Bai Tap Truyen Nhiet Tham Khao - Co Loi Giai

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Ky thuat nhiet

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<ul><li><p> BI 1: ( BAI 12.6 tr 276): Vach lo hi bang thep day 20 mm, = 58 W/mK; nhiet o kh lo tf1 = 1000 oC ; ap suat hi p = 34 bar. HSTN cua kh loti vach 1 = 116 W/m2K ; t vach lo en nc 2 = 2320 W/m2K.Xac nh q , nhiet o be mat trong va ngoai vach lo.</p><p>Giai:Nhiet o nc soi: tf1 = 240 oC</p><p>HSTN qua vach phang: k = 106,4 W/m2K</p><p>MDN q = k(tf1 tf2) = 80864 W/m2K.</p><p>Nhiet o be mat trong va ngoai vach lo:</p><p>303 oC ; 275 oC</p><p>21</p><p>111k</p><p>++</p><p>=</p><p>11f1w</p><p>1qtt =2</p><p>221qtt fw +=</p><p>NHAN XET:</p><p>- Gi tr HSTN k so vi He so toa nhiet- Nhit o vach va chenh lech nhiet o vach</p></li><li><p> BI 2: Ong dan hi bang thep dtr/dng = 200 / 216 mm co 1 = 47 W/(mK)c boc mot lp cach nhiet day 120 mm, co 2 = 0,8 W/(mK). Nhiet o hi la t1= 360 oC ; he so TNL pha hi 1 = 120 W/(m2K) . Khong kh ben ngoai co t2 = 25 oC; 2 = 11 W/(m2K).- Hay tnh ton that nhiet tren 1 m ong qL</p><p>- Xac nh nhiet o be mat trong va ngoai cua lp cach nhiet.</p><p>Giai: He so truyen nhiet, tnh theo 1m chieu dai ong</p><p>32</p><p>1</p><p>11</p><p>1ln211</p><p>1</p><p>ddd</p><p>d</p><p>k</p><p>i</p><p>i</p><p>i</p><p>L</p><p> ++= + mKWkL /412,1708,0</p><p>1 ==</p><p>qL = kL(tf1 tf2) = x 1,412(360 25) = 1485,28 kW/mTon that nhiet, tnh cho 1m ong:</p><p>Nhiet o be mat lp cach nhiet:</p><p>Cd</p><p>qtt oLfw 3,1191</p><p>3223 =+= Cd</p><p>dqtt Lww0</p><p>2</p><p>3</p><p>232 2,340ln2</p><p>=+= </p></li><li><p> Giai: TN qua vach tru 3 lp</p><p> BI 3: (BAI 12.9 tr 277): ong dan gio nong cho lo cao, toc o gio 1 = 35 m/s; tf1 = 800 oC. co 03 lp : gach chu la 1 = 250 mm , 1 = 1,17 W/m; thep 2 = 10 mm , 2 = 46,5 W/mK; cach nhiet ngoai 3 = 200 mm , 3 = 0,174 W/mK; ngknh trong d1 = 1000 mm, khong kh xung quanh tf2 = 10 oC , 2 = 4 m/s.</p><p>Tnh ton that nhiet tren 1 m ng ong (bo qua bc xa).