The Effects of Channel Curvature and Protusion Height on Nucleate Boiling and the Critical Heat Flux of a Simulated Electronic Chip

The quest for higher power yet smaller electronics has given rise to the need for very effective cooling of these electronics. Because one of the foremost problems in electronics cooling is achieving high heat flux cooling within small packages while expending minimal pumping power, one focus of this study was to investigate the effects of channel curvature on the CHF. Experimental data were obtained for flow rates of 1-7 m/s, subcoolings of 5-35 C, and radii of curvature of 25.4 and 50.8 mm. A correlation was obtained for these data which provided an excellent fit. One condition that has been ignored in the literature is the effect of the simulated heat source not being flush with the flow channel wall. In manufacturing an electronics cooling device, it will be very difficult to maintain the flush chip condition because of the dissimilar materials involved and the numerous thermal cyclings that the device will go through. Experiments showed a significant effect on CHF of the simulated heat source not being flush. A series of data was obtained for flow velocities of 1-4 m/s and subcoolings of 20-35°C. CHF data were obtained for a surface recessed 0.127 mnu, a flush surface, and surfaces protruded 0.229, 0.457, and 0.635 mm into the flow stream

Characterizing Episodic Stream Acidification Using a Concentration-Duration-Frequency Methodology in Watersheds of the Great Smoky Mountains National Park

Episodic stream acidification occurs as storm events temporarily reduce acid neutralizing capacity and pH. Stream acidification is suspected to have damaging effects on the health of aquatic ecosystems and biota and is dependent on various watershed characteristics such as drainage area, elevation, slope, and surficial geology. Here, a stochastic modeling approach is applied to continuous pH data for multiple stream monitoring sites within the Great Smoky Mountains National Park in order to characterize episodic acidification responses during stormflows for different streams. The approach summarizes voluminous pH data recorded by water quality sondes at 15-minute intervals into concentration-duration-frequency relationships. Unique to this study is the ability to characterize the episodic acidification response to watershed attributes without using baseflow or single-point stormflow measurements. A slope metric of mean pH event duration, a measure of episodic acidification response was determined to correlate with basin area and elevation. In contrast, baseflow studies have shown elevation to be the main driver of chronic acidification. It appears that during stormflows transport and flushing of stored anions and cations govern the response of streams included in this study

The sale and shipment of coal

The Coal Industry in South Africa exported 54,5 million tons in 1993, providing R4,2 billion in export revenues, second only to gold. Apart from small parcels of coal exported through Durban and Maputo, coal is exported through the Richards Bay Coal Terminal. As new producers such as Indonesia, Columbia and China enters the International Market, equally (and sometimes better) placed than South Africa to penetrate markets in Europe and the Far East, the South African Coal Industry cannot afford to damage its' competitive position through accusations of "hot coal" problems. In this thesis, the phenomenon of spontaneous healing, combustion and methane emission from coal cargoes, will be discussed, and the F.O.B. sales of coal will be commented upon

Reconnaissance surveying of Bechevin Bay, AK using satellite-derived bathymetry

Recently, a remote sensing study has been conducted over Bechevin Bay Channel, Alaska as part of a collaboration project between NOAA and the U.S. Coast Guard (USCG). The goal of the study to develop a procedure to prioritize survey areas and plan the annual deployment of Aids to Navigation (AtoN) along the channel. Bechevin Bay is considered a priority for marine surveying because it constitutes the easternmost passage through the Aleutians from the Bering Sea to the Gulf of Alaska. The channel is located in a mud flat area, where every winter the passage is closed due to ice cover. As a result, the path of the channel may change after sea ice has melted. Because of the geographic location of Bechevin Bay, many resources are required in order to conduct an annual survey to map the channel’s path. The surveys are typically conducted by the USCG buoy tenders using small boats and reconnaissance-style single beam lines. This paper presents the use of single-image satellite-derived bathymetry (SDB) as an economic alternative approach. The study compares the performance using different band ratios. Datasets that were used in the study included Landsat 8 and WorldView 2 (WV-2) imagery

High Heat Flux Cooling for Spacecraft Electronics

An experimental investigation of flow boiling in a curved channel has been performed to ascertain its value in electronics cooling applications. Results have been obtained for flow velocities of 1 to 5 m/s and subcooling of 0.5 to 40 K. These results were compared to those of straight channel under identical velocity and subcooling conditions. The critical heat flux of the curved channel was found to be greater than that of the straight channel. In some cases the increase was found to be marginal, however. An unexplained temperature shift in the nucleate boiling regime was experienced during some experiments. Because this shift only occurred for the first test of the day, it is thought to be related to the incipience phenomenon often experienced in pool boiling experiments. Finally, true incipience overshoot and nucleate boiling regime hysteresis were found to be negligible