Hibiscus sabdarifla (Roselle) powder was produced by pilot scale spray drying using single strength and vacuum concentrated water extract of its calyces. Powders were analyzed for moisture, protein, vitamin C, total soluble solids (TSS), pH, particle size, bulk density, solubility, dispersibility, hygroscopicity, and microbiological status. The lowest inlet air temperature (198.5"C) resulted in the product with best protein content (12.43%), retention of vitamin C (82.76 mg/ lOOg), and solubility (dissolving in 97 set); as well as the highest moisture content (3.78%) in the product. The powder showed a noticeable tendency to stick to internal surfaces of the drying chamber particularly with concentrated solutions at higher temperatures.

Heat transfer rates were measured for steam-heated, rotating cans containing potato spheres in water. Can rotational speed (9.3-101 rpm), sphere size (22.2-35.0 mm), and potato volume fraction (0.107-0.506) were varied in 14 triplicated experiments. Overall heat transfer coefficients were correlated within 225% with physical properties and operating variables by an equation derived by dimensional analysis. Film coefficients (h,) for heat transfer from the water to potatoes in the can were determmed by thermocouple measurement of potato surface temperatures; values were found to be finite and nearly invariant, averaging h, = 160 * 30 W/m*K. The lack of variation of hp suggested that for the experimental conditions tested, there was little relative motion between liquid and particles.

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