</p><p>Ton that nhiet tren 1 m ng ong: ( )21 ffll ttkq = 121</p><p>1</p><p>11</p><p>1ln2111</p><p>+=+ ++== </p><p>n</p><p>n</p><p>i i</p><p>i</p><p>ill dd</p><p>ddk</p><p>R Vi d2 = d1 + 21</p><p>d3 = d2 + 22d4 = d2 + 23</p><p> Can tnh HSTN pha trong va pha ngoai ong </p></li><li><p> Tnh 1: Khong kh chuyen ong cng bc trong ongKTXD la d1 = 1m; NX la tf1 = 800 oC</p><p>Ref1 = 2,6*105 &gt; 104 -&gt; chay roiNuf1 = 0,018 Ref10,8 = 382 -&gt; 1 = 27,4 W/m2K</p><p>Tnh 2: Khong kh chuyen ong ngang ong nKTXD la d4 = 1,92m; NX la tf2 = 10 oC</p><p>Ref2 = 5,45*105 &gt; 104 -&gt; chay roiNuf2 = 0,245 Ref20,6 = 680 -&gt; 2 = 8,85 W/m2K</p><p>KET QUA: kl = 0,94 W/m2K ql = 2330 W/m</p></li><li><p>tkFQ =</p><p>C</p><p>tt</p><p>ttt o136</p><p>100180ln</p><p>100180</p><p>lnmin</p><p>max</p><p>minmax ===</p><p>tkQF =</p><p>BI 4: Can gia nhiet dau G2 = 1000 kg/h t t2 = 20 oC en t2 = 180 oCbang khoi nong co t1 = 280 oC. Biet t1 = 200 oC; k = 35 W/(m2K); cp1 =1,1 kJ/(kgK); cp2 = 2,3 kJ/(kgK).Tnh dien tch TN (F) khi bo tr dong chuyen ong ngc chieu.</p><p>GIAI: S dung PT TRUYEN NHIETChenh lech nhiet o tai hai au thiet b:</p><p>t1 - t2 = 280 180 = 100 oC = tmint1 - t2 = 200 20 = 180 oC = tmax</p><p>o chenh nh/o trung bnh:</p><p>Nhiet lng cap cho dau: Q = G2 cp2 (t2 - t2 ) = 1000 . 2,3 (180 20)/3600 = 102,2 kW</p><p>Vay = 102,2 / (0,035 . 136,1) = 21,46 m2</p></li><li><p>BI 5: Thiet b un nc nong bang khoi thai t CT, loai lu ong ngc chieu, co cac thong so sau:Pha khoi nong: G1 = 0,8 kg/s; cp1 = 1,12 kJ/(kgK); t1 = 450 oC.Pha nc: G2 = 3,2 kg/s; cp2 = 4,18 kJ/(kgK); t2 = 50 oCDien tch truyen nhiet F = 15 m2; k = 85 W/(m2K). a) Hay tnh Q; nhiet o ra cua khoi va nc.b) Neu ong c van hanh non tai vi G1* = 0,5G1, cac ieu kien ban au khac khong thay oi th nhiet lng trao oi va nhiet o nc ra se la bao nhieu?</p><p>GIAI: a) Tnh Q va nhiet o cuoi cac chat, dung pp NTUChenh lech nhiet o tai hai au thiet b:</p><p>C1 = G1 cp1 = 0,8 . 1,12 = 0,896 kW/K = CminC2 = G2 cp2 = 3,2 . 4,18 = 13,376 kW/K = Cmax</p><p>Nhiet lng truyen cc ai: Qmax = Cmin (t1 - t2 ) = 0,896 (450 50) = 358,4 kW</p></li><li><p>maxmin</p><p>*CCC = = 0,896 / 13,376 = 0,067</p><p>NTU = kF/Cmin = 85 . 15 / 896 = 1,42Hieu suat thiet b (tra o th): = 0,72Nhiet lng trao oi: Q = Qmax = 0,72 . 358,4 = 258 kWNhiet o khoi thoat: t1 = t1 Q/C1 = 450 258 / 0,896 = 162 oCNhiet o nc ra: t2 = t2 + Q/C2 = 50 + 258 / 13,376 = 69,3 oC</p><p>b) Neu ong c van hanh non tai vi G1* = 0,5G1Cmin giam 2 lan -&gt; C* giam 2 lan = 0,033</p><p>NTU tang 2 lan = 2,84Qmax giam 2 lan</p><p>HS truyen nhiet luc o = 0,92</p><p>Do vay: Q = 0,92. 