Kurichi Kumar

A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study

Abstract A computational fluid dynamic study was carried out to investigate airflow pattern, temperature, and humidity profile at different levels in the drying chamber. Good agreement was obtained with published experimental data. The effects of operating pressure, heat loss from the chamber wall and inlet air conditions on the gas flow pattern, droplet trajectories, and overall dryer performance also were investigated. Results are presented and discussed in terms of the gas velocity, temperature, and humidity profiles within the chambers. The volumetric evaporation values, heat transfer intensity, and thermal energy consumption per unit evaporation rate were computed and compared for drying of a 42.5% solids solution in a spray chamber 2.215 m in diameter with a cylindrical top section 2.005 m high and a bottom cone 1.725 m high. Wall regions subject to formation of undesirable deposits are also identified.

Simulation of a Spray Dryer Fitted with a Rotary Disk Atomizer Using a Three-Dimensional Computional Fluid Dynamic Model

Abstract Spray dryers fitted with a rotary disk atomizer are widely used in many industries requiring high throughputs to produce powders from liquid streams. The interaction between droplets or particles and the drying medium within the drying chamber is still not well understood and hence difficult to model reliably. In this article CFD results are presented to describe the behavior of the performance of a spray dryer fitted with a rotary disk atomizer in a cylinder-on-cone chamber geometry. Four different turbulence models, i.e., standard k − ε, RNG k − ε, Realizable k − ε, and Reynolds stress models were tested and compared to simulate the swirling two-phase flow with heat and mass transfer in the chamber. The results of this investigation can provide further insight into turbulent swirling flow modeling. The predicted results, such as, air flow patterns, air velocity and temperature, distributions, particle/droplet trajectories, drying performance etc., are obtained using the CFD code FLUENT6.1. Comparison with available limited experimental data shows that CFD results display reasonable agreement. Predicted results also show that the RNG k − ε model performs better in this specific case.

Use of Computational Fluid Dynamics to Evaluate Alternative Spray Dryer Chamber Configurations

Abstract A computational fluid dynamic simulation study was carried out to compare the gas flow and temperature patterns as well as particle trajectories for a pressure nozzle atomized liquid slurry spray dried in four different chamber geometries. The gas and liquid conditions are held the same for all four chamber geometries. The gas flow is co-current and enters and exits centrally thus maintaining a two-dimensional axi-symmetric flow pattern. It is found that as a result of variations in the gas flow and thermal patterns in the four configurations examined (viz cylinder-on-cone, conical, hour-glass shaped, and lantern-shaped axi-symmetric) the droplet trajectories, residence times, and drying times vary. It was noted that the effective chamber volume occupied by drying particles depends on the chamber design.

A Three-Dimensional Simulation of a Spray Dryer Fitted with a Rotary Atomizer

Abstract Spray dryers fitted with rotary atomizers are commonly used in diverse industries to produce engineered powders on a large scale. Scale-up of such units is still largely empirical and based on prior experience and know-how. In the present study, a three-dimensional spray dryer with rotary atomizer is investigated numerically with a commercial CFD code. Continuous-phase, i.e., air, conservation equations are formulated in the Eulerian model while the droplet or particle equations are set up in the Lagrangian model. Two-way coupling between the continuous and dispersed phases is taken into account in the governing equations. The stochastic approach is used to predict the particle trajectories. The RNG k − ϵ turbulence model was used. Typical results, viz. air velocity, temperature, humidity profiles, and particle trajectories are presented and discussed. Compared with the pressure nozzle spray dryer, more volume of drying chamber is used effectively by the rotating disc type spray dryer. It is found that evaporation and drying take place mainly in the region and in the vicinity of first contact between air and spray. A parametric study is presented and, where appropriate, comparison is made with experimental data obtained with the simulated spray dryer.

A numerical study of the interaction of water spray with a fire plume

Water spray-based fire extinguishing equipment such as sprinklers has been widely used in fire suppression and control. However, the fire extinguishing mechanism in such devices is not well understood due to the complexity of the physical and chemical interactions between water spray and fire plume. Currently, quantitative approaches (e.g. numerical modeling) to estimate the performance and effectiveness of water spray systems have not been developed to a stage where they can be used to optimize the design for different operating environments and types of fire. In the present work, a numerical simulation approach is introduced to provide a quantitative analysis of the complex interactions occurring between water spray and fire plume. The effects of several important factors (namely water spray pattern, water droplet size and water spray flow rate) on the fire suppression mechanism are investigated. The simulations show that the water spray with solid cone pattern and finer water droplet size is more effective in extinguishing fires than the one with hollow cone pattern and coarse water droplet size. To suppress a fire, the water spray flow rate has to be more than a certain critical value. However, using too high water spray flow rate does not increase fire suppression efficiency but only leads to increased operational cost because of the excess water flow rate. In the current paper, the principles of fire suppression with water spray are also discussed, which are useful in designing more effective water spray fire suppression systems.

