Yuav ua li cas Nucleation ntawm Boiling Npuas ntawm PTFE Rhaub Deg cuam tshuam rau cov cua sov hloov?

Thaum lub PTFE immersion rhaub yog rhuab saum toj no qhov kub thiab txias nws tsis tsuas yog cua sov cov kua ib puag ncig ntsiag to. Hloov chaw, nws dhau los ua qhov chaw zoo nkauj ntawm cov vapor tawg me me. Cov npuas me me nucleate nyob rau saum npoo ntawm lub plhaub, txhim kho sai, tshem tawm thiab nce los ntawm cov kua, tshem tawm cov thermal zog ntau hauv cov txheej txheem. Qhov kev hloov pauv no los ntawm cov kua convection ib txwm mus rau nucleate boiling yog ib qho kev hloov pauv tseem ceeb tshaj plaws hauv kev coj tus cwj pwm thermal ntawm lub rhaub.

Kev sib cuam tshuam ntawm tus PTFE nto thiab vapor npuas tsim txiav txim siab qhov ua tau zoo ntawm cov cua sov hloov mus rau hauv cov dej nyob ib puag ncig hauv kev tshawb fawb ntawm nucleate boiling PTFE rhaub saum npoo cua sov.

Yog vim li cas PTFE coj txawv txawv hauv boiling
Kev cuam tshuam ntawm lub tiaj tus, qis - lub zog nto
PTFE tau lees paub zoo rau nws cov khoom tsis zoo - nplaum thiab lub zog qis heev. Tib yam zoo uas muab PTFE nws cov tshuaj tiv thaiv thiab tiv thaiv fouling kuj cuam tshuam li cas boiling yog pib ntawm nws nto.

Lub vapor npuas tsuas tuaj yeem nthuav tawm yog tias muaj qhov chaw minuscule nucleation uas ruaj khov rau lub hnab me me ntawm cov pa. Cov khawb me me, qhov pits, thiab qhov tsis xws luag ntawm cov hlau ntxhib ib txwm ua haujlwm ua qhov chaw nucleation.

PTFE ua txawv vim:

Qhov saum npoo yog smoother.

Lub zog saum npoo yog tsawg

Cov kua dej muaj qhov ua tsis zoo

Thawj qhov kev tawm tsam rau kev tsim npuas ruaj khov

Yog li, boiling feem ntau yuav tsum tau siab dua ntawm superheat pib.

Superheat yog dab tsi?
Superheat yog qhov sib txawv ntawm lub rhaub dej kub thiab qhov kub ntawm cov kua. Txij li thaum PTFE resists npuas nucleation, lub plhaub saum npoo yuav tsum yog kub dua li cov hlau sib npaug ua ntej vapor npuas tuaj yeem tsim tau zoo.

Qhov no qhia txog kev ncua me me hauv qhov pib ntawm boiling.

Lub PTFE tuav mus rau qhov kub thaum xub thawj, tab sis thaum nws pib, nws npau taws nrog kev npau taws me ntsis txawv txawv.

Hloov ntawm Convection mus rau Nucleate Boiling
Cua sov ntawm Natural Convection
Lub tshav kub thauj ua ntej qhov pib ntawm nucleate boiling yog dominated los ntawm ntuj convection. Nyob rau hauv no regime:

Cov kua dej sov nce mus rau hauv lub hnab

Nws yog hloov los ntawm cov kua txias

Thaum tshav kub kub hloov lwm lub tsev yog tseem me ntsis

Cov kua dej yog qhov me me thiab txwv.

Pib ntawm Nucleate Boiling
Thaum lub superheat qhov pib dhau lawm, npuas nucleation tuaj yeem tshwm sim sai. Active nucleation sites ntawm PTFE sheath nto pib tsim vapor npuas.

