Cooling by Immersion in Liquid Nitrogen
Copyright © 1986, American Association of Physics Teachers. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Association of Physics Teachers. The following article appeared in the American Journal of Physics 54.6, and may be found at http://ajp.aapt.org/resource/1/ajpias/v54/i6/p554_s1
When an object is cooled by immersion in a liquid, there is an unexpected increase in the violence of boiling just before the boiling stops. Most people seem fascinated by this phenomenon yet few are acquainted with its explanation in terms of a change in the heat‐transfer mechanism from film boiling to nucleate boiling. We have developed two variations of an intermediate level undergraduate laboratory experiment to measure the heat‐transfer rate after a sample is immersed in liquid nitrogen. The temperature of the sample, as measured by a thermocouple, is recorded as a function of time using either a potentiometer strip‐chart recorder or a digital voltmeter–microcomputer combination. The heat‐transfer rate as a function of sample temperature is computed from these results, and the reason for the effect is clearly seen.