chapter 1-basic concept of fluid mechanics

8/9/2019 CHAPTER 1-Basic Concept of Fluid Mechanics

http://slidepdf.com/reader/full/chapter-1-basic-concept-of-fluid-mechanics 1/30

BASIC CONCEPTS

OFFLUID

MECHANICS

chapter1

1

http://www.google.com/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=VVAMlbvi7iYNAM&tbnid=8s1SmU3vBGXo3M:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.fluids.eng.vt.edu%2Fmsc%2Fgallery%2Fgall.htm&ei=hSvJUb7xOIbkrAeM-oG4AQ&bvm=bv.48293060,d.bmk&psig=AFQjCNEs19tB1lcTMmO-SLryyLLYS2lnHA&ust=1372224689181047

http://www.google.com/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=VVAMlbvi7iYNAM&tbnid=8s1SmU3vBGXo3M:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.fluids.eng.vt.edu%2Fmsc%2Fgallery%2Fgall.htm&ei=hSvJUb7xOIbkrAeM-oG4AQ&bvm=bv.48293060,d.bmk&psig=AFQjCNEs19tB1lcTMmO-SLryyLLYS2lnHA&ust=1372224689181047



OBJECTIVES

After completing this chapter, student shouldbe able to;

• Compare between a gas, liquid and solid

• Describe pressure and temperature scales• Apply physical properties of uids

2



INTRODUCTION TO FLUIDMECHANICS Flui Mecha!ic" is a section of applied mechanics, concerned with

the "tatic a! #!a$ic %& li'ui a! (a"e".

Knowledge of uid mechanics is essential for the chemical engineerbecause the majority of che$ical pr%ce""i!( operations areconducted either partiall# %r t%tall# i! )ui pha"e.

he handling of liquids is much simpler, cheaper and less troublesome

than handling solids. !"en in many operations a solid is handled in a#nely di"ided state so that it stays in suspension in a uid.

3



FLUID AND THEIR PROPERTIES

Di-ere!ce" Bet+ee! S%li" A! Flui"

• he $%lecule" %& a "%li are usually cl%"ert%(ether than those of a uid. he attracti.e

&%rce" between the molecules of a solid are "%lar(e that a "%li te!" t% retai! it" "hape.

• his is not the case for a )ui, where theattracti"e forces between the molecules are"$aller.

5




Li'ui" a! /a"e"

•A (a" is comparati"ely ea"# t% c%$pre"" %rc%$pre""i*le. Changes of .%lu$e +ithpre""ure are lar(e, cannot normally neglect

and are related to cha!(e" %& te$perature.

•A gi"en mass of a gas has !% 2e .%lu$ea! +ill e2pa! c%!ti!u%u"l# unlessre"trai!e by a containing "essel. $t will

c%$pletel# ll a!# .e""el in which it is placedand therefore does !%t &%r$ a &ree "ur&ace

7




S%li3 Li'ui" a! /a"e"

8

http://www.google.com/url?sa=i&rct=j&q=solid%2Bliquid%2Band%2Bgas&source=images&cd=&cad=rja&docid=uKglKTUqGFKx-M&tbnid=Tsn-6k4L1CIrCM:&ved=0CAUQjRw&url=http%3A%2F%2Fy5atschool.edublogs.org%2Ftag%2Fsolids%2Ffeed%2F&ei=4v3HUd2oDIjTrQeAg4HoDQ&bvm=bv.48293060,d.bmk&psig=AFQjCNEQhcI24JfmhSXdmEY2n67yDuYOLA&ust=1372147407711163



PRESSURE

At$%"pheric Pre""ure3 pat$

• he earth is surrounded by an atmosphere many mileshigh. he pressure due to this atmosphere at the surfaceof the earth epe!" up%! the hea %& the air a*%.ethe "ur&ace.

• he air is compressible; therefore the e!"it# i"i-ere!t at i-ere!t hei(ht. Due to the weight ofatmosphere or air abo"e the surface of earth, it is di+cultto calculate the atmospheric pressure. o, atmosphericpressure is measured by the height of column of liquidthat it can support.

• At$%"pheric pre""ure at "ea le.el is about 1617859:N;$5, which is equi"alent to a head of 16789 $ %&+ater or <=6 $$ %& $ercur# appro(imately, and itdecreases with altitude.

10



PRESSURE

11

At$%"pheric Pre""ure3 pat$

http://www.google.com.my/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=i2oAQ_E5rVrWSM&tbnid=iWB105k5EQx1hM:&ved=0CAUQjRw&url=http%3A%2F%2Fautorepair.about.com%2Flibrary%2Fweekly%2Faa061904f.htm&ei=srLHUffnGcvQrQeHxYDoDQ&bvm=bv.48293060,d.bmk&psig=AFQjCNE1H-PTfqI_1Uw7VdTMX17YG-5jeg&ust=1372126574601106

http://www.google.com.my/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=gcSoZyXcqVCkLM&tbnid=yMB330AXteJL6M:&ved=0CAUQjRw&url=http%3A%2F%2Fhendrix2.uoregon.edu%2F~imamura%2F102%2Fsection2%2Fchapter13.html&ei=wK7HUdTYIsmsrAeMkoGoAg&bvm=bv.48293060,d.bmk&psig=AFQjCNE1H-PTfqI_1Uw7VdTMX17YG-5jeg&ust=1372126574601106



PRESSURE

12

/au(e Pre""ure3 p/

• $t is the pressure, $ea"ure +ith the help%& a pre""ure $ea"uri!( i!"tru$e!t, inwhich the at$%"pheric pre""ure i" ta:e!

a" atu$; in other words the atmosphericpressure at the gauge scale is mar-ed &ero.

