An Experimental Study of the Friction Factor and Mass Transfer Performance of an Offset-Strip Fin Array at Very High Reynolds Numbers

Abstract

Thermal-hydraulic performance data for offset-strip fin arrays are readily available in the range Re<10,000. However, in emerging applications in automotive and aerospace systems, where fan power is not a constraint and compactness is important, it may be desirable to operate offset-strip fin heat exchangers at very high Reynolds numbers. In this paper, friction factor and mass transfer performance of an offset-strip fin array at Reynolds numbers between 10,000 and 120,000 are characterized. A scale-model, eight-column fin array is used in pressure drop and naphthalene sublimation experiments, and the data are compared to predictions of performance given by available analytical models and extrapolations of the best available correlations. The friction factor data follow the correlation-predicted trend of decreasing monotonically as the Reynolds number is increased to 20,000. However, at higher Reynolds numbers, the friction factor increases as the Reynolds number increases and local maxima are observed in the data. Over the range investigated, the modified Colburn j factor decreases monotonically as the Reynolds number increases. For Reynolds numbers in the range 10,000<Re<120,000, well beyond that covered by state-of-the-art correlations, both the friction factor and Colburn j factor are roughly twice that predicted by extrapolating the best available correlations. The higher-than-predicted Colburn j factor at very high Reynolds numbers is encouraging for the use of offset-strip fin heat exchangers in emerging applications where compactness is of high importance.