NUMERICAL ANALYSIS OF TURBULENT GAS-SOLID FLOWS IN A VERTICAL PIPE USING THE EULERIAN TWO-FLUID MODEL

Turbulent gas-solid flows are readily encountered in many industrial and environmental processes. The development of a generic modeling technique for gas-solid turbulent flows remains a significant challenge in the field of mechanical engineering. Eulerian models are typically used to model large systems of particles. In this dissertation, a numerical analysis was carried out to assess a current state-of-the-art Eulerian two-fluid model for fully-developed turbulent gas-solid upward flow in a vertical pipe. The two-fluid formulation of Bolio et al. (1995) was adopted for the current study and the drag force was considered as the dominant interfacial force between the solids and fluid phase. In the first part of the thesis, a two-equation low Reynolds number k-ε model was used to predict the fluctuating velocities of the gas-phase which uses an eddy viscosity model. The stresses developed in the solids-phase were modeled using kinetic theory and the concept of granular temperature was used for the prediction of the solids velocity fluctuation. The fluctuating drag, i.e., turbulence modulation term in the transport equation of the turbulence kinetic energy and granular temperature was used to capture the effect of the presence of the dispersed solid particles on the gas-phase turbulence. The current study documents the performance of two popular turbulence modulation models of Crowe (2000) and Rao et al. (2011). Both models were capable of predicting the mean velocities of both the phases which were generally in good agreement with the experimental data. However, the phenomena that small particles cause turbulence suppression and large particles cause turbulence enhancement was better captured by the model of Rao et al. (2011); conversely, the model of Crowe (2000) produced turbulence enhancement in all cases. Rao et al. (2011) used a modified wake model originally proposed by Lun (2000) which is activated when the particle Reynolds number reaches 150. This enables the overall model to produce turbulence suppression and augmentation that follows the experimental trend. The granular temperature predictions of both models show good agreement with the limited experimental data of Jones (2001). The model of Rao et al. (2011) was also able to capture the effect of gas-phase turbulence on the solids velocity fluctuation for three-way coupled systems. However, the prediction of the solids volume fraction which depends on the value of the granular temperature shows noticeable deviations with the experimental data of Sheen et al. (1993) in the near-wall region. Both turbulence modulation models predict a flat profile for the solids volume fraction whereas the measurements of Sheen et al. (1993) show a significant decrease near the wall and even a particle-free region for flows with large particles. The two-fluid model typically uses a low Reynolds number k-ε model to capture the near-wall behavior of a turbulent gas-solid flow. An alternative near-wall turbulence model, i.e., the two-layer model of Durbin et al. (2001) was also implemented and its performance was assessed. The two-layer model is especially attractive because of its ability to include the effect of surface roughness. The current study compares the predictions of the two-layer model for both clear gas and gas-solid flows to the results of a conventional low Reynolds number model. The effects of surface roughness on the turbulence kinetic energy and granular temperature were also documented for gas-particle flows in both smooth and rough pipes

Regiospecific synthesis of some novel N-nucleosides of 4-amino-5-substituted-1,2,4-triazole-3-thiones and their in-vitro antimicrobial activity

4-Amino-5-substituted-1,2,4-triazole-3-thiones were prepared by following two different reaction routes and comparing the effectiveness of using different reaction conditions. The coupling of aminotriazoles with acetylated α-bromo-D-glucose furnished protected N-nucleosides regiospecifically. The reagents used gave only one regioisomer N-glycosides not the other S-nucleosides. The protected nucleosides upon deacetylation using methanolic ammonia afforded deprotected products. The chemical structures of synthesized compounds were confirmed by FT-IR, 1H NMR, 13C NMR, mass spectroscopic and elemental analysis data. All of the synthesized compounds were tested against ten different gram positive and gram negative bacterial strains which exhibited moderate to good antibacterial activity. The deprotected nucleosides portrayed high antibacterial activity than 4-amino-5-substituted-1,2,4-triazole-3-thiones and protected nucleosides against selected bacteria

Drug potency effects of three anthelmintics against natural fascioliasis with hematological values in goat

The purpose of the study was to compare the effectiveness of three anthelmintics against naturally occurring fascioliasis in goats as well as how they affected various hematological values over the course of 28 days. For this investigation, out of 417 goats, 60 were selected who were suffering from liver fluke infection. After being randomly divided into four groups of 15 animals each, the first three groups got treatment with triclabendazole, oxyclozanide, and nitroxynil while the fourth group was kept as a control group and received no medication. The results of the study showed that the egg per gram (EPG) count of the treatment groups significantly decreased successively (P < 0.01) on days 3rd, 7th, 14th, and 28th, whereas the control group produced significantly from day 3rd through the experimental period. Results revealed that the mean EPG was reduced by 78.40 %, 73.33 %, and 83.11 %, respectively, following treatment with triclabendazole, oxyclozanide, and nitroxynil, while the mean EPG production was 22.66 % in the control group. Hematological parameters including Hb, PCV, and TEC values, were lower before the treatment but turned to increase significantly (P < 0.01) on study day 28th, however, the mean TLC values were decreased substantially (P < 0.01) compared to the untreated control group. This result may indicate that all three anthelmintics were efficient, but nitroxynil had a relatively higher efficacy against goat fascioliasis regarding on the EPG and hematological indices

