Microspray quenching on nanotextured surfaces via a piezoelectric atomizer with multiple arrays of micronozzles

We present an experimental study on heat transfer characteristics with the goal to enhance the cooling performance of a water spray impinged on smooth, polished copper surfaces and three different types of nanotextured surfaces with different thicknesses of diamond-like carbon (700 and 1000 nm), multi-wall carbon nanotube (50, 100 and 150 nm), and graphene nanotextured surfaces (1, 2, 5, and 10 nm). A multiple spray was produced by a commercial piezoelectric (PZT) actuator (power = 1.5 W and frequency 104 kHz) with a nozzle hole size of dj = 35 µm and a corresponding mass flow rate of 5.33 × 10−4 kg/s at a spray height of 50 mm. Relevant data for both the transient and steady state boiling heat transfers (BHT), as well as the quench tests were obtained and discussed. Furthermore, the effect of the nanotextured surface thickness on cooling performance was extensively examined. Results indicated that the nanotextured surfaces enhanced the spray cooling performance mainly due to the improved wettability and liquid spreading that they provided especially for graphene thin films. A somewhat high critical heat flux (CHF) of nearly 310 W/cm2 (the corresponding heat transfer coefficient, HTC ≈ 3 W/cm2 K) under a specific working condition for graphene thin-film surfaces with 1 nm thickness was found. Furthermore, the thermal conductivity effect was also noted and significant influence on BHT and CHF was found for graphene nanotextured surfaces.