Conventional Hot-Wire Anemometer

Transcription

1 Convnonal Ho-Wr Anmomr

2 cro Ho Wr

3 Avanag much mallr prob z mm o µm br paal roluon array o h nor hghr rquncy rpon lowr co prormanc/co

4 abrcaon roc I µm lghly op p layr 8µm havly boron op ch op layr

5 abrcaon roc II

6 cro Ho Wr

7 Opraon rncpl o cro Ho Wr - Ho wr anmomry u h convcv ha ranr rom rom ha nor o h urrounng lu o maur h vlocy. - h amoun o ha ranrr pr un m nrr rom an lcrc gnal ha rla o h mpraur o h nor. - h gnal rul rom h unqu rlaonhp bwn h mpraur an ranc o h nor. o [ - o ] whr o an o ar h ranc an mpraur a a rrnc conon, an : mpraur cocn o ranc C - Ovrha rao o / [ o - o ] / o - v ovrha rao - o / o - o / o o

8 Bac ha ranr mchanm - Ha nrouc no h nng lmn by Joul hang an lo by convcon, conucon an raaon. q ka / x x q c hs h: convcv ha ranr cocn S: ara : mpraur o nor : mpraur o lu nvronmn Q mc o [ - o ] q r σs 4 4 σ: San-Bolzmann conan 56.7 nwm - K -4 S: raang ara : mpraur o nor : mpraur o lu nvronmn h raaon lo much l han h convcon lo.

9 - h m ra chang o nrgy whn h nng lmn mu qual h rnc bwn h powr npu an h ha lavng h vc. Q Q h m ra chang o nrgy whn h nng lmn,, h lnarz nrgy quaon: h nrgy quaon q q c q r

10 h Conan Currn Anmomr / o ruc h currn lucuaon o a rlavly mall valu rqur / << So mu b larg. h x ror houl b ucnly larg o lmna h pobly o accnally burnng ou h wr whn hr h varabl ror or h vlocy cra. h currn hrough h nor can b rmn by maurng h volag rop acro.

11 Govrnng Equaon or conan currn mo o opraon,, h ym orc by h vlocy lucuaon alon. m Conan

12 m Conan o rmn m conan, an nananou chang n currn or vlocy Soluon: τ τ τ xp m Conan

13 m Conan o a cro Ho Wr I a nay ha balanc ovr a mcro ho wr: Q Q mc ρhwc l o [ - o ] hc S hc w h l ur hwcl ρ ] hc w h l [ ρhwcl [ hc w h l ] l [ hc w h l ] ρhwcl hc w h l ρhwcl [ hc w h l ]

14 m Conan o a cro Ho Wr II b ay a ha balanc ovr a mcro ho wr: hu: l h w h c ] [ ] [ c l h w h c Emaon o h m conan, : ] [[ ] ] [ [ ] [ c hwcl hwcl l h w h hwcl ρ ρ ρ hwl c hwcl ρ ρ - / - / - o / o hwl c hwcl ρ ρ maral gomry Oprang conon

15 m Conan o a cro Ho Wr III or polylcon nor: ρhwcl ρc hwl maral gomry Oprang conon ρ.gm / c.7 Joul / gmk Ω % / K h.5µm w µm l µm ρhwcl ρc hwl µ c.5 ma

16 h Conan mpraur Anmomr CA h bac lmn o a conan mpraur anmomr crcu ar a rnal c amplr, h nng lmn an a rrnc volag. h nor plac n on lg o a Whaon brg. h currn hrough h lmn gv a volag. A rrnc volag u by h back amplr o rmn how much h ranc, an hnc mpraur, o h nor ha chang. h oban by. 4 h wo volag orm h npu o h rnal amplr. h amplr oupu currn nvrly proporonal o h ranc chang n h nor. 5 h currn back no h op o h brg an ror h nor ranc an mpraur o hr orgnal valu.

17 CA Equaon h conan mpraur mo o opraon o a howr man ha h mpraur or ranc lucuaon o h nng lmn ar nglgbl compar o h currn lucuaon. / <<,, /,, h ynamc rpon o h conan mpraur anmomr ar rmn by hr bac quaon ha h brg, h nng lmn, an h amplr. brg: [ ] [ ] Nglc h nonlnar n orr rm an [ ] [ ] / /

18 a Inally wo o h brg hav qual volag, h rnal npu o h amplr zro, gvng a zro oupu. Balanc brg: b nr balanc conon, an o volag a o h amplr. h volag ablh a man currn hrough h nor, whch mak h brg m o hav a lghly hghr ranc n on lg. hu on can conr h man ranc n h nor o b δ δ unbalanc paramr whch rmn h nor oprang mpraur an ovrha. δ δ o

19 c or compln, a gnal nrouc hrough a ror.i larg compar o h ohr ror n h brg, h volag no h amplr gvn by g, whr h gnal gnraor volag, an g h anuaon u o an h brg. g δ ] [ ] [ ] [ g δ Nglc h nonlnar n orr rm an ub g ] [ δ g δ nr balanc conon: g δ

20 h nng lmn: b a o [ - o ] / o a b

21 h amplr: A µ m conan Amplr c gan ] [ h ynamc rpon o h conan mpraur anmomr b a g δ A µ 4 Combn an o lmna, o lmna an 4 bcom ]} [ { S S ω ω ζω

22 ]} [ { S S ω ω ζω rquncy naural K : / / µ ω vlocy h y o nv S : gnal : h y o nv g S paramr gan ym A K : cn ampngco K K : / / µ δ ζ

23 or h ollowng paramr: 6 c : mcro ho wr m conan µ 5 c : amplr m conan.5 A : amplr gan A K : ym gan paramr ω 5 6 / 8.5 /. c h characrc rquncy : ω 5 hz π

24 rquncy oluon r orr ym: m conan hrmal lag orcng uncon.g. conan currn ho-wr Scon orr ym: ω ζ ω S ω ronanc rquncy ζ- ampng cocn S - nvy orcng uncon.g. conan mpraur ho-wr