Why Does PFA's Non-Stick Characteristic Sometimes Reduce the Heating Efficiency When Dealing with High-Viscosity Media?

Thaum tsim lub tshuab tso cua sov rau cov dej viscosity siab xws li cov nplaum nplaum kub, cov tshuaj polymer cov ntsiab lus, bitumen los yog epoxy resins, engineers feem ntau hais tias PFA (perfluoroalkoxy alkane) sheaths rau lawv yuav luag universal tshuaj tiv thaiv thiab superb non{0}} nplaum nto. Qhov du, qis -kev sib txhuam fluoropolymer npog yuav tsum tshem tawm cov khoom ua kom tiav- ntawm qhov tso nyiaj, txo qis ntawm kev tu lub sijhawm thiab ua kom cov cua sov kom huv si mus ib txhis. Txawm li cas los xij, cov ntaub ntawv teb los ntawm cov kab ua haujlwm txuas ntxiv polymer thiab cov nplaum tuav cov tso tsheb hlau luam qhia qhov tshwm sim xav tsis thoob: qhov tsis zoo - tus yam ntxwv uas ua rau PFA xav tau tuaj yeem, nyob rau hauv qee qhov dej ntws ntws, txo qhov muaj peev xwm hloov hluav taws xob ntau. Qhov no yog ua los ntawm kev txhim kho ib tug ruaj khov thermally insulating ciam txheej txheej uas sticks weakly rau lub rhaub, tab sis yog tuav tawm tsam nws los ntawm lub siab viscosity ntawm tej kua. Txhawm rau kom nkag siab qhov cuam tshuam no, peb yuav tsum tau saib cov dej dynamics ntawm lub rhaub -kua interface thiab tsis yog ntawm cov khoom tsis muaj.

Qhov qis-Adhesion Nto Viscous Sublayer Phenomenon
Nyob rau hauv ib qho kev quab yuam los yog ntuj convection cua sov, cov kua txheej nyob ze rau ntawm cov phab ntsa khoom muaj qhov qis tshaj tawm tshaj qhov ntau ntws. Rau cov kua dej uas tsis muaj viscosity xws li dej los yog cov kua qaub diluted, cov ciam teb no feem ntau yog tsawg dua 0.5 hli tuab thiab nws cov nyhuv insulating me me piv rau tag nrho cov tshav kub hloov coefficient. High -viscosity media (ntawm no txhais tau tias yog dynamic viscosity> 500 cP ntawm kev ua haujlwm kub) ua qhov sib txawv. Lub zog diffusivity tsawg heev uas cov viscous sub- txheej tuaj yeem yog 3-8 hli los ntawm lub tshuab cua sov, tshwj xeeb tshaj yog nyob rau hauv cov tso tsheb hlau luam quiescent yam tsis muaj kev ntxhov siab.

Cov txheej no txav maj mam ntawm tus qauv hlau rhaub nrog qhov nruab nrab ntawm qhov roughness (Ra 0.8-1.6 µm). Thaum tshav kub kub pauv tshwm sim los ntawm ntuj convection nyob rau hauv lub txheej nws tus kheej, tsim micro-scopic mixing eddies kom refresh cov kua nyob rau hauv kev sib cuag nrog lub kub phab ntsa. Los ntawm qhov sib txawv, PFA nto muaj lub zog qis heev (tus nqi ib txwm 18-20 mN / m) thiab zoo heev (Ra nquag<0.2 µm) and this prevents any inclination of the adjacent layer to detach or roll over. The high-viscosity fluid just glides over the fluoropolymer surface without producing disruptive flow patterns. As a result, the thermal boundary layer is much thicker and more stagnant than that on a surface with intermediate roughness or higher adhesion. Infrared thermography quantitative measurements of the steady‑state boundary layer thickness on PFA were 2.3 times that of a stainless steel 316 sheath for the same power input and tank geometry in a bath of 10,000 cP silicone oil at 150 °C.

Quantification ntawm lub tshav kub hloov txim: los ntawm kev xav mus rau cov ntaub ntawv ntsuas.
Qhov txo qis hauv cov cua sov ua kom zoo yog qhov tshwm sim ncaj qha ntawm Fourier txoj cai raws li siv rau cov viscous sub-layer. Lub tshav kub ntws q yog qhia raws li q=h (Tsurface − Tbulk) qhov twg h yog lub convective heat transfer coefficient. Rau cov kua dej Pr siab (Pr> 100, feem ntau rau cov xov xwm viscous) Nusselt tus lej sib raug zoo Nu=h·L/k muaj qhov cuam tshuam loj heev ntawm phab ntsa "wettability" lossis adhesion feature, uas PFA lub hom phiaj txo qis. Kev sim cov ntaub ntawv los ntawm kev soj ntsuam kuaj uas siv 50,000 cP polybutene kua ntawm 180 degree, ua nrog zoo tib yam heater geometries nrog rau kev zam ntawm cov ntaub ntawv sheath, qhia tau hais tias PFA- sheathed heater mus txog qhov siab tshaj plaws ntawm qhov kub ntawm 220℃ua ntej mus txog ib tug kub flux ntawm ib tug ^ 1 cm 2. (Ra 1.2 µm) mus txog 2.9 W / cm^2 nyob rau hauv tib qhov kub thiab txias txwv. Hauv lwm lo lus, qhov tsis yog -stick xwm ntawm PFA txo qis lub zog muaj txiaj ntsig zoo li ntawm 38% rau qhov tshwj xeeb siab - viscosity kua. Qhov no yog qhov pom tseeb ntau dua thaum cov kua muaj cov khoom tshem tawm lossis cov fibers, uas nyob rau ntawm qhov chaw ntxhib yuav ua haujlwm raws li micro-agitators, tab sis ntawm PFA tsuas yog hla dhau yam tsis muaj kev cuam tshuam ntawm ciam txheej.

