Cold Flow Studies Research Articles

The effect of swirl burner design configuration on combustion and emission characteristics of lean pre-vaporized premixed flames

The present paper experimentally provides a quantitative comparison between the aerodynamic flow field at non-reaction conditions (cold flow) and the combustion and emission characteristics (hot conditions) of two swirl burners having the same swirl number of 0.55 but with two different configurations. The first burner features an annular outer swirler (swirl angle of 40°) and multiple central circular jets, leading to “low swirl combustion”, whereas the second burner has a blocked central passage and an outer swirler (swirl angle of 35°) resulting in “high swirl combustion”; featuring a central recirculation zone. The cold flow study is conducted using a calibrated five-hole probe while the combustion and emission characteristics are obtained via measurements of flame temperatures and the dry volumetric analysis of CO and NOx emissions. Each burner is coaxially mounted to a vertical cylindrical combustor; inside which a lean (equivalence ratio: ϕ = 0.75), pre-vaporized (preheated to a temperature of 523 K) partially premixed mixture of Jet A-1 fuel and air are admitted. The former low swirl combustion burner gives a bulk stable and uniform reaction zone (W-shape) close to the burner exit with a very slight lifting; confirming the concept of “stable lifting” while reducing the pressure drop across the burner exit and eliminating hot spots in the reaction zone. The high swirl combustion burner exhibits a strong central recirculation zone (better flame stability) that is surrounded by an outer V-shape reaction zone having comparatively higher peak levels of temperature, CO and NOx that would lead to greater liability of higher exhaust emission.

Parametric study of particles homogenization in cold-flow riser reactors

Fluid Catalytic cracking (FCC) process are frequently used for the upgrading of heavy crude oil into more valuable products. Traditionally, the FCC process occurs in a riser reactor, where both vaporised hydrocarbon feed-stock and solid catalyst flow in the direction against gravity. This kind of reactor presents heterogeneous flow distributions that affect the axial and radial flow structures, as well as the product quality. To understand the effect of operational variables over riser flow distribution, a numerical study of the two-phase cold-flow in the pre-acceleration zone of a riser reactor fed with catalyst particles used in this kind of reactors is presented in this work considering a two-dimensional model. The Computational Fluids Dynamics (CFD) software ANSYS® Fluent® is used to study two-dimensional gas (air) and solid (catalyst particle) flow in a riser section of a cold-flow Circulation Fluidized Bed (CFB) system under different flow inlet conditions (i.e., either for the gas and solid flux), as well the particle diameter size. An Eulerian-Eulerian approach, including the turbulence ( κ − ε model) and the Kinetic Theory of Granular Flow (KTGF) models, are solved for the gas phase and the solid particles treated as a dispersed phase. The implemented computational model is validated by comparing numerical results for solid velocity and volume fraction distribution to values reported by peers. As expected, a higher concentration towards the axis of the reactor is obtained for the solid volume fraction values. The R N I index estimated for gas velocities of 3 m/s and 4 m/s are significantly lower than the others, indicating that as the inlet gas velocity is reduced, a more homogeneous profile is obtained. Finally, the numerical results obtained shown closer to the experimental data used for the validation as the steady-state is attained.

Formulation Development of Rotigotine Transdermal System Using Dot-Matrix Technology

The purpose of this research was to prepare and evaluate drug-in-adhesive type patches of rotigotine using dot-matrix technology, which is the new generation of drug-in-adhesive transdermal delivery system (TDS) that deliver drug therapy through less patch surface area and without compromising adhesion. Preformulation studies, like solubility in permeation enhancers, compatibility study, transmission study, uptake study, and crystallization study of rotigotine in various pressure-sensitive adhesive (PSA) polymers were performed. Transdermal system was prepared by solvent casting method. Central composite design (CCD) was chosen for optimization of the formulation. Design of experiment (DoE) was used to study the impact of critical formulation parameters, like silicone adhesive concentration, povidone K29/32 concentration, and propylene glycol concentration. Crystallization study of rotigotine in different PSAs suggested that crystal inhibitor is required to load drugs above 5%. Selection of optimum batch was made using a constraint-based graphical optimization technique. The optimum batch exhibited desired in vitro adhesion parameters, like peel, tack, shear, and permeation rate, which is suitable for 3 days’ wear properties and desired permeation rate. The optimum batch was evaluated for appearance, weight of matrix, thickness, % assay of drug content, in vitro adhesion testing, cold flow study, and ex vivo skin permeation studies. Backing film Scotchpak 9730 and release liner Scotchpak-1022 was selected based on transmission and uptake study of rotigotine. Stability study indicates that developed formulation remains stable. The present research confirms the feasibility of developing rotigotine transdermal system using novel technology.

