Thermoelectric prototype applied to freezing of gelatin gel under high rates.

Resumo

Small thermoelectric refrigeration systems can reach temperatures under 0 °C in short time periods and keep them with 0.1 °C precision, so they are indicated to freezing studies. In this work a thermoelectric prototype was used to gelatin gel fast freezing. To evaluate the effect of plate inertia on the ice crystal structure were compared the results of two test series: plate-sample set stabilization at 3.0 ± 0.1 °C to application of 24.5 W of electric power; plate stabilization at 24.5 W of electric power (-20 ± 2 °C) to sample insertion. Thermograms were recorded simultaneously to temperature sensors located at four upper edges of the plate-sample interface, characterizing the freezing curves. After freezing the samples were lyophilized allowing the visualization of the ice crystals formed by optical microscopy under ambient temperature. The differences obtained between the plate extremity temperatures of the horizontal plain resulted in the ice structure, emphasizing the importance of the monitoring position specification and the sample lamination to evaluate qualitatively the ice crystals. The obtained images to five cut plains related to the sample center proved that the system inertia to reach the minimum temperature leads to an increase in the size of ice crystals when compared to the procedure started with the frozen plate. The results proved the effectiveness and precision of the device to different studies of freezing curves and subsequent effects on the ice crystals formation.

DOI: http://dx.doi.org/10.14685/rebrapa.v2i1.38