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Numerical Analysis of Draft Tube Vortices of Francis Turbine with Experimental Validation
Full text linkAlthough hydraulic turbines are designed for the Best Efficiency Point (BEP), turbines are mostly operated at off-designed conditions due to variation in flow and load. The turbine’s efficiency decreases during the operation away from BEP. Draft tube vortices, generated while operating away from BEP are one of the causes for the decrease in efficiency, enhancing vibration problems, as well as the deterioration of the turbine in some cases. The objective of present study is to model and analyze the vortex rope formation using open source CFD codes. This paper presents numerical analysis of vortex formation in a high head Francis turbine at different operating conditions. Analysis is performed by using OpenFOAM solvers. The κ-ω SST turbulence model is employed in the Reynolds averaged Navier-Stokes’s equations in this study. The computing domain includes the runner and draft tube cone, which is discretized with full three-dimensional mesh system of unstructured tetrahedral shapes. The finite volume method is used to solve the governing equations of mixture model. The tendency of vortex formation in the draft tube cone agrees well with the experimental results with an average deviation of 5.43% in the axial velocity downstream of runner. The nature of vortex is analyzed at different load conditions from 70% of BEP to 117% of BEP
Mathematical modelling of the transmission dynamics of malaria infection with optimal control
Full text linkIn this study, we formed a mathematical model for the transmission of malaria infection in other to explore the transmission dynamics and optimal control. We considered the Sh , Eh , Ih , Rh , Sv , Ev , Iv model with optimal control considering the effect of two optimal controls (Use of bed net and Treatment). The positivity and boundedness, reproduction number, stability and optimal control analysis were carried out accordingly. Numerical simulations were done. We further discovered the conditions necessary for the stability of both disease-free equilibrium (DFE) and endemic equilibrium. The DFE is asymptotically stable. Also, the endemic equilibrium is stable. The numerical simulation also shows the effective use of bed net and Treatment on the curve. Finally, we deduce that the use of bed nets and treatment over a long period can eventually help to flatten the curve of infection. However, this control intervention has no significant impact on the mosquito population
Multi-response optimization of bambara nut milling- sieving machine
Full text linkResponse Surface Experimental design was used to investigate the optimal operational parameters and response of bambara nut milling–sieving machine; Performance result revealed particle size of milled flour, number and speed of the paddle as these machine process/operational parameters with significant influence on its performance while throughput and extraction efficiency constitutes its functional performance indicators. Extraction of the grain starch granules from its fiber depends on the particle size of the milled grain and paddle parameters. In addition, the multi-response performance simulation of this machine predict 1080 rpm, 4 paddles and 35 μm respectively for speed of the paddles, number of paddles and particle size of bambara flour as values require for its optimal operation with optimal value of throughput and extraction efficiency of 117.8 kg/h and 98.45% respectively which indicates that the novel bambara nut milling-sieving machine reduced the food loss to chaff in this sector to 1.55% against 15.82% associated with the widely used semi-mechanized system. It also promotes hygiene in this sector because it eliminated human contact with the milled grain during sieving operation. Its operation with the optimal parameters derived in this study is therefore recommended to both small and medium scale bambara flour producers to enhance quantity and quality bambara flour production for food security and poverty alleviation
Study and Optimization of Existing Ventilation System of Public Buses Using Computational Fluid Dynamics
