An experimental investigation was performed to study the confined boiling heat transfer characteristics over a saturated porous structure using distilled water as the working fluid. A thin stainless steel resistive foil stretched between two copper electrodes was used to heat a saturated porous plate with an effective pore size of 50 gm. The temperature distribution on the foil heater was measured using a high speed thermal imaging camera. The effect of the gap height between the heater and the porous plate on the heat transfer was investigated for gap heights ranging from 0 um to 1000 um and for heat fluxes ranging from 11.7 kW/m2 to 58.3 kW/m2. It was observed that the highest heat transfer rate was obtained at a gap height of approximately 600 pm. The main heat transfer mechanism is thought to be confined boiling in the small gap between the heating surface and the saturated porous structure. It was observed that the effect of the subcooled liquid temperature did not have a significant effect on the heat transfer. The effect of the pore size in the porous plate was investigated by repeating the measurements with a porous plate of 200 gm pore size. It was observed that the thermal resistance for the plate with a 200 gm pore size was significantly higher than the plate with 50 gm pores for gaps less than 300 gm. At a larger gap height of 600 gm, similar heat transfer performances were obtained for the two porous media. / Thesis / Master of Applied Science (MASc)

No / Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water¿air, water¿LNAPL and LNAPL¿air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water¿air, water¿LNAPL and LNAPL¿air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water¿air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting.

No description available.

Extensive research has been carried out in both field and laboratory to explain water and solute movement under both saturated and unsaturated conditions. The importance of such work is obvious, since any attempt at exploring land reclamation by leaching or nutrient movement in plant feeding (to name only two) is subject to interpretations and theories of moisture flow. Water flow through soil during reclamation by leaching can be termed miscible displacement since soil water and leaching water do not have a distinct fluid-fluid interface and will physically mix. It is probable that miscible displacement investigations can contribute to an understanding of time-ion concentration relationships in land drainage. Much work is and has been done in the laboratory on moisture flow with particular reference to miscible displacement theories. This project investigates a portion of the overall miscible displacement phenomena in the field under conditions which would exist in practice. Specifically, an attempt is made to determine the relative importance of hydrodynamic dispersion and diffusion in a tile drained soil over a relatively impermeable clay using chloride as a tracer.

Soils bear natural and artificial structures and sustain agricultural and biological activities. Understanding soil behaviour is the key to appropriating the benefits derivable from this material. Engineers are usually interested in the mechanical aspect of soil behaviour. This involves the study of volume change and shear response to applied stresses. In the past, soil shear and volume change behaviour were studied independently. But many practical problems involve shearing accompanied by volume change, therefore, it is desirable to consider this interaction in modelling soil behaviour. The critical state theory (Roscoe et al. 1958) was developed to combine both shear and volume change behaviour of soils. Early soil mechanics theories including the critical state theory, were developed for saturated soils. Because unsaturated soils are encountered in many situations, there is the need to adapt earlier theories or to formulate new ones for unsaturated soils. The major differences in the physical behaviour of saturated and unsaturated soils are due to an internal stress called matric suction formed at the air-water interface in the soil pores. Theories developed for unsaturated soil mechanics are based on the inclusion of the effect of matric suction on soil behaviour. In this study, the applicability of two major frameworks (i.e., critical state theory and unsaturated soil mechanics) to the study of agricultural soil behaviour was investigated. Soil behaviour was considered within a modified critical state framework that permits the application of critical state theories to an unsaturated soil. An experimental program involving tests in a modified state-of-the-art triaxial testing system was undertaken. Critical state soil parameters were obtained and state boundaries identified. The role of matric suction and soil structure on state parameters are presented. Changes in matric suction caused a shift (translation) in state boundaries, while changes in structure caused a rotation of the state boundaries. Results also showed that the assumption that matric suction is a constant variable depends on the stress level in the soil. Under low stress regimes, this assumption seems justifiable, however this is questionable under high stress regimes. This study also showed the importance of consideration of suction in the analysis of agricultural soil behaviour.

