Chamber Diameter Research Articles

Design, fabrication, and investigations of prototype supersonic micro-ejector for innovative cooling system of electronic components

Innovative approach for electronics cooling was proposed, i.e. heat generated by a part of electronic equipment, e.g. CPU, is absorbed by heat driven micro-ejector refrigeration system that can provide cooling of other electronic components, e.g. GPU. It was demonstrated the procedure of design, fabrication, and experimentation on the supersonic micro-ejectors for the case of isobutane as a working fluid for such system. It was demonstrated that it possible to design and fabricate the micro-ejector of cooling capacity in the range 3 W suitable for cooling of electronic equipment. For the discussed micro-ejector entrainment ratio obtained was app. 0.20 under conditions of the motive heat source temperature app. 60 °C and evaporation temperature app. 22 °C. There were demonstrated difficulties in fabrication of the supersonic ejector due to small dimensions of the motive nozzle as well as mixing chamber. Required throat diameter of the motive nozzle was less than 200 μm and the diameter of the mixing chamber was 260 μm. For reported tests conditions the boundary temperature of the on-design operation condition was between 21 – 25 °C. However, the operation of the micro-ejector under off-design operation regime was stable and repeatable. Micro-ejector tests required an indirect method of measurement of critical motive mass flow rate to be applied. The performance line of tested ejector fits to ejectors theory and meet the basic assumptions in terms of thermal capacity and operating temperature. CFD technique used for numerical predictions of the ejector performance fits to experimental measured values with acceptable accuracy.

Prediction of atomization characteristics of pressure swirl nozzle with different structures

The structure of the pressure swirl nozzle is an important factor affecting its spray performance. This work aims to study pressure swirl nozzles with different structures by experiment and simulation. In the experiment, 10 nozzles with different structures are designed to comprehensively cover various geometric factors. In terms of simulation, steady-state simulation with less computational complexity is used to study the flow inside the nozzle. The results show that the diameter of the inlet and outlet, the direction of the inlet, the diameter of the swirl chamber, and the height of the swirl chamber all affect the atomization performance, and the diameter of the inlet and outlet has a greater impact. It is found that under the same flow rate and pressure, the geometric differences do have a significant impact on the atomization characteristics, such as spray angle and SMD (Sauter mean diameter). Specific nozzle structures can be customized according to the actual needs. Data analysis shows that the spray angle is related to the swirl number, and the SMD is related to turbulent kinetic energy. Through data fitting, the equations for predicting the spray angle and the SMD are obtained. The error range of the fitting equation for the prediction of spray angle and SMD is within 15% and 10% respectively. The prediction is expected to be used in engineering to estimate the spray performance at the beginning of a real project.

Mechanism study on the influence of combustion models and spray gun geometric parameters on high-velocity oxygen-fuel (HVOF) thermal spraying

HVOF thermal spraying technology has unique advantages for spraying WC-12Co ceramic powder. The spraying process is complex, involving the gas-liquid-solid multiphase flow, chemistry, heat transfer and intelligent control. It is vital to quantitatively reveal the reaction mechanism of combustion components, which optimizes the thermal spraying process and improves the coating quality. A numerical model of HVOF thermal spraying was established, including the gas dynamics model, chemical thermodynamics model and discrete phase model for spraying particle. The difference between the eddy dissipation model (EDM) and EDC model in the traditional calculation was compared. The results show that the EDC model reveal the chemical reaction mechanism of the combustion in detail step by step, and quantitatively display the exothermic phenomenon during whole spraying. The exothermic reaction predicted by the EDC model continues into the air domain with the flame flow. The geometric structure of spray gun was analyzed based on the EDM model. The results show that the diameter of the combustion chamber is 30.2 mm, the diameter of the parallel nozzle is 10.5 mm, and the length from the particle inlet to the nozzle starting point is 13.3 mm, the flight temperature and velocity for particles are relatively high.

