Net Cycle Research Articles

Kinematics of a novel reciprocating endodontic handpiece.

To analyse the kinematics of the Reciproc Direct® contra-angle reciprocating device with different motor sources. Reciproc Direct contra-angle (VDW GmbH, Munich, Germany) was tested with new micro-motor sources. The micro-motor groups were as follows: a brushless electric micro-motor, a brushed electric micro-motor and an air-driven micro-motor. The electric micro-motor sources were also divided intofour subgroups as 10000, 15000, 20000 and 25000rpm. The maximum air pressure of the air-driven micro-motor was adjusted to 2 and 3kgfcm-2 . A custom target object was attached to the Reciproc Direct, and reciprocating motions were recorded with a high-speed camera at 1200frames per second. The following kinematic parameters were calculated: duration of each reciprocating motion, engaging and disengaging angles, cycle rotational speeds, engaging and disengaging rotational speeds, net cycle angle, total cycle angle and number of cycles to complete full rotation. One-way anova was used where applicable, followed by Tukey's multiple comparison tests, to compare the kinematic values of reciprocating motion for each micro-motor/Reciproc Direct combination. The Kruskal-Wallis test followed by Dunn's multiple comparison test was used for non-normally distributed data. Statistical analysis was performed (α=0.05). For the brushless micro-motor, median engaging angle was 186.5° at 10000rpm and 188.0° at 15000rpm which were significantly different than median engaging angles at 20000 (188.5°) and 25000 (189.3°) rpm (P<0.05). For the brushless micro-motor, median cycle rotational speed was 372.5rpm at 10000 and 459.8rpm at 15000rpm which were significantly different than median cycle rotational speed at 20000 (576.2rpm) and 25000 (677.8rpm) rpm (P<0.05). For the brushed micro-motor, median cycle rotational speed was 293.5rpm at 10000 and 386.3rpm at 15000rpm which were significantly different than median cycle rotational speed at 20000 (508.9rpm) and 25000 (597.6rpm) rpm (P<0.05). Rotational speeds were influenced significantly by motor sources even when the Reciproc Direct was used at speeds recommendedby the manufacturer. This could indicate that thekinematics of the Reciproc Direct are dependent on the power of the rotating motor.

Influence of various carbon capture technologies on the performance of natural gas-fired combined cycle power plants

Carbon capture and storage (CCS) technology has been studied actively in recent years to address global warming. This paper aimed to make a consistent comparison of different capture technologies applied to the natural gas-fired combined cycle (NGCC). Multiple power plant systems based on a standard NGCC using three different carbon capture technologies (post-combustion, pre-combustion, and oxycombustion) were proposed, and their net performance was compared. The optimal pressure ratio of the oxy-combustion technology system was obtained. The variations in the net cycle performance of the three systems were compared using the specific CO2 capture. The net power of the post-combustion capture scheme is lower than that of all other systems, but it has the highest efficiency. However, its biggest disadvantage is a much lower CO2 capture rate than the oxy-combustion capture which exhibits nearly 100 % capture rate. The conclusion is that the oxy-combustion capture would provide both the highest net efficiency and power output if a high capture rate of over 92 % was required.

A comparative performance analysis of a solid oxide fuel cell and gas turbine combined cycles with carbon capture technologies

This study presents a performance prediction of triple combined cycles that use a solid oxide fuel cell (SOFC) and a gas turbine combined cycle (GTCC) with carbon capture technologies. Post- and oxy-combustion capture technologies were comparatively analyzed. The component design parameters of a commercial F-class gas turbine and SOFC were used. Minimizing the turbine inlet temperature (i.e., no extra fuel supplied to the combustor) resulted in higher net cycle efficiency. With post-combustion capture, the net cycle efficiency reached approximately 70 % when no fuel was supplied to the combustor, but the maximum CO2 capture rate was limited to 80 %. When a dual combined cycle was adopted, the CO2 capture rate increased to 91 %, while the net efficiency was approximately 69 %. With oxy-combustion capture, the optimum pressure ratio was higher than in the normal triple combined cycle, and the net cycle efficiency was lower than that of the post-combustion cycle. However, there was a critical advantage of a larger power output with nearly complete carbon capture. The impact of the location of the oxygen supply was examined in the oxy-combustion cycle with extra fuel supplied to the combustor, and supplying all the fuel to the SOFC improved the cycle performance.