The objective of this investigation is to measure and analyze surface temperature fluctuations in pool boiling. The surface temperature fluctuations were recorded on silicon surfaces with and without multi-walled carbon nanotubes (MWCNT). Novel Thin Film Thermocouples (TFT) are micro-fabricated on test substrates to measure surface temperatures. A dielectric liquid refrigerant (PF-5060) is used as test fluid. Both nucleate and lm boiling regimes are investigated for the silicon test substrates. Dynamics of nucleate boiling is investigated on the CNT coated substrates. High frequency temperature fluctuation data is analyzed for the presence of determinism using non-linear time series analysis techniques in TISEAN(copyright) software. The impact of subcooling and micro/nano-scale surface texturing using MWCNT coatings on the dynamics of pool boiling is assessed. Dynamic invariants such as correlation dimensions and Lyapunov spectrum are evaluated for the reconstructed attractor. A non-linear noise reduction scheme is employed to reduce the level of noise in the data. Previous investigations in pool boiling chaos, reported in literature were based on temperature measurements underneath the test surface consisting of single or few active nucleation sites. Previous studies have indicated the presence of low-dimensional behavior in nucleate boiling and high-dimensional behavior in CHF and film boiling. Currently, there is no study detailing the effects of multiple nucleation sites, subcooling and surface texturing on pool boiling dynamics. The investigation comprises of four parts: i) in situ micro-machining of Chromelalumel (K-type) TFT, ii) calibration of these sensors, iii) utilizing these sensors in pool boiling experiments iv) analysis of these fluctuations using techniques of nonlinear time series analysis. Ten TFT are fabricated on a rectangular silicon surface within an area of ~ 3.00 cm x 3.00 cm. The sensing junctions of the TFT measure 50 mm in width and 250 nm in depth. Surface temperature fluctuations of the order of i) 0.65-0.93 degrees C are observed near ONB ii) 2.3-6.5 degrees C in FDNB iii) 2.60-5.00 degrees C at CHF and iv) 2.3-3.5 degrees C in film boiling. Investigations show the possible presence of chaotic dynamics near CHF and in film-boiling in saturated and subcooled pool boiling. Fully-developed nucleate boiling (FDNB) is chaotic. No clear assessment of the dynamics could be made in the onset of nucleate boiling (ONB) and partial nucleate boiling (PNB) regimes due to the effects of noise. However, the frequency spectra in these regimes appear to have two independent frequencies and their integral combinations indicating a possible quasiperiodic bifurcation route to chaos. The dimensionality in FDNB, at CHF and in film-boiling is lower in saturated pool boiling as compared to values in corresponding regimes in subcooled pool boiling. Surface temperature fluctuations can damage electronic components and need to be carefully controlled. Understanding the nature of these fluctuations will aid in deciding the modeling approach for surface temperature transients on an electronic chip. Subsequently, the TFT signals can be employed in a suitable feedback control loop to prevent the occurrence of hotspots.

Revised; Originally published: 05/2008 / The article provides information about different types of dietary fats and promotes consumption of healthy fats in moderation as part of a balanced diet. The prevalence of fat-free products in grocery stores may give some health-conscious consumers the perception that all dietary fats are unhealthy. However, fats are absolutely vital for proper physiological functioning, and it is imperative that fats are included in a healthy diet. Fats are classified as saturated, monounsaturated, or polyunsaturated. Both types of unsaturated fats, when consumed in moderation, can help lower cholesterol and decrease the risk of heart disease, especially when they replace saturated and trans fats. We provide tips for selecting healthier fats, along with a guide for consuming appropriate portions of fat.

The phytotoxicities of monensin, the 10:2 saturated fluorotelomer carboxylic acid (10:2 FTCA), and atrazine to freshwater macrophytes were investigated in three microcosm-based assessments. Both responses of plants grown as individuals in “cone-tainers” and those grown in mixed and monocultures were examined to permit comparison of the toxicological sensitivities of macrophytes under each planting design, and investigation of whether interactions between neighbours may modify plant response to an environmental contaminant. Exposures of monensin and the 10:2 FTCA at environmentally relevant concentrations were found to produce few significant effects in the higher aquatic plants across all growth conditions, thus direct comparisons of effective concentrations were not conducted. Significant differences between relative growth rates (RGR) of plant grown in assemblages versus individually indirectly indicate that over longer exposure durations toxicity may be underestimated using the individual “cone-tainer” method. RGRs and sensitivities of plants to atrazine were found to be in the same range across planting methods, demonstrating that responses of aquatic plants in the individual-test system reflected those observed in model populations and two-species communities. A lack of observed relations between plants in the mixed and monoculture tests, however, meant that the potential for modification of toxicity through plant interactions was not investigated.

The phytotoxicities of monensin, the 10:2 saturated fluorotelomer carboxylic acid (10:2 FTCA), and atrazine to freshwater macrophytes were investigated in three microcosm-based assessments. Both responses of plants grown as individuals in “cone-tainers” and those grown in mixed and monocultures were examined to permit comparison of the toxicological sensitivities of macrophytes under each planting design, and investigation of whether interactions between neighbours may modify plant response to an environmental contaminant. Exposures of monensin and the 10:2 FTCA at environmentally relevant concentrations were found to produce few significant effects in the higher aquatic plants across all growth conditions, thus direct comparisons of effective concentrations were not conducted. Significant differences between relative growth rates (RGR) of plant grown in assemblages versus individually indirectly indicate that over longer exposure durations toxicity may be underestimated using the individual “cone-tainer” method. RGRs and sensitivities of plants to atrazine were found to be in the same range across planting methods, demonstrating that responses of aquatic plants in the individual-test system reflected those observed in model populations and two-species communities. A lack of observed relations between plants in the mixed and monoculture tests, however, meant that the potential for modification of toxicity through plant interactions was not investigated.

Thesis (M.S.)--Michigan State University. Dept. of Chemical Engineering and Material Science, 2008. / Title from PDF t.p. (viewed on July 29, 2009) Includes bibliographical references (p. 34-41). Also issued in print.