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Number of results: 26
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Abstract

The objective of this work is to present an energy analysis of different absorption refrigerating systems operating with diverse refrigerants. Also is applied the method of experimental design to optimize configurations proposed by the absorption pairs used and the operating conditions. Both acceptable coefficient of performance and low operating generator temperature are scrutinised. Therefore, a computer program is developed. An investigation of the thermodynamic properties is presented. Results show the coefficient of performance evolution versus respectively the evaporator temperature, temperature of condensation and generator temperature. A particular interest is devoted to the intermediate pressure effect on the performance of different systems. In order to better converge in the selection of the configuration and the refrigerant, which can ensure a high coefficient of performance associated to relatively low operating generator temperature the plan of experiments has been developed, taking in account all parameters influencing the system performance and the function of operating temperature. Results show that the refrigerating machine containing a compressor between the evaporator and the absorber has a coefficient of performance quite acceptable and that it can work at low generator temperature for about 60 ◦C and using the NH3/LiNO3 as refrigerant.
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Abstract

The policy of sustainable development seeks to improve energy efficiency of industrial equipment. Efforts to improve energy efficiency also apply to the paint shops, where the recovery of waste heat is sought. The main source of a large amount of low-temperature waste heat in the paint shop is the spray booth. The second place where a large amount of low temperature waste heat is released is the room where the compressed air is prepared. Low energy efficiency of air compressors requires a large electric power supply. As a result, the emitted large heat fluxes become waste energy of the technological process. Heat is equivalent to up to 93% of the electric power supplied in the air compression process. There are solutions for recovering heat from compressors coming from the oil cooling water, but then the waste heat from the cooling of the compressed air and from the electric motor is released into air in the room. A method for recovering low-temperature waste heat from the air preparation room by means of an air-source heat pump has been proposed. An energy balance of the air compression and dehumidification process for the paint shop was made. A Matlab’s built-in numerical model includes air compressor and dehumidifier, heat recovery and accumulation for the purposes of use in the spray booth. A simulation experiment was carried out on the effectiveness of heat recovery from the air preparation room. The use of combined energy management in paint shops was proposed.
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Abstract

Recycling construction and demolition waste not only reduces project costs; and saves natural resources, but also solves the environmental threat caused by construction waste disposal. In this paper, C25 waste road concrete is used as an experimental material, the uniaxial compression strength and tensile splitting strength of C25 RAC whose coarse aggregate replacement rate is 0%, 25%, 50%, 75%, and 100% are tested under the condition that the water-to-cement ratio is 0.47, 0.55 and 0.61. The results show: (1) the uniaxial compression strength and tensile splitting strength decrease with the increase of RAC; (2) for concrete with the same water-to-cement ratio, when the coarse aggregate replacement rate changes from 0% to 50%, the uniaxial compression strength and tensile splitting strength of RAC changes slightly. When the coarse aggregate replacement rate changes from 50% to 100%, the uniaxial compression strength and tensile splitting strength of RAC decreases rapidly
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Abstract

Searching for new refrigerants is one of the most significant scientific problems in refrigeration. There are ecological refrigerants commonly known: H2O and CO2. H2O and CO2 known as natural refrigerants, but they have problems:a high freezing point of H2O and a low triple point of CO2. These problems can be solved by the application of a hybrid sorption-compression refrigeration cycle. The cycle combines the application possibility of H2O in the high temperature sorption stage and the low temperature application of CO2 in the compression stage. This solution gives significant energy savings in comparison with the two-stage compressor cycle and with the one-stage transcritical CO2 cycle. Besides, the sorption cycle may be powered by low temperature waste heat or renewable heat. This is an original idea of the authors. In the paper an analysis of the possible extension of this solution for high capacity industrial refrigeration is presented. The estimated energy savings as well as TEWI (Total Equivalent Warming Impact) index for ecological gains are calculated.
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Abstract

