Effect of operating parameters on functional fatigue characteristics of an Ni-Ti shape memory alloy on partial thermomechanical cycling

In this study, the influence of upper cycle temperature (maximum temperature in a cycle) and the magnitude of applied stress on the functional properties of an SMA during partial thermomechanical cycling has been studied. A near-equiatomic NiTi SMA was chosen and tested under different upper cycle temperatures (between martensite finish (Mf) and austenite finish (Af) temperatures) and stress level (below and above the yield strength of the martensite). The upper cycle temperature was varied by controlling the magnitude of the current supply. The results show that a raise in the upper cycle temperature causes the permanent strain to increase and also lowers the stability. However, decreasing the stress imposed to a value lower than the yield strength of the martensite improves cyclic stability. The upper cycle temperature was found to influence the crack nucleation, whereas the applied stress level the crack propagation during partial thermomechanical cycling of SMAs. Therefore, decreasing the upper cycle temperature as well as the magnitude of stress applied to lower than the yield stress of martensite have been found to be suitable strategies for increasing the lifespan of SMA-based actuators during partial thermomechanical cycling.

Thermodynamic Efficiency Maximum of Simple Organic Rankine Cycles

The increase of the maximal cycle temperature is considered as one of the best tools to increase cycle efficiency for all thermodynamic cycles, including Organic Rankine Cycles (ORC). Technically, this can be done in various ways, but probably the best solution is the use of hybrid systems, i.e., using an added high-temperature heat source to the existing low-temperature heat source. Obviously, this kind of improvement has technical difficulties and added costs; therefore, the increase of efficiency by increasing the maximal temperature sometimes has technical and/or financial limits. In this paper, we would like to show that for an ideal, simple-layout ORC system, a thermodynamic efficiency-maximum can also exist. It means that for several working fluids, the thermodynamic efficiency vs. maximal cycle temperature function has a maximum, located in the sub-critical temperature range. A proof will be given by comparing ORC efficiencies with TFC (Trilateral Flash Cycle) efficiencies; for wet working fluids, further theoretical evidence can be given. The group of working fluids with this kind of maximum will be defined. Generalization for normal (steam) Rankine cycles and CO2 subcritical Rankine cycles will also be shown. Based on these results, one can conclude that the increase of the maximal cycle temperature is not always a useful tool for efficiency-increase; this result can be especially important for hybrid systems.

Investigation of the working process of a diesel engine when operating on anhydrous fuel, coarse and micro-heterogeneous water-fuel emulsion

Оксиды азота являются наиболее опасными химическими соединениями, находящимися в составе отработавших газов судовых дизелей. Уменьшение содержания оксидов азота является весьма сложной задачей, так как это связано с ограничениями максимальной температуры цикла, термического КПД и, следовательно, с ограничениями по топливной экономичности. Одним из эффективных способов уменьшения концентрации оксидов азота является применение водотопливных эмульсий. Недостатком применения эмульсии является увеличение удельного расхода топлива. Целью работы является исследование возможности одновременного снижения уровня вредных выбросов и расхода топлива при работе дизеля на ВТЭ. В статье приведены описание экспериментальной установки и результаты экспериментальных исследований дизеля Ч10,5/12 на безводном топливе, грубой и микрогетерогенной водотопливных эмульсий с содержанием воды 15% при работе по винтовой характеристике. С использование полученных в ходе испытаний дизеля индикаторных диаграмм выполнен сравнительный анализ рабочего процесса на различных топливах. Полученные результаты выполненных исследований подтвердили эффективность использования микрогетерогенной эмульсии, в сравнении с грубой эмульсией для снижения выбросов оксидов азота с отработавшими газами в судовых дизельных энергетических установках и уменьшения удельного расхода топлива. Nitrogen oxides are the most dangerous chemical compounds which come out with the exhaust gases of marine diesel engines. Reducing nitrogen oxides is challenging due to limitations on maximum cycle temperature, thermal efficiency, and hence fuel economy limitations. One of the effective ways to reduce the concentration of nitrogen oxides is the use of water-fuel emulsions. The disadvantage of using an emulsion is the significant fuel consumption increase. This article describes the experimental setup and the results of experimental studies of a Ч10.5/12 diesel engine on anhydrous fuel, coarse and micro-heterogeneous water-fuel emulsions with a water content of 15% when operating in service. Performance diagrams obtained during the diesel engine tests let the authors get a comparative analysis of the working process using various fuels. The results confirmed the effectiveness of using a micro-heterogeneous emulsion, in comparison with a coarse emulsion, to reduce emissions of nitrogen oxides with exhaust gases in marine propulsion systems and to reduce fuel consumption.