358,4 / 2 = 164,8 kWt2 = 50 + 164,8 / 13,376 = 62,3 oC</p></li><li><p>BI 6 : Thiet b un nc nong bang hi nc, kieu chum ong.- Tong lu lng nc Gn = 10 kg/s; toc o nc trong ong 19/17 la w = 1m/s; t2 = 30 oC va t2 =70 oC.- Hi nc co p = 2 bar, x = 0,9. Nc ngng ra khoi bnh co tK = 90 oC.Biet HS toa nhiet pha hi ngng tu 1 = 8000 W/(m2K); nhiet tr dan nhiet cua vach ong </p><p>Tnh dien tch F cua thiet b va lu lng hi can cung cap. (Cho phep bo qua anh hng phng hng dong nhiet va coi he so t =1</p><p>WKm200017,0=</p><p>tkQF =NHAN XET:S dung PT TRUYEN NHIET e tnh FONG MONG nen co the tnh HSTN k theo CT vach phang. (Nhiet tr dan nhiet a cho la cua vach phang)Can tnh 2 pha nc chay trong ong e xac nh HSTN kTm nhiet o hi vao e tnh ttb. Ap suat hi la a/s tuyet oiTnh Q: nhiet lng nc nhan c</p></li><li><p>cp = 4,174 kJ/kgK ; = 64,8.10-2 W/mK Prf = 3,54 </p><p>TC Reynolds: 46 103060010.556,0017,01Re &gt;=== </p><p>trf</p><p>wd-&gt; chay roi</p><p>Ong thang: R = 1; Gia thiet L/d &gt; 50: l = 1. PTTC:Nuf = 0,021Ref0,8Prf0,43 = 0,021 x 306000,8 X 3,540,43= 137,5</p><p>TSVL cua nc </p><p> = 0,556.10-6 m2/s ; </p><p>NX: t2 = 0,5(30 + 70) = 50 oC </p><p>( )KmWd</p><p>Nutr</p><p>f2</p><p>2</p><p>2 /5241017,010.8,645,137 ===</p><p>2. He so truyen nhiet</p><p>21</p><p>111k</p><p>++</p><p>= =2062 W/(m2K)</p><p>Giai:1. Tnh he so toa nhiet 2 pha nc chay trong ong</p></li><li><p>Ctt</p><p>ttt o5,55</p><p>23,5060ln</p><p>23,5060</p><p>lnmin</p><p>max</p><p>minmax ===</p><p>tkQF =</p><p>5. Cong suat thiet b = Nhiet lng can e gia nhiet ncQ = Gn cpn (t2 - t2 ) = 10 . 4,174 (70 30) = 1672 kW</p><p>6. Dien tch BMTN:= 1672 / (2,062. 55,5) = 14,6 m2</p><p>7. Lu lng hi can: G = Q/(ih ik) = 1672 / (2486,6 377) = 0,79 kg/s= 2853 kg/h</p><p>3. Thong so hi nc: p = 2 bar, co ts = 120,23 oC; i= 504,8 kJ/kgr = 2202 kJ/kg. Hi bao hoa am, x = 0,9: ih = i+ rx = 2486,6 kJ/kg</p><p>4. o chenh nhiet o TB: tmax = 60 oC ; tmin = 50,23 oC</p></li><li><p>BI 7: Trong mot TBTN, nc chay trong ong co dtr/dng = 28/32 mm viG2 = 1 kg/s, nhiet o nc vao: tf2 = 25 oC ; ra tf2 = 95 oC ; Hi: tf1 = 120 oC. He so TNL pha hi 1 = 4000 W/m2K ; vach co v = 45 W/mK.</p><p>- Hay tnh HSTN ve pha nc 2. Xem (Prf/Prw)0.25 = 1.- Xac nh HSTN k va mat o dong nhiet trung bnh tren 1 m ong qL.