Recent investigations of micro engines have documented the problem of low efficiency of steady compression devices [2]. As a solution, the application of unsteady processes has been proposed [1, 6, 17-20]. Closer investigations have shown the applicability of pure unsteady devices for gas compression, but it is also shown that they are practically not applicable for torque generation [21]. A new concept of the wave engine has to be developed. This paper presents such a new concept and numerical investigation of the hybrid wave engine. A hybrid wave engine combines in a single machine components realizing unsteady compression, steady expansion, and mixed unsteady and steady scavenging due to the centrifugal force action. MEMS technology requires or prefers a flat geometry. Therefore, the use of a radial type of wave compression device for air compression is proposed. A numerical, two-dimensional complete model of this device was built, and several numerical simulations of engine operations were performed. The numerical model includes the simplified model of the combustion chamber closing the flow loop between the high-pressure compressed air port and the high-pressure hot exhaust gas port. The model represents the complete flow scheme of the hybrid wave engine. A special type of turbine in radial configuration with serial flow layout is used for torque generation.
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Abstract

The aim of this paper is to analyze various CO2 compression processes for post-combustion CO2 capture applications for 900 MW pulverized coal-fired power plant. Different thermodynamically feasible CO2 compression systems will be identified and their energy consumption quantified. A detailed thermodynamic analysis examines methods used to minimize the power penalty to the producer through integrated, low-power compression concepts. The goal of the present research is to reduce this penalty through an analysis of different compression concepts, and a possibility of capturing the heat of compression and converting it to useful energy for use elsewhere in the plant.
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Abstract

An uniaxial compression mechanical model for the roof rock-coal (RRC) composite sample was established in order to study the effects of height ratio of roof rock to coal on the structural strength of composite sample. The composite sample strengths under different height ratios were established through stress and strain analysis of the sample extracted from the interface. The coal strength near the interface is enhanced and rock strength near the interface weakened. The structural strength of composite sample is synthetically determined by the strengths of rock and coal near and far away from the interface. The area with a low strength in composite sample is destroyed firstly. An analytical model was proposed and discussed by conducting uniaxial compression tests for sandstone-coal composite samples with different height ratios, and it was found that the structural strength and elastic modulus decrease with a decrease in height ratio. The coal strengths far away from the interface determine the structural strengths of composite sample under different height ratios, which are the main control factor for the structural strength in this test. Due to its lowest strength, the rock near the interface first experienced a tensile spalling failure at the height ratio of 9:1, without causing the structural failure of composite sample. The coal failure induces the final failure of composite sample.
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Abstract

In this paper the influence of high power airborne ultrasound on drying biological material (Lobo apple) properties is considered. Apple samples were dried convectively at 75 ◦C and air flow of 2 m/s with and without ultrasound assist at 200W. During experiments, sun-drenched and not sun-drenched part of fruits were considered separately to show, how the maturity of the product influences dry material properties. Dried apple crisps in a size of small bars were subjected to compression tests during which acoustic emission (AE) was used. Analysis of AE and strength test results shows that correlations between received acoustic signals and sensory attributes (crispness, brittleness) of dried apples can be found. It was noted that ultrasound improved fruit brittleness in comparison with pure convective processes, where fruit maturity determines a kind of destruction and behaviour of dried apple crisps.
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Abstract

The paper presents Improved Adaptive Arithmetic Coding algorithm for application in future video compression technology. The proposed solution is based on the Context-based Adaptive Binary Arithmetic Coding (CABAC) technique and uses the authors mechanism of symbols probability estimation that exploits Context-Tree Weighting (CTW) technique. This paper proposes the version of the algorithm, that allows an arbitrary selection of depth D of context trees, when activating the algorithm in the framework of the AVC or HEVC video encoders. The algorithm has been tested in terms of coding efficiency of data and its computational complexity. Results showed, that depending on depth of context trees from 0.1% to 0.86% reduction of bitrate is achieved, when using the algorithm in the HEVC video encoder and 0.4% to 2.3% compression gain in the case of the AVC. The new solution increases complexity of entropy encoder itself, however, this does not cause an increase of the complexity of the whole video encoder.
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Abstract