Performance Enhancement of a Molten Carbonate Fuel Cell/Micro Gas Turbine Hybrid System With Carbon Capture by Off-Gas Recirculation

The demand for clean energy continues to increase as the human society becomes more aware of environmental challenges such as global warming. Various power systems based on high-temperature fuel cells have been proposed, especially hybrid systems combining a fuel cell with a gas turbine (GT), and research on carbon capture and storage (CCS) technology to prevent the emission of greenhouse gases is already underway. This study suggests a new method to innovatively enhance the efficiency of a molten carbonate fuel cell (MCFC)/micro GT hybrid system including carbon capture. The key technology adopted to improve the net cycle efficiency is off-gas recirculation. The hybrid system incorporating oxy-combustion capture was devised, and its performance was compared with that of a post-combustion system based on a hybrid system. A MCFC system based on a commercial unit was modeled. Externally supplied water for reforming was not needed as a result of the presence of the water vapor in the recirculated anode off-gas. The analyses confirmed that the thermal efficiencies of all the systems (MCFC stand-alone, hybrid, hybrid with oxy-combustion capture, hybrid with post-combustion capture) were significantly improved by introducing the off-gas recirculation. In particular, the largest efficiency improvement was observed for the oxy-combustion hybrid system. Its efficiency is over 57% and is even higher than that of the post-combustion hybrid system.

Productivity, Costs, and Selected Environmental Impacts of Remote-Controlled Mini Forestry Crawlers

An effective way to reduce off-road traffic in forests is to implement greater distances between skid trails. However, this implies that trees beyond the boom reach of the harvester need to be felled motor manually before being winched to the skid trail, for example using a remote-controlled mini forestry crawler (MFC). They are only a few local studies which have evaluated the performance of such MFCs. The use of MFCs for wood extraction operations in mixed soft- and hardwood stands is presented in this study conducted in Southwestern Germany. The aim of this study was to analyze the productivity, costs, and selected environmental impacts of mini forestry crawlers during winching operations through a time study. Using statistical regression, time consumption was analyzed in order to determine significant explanatory variables. Environmental impacts were evaluated using the life cycle assessment (LCA) methodology with Umberto software. The mean net cycle time was 4.82 min and the net productivity rate was 7.77 m3 by productive machine hour (PMH0). Explanatory variables which significantly affected the net cycle time were the winched volume, the number of trees per load, and winching distance. Environmental analysis showed that inputs of fossil energy were mostly due to diesel and lubricant consumption. Raw materials for machine manufacture and maintenance showed the highest impact in human toxicity potential category. The MFCs showed good environmental performances, but the harvesting system should become more productive in order to be more cost effective.

Adapting the zero-emission Graz Cycle for hydrogen combustion and investigation of its part load behavior

A modern energy system based on renewable energy like wind and solar power inevitably needs a storage system to provide energy on demand. Hydrogen is a promising candidate for this task. For the re-conversion of the valuable fuel hydrogen to electricity a power plant of highest efficiency is needed.In this work the Graz Cycle, a zero-emission power plant based on the oxy-fuel technology, is proposed for this role. The Graz Cycle originally burns fossil fuels with pure oxygen and offers efficiencies up to 65% due to the recompression of about half of the working fluid. The Graz Cycle is now adapted for hydrogen combustion with pure oxygen so that a working fluid of nearly pure steam is available. The changes in the thermodynamic layout are presented and discussed. The results show that the cycle is able to reach a net cycle efficiency based on LHV of 68.43% if the oxygen is supplied “freely” from hydrogen generation by electrolysis.An additional parameter study shows the potential of the cycle for further improvements. The high efficiency of the Graz Cycle is also achieved by a close interaction of the components which makes part load operation more difficult. So in the second part of the paper strategies for part load operation are presented and investigated. The thermodynamic analysis predicts part load down to 30% of the base load at remarkably high efficiencies.

