Performance Study of a Bladeless Microturbine

The paper presents a comprehensive numerical and experimental analysis of the Tesla turbine. The turbine rotor had 5 discs with 160 mm in diameter and inter-disc gap equal to 0.75 mm. The nozzle apparatus consisted of 4 diverging nozzles with 2.85 mm in height of minimal cross-section. The investigations were carried out on air in subsonic flow regime for three pressure ratios: 1.4, 1.6 and 1.88. Maximal generated power was equal to 126 W and all power characteristics were in good agreement with numerical calculations. For each pressure ratio, maximal efficiency was approximately the same in the experiment, although numerical methods proved that efficiency slightly dropped with the increase of pressure ratio. Measurements included pressure distribution in the plenum chamber and tip clearance and temperature drop between the turbine’s inlet and the outlet. For each pressure ratio, the lowest value of the total temperature marked the highest efficiency of the turbine, although the lowest static temperature was shifted towards higher rotational speeds. The turbine efficiency could surpass 20% assuming the elimination of the impact of the lateral gaps between the discs and the casing. The presented data can be used as a benchmark for the validation of analytical and numerical models.

Stress Corrections After Necking Using a Two-Parameter Equation for the Radius of Curvature

Uniaxial tensile tests were conducted at room temperature, 100 °C and 150 °C, for obtaining necking-corrected stress–strain curves until fracture. The necking correction is based on specimen contours estimated from images recorded during testing. Axisymmetric tensile specimens of an AA6082 alloy artificially aged at different times were tested. The radius of the minimal cross-section area and the necking-curvature radius R were experimentally obtained. For all cases, a/R as a function of the strain after the onset of necking ɛ − ɛu shows a characteristic nonlinear transition into a linear asymptotic relationship. Based on the tests, a new two-parameter curve was proposed for the a/R relationship. The slope of the linear part of the new model equals 1.1, as in the Le Roy model. An additional parameter is introduced, which controls the part of the curve with the nonlinear transition. This region increases at increased testing temperature and varies for different aging times. The proposed equation and the necking corrections were verified by finite element modeling analysis.

The Efficacy of Posterior Turbinoplasty in Combination with Tonsillectomy and Adenoidectomy in Pediatric Sleep Disordered Breathing Patients

Background and Objectives Tonsillectomy and adenoidectomy (T&A) are effective for the treatment of pediatric sleep disorder breathing. However, in some pediatric patients, there remain unresolved snoring and mouth breathing problems after the operation. This study is aimed at evaluating the efficacy of coblation of hypertrophic posterior turbinate in combination with tonsillectomy and adenoidectomy.Subjects and Method We analyzed data from 50 children aged between 5 to 13 years old who were scheduled to undergo T&A operation from June 2018 to December in 2018. We randomly divided them into two groups. The first group consisted of 25 patients who were scheduled to perform only tonsillectomy and adenoidectomy. The second group was 21 patients who were scheduled to perform posterior turbinoplasty in combination with tonsillectomy and adenoidectomy. We evaluated preoperative and postoperative polysomnogram [Apnea-Hypopnea Index (AHI), O2 saturation], acoustic rhinometry (minimal cross section area, nasal volume), and Korean Obstructive Sleep Apnea-18 Survey (KOSA-18) score.Results After additional turbinoplasty (coblation of hypertrophic posterior turbinate), the rate of snoring and mouth breathing remaining was decreased. There were significant improvements in AHI, oxygen saturation, Visual Analog Scale and Epworth Sleepiness Scale in two groups. Symptoms (snoring and mouth breath) remaining postoperatively was much more decreased in the posterior turbinoplasty combined with T&A group than in the single T&A group in terms of KOSA-18.Conclusion When it comes to pediatric sleep disorder breathing surgery, nasal cavity evaluation is an important factor for patient’s postoperative satisfaction for sleeping and snoring. For pediatric sleep disorder breathing patients with hypertrophic posterior turbinate, who are scheduled to do tonsillectomy and adenoidectomy, an additional coblation of posterior turbinate should be considered.

Improved Boiling Heat Transfer in Dry Etched Microchannels With Laser Structured Surfaces

The currently available microchannel fabrication techniques ranging from various etching methods and micro electrical discharge machining to laser microfabrication have some apparent advantages and weaknesses when compared one to another. Manufacturing process should satisfy several important criteria: diversity of the working material, the minimal fabricated feature size, the capability of 3D structuring, the precision and surface quality, maximum aspect ratio, the production costs, etc. This study focuses on combining the benefits of dry etching and laser structuring of a silicon substrate in order to produce microchannels with a capability of an improved heat transfer during boiling. The microchannels with a minimal cross section of 50×50 μm were etched in silicon and afterwards laser structuring was employed in order to make surface topography more appropriate for boiling heat transfer. The laser treatment resulted in micron sized cavities at the bottom of the microchannels, which lowered the temperature of the onset of boiling and improved the heat transfer during flow boiling. The performed combination of manufacturing methods proved to be complementary and cost effective.

The effect of smoking on physiological decongestion of the nasal mucosa in human

BACKGROUND: Exercise is known to decongest the nasal mucosa which results in increased nasal patency. In a recent study it was suggested that smoking might influence the effect of exercise on the nasal mucosa. This implies that smoking may cause neurological damage to the normal nasal physiology, which has not previously been shown. The aim of this study was to investigate whether there was a difference in nasal mucosal reaction to exercise between smokers and non-smokers. METHODOLOGY: Forty-two smokers and non-smokers underwent acoustic rhinometry to register nasal geometry before and after cycling on an ergometer cycle. A structured interview was used for questions about smoking habits and airway symptoms. RESULTS: Both smokers and non-smokers had a significant increase in MCA (minimal cross-section area) and total nasal volume after exercise. There was no statistical significant difference between smokers and non-smokers. CONCLUSIONS: Smoking does not seem to affect the normal physiological decongestion of the nasal mucosa after exercise.

Multiple Submucosal Out-Fracture of the Inferior Turbinates: Evaluation of the Results by Acoustic Rhinometry

A multiple submucosal out-fracture of the inferior turbinates was made in 21 patients with nasal obstruction due to hypertrophy of the inferior turbinates. Before surgery, an endoscopic evaluation and an acoustic rhinometry was performed in all the cases. The operation was done under general anesthesia and bilaterally in all the patients. Three months after surgery, a postoperative acoustic rhinometry was done and an increase of the minimal cross-section area was achieved in all the cases. Acoustic rhinometry performed in 100 normal cases was used as a control group.