Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating

Predicting the onset of nucleate boiling heat flux of one-side heated flat heat sink in sub-cooled flow conditions for fusion divertor cooling

“…In particular, as in the high subcooling condition, the vapor of the flow path wall is condensed at a high-speed, high-velocity and highpressure conditions, the size of the departing vapor is small; hence, it is difficult to find it through the window. Therefore, in the subcooled flow condition, the ONB is detected mainly by using the change in heat-transfer performance, which is the thermo-hydraulic characteristic of ONB [13,16]. Figure 8 depicts the change trend of In this regime, boiling does not occur because sufficient heat is not transferred to the channel so that vapor can be created inside the channel.…”

“…Because CHF causes major damage to the cooling system, the experiment ends when the CHF is reached. Therefore, the straight lines of the wall temperature in the SP and TP regimes symbolize the heat-transfer mechanism in the corresponding flow regimes, and the intersection of the two straight lines can be defined as an ONB where the flow regime transitions from the SP regime to the TP regime [13,16]. The blue dotted line represents the detected ONB heat flux, and it can be seen that the flat heat sink has an ONB heat flux of approximately 1900 kW m −2 at a pressure of 10 bar, a mass flow rate of 0.315 kg s −1 , and a subcooling of 40 °C.…”

“…The correlations presented in previous studies were developed under uniform heating conditions, but in nuclear power plant fuel rods, they have a non-uniform power distribution [15] and not uniform heating. Therefore, Kim et al [16] analyzed the effects of heat flux distribution and non-uniformity of heating conditions on the ONB. They analyzed the difference between the case where the same heat flux was uniformly applied to the heat-transfer area and the case where non-uniform heating was applied, in which both ends of the channel were loaded with a higher heat flux than the middle of the channel.…”