Propriedades físicas e pré-resfriamento de umbu (Spondias tuberosa Arruda Câmara).

Abstract

The objective of this work was to identify umbu's physical properties (dimensions, volume, mass, specific gravity, roundness ans sphericity), its thermal properties (specific heat, film coefficient, conductivity and thermal diffusivity, lag factor, cooling rate, and cooling half - time) and its behavior when submitted to precooling by forced air at 2-8 rn/s under six cooling temperatures (-20.3°C; -17.0°C; -15.5°C; -13.6°C; -11.9°C; e- 9 . 8ºC). The values obtained for the dimensions, measured under three perpendicular axis, are 3 6 . 0 , 34.0 and 32.0 mm for the longitudinal axis, major transversal and minor transversal (average values) respectively, the average volume obtained is 22.0 cm3 ; the average mass and specific gravity are 24.0 g and .06 g/cm3, respectively. As regards thermal properties , the values of specific heat is 0 . 6 6 6 7 c a l / g " C ; the film coefficient has an average value of 47000 cal/hm2 ° C ; the average conductivity and thermal diffusivity are around 167.0 cal/hm°C and 0.06575 X 106 rn2/s respectively; the lag factor, cooling rate and the cooling half - time have average values of 1.3, 5.4 h~1 and 0.13 h. Under experimental conditions it is concluded that umbu has regular forms. Its sphericity varies between 86 and 98%, its roundness between 79.9 and 99.0%, its volume beetwen 15.0 and 32 cm3 and its specific gravity between 1.02 and 1.18 g/cm3. The thermal conductivity of umbu varies from 157 t o 178 cal/hm°C, positioning itself in an intermediate range between grain and small-seed fruits ; the thermal diffusivity between 0.05941 and 0.07004 m2/s; the specific heat obtained is 0.6667 cal/g°C. The precooling under the applied conditions did not show differences in the cooling time over the range of cooling medium between -10°C and -20°C, as i s show by cooling factor, inclination factor and cooling haIf - time wich did not present rising values within creasing cooling temperature, indicating the ™10°C temperatures as being more economical.