</p><p>- Chieu dai can thiet cua ong la bao nhieu? </p><p>Giai:</p><p>TSVL cua nc = 983,2 kg/m3 ;cp = 4,179 kJ/kgK ; = 65,9.10-2 W/mK </p><p>Prf = 2,98 </p><p>Van toc nc : s/m,,,d</p><p>Gwtr</p><p>65102802983</p><p>14422 =</p><p>==</p><p>TC Reynolds: 46 10966521047800280651 &gt;=== .,,,wdRe trf</p><p>1. He so toa nhiet 2Nhiet o TB cua nc trong ong: tf2 = 0,5(25 + 95) = 60 oC </p><p> = 0,478.10-6 m2/s ; </p></li><li><p>Do che o chay roi nen ta co PTTC:</p><p>Nuf = 0,021Ref0,8Prf0,43 = 0,021 x 966520,8 x 2,980,43 = 326,76</p><p>Km/W,,.,,</p><p>dNu</p><p>trf</p><p>22</p><p>2 5769002801096576326 ===</p><p>2. He so truyen nhiet va nhiet lng truyen</p><p>trtr</p><p>ng</p><p>vng</p><p>L</p><p>ddd</p><p>lnd</p><p>k</p><p>21</p><p>1211</p><p>1</p><p>++=</p><p>mK/W,</p><p>,,ln</p><p>,</p><p>kL 2473</p><p>0280576901</p><p>2832</p><p>4521</p><p>032040001</p><p>1 =++</p><p>=</p><p>qL = kL(tf1 tf2) = x 73,24(120 60) = 13,798 kW/m3. Chieu dai ong can thiet</p><p>Nhiet can cap cho nc:</p><p>kW,)(,)tt(cGQ 'f''fp 532922595179412222 ===</p><p>Chieu dai ong: (Kiem tra L/d !) m,,</p><p>,qQL</p><p>L</p><p>22179813</p><p>53292 ===</p></li><li><p> Bai 1 (nh 10.2) Tng lo nung: h = 2,5 m; F = 39 m2; tw = 90 oC ; khong kh xung quanh tf = 30 oC. </p><p>Tnh va ton that nhiet Q.</p><p>KTX: l = h = 2,5 m</p><p>NX:2</p><p>ttt wfm</p><p>+= C602</p><p>3090 o=+= Tm = 333 oK</p><p>Chenh lech N:fw ttt = C603090 o==</p><p>TSVL tai tm = 60 oC ( phu luc Bang 22):</p><p>KmW 109,2 2m = sm1097,18 26m =696,0Prm =</p><p>( ) = mPrGr 1010 1034,5696,01067,7 =</p><p>Giai</p><p>2</p><p>3</p><p>mm</p><p>thgGr </p><p> = = 7,67 x 1010</p></li><li><p>Chay roi 135,0C =31</p><p>n =</p><p>PTTC:</p><p>( ) 31mm PrGr135,0Nu = ( ) 508101034,5135,0 31 ==HSTN:</p><p>h</p><p>Nu mm= KmW 9,55,2</p><p>109,2508 22</p><p>==</p><p>Nhiet lng ton that:</p><p>( )fw ttFQ = kW 13,8 W1380606399,5 ===</p></li><li><p>Bai 2 (nh 10.7)Ong dan kh nong nam ngang : d = 0,5 m; tw = 470 oC ; khong kh</p><p>xung quanh tf = 30 oC. Tnh va ton that nhiet ql.Neu d* = d/2 th * = ?</p><p>KTX:</p><p>NX:2</p><p>ttt wfm</p><p>+= C2502</p><p>30470 o=+= Tm = 523 oK</p><p>Chenh lech N: fw ttt = Co44030470 ==TSVL tai tm = 250 oC ( phu luc Bang 22):</p><p>KmW 1027,4 2m = sm1061,4026</p><p>m=</p><p>68,0Prm = 2m</p><p>3</p><p>mtdg</p><p>Gr = ( )</p><p>8122</p><p>3</p><p>10255,61061,40 523.