Numerical and experimental study of the ocean thermal energy capture process utilizing metal foam–phase-change material (PCM) composites

Ocean thermal energy (OTE) is an ideal in-situ retrievable energy source for underwater profiling vehicles to maintain their long-term mission capacity. A potential method to capture OTE is to utilize the volume change in metal foam–phase-change material (PCM) composites. In this study, a numerical model for the phase change and energy conversion processes was established. The solidification and melting process were observed experimentally to validate the proposed model. Based on the numerical model, a parametric study was conducted to demonstrate the influence of the back pressure, metal foam, ambient temperature and chamber diameter on the phase change process. The results indicate that (i) increasing the back pressure reduces the temperature difference between the solid phase area and the environment, thus increasing the melting time; (ii) adding copper foam with low porosity in the phase-change chamber can effectively improve the net power density of an ocean thermal engine; (iii) the net power density is significantly affected by the hot end temperature; (iv) reducing the inner diameter of the phase-change chamber can reduce the phase transition time. However, to maximize the net power density, an appropriate inner diameter and back pressure must be selected; and (v) after optimization, the net power density is increased by 151.7 %, which reflects the value of the proposed numerical model in engineering applications.

A method of matching the combustion chamber diameter based on spray characteristics for lateral swirl combustion system

To summarize a method of matching the combustion chamber diameter for lateral swirl combustion system (LSCS), at engine speeds of 1800 r/min and 2500 r/min, under 25%–100% loads and excess air coefficients (φa) of 1.2–2.0, the combustion and emission performance of LSCSs with different combustion chamber diameters was experimentally studied. Experimental results indicate that, with combustion chamber diameter of 88 mm, LSCS obtains the most favorable combustion performance, increasing the indicated thermal efficiency by 0.76%–4.03%. In addition, combustion chamber diameter affects the LSCS combustion performance more evidently under low load (25% load) and high excess air coefficient (φa of 2.0) conditions. Simulation research was performed under typical working conditions (at engine speed of 1800 r/min and 2500 r/min, under 50%–100% loads and φa of 1.2–2.0) to match the optimal combustion chamber diameter, and to study the corresponding spray characteristics. Simulation results show that, the optimal LSCS combustion chamber diameter and fuel spray penetration distance shows approximate liner relation. Therefore, the spray excess penetration coefficient τ is proposed, representing the interaction intensity between fuel spray and combustion chamber wall. For LSCS, when τ reaches its characteristic value of 1.5, the combustion chamber diameter matches well with the fuel spray penetration distance.

Left atrial area as a simple predictor of paroxysmal AF in patient with acute ischemic stroke

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The most important cardiogenic reason of acute Ischemic stroke (AIS) is atrial fibrillation (AF). Left atrial (LA) enlargement (atriopathy) is one of the risk factors of atrial fibrillation. Basic bio-metric measurements (height , weight and BSA) in patients with AIS can be challenging due to immobilization, therefor estimation of LA size using recommended parameter (left atrial volume index) is often not possible in every day practice. Aim To assess the discriminant value of different LA size parameters for detection of known paroxysmal AF in patients with acute ischemic stroke. To estimate best cut-off value of LA size parameters which predict presence of paroxysmal AF in patients with AIS. Materials and methods A database of 663 consecutive patients admitted to a neurology department with the diagnosis of acute ischemic stroke (AIS) who underwent transthoracic echocardiography (TTE) were analysed. After exclusion of 117 patient with persistent or permanent AF (present during TTE) the examined group comprised of 546 patients. Average age was 70,1years (20-97yrs), 53% were women. From the examined group 56 (10,3%) had known (from past medical history or diagnosed during the hospitalization in ecg, telemetry or holter monitoring) paroxysmal AF. 35,6% of examined patients required bedside echocardiography due to immobilization. The predictive values for the presence of paroxysmal AF were assessed for: LA antero-posterior diameter (LAd) in parasternal long axis , LA area in four chamber diameter (LAA), as well as LAd and LAA indexed to aorta diameter(Ao) (innere-to-inner method on the level of sinus of Valsalvy). Receiver Operating Characteristic (ROC) curves, area under the curve (AUC), specificity and sensitivity were analysed, Younden index was used for the estimation of cut-off values. Results ROC – curves of all examined parameters are presented in fig. 1. The AUC of LAd, LAA, LAd/Ao and LAA/Ao were: 0,60; 0,73 0,72; 0,81 respectively. Differences in AUC were statistically significant (p<0,05). The best cut of value for LAA/Ao was 7,2cm2/cm , with sensitivity of 0,90 and specificity of 0,59. 112 of 490 (23%) patient without known paroxysmal AF exceeded the estimated cut-off point. Conclusions 1. In 1/3 of patients with AIS the assessment of recommended parameter of LA size (LAVI) can be difficult in clinical practice. 2. A simple, widely available parameter of left atrial size (LAA/Ao) has the best predictive value for the detection of patients with known paroxysmal AF. 3. Nearly ¼ of patients without known AF presenting with AIS have atriopathy which can be connected to not recognized arrhythmia. 4. LAA/Ao can be used as a simple, widely available parameter for the selection of patient for more profound prospective screening for AF in patients with AIS.

