Development of hybrid biphilic surfaces using a hydrophobic coating and laser texturing

Abstract

V nalogi obravnavamo vpliv različno strukturiranih površin aluminija na izboljšanje prenosa toplote pri mehurčastem vrenju redestilirane vode v bazenu. Posamezne vzorce smo pripravili z različnimi kombinacijami laserskega strukturiranja in nanosa hidrofobnega premaza. Eksperimentalno smo ovrednotili vrenje na neobdelani površini, hidrofobni površini, dveh hidrofilnih površinah in štirih bifilnih površinah, ki smo jih obdelali z različnimi laserskimi parametri ter na dveh bifilnih površinah, ki nista imeli hidrofobnega premaza. Površine smo testirali na merilni progi za nasičeno vrenje v bazenu pri atmosferskem tlaku. Na merilni progi smo zabeležili vrelne krivulje do nastopa kritične gostote toplotnega toka (CHF) in iz njih izračunali koeficiente toplotne prestopnosti za posamezen vzorec. Pri analizi podatkov smo dobljene rezultate primerjali z referenčno površino (neobdelana aluminijasta površina). Vrednosti CHF so dosegale vrednosti med 890 kW/m2 in 1480 kW/m2. Najvišje vrednosti CHF in koeficienta toplotne prestopnosti so dosegale bifilne površine. Najvišja izmerjena vrednost CHF (1480 kW/m2) je predstavljala 30 % izboljšanje vrednosti CHF referenčne površine, kar pa je pomenilo zvišanje za 320 kW/m2. Zvišanje koeficienta toplotne pristopnosti pa je bilo 83 % in je tako dosegalo vrednosti 61,7 kW/m2K. Dokazali smo, da z lasersko strukturiranimi bifilnimi površinami lahko izboljšamo parametre vrenja v bazenu in s tem bistveno pripomoremo k izboljšanju prenosa toplote.In this work, we investigate the influence of aluminuim surfaces with different structures on enhanced pool boiling heat transfer of twice distilled water. Individual samples were modified by using different combinations of laser texturing and hydrophobization. An untreated surface, a hydrophobic surface, two hydrophilic surfaces and four biphilic surfaces textured with different laser processing parameters as well as two biphilic surfaces without a hydrophobic coating were experimentally tested. Surfaces were tested on saturated pool boiling experimental setup. Boiling curves up to the CHF values were measured and heat transfer coefficient was calculated. In the analysis, the results were compared with the reference surface (raw aluminium surface). CHF values reached values between 890 kW/m2 and 1480 kW/m2. The highest measured values of CHF and heat transfer coefficient were reached by biphilic surfaces (1480 kW/m2) which represent a 30 % improvement regarding to the reference surface. Heat transfer coefficient improvement reached up to 83 % and achieved the highest value at 61,7 kW/m2K. We have demonstrated that laser-structured biphilic surfaces can improve the pool boiling parameters and can significantly contribute to the improvement of boiling heat transfer