Kev sib piv ntawm cov raj tooj liab thiab stainless hlau tshav kub hloov raj yog raws li nram no:
1. Kev sib piv ntawm cov raj tooj liab thiab stainless hlau tshav kub hloov raj: thermal conductivity
Txij li cov thermal conductivity ntawm cov raj tooj liab yog 100W / m degree thiab cov hlau stainless hlau yog 13W / m degree, qhov no yuav ua rau muaj kev cuam tshuam tag nrho cov tshav kub hloov coefficient. Txawm li cas los xij, cov phab ntsa tuab ntawm cov hlau tsis muaj steel hlau tuaj yeem raug txo mus rau 0.5 ~ 0.8 hli, thaum phab ntsa tuab ntawm cov hlau tsis tuaj yeem tsawg dua 1.2 hli vim muaj zog, yaig thiab hnav.
Raws li cov qauv: Rc=(1) Qhov twg: Rc--thermal resistance, m2k/w. λ-- thermal conductivity, W/(mk).
δ-- raj phab ntsa thickness, m
Thaum cov khoom siv lub raj tsis tu ncua thiab λ tsis hloov pauv, raws li cov qauv (1), qhov me me δ, Rc me dua, thiab qhov loj dua qhov kub hloov coefficient. Qhov no tuaj yeem nqaim qhov sib txawv ntawm tag nrho cov tshav kub hloov coefficient ntawm stainless hlau raj thiab tooj liab.
Txij li cov phab ntsa sab hauv thiab sab nrauv ntawm cov raj tooj liab yog rougher dua li cov hlau tsis muaj steel, lawv yog cov scaling, uas ua rau cov thermal tsis kam ntawm tooj liab, uas nyob rau hauv lem ua rau qhov sib txawv ntawm tag nrho cov tshav kub hloov coefficients ntawm tooj liab raj thiab stainless hlau raj.
II. Kev sib piv ntawm cov raj tooj liab thiab stainless hlau tshav kub hloov raj: convection tshav kub tso
Thaum siv cov hlau tsis muaj steel hlau lossis cov raj tooj liab, tus nqi ntws hauv lub raj yog turbulent. Qhov loj tshaj plaws uas cuam tshuam rau convection thaum tshav kub kub tso tawm yog lub thickness ntawm lub laminar hauv qab txheej, vim hais tias lub tshav kub hloov nyob rau hauv laminar hauv qab txheej yog kub conduction, thiab thermal conductivity ntawm dej yog tsawg heev. Nyob rau hauv tib lub xeev ntws, lub thickness ntawm laminar hauv qab txheej nyob ntawm qhov roughness ntawm lub puab phab ntsa ntawm lub raj. Muaj oxide nyob rau sab hauv ntawm lub raj tooj liab, thiab nws qhov roughness yog ntau dua li ntawm cov hlau stainless. Lub thickness ntawm lub laminar hauv qab txheej ntawm lub raj tooj liab yog ntau dua li ntawm lub laminar hauv qab txheej ntawm stainless hlau raj. Qhov no ua rau lub convection tshav kub tso coefficient ntawm stainless hlau raj ntau dua li ntawm lub raj tooj liab.
Rw=(2)
Qhov twg: Rw--convection tshav kub tso tawm thermal kuj, m2k/w. w--convection heat release coefficient, w/m2.k. Raws li formula (2), qhov loj w yog, qhov me Rw yog.
III. Kev sib piv ntawm tooj liab raj thiab stainless hlau tshav kub exchanger tube: condensation tshav kub tso coefficient
Muaj ob hom condensation tshav kub tso coefficients: zaj duab xis condensation thiab hlaws condensation. Cov hlaws condensation tshav kub tso tawm coefficient yog ntau dua li cov yeeb yaj kiab condensation tshav kub tso coefficient. Txawm li cas los xij, nws tsis paub meej tias cov phab ntsa sab nrauv ntawm lub raj hlau stainless lossis lub raj tooj liab muaj cov hlaws ntau dua, tab sis nws tuaj yeem hais tias feem ntau ntawm cov phab ntsa sab nrauv ntawm ob lub raj yog zaj duab xis condensation. Lub tshav kub tso tawm coefficient ntawm zaj duab xis condensation yog ze ze rau lub thickness ntawm cov zaj duab xis, vim hais tias nyob rau hauv cov zaj duab xis yog tshav kub conduction, thermal conductivity ntawm cov dej zaj duab xis yog tshwj xeeb tshaj yog tsawg, thiab cov thickness ntawm cov zaj duab xis nyob ntawm lub roughness ntawm cov zaj duab xis. sab nrauv ntawm lub raj. Cov phab ntsa sab nrauv ntawm lub raj tooj liab yog ntau rougher dua li ntawm cov hlau tsis muaj steel vim yog txheej oxide. Yog li ntawd, lub condensation tshav kub tso coefficient ntawm lub sab nrauv phab ntsa ntawm lub stainless hlau raj yog loj dua li ntawm sab nrauv phab ntsa ntawm lub raj tooj liab.
Rm =(3)
Qhov twg: Rm--condensation tshav kub tso tawm thermal kuj ntawm sab nrauv phab ntsa ntawm lub raj, m2k/wm--condensation tshav kub tso coefficient ntawm sab nrauv phab ntsa ntawm lub raj, w/m2.k. Raws li formula (3), qhov loj dua m yog, qhov me Rm yog.
IV. Zuag qhia tag nrho cov tshav kub hloov coefficient ntawm kev ua tau zoo sib piv ntawm tooj liab raj thiab stainless hlau tshav kub exchanger raj
K=(4)
Qhov twg: R--tag nrho thermal resistance, m2k/w. K--tag nrho cov tshav kub hloov coefficient, w/m2.k.
Los ntawm (4), nws tuaj yeem pom tau tias: yog tias lub convection thermal tsis kam, thermal conductivity tsis kam thiab condensation tshav kub tso tawm thermal kuj raug txo, tag nrho cov thermal kuj yuav raug txo: yog tias tag nrho cov thermal kuj txo, tag nrho cov cua sov hloov. coefficient yuav nce.
Nyob rau hauv tib lub phab ntsa thickness, tag nrho cov tshav kub hloov coefficient ntawm stainless hlau raj yog 6% qis dua cov tooj liab raj. Vim yog siv cov hlau tsis muaj steel hlau uas nyias nyias dua li cov raj tooj liab, tag nrho cov cua sov hloov coefficient thiab condensation cua sov tso tawm coefficient ntawm stainless hlau raj yog loj dua li ntawm cov hlab tooj liab, uas txhim kho tag nrho cov tshav kub hloov coefficient ntawm stainless hlau hlab.