Flow and Heat Transfer Characteristics of Confined Noncircular Turbulent Impinging Jets

Abstract A three dimensional computational fluid dynamic investigation is carried out to predict the turbulent flow and surface heat transfer under an impinging air jet issuing normally from a single noncircular orifice in a plate held parallel to the target surface. Static pressure distributions, velocity fields and local as well as average Nusselt number on the impinged surface are presented for square, elliptic, and rectangular orifices and compared with those for a circular orifice. Effects of jet Reynolds number as well as spacing between the nozzle plate and the impinged surface are examined using a two-layer κ–η turbulence model. Results show flow structure similarities between the characteristics of rectangular and elliptic jets of equal aspect ratio. Further, it is observed that noncircular impinging jets can provide higher average heat transfer rates than corresponding circular jets for certain geometric parameters viz. nozzle-to-plate spacing and the size of the averaging area used to compute the average Nusselt number.

An improved micro-combustor design for micro gas turbine engine and numerical analysis

An improved design to stabilize the combustion in a micro gas turbine engine is proposed and analysed through computational modelling in this paper. The new design distinguishes from the original MIT design by adding another wafer layer of micro channel to regulate the fluid flow velocity distribution and direction near the combustor entrance. As a result, the fuel/air mixture flow velocity decreases along the flow path before entering into the combustion chamber. This special flow velocity distribution feature effectively prevents the flame from propagating to the flow upstream and burning in the recirculation jacket of the micro gas turbine engine under the conditions of high equivalence ratio of fuel to air or low heat loss on the outer wall. In addition, the flow pattern in the combustion chamber with the improved design can stabilize the flame under the condition of higher fuel/air mixture mass flow rate, and avoid blowing out the flame. The performance of the micro-combustor with the improved design is also studied through computational fluid dynamics (CFD) based numerical simulation. The simulation results are compared with those of the micro-combustor with the original design under the same operating conditions. Hence, it can be concluded that under conditions of higher equivalence ratio or lower heat loss or higher mass flow rate, the flame can be stabilized in the combustor with the improved design, while the flame will flash back and burn in the recirculation jacket or be blown out for the combustor with the original design. The simulation results also demonstrated that the new design may provide us with a micro-combustor with higher power density by significantly extending stable operating ranges, e.g. the fuel/air mixture mass flow rate range.

Evaluation of CFD modeling methods for fire-induced airflow in a room

Methods for exploiting the technique of computational fluid dynamics (CFD) to model fires and the associated fundamental processes of combustion and radiation are appraised by applying the CFD model JASMINE to simulate the fire-induced airflow in a room-sized compartment. For a systematic evaluation of these methods describing the fundamental processes and the associated mathematical formulation, a two-stage-verification and validation procedure is adopted here. In the verification stage, a number of important model parameters, e.g., the choice of fire source model (e.g., combustion model vs. volumetric heat source (VHS) model), radiation transport model (e.g., six-flux vs. discrete transfer radiation model), gas property model (e.g., constant absorption coefficient vs. grey gas model), design and resolution of the numerical grid, etc. are assessed by comparing the predicted results against a specific fire scenario selected from the data of Steckler, K.D., Quintiere, J.G. and Rinkinen, W.J. (1982). Flow Induced by Fire in a Compartment, NBSIR B2-2520, National Bureau of Standards, Pittsburgh [2]. The validation stage has then focused on the detailed comparison of the CFD fire model against the comprehensive data set of Steckler et al. [2] for a wide range of fire scenarios covering a range of fire strengths (i.e., heat release rates), fire source locations, the sizes and shapes of the ventilation opening (i.e., door or window). Such a systematic study has demonstrated the predictive capability of the CFD methodology in reproducing detailed thermal and flow field behavior of the enclosure fires, and has also shown that the predictive accuracy of the CFD methodology can be significantly improved by careful selection of the fire models and model parameters. Some guidance on the use of CFD methodology has been provided for performing the fire modeling properly and effectively for performance-based fire safety design.

Hybrid Face Recognition with Locally Discriminating Projection

The face recognition task involves extraction of unique features from the human face. Manifold learning methods are proposed to project the original data into a lower dimensional feature space by preserving the local neighborhood structure. LPP should be seen as an alternative to Principal Component Analysis (PCA). When the high dimensional data lies on a low dimensional manifold embedded in the ambient space, the Locality Preserving Projections are obtained by doing the optimal linear approximations to the Eigen functions of the Laplace Beltrami operator on the manifold. However, LPP is an unsupervised feature extraction method because it considers only class information. LDP is the recently proposed feature extraction method different from PCA and LDA, which aims to preserve the global Euclidean structure, LDP is the extension of LPP, which seeks to preserve the intrinsic geometry structure by learning a locality preserving submanifold. LDP is a supervised feature extraction method because it considers both class and label information. LDP performs much better than the other feature extraction methods such as PCA and Laplacian faces. In this paper LDP along with Wavelet features is proposed to enhance the class structure of the data with local and directional information. In this paper, the face Image is decomposed into different subbands using the discrete wavelet transform bior3.7, and the subbands which contain the discriminatory information are used for the feature extraction with LDP. In general the size of the face database is too high and it needs more memory and needs more time for training so that to improve time and space complexities there is a need for dimensionality reduction. It is achieved by using both biorthogonal wavelet transform and LDP the features extracted take less space and take low time for training. Experimental results on the ORL face Database suggests that LDP with DWT provides better representation and achieves lower error rates than LDP with out wavelets and has lower time complexity. The subband faces performs much better than the original image in the presence of variations in lighting, and expression and pose. This is because the subbands which contain discriminatory information for face recognition are selected for face representation and others are discarded.