Despite the growing importance of packet switching systems, there is still a shortage of thorough analyses of VoIP transmission effect on speech and speaker recognition performance. Voice over IP transmission systems use packet switching. There is no guarantee of delivery. The main disadvantage of VoIP is a packet loss which has a major impact on the performance experienced by the users of the network. There are several techniques to mask the effects of a packet loss, referred to as packet loss concealment. In this study, the effect of voice transmission over IP on automatic speaker verification system performance was investigated. The analyzed system was based on MAP-EM-GMM modelling methods. Four various speech codecs of H.323 standard were investigated with special emphasis placed on the packet loss phenomenon and various packet loss concealment techniques.
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Abstract

Recently a new technology of piezoelectric transducers based on PZT thick film has been developed as a response to a call for devices working at higher frequencies suitable for production in large numbers at low cost. Eight PZT thick film based focused transducers with resonant frequency close to 40 MHz were fabricated and experimentally investigated. The PZT thick films were deposited on acoustically engineered ceramic substrates by pad printing. Considering high frequency and non-linear propagation it has been decided to evaluate the axial pressure field emitted (and reflected by thick metal plate) by each of concave transducer differing in radius of curvature - 11 mm, 12 mm, 15 mm, 16 mm. All transducers were activated using AVTEC AVG-3A-PS transmitter and Ritec diplexer connected directly to Agilent 54641D oscilloscope. As anticipated, in all cases the focal distance was up to 10% closer to the transducer face than the one related to the curvature radius. Axial pressure distributions were also compared to the calculated ones (with the experimentally determined boundary conditions) using the angular spectrum method including nonlinear propagation in water. The computed results are in a very good agreement with the experimental ones. The transducers were excited with Golay coded sequences at 35-40 MHz. Introducing the coded excitation allowed replacing the short-burst transmission at 20 MHz with the same peak amplitude pressure, but with almost double center frequency, resulting in considerably better axial resolution. The thick films exhibited at least 30% bandwidth broadening comparing to the standard PZ 27 transducer, resulting in an increase in matching filtering output by a factor of 1.4-1.5 and finally resulting in a SNR gain of the same order.
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Abstract

Three commercially available intercooled compression strategies for compressing CO2 were studied. All of the compression concepts required a final delivery pressure of 153 bar at the inlet to the pipeline. Then, simulations were used to determine the maximum safe pipeline distance to subsequent booster stations as a function of inlet pressure, environmental temperature, thickness of the thermal insulation and ground level heat flux conditions. The results show that subcooled liquid transport increases energy efficiency and minimises the cost of CO2 transport over long distances under heat transfer conditions. The study also found that the thermal insulation layer should not be laid on the external surface of the pipe in atmospheric conditions in Poland. The most important problems from the environmental protection point of view are rigorous and robust hazard identification which indirectly affects CO2 transportation. This paper analyses ways of reducing transport risk by means of safety valves.
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Abstract

The paper analyzes the estimation of the fundamental frequency from the real speech signal which is obtained by recording the speaker in the real acoustic environment modeled by the MP3 method. The estimation was performed by the Picking-Peaks algorithm with implemented parametric cubic convolution (PCC) interpolation. The efficiency of PCC was tested for Catmull-Rom, Greville, and Greville two- parametric kernel. Depending on MSE, a window that gives optimal results was chosen.
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Abstract

Paper deals with theoretical analysis of possible efficiency increase of compression refrigeration cycles by means of application of a twophase ejector. Application of the two phase ejector in subcritical refrigeration system as a booster compressor is discussed in the paper. Results of exergy analysis of the system operating with various working fluids for various operating conditions have been shown. Analysis showed possible exergy efficiency increase of refrigeration compression cycle.
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Abstract

