Initial Metal Temperature Research Articles

Modeless Start-Up Control for Operational Flexibility of Combined Cycle Power Plants

The flexible operations of gas turbine combined cycle power plants, especially with reduction of start-up time, are important. In this paper, the modeless start-up method without determination of the start-up curves corresponding to the start-up modes (e.g., hot start, warm start, and cold start) were developed. This method generates the start-up curves in which the start-up time is minimized against the initial steam turbine metal temperature by optimizing the start-up parameters. Based on the candidates of these start-up parameter values obtained during the optimization process, the look-up tables corresponding to the initial metal temperature for the parameters are estimated. The start-up time of the start-up curves generated by referring to the look-up tables continuously vary against the initial metal temperature without exceeding the thermal stress limit of the steam turbine rotor. The results obtained by the developed method show that modeless start-up curves for gas turbine combined cycle power plants can be generated. In addition, by visualizing the relationship of the start-up time and the initial metal temperature, the start-up curves can be interactively selected to facilitate planning of the plant start-up schedules.

Absorption of Nitrogen by Melts of the Fe–C System During Metal Blowing with Oxygen

Kinetics of nitrogen absorption and desorption by melts of the Fe–C system with surface and volumetric oxidation in a stream of oxygen containing 0.2% of nitrogen with an initial metal temperature of 1350–1600°С, [С] = 0.8–3.8%, oxygen flow 0.24–1.8 liter/(minŊkg), are studied. It is established that there is excess chemical potential of nitrogen in a boundary layer compared with the nitrogen content in a gas stream.

Experimental Investigation Into Thermal Behavior of Steam Turbine Components—Temperature Measurements With Optical Probes and Natural Cooling Analysis

The steam turbine cooldown has a significant impact on the cyclic fatigue life. A lower initial metal temperature after standstill results in a higher temperature difference to be overcome during the next start-up. Generally, lower initial metal temperatures result in higher start-up stress. In order to optimize steam turbines for cyclic operation, it is essential to fully understand natural cooling, which is especially challenging for rotors. This paper presents a first-in-time application of a 2D numerical procedure for the assessment of the thermal regime during natural cooling, including the rotors, casings, valves, and main pipes. The concept of the cooling calculation is to replace the fluid gross buoyancy during natural cooling by an equivalent fluid conductivity that gives the same thermal effect on the metal parts. The fluid equivalent conductivity is calculated based on experimental data. The turbine temperature was measured with pyrometric probes on the rotor and with standard thermocouples on inner and outer casings. The pyrometric probes were calibrated with standard temperature measurements on a thermo well, where the steam transmittance and the rotor metal transmissivity were measured.

The effect of vacuum rarefaction during foundry by gasified models

The cooling of liquid metal in the process of filling the mold during foundry by gasified models is investigated based on an analysis of the equation of thermal conductivity during thermal destruction of the model material. It is shown that crystallization of metal is expanded top-down, and the intensity of cooling increases as the pouring rate increases and rarefaction in a casting box increases. An equation for calculating the temperature of the metal surface that takes into account the energy of thermal destruction of the model material, pouring rate, initial temperature of metal, rarefaction in the casting box, and the cross-section area of the casting during foundry by gasified models is suggested.

Effects of rolling parameters on work-roll temperature distribution in the hot rolling of steels

Temperature variations of work-rolls in the process of hot rolling of slabs were analyzed by solving heat conduction equation with time-dependent boundary conditions. The Raylieght-Ritz and the finite-element methods were employed to solve the governing equation. To improve the accuracy, the thermal relationship between rolling metal and work-rolls was taken into account as well as the effects of different parameters such as interface heat transfer coefficient, rolling speed, and slab initial temperature were considered in the calculations. To verify the employed model, a comparison was made between the predicted and the recorded time-temperature history and good agreement was observed. Modelling results show that the interface heat transfer coefficient and rolling speed are important factors that vary effectively the temperature field within the work-roll. In addition, the interface heat transfer coefficient is affected by the other parameters and factors such as flow stress behavior of the metal being rolled and initial temperature of metal. Therefore, in order to determine an accurate temperature field within the work-rolls, flow behavior and temperature distribution in the rolling metal should also be calculated at the same time.

