Table of Contents

  • MACHINES

    • DESIGN AND PERFORMANCE ANALYSIS OF OBSTRUCTION FLOW MEASUREMENT DEVICES FOR LOW AIR FLOW RATES USING CFD ANALYSIS

      pg(s) 143-148

      This study, considering need of fresh air in the air-conditioning system in a small residence, geometrical dimensions of a flow nozzle and an orifice plate were determined by theoretical equations in the literature. The measurement performances of designed flow meters were compared with numerical method using Computational Fluid Dynamics (CFD). The measured air flow rate is in the range of 80-300 m3/h and Reynolds numbers at the inlet of flow meters are 12,000-46,000. The β ratio of designed flow meters is chosen to be  0.45  in order to avoid excessive increase of pressure drop. Three dimensional numerical models were created to control the accuracy of flow
      meters. The results from numerical solution show that permanent pressure loss in the orifice plate is 2.6 times greater than the flow nozzle. Lower pressure and energy loss occur in the flow nozzle compared to the orifice plate. In a system where continuous measurement for the purpose of velocity control of fans is carried out, it has been found that electric power consumption of the fans will increase by 4.85 W and 12.42 W, respectively, at the flow rates of 150 and 200 m3/h for flow nozzle.

    • HEAT PUMP HEATING SYSTEM OPTIMISATION

      pg(s) 149-152

      The goal of this paper is to minimalize the gap between the heat pump’s compressor COP and the system COPs. A water-water heat pump was installed in a family house without piped floor heating, with 13 radiators, together with a 300 litres thermal storage and 200 litres hot water storage tank. Some measurements are published, taken before and after the system optimisation. The measured compressor COP is compared with theoretical data published by the device producer. The results show that the power consumption was decreased by 15 percent after the system optimisation. The influence of the equithermal curve settings and the power of the submersible pump are analysed and the results are presented. The seasonal COP (SCOP) for Bratislava area is calculated. for the system under consideration.

    • THE INFLUENCE OF THE TOOTH PROFILE SHAPE ON THE STRESS-STRAIN STATE IN THE GEAR

      pg(s) 153-156

      The shape of the tooth profile affects the stress-strain state in the gear. In the case of a fatigue failure the stress state is a decisive criterion for the lifetime of the gear. The shape of the tooth flank affects the magnitude of the contact pressure in the contact of the meshing teeth. The consequence of which are surface cracks and pitting. The shape of the tooth root influences the magnitude of the root stress, which, when limit is exceeded, leads to root cracks and teeth breakage. Many different types of gearing are known, but in the practice most widely used is the involute one. Other types of gearing become interesting especially when polymer materials are being used. If the gears are injection molded the type of gearing does not affect the cost of the tool. In the case of metal gears, standardized tools for involute gearing make the use of other special types of gearing economically unjustified. Our research is focused on the S-gears, which got their name from the S-shaped path of contact. The paper presents the research of how the defining parameters of S-gears impact the stress-strain state in the gear. This was done using a numerical model which simulates gear meshing. The stress state of two different types of S-gears was compared with the stress state in an involute gear of the same dimensions (same module, number of teeth and width). It was found that with a proper choice of gearing type we can improve the load bearing capability of the gear pair. With use of our numerical model we have also analyzed the impact of the tip relief on the stress state. The numerical model was validated for the case of meshing steel involute gears, where we can compare the results of the model with the results according the ISO 6336 calculation. A good match between the results of the model and results according the standard was obtained. After validation the same numerical model was used for the calculation of the stress-strain state in S-gears. This was calculated then for metal and polymer (POM/PA) gear pairs.

    • ANALYTICAL AND FINITE ELEMENT IN-PLANE VIBRATION ANALYSIS OF A GANTRY CRANE

      pg(s) 157-159

      Every object in nature has an infinite number of vibration frequency and amplitude as called “Natural Vibration Frequency”. Developing computer capacities allow calculating of natural frequencies and shapes of complex structures more accurate and understandable. In this study, a dual-trolley (2×400 tons) heavy-duty overhead gantry crane that can carry loads up to 800 tons was analysed by mathematical and finite element methods. The mathematical method is based on Euler-Bernoulli transverse vibration approach. On the other hand, finite element method is one of the most common numerical methods that can solve many engineering problems in a range from solid mechanics to acoustic. The generated solid model was analysed by the finite element method with the help of ANSYS Workbench 14.5 which is a commonly used analysis program. The obtained values of natural frequencies at mathematical calculations and finite element analysis were compared and presented.

