{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

13 - 41D cHnP-ren 13 THE TRANSFER tel HEAT It An asrrenaur...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 41D cHnP-ren 13 THE TRANSFER tel: HEAT It]. An asrrenaur in the space shuttle has rwe ehjeIcts that are identi- cal in all respects. except that cne is painted black and the ether is painted silver. Initially. thejIr are at the same temperature. When taken here inside the space shuttle and placed in cuter space. which cbject. if either. ccels dcwn at a faster rate“? (a) The abject painted blank (b) The ebject painted silver {1:} Beth ebjects ccei dewn at the ILEI'JIS same rate. {d} it is net pessible tc determine which dewn at the faster rate. 11 The emissivity e {If ehject B 1s Ti": that cf chjeet A.alth1-_II ebjeets are identicai 1n sine and shape. If the cbjeets radiate I'I enerngr per secend, what 1s the ratie HIT... cf their Kelvin I-'I'I'- -:'_ three“? not (hit pit {Ins tea. 'I 1' . Here in Instructors.- t'lt'est ef the hemeweni: pmhients in this chapter are uvuiiuht'efitr assignment we en eniine hemewerir management prep -.5-' us WileyPLUS er Wehdssign. and these merited with the term a tH'E presented in WiieerLUS using e guided utterieifisrvner titer pinvides enhanced ittteruetiviur. See Preface fer additienni dereiis. Here: Fer emblems in this set. use the vet'uesfisr instruct eendttctivitt'es given in Ihhie iii unless stated ethaneise. IIII'I Sclntiun is in the Student Suluflens Manna]. IvvnIv Snluflnn is available enline at www.cdtepenflecflegeientuefl Sectinn 13.2 Cnntluetien l. The ameunt cf heat per secend ccnducted frcm the bleed capillaries beneath the skin re the surface is 240 It's. The en-I erg}I is transfened a distance cf 2.0 n lit—3' n1 thrcugh a bed}; whcse surface area is 1.6 mi. Assuming that the thermal cenductivity is that cf beder fat. determine the temperature difference between the capil- laries and the surface ef the skin. 2. The temperature in an electric even is 160 “C. The temperature at the enter surface in the kitchen is fit] ”C. The even {surface area = l.t'1 mi) is insulated with material that has a thickness cf Milt} m and a ther- mal ecntiuntivity cf H.045 Jt'is . tn ' C“). {a} Hew lunch energj,r is used tn eperate the even fer sin hears? {h} Int a price cf Sillfl per ltilewatt hunt for electrical energy. what is the ccst ef cperating the even“?I 3. llll'l Concept Elntuletlnn 13.1 at wwwwriiejscetnfcnilegeicutnell illustrates the cnncepts pertinent in this prcblern. A persen’s bed}; is cevered with 1.15 1111 cf weel clething. The thickness cf the went is 21.] it 10““ m.'l"hete1nperan1reattheeutside surface efthe weelis 11 “C. and the sltin temperantre is as “C. Hew much heat per secend rises the persen lcse due re cenductieh‘t" It @' 'rIIIrI cbjects are maintained at censtunt temperatures. ene her and ene celtl. TwIn identical bars can be attached end re end. as in part In efthe drawing. nrcnecntep efthecther. as in parth. When either cf these arrangements is placed between the her and the celd ebjects fer the satne ameunt ef time. heat Q flcws frnm left tc right. Find the ratie 9J9... 5. Item Due re a temperature difference dT. heat is ccndncted. thrcugh an aluminum plate that is D.fl35 m thick. The plate is then replawd by a stainless steel plate that has the same temperature dif- ference and cress-secticnal area. Hew thick shean the steel plate be se that the same ameunt cf heat per secend is cenducted threugh it'iIr n. ® The bleclt in the drawing has dimensiens t... s 21.. s an... where LII, = I330 m. The bleclt has a thermal ccnductivity cf 25!] Ms -m-C°}. 