The main objective of this investigation is to assess the feasibility of strengthening of corroded (damaged) square hollow steel tubular sections subjected to compression and to develop or predict the suitable wrapping scheme of fibre reinforced polymer (FRP) to enhance the structural behaviour of it.For this study, compact mild steel tubes were used with the main variable being FRP characteristics. Carbon fibre reinforced polymer (CFRP) fabrics was used as horizontal strips (lateral ties) with other parameters such as the number of layers and spacing of strips. Among fourteen specimens, six were externally bonded by CFRP strips having a constant width of 50 mm with a spacing of 20 mm and the remaining six were externally bonded by CFRP strips having a constant width of 70 mm with a spacing of 20 mm, two columns were unbonded. Experiments were undertaken until the failure of columns to fully understand the influence of FRP characteristics on the compressive behaviour of the square sections including their failure modes, axial stress-strain behaviour, enhancement in the load carrying capapcity, and effect of distribution of CFRP layers. Finally, the behaviour of externally bonded hollow tubular sections was compared with one another and also with the control specimens. Evaluation of the results will lead to optimum CFRP jacketing/wrapping arrangements for the steel tubes considered here.
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Abstract

Recently, attempts have been made to use porous metal as catalysts in a reactor for the hydrogen manufacturing process using steam methane reforming (SMR). This study manufactured Ni-Cr-Al based powder porous metal, stacked cubic form porous blocks, and investigated high temperature random stack creep property. To establish an environment similar to the actual situation, a random stack jig with a 1-inch diameter and height of 75 mm was used. The porous metal used for this study had an average pore size of ~1161 μm by rolling direction. The relative density of the powder porous metal was measured as 6.72%. A compression test performed at 1073K identified that the powder porous metal had high temperature (800°C) compressive strength of 0.76 MPa. A 800°C random stack creep test at 0.38 MPa measured a steady-state creep rate of 8.58×10–10 s–1, confirming outstanding high temperature creep properties. Compared to a single cubic powder porous metal with an identical stress ratio, this is a 1,000-times lower (better) steady-state creep rate. Based on the findings above, the reason of difference in creep properties between a single creep test and random stack creep test was discussed.
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Abstract

The criteria, with which one should be guided at the assessment of the binding properties of bentonites used for moulding sands, are proposed in the paper. Apart from the standard parameter which is the active bentonite content, the unrestrained growth indicator should be taken into account since it seems to be more adequate in the estimation of the sand compression strength. The investigations performed for three kinds of bentonites, applied in the Polish foundry plants, subjected to a high temperature influences indicate, that the pathway of changes of the unrestrained growth indicator is very similar to the pathway of changes of the sand compression strength. Instead, the character of changes of the montmorillonite content in the sand in dependence of the temperature is quite different. The sand exhibits the significant active bentonite content, and the sand compression strength decreases rapidly. The montmorillonite content in bentonite samples was determined by the modern copper complex method of triethylenetetraamine (Cu(II)-TET). Tests were performed for bentonites and for sands with those bentonites subjected to high temperatures influences in a range: 100-700ºC.
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Abstract

Quantitative ultrasound has been widely used for tissue characterization. In this paper we propose a new approach for tissue compression assessment. The proposed method employs the relation between the tissue scatterers’ local spatial distribution and the resulting frequency power spectrum of the backscattered ultrasonic signal. We show that due to spatial distribution of the scatterers, the power spectrum exhibits characteristic variations. These variations can be extracted using the empirical mode decomposition and analyzed. Validation of our approach is performed by simulations and in-vitro experiments using a tissue sample under compression. The scatterers in the compressed tissue sample approach each other and consequently, the power spectrum of the backscattered signal is modified. We present how to assess this phenomenon with our method. The proposed in this paper approach is general and may provide useful information on tissue scattering properties.
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Abstract

The telemetry data are essential in evaluating the performance of aircraft and diagnosing its failures. This work combines the oversampling technology with the run-length encoding compression algorithm with an error factor to further enhance the compression performance of telemetry data in a multichannel acquisition system. Compression of telemetry data is carried out with the use of FPGAs. In the experiments there are used pulse signals and vibration signals. The proposed method is compared with two existing methods. The experimental results indicate that the compression ratio, precision, and distortion degree of the telemetry data are improved significantly compared with those obtained by the existing methods. The implementation and measurement of the proposed telemetry data compression method show its effectiveness when used in a high-precision high-capacity multichannel acquisition system.
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Abstract

