Rau Titanium Rhaub Rhaub Rhaub Boiling Sugar Solution, Vim Li Cas Qhov Siab Tshaj Kub Kub Flux Limited los ntawm Burnout Point, Tsis yog Corrosion Rate?
Tso lus
Rau cov txheej txheem engineers siv lub titanium immersion rhaub nyob rau hauv boiling qab zib tov (sucrose los yog qabzib phoov), qhov zoo tshaj plaws kub flux uas yuav ua tau tiav yog txwv los ntawm lub burnout point (tseem ceeb tshav kub flux, CHF) thiab tsis yog los ntawm corrosion tus nqi ntawm titanium. Cov ntsiab lus qab zib yog viscous heev, muaj qhov nro siab thiab zoo li caramelise ntawm qhov kub siab dua. CHF rau titanium rhaub hauv cov kua qab zib npau npau (40-60℃Brix) feem ntau yog 30-50% qis dua hauv dej-li 6-10 W / cm2 piv rau 12-15 W / cm2 rau dej. Saum toj no CHF, zaj duab xis boiling tshwm sim thiab ib tug ruaj khov vapor txheej yog tsim nyob rau hauv lub rhaub nto. Cov txheej vapor insulates lub rhaub, thiab qhov kub thiab txias ntawm qhov chaw nce sai (rau 200-300 degree) thiab caramelizes, chars thiab hlawv tawm. Corrosion tus nqi ntawm titanium hauv cov kua qab zib yog tsawg heev (< 0.01 mm/year) even at high temperature. This is because sugar solutions are neutral (pH 5-7) and non-corrosive. The limiting factor is thermal, not chemical.
Yuav ua li cas qab zib Solutions hlawv tawm
Qhov tseem ceeb ntawm cov hluav taws kub kub (CHF) yog qhov kub siab tshaj plaws ntawm qhov kev hloov ntawm nucleate boiling rau zaj duab xis boiling. Nyob rau hauv lub nucleate boiling, cov npuas nucleate ntawm qhov chaw, cais thiab nce. Npuas detachment yog suppressed los ntawm high viscosity (10-100 × dej) thiab nto nro (1.2-1.5 × dej) ntawm qab zib tov. Cov npuas loj dua thiab nyob ntev dua ntawm qhov chaw, txhawb kev sib koom ua ke thaum ntxov rau hauv cov yeeb yaj kiab vapor. Lub vapor zaj duab xis stabilizes thiab qhov kub ntawm qhov chaw nce ntawm qhov kub qis dua hauv dej. Qhov kub siab ua rau cov piam thaj mus rau caramelize (tshaj li 160 degree) ua rau muaj zog insulating carbonaceous txheej. Qhov tso nyiaj ntxiv insulates qhov saum npoo, nce qhov kub mus rau> 300℃qhov twg titanium oxidizes thiab lub rhaub kub tawm. Tus nqi corrosion ntawm titanium hauv cov kua qab zib (pH 5-7, 100-120 degree) yog tsawg dua 0.01 hli / xyoo thiab 1.5 hli phab ntsa yuav kav> 150 xyoo los ntawm corrosion ib leeg.