1n drawings A. B. and C. heat is ccndected threugh the blcclt in three different directicns; in each case the temperature cf the warmer surfaee is 35 ”C and that cf the eccler surface is 19 ”C. Determine the heat that flaws in 5.0 s fer each case. T'I‘hh teen represents a hiurnedical applieuflum Ptebiern e cembinaticn cf facters edit. 1s called the centtucI human bcItler has the abihtjr tn varjII the cenductance cf the lift heath the skin by means cf vasecensn-ieticn and v : I I_I' II_II.'- which the flew cf bleed re the veins and capillaries am In I_"II ,1}: sltin' 1s decreased and increased. respectively. The ccnductaacn . adjusted ever a range such that the tissue beneath the skin is" -.- lent tc a thickness ef‘fl. DEE! tum cf Stvrcfeam er 3. 5 mm cf ' what facter can the bed},r adjust the cenducrance'i' ii. A cepper pipe with an cuter radius cftitilli tn runs from-:- deer wall faucet tnte the interier cf a heuse. The tempereturnu i3- faucet 1s 4. fl l“C. and the temperature cf the pipe. at 31] n1 II II_ faucet. is 25 “C. in fifteen minutes. the pipe ecnducts a anal-33s cf heat tn the catttlccr faucet them the heuse interier. FindI radius cf the pipe. Ignnre a113Ir water inside the pipe. ' it. Ccnsultltttfiflflnhduflbhtflatmmfleymmfn I re espiete a medei fer sclving thispreblem. Cine end cfe I I=- maintainedatflfldnfl. wh1ied1eetherend1skeptataccnstenti temperature. Thecress-secticnaiareaefmeharisldtt ltiIf Because cf insulaticn. there 1s negligible heat less thrcugh III. ;: cf thebst. Heat flaws threugh the bar. hewever. atthe rate eff. ii}- Whatisthetemperatureefrhehararapcintfl. ifimfremtheii '1 1D. a A well in a hcuse centains a single windew. Thew ccnsistscfasingle pane efgiass whcseareeisfljfimiend-E thickness 15 2. 0 mm. Treat the wall as a slab cf the insulating II___ T. T III“ m In the ccnductien equalien Q= (he a It'I'I II whose area and thickness are IE n1I and illfi m. respec- | is lost via conduction through the wall and the window. 1 ' difference between the inside and outside is the I'llz-I 'the wall and the window. (If the total heat lost by the wall _'_Iwindow. what is the percentage lost by the window? ILeernlnnWare 13.1 at wwntwlleynomlcnllegefcnlnell the appmach talten' 1n problems such as this one. A composite from stainless steel and Iron and I_'II"III of 0.5!] m. The cross section of this E” rod is shown in me drawing and at a square within a circle. The square '11 of the steel is LII cm on a side. II tu-re at one end ofthe rod is 23 “C. :IE'T at the other end. Assuming that .-__I_ exits through the cylindrical outer sur- Ii”: I the total amount of heat conducted rod' 1n two minutes. III-bled: piece of heat-shield tile from the space shuttle measures -"I"'II'TI':I_ 11 side and has a thennal conductivity of flflfifi Ms Im -C°). surface of the tile is heated to a temperature of Ilfifl 1”C. i”: .__ituter surface is maintained at a temperature of 2t}..lI°C lunch heat flows from the outer to the mner surface of the tile III '! “I" {b} If this amount of heat were transferred to two :19.”th of liquid water. by how many Celsius degrees would the I III -_oftl1e water rise? Tine building materials plasterboard [k= I]. fit} .lIitsI m- C9911]. ' -" Illdfi Ilts- mI Cal]. and FE III I!{s-1nC°}]. are ____ Itegether as the draw- I": !