This paper addresses the problem of tampering detection and discusses methods used for authenticity analysis of digital audio recordings. Presented approach is based on frame offset measurement in audio files compressed and decoded by using perceptual audio coding algorithms which employ modified discrete cosine transform. The minimum values of total number of active MDCT coefficients occur for frame shifts equal to multiplications of applied window length. Any modification of audio file, including cutting off or pasting a part of audio recording causes a disturbance within this regularity. In this study the algorithm based on checking frame offset previously described in the literature is expanded by using each of four types of analysis windows commonly applied in the majority of MDCT based encoders. To enhance the robustness of the method additional histogram analysis is performed by detecting the presence of small value spectral components. Moreover, computation of maximum values of nonzero spectral coefficients is employed, which creates a gating function for the results obtained based on previous algorithm. This solution radically minimizes a number of false detections of forgeries. The influence of compression algorithms' parameters on detection of forgeries is presented by applying AAC and Ogg Vorbis encoders as examples. The effectiveness of tampering detection algorithms proposed in this paper is tested on a predefined music database and compared graphically using ROC-like curves.
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Abstract

In this paper were conducted virtual tests to assess the impact of geometry changes on the response of metallic hexagonal honeycomb structures to applied loadings. The lateral compressive stress state was taken into consideration. The material properties used to build numerical models were assessed in laboratory tests of aluminium alloy 7075. The modelling at meso-scale level allow to comprehensive study of honeycomb internal structure. The changes of honeycomb geometry elements such as: fillets radius of the cell edges in the vicinity of hexagonal vertexes, wall thickness were considered. The computations were conducted by using finite element method with application of the ABAQUS finite element method environment. Elaborated numerical models allowed to demonstrate sensitivity of honeycomb structures damage process response to geometry element changes. They are a proper tools to perform optimization of the honeycomb structures. They will be also helpful in designing process of modern constructions build up of the considered composite constituents in various branches of industry. Moreover, the obtained results can be used as a guide for engineers. Conducted virtual tests lead to conclusion that simplification of the models of internal honeycomb structure which have become commonplace among both engineers and scientist can lead to inaccurate results.
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Abstract

In the current study, the hot deformation of medium carbon V-Ti micro-alloyed steel was surveyed in the temperature range of 950 to 1150°C and strain rate range of 0.001 to 1 s–1 after preheating up to 1200°C with a compression test. In all cases of hot deformation, dynamic recrystallization took place. The influence of strain rate and deformation temperature on flow stress was analyzed. An increase in the strain rate and decrease in the deformation temperature postponed the dynamic recrystallization and increased the flow stress. The material constants of micro-alloyed steel were calculated based on the constitutive equations and Zener-Hollomon parameters. The activation energy of hot deformation was determined to be 458.75 kJ/mol, which is higher than austenite lattice self-diffusion activation energy. To study the influence of precipitation on dynamic recrystallization, the stress relaxation test was carried out in a temperature range of 950 to 1150°C after preheating up to 1200°C. The results showed no a stress drop while representing the interaction of particles with dynamic recrystallization.
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Abstract

This paper presents the parameters of the reference oxy combustion block operating with supercritical steam parameters, equipped with an air separation unit and a carbon dioxide capture and compression installation. The possibility to recover the heat in the analyzed power plant is discussed. The decision variables and the thermodynamic functions for the optimization algorithm were identified. The principles of operation of genetic algorithm and methodology of conducted calculations are presented. The sensitivity analysis was performed for the best solutions to determine the effects of the selected variables on the power and efficiency of the unit. Optimization of the heat recovery from the air separation unit, flue gas condition and CO2 capture and compression installation using genetic algorithm was designed to replace the low-pressure section of the regenerative water heaters of steam cycle in analyzed unit. The result was to increase the power and efficiency of the entire power plant.
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Abstract

Three-dimensional (3D) finite element analyses (FEA) are performed to simulate the local compression (LC) technique on the clamped single-edge notched tension (SE(T)) specimens. The analysis includes three types of indenters, which are single pair of cylinder indenters (SPCI), double pairs of cylinder indenters (DPCI) and single pair of ring indenters (SPRI). The distribution of the residual stress in the crack opening direction in the uncracked ligament of the specimen is evaluated. The outcome of this study can facilitate the use of LC technique on SE(T) specimens.
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