Raspodela rashladnog fluida i ulja u rashladnim sistemima na primeru automobilskog klima-uređaja
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Apstrakt
U radu je prikazan polu-empirijski model za predviđanje količine rashladnog fluida i lubrikanta (sredstva za podmazivanje) i u mikronanalnom kondenzatoru i u isparivaču sa orebrenim pločama jednog klima-uređaja (sistema za klimatizaciju). Na modelu je razmenjivač toplote diskretizovan u konačne zapremine. Temperatura, pritisak i masa su izračunati primenom korelacija prenosa toplote, pada pritiska i udela praznine na svaku od ovih zapremina. Rashladni fluid i lubrikant su tretirani kao zeotropska mešavina sa klizanjem temperature. Budući da rashladni fluid isparava ili se kondenzuje, izvršena je procena termofizičkih svojstava u skladu sa promenom koncentracije lubrikanta. Pretpostavka je da se ulje zadržava u mešavini rashladnog fluida i ulja u koncentraciji koja se menjala tokom fazne promene u kondenzatoru i isparivaču. Eksperimentalni podaci sa R134a i uljem PAG pokazuju slaganje od 20% sa modelom rashladnog fluida i zadržavanja ulja u isparivaču. Međutim, u kondenzatoru, masa lubrikanta je stalno bila predviđana u manjoj vrednosti, dok je masa rashladnog fluida bila predviđena u istoj vrednosti kao u isparivaču (u okviru greške od 15%). Takođe predviđanje manje vrednosti lubrikanta postalo je značajnije pri višem koeficijentu cirkulacije ulja (Oil Circulation Ratio - OCR). Analiza je pokazala da se sredstvo za podmazivanje odvojilo iz toka u kolektoru kondenzatora i počelo da se akumulira u kanalima na dnu. Temperaturni profil na infracrvenoj slici podržava ovu hipotezu, jer je temperatura u kanalima na dnu bila znatno niža.
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