Mechanical & Materials Engineering, Department of


First Advisor

George Gogos

Date of this Version



A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Mechanical Engineering and Applied Mechanics

Under the supervision of Professor George Gogos

Lincoln, Nebraska, November 2023


Copyright 2023, Peter Efosa Ohenhen


In the present work, the integration of femtosecond laser surface processing (FLSP) with copper hydroxide on hybrid surfaces was examined. The goal was to determine the impact on pool boiling enhancement. The samples for the investigation were fabricated by first functionalizing with FLSP, and the process was then followed by citric acid cleaning (CAC) to eliminate the oxides generated on the copper surface during the FLSP process. After the citric acid cleaning, the samples were immersed in ethanol and subjected to an ultrasonic bath for 25 minutes. This step was performed to eliminate any residual citric acid and loose particles. Copper hydroxide nanoneedles (NN) were then synthesized on the FLSP surface. Lastly, some selected samples were heat-treated (HT) at 200°C for 30 minutes to ensure the nanoneedles were secured in place even after several pool boiling runs. The study showed that heat-treated nanoneedle surfaces offer enhanced pool boiling performance compared to untreated ones, and the results are consistent and repeatable. Sample E (FLSP+CAC+NN+HT) exhibited a critical Heat Flux (CHF) of 116.1 W/cm2 and a heat transfer coefficient (HTC) of 50.5 kW/m2-K which outperformed sample C (FLSP+CAC+NN) that exhibited a CHF of 100 W/cm2 at an HTC of 45.2 kW/m2-K. It was observed that the inclusion of nanoneedles resulted in diminished performance when compared to a polished copper surface. The decline was attributed to the decomposition of copper hydroxide into copper oxide, consequently introducing insulating material to the surface. Boiling inversion was observed on all tested nanoneedle surfaces.

Advisor: George Gogos