=: I-.TI1EI temperatures ill I land outside surfaces are I} ‘C. respectively. Each .11“; the same thickness I'onal area. Find the {a} at the plaster- intedace and (In Elt ¢_ III interface. IE-Jcopper rod has a length of 1.5 m and a cross-sectional area 'I ‘ mi. Due end of the rod is in contact with boiling water with a mixture of ice and water. What is the mass of ice -I_fi_1a_t melts? Assume that no heat is lost through the side '92". Inst of water is boiling under one atmosphere of pressure. I beat enters the pot only through its bottom. which is cop- 575?:- un a heating element. I11 two minums. the mass of water I is n1= {145 kg. The radius of the pot bottom is and the thickness is L= 2..Ilmm What' 1a the tempera- III-beating element 1n contact with the port? I_=I-'t'||l '-l i I -._._Il|ll' I Plastcr— Brick Wood . I I III Example 3 discusses an approach to problems """M iii The ends of a thht bar are maintained at different tem- proint I113 111 from the cooler and is 23 “C and the the warmer end 1s 43 9rC. Assuming that heat flows ' IIEI'IIgth of the bar {the sides are insulated}. find the We lolulloll 13.1? at www.wiley.com.teollege! I III in solving this problem. In an aluminum pot. I]. IS ltg ”t “Eboils away in fournnnums. Thebottomofthepotis Whiclrandhas a surface areaofllfllfi m1. prrevent the II. I I I_ too rapidly. a stainless steel plate has been placed I and the heating element. The plate is 1.4 :II: III‘3 at III temperature of the cooler end' 1s II “C. while the rem-I PROBLEMS 411 thick. and its area matches that of the pot. Assuming that heat is con ducted into the water only through the bottom of the pot. find the tem- perature at {a} the aluminum-steel interface and 1b) the steel surface in contact with the heating element. “13. The drawing shows a solid cylindrical rod made from a center cylinder of lead and an outer concentric jacket of copper. Except for its ends. the rod is iridulated (not shown}. so that the loss of heat from the curved surface is negligible. When a temperature difference is maintained between its ends. this rod conducts one-half the amount of heat that it would conduct if it were solid copper. Determine the ratio of the radii rlt'rz. Lend cIIIsIII ** Ill. Inn m Two cylindrical rods have the same mass. Cine is made of silver {density = III 50h kgfflll}. and one is made of iron {density = 'Illdrfl lrgfmi}. Both rods conduct the same amount of heat per second when the same temperature difference is maintained across their ends. What is the ratio {silver-ItoI-iron] of {a} the lengths and {h} the radii of these rods? Section 13.3 Radiation an. 0 Ligbtbulb 1 operates with a filament temperature _of area it. whereas light bulb 2 has a filament temperature of 21th?i K. Both fila- ments have the same emissivity. and both bulbs ‘radiate the same power. Find the ratio Add; of the filament areas of the bulbs. 21. an 1111qu How many days does it take for a perfect black-body cube [IIIIIIII m on a side. Sill} “le to radiate the same arnouut of energy that a one-hundred-watt light bulb uses in one hour? 22. In an old house. the heating system uses radiators. which are hol- low metal devices through which but water or steam circulates. _In one room the radiator has a dark color {emissivity = {1.25}. It has a tern- perature of 62 "C. The new owner of the house paints the radiator a lighter color (emissivity = 0.513}. Assuming that it emits the same radiant power as it did before being painted. what is the temperature {in degrees Celsius} of the newly painted radiator? 23. A person is standing outdoors in the shade where the temperature is 23 “C. {a} What is the radiant energy absorbed per second by his head when it is covered with hair? The surface area of the hair (as- sumed to be flat) is ldfi cm2 and its emissivity is 0.35. {b} What would be the radiant energy absorbed per second by the same person if he were held and the emissivity of his hegd were ELdS‘? 