THE MACARONI DRYER
Based on data obtained from the laboratory dryer, a 500?kg macaroni solar dryer was designed, tested, and applied by a food company in Ho Chi Minh City. The dryer is based on the air reversal principle (fig. 2), which has been applied widely for paddy drying in the Mekong Delta and Vietnam since 2001 (Hien et al., 2003). Advantages of air reversal drying include: saving of land space; mechanization, meaning less manual labor; and multi‐crop use, including high‐moisture products such as coffee, sliced cassava, and longan. The dryer has three components: a two‐stage axial‐flow fan, a drying bin containing 500 kg of macaroni wherein the air flow can be set upwards or downward, and a solar collector. The collector consists of two parallel 1 m diameter, 25 m long horizontal cylinders, made from heavy polyethylene (PE) transparent sheet, with black PE sheet inside as heat absorbers (fig. 3). In this case, the solar collector replaces the coal furnace of an existing macaroni dryer, which had consumed 6 kg of coal per hour for a drying a batch in 5 h. Drying tests were conducted while ambient conditions, including solar radiation, were recorded every 15 min. Ten samples, each with 500 g of macaroni enclosed in nylon‐net bags, were embedded in the drying mass (five at the top and five at the bottom) and weighted every hour. When drying stopped, the final moisture content (MC) of the samples was measured by the oven method, from which the initial MC could be derived.