Changes in corneal high order aberrations and anterior chamber parameters following scleral fixated intraocular lens implantation

BackgroundTo evaluate the change in corneal high order aberrations (HOAs) and anterior chamber parameters following scleral fixation in aphakic patients using the Scheimpflug camera system. MethodsThis retrospective study included patients who were aphakic after phacoemulsification surgery and underwent scleral-fixed intraocular lens (SF-IOL) implantation with Z suture technique between 2010 and 2022. Preoperative and postoperative best corrected visual acuity (BCVA), anterior segment parameters and corneal aberrations were evaluated with a combined Scheimpflug-Placido disk corneal topography device (Sirius Costruzione Strumenti Oftalmici, Florence, Italy). The following values were recorded: Simulated keratometry (SimK), flat meridian (K1), steep meridian (K2), iridocorneal angle (ICA), temporal anterior chamber angle (T-ACA), nasal anterior chamber angle (N-ACA), horizontal anterior chamber diameter (HACD), anterior chamber volume (ACV), corneal volume (CV), total Root Mean Square (RMS), high order aberrations (HOAs), spherical aberration, coma, trefoil, quadrifoil, and secondary astigmatism. ResultsThe study included 31 eyes of 31 patients (mean age: 63.00 ± 19.41 years, 17 males/14 females). Postoperative BCVA was better than preoperative BCVA (p = 0.012). Postoperatively, there was a statistically significant increase in ACV and CV values and a statistically significant decrease in K2 (p = 0.009, p = 0.032, p = 0.015). Preoperative T-ACA and preoperative and postoperative ACV were negatively correlated with postoperative intraocular pressure (r=-0.427 p = 0.033, r=-0.406 p = 0.032 and r=-0.561 p = 0.001). There were statistically significant postoperative increases in corneal RMS, trefoil and HOAs for 3 mm pupil diameter (p = 0.0177, p = 0.001, p = 0.031) and in corneal RMS, trefoil and quadrifoil aberrations for 6 mm pupil diameter (p = 0.033, p = 0.001, p = 0.001). ConclusionsIn conclusion, SF-IOL implantation with Z-suture technique used for visual rehabilitation of aphakic patients may affect visual quality by increasing corneal HOAs while improving visual acuity.

Heat Transfer Characteristics of Oil-Based Drill Cuttings in Thermal Desorption Chambers

Thermal desorption technologies have been extensively applied for the disposal of oil-based drill cuttings. Fluent-software-based phase changes in multiphase flow models within thermal desorption chamber temperature field simulations were examined to study the effects of oil-based drill cuttings fluid content and feed rates, nitrogen content, thermal desorption chamber length and diameter, and extraction tube position on the thermal desorption chamber and temperature field. Our results demonstrate that these factors had a considerable influence on the temperature field of the chamber, with the liquid content of the oil-based drill cuttings having the greatest influence. The heat transfer process was enhanced by appropriately increasing the diameter and length of the chamber and reasonably setting the extraction tube. When the chamber length was insufficient, there was a risk that the outlet temperature would be extremely low and the oil content of the residue would exceed the standard. The higher the feeding and nitrogen entering rates of the oil cuttings, the higher the liquid content of the oil cuttings and the lower the temperature in the chamber. Based on the heat transfer characteristics of the oil-based drill cuttings in the thermal desorption chamber, this study provides a theoretical basis for the design and application of oil-bearing cutting thermal desorption devices.

