• Energy Research

Abstract The present study aims at investigating numerically the effect of changing height ratios of cylinder and cone on the cyclone performance. Ratios of the cylindrical and conical segments are changed in a way that the total cyclone height remains the same. Eight different models with increasing barrel height viz. H/D = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 (wherein H/D = 4.0 corresponds to the cyclone model without a conical segment) are evaluated. All the cyclones operate at a Reynolds number (based on a body diameter of 0.205 m) of 2.71 · 105. The fluid domain is discretized with Cartesian mesh using Ansys workbench 16.2. The velocity and pressure fields, collection efficiency, and pressure drop in each model are predicted using large-eddy simulation (LES) with standard Smagorinsky model (Cs = 0.1) for sub-grid scales. Conclusive results indicate that increasing the length of the cylindrical segment significantly reduces the pressure drop with a marginal decrease in the collection efficiency. Furthermore, the cylinder-to-cone ratio affects the fluctuating field much more than the mean flow field. The frequency with which the vortex core precesses is also presented for each model.

AbstractFood losses and hunger around the world are majorly attributed to the lack of diverse food processing technologies and standardized methods. Solar energy is a potential solution for drying agricultural products, but traditional solar drying methods are not yet widely used. This study developed a finite element model using COMSOL Multiphysics to assess the performance of a passive greenhouse dryer for drying food products. The proposed model was used to simulate the drying of potato slices, and the results showed that the dryer was able to reduce the moisture content of the potato slices from 1 to 0.005 in 3 h. The drying efficiency was 20.52%, the relative humidity inside the drying chamber was 25.2%, and the energy and exergy efficiencies were 63.46% and 94.01%, respectively. Overall, the results of this study suggest that the passive greenhouse dryer is a suitable drying method for potato chips. The model developed in this study can be used to further optimize the design of the dryer and to evaluate its performance for other food products.

The present study focuses on performing multi-objective optimization of the cyclone separator geometry to lower the pressure losses and enhance the collection efficiency. For this, six geometrical entities, such as the main body diameter of the cyclone, the vortex finder diameter and its insertion length, the cone tip diameter, and the height of the cylindrical and conical segment, have been accounted for optimization, and the Muschelknautz method of modeling has been used as an objective function for genetic algorithms. To date, this is one of the most popular mathematical models that accurately predicts the cyclone performance, such as the pressure drop and cut-off particle size. Three cases have been selected from the Pareto fronts, and the cyclone performance is calculated using advanced closure large-eddy simulation—the results are then compared to the baseline model to evaluate the relative improvement. It has been observed that in one of the models, with merely a 2% reduction in the collection efficiency and an increase of 12% in the cut-off particle size, more than a 43% reduction in pressure drop value was obtained (an energy-efficient model). In another model, a nearly 25% increment in the collection efficiency and a reduction of 42% in the cut-off particle size with a nearly 36% increase in pressure drop value were observed (a high-efficiency model).

Abstract This study analyzed the effect of the angle of the inlet duct bend on the separation efficiency and pressure drop in cyclone separators. The design of the inlet to the cyclone chamber is a significant parameter that has been analyzed to date only in a few research studies. Following the literature review of this subject, 20 bend angles (10 in the vertical plane and 10 in the horizontal plane) were proposed and analyzed by means of the computational fluid dynamics code Fluent V18.2. As a closure model to the Reynolds-averaged Navier–Stokes equation, the Reynolds stress model was used, as it solves the transport equations for Reynold’s stresses and the dissipation rate - this model is capable of accounting highly curved streamlines prevailing inside the cyclone separators. The discrete phase model with one-way coupling was used, in which the trajectory of solid particles was calculated based on Lagrangian formulation. Conclusive results indicate that the bend angle (in both planes) marginally affects the collection efficiency (the maximum difference being 3.1%), whereas its effect on Eu is highly significant (the difference being 5700%) - all the comparisons were made with respect to the base variant at 0° angle.

The performance parameters of a gas cyclone, viz., pressure drop and cut-off diameter, are highly sensitive to its geometry. Cyclone length strongly affects the pressure drop as well as the collection efficiency. The contribution of the present study is therefore twofold. First, the effect of variation in the cylinder as well as the cone lengths on cyclone performance parameters with respect to the standard cyclone model is examined. Second, comparison is presented among the two geometrical variables for similar increase in their lengths. The performance and the velocity field are predicted computationally on ten different test models. It has been found that increasing the cylinder length by up to 5.5 times the cyclone diameter saves about 34% in the pressure loss and enhances the collection efficiency by about 9.5%. On the other hand, increasing the cone length by up to 6.5 times the cyclone diameter shows nearly a 29% reduction in the pressure loss and about an 11% increase in collection efficiency. It is also shown that apart from optimizing the cyclone length, the designed inlet velocity of the cyclone must be considered.

The analysis of a single-phase flow field inside a cyclone separator has been performed using large-eddy simulation (LES) using Lattice-Boltzmann method based CFD code XFlow. The simulations are performed over the uniform grids with a total of 1.05 million cubic cells. Based on the inlet velocity and main body diameter, the Reynolds number (Re) amounts 14,000. To model the effects of small scales and to account for the near-wall damping, wall-adapting local eddy-viscosity (WALE) model is used. The Spatio-temporal behavior of the large coherent structure ‒ especially the one in the core region ‒ is also very well captured. LES elucidates a good agreement of the mean as well as fluctuating (expressed as the root-mean-square error values) components of velocity with the measured values. The non-dimensional frequency estimated by LES ‒ based on the fluctuating axial velocity, tangential velocity, and static pressure values ‒ agrees well to the experimental value.

Abstract The present work deals with the study of varying diameters on the performance of the gas cyclones. Three different diameters viz. 0.8D, 1.0D, and 1.2D have been considered (D being the standard diameter of cyclone and the constants are the scaling factors) and their effects on the pressure drop, collection efficiency, and cut-off diameter have been evaluated. Navier-Stokes equations are discretized using finite volume methods which are solved iteratively with commercially available CFD code FLUENT 6.3.2 on block unstructured hexahedral mesh. Reynolds stress model (RSM) has been used as a closure model for Reynolds averaged Navier-Stokes equations, which solves for stress tensors together with the equation for the dissipation rates. It has been found that increase in cyclone diameter increases the collection efficiency at the expense of increasing pressure drops across the gas cyclones.

Abstract The study explored areas related to the effect of installing an additional element in the axis of the cyclone separator (in the form of a rod with a circular cross-section) on its performance. 30 geometrical variants (the variable parameters included rod diameter and length) were used for this purpose. The research was carried out using three methods – CFD (based on LES and DPM models), experimental research and stereo-PIV. The use of three research methods made it possible to conduct the process of validating the results. The placement of a rod with a circular cross-section on the axis of the cyclone separator significantly improved its performance (overall separation efficiency, Stk50 and Eu). The most beneficial variant led to an increase in the overall separation efficiency by 8.2% and a reduction in Stk50 by 25.5%. In the case of a pressure drop (expressed as Eu), all variants generated a lower value of Eu than the base variant - the maximum reduction observed was 23.9% (as compared to the base model). Additionally, to comprehensively study the effect of using an additional element on the flow field, the mean and fluctuating velocity and pressure fields were analyzed for individual variants and compared with the standard geometry. Furthermore, it was observed that the use of a rod stabilized the flow in the region confined to the inner vortex, increased the symmetry of the flow, and improved the performance of cyclone separators.