Experimental study on rapid solidification process using a novel ultrasound technique

Solidification rate is a crucial parameter affecting the microstructure formation in rapid contact solidification processes. A novel ultrasound technique has been developed for measuring the phase-change interface movement during a rapid contact solidification process. This new method utilized the echoes from two reflection interfaces for tracking the solidification front. It is therefore possible to eliminate the temperature effect on the sound speed in metals. The rapid solidification experiments were conducted by impacting an aluminum substrate onto a shallow liquid alloy 158. Echo signals were detected successfully and the phase change front position was determined with high resolution. A theoretical resolution of 4.5 μm can be achieved under current conditions. Experiments were conducted to study the effects of initial metal temperature, liquid pool thickness and impact height on a rapid contact solidification process. The experimental results show that with an increasing impact height, the solidification rate increases which means the thermal contact resistance is decreased. Therefore, the newly developed method can provide useful data for correlating the thermal contact resistance in rapid contact solidification processes.

An electrochemical mass transfer investigation in the presence of simultaneous subcooled pool boiling

Mass transfer rates were investigated in the presence of simultaneous subcooled pool boiling at a vertical cylindrical electrode using the electrochemical limiting diffusion current technique. Various concentrations of equimolar ferri/ferrocyanide (0.01-0.20M) in 0.5M NaOH electrolyte were used. The initial metal temperature was 500° C and liquid subcooling was varied between 25 and 80° C. Transient temperature and limiting current histories were recorded following sudden immersion of the hot electrode and Schlieren photographs were taken for a range of electrode temperatures. In the nucleate boiling regime, the variation of mass transfer coefficient with temperature difference between electrode and electrolyte showed similar trends to the variation of heat transfer with temperature difference. Film boiling was briefly observed at low subcooling, eg. 27° C

ICONE11-36033 EXPERIMENTAL STUDY OF THERMAL-HYDRAULIC BEHAVIOR OF COOLANT OUT OF NEUTRON REFLECTOR FOR APWR DURING REFLOODING OF LARGE BREAK LOCA

An experimental study was carried out to investigate the steam-water two-phase flow of coolant in the Neutron Reflector (N/R) during the reflooding of large break Loss OF Coolant Accident (LOCA). The experimental apparatus simulated the geometry of one hole of a typical N/R cooling-hole (including the corresponding thermal capacity), the lower and the upper plenum. The steam and water were used as the practical working fluids. The water flow rate at the inlet was kept constant at a fixed level through the injection pump. The boundary conditions including the LOCA phenomena, which were estimated by an analytical code, were supplied through the measurement of the system pressure and the entrance temperature of the water. The system pressure, temperature, and flow rate of steam and water were measured simultaneously to investigate the thermal-hydraulic behaviors at the end of the cooling-hole. Further, the behavior of liquid lumps and droplets flow during the simulated reflooding was observed at the outlet of the test section. The closed inspection revealed that the flow condition out of the test section were changing during the simulated reflooding and was classified into three stages. At the initial stage, the liquid lumps and the droplets flowed continuously like a fountain. At the medium stage, misty flow appeared, i. e. dispersed small droplets and/or liquid lumps flowed in steam flow. At the final stage, the liquid lumps flowed periodically with a little amount of steam flow. In this study, the effects of the reflooding velocity, the initial metal temperature, the reflooding water temperature and the upper plenum pressure were clarified. For the lower reflooding velocity, the ratio of steam flow rate increased. For the higher initial metal temperature, the integration of steam and water flow rate increased. The reflooding water temperature and the pressure of the upper plenum at the experimental conditions had little effects on the thermal hydraulic behavior of the coolant at the outlet of the test section.

Experimental Study of the Combustion of Sodium-Application of the Method of Combustion Residue Analysis

Abstract The combustion of sodium pools in air or in mixtures of N2/O2 with low oxygen contents has been studied for initial metal temperatures ranging from 365 to 620°C. The analysis of the combustion products, sodium monoxide (Na2O), sodium peroxide (Na2O2) in the residues and aerosols of Na2O2, and unburned sodium has shown that three successive stages are occurring. During the first stage, the whole surface of sodium pool burns. The only products are thus Na2O in the crust and the aerosols of Na2O2. The combustion rate has been measured for different temperatures, with an initial oxygen ratio of 20, 15 or 10 percent in nitrogen mixture and for three different flow rates of the combustible mixture. During the second stage, burning and extinguished zones coexist. In the latter the formation of aerosols ceases arid the crust monoxide is progressively oxidized into peroxide. This oxidation is the only phenomenon still observed during the last stage. In all cases, some sodium remains unburned, probably due to a progressive blocking of the capillary rising of the metallic sodium towards the surface during the second stage