Infra-red Radiation drying is a recommendable way for Satsuma Orange ‘citrus unshiu marc.’ especially in the humid circumstances, because the water adhered on the fruit in the ‘washing process’ is removed completely in a short drying period (60sec.)
In order to investigate the drying characteristics and to contribute to the proper use in the packing house line, some fundamantal experiments were conducted and the following results were obtained:
(1) Surface temperature of Satsuma Orange increased with the infra-rad radiation periods.
The rate of temperature rise of the fruit due to the time of the radiation was 1.8°C/sec. from 0 to 10sec., 0.475°C/sec. from 10 to 30sec., and 0.425°C/sec. from 30 to 50sec.
The rate was slowed down with the increase of the radiation time (Fig. 4).
(2) Change of inner fruit temperature at the point of 3mm below the surface was nearer to the surface temperature for the radiation periods.
Changer of fruit temperature deeper than 6mm below the surface was very slow, and rather affected by the heat-transfer than by the radiation (Fig. 5).
The rise of fruit temperature at the point of 10mm below the surface was 1.0°C by the radiation for 30sec.
(3) Change of the surface fruit temperature was observed after the radiation for 20sec. followed by air flow of normal temperature (Fig. 6, 7, 8).
Duration of effective drying time immediately after the infra-red radiation was proportional to the irradiation periods, and was inversely proportional to the air velocity (Tab. 1).
(4) The amount of water evaporated from fruit's surface, by infra-red radiation, for 20sec. followed by air flow of normal temperature for 40sec., was observed (Fig. 10).
The drying rate of the fruit increased with the irradiation times, and the rate was not so much affected by air velocities from 1.25 to 3.85m/sec.
(5) Water evaporated from the fruit was observed for the air-flowing periods immediately after the radiation (Fig. 11).
The evaporation increased due to the radiation accompanied with air flow for less than 2 minutes, but was not changed so much by the air flowing time longer than that.
(6) Drying rate between the infra-red radiation and the heated-air drying was compared.
The water adhered on the fruit was not evaporated sufficiently by the heated-air drying (26.7°C) for 2 minutes.
The water was evaporated perfectly by the radiation for 10sec. followed by the air flow of normal temperature for 60sec. (Fig. 14).

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