Mapping of horizontal refrigerant two-phase flow patterns based on clustering of capacitive sensor signals

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Description and initial operating performance of the Langley 6-inch expansion tube using heated helium driver gas

A general description of the Langley 6-inch expansion tube is presented along with discussion of the basic components, internal resistance heater, arc-discharge assemblies, instrumentation, and operating procedure. Preliminary results using unheated and resistance-heated helium as the driver gas are presented. The driver-gas pressure ranged from approximately 17 to 59 MPa and its temperature ranged from 300 to 510 K. Interface velocities of approximately 3.8 to 6.7 km/sec were generated between the test gas and the acceleration gas using air as the test gas and helium as the acceleration gas. Test flow quality and comparison of measured and predicted expansion-tube flow quantities are discussed

Detonation Diffraction Through a Mixture Gradient

A simple one-dimensional model of a self-propagating gaseous detonation consists of a shock wave tightly coupled to a reaction zone, propagating through a combustible gas mixture as shown in Fig. 1 (Strehlow 1984). A feedback mechanism exists in that the shock wave generates the thermodynamic conditions under which the gas combusts, and the energy release from the reaction zone maintains the strength of the shock This is in contrast to a flame, or deflagrative combustion, in which thermal and species transport processes dominate. Given a particular set of initial conditions, a self-propagating detonation wave travels at a constant Chapman-Jouguet velocity (VCJ) on the order of a few thousand meters per second, with associated pressures and temperatures of tens of bar and several thousand degrees, respectively. A detonation is actually a three-dimensional shock-reaction zone complex with a dynamic wavefront composed of curved incident, mach stem, and transverse shock waves as depicted in Fig. 2 (Strehlow 1970). The transverse shocks sweep across the wavefront and the triple-point paths form a diamond-shaped cellular pattern. The cell width [Greek lambda] is a characteristic length scale of detonations, indicative of the coupling between gasdynamic and chemical processes

Intube two-phase flow probabilities based on capacitance signal clustering

To study the objectivity in flow pattern mapping of horizontal two-phase flow in macroscale tubes, a capacitance sensor is developed for use with refrigerants. Sensor signals are gathered with R410A in an 8mm I.D. smooth tube at a saturation temperature of 15°C in the mass velocity range of 200 to 500kg/m²s and vapour quality range from 0 to 1 in steps of 0.025. A visual classification based on high speed camera images is made for comparison reasons. A statistical analysis of the sensor signals shows that the average and the variance are suitable for flow regime classification into slug flow, intermittent flow and annular flow by using a the fuzzy c-means clustering algorithm. This soft clustering algorithm perfectly predicts the slug/intermittent flow transition compared to our visual observations. The intermittent/annular flow transition is found at higher vapour qualities, but with the same trend compared to our observations and the prediction of [Barbieri et al., 2008, Flow patterns in convective boiling of refrigerant R-134a in smooth tubes of several diameters, 5th European Thermal-Sciences Conference, The Netherlands]. The intermittent/annular flow transition is very gradual. A probability approach can therefore better describe such a transition. The membership grades of the cluster algorithm can be interpreted as flow probabilities. These probabilities are further compared to time fraction functions of [Jassim et al., 2008, Prediction of refrigerant void fraction in horizontal tubes using probabilistic flow regime maps

The Effects of Humming and Pitch on Craniofacial and Craniocervical Morphology Measured Using MRI

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