24. A baking dish is removed from a hot oven and placed on a cool- ing rack. As the dish cools down to 35 “C from 125 ‘'C. its net radiant power decreases to 12.0 W. What was the net radiant power of the halting dish when it was first removed from the oven? Assume that the temperaune in the kitchen remains at 22 “C as the dish cools down. 25. MultipleIIConcept Example 3 reviews the approach that is used in problems such as this. A personeats a dessert that contains 2150 Calories. (This “Calorie” unit. with a capital C. is the one used by nutritionists; l Calorie I": 41315 .I. See Section 12.2.} The skin temperature of this individual is 3d “C and that of her environment is El ”C. The emissivity of her skin is {1.25 and its surface area is 1.3 m1. How much time would it take for her to emit a net radiant energy from her body that is equal to the energy contained in this dessert? 25. o Anobjectisinsidearoomthathasaconstamtemperahtreof 293 K. ‘II'ia radiation. the object emits three times as much power as it absorbs from the room. What is the temperature (in ltelvins} of the object? Assume that the temperature of the object remains constant. 412 cutie-ran 1a THE Tanner-"Eta ctr: HEAT 11'. III! Review Mulfipleflencept Example 3 befere attempting this ‘31. a Part {a} ef the drawing shews a rectangular bar it I preblem. Suppese the steve in that example had a surface area ef euly. mensiens are I... at 2L, “at 3L9. The hat is at the same can. I II3Ij3 2.00 In”. 1What weuld its temperature [in ltelvinsl have in be se that it peranrre as the teem (net shewn} 1n which it is lecated. 'l‘lte'li33‘3 still generated a net pewer ef T30!) 99"? risen cut. lengthwise. inte twe identical pieces. as shewn rupart 23. a Sirius B is a white star that has a surface temperature [in “1‘3 drawing. Th5 “mm if each 9199915 "19 59919- 35 t -33 lIteivins] that is fear times that ef eur sun. Sirius E radiates enly eriginal bi“ l“) What '5 “1‘3 “1"“ “f me WEI W bl'. ”.z [ill-=10 times the pewer radiated by the sun. flur sun has a radius ef bar'sinpart(b}efthe dtpwingte '31“ ”1131':me PERM}? {'1 15.915 it H)“ m. Assuming that Sirius B has the same emissivity as the that thi temperature 9‘“ file 5'9319 931' in Pit-IT {u} 15 450 .9 K. sun, find the radius of Sirius B. weuld the temperature (in kelvins} ef the meet and the tweI' part {it} have In he se that the twe bars abserb the same pewer 29. earn A car parked in the sun abserbs energy .at a rate cf see watts single bar‘ n1 PM {a}? per square meter at surface area. The car reaches a temperature at which it radiates energy at this same rate. Treating the car as a perfect radiater (Is = 1], find the temperature. 3t}. Multiple-Ceneept Example 3 discusses the ideas en which this preblem depends. luteruetlve Learnlnalllt‘are 13.1 at www. wheymfenflegefentnell reviews the cencepts that are in- 3 velved' 1n this preblem. Suppese the skin temperature ef a naked per- "33. III'I'I A selid cylinder is radiating pewer. It has a length draff 33333 sun is 34 ”C when the persen is standing inside a meet whese times its radius. It 1s cut inteanumberef smaller cylinders“. temperature is 25 ”C. The slrin area ef the individual is 1.5 ml. which hasthesamelength. Each smallcylindethasthessmeqf {a} Assuming the emissivity is (LED. find the net less ef radiant pewer aurre as the eriginal cylinder. The tetal radiant pewer emitted; 333.33. frem the bedy. {b} Detennine the number ef fee-d Caleries ef en- pieces is twice that emitted by the eriginal cylinder. Heni’l-jI ergy {1 feed Calerie = 4186 I} that are lest in ene heur due in the net smaller cylinders are thete'il 3 less rate ebtained in part {a}. Metabelic cenversien ef feed inte en- “343 fine and flf a [3.3 2354“ 9999'” red with 3 33.31.3355 swimj I-3 HEY 19919995 “11351991 I .2 st “1"" 1n2 is driven late the center ef a sphere ef see: 333'- ‘31. @ Liquid helium is ate-red at its beiling—peint temperature ef (radius 2 13.15 m]. The pertien ef thered that 1s embedded in I'3:..:. 