• he gauge pressure can be either p%"iti.e %r!e(ati.e depending on whether the pressureis a*%.e at$%"pheric pre""ure >ap%"iti.e .alue? %r *el%+ at$%"phericpre""ure >a !e(ati.e .alue?.

http://www.google.com.my/url?sa=i&rct=j&q=boiler%2Bpressure%2Bgauge&source=images&cd=&cad=rja&docid=uxHixhiw4qCixM&tbnid=10que3nhoXSgpM:&ved=0CAUQjRw&url=http%3A%2F%2Fshop.ajreeves.com%2Fpressure-gauge---boiler-test-4-6677-p.asp&ei=xLbHUaaXFMbQrQeOwoGQAw&bvm=bv.48293060,d.bmk&psig=AFQjCNGH-AXLIIsR560hUrnT9XXAIf450g&ust=1372129292237241





PRESSURE

13

A*"%lute Pre""ure3 pA

•$t is the pressure equal to the algebraic "u$ %&the at$%"pheric a! (au(e pre""ure".

Example 1

What is the pressure gauge of air in the cylinder if the atmosphericgauge is 101.3 kN/m2 and absolute pressure is 460 kN/m2 .

[Ans: 358.7 kN/m2 ]



PRESSURE

14

Example 1

What is the pressure gauge of air in the cylinder if the atmospheric gauge is

101.3 kN/m2 and absolute pressure is 460 kN/m2.

Solution



TEMPERATURE

15

• Te$perature is a physical quantity that is a$ea"ure %& h%t!e"" a! c%l!e"" on anumerical scale.

• y international agreement the "ta!ar

2e p%i!t is the easily reproducible triplep%i!t %& +ater. hese are represented bythe "tate %& e'uili*riu$ *et+ee! "tea$3ice a! li'ui +ater.



TEMPERATURE

16

http://www.google.com/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=iRZ_59xqbSJGuM&tbnid=zZ5ofkFF7HQJ0M:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.eoearth.org%2Farticle%2FTemperature&ei=0N3HUYHZGsPRrQe70YCABQ&bvm=bv.48293060,d.bmk&psig=AFQjCNE0aOSn9wGLif52Uh7e_x0N9-8CMA&ust=1372138950043530

http://www.google.com/url?sa=i&rct=j&q=&source=images&cd=&cad=rja&docid=cAHLwGBCAxTZlM&tbnid=TdQZRDY074SMIM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.merequipment.com%2Fblog%2Fservice-training%2F&ei=YNzHUZH3JMP4rQeOioC4Bg&bvm=bv.48293060,d.bmk&psig=AFQjCNE0aOSn9wGLif52Uh7e_x0N9-8CMA&ust=1372138950043530



TEMPERATURE

17

E2a$ple 175Con"ert the temperaturebelow*

i. /001! to " .

ii. /20 1! to 1#

iii. 342 1# to $

i". 520 $ to "

". 560 " to 1#



TEMPERATURE

18

E2a$ple 175

Con"ert the temperaturebelow*

i. /001! to " .

ii. /20 1! to 1#

iii. 342 1# to $

i". 520 $ to " ". 560 " to 1#



PH@SICAL PROPERTIES OFFLUIDS

19




20



21


γ w 7 5o

C 8 9.:6-<m3

=w 7 5o

C 8 6000-g<m3



22




Vi"c%"it#

•A uid at rest cannot resist shearing forces butonce it is in motion, "heari!( &%rce" are set upbetween layers of uid mo"ing at di>erent"elocities.

• he "iscosity of the uid determines the a*ilit# %&the )ui i! re"i"ti!( these "heari!( "tre""e".

23




Sur&ace te!"i%!

•urface tension is a pr%pert# that re"ult" from theattracti.e &%rce" $%lecule".

•urface tension acts somewhat li-e a l$ at thei!ter&ace *et+ee! the li'ui +ater "ur&ace a!

the air a*%.e it. he water molecules beneath thesurface are attracted to each other and to those atthe surface.

•?uantitati"ely, surface tension is measured as the+%r: per u!it area re'uire t% $%.e l%+er$%lecule" t% the "ur&ace %& the li'ui7 heresulting units are force per unit length, such as <m.

24




Sur&ace te!"i%!

25




E2a$ple 178

i.Determine mass density, % of uid @in &g'm if mass is 520 g and the "olume is 9 cm.

ii.Determine speci#c weight, γ of uid @in &N'm if the weight of uid is 6 0N and the "olume is 200 cm2.

iii.Determine speci#c gra"ity of uid in ii.

i".Determine speci#c "olume, of uid in i.

26




E2a$ple 178

27




E2a$ple 178

28




E2a$ple 178

29




E2a$ple 178

30


chapter 1-basic concept of fluid mechanics

Documents