Nyob rau theem no:

Nce nyob rau hauv tus nqi ntawm npuas tsim

Txhim kho qhov sib xyaw ua kua

Nto turbulence yog nce

Ib qho kev txhim kho sai ntawm kev hloov hluav taws xob

Qhov no yog qhov pib ntawm nucleate boiling uas yog ib qho ntawm cov khoom siv hluav taws xob sib kis tau zoo tshaj plaws hauv cov kua cua sov.

Vim li cas Nucleate Boiling Txhim Kho Thaum Kub Hloov
Bubble Motion raws li ib tug Mechanism ntawm Thaum tshav kub kub thauj mus los
Hauv nucleate boiling, npuas ua haujlwm rau ntau lub luag haujlwm tseem ceeb hauv thermal ib txhij.

Thaum npuas tsim thiab thaum lawv tawg:

Latent cua sov ntawm vaporization absorbed cua sov

Tshiab, cov kua dej txias dua tuaj rau saum npoo

Ciam cov khaubncaws sab nraud povtseg

Kev cuam tshuam hauv zos nce siab heev

Qhov kev kub ntxhov ntawm cov kua no ua rau kom cov cua sov hloov coefficient ntau heev.

Thermal zog tuaj yeem raug tshem tawm ntawm lub tshuab cua sov kom zoo dua li qhov yooj yim convection los ntawm nucleate boiling.

Me me, nrawm-Bubbling Away (txuas ntxiv)
Qhov saum npoo du ntawm PTFE txhawb kev tsim cov npuas me me ntau dua li ob peb qhov loj txuas. Lub zog nto qis pab ua npuas kom tawm sai sai thaum lawv loj dua qhov loj me.

Fast npuas tawm muaj ntau yam zoo:

Daim pam los ntawm vapors txo

Txhim kho kua hloov

Ntau zog nucleation cycles.

Txhim kho nto cheb

Cov kua txav mus thiab cov npuas npuas tawm hauv qhov chaw ntws tawm ntawm lub qhov txhab mus tas li, yog li ua kom muaj txiaj ntsig ntawm kev sib pauv thermal.

Watt Density Qhov tseem ceeb
Boiling Regime Power Matching of Rhaub
Lub watt ceev yuav tsum tau txiav txim siab xaiv xws li tias PTFE immersion rhaub ua hauj lwm yam xyuam xim nyob rau hauv lub nucleate boiling tsoom fwv.

Cov ntsiab lus tseem ceeb yog:

Cov khoom ua kua

Kua boiling kub

viscosity ntawm cov kua

Tank agitation theem

Flow ceev

Cov cua kub sib txawv

Yog hais tias lub watt ceev tsis siab txaus, boiling tej zaum yuav tsis tag kev loj hlob, uas yuav txwv thermal ua hauj lwm. If the watt density is too high, the boiling process may become unstable and hazardous.

dej agitation thiab txav
Mechanical agitation los yog yuam kev ncig uas ua rau muaj kev cuam tshuam zoo rau tus cwj pwm ntawm nucleate boiling:

Kev tshem tawm sai dua ntawm vapor npuas

Txhim kho kua refilling

Txhim kho qhov tseem ceeb ntawm cov cua sov flux

Stabilization ntawm tshav kub hloov

Cov txheej txheem zoo agitated feem ntau muaj peev xwm txhawb nqa cov watt loj dua kom nyab xeeb dua li cov kua dej stagnant.

Film Boiling thiab Critical Heat Flux

Nucleate boiling yog qhov xav tau heev tsuas yog nyob rau hauv kev nyab xeeb kev ua haujlwm txwv Qhov kev txwv siab dua no hu ua qhov tseem ceeb ntawm cov cua sov (CHF).

Hauv Fr. ces:

Qhov tsim ntawm npuas tau tuab heev

Vapor pam pib tsim

Txo cov kua muaj nyob rau hauv sheath

Saum toj no txwv txoj cai ntawm boiling yog qualitatively txawv.

