A Study on Mass Transfer between Recirculation Zone and Outside Flow of Annular Premixed Flame

The stability limits were measured for a double concentric propane-air premixed jet flame. The burner tubes have an 8 mm inner diameter with rims of 0-7 mm thicknesses. The flame was stabilized in a higher velocity region where the rim is of sufficient thickness because of a recirculation zone forming behind a thick rim. For the recirculation zone, the aerodynamic structures such as the length and flow directions were investigated as well as the thermodynamic structures, that is, the distribution of temperatures, gas components concentration and local mixing ratio. The results showed that the real mixing ratio of the recirculation zone changed with the flow conditions. The real mixing ratio was measured by CO2 trace method with cold flow, and was predicted successfully with a simple assumption for the ratio of the mass exchanges.

Numerical investigation of the local extinction and re-ignition mechanisms of premixed flame in a micro combustor with a flame holder and preheating channels

In the present paper, an experimental and numerical investigation of fluid flow and heat transfer in the case of wall injection besides main flow through a circular sudden enlargement are studied. The injected flow is achieved through an annular slot placed around the inner side wall of the step. The static pressure variation along the sudden enlargement length is measured and calculated at different values of injection ratio ( Q ) and injection flow angles. The average heat transfer with Reynolds number (ReJ) of injected flow at different values of the inlet flow angle is obtained. The velocity, turbulent kinetic energy and temperature contours are presented in this study. Reynolds number of injected flow is varied between 320 and 840, Reynolds number of main flow is between 5895 and 8450 and the injection flow angles are 0 o , 15 o , 30 o , 45 o and 60 o . In the injection case, the results indicate that, the pressure recovery coefficient increases by decreasing the injection ratio and increasing the flow angle. The average heat transfer coefficient increases as both injection Reynolds number and the injection flow angle increase. The numerical results showed that two recirculation zones generate behind the step between the injection flow and the main flow. The size of these recirculation zones decreases by increasing the injection flow rate. The turbulent kinetic energy increases within region between the recirculation zones and main zone also, it decays by injecting flow in the recirculation zone. The length for higher value of flow temperature decreases by injecting flow in the recirculation zone, and that length increases as the injection flow rate increases. The comparison between the experimental results and the numerical results gives good agreement using the k-e model with Leschziner and Rodi correction.

In the present work, a convergent–divergent nozzle with a multi‐inlet combustion chamber of a rocket engine is numerically investigated to precisely understand the flow dynamics and variation of flow properties like pressure, temperature, and velocity distribution. The work also deals with a modified combustion chamber having multiple inlets. According to the entry conditions, when the propellants enter the combustion chamber, they are burning due to high velocity and temperature. Then there is a rapid increase in temperature and pressure in the combustion chamber, and afterward, they decrease over the nozzle's length. In this study, three configurations have been prepared in the design modular of ANSYS, a combined setup of the convergent–divergent nozzle with a combustion chamber with four inlets, six inlets, and one with increased combustion chamber length called a modified combustion chamber configuration. In this analysis, an investigation is performed to see the effect of multi‐inlet and increased length of the combustion chamber on the convergent–divergent nozzle's exit velocity. The results show that the configuration with six inlets modified combustion chamber has a 26.3% increase in velocity than six inlets and 38.6% higher exit velocity than four inlets convergent–divergent nozzle of the rocket engine.

Gas–liquid mass transfer in the gas–liquid–solid mini fluidized beds

Effects of in-nozzle flow and low-pressure zone on spray targeting of multi-hole gasoline direct injection injector

Abdominal Aortic Aneurysms (AAAs), i.e., focal enlargements of the aorta in the abdomen are frequently observed in the elderly population and their rupture is highly mortal. An intra-luminal thrombus is found in nearly all aneurysms of clinically relevant size and multiply affects the underlying wall. However, from a biomechanical perspective thrombus development and its relation to aneurysm rupture is still not clearly understood. In order to explore the impact of blood flow on thrombus development, normal aortas (n = 4), fusiform AAAs (n = 3), and saccular AAAs (n = 2) were compared on the basis of unsteady Computational Fluid Dynamics simulations. To this end patient-specific luminal geometries were segmented from Computerized Tomography Angiography data and five full heart cycles using physiologically realistic boundary conditions were analyzed. Simulations were carried out with computational grids of about half a million finite volume elements and the Carreau-Yasuda model captured the non-Newtonian behavior of blood. In contrast to the normal aorta the flow in aneurysm was highly disturbed and, particularly right after the neck, flow separation involving regions of high streaming velocities and high shear stresses were observed. Naturally, at the expanded sites of the aneurysm average flow velocity and wall shear stress were much lower compared to normal aortas. These findings suggest platelets activation right after the neck, i.e., within zones of pronounced recirculation, and platelet adhesion, i.e., thrombus formation, downstream. This mechanism is supported by recirculation zones promoting the advection of activated platelets to the wall.

