The collector used inexpensive materials such as bamboo
slats and plastic cords, and was installed on open ground instead on a rooftop. Thus, the investment cost was significantly reduced compared to the steel‐frame collector used for Vol. 52(4): 1255-1259 1257 Figure 4. SRA‐4B dryer with upward airflow. Figure 5. SRA‐4B dryer with downward airflow, using solar heat. Figure 6. At sunset, the coal furnace is fired. the macaroni dryer. The solar collector and the coal furnace can be used separately or in combination (fig. 6). Tests were done at Long‐An Province in March 2007, the driest month of the year. The MC was measured every hour by a Korean‐made GMK‐303RS MC meter, which had been calibrated against the drying oven. The airflow was obtained by multiplying the drying bed area by the average superficial velocity, measured by a rotameter at 30 points over the drying bed. The rotameter had been calibrated by the orifice method (Ower and Pankhurst, 1997). The contribution of solar energy was examined by two calculations. One calculation used the index product (Ip, °C・h), which is the product of the temperature increase and the corresponding heating time. The I p using solar energy was compared to the total Ip using both coal and solar energy; the ratio indicated the share of solar heat. The second calculation considered the percentage saving of coal due to solar energy, compared to the case in which only coal was used without solar heat. Table 1 in the Results and Discussion section illustrates these calculations.