Performance of a Scraped-Surface Heat Exchanger Under Ultra High Temperature Conditions: A Dimensional Analysis |
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| Authors: | ROBERTO CUEVAS MUNIR CHERYAN VERNON L PORTER |
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| Affiliation: | Authors Cuevas, Cheryan, and Porter are, respectively, graduate research assistant, associate professor of food engineering, and professor assistant, Dept of Food Science, Dairy Manufactures Building, Univ. of Illinois, 1302 W. Pennsylvania Ave., Urbana, IL 61801. |
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| Abstract: | Performance characteristics of a pilot-scale scraped-surface heat exchanger (Contherm Model 6 × 2) under UHT operating conditions were evaluated. Outlet temperature and overall heat transfer coefficient (U) were significantly affected by rotational speed of the blades, mass flow rate of feed, feed inlet temperature, steam pressure and solids content of the model low-acid liquid food (soy extracts). The scraping action of the blades greatly improved the performance up to about 350 rpm; higher blade speeds had little or no effect and sometimes decreased U values. Application of dimensionless models showed that the effect of axial Reynolds number (ReA) on the Nusselt number was more significant in the turbulent regime (ReA > 1800), while rotational Reynolds number above 105 had a significant effect at all values of ReA between 1200 and 3700. At very high values of the Taylor number (> 1010) when laminar axial flow conditions prevailed, Nusselt number decreased with increase in rotational Reynolds number. |
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