Faculty of Engineering, Earth Resources Engineering

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Browsing Faculty of Engineering, Earth Resources Engineering by Author "Dissanayake, DMDOK"

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    item: Thesis-Abstract
    Flow behavior of mineral particulates through conical silos
    Rohitha, LPS; Fernando, WLW; Dissanayake, DMDOK
    Silo or Bin is used very widely in Mining, Processing, Pharmaceutical, Cement, Ceramics and Packaging industries. The purpose of the silo is to hold material until it is ready to use in subsequent processes such as processing, chemical, physical or transport. According to the Oxford Dictionary ( DK illustrated), a Silo is a pit or airtight structure in which green crops are kept for fodder or it can be a pit or a tower for the storage of grains ,cement etc, or it is an underground storage chamber for guided missiles. The capacity of a silo may vary from Kgs. to Tons. In this research, a silo is used as a conical shaped container with an orifice through which mineral sands of varying sizes were allowed to pass and their flow behavior were examined with respect to their material physical properties and silo parameters. In the first stage of the project, the flow behavior was studied using beach mineral sands with glass funnels with orifice diameters 3.5, 4.8 and 8.0 mm and heights 8, 10 and 24cm respectively to simulate silos of varying orifice. The capillary part of the funnels were cut uniformly at the neck regions to prepare them for the tests. It was decided to use naturally occurring geo-materials of different mineralogical, chemical, and physical characteristics for the investigation. For this purpose, samples of beach sand from several locations along the western coast of Sri Lanka were collected and sampled using the sampler riffler, thereafter sieved through 2mm sieve to remove sea shells and other extraneous impurities followed by spiral separation and tabling. Subsequently, magnetic separation and high tension separation were carried out to separate magnetic and non magnetic fractions according to the standard procedure. The fractions separated consisted of ilmenite, rutile, garnet and zircon. A sample of silica was also obtained from the glass sand deposit at Naththandiya. Each sand sample was sifted using the standard test sieves. Before conducting the flow properties of these minerals they were dried at 110°C for 2 hours and the test was conducted 3 times and the average flow rate obtained thus was plotted against the particle size and the diD ratio for each material. Where, d = average particle size diameter and, D = funnel orifice diameter. Interpretation of flow rate measurements and analysis of data indicate that all beach mineral sands used in the study had the same flow rate pattern. The mass flow rate vs diD curves consisted of three significant zones representing bridging effect, constant gradient zone with a negative gradient and the no-flow zone, which spilled over to the fine particle fractions. The effects of charge particle nature, moisture contained, repose angle, surface morphology of mineral and the orifice diameter of the funnel on the flow properties were also investigated. As the particles studied were naturally occurring, they were sub-angular having rounded edges. Another series of experiments were conducted using spherically shaped silica gel particles having diameters 1.2,2.2, and 3.3 mm respectively. In the second stage, a pilot plant in the form of a conical silo was fabricated in the workshop and the experiments were conducted using mineral samples each sample weighed approximately 3 to 6 kg. The samples for the second stage was obtained from two sources, Lanka Mineral Sands Ltd and the river sand pits at lngiriya. After a tedious process of size separation mostly involving sorting of particles of different size fractions by hand picking and sieving. The results obtained agree very closely with those obtained using the glass funnels. It is evident that there are three zones in the performance curve -flow rate vs particle size with the bridging effect region corresponding to diD ratios of 1/4 to 115 for relatively larger size particles and the region exhibiting the 'floc effect' resulting from residual charges in the fine sizes and air trapped within the floes. The mineral particles used were pre-dried (dried at 110°C for two hours).However, the presence of moisture in the powder seems to have a significant contribution on the flow rate. - The importance of the performance curve and its characteristic features have been discussed and also the relevance of the performance curve in designing silos.
