On the effect of silver nanoparticles deposition on porous copper foams on pool boiling heat transfer enhancement: an experimental visualization

Distilled water pool boiling experiments are conducted to investigate the effect of deposing silver nanoparticles via boiling-induced deposition method on porous foam covers on pool boiling performance and bubbles dynamic behavior. Two copper foams, named foam No. 1 (with 85% porosity and pore density of 30 PPI) and No. 2 (with 90% porosity and pore density of 40 PPI), are welded on copper specimens (Conical frustum) and then coated by silver nanoparticles using DZ nano-coolant nanofluid with a concentration of 25 mg/L. All the experiments are carried out at atmospheric pressure on both uncoated and nano-coated foams. The findings reveal that compared to a polished plain copper surface, uncoated foams No. 1 and No. 2 improve average boiling heat transfer coefficient by 58% and 86% and reduce wall superheat at ONB by 4.7 °C and 5.3 °C, respectively. However, due to the generation of more bubbles with smaller sizes and lower release periods on coated foams compared to uncoated ones, deposing nanoparticles on foam No. 1 and No. 2 contributes to further enhancements in heat transfer coefficients by 18% and 9% (at the best performance), respectively, and 0.3 °C further reduction in wall superheat at ONB. To evaluate the effectiveness of nanoparticle deposition on foam covers as a hybrid enhancement technique, the experimental results are compared with the results attained for nano-coated polished copper surface and also copper foam covers enhanced further by manipulating their wettability and macro-scale structure. The comparison results indicate that the coated foams perform better than the coated polished plain surfaces, notably at low heat fluxes. Also, the nanoparticle deposition on foam covers is seen to be of superior performance compared to the aforementioned hybrid enhancement techniques.