Pakistan's persistent energy crisis and performance of private power producers

The study examines the linkage between profitability and working capital management of private sector power producers of Pakistan. The energy crisis resulted in increased reliance on independent power producers (IPPs), which lead to various financial irregularities. Data for a period of seven years (2008–2014) was collected from 11 IPPs listed on the Karachi Stock Exchange descriptive analysis, ANOVA, and regression analysis, along with trend analysis and other diagnostic tests, were deployed to examine the association between five working capital ratios and net operating profit. Net trading cycle, current assets and current liabilities were found to exhibit significant relationship with profitability of IPPs. The findings suggest that the persistent problem of circular debt can be minimised through supply chain excellence, which can be realised through vigilant selection of suppliers and vendors on the part of private power producers. Since working capital management significantly influences the performance of IPPs, the study persuades undertaking of taking corrective measures before pursing long-term goals of installing new units. Dynamic business model is recommended that enhances collaboration and brings financial viability to the power sector.

Influence of selected cycle components parameters on the supercritical CO2 power unit performance

The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.

R1234yf and R1234ze as alternatives to R134a in Organic Rankine Cycles for low temperature heat sources

This paper compares the predicted organic Rankine cycle performance of two low global warming potential working fluids, R1234yf and R1234ze, alternatives to R134a over a wide range of evaporating temperatures and condensing temperatures for a given thermal power input. The results show that R1234yf would require 18.3% to 25.8% higher pump power and would enable up to 13.9% lower net cycle efficiencies than R134a over the range of cycle conditions examined in this work. In the other hand, R1234ze would require 15.7% to 20.2% lower pump power and would enable up to 13.8% higher net cycle efficiencies than R134a, over the range of cycle conditions analyzed. Both alternative fluids net cycle efficiency is benefitted substantially by a recuperator. The differences with R134a in net cycle efficiency are accentuated for high evaporating and condensing temperatures.

Kinematic analysis of new and used reciprocating endodontic motors in 2 different modes.

The actual reciprocating angles of endodontic motors might differ from the manufacturers' set values. This study analyzed the effect of clinical usage on the kinematics of reciprocating endodontic motors with 2 different reciprocal modes. 1 new and 3 used reciprocating endodontic motors (X-Smart Plus, Dentsply Maillefer) with 2 different reciprocating modes, WaveOne mode (W-mode) or Reciproc mode (R-mode), were analyzed. An angle measurement disc was inserted into a contra-angle. Reciprocating motions were recorded with a high-speed camera at 1,200 fps and analyzed on a computer. The following kinematic parameters were calculated: duration of each reciprocating motion, engaging and disengaging angles, cycle rotational speeds, engaging and disengaging rotational speeds, net cycle angle, total cycle angle, and number of cycles to complete full rotation. One-way ANOVA and Kruskal-Wallis test followed by multiple comparison tests were used for statistical analysis (p = 0.05). In W-mode, the actual engaging angles of all used and new motors were different from the manufacturer's set values (p<0.0001), whereas there was no difference between actual engaging angles among the motors (p>0.05). In R-mode, the actual engaging angles of all used and new motors were similar to the manufacturers' set values (p>0.05). There was no difference between the actual engaging angles among motors (p>0.05). Both the W-mode and R-mode showed statistically different values of actual disengaging angles for all used and new motors when compared with the manufacturers' set value (p<0.0001). This study confirmed that the actual kinematics of reciprocating endodontic motors differ from the manufacturers' set values. Some kinematic parameters were influenced by the clinical usage of the motors.

Efficiency of Working Capital Management and Profitability of UAE Construction Companies: Size and Crisis Effects

This paper aims to examine the relationship between the efficiency of working capital management and profitability of construction firms listed in the United Arab Emirates stock markets. The results show negative and significant relationship between net trade cycle for all construction firms and large construction firms. The coefficient of small firms is positive and insignificant, this indicates that small construction firms do not manage their working capital efficiently. The results also show negative and significant relation between the net trade cycle and profitability of construction firms during crisis periods. This indicates that UAE construction companies are more efficient in managing their working capital during crisis period.