Ntsuas qhov pheej hmoo ntawm CHF thiab Burnout hauv Qab Zib Solutions piv rau Dej
Fluid Concentration (Brix) Viscosity @ 100ºC (cP) CHF (W/cm2) Smooth Ti CHF (W/cm2) Burnout Limit Pom Zoo Max. Kev khiav hauj lwm Flux (W / cm2)
Dej 0 0.28 12-15 15-18 CHF 8-10
Qab zib tov 20 1.5 10-12 12-15 CHF 6-8
40 15 7-9 9-11 Caramelize 4-6
Qab zib tov 60 80 4-6 6-8 Caramelization 3-4
Qab Zib tov 70 (tseem ceeb) 200 2-3 3-4 Caramelization 1.5-2 Caramelized deposit (tom qab burnout) N/AN/A < 1 N/A Deposit N/A
Qab Zib Tshuaj Kub Kub: Ib Daim Ntawv Qhia Raws li Scenario
Concentration of Sugar Solution℃BrixOperating Temperature (C) Pom zoo Max Thaum tshav kub kub Flux (W/cm2) Xav Tau Titanium Corrosion Rate (mm/xyoo) Limiting Factor
20 100 6-8 < 0.005 CHF (kub-tawm)
40 105 4-6 < 0.005 Caramelization 50 110 3-4 < 0.005 Caramelization 60 115 2-3 < 0.005 Caramelization 70 120 1.5-2 < 0.005 Viscosity (yuav tsum tau ntws)
Dilute qab zib (< 20° Brix) 100 8-10 < 0,005 CHF (as water)
Txhua qhov yuam kev ncig concentrationAny 2 × saum toj no qhov tseem ceeb <0.005 Flow nce CHF
Engineering Mitigations los txhim kho CHF hauv Qab Zib Solutions
Three mitigations increasing CHF for heating of sugar solution when higher heat flow is necessary. The first mitigation is through forced circulation (pumping) over the heater surface. An increase in flow velocity from 0.5 to 1.0 m/s increases CHF by 50 to 100%. It sweeps away bubbles before they cluster. In a 40° Brix sugar solution forced circulation enhances CHF from 6 W/cm² to 10-12 W/cm². The second mitigation is the roughened heating surface. The density of nucleation sites is increased by sandblasting or milling the grooves, which promotes bubble separation and retards film boiling. The roughened titanium surface (Ra 2–3 µm) is used for enhanced CHF in sugar solutions (20–30 %). The third mitigation is a polished surface (Ra < 0.2 µm) for sugar at high concentration (>60℃Brix). Ib tug du nto txo qhov adherence ntawm caramelized deposits, uas ua rau lub rhaub ua hauj lwm ntawm ib tug ntau dua kub flux ua ntej lub deposition ntawm deposits ua rau overheating.
Cov ntsiab lus: Burnout (CHF) Limits Thaum tshav kub kub, Tsis Corrosion Rate nyob rau hauv qab zib tov
Qhov kub siab tshaj plaws rau lub tshuab cua sov titanium thaum cua sov cov kua qab zib npau npau yog txwv los ntawm qhov kub hnyiab (tseem ceeb heev kub flux) thiab tsis yog los ntawm tus nqi corrosion ntawm titanium. Cov tshuaj qab zib tsis yog-corrosive rau titanium (pH 5-7, corrosion rate < 0.01 mm / xyoo) thiab tej zaum yuav ua rau lub neej kev pab ntawm> 100 xyoo vim yog corrosion ib leeg. Txawm li cas los xij, qhov viscosity siab thiab qhov nro ntawm cov kua qab zib txo cov CHF mus rau 4-10 W / cm² (nyob ntawm qhov concentration) tawm tsam 12-15 W / cm² rau dej. Kev ua haujlwm saum toj no CHF ua rau cov yeeb yaj kiab kub, qhov kub thiab txias nce mus rau 200-300 degree, caramelization, charring thiab burnout. Rau cov kev daws teeb meem ntawm 40-60℃Brix, qhov siab tshaj plaws kub flux qhia rau atmospheric boiling yog 3-6 W / cm^2. Thaum xav tau kom muaj cua sov ntau ntxiv, roughened los yog polished nto tuaj yeem txhawb CHF los ntawm 20-100% nrog kev yuam kev. Piv txwv li, thaum siv lub tshuab cua sov titanium hauv kev pabcuam qab zib, tus neeg muag khoom yuav tsum paub txog qhov concentration ntawm cov tshuaj, qhov kev kwv yees txaus txaus, thiab lub zog ntom ntom uas tsim nyog txhawm rau txhawm rau kwv yees CHF thiab xaiv qhov kev kho saum npoo kom tiv thaiv kev hlawv.