Design of experiments and analysis of dual fluidized bed gasifier for syngas production: Cold flow studies

Biomass gasification is a thermo-chemical process widely accepted as a future technology for syngas production. Numerous types of gasification systems have been proposed and studied in the past. Recent developments have shown that Dual Fluidized Bed (DFB) gasifier are commercially more attractive for production of the hydrogen-rich syngas as compared to others. DFB gasification system is very complex in construction and operation. Hence, a detailed understanding of hydrodynamics in such systems is essential for optimum design and scale-up. Hydrodynamics of DFB gasifier mainly depends on the Solid Circulation Rate (SCR). SCR is governed by riser velocity, gasifier velocity, and loop seal velocities. In present work, Central Composite Rotatable Design (CCRD) based Response Surface Method (RSM) was employed to determine the effect of riser velocity, gasifier velocity, recycle chamber velocity, supply chamber velocity, and vertical supply chamber velocity and their interaction on the SCR. Adequacy of regression model developed from RSM was confirmed using ANOVA analysis. The value of coefficient of determination (R2) of the model was 0.9729, which confirms model represents the experimental results satisfactorily. Riser and recycle chamber velocity were found to be most significant parameters, plays an important role in SCR in DFB gasifier.

Design, Development and Delivery of Rasagiline Mesylate from Monolithic Drug in Adhesive Matrix Patches

The purpose of this research was to prepare and evaluate monolithic drug-in-adhesive type patches of Rasagiline Mesylate (RM) containing penetration enhancer and having seven day wear property. Preformulation studies like solubility in permeation enhancers, compatibility study, transmission study, uptake study and crystallization study of Rasagiline Mesylate in various pressure sensitive adhesive polymers were performed. Transdermal system was prepared by solvent casting method. The effects of various permeation enhancers (Propylene Glycol, Oleic Acid, Isopropyl Palmitate, and lauryl lactate) on the ex-vivo transcutaneous absorption of Rasagiline Mesylate through human cadaver skin were evaluated by modified Franz diffusion cell system. Ex-vivo transcutaneous absorption of prepared transdermal patch was performed using different concentration of Lauryl lactate (3%, 5%, and 7%). In-vitro Adhesion testing (Peel, tack shear etc.) was performed on different dry GSM (Grams per Square Meter) of patch like 80GSM, 100 GSM and 150 GSM. The final transdermal patches were tested for appearance, weight of matrix, thickness, % assay of drug content, in-vitro adhesion testing, cold flow study and ex-vivo skin permeation studies. Based on crystallization study and adhesion testing, Durotak-4098 (14% drug concentration) was selected as pressure sensitive adhesive. Patch containing Lauryl lactate showed highest cumulative permeation compared to other permeation enhancers. The patch containing 5% laurel lactate showed greater transdermal flux (2.36 µg/cm2 /hr). Patch with 150 dry GSM showing promising adhesion properties. Backing film Scotchpak 9723 and release liner Saint Gobain 8310 was selected based on transmission and uptake study of Rasagiline Mesylate. Stability study indicates that developed formulation remains stable. In conclusion, the present research confirms the practicability of developing Rasagiline Mesylate transdermal system.

