19-08-2014, 10:44 AM
Single as well as multiphase jet reactors are widely used in environmental and biological applications, nuclear reactors, solid suspension e.g., leaching or crystallization, liquid blending, fast reactions and many more as an alternative to the conventional reactors. Optimization of jet loop reactor (JLR) varies based on the application for which it has to be designed. For energy efficient blending, reactor needs to be optimized in such a way that it produces dominant convective flow with secondary circulation.
Single as well as multiphase jet reactors are widely used in environmental and biological applications, nuclear reactors, solid suspension e.g., leaching or crystallization, liquid blending, fast reactions and many more as an alternative to the conventional reactors. Optimization of jet loop reactor (JLR) varies based on the application for which it has to be designed. For energy efficient blending, reactor needs to be optimized in such a way that it produces dominant convective flow with secondary circulation.
Similarly, in order to carry out mass transfer controlled applications, one should ensure better mixing down to smallest possible scales i.e. micro mixing. In case of solid suspension, sufficient turbulence levels should be provided at the bottom of the vessel to lift solid particles and enough convective flow in order to keep them in suspension state. For all the above mentioned applications, understanding of turbulence quantities and flow structures are important. This can be achieved by detailed experimental and computational fluid dynamics.
Experimental fluid dynamics has been carried out using various flow measurement techniques such as HFA (hot film anemometry), LDV (laser Doppler velocimetry) and PIV (particle image velocimetry).
Mean velocities, k, turbulent eddy diffusivity and quantitative analysis of flow instabilities and turbulent structures have been accurately evaluated using these techniques in a complimentary way.
One of the important finding was the development of an algorithm for the estimation from PIV with the support of HFA data.
The estimated mean and turbulent quantities have been used to validate the CFD models (k- model, Reynolds stress model (RSM) and large eddy simulation (LES)). A comprehensive comparison of the predictive ability of these models has been presented and an attempt has been made to understand the relative performance of these models. Initially, systematic study for benchmarking the k-e model parameters and their optimization in JLRs has been carried out and hybrid model has been proposed which has been found superior than std k-model. Further, it was also thought desirable to deploy the Reynolds stress model (RSM) and LES models in order to identify the limitations of k-e model and to study the local dynamics of the flow respectively.
Availability of extensive measurement techniques and LES simulations leads a way for in-depth analysis of turbulent structures. In this regard, many novel mathematical techniques have been employed, and the relative advantage of a technique has been utilized to uncover some pertinent aspects of flow structures. Fourier and wavelet transform based techniques have been used to identify the flow instabilities and to find the localized information of flow structures by surrogate and LIM methods from point and planar data respectively. The isolated structures can be phase averaged to obtain the scale wise energy content in the structure. In order to get the interaction of structures, fractal spectrum of thepoint as well as planar data has been evaluated based on wavelet transform modulus maxima (WTMM).
The methodology involves the classification of singularities and a number distribution for the formation singularities have been evaluated to obtain the exponent for the break up of structures. A relationship of this distribution has been identified with phase average velocity. The information of length scale, velocity scale, interaction exponent have been used further for the evaluating the effect on micro and macro mixing. Heat transfer characteristics have been evaluated from the experimental data collected on steam jet using HFA wavelet based analysis has been carried out to evaluate the surface renewal rate and has been correlated to study the theories of heat transfer from the literature.