Design and optimization of a runner for a gravitational vortex turbine using the response surface methodology and experimental tests

In this work, four runners for a gravitational vortex turbine (GVT) were initially analyzed numerically with the aim of selecting the one with the best efficiency (η). The selected rotor was optimized using the response surface methodology (RSM). Four design factors were considered: the number of blades (M), the twist angle (λ), the relationships between the runner upper (D) and lower (d) diameters, and the upper chamber diameter (Dcd); i.e., D/Dcd and d/Dcd, respectively. For the numerical analysis, a three-dimensional (3D) computational domain in ANSYS Fluent software with the K−ϵ RNG turbulence model and the six degrees of freedom (6-DoF) user defined function (UDF) method was utilized for the unsteady flow simulations. The η versus (vs.) the angular velocity (ω) curve was monitored during the CCD for all the treatments tested. The highest η was 0.522 under optimal design conditions; i.e., for M, λ, D/Dcd and d/Dcd equal to 6, 55°, 0.5 and 0.23, respectively. The optimal runner was built using a 3D printing and was experimentally tested utilizing a hydraulic bench. The experimental and numerical η vs. ω curves were compared. A difference of 5.1% between the maximum values of η was found.

Structural Optimized Design of a Powder Mixer for Multi-Material Directed Energy Deposition Based on CFD-DPM

Directed energy deposition (DED) offers an unprecedentedly convenient and efficient additive manufacturing approach to novel alloy designs such as high entropy alloys. As a critical component of the novel DED system, a powder mixer to stably and uniformly mix different powders plays an important role in the DED process. In this paper, the computational fluid dynamics-discrete phase model (CFD-DPM) method was used to simulate the characteristics of the gas-solid coupled fluid inside the powder mixer. The influence of the structural details of the powder mixer on the motion characteristics of the gas-solid coupled fluid was investigated by numerical simulation. Based on the numerical simulation results, the range of parameters of critical structure such as the inlet angle, the diameter and height mixing chamber, and the height of the bottom was determined. The difference in powder mixing uniformity among different powder mixers was qualitatively analyzed through powder mixing experiments. The BSE-EDS results of mixed powder samples show that the mixer with reasonable structural parameters has better mixing uniformity. In summary, this work provides a powerful reference for the rapid optimization design of the powder mixer structure.

Optimization of geometric parameters of ejector for fuel cell system based on multi-objective optimization method

ABSTRACT In this study, the multi-objective orthogonal experiment is employed to optimize the geometric parameters of the ejector. The optimization objective is determined by applying linear weighting to the entrainment ratios for 100 SLPM and 990 SLPM operating conditions. Four geometric parameters are optimized, including the nozzle exit diameter, nozzle exit position, mixing chamber length, the mixing chamber diameter. Moreover, Computational Fluid Dynamics simulations are performed, and the effects of each geometric parameter and the interaction between parameters on the performance of the ejector are ranked by range analysis. The results show that the mixing chamber diameter has the most significant impact on the optimization objective, and the degree of influence of the other factors and interactions on the entrainment ratio varies for different operating conditions. Compared with the initial parameters, the parameters obtained by the multi-objective optimization method have an average improvement of 96% in entrainment ratio over the full operating range, and the experimental results are in general agreement with the simulation results. The adaptability analysis of the ejector performance indicates that the ejector optimized by the multi-objective optimization method can meet the hydrogen excess ratio requirements for the full operating range of the fuel cell system.