Full text linkAmong all of the public transport, public buses are the major means of transportation for the people on daily basis. In both urban as well as in rural areas, a large number people travel through public bus regularly. Despite of this usage, public buses in developing countries like Nepal are equipped with minimum or zero facilities to the passengers. The maximum number of public buses, used for medium and short routes, are not air-conditioned and air has to be regulated naturally throughout the bus to provide the passengers with adequate thermal comfort. Furthermore, the operating buses are old, noisy and uncomfortable. With rising pollution in the environment, there is also a high chance of passenger compartment being contaminated with pollutants like particulate matters since there is frequent movement of people in peak hours. Therefore, as a solution to these problems, the research is being carried out. The study and optimization of the existing ventilation system of the buses enabling the efficient flow of air ensuring better thermal comfort for the passenger is accomplished. The bus operation region is accordance to Nepal city area and especially summer temperature is focused. The interior design of the bus is with reference to TATA star bus series and the manlike shape of the passengers are as per Body Mass Index (BMI) of Nepalese people and 3D designed in Solidworks. Through several number of design modifications and test using computational fluid dynamics, finally the design with the optimum result is selected and advised to be opted for efficient performance of ventilation in public buses. For the CFD simulations turbulence model of k-epsilon and tetrahedral mesh is applied in ANSYS. And with a mean observation, among all the roof vents orientations, the case with roof ventilation at the front and backside provides the optimum result among the optimized design with effective temperature of 305.53 K and mean velocity of 14.77 m/s
Differential Transform Method Approach to the Study of an MHD Flow of a Third Grade Fluid with Reynolds’ Model Viscosity and Joule Heating
Full text linkIn this research, the Differential Transform Method (DTM) approach was utilized to analyze a third-grade fluid, a non-Newtonian substance, flowing within a circular duct subjected to magnetic force and joule heating, while incorporating Reynolds' model viscosity. When both the joule heating parameter (J) and the magnetic parameter (M) are zero (J = M = 0), the midpoint temperature (θ(0)) results demonstrate that DTM converges faster compared to the Adomian decomposition method (ADM), with a difference of about 10−2 between the two methods. Graphical representations of the fluid's velocity and temperature reveal that an increase in magnetic force decreases both velocity and temperature, whereas higher values of the joule heating factor lead to an increase in flow velocity and a reduction in the fluid's temperature at the midpoint of the duct
Optimization of Spray Dryer Design for Small Scale Drying of Milk Using Computational Fluid Dynamics
Full text linkSpray drying technology has long been the industry standard for producing quality powdered products such as milk powder, coffee, juice powder, and pharmaceutical products. Spray dryers convert liquid or slurry directly into powdered form with the help of an atomizer and hot drying gas. One of the applications of such technology can be in the milk industry of Nepal. Spray drying of milk can increase the shelf life of milk and significantly reduce its volume, making it easy for storage and transport. This paper is concerned with the design of such a spray dryer for community-based applications. The drying chamber was designed based on previous literature on the topic. Then the analysis and refinement of the initial design were done using the ANSYS Fluent CFD package. An Eulerian-Eulerian framework was utilized to model the problem. The dimensions and thermo-physical properties were optimized for a drying capacity of 400 kg milk in 8 hours. The optimum inlet conditions were found to be 400 K, 0.385 kg/s for hot air inlet, and 318 K, 0.014 kg/s for milk inlet. The length and diameter of the dryer were optimized to 3700 mm and 1790 mm respectively. The airflow pattern at the axial region of the dryer was found to be downward directed, and that at the peripheral region was found to be turbulent with recirculating eddies. According to the observed trend in the transient simulation, the temperature of the milk reaches a value of 385 K at the inlet for a brief period of 0.78 s and then lowers to 365 K and eventually reaches 340 K while exiting the chamber after two seconds of injection. These results are improvements from previous industrial-scale spray dryers as the maximum temperature inside the dryer and the particle-residence-time were reduced. All of this leads to low thermal degradation of milk while drying
Water Corrosion and Scale Formation Problem and Its Solution in Water Supply Schemes – A Case Study on Padampokhari and Mahendranagar Scheme
