TEXNOLOGIK HISOB
Issiqlik almashinish apparati hisobi uchun berilgan qiymatlar:
Jarayonning davomiyligi oβrnatilgan rejimga chiqish vaqti bilan belgilanadi;
Issiqlik almashtirgichning kirish qismida isitiladigan muhitning sarfi funksiyasi
ππ):
(
π
π
πΊ (π) = {π0.25 + π1400 + 40, π < 4500
π₯
36, π > 4500
Isitiladigan aralashmaning boshlangΚ»ich temperaturasi π‘π₯π va bu isitadigan agent harorati (issiq issiqlik tashuvchi) π‘ππ:
π‘π₯π = 21 β
π‘ππ = 114 β
Isituvchi agentning issiqlik-fizik xususiyatlari: zichlik ππ, issiqlik oΚ»tkazuvchanlik ππ, dinamik qovushqoqlik ππ, solishtirma issiqlik sigΚ»imi ππ:
ππ
ππ = 986 π3
π
ππ = 0.662 π β πΎ
ππ = 0.00054 ππ β π
π½
ππ = 4190 ππ β πΎ
Isitiladigan aralashmaning issiqlik-fizik xususiyatlari: zichlik ππ₯, issiqlik oΚ»tkazuvchanlik ππ₯, dinamik qovushqoqlik ππ₯, solishtirma issiqlik sigΚ»imi ππ₯:
ππ
ππ₯ = 4190 π3
π
ππ₯ = 0.618 π β πΎ
ππ₯ = 0.000804 ππ β π
π½
ππ₯ = 4180 ππ β πΎ
Issiqlik almashinish qurilmasi parametrlari: kojux diametri π·, quvur diametri
ππ‘, qadamlar soni π§, quvurlar soni π, quvur uzunligi πΏ, issiqlik almashinish yuzasi
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πΉ, boΚ»limlar orasidagi oqim tasavvurlar maydoni π π, quvurlararo bir xod koΚ»ndalang kesim yuzasi π π‘:
π· = 800 ππ
ππ‘ = 20 Γ 2 ππ
π§ = 6
π = 614
πΏ = 3 π
πΉ = 110 π2
π π = 0.04 π2
π π‘ = 0.007 π2
Quvur boΚ»shligΚ»ida suyuqlik oqimi rejimini aniqlash uchun quyidagi ifoda ishlatiladi:
4πΊπ
π
ππ =
ππππβ. π π
π‘ π§ π
Quvurlararo boΚ»shliqda suyuqlik oqimi rejimini aniqlash uchun ifoda ishlatiladi:
πΊπ₯ππ‘ππ β.
π
π = π‘
π₯ π πππ₯
Dasturiy qism uchun kerakli parametrlar:
π‘1 = 16.7 π
π‘2 = 34 π
Feedforward Gain-1: 1.2
Feedforward Gain-2: 25
Disturbance Gain: 32
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Issiqlik almashinish apparatini hisoblashda, avvalo, apparatning taxminiy issiqlik almashinish yuzasini topamiz va shunga binoan apparat konstruktiv parametrlarini tanlab olamiz. Soβngra, koβp yoβlli issiqlik almashinish apparati uchun haroratning oβrtacha farqini hisoblaymiz. Va ninoyat, issiqlik oβtkazuvchanlik koeffitsiyenti π ning qiymatini hisoblaymiz va tanlagan qurilmamiz yuzasi zaxirasini oxirgi chiqqan natija orqali hisoblab olamiz.