Quantitative measurements and morphological evaluation of fetal cardiovascular structures with fetal cardiac MRI

PurposeFetal cardiac magnetic resonance imaging (FCMR) can be used as an imaging modality in fetal cardiovascular evaluation as studied in recent years. We aimed to evaluate cardiovascular morphology using FCMR and to observe the development of cardiovascular structures according to gestational age (GA) in pregnant women. MethodIn our prospective study, 120 pregnant women between 19 and 37 weeks of gestation in whom absence of cardiac anomaly could not be excluded by ultrasonography (US) or, who were referred to us for magnetic resonance imaging (MRI) for suspected non-cardiovascular system pathology, were included. According to the axis of the fetal heart, axial, coronal, and sagittal multiplanar steady-state free precession (SSFP) and 'real time' untriggered SSFP sequence, respectively, were obtained. The morphology of the cardiovascular structures and their relationships with each other were evaluated, and their sizes were measured. ResultsSeven cases (6.3%) contained motion artefacts that did not allow the assessment and measurement of cardiovascular morphology, and three (2.9%) cases with cardiac pathology in the analysed images were excluded from the study. The study included a total of 100 cases. Cardiac chamber diameter, heart diameter, heart length, heart area, thoracic diameter, and thoracic area were measured in all fetuses. The diameters of the aorta ascendens (Aa), aortic isthmus (Ai), aorta descendens (Ad), main pulmonary artery (MPA), ductus arteriosus (DA, superior vena cava (SVC), and inferior vena cava (IVC) were measured in all fetuses. The left pulmonary artery (LPA) was visualised in 89 patients (89%). The right PA (RPA) was visualised in 99 (99%) cases. Four pulmonary veins (PVs) were seen in 49 (49%) cases, three in 33 (33%), and two in 18 (18%). High correlation values were found for all diameter measurements performed with GW. ConclusionIn cases where US cannot achieve adequate image quality, FCMR can contribute to diagnosis. The very short acquisition time and parallel imaging technique with the SSFP sequence allow for adequate image quality without maternal or fetal sedation.

Effect of pre-chamber geometrical parameters and operating conditions on the combustion characteristics of the hydrogen-air mixtures in a pre-chamber spark ignition system

The pre-chamber spark ignition system is a promising advanced ignition system adopted for lean burn spark ignition engines as it enables stable combustion and enhances engine efficiency. The performance of the PCSI system is governed by the turbulent flame jet ejected from the pre-chamber, which is influenced by the pre-chamber geometrical parameters and the operating conditions. Hence, the current study aims to understand the effects of pre-chamber volume, nozzle hole diameter, equivalence ratio, and initial chamber pressure on the combustion and flame jet characteristics of hydrogen-air mixture in a passive PCSI system. Pre-chamber with different nozzle hole diameters (1 mm, 2 mm, 3 mm, and 4 mm) and volumes (2%, 4%, and 6% of the engine clearance volume) were selected and manufactured in-house. The experimental investigation of these pre-chamber configurations was carried out in a constant-volume combustion chamber with optical access. The flame development process was captured using a high-speed camera at a rate of 20000 fps, and the images were processed in MATLAB to obtain quantitative data. The combustion characteristics of hydrogen-air mixtures with the PCSI system improved when compared to the conventional SI system; however, the improvement was more significant for ultra-lean mixtures. Early start of combustion and shorter combustion duration were observed for PCSI – D2 and PCSI – D3 configurations, respectively and improved combustion and flame jet characteristics were also noted for these configurations. With the increase in pre-chamber volume, ignition energy associated with the flame jet increases, which reduces the combustion duration and the ignition lag.

Agreement of Corneal Diameter and Anterior Chamber Depth Measurements with the IOLMaster 500 and the IOLMaster 700 Optical Biometers in Myopic Eyes.