Zaj Dab Neeg Boiling Transition
Tshaj qhov tseem ceeb ntawm cov hluav taws kub kub, cov txheej txheem txuas ntxiv ntawm cov vapor tuaj yeem tsim nyob ib ncig ntawm lub tshuab cua sov. Qhov no yog hu ua film boiling.

Zaj duab xis boiling yog teeb meem vim vapor yog ib tug kuj tsis zoo tshav kub kis nruab nrab piv rau cov kua. Qhov kub ntawm lub rhaub dej tuaj yeem nce siab.

Qhov tshwm sim tuaj yeem yog:

Overheating ntawm PTFE

Sheath puas

Thaum tshav kub kub degradation

Cua sov, tsis ua haujlwm

Lub neej ua haujlwm luv dua

Nws yog qhov tseem ceeb, hauv kev tsim cov cua sov PTFE, ua haujlwm zoo hauv qab CHF.

Vim li cas PTFE tuaj yeem txhawb nqa Boiling kom zoo
Thermal Performance Counterintuitive
PTFE tej zaum yuav paub zoo tshaj plaws rau nws cov rwb thaiv tsev thiab tshuaj inertness tab sis nws tus cwj pwm nto thaum lub sij hawm nucleate boiling yuav ua tau zoo heev nyob rau hauv muab kub hloov tom qab boiling yog pib.

Qhov sib tov ntawm:

Npuas ejection sai

Agitation ntawm cov kua hnyav

Nruam nucleation 

Ua tau zoo latent tshav kub rho tawm

tsim ib tug heev nquag thermal interface.

Rau ntau daim ntawv thov cua sov nrog kev tswj boiling, qhov no yog vim li cas PTFE immersion heaters raug tsim yog heev npaum.

Cov tswv yim xav txog hauv Kev Tsim
Sizing ntawm Cua sov
Kev ua haujlwm nyab xeeb yog nyob ntawm qhov sib txuam ntawm:

Watt ceev cua sov

Cov kua dej chemistry

Qhov kub ntawm kev ua haujlwm

Tank tsim

Cov qauv ntws

Rhaub tshaj -sizing ua rau muaj kev pheej hmoo ntawm zaj duab xis boiling thiab overheating hauv zos.

Cov xwm txheej ntawm Nto
PTFE yog inherently foul resistant. Txawm li cas los xij, kev tso nyiaj ntau dhau los yog cov sludge tsim- tuaj yeem cuam tshuam cov npuas dynamic thiab txwv kev xa hluav taws xob.

Kev tshuaj xyuas tsis tu ncua muab tus cwj pwm tsis tu ncua nucleate boiling.

Qhov System Control Stability
Kev tswj qhov kub thiab txias kom tsis txhob muaj qhov tsis tsim nyog rau kev caij tsheb kauj vab thiab tiv thaiv kev kub ntxhov hauv cov cua sov uas tuaj yeem ua rau npau taws.

Summary thiab xaus
Qhov kub ntawm PTFE lub rhaub dej yog ob- sab thermal nyhuv. Tus du, qis- lub zog sheath inhibits npuas tsim thaum xub thawj thiab yuav tsum tau superheat ntau dua ua ntej nucleation pib. Tab sis thaum qhov teeb meem no raug ua txhaum cai, nucleate boiling yog heev muaj zog thiab xav tsis thoob, zoo heev boosting lub zog ntawm tshav kub rau hauv cov kua.

Qhov teeb meem tseem ceeb hauv engineering hauv nucleate boiling tshav kub kis tau los ntawm PTFE rhaub qhov chaw yog kom sib npaug tswj nucleate boiling thiab teeb meem zaj duab xis boiling. When watt density, fluid agitation and heat control are properly chosen, the boiling process remains safely inside the highly efficient nucleate regime.

Qhov nyuaj txav ntawm npuas thoob plaws PTFE sheath thaum kawg hais tias yuav ua li cas aggressively lub thermal hwj chim yuav raug thawb thaum khaws cia kev nyab xeeb thiab kev cia siab ntawm lub rhaub.