Enhancement of pool-boiling heat transfer using nanostructured surfaces on aluminum and copper

Enhanced pool-boiling critical heat fluxes (CHF) at reduced wall superheat on nanostructured substrates are reported. Nanostructured surfaces were realized using a low temperature process, microreactor-assisted-nanomaterial-deposition. Using this technique we deposited ZnO nanostructures on Al and Cu substrates. We observed pool-boiling CHF of 82.5 W/cm² with water as fluid for ZnO on Al versus a CHF of 23.2 W/cm² on bare Al surface with a wall superheat reduction of 25–38 °C. These CHF values on ZnO surfaces correspond to a heat transfer coefficient of ～23,000 W/m² K. We discuss our data and compare the behavior with conventional boiling theory.     

Evaluating the performance of algebraic operations on storage schemes for large sparse matrices

We study the performance of algebraic operations on large sparse matrices stored on secondary storage and show how the traditional algorithms can be fine-tuned in order to minimize the number of page accesses. We develop cost equations for performing multiplication, transposition, and Gaussian elimination on various secondary storage schemes for sparse matrices and show how these can be incorporated into a selection model which chooses the optimal sequence of storage schemes for a given mix of operations. Furthermore, we present the results of a number of experiments and compare our analytical results with experimental results obtained on synthetically generated data.This work was supported in part by NASA under grant number NAG-1-348.     

Laser-induced Spray Jet Cleaning Using Isopropyl Alcohol for Nanoparticle Removal from Solid Surfaces

Recent studies demonstrated that laser-induced spray jet cleaning (LSJC) based on optical breakdown of a water droplet is an effective way to remove nanoscale contaminant particles from solid surfaces with use of small amount of water. In this work, an LSJC process using isopropyl alcohol (IPA) as a non-water cleaning agent was developed. High-speed spray jet composed of atomized micro droplets of IPA was generated by inducing optical breakdown in the droplet. The particle removal efficiency was slightly lower than that of the LSJC using water droplets but it was high enough to remove 30 nm polystyrene latex particles completely and 10 nm gold particles partially from silicon wafers. Optical microscopy and secondary ion mass spectrometry confirmed that the LSJC process using IPA caused no watermark problem commonly observed in water-based cleaning processes without a special rinsing and drying process.