Numerical simulations of steady perforated-plate stabilized Syngas air pre-mixed flames

Tidal energy offers significant potential as a sustainable and predictable renewable energy source. Accurate characterization of tidal resources is critical for identifying optimal sites and designing efficient energy conversion systems. In order to optimise the process of identifying regions with a high tidal energy potential as well as to provide data for studies on the global or regional potential of tidal energy, satellite data can play a significant role. Not only is it available for all regions around the globe, but also in a lot of forms it is available without any access restrictions. The research aims to assess the accuracy and reliability of the new code based on the satellite-derived AVISO model in diverse tidal environments, providing insights for improving tidal energy resource assessments. FES2014 and FES2022 build on analysis of sea surface height and velocity fields as collected by satellite imagery. The primary objective is to evaluate the performance of a satellite-data-driven tidal code in predicting key parameters, including tidal range, velocity profiles, and energy potential, by benchmarking its outputs for the North Atlantic. The results of the analysis are compared against ResourceCode, an online platform developed by the French Research Institute for Exploitation of the Sea (IFREMER) that provides tools, datasets, and models for marine research. ResourceCode is based on a simulation tool which considers bathymetry maps and various hydrodynamic parameters. This comparison aims to identify discrepancies, assess the suitability of the code for different environments, and propose improvements for enhanced precision in tidal resource characterization. In order to quantify potential deviations between the two bases, three different validation cases have been selected: A high flow velocity site in Raz Blanchard A high flow velocity site in Fall of Warness A tidal range site on the estuary of river Mersey Spatial and temporal variability in tidal predictions were used to quantify the agreement between the two data sources. The preliminary results highlight small discrepancies between the new AVISO-based tidal code and the ResourceCode across the sites considered. Across the different locations, maximum tidal velocities presented a divergency lower than 5%. Similarly, the average tidal velocity and potential energy showed a decent agreement, resulting in a difference of 10% on average. These findings indicate strong performance of both codes in high-velocity tidal environments. This study demonstrates that while both the AVISO-based tidal code and the Resource code provide reliable estimates in high-velocity coastal regions, the new code overestimates the condition possibly for the missing interaction with wind. The AVISO-based code is a good option for an overview of the energy potential of a country and seeking possible locations. When ResorceCode is more accurate of detail location as among islands in an archipelago and temporal prediction. The discrepancies between the two codes leave room for improvement in the robustness of the AVISO-based code, where at the same time it can enable developers and suppliers in ocean energy sector to expand their market and define potential allocation outside of Europe.

A linear, travel time tomography study of the most active shield volcano of the world, Kilauea Volcano, Hawaii, was undertaken to determine the lateral heterogeneities produced by its intricate magmatic and tectonic environment. Kilauea provides an ideal setting to do tomography because of its dense seismograph array and many local earthquakes that allow excellent ray coverage of complex subsurface features. Local P wave data from ∼ 12,295 events were inverted using a one‐dimensional layered velocity model. Inversions were done for two cell sizes (5×5×5 km and 1×1×1 km) to resolve structural regions on different length scales. This study provided a view of the average velocity variations relative to a one‐dimensional velocity model. Analysis and interpretation of the tomographic images allowed us to infer the following model. The main shallow magma reservoir is delineated by a slow velocity region southeast of the summit from 0 to 2 km depth. There is a distinct high velocity region centered northwest of the summit from 0 to 2 km depth that represents a cap of dense, intrusive dikes surrounding the magma chamber. We suggest that the shallow reservoir is a narrow, compartmentalized region of sills and dikes, centered just south‐southeast of Halemaumau caldera. Below the main reservoir, the summit is imaged as a slightly fast region from 5 to 10 km in the coarse model indicating that the main conduit is structurally defined by an intrusive dike complex until about 10 km. The rift zones of Kilauea are imaged as major, high velocity entities, widening to the south with depth until 6 km. These fast anomalies are related to the sheeted dike complexes along the rifts. On a finer scale, slow anomalies suggest the presence of magma pockets centered at 0–2 km depth beneath Mauna Ulu, Makaopuhi and Puu Oo, along the east rift zone (ERZ). Two significant high velocity regions along the lower ERZ near Kalalua and Kaliu are inferred to represent intrusive barriers to magma injection along the shallow (0–4 km) ERZ conduit. The southwest rift zone may have an intrusive barrier related to a high velocity region just southwest of Mauna Iki. The Hilina and Kaoiki fault zones are imaged as slow features at shallow depths (< 5 km) related to the open fractures and scarps along the normal faults. The Koae fault system is imaged as a slightly fast shallow structure (< 6 km) possibly related to intrusive diking from the adjacent rift zones that fill and may even induce the extensional structures associated with this complex fault zone. Continued inversions with the immense amount of seismic data collected for Hawaiian events will allow the detailed development of a three‐dimensional structural model for Kilauea. Such a model will be extremely useful to seismologists and petrologists alike for understanding the tectonic growth and magmatic evolution of this dynamic shield volcano.