</p><p>4405,081,9 == </p><p>( )mPrGr 88 10253,468,010255,6 ==</p><p>Giai l = d = 0,5 m</p></li><li><p>Chay roi, C = 0,135 31</p><p>n =</p><p>PTTC:</p><p>( ) 311350 mm PrGr,Nu = ( ) 510181025341350 31 ,,, ==HSTN:</p><p>d</p><p>Nu mm= KmW67,85,0</p><p>1027,45,1012</p><p>2</p><p>==</p><p>Nhiet lng ton that tren 1m ong:</p><p>( )fw ttFq === 0445,014,367,8 kW/m 6 W/m5989,2 =</p><p>Khi d* = d/2 Gr giam 23 = 8 lan, tc Ra* = (Gr*.Pr) = 5,3 x 107 . Van chay roi. Che o automodel : khong oi</p></li><li><p>Bai 3: (10.12)Tm t va q qua lp khong kh trong mot khe hep = 20 mm, tw1 = 200 oC,tw2 = 80 oC.</p><p>Neu be day giam 2 lan th t se the nao?</p><p>2</p><p>21 wwf</p><p>ttt</p><p>+= C1402</p><p>80200 o=+=</p><p>Theo phu luc thong so vat ly cua khong kh ta c:</p><p>Km.W 0349,0f = sm108,27 26f =684,0Prf =</p><p>Tieu chuan Gr:</p><p>21 ww ttt = Co12080200 ==</p><p>2f</p><p>3</p><p>f</p><p>tlgGr</p><p>= 4122</p><p>3</p><p>109521082741</p><p>120020819 == ,</p><p>,3</p><p>,,</p><p>Giai</p></li><li><p>Khi be day giam 2 lan: Gr giam 23 = 8 lan, tc Ra* = (Gr*.Pr) = 2,52 x 103 . t giam (23)1/4 = 23/4 = 1,68 lan. </p><p>( )fPrGr 44 1001782684010952 == ,,,( ) 1452180 250 ,PrGr, ,t ==</p><p>= ttm.KW 07486,00349,0145,2 ==</p><p>= tq t</p><p>2mW ,</p><p>,449</p><p>020</p><p>120074860 ==</p></li><li><p>Bi 1 (10.14)Dau may bien ap chay trong ong d = 10 mm, tf= 80 oC, tf= 40 oC, vi lu</p><p>lng G = 120 kg/h. Nhiet o be mat ong tw = 30 oC, - Tnh chieu dai ong L.- Tnh Q cua 5 ong (song song).</p><p>Nhiet o trung bnh cua dau:</p><p>tf = 0,5 (tf+ tf) = 0,5 (80 + 40) = 60 oC</p><p>Tra thong so vat ly cua dau may bien ap 60 oC (PL Bang 24):</p><p>3856 m/kg= cp = 1, 905 kJ/kgK mKW,10720=</p><p>sm , 2610765 = = 7,1.10-4 1/K 887,Prf = 202=wPr</p><p>Giai:</p><p>Toc o dau chay trong ong</p><p>=== 24</p><p>dG</p><p>FVw s/m,</p><p>,4960</p><p>01085636001204</p><p>2 =</p><p>;</p><p>;</p><p>;</p><p>; ;</p></li><li><p>Tieu chuan Reynolds: ==</p><p>ff</p><p>dRe 858</p><p>10765</p><p>01049606 =</p><p>,,,</p><p>V Ref &lt; 2200 : chay tang</p><p>( )( ) 5625410765 30600101017819 2634</p><p>,,</p><p>,,, =</p><p>PTTC khi chay tang, gia thiet L/d 50 :25,0</p><p>w</p><p>f1,0f</p><p>43,0f</p><p>33,0ff Pr</p><p>PrGrPrRe15,0Nu </p><p>=</p><p>581820288756264887858150</p><p>25010430330 ,,,,,</p><p>,,,, =</p><p>=</p><p>He so toa nhiet: ==d</p><p>Nu ff KmW ,,</p><p>,, 21199</p><p>010</p><p>107205818 =</p><p>( ) == 2</p><p>3wf ttdgGr</p><p>Nhiet lng dau nha ra trong 1 ong:</p><p>Q1 = Gcp(tf tf) = ( ) kW,, 542408090513600120 =</p></li><li><p>T PT: Q1 = dL(tf tw) Chieu dai ong</p><p>Suy ra ( ) == wf ttdQL 1 ( ) m,,, 541330600101199</p><p>2540 =</p><p>Kiem tra 50 ,</p><p>,</p><p>d</p><p>L &gt;== 1354010</p><p>5413do o he so l = 1.