High temperature solar thermochemical process for production of stored energy and oxygen based on CuO/Cu2O redox reactions

A novel solar chemical looping air separation (Sol-CLAS) system is proposed here, in which oxygen carrier particles, composed of CuO as the active ingredient and MgAl2O4 as the inert support, are employed to provide both solar thermal energy storage for power generation and to separate oxygen from air. The process has been simulated using codes developed in MATLAB and Aspen Plus software for the average diurnal solar insolation of Port Augusta, South Australia. The simulation predicts that 1000°C can be achieved in both the solar reduction and oxidation reactors, whose identical temperature results in low exergy destruction. A net cycle efficiency of 46% is predicted with the oxygen co-product of 0.023m3/MJ of input solar energy. The calculations also show that 81% of the total input solar energy to the system is stored as combined chemical and sensible heat in the oxygen carrier particles. The required enthalpy of reaction is 26% of the net absorbed input solar energy which is stored as chemical heat in the particles and consequently used for oxygen production. The variations of temperature and composition in different flow streams, total flow rate of oxygen produced per day, the amount of particles stored in the tanks, together with the fraction of sensible and chemical storages are also reported. Also reported is the sensitivity to the effects of main operating parameters of reservoir temperature and conversion of particles are also reported.

Integration of a Pressurized-Air Solar Receiver Array to a Gas Turbine Power Cycle for Solar Tower Applications

The thermal performance of an array of pressurized-air solar receiver modules integrated to a gas turbine power cycle is analyzed for a simple Brayton cycle (BC), recuperated Brayton cycle (RC), and combined Brayton–Rankine cycle (CC). While the solar receiver's solar-to-heat efficiency decreases at higher operating temperatures and pressures, the opposite is true for the power cycle's heat-to-work efficiency. The optimal operating conditions are achieved with a preheat stage for a solar receiver outlet air temperature of 1300 °C and an air cycle pressure ratio of 9, yielding a peak solar-to-electricity efficiency—defined as the ratio of the net cycle work output divided by the solar radiative power input through the receiver's aperture—of 39.3% for the combined cycle configuration.

A Study of the Relationship between Net Trade Cycle and Liquidity of Small Firms

This paper aims to examine the relationship between the efficiency of working capital management, firm’s size and liquidity. This relation is analyzed using Generalized Method of Moment System Estimation applied to dynamic panel data for a sample of 5802 non-financial firms listed in the major US markets for the period 1990-2004. The results show negative and significant relationship between net trade cycle as a comprehensive measure of the efficiency in working capital management and liquidity for small firms

Working Capital Management and Performance of Kuwait Construction Companies

The purpose of this paper is to investigate the relationship between working capital management efficiency and performance of construction companies listed in the Kuwait Stock Exchange. The relationship is examined using dynamic panel data two- steps robust system estimation for the period 2001-2013. The analysis is applied at all the levels of the full sample as well as at the divisions’ levels of the sample by crisis and non-crisis periods, and by size. The results show negative and significant relationships between net trade cycle as a comprehensive measure of the efficiency in working capital management and performance for large firms during the full sample period while the relations between net trade cycle and performance for small firms are insignificant. This indicates that large construction companies in Kuwait are more efficient in managing their working capital than the small companies

Current Assets Management of Small Enterprises

The purpose of this paper is to investigate the relationship between firm’s net trade cycle, its size, and liquidity as a measure of efficiency in working capital management. The relation between the firm’s net trade cycle and its liquidity is examined using Generalized Method of Moment System Estimation applied to dynamic panel data for a sample of 5802 U.S. non-financial firms listed on the New York Stock Exchange, American Stock Exchange, NASDAQ Stock Market, and Over the Counter Market for the period 1990-2004 (87030 firm-year observations). The analysis is applied at the levels of the full sample and divisions of the sample by size.The results show a negative and significant relationship between net trade cycle as a comprehensive measure of efficiency in working capital management and liquidity for small firms. Most of the literature available focuses on the large firm’s experience in working capital management. The small firms generally face liquidity problems and have limited access to external capital and studies on their efficiency in working capital management are scant. In this context, the present study investigates the relation between the firm’s net trade cycle and liquidity of small firms.

