Visualization analysis of heat transfer and flow behavior in flat-plate pulsating heat pipe with sintered powder wick layer

Within this work, a flat-plate pulsating heat pipe (FPPHP) utilizing sintered powder wicks on both the channel walls and bottom was proposed. Using visualization techniques, the vapor-liquid flow pattern evolution, quasi-steady flow motion modes, and heat transfer performance of the FPPHP with sintered powder wicks as well as a FPPHP with smooth channels were analyzed. And more, through comparison, the influence of the sintered powder wicks on the thermo-hydrodynamic characteristics of the FPPHPs was summarized. Results indicate that the vapor-liquid flow patterns existing in both FPPHPs predominantly consist of bubbly flow, slug flow, annular flow, along with the transitional flow from bubbly to slug flow. Under vertical orientation, the quasi-steady flow motion modes of the FPPHPs include stagnation (S), intermittent pulsation (S&P), and small pulsations/large pulsations (P). These modes are accompanied by various vapor-liquid flow behaviors, such as bubble growth and aggregation, the coalescence between bubbles and slugs, and the fragmentation of extended slugs. After start-up, the thermal resistance of the FPPHP with sintered powder wicks is lower than that with smooth channels under different filling ratios, which demonstrates the beneficial influence of introducing capillary wicks on heat transfer of FPPHP.