</p><p> Nang suat cua thiet b co 05 ong:</p><p>Q = nQ1 = 5 x 2,54 = 12,7 kW</p></li><li><p>BNH NGNG</p></li><li><p> Bi 2: Bnh ngng co 150 ong (song song), ng knh trong d = 20 mm. Lu lng nc vao bnh G = 84 kg/s, tf= 30 oC, tf= 50 oC. Nhiet o trungbnh BM ong tw = 70 oC. </p><p>- Tnh he so toa nhiet trong ong.- Tnh L moi ong.</p><p>a) He so toa nhiet Nhiet o trung bnh cua nc: tf = 0,5(30 + 50) = 40 oC</p><p> = 992,2 kg/m3 ; cp = 4,174 kJ/kgK ; = 63,5.10-2 W/mK = 0,659.10-6 m2/s ; Prf = 4,31 ; Prw = 2,55</p><p>TSVL</p><p>Giai:</p><p>Toc o nc chuyen ong trong ong</p><p>== ndGw 24</p><p>s/m,,,</p><p>811500202992</p><p>8442 =</p><p>==wdRef 46 1054628106590</p><p>02081 &gt;=</p><p>,,,</p></li><li><p>Gia thiet L/d &gt; 50 -&gt; l = 1PTTC co dang:</p><p>250430800210</p><p>,</p><p>w</p><p>f,f</p><p>,ff Pr</p><p>PrPrRe,Nu </p><p>=</p><p>58276552314314546280210</p><p>25043080 ,</p><p>,,,,</p><p>,,, =</p><p>=</p><p>==d</p><p>Nuf Km/W,,,, 2</p><p>2</p><p>587810201056358276 =</p><p>b) Nhiet lng nc nhan c</p><p>Q = Gcp(tf tf) =</p><p>Chieu dai moi ongtdn</p><p>QL =</p><p>( ) m,,, 8252407002058781150107012 3 ==</p><p>Kiem tra lai gia thiet L/d = 2,825/0,02 = 141 &gt; 50: thoa man</p><p>84 x 4,174(50 30) = 7012 kW</p></li><li><p>Bi 3: (nh 10.23)Khoi chuyen ong trong ong (0,4 x 0,8) m, L = 10 m. Lu lng G = 4,8 </p><p>kg/s, nhiet o trung bnh tf = 300 oC. Tnh he so toa nhiet . Xem Prf = Prw.</p><p>KTX: tng ng UF4d t = ( ) m,,,</p><p>,, 53308040280404 =+</p><p>=</p><p>Khi tf = 300 oC, TSVL cua khoi (PL B. 23)</p><p>TSVL: = 0,617 kg/m3 ; = 4,84.10-2 W/mK ; = 45,81.10-6 m2/s; Pr = 0,65</p><p>Toc o khoi trong ong</p><p>FG</p><p>FVw == s/m,,,,</p><p>, 32480406170</p><p>84 ==</p><p>ff</p><p>dRe </p><p>= 46 102827301081455330324 &gt;=</p><p>= ,,,</p><p>Giai:</p></li><li><p>Che o chay roi</p><p>PTTC: l</p><p>,</p><p>w</p><p>f,f</p><p>,ff Pr</p><p>PrPrRe,Nu </p><p>=</p><p>2504308000210</p><p>= 0,021.2827300,8.0,650,43.1,05 = 420</p><p>V 7185330</p><p>10,</p><p>,d</p><p>L == nen he so l = 1,05 (Bang 8.1)</p><p>Do o dNu ff</p><p>= KmW ,,</p><p>, 21385330</p><p>210844420 =</p><p>=</p></li><li><p>Bi 4: (nh 10.37) Ong dan kh nong d = 500 mm, at ngoai tri, gio thoi = 2 m/s xien goc</p><p>60o. Nhiet o moi trng tf = 30 oC, nhiet o BM ong tw = 470 oC. Tnh ton thatnhiet /1 m ong.