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38 5 Freezing Different Samples using Peltier Cooling Viability [%] 100 90 80 70 60 50 40 30 20 10 0 30 40 45 68 Freezing time [s] Figure 5.6: Viability results of freezing E. coli cells with Peltier cooling in freezing chamber II 5.2.4 Freezing experiments in design II with PBS–buffer and LB–medium relating to the volume and the temperature These experiments showed that pressure air was not needed for short freezing–thawing experiments, because the cooling block had a temperature of about 0 ◦ C during the whole experiment. Experiments with PBS–buffer and LB–medium relating to the freezing time over volume The results of the measurement of the PBS–buffer volume against the average of the freezing time yielded a decrease of the time (Fig. 5.7, data are shown in the Appendix). But we would have expected a linear relationship between the sample volume and the freezing time. One problem might be the exact determination of the freezing point. It could also be possible, that the calibration of the pipettes was not exact. Also the deviation at 10 µl PBS–buffer to higher values and LB–medium to lower values might occur because of different pipettes since the experiments were not conducted at the same day. To determine this, the calibration of the pipettes was checked and the experiments were reiterated. This reiteration was per- formed with a single pipette, which was proven to be well calibrated. The deviation over the whole pipetting volume was only ±1 %. As a result of this reiteration the measuring data for PBS–buffer and LB-medium showed an approximately linear decrease with almost the same slope, but exhibited moderate standard deviations (shown in Fig. 5.8, data are shown in the
Freezing time [s] 50 45 40 35 30 25 20 15 10 5 0 5.2 Results and discussion 39 PBS-buffer LB-medium 0 5 10 15 20 25 Volume [µl] Figure 5.7: Averages of the freezing times against the different volumes of PBS–buffer and LB–medium. The standard deviation is shown Appendix). Due to this result, it can be concluded that in the former experiments pipettes were used whose calibration was incorrect. The absolute values of the freezing times were different, because of the different parameters of PBS–buffer and LB–medium, for example the salt concentration. Therefore, it can be assumed that the freezing time decreased linear with the sample volume. Experiments with PBS–buffer relating to the temperature over time The temperature in a PBS–drop was measured during freezing and the experiment was repeated three times. As expected the resulting curves had a plateau during the phase tran- sition. The curve of the first and the third experiment were very much the same, except for the end temperature: in the first experiment the temperature was −10.9 ◦ C, in the third experiment −9.1 ◦ C after 4 min. In the second experiment, the temperature in the PBS–buffer drop reached the 0 ◦ C 30 s later as in the other two experiments. The end temperature was −9.2 ◦ C (Fig. 5.9, data are shown in the Appendix). The absolute temperatures were not so important, due to the hole in the top cover a negative heat transfer occurred and the metal temperature sensor was also conducting heat out of the system. So the experiments showed that the Peltier element was working stable but not 100 % reproducible. A minimal temperature of −11.4 ◦ C was measured after 10 min of freezing. Verifying the thermometer accuracy, the results showed a difference of about 1 ◦ C between the two mercurial thermometers and the VOLTCRAFT temperature sensor. Most probably the values from the sensor were about 1 ◦ C too high.
Page 1: Danmarks Tekniske Universitet Insti
Page 5: Zusammenfassung Diese Arbeit besch
Page 8 and 9: 8 Contents 6 Development of a Bio-M
Page 10 and 11: 10 Nomenclature COC Cyclo-olefin co
Page 12 and 13: 12 1 Introduction sampling system w
Page 14 and 15: 14 2 Overview of Small-Scale Cultiv
Page 17 and 18: 3 Theoretical Considerations of Pol
Page 19 and 20: 100µm 3.2 Topas R○ and the CNC m
Page 21 and 22: 3.2 Topas R○ and the CNC micromil
Page 23 and 24: 4 Basic Principles of a Peltier Ele
Page 25: p-semiconductor p-semiconductor 4 B
Page 28 and 29: 28 5 Freezing Different Samples usi
Page 42 and 43: 42 6 Development of a Bio-Microreac
Page 64 and 65: 64 7 Concluding Remarks Reactor cha
Page 67 and 68: Appendix Freezing experiments with
Page 69: Experiments with 20 µl PBS-buffer
Page 72 and 73: 72 List of Figures 6.8 Heat wire de
Page 75 and 76: Bibliography [1] Arisawa, H.; Brill
Page 77 and 78: Bibliography 77 [26] Mark, H. F.: E
Page 79: Bibliography 79 [50] Zimmermann, H.

C - DTU Nanotech - Danmarks Tekniske Universitet

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