Issiqlik almashtirgichni hisoblash
Qurilmaning termal yuki:
Q = G1∙c1∙(t1n–t1 gacha),
qayerda bilan1= 1850 J/kg∙K – bitumning issiqlik sig'imi [19]; G1- bitumning ommaviy iste'moli. Qabul qiling G1=2000 kg/soat = 0,56 kg/s
Q - issiqlik oqimi, termal hisobdan. Q= 35210,1 kJ/soat = 9780,58 Vt Bitumning oxirgi harorati
t1k
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G1 c1 t1n -Q
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G1 c1
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t
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0,561850250-9780.58
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=503K=2300BILAN
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1k
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0,561850
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O'rtacha harorat farqi:
tm= t1n–t2k= 250 - 60 = 190 ºS
tb= t1 gacha–t2n= 230 - 20 = 210 ºS
Munosabatdan beri∆ b=210= 1.11<2, Bu
∆m 190
tsr tb / 2,∘BILAN
tm
tChorshanba 190210 / 2 200 C
O'rtacha havo harorati:
t2 chorshanba
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t2k t2 n
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∘BILAN
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2
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t
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6020
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40C
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2 chorshanba
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2
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Bitumning o'rtacha harorati:
t t1n tChorshanba ;
1wd 2
(50)
(51)
t
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250200
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225S
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1wd
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2
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Havo oqimi
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G2
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Q
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(52)
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(t
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-t
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c
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2
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qaerda c2= 29 kJ/kg∙K – havoning issiqlik sig'imi [20].
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G2
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9780.58
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8.43
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kg/soat
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29(60-20)
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Issiqlik almashtirgichning taxminiy tanlovi.
Biz issiqlik uzatish koeffitsientining taxminiy qiymatini havo-suyuqlik issiqlik uzatish holati uchun qabul qilamiz Kor = 25 Vt/m2∙K [20], keyin taxminiy issiqlik uzatish yuzasi:
Fop
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Q
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(53)
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Kop
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tChorshanba
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bu erda Q - issiqlik oqimi, termal hisobdan, W Kor - issiqlik uzatish koeffitsienti, Vt/m2∙K
Fop
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9780.58
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1,95 m2
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25200
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Fop= 9780,58/∙25∙200 = 1,95 m2.
Biz issiqlik almashinuvi yuzasiga yaqin issiqlik almashtirgichni qabul qilamiz:
F =2m 2, korpus diametri bilan bitta o'tish D=159
n = 19 trubka 20 × 2 uzunligi l = 1 m [21].
Devordan havoga issiqlik uzatish koeffitsienti:
mmi
(54)
Qayerda2= 0,027 Vt/mK - havoning issiqlik o'tkazuvchanligi 40Nu bilan2- Havo uchun Nusselt mezoni.
Reynolds mezoni:
Re2= G2/[0,785dvn2] =0,43 /[0,7850,0181.8710-3] = 16790.
2=1,8710-3-40 da havoning dinamik yopishqoqligiBILAN
Harakat rejimi bu holda Nusselt mezoniga ko'ra turbulentdir:
Nu2= 0,021Re20.8Pr20.42(Pr2/Prst2)0,25
qaerda Pr2= 7.02 - havo uchun Prandtl mezoni 40S Biz birinchi taxminiy munosabat sifatida qabul qilamiz (Pr2/Prst2)0,25
Nu2= 0,021167900,87.020,43= 94.3.
2 94.3 0,027 141.45Vt/m2∙K0,018
Bitumdan devorga issiqlik uzatish koeffitsienti:
1 Nu11
dn
(55)
Qayerda1= 0,2 Vt/mK - bitumning issiqlik o'tkazuvchanligi, Nu1– Bitum uchun Nusselt mezoni. Reynolds mezoni:
Re1
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G1 dn
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(56)
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S
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mtr
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1
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qaerda Smtr= 0,005 m2- qismlar orasidagi oqimning ko'ndalang kesimi maydoni,1= 1.5910-3Pas – bitumning dinamik viskozitesi 240 daC [20].
Re1
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0,560,02
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=2521
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0,0051.5910-3
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Bunday holda, Nusselt mezoni:
Nu1= 0,24Re0,6Pr10.36(Pr1/Prst1),
qaerda Pr1= 8.8 - Bitum uchun Prandtl mezoni.
Birinchi taxmin sifatida biz munosabatni qabul qilamiz (Pr1/Prst1)0,25Nu1= 0,2425210,68.80,36= 55.2.
55.2 0,2 552 Vt/m2 ∙K
1 0,02
Devorning issiqlik qarshiligi:
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st
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r
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r
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st
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1
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(57)
st= 17,5 Vt/mK - zanglamaydigan po'latdan issiqlik o'tkazuvchanligi;
1/r1=1/r2=2900 Vt/mK – neft mahsulotlari uchun devor ifloslantiruvchi moddalarning issiqlikka chidamliligi[1, bet. 354]
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0,002
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1
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4.6
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-4
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m∙K/Vt
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17.5
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2900
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2900
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Issiqlik uzatish koeffitsienti:
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TO
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1
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(58)
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1
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(
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TO
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1
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106.6Vt/m2∙K
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1
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4.610-4
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1
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(
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552
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141.45
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Issiqlik uzatish yuzasi:
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F
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Q
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(59)
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