Experimental investigation of transient heat flux effects on local wall superheat fluctuations in pool boiling

Pool boiling, as an energy-efficient and environmentally sustainable thermal management solution, demonstrates strong potential for cooling advanced semiconductor devices. Under practical operating conditions, the transient and spatially non-uniform power dissipation of heating elements can lead to the formation of localized hot spots on the surface, thereby posing challenges to the thermal management of semiconductor devices. In this work, a silicon chip integrated with a thin-film heater and a temperature-sensitive resistor was developed to measure local transient wall superheat under transient heat-flux conditions using a micro-resistance temperature detector. Temperature measurements were time-synchronized with high-speed imaging to correlate bubble dynamics with the transient thermal response. Based on the experimental results, the local wall superheat in the nucleate boiling regime exhibits pronounced fluctuations, particularly in the vicinity of the onset of nucleate boiling (ONB) and the critical heat flux (CHF). Under low transient heat-flux conditions, a brief high-temperature peak was observed in the local wall superheat, with the peak value increasing by up to 184.3% relative to the corresponding steady-state superheat. The fluctuation frequency of the local wall superheat in the single-phase convection regime is closely correlated with bubble dynamics in the boiling regime. Meanwhile, the time-averaged local wall superheat shows a considerably weaker dependence on the heat flux in the boiling regime.