A-235?

Q: Quiz schedule? A: No, pop quiz for tophat, written quiz in class

Q: tophat and textbook, mandatory?A: Yes to both

Q: Eqn. sheet for exam & quiz?A: I will provide if needed. You do not compose it.

Q & A

Join code: 827583 (well have the first quiz from tophat next Monday)

Tophat.com

a. Take attendance b. Others

Energy: energy measures the ability to do work, and can take various forms: mechanical (including KE, PE); chemical; nuclear; electromagnetic (e.g.light); elastic and thermal.

Energy Conservation: First Law of Thermodynamics.

Equilibrium: System has no tendency to change

Equilibrium direction: Second Law of Thermodynamics.

Steady State: Fluxes are finite, but dont change with time.

Concepts

Equilibrium vs. Steady State

Please watch this video: http://tll.mit.edu/help/equilibrium-vs-steady-state

Concepts

Length (m) Area (m2)

Volume (m3) Mass (kg)

Force (N) Time (s)

Velocity (m/s) Acceleration (m/s2)

Pressure (Pa) Temperature (K)

Energy (J) Power (W)

What do we measure?

Force

In physics, a force is that which can cause an object with mass to accelerate. Force has both magnitude and direction, making it a vector quantity.

Newtons second law: F=ma

http://en.wikipedia.org/wiki/Force#Units_of_measurement

[F] = kg m s2 = N = Newton

Units of Force SI [F] = [ma] = kg.m.s-2=N=Newton, the force needed to accelerate 1 kg by 1 ms-2

English: 1 lbf = the pound force = the force needed to

accelarate 1 lbm by 32.174 ft/s2

Newtons Law becomes: F = 1

gcma

" = 32.174 . . 2 " = 1 . . 2

Force and Weight

English Units: 1lbf = (1/gc)x1lbmx32.174 fts-2

i.e. gc = 32.174 9 (lbm)(lbf)-1(ft)(s)-2

1 lbf is equivalent to 4.4482216 N

Weight = force of gravity on a body (in N or lbf)

Force

An example:An astronaut weighs 730 N in Oklahoma, where g = 9.792m s2

What is:(a)The mass of the astronaut;(b)His weight at the moon where

g = 1.67m s2

Force

Solution:

(a) We have F=ma=mg

m = Fg =730kgms29.792ms2 = 74.55kg

(b)

Fmoon = mgmoon = 74.55 1.67kgms2 = 124.5N

Temperature

[Simply stated] Temperature is the degree of hotness or coldness of a substance, as measured on a thermometer.

T is a measure of a molecules average kinetic energy:

k = Boltzmanns constant=R/NA=1.38066x10-23 JK-1; T = absolute temperature (K)

Exercise: What is the average velocity of O2 molecules in a gas at 300 K?

21 32 2m v kT=

Temperature

Average velocity of O2 molecules at 300 K:

v2 = 3kT / m = (3)(1.3807 1023)(300)(6.0231023) / 0.032 m2 / s2

= 233,886.1 m2 /s2

v = 483.6 m/s

Temperature

Note: As we raise T molecules move faster, and if we lower T they move slower. At the absolute zero, T=0 K,molecules stop moving.

1081 mi/hr Why I don't feel O2 moving around?

Temperature Conversions

FahrenheitoF = (9/5 oC) + 32

Celsius or CentigradeoC = 5/9 (oF - 32)

RankineR = oF + 459.67

KelvinK = oC + 273.15

Temperature: Fixed Points

Phase changes for common substances occur at certain fixed temperatures and we use these fixed points to establish a temperature scale.

At standard atmospheric pressure water boils at 100oC (=212oF=373.15 K)

At standard atmospheric pressure water freezes at 0oC (32oF)

Absolute Zero

If we cool to a sufficiently low temperature the molecules cease moving and we call this the absolute zero of temperature,

T=0 K

t = -273.15 C = -459.67 F

Temperature Measuring Devices

Expansion Thermometers Liquid in glass (Hg, EtOH) Bimetallic Filled system / distant reading

Pyrometers Thermocouple Resistance Radiation and optical pyrometers

http://simple.wikipedia.org/wiki/Thermometer

Pressure

Normal force exerted on a unit area Measured in Pa (other units: bar, atm, mm Hg) Atmospheric pressure at sea level is 101325 Pa,1 atm, 760.0 mm Hg

Exercise:Which exerts more pressure, a 2000 pound elephant with a 0.5 ft radius foot, or a 150 pound woman rocking on her heels with a 0.5 in. radius?

222

2

22

5.9479.02

1502

2heels,79.0rS inch 0.5rpound 150W

:an womanFor

4.41.1134

20004

4, 1.113S inch 60.5footr pound; 2000W

:elephantan For

inchpound

SWP

inch

inchpound

SWP

legsinchr

=

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Pressure

Gage and Vacuum vs. Absolute Pressure- Absolute Pressure = Atmospheric Pressure + Gauge Pressure

- Vacuum = Atmospheric Pressure - Absolute Pressure

(No absolute pressure gages)1 bar = 14.5038 psi

Manometer

Pressure Measuring Devices

http://www.efunda.com/formulae/fluids/manometer.cfm http://www.tpub.com/content/fc/14104/css/14104_234.htm

Bellow Gauge

Pressure CalculationExample 1: A mercury manometer at 27 oC reads 60.5 cm. The local gravitation acceleration is g = 9.784ms2What pressure does this correspond to ?

for HgAt 27 oC, = 13.53g cm3P = hg= 60.5cm 13.53gcm3 9.784ms2

= 0.605m 13.531000 (100)3kgm3 9.784ms2

= 0.605 13.531000 9.784kgm1s2= 80090Pa = 80.090KPa = 0.8009bar

http://www.onlineconversion.com/http://www.unitconversion.org/

1.Online Unit Conversion (over 5,000 units, and 50,000 conversions)

2. Free SoftwaresFor Windows:A free Engineering unit conversion software called Uconeer, Version 2.4 could be downloaded fromhttp://www.katmarsoftware.com/Uconeer.htm

For Mac:Search in the Dashboard for the free widget namedUnit Converter, easy to install, and easy to use.

Units