Određivanje stagnantne toplotne provodljivosti baliranog sojinog ostatka

Abstract

U ovom radu prikazani su rezultati eksperimentalnih istraživanja određivanja stagnatne toplotne provodljivosti poroznog sloja balirane biomase, koja predstavlja jednu od najvažnijih termofizičkih karakteristika ovog materijala sa tačke gledišta sagorevanja u potisnim ložištima (sa tzv. cigaretnim sagorevanjem). Dobijena zavisnost značajna je za optimalizaciju procesa sagorevanja balirane biomase, kao i za proces modeliranja transportnih fenomena u poroznom sloju balirane biomase, pri tzv. cigaretnom sagorevanju. Radi određivanja stagnatne toplotne provodljivosti balirane sojine slame, osmišljena je odgovarajuća eksperimenatlna metoda i projektovana i izrađena odgovarajuća eksperimentalna instalacija. Eksperimentalnim istraživanjima ispitivan je uticaj, relevantnog parametra balirane biomase (poroznosti sloja) na stagnatnu toplotnu provodljivost. Na osnovu sprovedenih merenja, kao i analize eksperimentalnih rezultata, definisana je funkcionalna zavisnost stagnatne toplotne provodljivosti od poroznosti u opsegu od 0,45-0,8. Dobijeni rezultati pokazuju da smanjenjem poroznosti sloja dolazi do smanjenja vrednosti stagnatne toplotne provodljivosti, što može da se objasni smanjenjem zapremina pora, odnosno vazduha, koji aktivno učestvuje u procesu prenošenja toplote kroz porozni sloj. Stagnatna toplotna provodljivost, kao i njena zavisnost poroznosti, polazne su osnove u matematičkom modeliranju procesa sagorevanja balirane biomase po principu cigarete, a takođe mogu biti veoma značajni pri analizi eventualnih konstrukcionih izmena na ložištu, koje radi na ovom principu.

The paper presents results of experimental determination of the stagnant thermal conductivity coefficient of a porous bed formed by biomass bales. The said coefficient represents one of the most important parameters of the bed material specified when considering its combustion in the pusher-type furnaces (i.e. combustion of biomass bales in cigar burners). Correlation obtained is deemed very important for optimization of biomass bale combustion, as well as for modelling transport phenomena occurring in the porous bed formed by biomass bales during their combustion in cigar burners. In order to determine stagnant thermal conductivity coefficient of soy bean straw bales, appropriate experimental method and suitable experimental apparatus were designed and constructed. Experimental investigation was conducted in order to study the effects of relevant biomass bale parameter, i.e. porosity on the stagnant thermal conductivity coefficient. Based on analysis of the said measurement, the results of the functional dependencies of the stagnant thermal conductivity coefficient on the porosity, which was varied in the range 0.6 - 0.8, were defined. Performed experiments have shown that the stagnant thermal conductivity of baled straw decreases with decreasing porosity of the sample, which can be explained by reduction of the closed pores volume, and, accordingly, fluid within them has reduced ability of circulation which causes reduced intensity of heat transfer between the pore walls. The data obtained through investigation are deemed very useful in developing a detailed CFD model for combustion of straw bales in cigar burners.