Tutorial 2 - Week2 PDF

Preview

Summary

Week2...

Description

MEC2405(/(CHE2164( Tutorial(2( ! Book:!Çengel!&!Boles,!Thermodynamics:!An!Engineering!Approach,!8th!Edition! ! ! You!will!need!the!textbook!property!tables!to!be!able!to!answer!the! questions! ! Chapters(covered(this(week:(3,4! ! Problem(2-67(

! Water!is!pumped!from!a!lower!reservoir!to!a!higher!reservoir!by!a!pump!that! provides!20!kW!of!shaft!power.!The!free!surface!of!the!upper!reservoir!is!45!m! higher!than!that!of!the!lower!reservoir.!If!the!flow!rate!of!water!is!measured!to! be!0.03!m3/s,!determine!the!mechanical!power!that!is!converted!to!thermal! energy!during!this!process!due!to!frictional!effects.! ! Problem(2-69(

( An!oil!pump!is!drawing!44!kW!of!electric!power!while!pumping!oil!with! 𝜌 = 860 𝑘𝑔/𝑚! !at!a!rate!of!0.1!m3/s.!The!inlet!and!outlet!diameters!of!the!pipe! are!8!cm!and!12!cm,!respectively.!If!the!pressure!rise!of!the!oil!in!the!pump!is! measured!to!be!500!kPa!and!the!motor!efficiency!is!90%,!determine!the! mechanical!efficiency!of!the!pump.! ! ! ! !

Problem(2-77( ( When!a!hydrocarbon!fuel!is!burned,!almost!all!of!the!carbon!in!the!fuel!burns! completely!to!form!CO2!(carbon!dioxide),!which!is!the!principal!gas!causing!the! greenhouse!effect!and!thus!global!climate!change.!On!average,!0.59!kg!of!CO2!is! produced!for!each!kWh!of!electricity!generated!from!a!power!plant!that!burns! natural!gas.!A!typical!new!household!refrigerator!uses!about!700!kWh!of! electricity!per!year.!Determine!:! ! (a) the!amount!of!CO2!production!that!is!due!to!the!refrigerators!in!a!city!with! 300,000!households!where!the!electricity!is!generated!by!natural!gas,! (b) the!amount!of!CO2!production!due!to!the!refrigerators!in!the!same!city!if! the!electricity!was!generated!from!brown!coal,!which!produces!0.96!kg!of! CO2!per!kWh! (c) the!amount!of!CO2!production!due!to!the!refrigerators!in!the!same!city!if! the!electricity!was!generated!from!nuclear!power,!which!produces!0.10!kg! of!CO2!per!kWh.!(Note!that!even!though!the!power!generation!cycle!does! not!involve!emissions!from!combustion,!the!mining!of!the!uranium,!the! life!cycle!and!the!operation!of!the!plant!do).! (d) A!nuclear!power!cycle!generates!750!kg/year!of!high!level!radioactive! waste!for!every!1000!MW!generated,!once!the!reusable!components!of! the!spent!fuel!have!been!completely!recycled.!(The!fission!reaction!in!the! fuel!rod!will!stop!long!before!all!the!fissile!material!is!used!up,!so!most!of! the!spent!fuel!rod’s!mass!can!be!recycled!into!new!rods).!How!many!kg!of! waste!must!be!stored!every!year!due!to!the!energy!consumption!of!the! refrigerators!in!this!town?!! (e) Given!that!burning!coal!can!release!5.20!ton/yr/1000MW!of!naturally! occurring!uranium!into!the!atmosphere,!which!power!plant!produces! more!total!mass!of!radioactive!waste!(neglecting!the!difference!in! isotopes!and!the!rate!of!radioactive!decay)?! !

! (

(

!

Problem(3-23( Complete!this!table!for!H2O!by!using!your!textbook!property!tables.! ! T,(degrees(C( P,(kPa( v,(m3/kg( Phase(description( 140! ____! 0.05! ____________________! _____! 550! ______! Saturated!liquid! 125! 750! ______! ____________________! 500! ____! 0.140! ____________________! ! ! ! ! Problem(3-29( ( 10!kg!of!refrigerant!R-134a!fill!a!1.348-m3!rigid!container!at!an!initial! temperature!of!-40!degrees!C.!The!container!is!then!heated!until!the!pressure!is! 200!kPa.!Determine!the!final!temperature!and!the!initial!pressure.! ( ( Problem(3-48(

( A!piston-cylinder!device!contains!0.005!m3!of!liquid!water!and!0.93!of!water! vapor!in!equilibrium!at!600!kPa.!Heat!is!transferred!at!constant!pressure!until! the!temperature!reaches!200!degrees!C.! (a) What!is!the!initial!temperature!of!the!water?! (b) Determine!the!total!mass!of!the!water! (c) Calculate!the!final!volume! (d) Show!the!process!on!a!P-v!diagram!with!respect!to!saturation!lines.! ( (

( Problem(3-86( ( A!0.016773-m3!tank!contains!1!kg!of!refrigerant-134a!at!100!degrees!C.!! Determine!the!pressure!of!the!refrigerant,!using!:! (a) the!ideal!gas!equation! (b) The!generalized!compressibility!chart!! (hint:!see!A-15!on!p.922!of!your!textbook)! (c) The!refrigerant!tables! (hint:!see!A-13!in!your!textbook)! ( ( Extension(Problem((

( Problem(3-40(( Water!initially!at!200!kPa!and!300!degrees!C!is!contained!in!a!piston-cylinder! device!fitted!with!stops.!The!water!is!allowed!to!cool!at!constant!pressure!until!it! exists!as!a!saturated!vapor!and!the!piston!rests!on!the!stops.!Then!the!water! continues!to!cool!!until!the!pressure!is!100!kPa.!On!the!T-v!diagrams!sketch,!with! respect!to!the!saturation!lines,!the!process!curves!passing!through!both!the! initial,!intermediate!and!final!states!of!the!water.!Label!the!T,!P!and!v!values!for! end!states!on!the!process!curves.!Find!the!overall!change!in!internal!energy! between!the!initial!and!final!states!per!unit!mass!of!water.! !...