Numerical investigation of cold flow over regular and wavy V-gutters

In this paper, the numerical study of cold flow over two types of regular and wavy V-gutter flame holders has been presented. The edges of the V-gutter, which are smooth in the regular case, are shaped in a sinusoidal form with different phase angles on upper and lower edges. The three-dimensional numerical analysis has been performed using the finite volume method and the renormalization group k–ɛ model has been used for turbulence modeling. The results were compared and validated by an existing experimental work based on the particle image velocimetry method. This study provided the fluid flow structure behind the V-gutter, the dimensions of the recirculation region, the behavior of vortex shedding phenomenon, and the static pressure distribution in the wake area. According to the results, the recirculation length for the sinusoidal case with 90 ° of the phase difference is the largest compared with the other cases, which increases the mass flow rate of the fresh unburnt mixture into the recirculation region and improves flame stability. The results also show that the 90 ° wavy V-gutter case has the lowest pressure drop in the wake region, which reduces the drag coefficient against the main flow. The values of the Strouhal number are approximately the same and equal to 0.27 for both cases (the regular and the 90 ° cases). Therefore, it is concluded that the 90 ° wavy V-gutter shows better performance than the regular V-gutter in flame stabilization.

Studies on Stepped Air Ejector Diffusers incorporating Heat Transfer Effects

Abstract Air ejector diffusers are employed in gas turbine exhaust systems to cool the exhaust gases. These diffusers are developed as passive devices, which use the energy of the main flow to entrain the relatively cool ambient air through the annular slot openings. Multiple slot openings are provided along the length of ejector diffusers to lower the temperatures of the exhaust gases. This paper presents results of a 3-D numerical study carried out at a fixed Reynolds Number of 2.5×105 with a corresponding inlet Mach number of about 0.22 on three configurations of a non-circular ejector diffuser having an overall area ratio of 9. The three configurations being investigated are the best diffuser configurations established on the basis of cold flow studies reported in literature. The results are presented in terms of temperature distribution, entrainment mass flux rates and static pressure recovery. The results show that the higher number of slot openings improves cooling in the ejector diffuser as compared to thicker interfaces or inclination at the slot inlet.

Cold flow simulation of an internal combustion engine with vertical valves using layering approach

Complying with emission requirements and fuel consumption efficiency are the points which drive any development of internal combustion engine. Refinement of the process of combustion and mixture formation, together with in-cylinder flow refinement, is a requirement, valves and piston bowl and intake exhaust port design optimization is essential. In order to reduce the time for design optimization cycle it is used Computational Fluid Dynamics (CFD). Being time consuming and highly costly caring out of experiment using flow bench testing this methods start to become less utilized. Air motion inside the intake manifold is one of the important factors, which govern the engine performance and emission of multi-cylinder diesel engines. Any cold flow study on IC is targeting the process of identifying and improving the fluid flow inside the ports and the combustion chamber. This is only the base for an optimization process targeting to increase the volume of air accessing the combustion space and to increase the turbulence of the air at the end of the compression stage. One of the first conclusions will be that the valve diameter is a fine tradeoff between the need for a bigger diameter involving a greater mass of air filling the cylinder, and the need of a smaller diameter in order to reduce the blind zone. Here there is room for optimization studies. The relative pressure indicates a suction effect coming from the moving piston. The more the shape of the inlet port is smoother and the diameter of the piston is bigger, the aerodynamic resistance of the geometry will be smaller so that the difference of inlet port pressure and the pressure near to piston face will be smaller. Here again there is enough room for more optimization studies.

Flame acceleration in tube explosions with up to three flat-bar obstacles with variable obstacle separation distance

The effect of obstacle separation distance on the severity of gas explosions has received little methodical study. It was the aim of this work to investigate the influence of obstacle spacing of up to three flat-bar obstacles. The tests were performed using methane-air (10% by vol.), in an elongated vented cylindrical vessel 162 mm internal diameter with an overall length-to-diameter, L/D, of 27.7. The obstacles had either 2 or 4 flat-bars and presenting 20% blockage ratio to the flow path. The different number of flat-bars for the same blockage achieved a change of the obstacle scale which was also part of this investigation. The first two obstacles were kept at the established optimum spacing and only the spacing between the second and third obstacles was varied. The profiles of maximum flame speed and overpressure with separation distance were shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced at 80 to 100 obstacle scales about 4 times further downstream than the position of maximum turbulence determined in the cold flow studies. Similar trends were observed for the flames speeds. In both cases the optimum spacing between the second and third obstacles corresponded to the same optimum spacing found for the first two obstacles demonstrating that the optimum separation distance does not change with number of obstacles. In planning the layout of new installations, the worst case separation distance needs to be avoided but incorporated when assessing the risk to existing set-ups. The results clearly demonstrate that high congestion in a given layout does not necessarily imply higher explosion severity as traditionally assumed. Less congested but optimally separated obstructions can lead to higher overpressures.

