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The Physics Teacher -- December 2011 -- Volume 49, Issue 9, pp. 550

Why Do Objects Cool More Rapidly in Water Than in Still Air?

Craig F. Bohren

Pennsylvania State University, University Park, PA

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An Internet search for why objects, especially humans, cool more rapidly in water than in air, both at the same temperature, and by how much, yields off-the-cuff answers unsupported by experiment or analysis. To answer these questions in depth requires a smattering of engineering heat transfer, including radiative transfer, and the different thermophysical properties of the two fluids. The correct ratio for humans is closer to 2 than to 10, and if this were not so, swimming in cool water could be fatal.

© 2011 American Association of Physics Teachers

Acknowledgments

I thank Lee Grenci for questions that inspired me to write this article and John Wyngaard for pointing out the correct physical interpretation of the Grashof number.

Article Outline

  1. Natural (free) convection
  2. Cooling including radiation and thermal insulation

KEYWORDS and PACS

Keywords

cooling, heat transfer, physics education, radiative transfer, water

PACS

PUBLICATION DATA

ISSN

0031-921X (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physics Teachers

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1119/1.3661099

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