Monitoring of heat-induced carcinogenic compounds (3-monochloropropane-1,2-diol esters and glycidyl esters) in fries

3-Monochloropropane-1,2-diol (3-MCPD) esters and glycidyl esters (GE) are heat-induced contaminants which form during oil refining process, particularly at the high temperature deodorization stage. It is worth to investigate the content of 3-MCPD and GE in fries which also involved high temperature. The content of 3-MCPD esters and GE were monitored in fries. The factors that been chosen were temperature and duration of frying, and different concentration of salt (NaCl). The results in our study showed that the effect was in the order of concentration of sodium chloride < frying duration < frying temperature. The content of 3-MCPD esters was significantly increased whereas GE was significantly decreased, when prolong the frying duration. A high temperature results in a high 3-MCPD ester level but a low GE level in fries. The present of salt had contributed significant influence to the generation of 3-MCPD. The soaking of potato chips in salt showed no significant effect on the level of GE during the frying. The oil oxidation tests showed that all the fries were below the safety limit. Hence, the frying cycle, temperature and the added salt to carbohydrate-based food during frying should be monitored.

Influence of limiting the actuation strain on the functional fatigue behavior of Ni50.3Ti29.7Hf20 high temperature shape memory alloy

The cyclic stability and the fatigue life of NiTiHf alloys are very important for their functionality at high temperatures. The previous studies have shown that the increase in Upper Cycle Temperature (UCT) and the magnitude of applied stress decreased the cyclic stability and fatigue life of NiTiHf high temperature shape memory alloys due to plasticity with dislocation formation at high temperature. On the other hand, this study was dedicated to the effect of limited actuation strain against the applied constant stress to the functional fatigue life and the possible damage mechanism such as dislocation and crack formation. Strain limitation led to observe insignificant amount of accumulated irrecoverable strain but significant amount of crack formation such that the reason of the failure of Ni50.3Ti29.7Hf20 (at%) alloy was found to be the crack formation instead of dislocation accumulation.

First and Second Law Analysis of Supercritical CO2 Recompression Brayton Cycle

The present research concentrates on the energy and exergy analysis of the S-CO2 recompression Brayton cycle and the individual components irreversibilities by varying the different operating parameters. Results show that the cycle efficiencies and LTR effectiveness reduce by increasing minimum cycle temperature, but HTR increases. The effect of minimum cycle temperature is more critical on cycle performance than maximum cycle temperature. The reactor has the highest irreversibility followed by recuperators and pre-cooler. Exergy efficiency shows a downward trend as environment temperature enhances. However, the effect of turbine inlet temperature is very low on-cycle efficiency and optimum pressure ratio for lower compressor outlet pressure values, which is more significant by increasing this parameter.

Estimation of Maximum Cycle Temperature and Pressure Ratio for Optimum Design and Operations of Gas Turbine Power Plant

Aims: The performance of gas turbine is influenced by a number of factors which may be classified under three main headings: design limiting conditions, environmental dependent conditions and system respond condition. The design limiting conditions have been found to have influenced gas turbine performance most. In this study, two design limiting conditions (pressure ratio and maximum cycle temperature) were evaluated and estimated for optimal design and operations of gas turbine. Study Design: Hierarchical order in selecting the two design condition parameters was proposed. Methodology: Steady state energy and exergy concept was used to model the behavior of the plant. Results: Result obtained indicated that at maximum cycle temperature of 1173K, 1273K, 1373K, 1473K, 1573K, and 1673K,maximum pressure ratio for optimal performance were 19, 24, 29, 36, 44 and 51 respectively. Conclusion: These results provide insight into the performance behavior of gas turbine and also serve as a guide for operations and design optimization.

A study on relation between Pitta Pradhan Prakriti females and ovulation with the help of basal body temperature method

Prakriti indicates the predominance of natural Doshas which may interfere with the normal human physiology. The day of Ovulation may have some relation with Prakriti of females. In this competitive era females are facing many problems related to their menstruation such as painful menses, irregular menses, etc. in their adolescent age without any specific pathology in their reproductive system, which may cause problems related to infertility. Thus the present study enlightens the relation between Pitta Pradhan Prakriti females and Ovulation with the help of Basal Body Temperature method (BBT method). Methodology: To record the day of Ovulation in 30 Pitta Pradhan Prakriti females, basal body temperature method was selected. For confirmation, USG of ten females was done. Applications of proposed thought: In Pitta Pradhan Prakriti females by BBT method, we can observe that, whether the Ovulation is early or late as compared to normal 14th day of Ovulation and what are the effects of Pittadhikya on menstrual symptoms. Knowing the day of Ovulation will be helpful for identifying safe period and danger period. Conclusion: Pitta Pradhan Prakriti was found in 30 females. Vinishaya of Prakriti was done by percentage method and also by gradation method; grades were given on the basis of six Gunas. Day of Ovulation by B.B.T. method in Pitta Pradhan females was found to be the 14th and 15th day of menstrual cycle. Temperature rise on the day of Ovulation was found in the range 0.5°F - 0.7°F. By USG method, 90% results were matching related to day of Ovulation by BBT method.