The paper discusses the designing process of screw conveyors, with regard to the determination of the exploitation parameters of such devices with the use of the Discrete Element Method (DEM). The influence of the chosen model input parameters on the results of the simulations was examined. The key parameters which determine the exploitation characteristics of a screw conveyor were identified as follows: the size of a DEM particle, coefficients of internal and external friction. Experimental measurements of the laboratory screw conveyor provided the actual exploitation characteristics of a device used for the transportation of a limestone powder. The comparison of the results of the simulations and experiments gave satisfactory results. For this reason, DEM simulations were identified as an effective tool for determining and optimization of the construction and exploitation parameters of the screw conveyors
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The paper describes the problem of designing screw conveyors in terms of determining their exploitation characteristics. Based on the actual values of mass efficiency and power demand obtained in a laboratory experiment, the theoretical design methods and the numerical discrete element method model results were verified. The obtained results have shown that the currently used theoretical methods underestimate the mass efficiency and power demand compared to experiments when typical values of filling rate coefficient and progress resistance coefficient are used. It was also shown that the results of DEM simulations are in good agreement with the experiments in terms of mass efficiency and power demand. Based on the exploitation characteristics determined in DEM simulations for different constructions of the screw and different rotational speeds, multi-objective optimization of the exploitation parameters of the screw was performed in order to minimize the power demand of a screw conveyor and simultaneously maximize its mass efficiency. The optimization results showed that it is possible to find such construction and the rotational speed that will maximize the mass efficiency of the conveyor and keep the power demand low, reducing the exploitation costs of the device.
The article presents the problems of determining the mass efficiency of a rotary feeder depending on the selection of design parameters of the device, such as outer diameter, number of blades and rotational speed of the rotor. The hitherto theoretical methods of calculating the feeder efficiency were presented, as well as a new method of determining the device operation parameters was proposed. For this purpose, the numerical Discrete Element Method was used, which allowed simulating the transport of limestone powder in a cell feeder with various design variants. The results of the tests showed that the above design parameters affect the instantaneous efficiency of the feeder and thus impact the distribution of the dosed material during the operation of the device. Depending on the design solution, the simulation results gave information on the fill factor of the feeders. The study showed a significant potential of DEM simulation in the design of circular feeders intended for dosing bulk materials.
Article citation info: (*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl IntroductionHeat distribution networks are complexed structures being a combination of pipes of various diameters, which carry the heat, by a thermodynamic factor, from the source producing the network heat to its terminal receivers. The heat is used to technological, warming and municipal purposes. The basic problem of heat distribution networks in summer season is the decrease in the demand for heat, which is mostly used for preparing domestic warm water. A discussion on the possibility of increasing heat distribution networks load by utilization the heat to produce chilled water by using absorptive as well as adsorptive aggregates has taken place for a couple of years. In Scandinavian counties the interest is particularly visible, mainly because of higher temperatures of the heating factor [17]. The data shown in publications [7,13] are a proof of an increasing tendency of network coolants supplies. In the majority of Polish cities, too low temperature of distribution network water, which in summer season varies from 66 to 70°C in the source, and in fact is 8°C lower reaching the receiver, restricts the usage of adsorptive air conditioning systems working in decentralized units. The minimum temperature of a factor which supplies absorptive, bromine-lithium refrigerators is about 72°C, whereas the effective work is possible at temperatures 85-90°C [20]. Increasing the temperature of a heating factor to parameters 90/55°C, typical for Scandinavian countries, would lead to increasing the heat loss during the transfer [21,22]. The problem of low temperature of water supplying sorptive cooling aggregates in summer season do not apply to silica gel adsorptive appliances, whose performance is possible for a heating factor at temperatures just above 55°C.Designing and development of adsorptive cooling systems, based on the usage of silica gel and sulfur dioxide began in the 20 th of the previous century [14]. A modification of the construction and applying various pairs of adsorbent-adsorbate have been done in order STAńczyk E, kArwAT B, MAchnik r, niEdźwiEdzki J. Operational research of adsorption chiller aggregate utilizing heat from district heating to produce chilled water for air conditioning. Eksploatacja i niezawodnosc -Maintenance and reliability 2017; 19 (2): 254-259, http://dx
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