Full text linkThe water with low total dissolved solid (TDS) and pH value is corrosive in nature. Moreover, the water with high TDS and low pH values is scale forming. A low TDS and pH value dissolves intake structures, GI pipes, concrete reservoir, household plumbing systems and cementing structures when it comes in contact with it. Furthermore, the corrosive water causes nuisance and health-related problems. Excess intake of lead, aluminum, copper, iron, chromium etc. in human body due to corrosive water causes serious damage to the different human organs such as brain, kidney, nervous system, blood cells, and even degrade an IQ level. High TDS and low pH value causes scale formation which blocks the whole water supply system. This paper presents a method for identification of corrosive and precipitative water and propose a solution to normalize it. The corrosive and scale forming water is detected easily by measuring a chief indicator parameter, TDS. The increasing value of TDS from intake to tap stand notifies that the water is corroding, and its decreasing values denotes the scale formation. Corrosive water is stabilized using calcium carbonate stones which is easily available in nature. On the other hand, scale forming water is controlled by the structural modifications of intake, collection tank, pipeline and reservoir etc. which we have constructed or going to construct. To verify the proposed methods, case study on Padampokhari and Mahendranager water supply schemes are studied and presented here in detail
Effect of electrode geometry on surface modification of polyethylene terephthalate by dielectric barrier discharge produced in air at atmospheric pressure
Full text linkThis paper presents the effect of electrode geometry on the surface modification of polyethylene terephthalate (PET) as a function of distance using 50 Hz dielectric barrier discharge at atmospheric pressure conditions. The polymer samples were treated with a Gaussian shaped electrode using a 13 kV power supply at line frequency for 1 minute. The results demonstrated that plasma treatment with a Gaussian shaped electrode improves the sample's surface wettability significantly. It is seen that there is a remarkable decrease in contact angle at the center of the sample and a relatively smaller amount of decrement away from the center of the sample
Comparative Study on Performance and Design Optimization of Natural Draught Institutional Improved Cooking Stoves
Full text linkBiomass is one of the major sources of domestic energy in rural parts of developing countries. The use of efficient improved cooking stoves over inefficient traditional stoves plays a pivotal role in the reduction of pollutants and has a greater impact on environmental and human health. This paper aims to analyze the performance of natural draught institutional improved cooking stoves in terms of thermal efficiency and pollutant emissions. Two stoves with varying designs and dimensions were constructed and given the names Prototype I (P-I) and Prototype II (P-II). Thermal efficiency and other performance parameters were analyzed following a Water Boiling Test. The particulate matter of aerodynamic diameter less than 2.5 µm (PM2.5) and carbon monoxide (CO) were monitored for both prototypes. P-II performed better than P-I in terms of both thermal efficiency and pollutant emissions. The thermal efficiency of P-II was 31%, which was nearly 2-fold higher than that of P-I. Similarly, emissions of CO (4.6 ppm) and PM2.5 (174 µg/m3) in P-II were found to be reduced by approximately 50% and 75%, respectively. This study suggests that minor changes in design and dimension improve the performance of improved cook stoves, which may have substantial implications for energy, environment, and health
CFD Analysis of Temperature Distribution of Different Piping Arrangements Used in Radiant Floor Heating System
Full text linkThe rate of energy consumption on the household level for heating and cooling is increasing annually. Meeting future heating and cooling energy demand by alternative and promising technology like floor heating systems (FHS) should be the primary concern for engineers and designers. The floor heating system (FHS) maintains the desired indoor temperature with low-temperature fluid flowing inside the pipe than conventional heating systems. FHS has lower investment cost, lower energy consumption, better thermal comfort, and desired temperature up to human height. This paper aims to simulate and compare the temperature distribution for three different piping arrangements like double-wall serpentine, serpentine, and modulated spiral. The geometry was created in Solidworks. The system was modeled using sets of boundary conditions. The simulation results show that the spiral layout has a temperature distribution of 320 K at an outlet and has a temperature gradient of about 13°C between the inlet and outlet. This arrangement generates and heats the air uniformly in the room and provides better thermal comfort. Even serpentine has a small temperature gradient, and this system creates a periodic cycle of air movement in the room, which is the worst case in terms of thermal comfort. Doubled wall serpentine has a temperature gradient of 20°C, and this arrangement is the worst among the three layouts. The study concluded that spiral arrangement has a uniform temperature distribution among all the setup, heats the air uniformly, and provides better thermal comfort.