After reviewing all available literature on heat transfer to superheated steam at high temperatures and pressures, it was concluded that further investigation of this problem would be of value. The thesis was concerned with the derivation of three heat transfer film coefficient equations and their related error equations. The three equations thus derived were not used to determine the value of the heat transfer film coefficient. No experimentation was performed to obtain the necessary data required by the three equations for calculating the heat transfer film coefficient value. Instead an error analysis was made of the film coefficient equations using the derived error equations. Prediction of the most accurate film coefficient equation was made based on results obtained from this analysis. Recommendations for the test apparatus and arrangement, test section design, and experimental procedure were advanced based on the error analysis results. No attempt was made in the thesis to develop an experimental heat transfer film coefficient similar to the equations found in the reviewed literature. / Master of Science

The effect of superheat on the disruption of liquid droplets in a compressible gas flow was investigated experimentally in a small-scale, supersonic wind tunnel. Aerodynamically generated ethanol droplets of an average diameter of 0.1 mm were injected via a normal sonic jet into a Mach 1.8 freestream. Both nonsuperheated and superheated droplets were injected with initial Weber numbers of approximately 700. The droplets and flow structure were photographed using the shadowgraph method. The relatively high momentum of the liquid droplets typically caused them to pass out of the sonic jet structure. Nonsuperheated droplets showed no signs of disrupting after traveling over 200 mm downstream from the injection point. Only droplets with injection temperatures above the predicted boiling point at tunnel freestream static pressure (48°C) showed signs of disruption, typically after they left the sonic jet structure (30 to 100 mm downstream of the injection point). Droplets in this range of temperatures appeared to begin to boil from the downstream side of the droplet, shedding a vapor cloud before disrupting completely in the chaotic mode. Droplets with temperatures above the boiling point at the exit plane of the sonic jet began to disrupt in the chaotic mode almost instantly (within 1 exit nozzle diameter).

The focus of this study was to determine the effects of pretreatment of wheat straw by superheated steam (SS) alone or in combination with boiling water (BW) on biomass structure and yields of fermentation products (cell mass and fermentation end-products) by Clostridium thermocellum. Different cultivars of wheat straw were ground to a particle size less than 355 µm, and exposed to the following methods of pretreatment: i) 15 min soaking in 119 °C boiling water under absolute pressure of 193 kPa, followed by processing with SS at atmospheric pressure at different temperatures and retention times; ii) 15 min processing with SS at atmospheric pressure; and iii) 15 min soaking in 119 °C boiling water under absolute pressure of 193 kPa. Processing with SS was conducted at a variety of temperatures in the range of 180-220 °C. The severity of pretreatment was expressed through a treatment severity factor as a measure of harshness of treatment. Pretreatment combinations of boiling water with superheated steam at different retention times inside the SS chamber were also investigated. Wheat straw samples were then used as substrates in fermentation reactions with C. thermocellum. The most noticeable effects on biomass structure and fermentation were observed at the highest severity factor of 6.5, corresponding to 15 min pretreatment with boiling water followed by 15 min treatment with SS at 220˚C. This pretreatment provided the maximum increase in percentage of contribution of amorphous cellulose (% CAC), and the highest fermentation yield in terms of hydrogen, carbon dioxide, and ethanol production. / October 2015

Superheated steam (SS) drying of distillers’ spent grain (DSG) is a more energy efficient alternative to conventional hot air drying. SS drying at sub-atmospheric pressure (also referred to as low pressure) can prevent burning and lowering the quality of the food product. The objective of this study was to design, fabricate, and test a SS drying system that could operate at sub-atmospheric pressure for drying DSG. After the custom designed system was constructed, major problems associated with the system were identified. A number of tests were carried out and modifications were made to the system to resolve technical problems. Distillers’ spent grain was then successfully dried using the system under various levels of temperature from 95 to 115°C and pressure of either -25 or -20 kPa, with a SS velocity from 0.100 to 0.289 m/s.

