Papers by Keyword: Thermal Characteristics

Abstract: Powder mixed electric discharge machining (PMEDM) is a newly developed technology in which EDM is performed by mixing electrically conductive micro or nanoparticles with dielectric fluid. The electrically conductive tiny particles when come at the gap of electrode and work piece, they will begin to create spark by the induction of electrode voltage which enhances the material removal and surface finish of the machined surface. In this paper a brief review has been done on different aspects of powder mixed electric discharge machining. It is observed that the researches are done in three main directions. Firstly, experimental studies are done to show the effect of several input process parameters on responses mainly material removal rate (MRR), surface roughness and tool wear rate. Secondly, the metallurgical characteristics of the machined surface are analyzed to measure the white layer thickness and amount of powder material inclusion onto the surface. The third one is the investigation of thermal characteristics of the tool and work pieces during the machining process. In these three sections of researches, the results of the investigations have been discussed in this review. Keywords: powder mixed electric discharge machining, metallurgical characteristics, nano particles, material removal rate, surface roughness, tool wear rate, white layer thickness, thermal characteristics

Abstract: In Slovakia, since August 2016, a change in the thermal standard STN 73 0540-2 [6] has been in force, taking into account the objective of the European Directive, which since 2021 counts on the construction of buildings with almost zero energy consumption. One of the objectives of these changes is to reduce energy consumption in buildings min. by 20% till 2020. In this article it is compared the selected structures of the support exterior walls with regard to the criterion of the required thermo-technical characteristics of the building structure - coefficient of heat transfer of the structure U for the ultra-energy building according to STN 73 0540 part 2 from 2016 [3, 6]. Finally, the most cost-effective structure that meets the required thermal and technical parameters was the masonry structure with an additional by insulating the ETICS (with meaning External Thermal Insulation Composite System).

Abstract: Determination of characteristic of fireproof capability of examined fire-retardant coating by experiment-calculated method solving the inverse heat conduction problems based on the firing tests data. With the aim of determining the fire-resistance time of metal sheets with fire-retardant coating there are used experimental research methods of patterns behavior during heating according to the requirements of National Standards of Ukraine B.V. 1.1.-4-98 are used; mathematical and computer modelling of processes of unsteady heat transfer in the system “metal sheet – fire-retardant coating”; determination of thermal characteristics and characteristic of coating fireproof capability. Firing tests of metal sheets covered by the flame retardant “Amotherm Steel Wb” are carried out. Based on the obtained data (temperature from the unheated sheet surface) there are determined the thermal characteristics of formed coating depending on temperature and the characteristic of fireproof capability of examined coating for 30 minutes fire-resistance time. The effectiveness of intumescent coating “Amotherm Steel Wb” is proved and the dependence between its heat conduction coefficient and temperature during heating in experimental stove of metal sheet with this coating in standard temperature conditions is specified. The co-relation between the thickness of intumescent coating “Amotherm Steel Wb” and fire-retarding quality of metal constructions is identified. Besides the necessary minimum thicknesses of such coating from the thickness of metal sheet for importance of 30 minutes fire-resistance time are calculated.

Abstract: This study aims to analyze the thermal characteristics of Tetraselmis chuii (T.Chuii) microalgae in the presence of TiO₂ (Titanium dioxide). The experiment was carried out on thermal analyzer equipment under inert condition. The blended sample has a mass ratio of microalgae and TiO₂ that was 10:0.03 (wt%). The results of the thermal analysis show that the addition of TiO₂ can change the temperature characteristics during the reaction process. The Coats-Redfern method is applied to calculate activation energy (Ea) resulted in the value of the blended fuel in the second stage that was 56.9 kJ/mol lower than that of pure microalgae that was 70.68 kJ/mol and conversely in the third stage the value of activation energy for blended fuel was 264.57 kJ/mol higher than pure microalgae that was 223.25 kJ/mol. Overall results pointed out that TiO₂ had a significant impact on the thermal characteristic of Tetraselmis chuii during the pyrolysis process.

Abstract: In this study, TiN anode GaN Schottky barrier diodes (SBDs) with a low access sheet resistance of 28 Ω/□ were fabricated for microwave power transmission application. The performance of the diodes at room temperature (RT) is comparable with the ideality factor n and Schottky barrier height (SBH) were 1.28 and 0.47 eV for the 8-finger SBDs, 1.22 and 0.49 eV for the 16-finger SBDs, respectively. A low on-resistance of 5.71 and 3.58 Ω were obtained for 8-and 16-finger SBD at RT, respectively. The low series resistance induced by larger anode area of 16-finger SBDs results in a lower turn-on voltage of 0.47 V compared with that of 0.68 V for the 8-finger one. Besides, the temperature dependent current-voltage characteristics demonstrate that the TiN anode has a good temperature stability. And the temperature dependent performance of the 16-finger SBDs present a better uniformity than that of the 8-finger SBDs.

Abstract: Protected escape routes enable the rescuing of persons to the outside of a building on fire. They are characterized, in particular, by strict requirements relating to the aeration of such spaces. However, the fulfilling of these limits may impact the monitored thermal characteristics of the respective internal areas. The outlined dilemma will be illustrated by way of an example of a protected escape route aerated by positive-pressure ventilation.

Abstract: During of aluminum alloy materials, it is possible to find three surface types which can be distinguish as primary, secondary and tertiary sections. In practice this is a big problem in case of finding the basic parameters of roughness and waviness as described by ISO 4288. According to our research, it is possible to use optical microscopy in the first step and subsequently to scan the surface in 3D in order to distinguish the type of. Another problem is how to determine the boundaries between the individual structures. The article describes methods to distinguish the boundaries in a more precise way by the cumulative functions, leading to more accurate determination of the surface quality parameters.

Abstract: Finite element simulation is an effective method to study the thermal characteristics of high-speed motorized spindle, how to improve the simulation accuracy has become the key point of this research field. This paper presents a FEA method using ANSYS to precisely predict the thermal characteristics of high-speed spindle. Firstly, the heating and cooling characteristics of high-speed spindle are analyzed, main heating source, convective heat transfer coefficient, and thermal contact resistance are calculated. Secondly, FEA model of the machine center is built, the temperature field and thermal deformation of the spindle system are simulated. Thirdly, an experimental system to test thermal characteristics is designed, simulation results are compared with the experimental results. The result shows that the simulation errors are controlled in a relative low range, the FE modelling method can precisely predict the thermal characteristics of the motorized spindle.

Abstract: A numerical investigation has been carried out in the present work to study flow characteristics and thermal performance of a chevron type brazed plate heat exchanger (PHE). A local element-by-element analysis utilizing e-NTU method is employed for simulating the heat exchanger. In this approach, Nusselt number is expressed in terms of friction factor which in turn, is given as a function of chevron angle of the heat exchanger. Water has been used as cold and hot fluid. Effect of fluid flow rate and inlet temperatures on the heat duty, overall heat transfer coefficient, fluid outlet temperatures and pressure drop have been studied. When compared with literature results of intermating plate heat exchangers, chevron type plate heat exchanger gives greater heat transfer enhancement, though with increased pressure drop.

Abstract: Reduction of the costs in the operation of the building, due to energy-saving technologies, is a priority in the construction today. This article discusses some ways to reduce energy consumption of schools in hot climates such as the installation of solar collectors, using of triple-glazed windows and modern insulating materials. These methods of energy reduction are determined by the selected space-planning solutions, constructive features of the structure, financial possibilities and climatic conditions. Considering these above listed characteristics, the school was designed for the class A of energy efficiency.[1-4]