Failure analysis of a heat-resistant stainless steel ring in a gas turbine burner

Journal of Mechanical Science and Technology - Hot gas path components in gas turbines are damaged by several mechanisms due to aggressive environments. In this research, the cracking of an insert...     

Hopf bifurcation index for large scale power systems

In this paper, we propose a novel index for the prediction of the Hopf bifurcation (HB) in power systems. The proposed index has strictly less processing load and less computation time in comparison to former HB indices. It also uses modern control properties of the power system such as system matrix and critical eigenvalue. Therefore, stochastic subspace system identification (SSSI) is used as a tool for estimation and prediction of the proposed HB index. Combining beneficial properties of SSSI methods and the processing advantages of the proposed index, we project a new algorithm for power system monitoring. The algorithm is easy and straight-forward. We conduct several test conditions for the proposed materials using 2-area 4-machine system, New England 10-Machine and IEEE 50-machine system. Simulation outcome expresses good performance of proposed index in comparison to former HB indices. The proposed index has fairly linear behavior, without discontinuities with respect to increases of system load. It also has less computation load.     

Enumeration Order Equivalence in Rational Numbers

The enumeration of elements of c.e. sets in the theory of computability and computational complexity has already been investigated. However, the order of this enumeration has received less attention. The enumeration orders of elements of c.e. sets by means of Turing machines on natural numbers are investigated. In this paper, we consider the enumeration orders of elements of c.e. sets on rational numbers. We present enumeration order reducibility and enumeration order equivalence on rational numbers and propose some lemmas and theorems on these concepts. Also, we show that the theories here hold for Rc and we could repeat the same theories in this domain, in a same way.     

Electric Power Generation from Thermoelectric Cells Using a Solar Dish Concentrator

In this paper, design details, theoretical analysis, and outcomes of a preliminary experimental investigation on a concentrator thermoelectric generator (CTEG) utilizing solar thermal energy are presented. The designed CTEG system consisted of a parabolic dish collector with an aperture diameter of 1.8 m used to concentrate sunlight onto a copper receiver plate with 260 mm diameter. Four BiTe-based thermoelectric cells (TEC) installed on the receiver plate were used to convert the concentrated solar thermal energy directly into electric energy. A microchannel heat sink was used to remove waste heat from the TEC cold side, and a two-axis tracking system was used to track the sun continuously. Experimental tests were conducted on individual cells and on the overall CTEG system under different heating rates. Under maximum heat flux, a single TEC generator was able to produce 4.9 W for a temperature difference of 109°C, corresponding to 2.9% electrical efficiency. The overall CTEG system was able to produce electric power of up to 5.9 W for a 35°C temperature difference with a hot-side temperature of 68°C. The results of the investigation help to estimate the potential of the CTEG system and show concentrated thermoelectric generation to be one of the potential options for production of electric power from renewable energy sources.     

Design and Numerical Simulation of a Symbiotic Thermoelectric Power Generation System Fed by a Low-Grade Heat Source

All liquid heating systems, including solar thermal collectors and fossil-fueled heaters, are designed to convert low-temperature liquid to high-temperature liquid. In the presence of low- and high-temperature fluids, temperature differences can be created across thermoelectric devices to produce electricity so that the heat dissipated from the hot side of a thermoelectric device will be absorbed by the cold liquid and this preheated liquid enters the heating cycle and increases the efficiency of the heater. Consequently, because of the avoidance of waste heat on the thermoelectric hot side, the efficiency of heat-to-electricity conversion with this configuration is better than that of conventional thermoelectric power generation systems. This research aims to design and analyze a thermoelectric power generation system based on the concept described above and using a low-grade heat source. This system may be used to generate electricity either in direct conjunction with any renewable energy source which produces hot water (solar thermal collectors) or using waste hot water from industry. The concept of this system is designated “ELEGANT,” an acronym from “Efficient Liquid-based Electricity Generation Apparatus iNside Thermoelectrics.” The first design of ELEGANT comprised three rectangular aluminum channels, used to conduct warm and cold fluids over the surfaces of several commercially available thermoelectric generator (TEG) modules sandwiched between the channels. In this study, an ELEGANT with 24 TEG modules, referred to as ELEGANT-24, has been designed. Twenty-four modules was the best match to the specific geometry of the proposed ELEGANT. The thermoelectric modules in ELEGANT-24 were electrically connected in series, and the maximum output power was modeled. A numerical model has been developed, which provides steady-state forecasts of the electrical output of ELEGANT-24 for different inlet fluid temperatures.