Slot antenna in ridge gap waveguide technology

A Slot antenna design based on recently developed gap waveguide technology has been presented in this work. This antenna can be built easily by having the feed network on the bottom metal plate, where the ridge will be distributing the waves for equal excitation of each slot element, and the top metal plate will have the slots. Design and simulation results of the basic T-junction for a corporate-feed network and the single element slot show that it is possible to have an array antenna with BW of 15 % or more based on ridge gap waveguide technology

Ku band linear slot-array in ridge gapwaveguide technology

A Ku band 4×1 linear slot array antenna design based on recently developed gap waveguide technology is presented. The complete antenna has been built using two parallel plates where the bottom metal plate has the guiding ridge and periodic pins and the top metal plate is smooth. The antenna feed network consists of power dividers has been realized on the bottom metal plate, and the radiating slots are placed on the top metal plate. Design and simulation results of the linear array show that it is possible to have a slot array antenna with 20 % bandwidth based on ridge gap waveguide technology

Design of a dual-CP gap waveguide fed aperture array antenna

A slot array antenna with dual-circular polarisation (CP) is presented in this paper. To overcome the fabrication and loss challenges in mm-wave frequencies, the gap waveguide technique is utilised. The right and left hand circular polarisation (RHCP and LHCP) radiations are achieved using slots-fed stepped septum polariser on the longitudinal slot arrays. The waveguides and feeding layer are based on ridge gap waveguide. The experimental results demonstrate the |S-11| and axial ratio of proposed antenna array are lower than -10 and 2 dB, respectively over the frequency range of 29.1-31.7 GHz. The proposed antenna exhibits the measured peak gain of 27.2 dBic at 30.2 GHz. The results prove that the proposed array antenna is a brilliant choice for 30 GHz-band applications and could be developed to realise larger dual-polarised planar arrays

A wideband 3-dB directional coupler in GGW for use in V-Band communication systems

In this article, a broadband 3-dB directional coupler is proposed using groove gap waveguide (GGW) structures. Gap waveguide technology has been introduced to overcome manufacturing and assembling challenges of different millimeter-wave components and devices. The presented coupler has wideband coupling flatness with low return loss in 60-GHz frequency band and can be easily adapted to other frequency ranges. Experimentally, a sample prototype of the proposed 3-dB coupler has been designed and fabricated. The measured return loss and isolation are better than 20 dB and the power-split unbalance within \ub10.5 dB is obtained over the frequency range from 57 to 74 GHz (26% BW). The proposed structure has the capability of easily integrating with other millimeter-wave components

Design of a 38 dBi Slot Array on Gap Waveguide at 140 GHz

In this paper, a cavity-backed full-corporate feed slot array antenna based on ridge gap waveguide at 140 GHz is presented. In order to fabricate the proposed slot array by computerized numerical control (CNC) milling technology, the length of metallic pins is selected as large as possible. Since the full-corporate feed networks are very dense, and only one row of metallic pins is required to isolate the coupling effect between any two neighbored distribution networks. In the work, height value of the bed nails are well selected so that the mutual coupling are below -20 dB. The simulated results show that the proposed array antenna has an input impedance bandwidth of 11% better than -10 dB. The bandwidth covers 135-150 GHz frequency band. The simulated gain is higher than 38 dBi over 135-150 GHz

Design of A Wideband Array Antenna Prototype with Gap Waveguide for W-Band Wireless Links

This paper presents a wideband 45o slot arrayantenna for W-Band wireless links. The proposed antennaprototype consists of 44 slot array, a wideband T-junctionbased on a groove gap waveguide and a vertical transitionfrom WR-10 to groove gap waveguide. The simulated resultsshow that the proposed prototype has an impedance bandwidthof 26.5% with input reflection coefficient better than-10 dB

Analytical Solutions to Characteristic Impedance and Losses of Inverted Microstrip Gap Waveguide Based on Variational Method

This paper initially introduces analytical solutions to newly invented inverted microstrip gap waveguide (IMGW). By applying the classical variational method the characteristic impedance, dielectric loss, and conductor loss of the IMGW are obtained. The calculated characteristic impedance and losses of IMGWs with the present analytical method have been verified by commercial software CST. Furthermore, we have theoretically proved that the total loss of electromagnetic energy in the IMGW is much lower than that of covered microstrip line in millimeter waves (mmWs). Thereby, the IMGW has big advantages over covered microstrip lines for high-gain, high-efficiency array antennas in mmWs