</p><p>KmW, f21072 = sm 2f 61016 = 7010,Prf =</p><p>ff</p><p>dRe </p><p>= 41025661016502 =</p><p>= ,,</p><p>oi vi khong kh, khi Re &gt; 103</p><p>= 602450 ,Re,Nu ( ) 86171930102562450 604 ,,,, , ==</p><p>dNu</p><p>= KmW ,,</p><p>,, 2289</p><p>50</p><p>107286171</p><p>2</p><p>==</p><p>Ton that nhiet do oi lu</p><p>Giai: KTX d = 0,5 m NXD tf = 30 oC</p><p>Ql = dL(tw tf) = 9,28 . . 0,5 . 1.(470 30) = 6411 W</p></li><li><p> Bi 5 (10.42) Chum ong song song gom 8 hang, d = 60 mm, nhiet o trung bnh cua</p><p>dong khoi tf = 600 oC, toc o cho hep nhat w = 8 m/s. Nhiet o trung bnh cuavach tw = 120 oC. Tnh he so cua chum ong trong 2 trng hp:</p><p>a. Goc va = 90 ob. Goc va = 60 o</p><p>TSVL cua khoi tf = 600 oC</p><p>mKW ,f210427 = sm , 2f</p><p>6106193 = 620,Prf = Prw = 0,69</p><p>ff</p><p>dRe </p><p>= 36 101751271061930608 &gt;=</p><p>= ,,,</p><p>PTTC cho hang ong th 3:Neu goc va = 90 o th250</p><p>360650220,</p><p>w</p><p>f,f</p><p>,ff Pr</p><p>PrPrRe,Nu </p><p>= 546</p><p>250</p><p>,0,690,620,625127,7 0,22</p><p>,0,360,65 =</p><p>=</p><p>Giai:</p><p>dNu ff</p><p>=3 K2mW ,,,</p><p>, 55706007420</p><p>546 ==</p></li><li><p> Khong kh: 6501940 ,ff Re,Nu = = 50 sai so la 7,5%</p><p>HSTN trung bnh cua chum 8 day ong :</p><p>( )8</p><p>289060 33390</p><p>++= ,, KmW ,, 295393750 3 ==</p><p>Khi goc va = 60 o: Tra bang 8.5 tm c = 0,94.</p><p>Do o = 90 KmW ,,, 2750940953 =</p></li><li><p>T1 = 600 oK ; T2 = 400 oK</p><p>Mat o dong nhiet bc xa trao oi:</p><p>=</p><p>42</p><p>41</p><p>12 100100TTCq oqc)( </p><p>++=</p><p>42</p><p>41</p><p>21</p><p>1001002211TTC</p><p>c</p><p>o</p><p>[ ] 244 6145462</p><p>0502</p><p>801</p><p>801</p><p>675 m/W,</p><p>,,,</p><p>, =++</p><p>=</p><p>Bi 1: (11.5) Co 2 tam phang at song song, t1= 327 oC, t2 = 127 oC, oen 1= 2 = = 0,8. Gia co mang chan c = 0,05.</p><p>a. Tnh mat o dong nhiet TN BX gia 2 tam va tc.</p><p>b. Neu muon mat o dong nhiet giam 79 lan so vi khi khong co MC</p><p>th can bao nhieu mang?