The Meaning of Burn-Out

Jens and Leppert (J4), and, more recently, Barnett (B2), have emphasized the need to distinguish between a temperature-controlled surface and a heat-flux-controlled surface when referring to boiling phenomena. Failure to observe the distinction has caused some confusion in the literature, particularly as further complications arise from differences that exist between pool boiling and forced-convection boiling. 

A perfect temperature-controlled heat-transfer surface is difficult to achieve, but it is closely simulated in practice by using a control fluid on one side of, for example, a metal tube. The tube wall should be thin and, ideally, the heat-transfer resistance comparatively large for the other fluid on the working side of the tube the latter surface is then effectively temperature-controlled and responds only to changes in the control fluid. 

Pyrex jacket. The test fluid, distilled water, flowed vertically upwards through the annulus, while inside the heated tube a control fluid flowed which was either water or nitrogen gas, depending on the tube temperature required. 

Burn-out can have only one meaning with a temperature-controlled system, and that is physical burn-out, which occurs when the surface temperature is made high enough to result in a rupture. Physical burn-out is a function of the mechanical properties of the surface material and of any load stresses it may carry. 

Heat-Flux-Controlled Systems I. Pool Boiling 

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