Various systems involving two-phase flow and heat transfer, such as nuclear reactors, boilers, refineries, and refrigeration units are subject to thermohydraulic instability. A consequence is that the critical heat flux (CHF) may be much lowerthan under stable flow conditions. Mayinger et al. (1966) observed in a vertical test section for upflow with upstream compressibility two kinds of CHF conditions: a stable CHF and a pulsating CHF, with the latter being as much as 20 to 50 percent lowerthan the former. The pulsating CHF was preceded by low-frequency fluctuations of pressure, wall temperatures, and mass flux through the test section. An interesting fact is that below some specific inlet subcooling (ΔT{sub}(sub)), the pulsating flowcondition did not lead to physical burnout of the test section and the pulsation could be suppressed by further increasing the heat flux until stable CHF occurred. As a result, the dependence of CHF on ΔT{sub}(sub) showed a step function.
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