Mpeba effect – reality or fiction?

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Title: Mpemba effect – reality or fiction? (Hysteresis by water freezing)
Author: Pavel Böhm
Department: Department of Physics Education
Supervisor: Doc. RNDr. Jan Obdržálek, CSc., Institute of Theoretical Physics
Supervisor’s e-mail address: Jan dot Obdrzalek at mff dot cuni dot cz
Abstract: The aim of this thesis was to review theoretically and experimentally so-called Mpemba effect, where the initially hot water freezes sooner than the initially cold one.
Based upon already published theoretical and experimental works, a list of circumstances possibly supporting this phenomenon was created and discussed. Some situations were verified experimentally.
These experiments were carried out partly in laboratory using small amounts of distilled water (less than 1 ml), partly in 'kitchen conditions' using the tap water (about 200 ml) and a commercial home refrigerator. The time of freezing defined by freezing of the entire body of water was measured using the inflection points of cooling curves.
Unlikely to the Mpemba effect (and likely to the usual expectations), usually the sample of cold water freezes sooner than the hot one. The Mpemba effect occured rarely, mostly when the cooler was covered by the layer of the snow and the hot vessel could melt through it to reach better thermal contact than the cold vessel. Other observed cases were mostly inconclusive.

Table of Contents

1. Introduction
    1.1 Mpemba effect
    1.2 History
          1.2.1 Question
          1.2.2. Answer?
    1.3 Is physics wrong?
    1.4 Which freezes faster: hot water or cold one?
2. Which circumstances could support Mpemba effect?
    2.1 Change of refrigerator's activity
    2.2 Change of layer-vessel contact
    2.3 Change of the amount
    2.4 Change of circulation
    2.5 Chemical changes
    2.6 Microstructure changes
    2.7. Supercooling
    2.8. Influence of subjectivity (and "psychology")
3. Experimental verifying
    3.1 Supercooling
          3.1.1 Delayed start of freezing
          3.1.2 Repeated freezing and melting
          3.1.3 Overcooling temperature dependency on initial temperature
          3.1.4 Resume
    3.2 Change of the amount
          3.2.1 How were experiments carried out
          3.2.2 Experiments in the refrigerator
          3.2.3 Other authors' results
          3.2.4 Resume
    3.3 Change of layer-vessel contact
          3.3.1 First experiment
          3.3.2 Second experiment
          3.3.3 Resume
4 Conclusion
Appendix A: Derivation of Mpemba effect conditions caused by supercoolig
Appendix B: Experimenting with THMSG 600 apparatus (notes)
Appendix C: Bursting of Hot Water Pipes