4 °C - the National Sea Grant Library

RESULTS AND DISCUSSION
The computer program saved voltage, current, and cumulative watt-hrs vs time data.From
these, plots were generated to determine a given shrimp block’s thawing characteristics. With two
ohmic units runnmg simultaneously, eight quadrants were analyzed during a single experiment. One
of the eight quadrants determined the voltage level applied to the entire ohmic system. This quadrant
was the "limiting quadrant" and indicated the area in the shrimp block with the greatest conductivity.
This limiting quadrant was determined by observing from the graphics which quadrant first allowed
current at the given voltage level. During the initial period of thawing, the block has a high resistance,
and a high level of voltage is necessary to pass the set current. During the later stages the temperature
of the block is close to the freezing point, portions of it are partially thawed, and the resistance is
lower. The level of voltage necessary to pass the set current is low. In this period, the operation is
controlled by the surface temperature, indicated by frequent LED and relay off /on sequences. In all
experiments, the temperature of the shrimp was below the set point temperature (12.7° C) at all times.
This was also confirmed at the end of each-experiment by touching the thawed shrimp. In all cases,
the ohmically thawed shrimp was colder than the water immersion thawed shrimp.
Lab Test Analysis
Table 1 summarizes the results of the lab experiments. The thickness, net weight, time required
to thaw, electrical energy used, and the C.O.P. for each experiment is shown.
Table: 1. Operational Results of Lab Tests.
Test Thick. Net. Wt. Shrimp
cm g / water
Thaw time
min
Calc.
Watt-Hr
Theor .
Watt-Hr
COP
Set 1:1 5.4 2027 2.48 124 57.5 305.85 18.8
1918 2.07 124 55.8 307.42 18.2
Set 2 : ;*:; 1950 3.76 190 34.1 261.1 13.3
2
Set 3:1
3:81
4.45
1482
1814
1.79
2.12
100
176
87.3
60.9
250.9
288
35.5
21.6
4.45 2054 3.02 161 34.9 291.5 12.2
seta:
4.76 2223 3.84 137 87.89 295.98 30.4
4.45 1953 2.27 87 32.1 302.9 7.4
Sets? 4.45 1759 2.59 97 69.1 261.5 26.4
2 4.45 1556 2.47 97 36 234.6 15.3
Set 6:1 5.72 1878 2.16 155 42.2 296.1 14.3
2 5.08 1606 2.54 119 32 239.8 13.3
In pl
The results of the lab tests showed that the ohmic system worked as designed, with the
capability %of thawing two blocks simultaneously. Since the approximate thawing time of similar
by immersion thawing was reported in previous experiments, the lab test results proved that
the ohmic units could thaw shrimp blocks in a time period competitive with water immersion, without
the incidence of hot spots. Thus, the major obstacle of ohmic thawing has been solved, and the ohmic