Vim li cas "Clean Surface" dhau los ua qhov cuam tshuam thaum tsis txav mus los
Cov yam ntxwv tsis zoo tib yam uas txwv tsis pub ci - ntawm cov nyiaj tso cia kuj tseem txwv tsis pub tsim cov txheej txheem thermal ciam teb uas ruaj khov, uas tuaj yeem cuam tshuam ib ntus los ntawm kev hloov pauv. Nyob rau hauv ib lub tank nrog mechanical agitation los yog recirculation tus nqi no yog txo txij li thaum lub bulk ceev tsis tu ncua sweeps deb ntawm kub ciam teb txheej. Ntau cov txheej txheem siab -viscosity, txawm li cas los xij, txhob txwm siv qhov nruab nrab lossis tsis sib haum xeeb kom tsis txhob muaj cov kua dej los yog degradation ntawm shear-sensitive polymers. Hauv qhov xwm txheej zoo li no, lub plhaub tseem ceeb ntawm cov kua dej kub siab viscosity tuaj yeem ntim PFA sheath thiab ua raws li daim pam thermal. Cov duab infrared ntawm lub tshuab cua sov PFA hauv 100,000 cP bitumen ntawm 160℃rau ob teev tau pom qhov chaw ruaj khov ntawm cov kua dej li 5 hli tuab nrog qhov kub txog li 8-12℃tsawg dua li cov ntaub qhwv qhov chaw thaum qhov kub thiab txias ntau ntau tom qab. Lub tshuab cua sov hlau nrog tib lub geometry tab sis me ntsis siab dua lub zog saum npoo tsim tau pom cov plumes convective uas tshem tawm ntawm qhov chaw tsis tu ncua, ua rau 40% sai dua lub sijhawm sov so.

Phau Ntawv Qhia Kev Xaiv Sib Piv: Thaum Tsis yog - lo PFA Yog (lossis Tsis Yog) Qhov Zoo Tshaj Plaws rau Cov Cuab Yeej Cuab Yeej
Kev txiav txim siab ua raws li cov txheej txheem tseem ceeb, qhov viscosity ntau yam thiab qhov kev lag luam uas tau txais - tawm ntawm kev ntxuav yooj yim thiab thermal efficiency yog muab rau hauv cov lus hauv qab no. Ua ntej thaum kawg txiav txim siab ntawm cov khoom siv sheath engineers yuav tsum xyuas cov Prandtl tus naj npawb ntawm lawv tus kheej cov kua thiab cov ciam ciam txheej thickness los ntawm txoj kev ntawm ib tug yooj yim lab beaker xeem.

Txheej Txheem Txheej Txheem & Viscosity Range Pom Zoo Sheath Material & Nto Core Rationale rau cua sov Efficiency
High viscosity (1,000-100,000 cP) quiescent tank tsis muaj agitation ntev tuav lub sij hawmRoughened hlau (xws li stainless hlau, Incoloy) los yog PFA nrog tailored micro-textureMetal nto ua rau micro-convective cuam tshuam ntawm viscous sub-txheej txheem los ntawm PFA piv rau 3.0% 0.0 Txais kev tu ncua sij hawm rau siav ntawm cov nyiaj tso cia. *
High viscosity, nruam recirculation (Re> 2,300 nyob rau hauv lub cua sov voj) Standard smooth PFA Bulk flows sweeps ciam teb txheej tsis tu ncua. Nonstick kom zoo dua inhibits deposit build-up. Me me (<10%) heating efficiency penalty compared to metal.
Nruab nrab viscosity (100{1}}1000 cP), maj mam agitation los yog qee zaus stirringPFA nrog nto embossing los yog helical grooves Engineered kev ntxhib los mos tsoo cov ciam teb txheej thaum tseem tsis tau-stick tawm ntawm cov kua dej feem ntau. Kev sib haum xeeb zoo tshaj plaws rau kev hloov hluav taws xob thiab kev huv.

Polymer yaj (shear rhiab heev) (xws li PVC plastisol, PU prepolymer) Khaws tsis yog -stick, tsis txhob degrading cov khoom. Oversize heater los them rau 30-40% hluav taws xob hloov hluav taws xob