From a study of spectroscopic and plate material for the peculiar galaxy NGC 1275, the following observations are made. The main galaxy (V = 5200 km/s) has a smooth luminosity profile and is of type E or S0. Immediately south of the nucleus, this galaxy exhibits an early-type spectrum; immediately north of the nucleus, the stellar population is obscured. Further north of the nucleus, the stellar continuum (V = 5200 km/s) is of later type. In regions where optical obscuration is seen photographically, spectra show that the underlying continuum from the low-velocity galaxy is generally obscured, and strong emission from the high velocity is seen instead. There is generally a correlation in position between the obscuring knots and the high-velocity emission. The Balmer decrement is significantly steeper in the low-velocity emission lines than in the high-velocity system. No absorption lines or continuum are found in association with the high-velocity knots. There is a smooth variation of velocity across the high-velocity region, which is consistent with a picture of a rotating galaxy seen almost edge-on, with a maximum velocity of 150(sin i) km/s. It is believed that the most straightforward interpretation of these observations is that an intervening late-type galaxy, V = 8200 km/s, is seen along the line of sight to the main galaxy, V = 5200 km/s.

Experimental investigation on the effects of hydrogen addition on thermal characteristics of methane/air premixed flames

A theoretical analysis of turbulent jet diffusion flames is developed in which the flame is regarded as an ensemble of laminar diffusion flamelets that are highly distorted. The flow inhomogeneities are considered to be sufficiently strong to produce local quenching events for flamelets as a consequence of excessive flame stretch. The condition for flamelet extinction is derived in terms of the instantaneous scalar dissipation rate, which is ascribed a log-normal distribution. Percolation theory for a random network of stoichiometri c sheets is used to predict quenching thresholds that define liftoff heights. Predictions are shown to be in reasonably satisfactory agreement with experimentally measured liftoff heights of methane jet diffusion flames, within experimental uncertainties. UEL issuing from a tube or duct into an oxidizing atmosphere forms a jet in which combustion may occur. The associated combustion process is the most classical example of a diffusion flame. At sufficiently high velocities of fuel flow (fundamentally, at sufficiently large Reynolds numbers) the entire diffusion flame is turbulent. The turbulent jet diffusion flame begins at the mouth of the duct for a range of values of the exit velocity. When a critical exit velocity is exceeded, the flame abruptly is detached from the duct and acquires a new configuration of stabilization in which combustion begins a number of duct diameters downstream. Flames in this state, stabilized in the mixing region, are termed lifted diffusion flames, and the critical exit velocity at which they appear is called the liftoff velocity. The liftoff height is the centerline distance from the duct exit to the plane of flame stabilization. A further increase in the exit velocity increases the liftoff height without significantly modifying the turbulent flame height (the centerline distance from the duct exit to the plane at which, on the average, combustion ceases). There is a second critical value of the exit velocity, called the blowoff velocity, beyond which the flame cannot be stabilized in the mixing region. The present study addresses questions of the structure of lifted turbulent diffusion flames at exit velocities between liftoff and blowoff values. Attention is focused especially on the calculation of liftoff heights. Liftoff characteristics for turbulent jet diffusion flames are of practical importance in connection with flame stabilization. Conditions for liftoff and blowoff must be known in developing rational designs of burners, e.g., in diffusion-flame combustors for power production or in flaring applications for the petroleum industry. They are also of interest in connection with extinguishment of certain fires that may occur in oil or gas rigs. The present work is directed toward developing an improved fundamental understanding of liftoff phenomena that may later prove useful for these applications.

The effects of flow rate, combustor temperature rise, inlet temperature, nozzle exit diameter, and duct length on spectral content, directionality, radiated sound power, and thermoacoustic efficiency are deduced experimentally using an 8-in.-diam combustor. Even at a high exit velocity of 900 fps, the combustor-on noise is seen to dominate jet noise. Internal and far-field spectra are similar below 1000 Hz (broadband with spikes at longitudinal duct resonance frequencies). Directionality is weak except at exit velocities in excess of 550 fps. At a given nozzle exit temperature and diameter, the internal overall sound pressure levels appear to be related linearly to the far-field levels. The thermoacoustic efficiencies vary from 10 ~ to 10 ~ 4 .

Effects of trapezoidal bluff bodies on blow out limit of methane/air combustion in a micro-channel