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    item: Thesis-Abstract
    Investigation of the possibility of converting seawater to drinking water in Hambantota area by reverse osmosis
    Illangakoon, UI; Dissanayake, DMDOK; Walpolage, S
    Habantota is a district in the southern section of the dry zone, Sri Lanka. The population density 211 per square kilometer distributed variably depending mainly of availability of water and other facilities such as electricity and domestic requirements.4.1 % of total population live in urban areas towns). People who live in suburbs are the most affected by the non-availability of safe water for drinking and other domestic purposes. Only 33.4% of households use piped born water and 55.3% use water from wells and 6.2% use water from tube wells. It has been reported that 60% of the ground water is bad quality and according to the World Watch Institute one third of the world population will face water shortages by the year 2020. This would create a situation where there will not be enough safe water for human survival. Therefore an attempt was made to convert ground water and seawater to drinking water. In this research, a field study was conducted in Meegahajadura, 81°00' N and 6°21' E, a small village in Suriawewa Division from the north sector of the Hambantota District. Ten ground samples were taken from ten locations, from tube wells, which were 8 km radius from Meegahajadura junction. The water samples were chemically analyzed. The chemical properties of the ground water samples tested varied drastically due to its association with the local variations of superficial mineral deposits, lake deposits, paddy alluvium which are 'of variable compositions and dry soil. The number of samples tested was not adequate enough to find a geological trend of hard rock pattern. None of the samples tested were up to the permissible limit of drinking water standards outlined by SLS 614. This and SLS 894 clearly indicates the necessity for ground water treatment prior to drinking, A feasibility analysis was conducted as. a .9ualitative and a quantitative analysis. The research shows it is feasible to desalinate ground water in the Hambantota district to produce drinking water by RO. It is feasible to construct a brackish water RO plant of capacity 10m3 per day to produce drinking water for Meegahajadura. The unit cost of producing drinking water by a seawater RO plant reduces to about US$ I (Rs 100/=) per m3 per day by year 20 l O. It is feasible to produce 40,000 m3 per day by seawater RO plant to fulfill drinking and other domestic water requirements for the Hambantota district by the year 2021. Owing to the complex nature of predicting the operating conditions of the RO permeate water, which varies greatly on feed water quality, operating pressure, temperature, a mathematical model was formulated. The purpose of this formulation is to predict the product water conditions of various feed water having varying values of TDS. The model makes use of the Solution Diffusion Model and it employs feed water concentration of six solutes namely: Na +, Ca2+, Mg2+, Cl, and K+, and as a whole it comprises of 99% of seawater. It was verified experimentally using diluted seawater to predict the product flow rate and TDS, total rejection of solutes, individual concentration of 6 Solutes in the product. This formulated model was verified by running the 75000 GPD RO plant at the university by using diluted seawater as feed water making various concentrations of solutes. Plotting the experimental data and model on the same graph at constant RO pump pressure, it was calculated the error of fit o fthe experimental data to the model. The experimental observations of the product flow rate and TDS, total rejection of solutes, individual concentrations of 6 solutes in the product, the % solute rejection of individual solutes and plant recovery fit the model to an accuracy of less than 16%.
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    item: Thesis-Abstract
    Site suitability analysis for water harvesting structures in Suriyawewa, Hambantota district using GIS techniques
    Senanayake, IP; Puswewala, UGA; Dissanayake, DMDOK
    Sri Lanka receives an average annual rainfall varying from 900mm to 6000mm. However, the rainfall is not distributed equally over the island. Hence, traditionally, the country is divided into three main climatic zones as wet zone, dry zone and intermediate zone. Two thirds of the island is occupied by the dry zone, which receives less than 1750mm of average annual rainfall. The dry zone periodically has faced water stress conditions from the past, and Hambantota District appears to be a severely affected area, on the basis of surface water availability. With the ongoing development projects, the demand for water in the district will increase in the next few years. Therefore, implementation of a proper water management system as well as preservation of existing surface and groundwater resources is essential to overcome this problem. A methodology is developed to find the most suitable locations for water harvesting structures in Hambantota District by using Geographic Information System (GIS) techniques. Suriyawewa Divisional Secretariat area is selected as the research area considering its average climatic conditions and location within Hambantota District. This methodology can be generalized to the whole District in the first instance. The research area is hydrologically analyzed to discretize the area into catchments and the preferred catchments to harvest the runoff based on surface area, slope and rainfall are found by using GIS techniques. The selected catchments are then analyzed with geological data and drainage characteristics to find the most suitable catchments to construct reservoirs to store rainwater. The analysis yields four such locations, which were subsequently field verified for spatial accuracy. However detailed local investigations are necessary before proceeding to actual construction of the reservoirs. Groundwater recharging also plays an important role in water management, as groundwater represents 30.1% of the world’s fresh water resources. GIS techniques are employed to integrate data on land use, climate, soil, stream pattern and ground slopes, and consequently to find potential areas for groundwater recharging. Here also, detailed local investigation must precede any construction work in the selected areas. Also, potential areas to implement roof water harvesting projects in Suriyawewa are found by analyzing the rainfall and building cover by using GIS techniques. These areas are recommended to be used as project areas when implementing efficient roof water harvesting methods. The methodology adopted here for Hambantota District can be used for water management in other Districts of the Dry Zone of Sri Lanka such as Monaragala, Puttalam, Ampara, Badulla and Kurunegala, as a solution for water stress conditions in those areas. An increment in water harvesting can significantly increase the crop yields in these areas and improve the economy as most of the Districts in the Dry Zone are agriculture-based. Also, a proper water management system is a must for the industrial development of the area under focus, while it gives a solution to the problems regarding drinking water. Proper water supply plays a major role in infrastructure development of these areas and would form the foundation for the overall development of the country.