Surface Heat Transfer Coefficients for Steam/Air Mixtures in Two Pilot Scale Retorts

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Abstract
Surface heat transfer coefficients (h) for steam/air mixtures were studied in a vertical, positive flow retort and a horizontal, forced circulation Lagarde retort, using rectangular metal bricks. Influences of test brick orientation and fractional steam content (S), temperature, flow rate and direction of the heating medium on h values were studied. In both retorts, steam content was found to be the major factor (p < 0.05) influencing h, while temperature had no effect (p > 0.05). Flow direction and flow rate in the positive flow retort, and brick orientation in the Lagarde retort also influenced h. Exponential equations, h = a exp (bS), described relationships between h and S, with a and b dependent upon retort type, flow rate, flow direction and test brick orientation.