Biomass such as spent grain is difficult to dry when it is in the slurry form. Proposed industrial solutions are to compact wet biomass first and then dry it. Compaction develops desired granular form and increases surface area for drying but also brings new technical challenges. Superheated steam (SS) drying is advantageous over hot-air drying as it is more energy efficient. A problem associated SS drying is the initial condensation leading to disintegration of biomass compacts. The current research investigates the disintegration characteristics of distiller’s spent grain (DSG) compacts while being dried in SS. The study focuses on the DSG flowability, densification characteristics and disintegration behavior of DSG compacts as affected by SS drying conditions, soluble content and particle size distribution (PSD). DSG fractions with particle sizes from 300 to 850 µm were dried in SS at 150°C and hot-air at 45 and 150°C. Under these drying conditions bulk density and angle of repose (AOR) varied from 0.379 to 0.435 g/cm3 and 46.0 to 50.4°, respectively. The stress-relaxation data obtained during the compaction of DSG at different levels of compressive pressure (60.3-135.7 MPa), initial moisture content (15, 20 and 25% wet basis- wb) and soluble content (15 and 30%) were normalized and analyzed to determine the asymptotic modulus (EA) of the compacts. The highest EA of 174 MPa was obtained for DSG compacts produced with a compressive force of 135.7 MPa, initial moisture of 25% wb and soluble content of 0%. The percentage increase in volume of DSG compacts during drying in SS at 110 to 150°C temperature range was between 78 to 130%. A comparison between the physical properties of SS dried and hot-air dried compacts revealed the role of SS in accelerating the release of mechanical energy stored in the compacts. An increase of dimensions and a considerable increase in the hardness and EA of the compacts was obtained by adding up to 70% (w/w) solubles or by decreasing the PSD of wet distiller’s spent grain from d(0.9)=1283.6 to 812.8 µm. This study establishes that compaction of wet biomass followed by SS drying can lead to its effective utilization.

Superheated steam (SS) drying of distillers’ spent grain (DSG) is a more energy efficient alternative to conventional hot air drying. SS drying at sub-atmospheric pressure (also referred to as low pressure) can prevent burning and lowering the quality of the food product. The objective of this study was to design, fabricate, and test a SS drying system that could operate at sub-atmospheric pressure for drying DSG. After the custom designed system was constructed, major problems associated with the system were identified. A number of tests were carried out and modifications were made to the system to resolve technical problems. Distillers’ spent grain was then successfully dried using the system under various levels of temperature from 95 to 115°C and pressure of either -25 or -20 kPa, with a SS velocity from 0.100 to 0.289 m/s.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

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Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The present research is an experimental investigation of the atomization of a superheated pressurized liquid jet that is exposed to the ambient pressure due to a sudden depressurization. This phenomena is called flashing and occurs in several industrial environments. Liquid flashing phenomena holds an interest in many areas of science and engineering. Typical examples one can mention: a) the accidental release of flammable and toxic pressure-liquefied gases in chemical and nuclear industry; the failure of a vessel or pipe in the form of a small hole results in the formation of a two-phase jet containing a mixture of liquid droplets and vapor, b) atomisation improvement in the fuel injector technology, c) flashing mechanism occurrence in expansion devices of refrigerator cycles etc... The interest in flashing events is especially true in the safety field where any unexpected event is undesirable. In case of an accident, flammable or toxic gas clouds are anticipated in close regions of the release because of the sudden phase change . Due to the non-equilibrium nature of the flow in these near field regions, conducting accurate data measurements for droplet size and velocity is a challenging task resulting in scarce data in the very close area. This research has been carried out at the von Karman Institute (VKI) within the 5th framework of European Commission to fulfill the goal of understanding of source processes in flashing liquids in accidental releases. The program is carried out under name of FLIE (Flashing Liquids in Industrial Environments)(Contract no: EVG1-CT-2000-00025). The specific issues that are presented in this thesis study are the following:a) a comprehensive state of art of the jet break up patterns, spray characteristics and studies related to flashing phenomena; b)flashing jet breakup patterns and accurate characterization of the atomized jet such as droplet diameter size, velocity and temperature evolution through carefully designed laboratory-scale experiments; c) the influence of the initial storage conditions on the final atomized jet; d) a physical model on the droplet transformation and rapid evaporation in aerosol jets. In order to characterize the atomization of the superheated liquid jet, laser-based optical techniques like Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) are used to obtain information for particle diameter and velocity evolution at various axial and radial distances. Moreover, a high-speed video photography presents the possibility to understand the break-up pattern changes of the simulating liquid namely R-134A jet in function of driving pressure, superheat and discharge nozzle characteristics. Global temperature measurements with an intrusive technique such as thermocouples, non-intrusive measurements with Infrared Thermography are performed. Cases for different initial pressures, temperatures, orifice diameters and length-to-diameter ratios are studied. The break-up patterns, the evolution of the mean droplet size, velocity, RMS, turbulence intensity and temperature along the radial and axial directions are presented in function of initial parameters. Highly populated drop size and velocity count distributions are provided. Among the initial storage conditions, superheat effect is found to be very important in providing small droplets. A 1-D analytical rapid evaporation model is developed in order to explain the strong temperature decrease during the measurements. A sensitivity analysis of this model is provided.