Cold flow experimental study and computer simulations of a compact spouted bed reactor

Spouted beds are a very interesting class of gas–solid contactors that possess excellent heat transfer and mixing characteristics, while they are particularly suited to process coarse particles. Proper design of such beds requires the prediction of various hydrodynamic characteristics, such as the minimum spouting velocity and maximum spoutable height. Contrary to their typical initial applications, spouted beds have been finding recently more frequent use on the one hand at endothermic processes and on the other hand using much finer particle sizes. In the current work, the hydrodynamic characteristics of a laboratory scale spouted bed of 0.05m diameter have been investigated via cold flow studies using olivine particles of 3.55–5.00×10−4m size. Hydrodynamic parameters have been measured at this compact geometry and fine particle size and were compared with common literature correlations. An empirical correlation was derived to predict the fountain height for the studied fine particle spouted bed. Computer simulations have been further used to investigate the heat transfer characteristics of the bed under endothermic reactive conditions, using methane reforming as a case study. Given sufficient external heat supply, a spouted bed operating at a well-mixed regime can efficiently drive even highly endothermic reactions.

The acceleration of flames in tube explosions with two obstacles as a function of the obstacle separation distance

The separation distance (or pitch) between two successive obstacles or rows of obstacles is an important parameter in the acceleration of flame propagation and increase in explosion severity. Whilst this is generally recognised, it has received little specific attention by investigators. In this work a vented cylindrical vessel 162 mm in diameter 4.5 m long was used to study the effect of separation distance of two low blockage (30%) obstacles. The set up was demonstrated to produce overpressure through the fast flame speeds generated (i.e. in a similar mechanism to vapour cloud explosions). A worst case separation distance was found to be 1.75 m which produced close to 3 bar overpressure and a flame speed of about 500 m/s. These values were of the order of twice the overpressure and flame speed with a double obstacle separated 2.75 m (83 characteristic obstacle length scales) apart. The profile of effects with separation distance was shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced further downstream than the position of maximum turbulence determined in the cold flow studies. It is suggested that this may be due to the convection of the turbulence profile by the propagating flame. The present results would suggest that in many previous studies of repeated obstacles the separation distance investigated might not have included the worst case set up, and therefore existing explosion protection guidelines may not be derived from worst case scenarios.

Fluidization characteristics of a mixture of gasifier solid residues, switchgrass and inert material

Abstract Effective fluidization of materials present in the reactor bed is critical for optimizing reaction conditions in a fluidized-bed gasifier. An improper fluidization leads to inefficient conversion due to many reasons such as low heat and mass transfers, ineffective gas–solid phase reactions, and uneven reactor temperature in autothermal gasification. The objective of this study was to investigate effect of reactor bed composition, i.e. a mixture of gasifier solid residues (GSR), switchgrass, and inert material, on fluidization using a 0.25 m i.d. transparent column. In this cold-flow study, the amount of inert material, i.e. silica sand, in the bed was held at 20 kg. The switchgrass in the mixture ranged from 0.17 to 5% of the sand quantity while the GSR ranged from 5 to 35% of the switchgrass. The particle geometric sizes by mass of sand, GSR and switchgrass were 348 ± 1.6 μm, 80 ± 2.6 μm, and 10.3 ± 1.7 mm, respectively. For all conditions, with an increase in gas superficial velocity, i.e. ratio of volumetric gas flow and bed cross-sectional area, the pressure drop across the bed increased reaching a maximum level at the minimum fluidization condition. Results showed that when the bed consisted of only GSR and sand, with an increase in the GSR from 5% to 35%, the gas superficial velocity at minimum fluidization condition, called minimum fluidization velocity ( U mf ), decreased significantly ( p mf ) remained constant. When the bed consisted of GSR, switchgrass and sand, there were significant effects ( p U mf and dP mf . Fluidization improved with an increase in GSR up to 35% in the mixture. Overall, both U mf and dP mf increased with an increase in levels of GSR (5 to 35%) and switchgrass (0.17 to 3%) in the mixture. Fluidization characteristics were found to be strongly dependent upon mixture's effective properties, which were determined using properties of all mixture components. Correlations available in literature were used to predict U mf using effective properties of tertiary mixture with GSR, switchgrass and sand. Prediction of U mf from all selected correlations did not match well with the experimental data for the entire range of tertiary mixture compositions. Fluidization of bed materials sustained up to 3% level of switchgrass. However, segregation of bed materials and in-bed channelization caused ineffective fluidization at 5% level of switchgrass in the mixture.