  • TECHNOLOGIES

    • INCREASE OF REALIBILITY OF OPTIC-ELECTRONIC DEVICES BY MEANS OF FINISHING ELECTRON-BEAM PROCESSING OF THEIR OPTICAL ELEMENTS

      pg(s) 160-164

      The range of parameters of the electron beam (density of thermal effect Fn = 7∙106…8∙108 W/m² and travel speeds V = 5∙10-3…5∙10-2 m/s), within which there is an improvement in the performance characteristics of optical elements: increase of microhardness of the surface of elements from optical ceramics from 1,21∙103…2,83∙103MPa to 4,84∙103…7,15∙103 MPa and increase of the spectral transmission coefficient of IR-radiation by 4… 6% for elements of optical glass and for 5… 7% – for elements of optical ceramics; there occurs an increase in the critical values of the external heat flow leading to the destruction of the elements by 1,5…2 times, thus the increase of external pressure up to 107 Pa decreases the specified critical values by 1,3…1,5 times; critical values of thermoelastic stresses in optical elements at heating temperatures 300… 1200 K increase by 1,5…2,5 times, indicating an increase in resistance to thermal effects and increased external pressures of optical elements processed by an electronic beam; the values of critical heights of falling of a steel ball on their surface, leading to destruction of elements, increase from 0,18…1,1 m to 0,37…1,35 m, so, their resistance to mechanical shocks increases. It is established, that increase of durability of optical elements, processed by an electron beam, to external thermal and mechanical effects leads to the increase of probability of non-failure operation of optic-electronic devices under extreme conditions of operation to 10… 20%.

    • THE STRUCTURAL RELIABILITY AND ADEQUACY ASSESSMENT OF THE INDUSTRIAL ELECTRIC POWER SYSTEMS WITH LOCAL POWER PLANTS

      pg(s) 165-168

      In this paper methods of estimating the structural reliability and adequacy of the large industrial enterprises are considered. The combination of the sequential network reduction method and the Newton’s method is proposed for the calculation of structural reliability indices. Estimation of the adequacy is based on the random events simulation by Monte Carlo method.

    • PROSPECTS FOR DEVELOPMENT OF NUCLEAR ENERGY IN BULGARIA

      pg(s) 172-174

      The project to build a second nuclear power plant in Bulgaria emerged in the 70s of XX century. He repeatedly starts and stops over the past decades, mostly under the influence of external and internal policy decisions. Meanwhile, Bulgarian taxpayers pay large sums for errors and indecision of our political elite. Time specialists in this area say their arguments and take the best decision for Bulgaria instead of wasting money without end.

    • TRAFIC INDICATORS IN CONTEXT OF SUSTAINABLE TRANSPORT DEVELOPMENT

      pg(s) 175-177

      Sustainable transport, as one of the areas on which sustainable development should be founded, depends more and more on introduction of electric vehicles in daily traffic. This paper describes part of the results of wider research related to the analysis of all sustainable transport indicators. Since introduction of electric vehicles is supposed to be done stage by stage in the actual transport, deep understanding of its main parameters/indicators is a prerequisite for reliable analysis. The paper identifies traffic and vehicle structure parameters and rang them in hierarchic order. This structure can serve as substructure in more complex structure of all transport parameters in wider researches.

    • A PROCESSES CONTROL SIMULATION TOOL

      pg(s) 182-184

      The paper deals with a variable multifunctional simulation tool that enables to design and assemble animated models of various technological processes controlled by externally connected fuzzy logic unit. It enables to verify the correctness of fuzzy controller settings in the future control of real technological processes in practice. This tool represents an effective, innovative, and creative concept important to understanding control approach of technological processes modeling as an insight to behavior of real industrial processes and their control which is based on fuzzy logic. On the base of this animated simulation, real technological processes control can be realized successfully according to producer demands afterwards. Models of technological processes assembled by this simulation tool can be then externally controlled by various control strategies (traditional PID controllers, ON-OFF controllers,PLC controllers, fuzzy logic controllers etc.) via a proper real controller connected to the computer. In the paper, two-conveyor-belt system for product packing is shown. The goal consists in control of synchronization of products and boxes placed on individual conveyor belts in order to pack the product into the box. The main concern here is to improve dynamic performance and control efficiency with the help of assembling an animated model of the controlled technological process and its external control by a fuzzy logic unit.

  • MATERIALS