Issiqlik almashinish apparatining taxminiy yuzasini hisoblash ketma-ketligi:
1. Berilganlardan foydalanib, temperaturalar farqining oΚ»rtacha qiymatini topib olamiz:
45 β β 114 β
21 β β 45 β
βπ‘ππ. = π‘ππ β π‘π₯π = 114 β β 45 β = 69 β
βπ‘ππ. = π‘ππ β π‘π₯π = 45 β β 21 β = 24 β
βπ‘ππ. 69 β
= = 2.875 > 2
βπ‘ππ. 24 β
βtππ. β βtππ. 69 β β 24 β
βπ‘πΚ»ππ‘. = βtππ. = 69 β = 42 β
2.3 lg βtππ. 2.3 lg 24 β
Sovuq agentning oΚ»rtacha temperaturasi:
π‘π₯π + π‘π₯π 21 β + 45 β
π‘2 = 2 = 2 = 33 β
Qurilma stabil holatga kelganda sovuq agentni isitishga sarflanadigan issiqlik miqdori:
ππ π½
π = πΊπ₯ππ₯(π‘π₯π β π‘π₯π) = 36 π β 4180 ππ β πΎ (45 β β 21 β) = 3611520 π
= 3611.52 ππ
Isituvchi moddaning sarfi:
π 3611.52 ππ ππ
πΊπ = = = 12.5
ππ(π‘ππ β π‘ππ) 4190 π½ (114 β β 45 β) π
ππ β πΎ
Issiqlik almashinish qurilmasining taxminiy tanlovi. Qaysi issiqlik tashuvchisini quvur bo'shlig'iga yo'naltirish to'g'risida qaror uning harorati, bosimi, korroziyligi, issiqlik almashinuvi yuzalarini ifloslantirish qobiliyati, oqim tezligi va boshqalar bilan belgilanadi. Ushbu misolda, kichikroq oqim maydoni bo'lgan quvur bo'shlig'iga (parametrlar XI 2.3-jadvaldagi ko'p yo'nalishli issiqlik almashinish
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qurilmalari) issiqlik tashuvchisini quyi oqim tezligida yuborish tavsiya etiladi, ya'ni issiq eritma. Bu issiqlik tashuvchilarning harakat tezligini va mos keladigan issiqlik uzatish koeffitsientlarini tenglashtirishga imkon beradi, bu esa issiqlik uzatish koeffitsientini oshiradi. Bundan tashqari, sovuq suyuqlik oqimini halqa ichiga yo'naltirish orqali issiqlik almashtirgich qobig'ining issiqlik izolatsiyasidan voz kechish mumkin.
Ushbu misolda issiqlik tashuvchilarning xususiyatlari suvning xususiyatlaridan unchalik farq qilmagani uchun biz turbulent oqimga mos keladigan issiqlik uzatish koeffitsientining minimal taxminiy qiymatini olamiz (XI 2.1-jadvalga): ππ‘ππ₯. =
800 π Bunday holda, issiqlik almashinuvi yuzasining taxminiy qiymati:
π2βπΎ
π 3611.52 ππ
πΉπ‘ππ₯. = = = 107.5 π2
ππ‘ππ₯.βπ‘πΚ»rt. 800 π β 42 β
π2 β πΎ
XI 2.3 jadvaldan ko'rinib turibdiki, yuzasi yaqin bo'lgan issiqlik almashinish apparatlari korpusining diametri 500-800 mm. Bunday holda, faqat harakat soni 4
yoki 6 bo'lgan ko'p yo'nalishli qurilmalar 200 ga yaqin π nisbatlariga ega.
π§
Ushbu jadvaldan yuza qiymati yaqin boβlgan πΉπ‘. = 116 π2 issiqlik almashinish qurilmasi konstruktiv parametrlari:
Quvurlar orasidagi yuza: π π = 0.07 π2
Quvur uzunligi: 3 π
Korjux diametri: π· = 800 ππ
Quvur diametri: 20 Γ 2 ππ
Quvurlar soni: 618
Quvur yoβnalishlari soni: 6
Har bir yoβnalishdagi quvurlar soni: 103
Oβrtacha haroratlar farqini topish:
1. Ko'p yo'lli issiqlik almashinish qurilmalarilarda issiqlik tashuvchilar harakatining o'zaro yo'nalishi aralash yuzaga kelganligi sababli, o'rtacha harakatlantiruvchi kuch bir yo'lli issiqlik almashinish qurilmalariga qaraganda bir oz kamroq. O'rtacha logarifmik harorat farqi uchun tuzatish (1.5b) tenglama bilan aniqlanadi:
π‘ππ β π‘ππ 45 β β 114 β
π = π‘ β π‘ = 21 β β 114 β = 0.74
π₯π ππ
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π‘π₯π β π‘π₯π 21 β β 45 β
π
= = = 0.34
π‘ππ β π‘ππ 45 β β 114 β
π = βπ
2 + 1 = β0.342 + 1 = 1.05 1 β π
1 β 0.34
πΏ = 1 β π = 1 β 0.74 = 0.62
ln 1 β π
π ln 1 β 0.34 β 0.74
π 1.05
πβπ‘ = 2 β π(1 + π
β π) = 2 β 0.74(1 + 0.34 β 1.05) = 0.82
πΏ ln 2 β π(1 + π
+ π) 0.62 ln 2 β 0.74(1 + 0.34 + 1.05)
Haroratning oβrtacha farqini qaytadan hisoblaymiz:
βπ‘πΚ»rt. = βπ‘πΚ»rt.πβπ‘ = 42 β β 0.82 = 34.44 β
Qayta tuzatish kiritilgandan keyin issiqlik almashinish yuzasining taxminiy qiymati quyidagicha:
π 3611.52 ππ
πΉπ‘ππ₯. = = = 131 π2
ππ‘ππ₯.βπ‘πΚ»rt. 800 π β 34.44 β
π2 β πΎ
π ning qiymatini topish uchun ishlar ketma-ketligi:
Quvur boβshligβidagi reynolds soni:
4πΊ 4 β 12.5 ππ
π
π = π = π = 17884
ππππβ. π π π β 103 β 0.016 β 0.00054 ππ β π
π
π‘ π§ π
π½
ππππ 4190 ππ β πΎ β 0.00054 ππ β π
πππ = π = = 3.4
π 0.662 π
π β πΎ
Quvur ichidagi suyuqlikning issiqlik berish koeffitsiyenti quyidagicha boβladi:
ππ ππ πππ 0.25
πΌπ = ππ’ = 0.023 π
π0.8ππ0.4 ( )
πππβ. πππβ. π π πππ₯
π‘ π‘
0.662 π π
= 0.023 β π β πΎ β 178840.8 β 3.40.4 = 3917
0.016 π π2 β πΎ
Bu yerda πππ 0.25 ni qisqartirib yuborsak hamboβladi, chunki haroratlar farqi
( )
πππ₯
unchalik katta emas (βπ‘πΚ»rt. = 34.44 β).
3. Quvurlar orasidagi yuza π π = 0.07 π2, shunda:
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πΊ ππ‘ππ β. 36 ππ β 0.02 π
π
π = π₯ π‘ = π = 12793
π₯ π πππ₯ 0.07 π2 β 0.000804 ππ β π
π½
ππ₯ππ₯ 4180 ππ β πΎ β 0.000804 ππ β π
πππ₯ = π = = 5.43
π₯ 0.618 π
π β πΎ
4. Quvurlar orasidagi harakatlanayotgan suyuqlikning issiqlik berish koeffitsiyenti;
ππ₯ ππ₯ πππ 0.25
πΌπ₯ = π‘π. ππ’ = 0.24 π‘π. π
π0.6ππ0.36 ( )
π π π₯ π₯ πππ₯
π‘ π‘
0.618 π π
= 0.24 β π β πΎ β 127930.6 β 5.430.36 = 3970
0.02 π π2 β πΎ
Ikkala aralashma ham suvga yaqin xossalarga ega boβlganligi uchun termik ifloslanishga qarshiligi bir xil va π = π = 1 π . Ushbu suyuqliklarning
π π₯ 5800 π2βπΎ
korroziv faolligini hisobga olgan holda, quvur materiali sifatida zanglamaydigan po'latni tanlash Maqsadga muvofiq. Zanglamaydigan po'latning issiqlik
o'tkazuvchanligi π = 17.5 π .
π π‘ πβπΎ
Devor va aralashmalarning termik qarshiliklari yigβindisi:
πΏ πΏ 0.002 π 1 π 1 π
β π = π + ππ + ππ₯ = π + 5800 π2 β πΎ + 5800 π2 β πΎ
π π‘ 17.5 π β πΎ
π2 β πΎ
= 0.0005
π
Issiqlik almashish qurilmasining issiqlik oβtkazish koeffitsiyenti:
1 1
π = 1 πΏ 1 = 1 π2 β πΎ 1
πΌπ + β π + πΌπ₯ π + 0.0005 π + π
3917 π2 β πΎ 3970 π2 β πΎ
π
= 992
π2 β πΎ
Zarur boβlgan issiqlik almashinish yuzasi:
π 3611.52 ππ
πΉ = = = 105.7 π2
πβπ‘πΚ»rt. 992 π β 34.44 β
π2 β πΎ
Apparatdagi zaxiraviy yuza quyidagicha hisoblanadi:
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πΉπ‘. β πΉ 116 π2 β 105.7 π2
β= 100 % = β 100 % = 9.7 %
πΉ 105.7 π2
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