To assess the agreement in automated corneal diameter (CD) and anterior chamber depth (ACD, measured from corneal epithelium to lens) distances measurements between the IOLMaster 500 and 700 optical biometers in myopic eyes. One hundred and sixteen eyes of 116 myopic patients aged between 21 to 60 years were included in this study. Measurements of CD and ACD distances were taken with each biometer for all patients in the same session. A t-test and a p-value less than 0.05 was considered statistically significant when the measurements were compared. The agreement between biometers was studied by applying a Bland-Altman analysis. The mean CD values obtained using the IOLMaster 500 and 700 biometers were 12.26±0.35 mm and 12.13±0.34 mm, respectively. The mean ACD distance values were 3.61±0.29 mm and 3.62±0.31, for the IOLMaster 500 and 700 biometers, respectively. There were statistically significant differences between the two devices only for CD measurements (p<0.001), but not for ACD measurements (p=0.26). The limits of agreement obtained were wide in both types of measurements, being 0.422 mm for the CD distance and 0.389 mm for the ACD distance. There were statistically significant differences between the IOLMaster 500 and 700 biometers regarding CD but not in ACD measurements in healthy myopic eyes. These differences could be clinically significant in some cases. According to these results, medical judgement should be used to assess whether the two devices could be used interchangeably for CD and ACD measurements during the clinical practice.

Modeling and Optimal Design of a Desalination System Integrated Between a Glass-Covered Solar Collection Water Chamber and a Heat Dissipating Chimney

Abstract Solar thermal energy is trapped in a glass-covered water chamber/basin to provide the heat for evaporation of brackish water in a novel desalination system. To harvest clean water, a chimney is integrated with the water basin, which draws air into the chamber to be humidified by the vapor and then being ventilated via buoyance force. Uniquely, thermal conductive metal sheet is recommended to make the chimney, which allows the vapor in the humid air condenses easily when flowing up. The condensate at the inner wall of the chimney flows down to be collected as clean water. Mathematical modeling and numerical computation have been carried out to delineate the coupling of the buoyance-force-driven flow with the heat and mass transfer of air and water in the solar collection chamber and the condensation of vapor in the heat-dissipating chimney. The objective of the simulation and optimization of the system is to find the best match of the dimensions of the water chamber with a chimney to maximize the production of clean water and energy efficiency. The model has been used to simulation several cases (of water from 40 °C to 50 °C) with available experimental data from the authors’ previous work, and the agreement was satisfactory. The optimization studies found that there is a maximum air flowrate corresponding to a critical chimney height due to the requirement that the chimney is designated to dissipate heat as much as possible to condense water vapor. With the chimney height greater than the critical height, the airflow rate will have a slight decrease. Nevertheless, higher than a critical height is still needed for a chimney to condense more moisture. Optimized chamber diameters at different chimney heights are provided for reference of optimal system designs.

Echocardiographic values for normal conditioned and unconditioned North American whippets.

Echocardiographic reference intervals have not been reported for North American whippets, or for whippets that have undergone pet-level athletic training. To develop normal echocardiographic reference intervals for North American whippets and investigate differences in echocardiographic parameters based on athletic conditioning in pet whippets engaged in competitive sports. One-hundred healthy North American whippets. Dogs were examined at national shows between 2005 and 2009. Echocardiographic reference intervals were constructed and the effect of athletic conditioning on parameters of structure and function was assessed. Two dimensional, M-mode, Doppler and tissue Doppler reference ranges for healthy North American whippets are presented. Measures of left ventricular (LV) chamber diameter were larger in conditioned whippets (N=25) and remained significantly larger than in unconditioned whippets (N=16) when normalized for weight using allometric equations. Calculated LV mass was higher in conditioned dogs than in unconditioned dogs, and this difference persisted when LV mass was normalized by weight. Mitral E velocity was higher in conditioned dogs than in unconditioned dogs, whereas E/A and measures related to systolic function were not different. Pet whippets in peak athletic condition have larger hearts than do less conditioned whippets, but measures of systolic function are similar. Whippet pet athletes may show eccentric LV hypertrophy at peak condition. Normal values for cardiac size and function in North American whippets might be considered abnormal if population-specific whippet reference intervals are not used in analysis.

Commentary: Reliability, repeatability, and accuracy of Sirius topographer in assessing anterior segment morphology following laser peripheral iridotomy in primary angle-closure disease.

Commentary: Reliability, repeatability, and accuracy of Sirius topographer in assessing anterior segment morphology following laser peripheral iridotomy in primary angle-closure disease.