Numerical investigation of the flow and flame structure in an axisymmetric trapped vortex combustor

The main intention of the present investigation is to bring out the effect of the momentum flux ratio (MFR) on the flow and flame structure in an axisymmetric Trapped Vortex Combustor (TVC). In this study, the MFR was varied by changing the secondary air jet velocity, while keeping the fuel, primary and the mainstream air velocities constant. This study revealed that a single vortex, embedded within a flame on its edge was formed in the cavity for the low MFR case (MFR∼0.57) for which intense burning was observed at the shear layer. In contrast, for the higher MFR cases (MFR∼0.82 and 1.8), the flow and flame structures were altered considerably due to the occurrence of multiple vortices within the cavity. A comparison with the previous cold flow study revealed that the change in flow structure was attributed to the volume expansion due to the heat release during the combustion. Besides this, a counter rotating primary vortex was formed near the bottom wall, which grew in size with the MFR. As a result, the shape of the cavity flame was altered, which may protrude out of the cavity, leading to the local quenching of the flame. Hence, it could be concluded that the momentum flux ratio plays an important role in altering the flow and flame structures within the TVC cavity, thus affecting the performance of the combustor.

Effect of primary jet geometry on ejector performance: A cold-flow investigation

The following cold-flow study examines the interaction of the diffracted shock wave pattern and the resulting vortex loop emitted from a shock tube of various geometries, with an ejector having a round bell-shaped inlet. The focus of the study is to examine the performance of the ejector when using different jet geometries (primary flow) to entrain secondary flow through the ejector. These include two circular nozzles with internal diameters of 15 mm and 30 mm, two elliptical nozzles with minor to major axis ratios of a/ b = 0.4 and 0.6 with b = 30 mm, a square nozzle with side lengths of 30 mm, and two exotic nozzles resembling a pair of lips with axis ratios of a/ b = 0.2 and 0.5 with b = 30 mm. Shock tube driver pressures of P 4 = 4, 8, and 12 bar were studied, with the pressure of the shock tube driven section P 1 being atmospheric. High-speed schlieren photography using the Shimadzu Hypervision camera along with detailed pressure measurements along the ejector and the impulse created by the ejector were conducted.

Cold Flow Studies of Rice Husk, Saw Dust, and Groundnut Shell Fuels in a Fluidized Bed

Biomass is a low-grade energy source and must be upgraded for effective utilization of these residues as fuels. A fluidized bed technology permits a wide range of low-grade fuels of non-uniform size to be efficiently converted to other energy forms. Due to large density variations of fuel and inert solids in the bed, it is difficult to estimate hydrodynamic and mixing characteristics of the mixture in the bed. In the present work, three biomass fuels (i.e., rice husk, saw dust, and groundnut shells) are selected and their fluidization characteristics are estimated in the presence of sand bed. It is observed that, for good mixing and uniform distribution of biomass fuel with bed material, size of the sand particles plays a vital role and is found that the sand particles of mean diameter 0.66 mm for groundnut shells and sand particle size 0.44 mm for the other two fuels is best suited. The minimum fluidization velocity has been obtained from the experiential investigation for a fuel/sand two-component system and has been compared with the theoretical correlations available in the literature. A suitable correlation to determine the minimum fluidization velocity for the selected biomass fuels and sand mixture has been suggested.

