Microwave-Assisted Superheating and/or Microwave-Specific Superboiling (Nucleation-Limited Boiling) of Liquids Occurs under Certain Conditions but is Mitigated by Stirring

Molecules

Anthony Ferrari²  Jacob Hunt²  Albert Stiegman¹  Gregory B. Dudley¹  Marilena Radoiu²  Jean-Jacques Vanden Eynde² 

[1] Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA

关键词: superheating;    microwave;    reflux;    temperature;    boiling point;   

DOI  :  10.3390/molecules201219793

来源: mdpi

【 摘 要 】

Temporary superheating and sustained nucleation-limited “superboiling” of unstirred liquids above the normal atmospheric boiling point have been documented during microwave heating. These phenomena are reliably observed under prescribed conditions, although the duration (of superheating) and magnitude (of superheating and superboiling) vary according to system parameters such as volume of the liquid and the size and shape of the vessel. Both phenomena are mitigated by rapid stirring with an appropriate stir bar and/or with the addition of boiling chips, which provide nucleation sites to support the phase-change from liquid to gas. With proper experimental design and especially proper stirring, the measured temperature of typical organic reaction mixtures heated at reflux will be close to the normal boiling point temperature of the solvent, whether heated using microwave radiation or conventional convective heat transfer. These observations are important to take into consideration when comparing reaction rates under conventional and microwave heating.

【 授权许可】

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© 2015 by the authors; licensee MDPI, Basel, Switzerland.