CONVERGENT AND DIVERGENT ANGLES OF A SOLID-FUEL ROCKET NOZZLE AND ITS INFLUENCES ON THE MOTOR’S THRUST CURVE

The main goal of this work is to investigate how the angles of a convergent-divergent rocket nozzle influence the thrust curve of a solid-propulsion rocket. The work has been conducted within an academic rocketry team. As there is not clear reasoning on how to define these angles, the present research provides insights on how these geometrical parameters influence the performance of a rocket motor. A 2D-axisymmetric CFD domain is considered, comprising the fluid domain inside and outside the nozzle, to give room for the shock waves to happen and also accommodate the flow. The study comprises a baseline geometry and twelve modified designs, varying the convergent and the divergent angles of the nozzle. Since the convergent diameter must match the chamber diameter, it is fixed. For the divergent diameter, there is no such restriction; therefore, there are two possibilities: a divergent section with the same divergent diameter or with the same length as the baseline. The benchmark thrust curve is generated with a MATLAB code based on solid-fuel modeling and the De Laval theory. The curve is divided into six steady-state simulations, using boundary conditions of mass flow, pressure and temperature at the inlet and pressure and temperature at the outlet. The baseline geometry is simulated in Ansys Fluent and normalized by the MATLAB benchmark. A mesh study selects which mesh and turbulence model to use based on this normalization. The modified geometries are then compared to the baseline. The main quantity of interest is the thrust but quantities such as static pressure and average velocity at the nozzle exit aid the understanding of the changes in thrust.

FLUID BEHAVIOR INVESTIGATION ON A SINGLE-PHASE EJECTOR USING NUMERICAL APPROACH

This study aims to determine fluid flow behaviors and its property inside of an ejector for a single-phase system. Numerical simulation has been employed to investigate the efficiency of the ejector. The numerical process begins with model creation, mesh sensitivity study, turbulent model selection and validation study. Seven parts of ejector that can be optimized to achieve the objectives namely nozzle diameter, venturi tube neck diameter, nozzle distance, venturi tube neck length, straight pipe length, mixing chamber diameter, and mixing chamber length. Through these seven aspects, a total of 82 design points has been generated by CFD software and have obtained a candidate that provides optimized parameters that are 2.12mm, 18.93mm, 3.12mm, 80.71mm, 195.9mm, 138.63mm and 165.64mm. These parameters that contribute to the optimized output have contributed 0.0462% efficiency than before. This also shows that this ejector model does not require significant changes because this model is said to be close to the optimized ejector. Through these seven modifiable parameters, a total of 82 design points has been generated by MOGA algorithm and have obtained a candidate that provides optimized parameters that are 2.12mm, 18.93mm, 3.12mm, 80.71mm, 195.9mm, 138.63mm and 165.64mm. These parameters that contribute to the optimized output have contributed 0.0462% efficiency.

Influence of geometric parameters on the performance of ejector used in aeroengine air system

By using an ejector to draw low-pressure, low-temperature air into the aeroengine's air system, it is possible to significantly enhance the cooling effect of the hot component of the engine. It is very necessary to clarify the sensitivity of ejector performance to different geometric parameters, especially the receiving chamber height, mixing chamber diameter, and diffuser diameter, which are of great significance to improve ejector performance and save limited aeroengine space. Therefore, this paper investigated the effects of these three geometric parameters on the ejector's performance by numerical simulation. The results show that increasing the mixing chamber diameter can significantly improve ejector performance. When the compression ratio is 1.17 and the mixing chamber diameter is increased from 3 mm to 9 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 23.1 % and 7 %, respectively. Especially when the compression ratio is 1, simultaneously increasing the size of the receiving chamber, mixing chamber, and diffuser can greatly improve the ejector's performance. When the diameter of the mixing chamber is increased from 6 mm to 27 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 211 % and 39 %, respectively. The change in ejector structure will influence its flow field and then affect the mixing process. When the size of the ejector is too small, the strong background shock wave suppresses the mixing of the primary flow and the secondary flow, which then causes an increase in the total pressure loss. When the size of the ejector is too large, the eddy current loss leads to ejector performance reduction.