Experimental Study on Flow Boiling Heat Transfer Characteristics in Top-Connected Microchannels with a Ni/Ag Micro/Nano Composite Structure

Microchannel heat exchangers, with their large specific surface area, exhibit high heat/mass transfer efficiency and have a wide range of applications in chemical engineering and energy. To enhance microchannel flow boiling heat transfer, a top-connected microchannel heat exchanger with a Ni/Ag micro/nano composite surface was designed. Using anhydrous ethanol as the working fluid, comparative flow boiling heat transfer experiments were conducted on regular parallel microchannels (RMC), top-connected microchannels (TCMC), and TCMC with a Ni/Ag micro/nano composite surface (TCMC-Ni/Ag). Results show that the TCMC-Ni/Ag’s maximum local heat transfer coefficient reaches 179.84 kW/m2·K, which is 4.1 times that of RMC. Visualization reveals that its strongly hydrophilic micro/nano composite surface increases bubble nucleation density and nucleation frequency. Under medium-low heat flux, the vapor phase converges in the top-connected region while bubbles form on the microchannel surface; under high heat flux, its capillary liquid absorption triggers a thin-liquid-film convective evaporation mode, which is the key mechanism for improved heat transfer performance.