Evaluating lean thinking using value stream mapping in manufacturing industry - a case study

Value stream mapping is an important lean manufacturing tool used to improve business in a competitive market by eliminating non-value adding activities or wastes from the value stream of a product and improving in providing in process operations. This paper aims to address the application of lean manufacturing using value stream mapping (VSM) concepts in a casting organisation. Using value stream concepts, both current and future states maps of the organisation's shop floor scenarios have been discussed. Results of investigation demonstrated the net reduction of 14.28% in value added time and net cycle time of operation is reduced from 12 minutes to 9 minutes. Current state map and future state map are compared and important benefits occurred after successful implementation of VSM has been discussed and it leads to profit of about 357000 rupees annually.

Power Generation from Condenser Waste Heat in Coal-fired Thermal Power Plant Using Kalina Cycle

Abstract In any thermal power plant the major energy loss takes place in the condenser through its cooling water system. The objective of the present study is to convert this low grade waste heat from a 500 MWe subcritical coal-fired power plant into electricity by integrating Kalina Cycle System 11 (KCS 11) where ammonia-water binary mixture is used as working fluid. A computer simulation programme has been developed by MS-Excel and VBA to analyze the combined cycle plant configuration and parametric optimization based on thermodynamic equations. The parametric study is carried out based on variation of ammonia mass fraction and cooling water flow rate by keeping saturated vapour condition at turbine inlet. Result shows that the Kalina cycle is able to add about 13.49MWe electric power with a net cycle efficiency of 2.58%. There is an optimum cooling water flow rate that yields the maximum net cycle efficiency for a particular condenser design value in the Kalina cycle. Effect of ammonia mass fraction variations in the binary mixture is also studied by fixing turbine inlet temperature at 312.308K. The study shows that cycle performance improves with higher ammonia mass fraction. Effect of temperature rise across the main plant condenser increases the overall plant efficiency. Around 3.3 ton/h of CO2 emission can be reduced by electric power addition with the help of utilizing the condenser heat loss.

Optimization of a recompression supercritical carbon dioxide cycle for an innovative central receiver solar power plant

Peculiar thermodynamic properties of carbon dioxide (CO2) when it is held at or above its critical condition (stated as supercritical CO2 or sCO2) have attracted the attention of many researchers. Its excellent thermophysical properties at medium-to-moderate temperature range have made it to be considered as the alternative working fluid for next power plant generation. Among those applications, future nuclear reactors, solar concentrated thermal energy or waste energy recovery have been shown as the most promising ones. In this paper, a recompression sCO2 cycle for a solar central particles receiver application has been optimized, observing net cycle efficiency close to 50%. However, small changes on cycle parameters such as working temperatures, recuperators efficiencies or mass flow distribution between low and high temperature recuperators were found to drastically modify system overall efficiency. In order to mitigate these uncertainties, an optimization analysis based on recuperators effectiveness definition was performed observing that cycle efficiency could lie among 40%–50% for medium-to-moderate temperature range of the studied application (630 °C–680 °C). Due to the lack of maturity of current sCO2 technologies and no power production scale demonstrators, cycle boundary conditions based on the solar application and a detailed literature review were chosen.

Is There a Non-linear Relationship between Net Trade Cycle and Corporate Performance in Turkey?

&lt;p&gt;The aim of this study is to examine the relationship between working capital management and corporate performance for non-financial firms quoted in Borsa İstanbul for the period 2009-2014. The working capital investment decisions of the firms are utmost important since firms can continue their operations without discontinuance, raise their value and reduce risks as long as working capital level is attentively administered. Our research contributes to the working capital literature by investigating the non-linear relation between net trade cycle (NTC) and firm performance, utilising contemporary data and using system Panel GMM method. Our results indicate that there is a non-linear relationship between NTC and corporate performance. This means that there is an optimal NTC value where firm value is maximised. At this optimal working capital level, costs and advantages are poised. This implies that corporate executives should carefully manage their working capital investment and strive to be close to the optimal level as much as possible.&lt;/p&gt;