This article presents an account of the results of a survey recently carried out by the author into the current position of knowledge in the field of boiling heat transfer to cryogenic fluids, defined as liquids boiling below 185 K. Boiling regimes are described, and some account is given of the research situation. The survey is concluded with some remarks on the situation with regard to the prediction of heat transfer in industrial equipment boiling cryogenic fluids.
The boiling of cryogenic fluids--a survey
I. R. McDougall
Arguably, heat transfer to boiling liquids is the most important and widespread heat transfer process practised by industry. Less arguably, it remains the most intractable heat transfer process from the points of view of understanding, theory, and prediction. After countless millennia of boiling, only today are we within measurable distance of reasonable, theory-based predictions for the commonest of all liquids, water.
Understanding has, as almost always, lagged far behind practice; indeed, some would claim that theoretical elucidation of the boiling of water is largely an academic exercise, empirical method being manifestly successful. But the same cannot be claimed for the boiling of most other industrially interesting fluids, either because of their expense, or relative lack of experience with them, or both. This is perhaps particularly the case with cryogenic fluids, where within quite recent times much the greatest interest and effort was devoted to the problems of preventing ebullition, in other words, liquefaction.
Today this situation has radically changed: technological developments predicate substantially increased interest in the large scale use of boiling cryogenic fluids, for applications varying from superconductive electrical machines, through the problems of rocketry, to the transport and vaporization of natural and petroleum gases. Clearly, the overwhelming interest lies in the design of equipment for boiling cryogenic fluids. In this present article the term cryogenic fluids is reserved for liquids with boiling points below 185 K so that -in particular -the freons and ammonia are excluded.