</p><p>Giai:</p><p> Tnh nhiet o MC:Trng hp co 1 MC, xet trong ieu kien on nh nhiet</p><p>ta co: q1c = q2c = q(12)c</p></li><li><p>Vi</p><p>+=</p><p>441</p><p>1</p><p>1 100100111c</p><p>c</p><p>oc</p><p>TTCq</p><p>o</p><p>cc</p><p>c</p><p>C</p><p>qTT </p><p> +</p><p>=</p><p> 1</p><p>11</p><p>1001001</p><p>141</p><p>4</p><p>776675</p><p>10501</p><p>8016145</p><p>64 =</p><p> +=</p><p>,,,</p><p>,</p><p>Tc = 528 oK =&gt; tc = 255 oC</p><p>b) Xac nh so MC e q* = qo 79</p><p>Ta co: R* = 79Ro</p><p> +=</p><p> +</p><p> + 1</p><p>117912111</p><p>2121 c</p><p>n</p><p>Vi 1 = 2 = ta co: </p><p> =</p><p> 1</p><p>27812</p><p>c</p><p>n</p><p>Thay = 0,8 va c = 0,0539n = 78 x 1,5 n = 3</p></li><li><p>Bi 2 : Ong d = 0,5 m nam ngang, tw = 470 oC, w = 0,85 ; tf = 30 oC.Tnh ql: a) oan ong trong nha</p><p>b) oan ong ngoai tri, gio w = 2 m/s; = 60o</p><p>Giai: oan ong trong nha </p><p>* Ton that nhiet bc xa. Ong at trong phong rong: td = w</p><p>=</p><p>44</p><p>100100fw</p><p>owbxTT</p><p>CdLQ vi Tw = 743 oK ; Tf = 303 oK </p><p>= . 0,5 . 1 . 0,85 . 5,67(7,434 3,034) = 22422 W</p><p> Tong ton that nhiet tren 1 m chieu dai ong:Q = Ql + Qbx = 28411,3 W</p><p>** Ton that nhiet oi lu (nh bai 10.7) ; Kch thc xac nh l = d</p><p>tm = 0,5(tw + tf) = 0,5(470 + 30) = 250 oC</p><p>Gr = .. = 6,255.108 ; Ra = GrPr = . = 4,253.108</p><p>Nu = = 101,52 ; = = 8,67 W/m2oQl = dL(tw tf) = . = 5989,2 W</p><p>a)</p></li><li><p>b) oan ngoai trigio thoi 2m/s, goc va = 60 oC (nh bai 10.37)</p><p>Re = . = 6,25.104 ; Nu = . = 171,86</p><p> = = 9,28 W/m2o </p><p>Ton that nhiet do oi lu:Ql = = 6411 W</p><p> Ton that nhiet bc xa: giong nh cau a) Qbx = 22422 W Tong ton that nhiet:</p><p>Q = Ql + Qbx = 6411 + 22422 = 28833 W</p><p>) Ghi chu: Trong trng hp nay ton that nhiet cua 1m ong trong nha va ngoaitri khong qua khac nhau do bi thanh phan ton that chu yeu la do bc xa.</p><p>Bai 1: truyen nhiet qua vach phangBai 2: truyen nhiet qua vach truBai 2: truyen nhiet qua vach truBai 4: Tinh dien tich trao doi nhiet Bai 5: TDN luu dong nguoc chieuBai 6: TB dun nuoc nong kieu chum ongBai 7: TDN nuoc trong ong, hoi phia ngoaiBai 1: Tuong lo nungBai 2: Ong dan khi nam ngangBai 3: Khong khi trong khe hepBai 1: dau chay trong ongBai 2: Binh ngungBai 3: Khoi chuyen dong trong ongBai 4: Ong dan khi nong dat ngoai troiBai 5: Chum ong song songBai 1: 2 tam phang song songBai 2: ong nam ngang</p></li></ul>