4.2 K in a spherical cnntainer (r = 0.30 ml. The eentainer is a perfect is aim at i] ”C. The red is berisental and its ether end is f:.. blackbedy radiater. The cnntainer is surreunded by a spherical shield wall In a teem. The red and the reuse ate leept at a censtant I..'333. whese temperature is T? K. A vacuum exists in the space between the ture ef 24 T. The emissivity ef tlte' me is [1.91]. What Is the raise; 333- cnntainer and the shield. The latent heat ef vaperisatien fer helium is heat per secend gained by the sphere threugh cenductien e3 II 2.1 it 10“ Mtg. 1'i'fhat mass at liquid helium beils away threugb a heat per secend gained by the ice due in radiatien? Neglecti't I_'_': venting valve in ene hear? gained threugh the sides ef the red. 33 Tlllllll. PROBLEMS 35. alert Due end ef an iren pelter is placed in a fire whe1e the tem- ef uses. else suppose that metabnlic preeesses are predneing: peratur-e is 5132 ”C. and the ether end is kept at a temperature ef as “C. at a rate ef 115 its. What is the temperature ef the widest ' The pelter is 1.2 m lung and has a radius ef it] at Ill"Fl 1n. Igneriug which this persen eeuld stand and net experience a drep 111 II' 'Ii the heat lest slung the length ef the putter, find the ameunt ef heat peranrre‘i transmitted fivm are and sf the taker m the sfler in 5-9 t- as. The eencrete ei'en ef a building is ate at three. The re 3-6. fleeeept Elmullflen 1.3.1 at www.wlley.cmnfcnllege'cutnell inside the building is Elli] ”C. while the temperature eutside illustrates the cencepts pertinent in this preblem. A refrigerater has a Heat is cenducted tbreugh the wall. 1When the building is II'I.i-'T surface area cf 5.3 m1. It is lined with il.il‘i'5-m-tl1iclt ittsulatien whese the inside temperature falls in {H} “C. and beat cenductietti thermal cenductivity is il.il?:il His - tn *C“l. The interier temperature is Hewmer. the wall dues emit radiant energy when its - II .- :Ii333 kept at 5 “C. while the temperature at the eutsitle surface is 25 ”C. ill} ”C. The radiant energy emitted per secend per square ..-.--.3_i:'-' l-lew much heat per secend is being remeved item the unit? same as the heat lest per secend per square meter due in III 31'. The ameunt ef radiant pewer produced by the sun is apprexi- What 3'5 the emififlifitflr’ ‘1me W9“? mately 3.9 is: It};6 w. Assuming the sun in be a perfect blackbedy “Will. it selid sphere has a temperature at 3'93 K. The sphere is3I_.3._3 3 sphere with a radius ef 6.96 it ill“ m. find its surface temperature (in dawn and recast iute a cube that has the same emissivity II- ltelvins). . the same radiant pewer as the sphere. What' Is the eube’s l'l .".‘.‘3' 33. Censult Multiple-Cencept Example 3 in see the cencepts *4]. In a heuse the temperature at the surface et‘ a 1v"I-I:-i that are Went here. A person‘s body is. predueing energy 25 ”C. The temperature eutside at the window surface is fill} internally due te nsetabelic precesses. If the bedy leses mere energy is lest threugh the windew via eenductien, and the beat lest I"-3_' than rtsetabelic precesses are generating, its temperature will drep. if .end has a certain value. The temperature nuiside begins te' I |"I-'3-3 the drep is severe. it can be life-threatening. Suppese that a persen is the eenditiens inside the heuse remain the same. As a uncletlred and energy is being lest via radiatieu frnlrt a bedy surface lq-st per secend increases. What is the temperature at the I I area ef 1.41] ml. which has a temperature et‘ 34 “C and an emissivity dew surface when the but lest per secend deubles‘i' ...
View Full Document

{[ snackBarMessage ]}

Page1 / 3

13 - 41D cHnP-ren 13 THE TRANSFER tel HEAT It An asrrenaur...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online