Abstract
Experimental studies on the air-precooling of eggs were conducted and the following results were obtained.
1. Cooling rate of a single egg:
(1) Temperatures at the parts of an egg were not uniform in the cooling-air flow. Cooling rates of the parts of an egg were observed in the following order:
(1) upstream side (2) upper side (3) downstream and bottom side (4)center of egg.
Temperatures of the parts of an egg equalized earlier when the egg was positioned lengthwise than the one positioned crossway. (Fig. 3-(1))
(2) Cooling rate of egg increased with being smaller the egg, higher the air velocity and lower the air temperature, respectively, and was not much influenced from the degree of boiling of egg.
The lower the surrounding air temperature, the more sharp the fall of egg temperature.
If other conditions were fixed, however, the half cooling time of eggs was independent of the cooling-air temperature. (Fig. 3-(2) Fig. 4-(2), Table 1)
2. The relation between the egg location in container and the cooling rate of the egg:
(1) In room cooling, the cooling rate of egg in basket is lowerd with being the egg location nearer to the center of basket. (Fig. 5-(1))
(2) In air-blast cooing, the cooling rate of egg in basket is lowerd with being the egg located nearer to the bottom of basket. (Fig. 5-(2))
(3) The cooling rate of egg in basket, under parallel flowing air, is increased with being the egg located nearer to the bottom.
On the contrary, the cooling rate of egg in bucket is lowerd with being nearer to the bottom. (Fig. 5-(3))
(4) The cooling curves for the surface and center of an egg ran parallel in these method of air-cooling.
(5) Under the forced air cooling, the cooling rate of egg packed in carton consisisting of fillers-and-flats was lowerd with being the egg nearer to the center of carton, but the temperature gradient in egg was minimized. (Fig. 5-(4))
3. (1) Cooling rate of egg due to the kind of container was seen in the following order:
1 basket, 2 bucket (made of tin-plate), 3 polyethylene bucket. Cooling effect of air-blast was greater than the effect of parallel flow. (Fig. 6-(1))
(2) The cooling rate was expedited by perforating through the bottom plate of bucket. It is sufficient to perforate 20 holes of 13-mm diameter.
(3) The cooling rates of the center of centrally located eggs in three kind of packing systems were compared. (Fig. 6-(3))
4. The effect of air rate on the cooling rate of eggs in container was investigated.
The effect was more remarkable when the air rate was increased from 0 to 1.5m/sec compared with the one from 1.5 to 3 m/sec. (Fig. 7)
5. The relation between the air velocity and the cooling rate of stacked eggs: The value of m and the cooling time required to reach Y=0.1 (Y: Remaining fraction of initial temperature difference between eggs and cooling-air.) due to the cooling-air velocity were investigated. Cooling efficiency was not much increased by using air velocity larger than 4∼5m/s. (Fig. 8)
