Performance analysis of a solar-powered/fuel-assisted Rankine cycle with a novel 30 hp turbine

The subject of this analysis is a novel hybrid steam Rankine cycle, which was designed to drive a conventional open-compressor chiller, but is equally applicable to power generation. Steam is to be generated by the use of solar energy collected at about 100°C, and is then to be superheated to about 600°C in a fossil-fuel fired superheater. The steam is to drive a novel counter-rotating turbine, and most of its exhaust heat is regenerated. A comprehensive computer program developed to analyze the operation and performance of the basic power cycle is described. Each component was defined by a separate subroutine which computes its realistic off-design performance from basic principles. Detailed predicted performance maps of the turbine and the basic power cycle were obtained as a function of turbine speed, inlet pressure, inlet temperature, condensing temperature, steam mass flow rate, and the superheater's fuel consumption rate. Some of the major conclusions are: (1) the turbine's efficiency is quite constant, varying in the range of 68.5–76.5 per cent (75 per cent at design) for all conditions, (2) the efficiency of the basic power cycle is 18.3 per cent at design, more than double as compared to organic fluid cycles operating at similar solar input temperatures, at the expense of adding only 20 per cent non-solar energy. This, combined with the fact that actual organic Rankine cycles operate typically at temperatures above 140°C, predicts that this system would be economically superior by using less than half of the collector area and by also using less expensive collectors.     

Accumulation of oil and grease in soils irrigated with greywater and their potential role in soil water repellency

The potential impact of oil and grease (O and G) to soils irrigated with greywater (GW) was investigated. Greywater streams were sampled and analyzed for O and G content, along with corresponding GW-irrigated soils. Untreated kitchen GW averaged 200 mg L(-1) O and G, over an order of magnitude more than other GW streams. GW-irrigated soils showed O and G accumulation of up to 200 mg kg(-l) within the first 20-cm of depth. To determine the potential effects of such O and G accumulation on water movement in soil, capillary rise and water drop penetration time (WDPT) experiments were conducted. The results showed up to 60% decrease in capillary rise when sand containing 250 mg kg(-1) O and G was used. Interestingly, no additional reduction in capillary rise was observed at concentrations above 250 mg kg(-1). WDPT was observed to increase linearly with increased O and G content, up to 1000 mg kg(-1). This work demonstrated that O and G in GW used for irrigation can accumulate in soil and may lead to a significant reduction in the soils ability to transmit water.     

Self-organized nanotube serpentines

Carbon nanotubes have unique mechanical, electronic, optical and thermal properties, which make them attractive building blocks in the field of nanotechnology. However, their organization into well-defined straight or curved geometries and arrays on surfaces remains a critical challenge for their integration into functional nanosystems. Here we show that combined surface- and flow-directed growth enable the controlled formation of uniquely complex and coherent geometries of single-walled carbon nanotubes, including highly oriented and periodic serpentines and coils. We propose a mechanism of non-equilibrium self-organization, in which competing dissipative forces of adhesion and aerodynamic drag induce oscillations in the nanotubes as they adsorb on the surface. Our results demonstrate the use of 'order through fluctuations' to shape nanostructures into complex geometries. The nanotube serpentines and loops are shown to be electrically conducting and could therefore find a wide range of potential applications, such as receiving and transmitting antennas, heating and cooling elements, optoelectronic devices and single-molecule dynamos.     

Light transmission technique for the evaluation of colloidal transport and dynamics in porous media

Colloidal transport in porous media has been typically studied in column experiments from which data analysis was limited to the evaluation of effluent breakthrough curves and/or destructive sampling at the end of the experiments. The internal processes occur within a "black box", where direct observation is not possible and therefore are often poorly understood. In this paper, a nondestructive, noninvasive method is presented that allows for quantitative measurement of colloid distribution with unprecedented two-dimensional spatial and temporal resolution. This technique is well-suited to observing the effects of saturation transitions and physical heterogeneities on colloidal transport. The potential of this novel technique is explored by investigating the effect of particle size and concentration on flow dynamics under saturated and unsaturated conditions. In saturated-flow experiments, deviation from the classical advection-dispersion behavior is observed. In unsaturated systems, colloidal accumulation at the capillary fringe interface and a high deposition rate of microspheres to the unsaturated media are readily observed. The experimental system is limited to translucent porous media and fluorescent colloids and is only semiquantitative in variably saturated media; nevertheless, it holds great promise for elucidating many complex mechanisms that control or influence colloid transport in the subsurface.     

Effects of diameter, length, and circuit pressure on sound conductance through endotracheal tubes

We evaluated the acoustic frequency response of endotracheal tubes (ETs) to assess their effect on respiratory system sound transmission studies. White noise 150-3300 Hz was introduced into 4.0-, 6.0-, and 8.0-mm ETs and recorded at their proximal and distal ends. Four tubes of each size were studied at their original and normalized lengths, in straight and bent configurations, and at circuit pressures from 0 to 20 cmH2O. The characteristics of the sound transmission were compared using an analysis of variance for repeated measures. The average transmission amplitude varied directly with tube diameter. The position of peaks and troughs on the amplitude frequency distribution depended on tube length but not on tube diameter. The angle of the phase-frequency plot correlated well with the length of the tube and was independent of its diameter. A 90 degrees bend in the tube had no effect on its sound transmission. Increasing the circuit pressure above ambient modified the frequency response only if volume changes occurred in the test lung. When used to conduct sound into the respiratory system an ET affects the incident signal predictably depending on its length and diameter but not on its curvature or circuit pressure.