Jet cup attrition testing

Jet cup attrition testing is a common method for evaluating particle attrition in fixed fluidized beds and circulating fluidized beds. An attrition index, calculated from jet cup data, is used to compare with one or more reference materials. However, this method is far from perfect despite its popularity. Results obtained at Particulate Solid Research, Inc. (PSRI) in different-sized jet cups and a 29-cm (11.5-in.) diameter fluidized bed test unit did not provide the same ranking of catalyst with respect to particle attrition. To obtain a better understanding of attrition in a jet cup, both computational fluid dynamics (CFD) and cold flow studies were performed with a 2.5-cm (1-in.) diameter Davison-type jet cup and PSRI's cylindrical 7.6-cm (3-in.) diameter jet cup. Results showed that a significant amount of material in the Davison and PSRI jet cup remained stagnant. Based on these results and additional CFD modeling, PSRI designed a new jet cup, where most of the material was hydrodynamically active. The new jet cup showed a 25% increase in attrition compared to PSRI's cylindrical jet cup under similar conditions and run times. Results were also compared to cyclone attrition data for several materials at PSRI. The new jet cup provided data that correlated with attrition results from the 29-cm (11.5-in.) diameter fluidized bed unit.

Cold Flow Studies on the Effect of Injector Locations in a Directly Injected Cavity Based Combustor

Cold Flow Studies on the Effect of Injector Locations in a Directly Injected Cavity Based Combustor

English

The Ljungstrom air pre-heater is a regenerative type of heat exchanger used for preheating the combustion air, mainly in thermal power plant. The warm gas and cool air ducts are arranged to allow both the flue gas and the inlet air to flow simultaneously through the air preheater. The hot flue gas heats the rotor material and as the rotor rotates, the hot rotor section moves into the flow of the cold air and preheats it. The performance of Ljungstrom Air Preheater is depended on the heat transfer element profiles. New profiles are being designed in such a way that these new profile elements must be improving the efficiency of Air Preheater. In this context, it is felt necessary to develop new element profiles with lesser pressure drops for efficient heat transfer with less power consumption to improve overall efficiency of thermal power plants. In this research paper, two types of element profile (Flat Notched Crossed & Double Undulated elements) are tested using cold flow studies with the help of wind tunnel and compared their performance at different Reynolds numbers.

English

The numerical simulation of an integrated, liquid-fuelled ramjet engine comprising supersonicair intake, subsonic combustor and a convergent-divergent nozzle has been carried out and theresults are discussed in this paper. These results include cold flow studies, heat addition in thecombustor and full engine analysis with coupled simulation of supersonic air-intake andcombustion chamber along with the nozzle. Overall ramjet operation depends on the performanceof the air intake and the combustion chamber. The coupling phenomena are very dominant andperformance of air intake is affected vastly by the combustor operation and vice versa. In thispaper, a numerical analysis of integrated liquid ramjet engine considering coupling phenomenabetween various sub-systems viz., air intake, combustor and nozzle has been reported.

Cold flow studies of a slurry transport reactor–hydrocyclon system

The fluid dynamics of a new reaction system composed of a slurry transport reactor–hydrocyclon were studied using two column diameters at different gas and liquid linear velocities. The cold models used a gas collector in the top that allowed measurement of the gas disengaged by radial zones and a conductimetric probe that measured the frequency of the bubbles exiting from the top of the reactor. Gas and liquid hold-ups were determined. Liquid and solid tracers were also employed to determine the resident time distribution (RTD), global residence time, and the recycle of slurry near the wall. The results show the effect of sparger and disengaging design, as well as the effect of gas and liquid flow rate on the radial and axial gas hold-up profiles and on the recycle of slurry by the wall. This recycle is similar to those observed with a draft tube. No significant effect of column diameter was observed. A smooth circulation of slurry and solid was achieved through a mechanical optimization of the inlet and outlet of the reactor. It was demonstrated that the RTD of the system can be simulated using a set of continuous stirred tank reactors and plug flow reactor in a recycle (three parameters). Empirical equations are proposed for predicting the hold-up and the three parameters needed by the model. The similarity to a spouted bed reactor is discussed.