Design Optimization of Plate-Fin Heat Exchanger in a Gas Turbine and Supercritical Carbon Dioxide Combined Cycle with Thermal Oil Loop

This paper presents an investigation on the optimum design for a plate-fin heat exchanger (PFHE) of a gas and supercritical carbon dioxide combined cycle which uses thermal oil as intermediate heat-transfer fluid. This may promote the heat transfer from low heat-flux exhaust to a high heat-flux supercritical carbon dioxide stream. The number of fin layers, plate width and geometrical parameters of fins on both sides of PFHE are selected as variables to be optimized by a non-dominated sorting genetic algorithm-II (NSGA-II), which is a multi-objective genetic algorithm. For the confliction of heat transfer area and pressure drop on the exhaust side, which are the objective indexes, the result of NSGA-II is a Pareto frontier. The technique for order of preference by similarity to ideal solution (TOPSIS) approach is applied to choose the optimum solution from the Pareto frontier. Finally, further simulation is performed to analyze the effect of each parameter to objective indexes and confirm the rationality of optimization results.

The Physics of Interdigitated Dielectrometry Sensors and Application as In-Situ Oil Oxidation Monitoring

<p>Monitoring of hydrocarbon oxidation is of great importance in many industry applications and reliable in-situ measurements are a challenge. In literature, it was shown that new versus degraded hydrocarbons show a change in their dielectric properties. In this thesis, the degradation of the oil was investigated by means of two thermal oil degradation experiments and the Fourier transform infrared spectroscopy. In addition, the impact. on the dielectric properties were determined using a novel type of a dielectric test cell that is temperature compensated. It was found that ketones, acids and moisture were generated through a thermal oil aging process. These products have been found to change in the dielectric properties of the liquid which are reflected through the complex permittivity. Ketones increased largely the real part of the permittivity and organic acids affected predominantly the imaginary part of the complex permittivity in a nonlinear fashion, which could be described using a modified polaron theory model. These measurements served as the base for the development of a novel kind of interdigitated sensor that can measure the dielectric properties such as the relative permittivity and the intrinsic conductivity with high accuracy and precision, without being affected by temperature. This is a crucial step in the development of a suitable in-situ sensor, as it does not need to undergo a complicated temperature curve compensation or calibration using calibration-liquids. The interdigitated sensor, made using cost efficient printed circuit board technology, exhibited an accuracy in measuring the complex permittivity of about 99%. The sensing precision was practically limited by the measurement instrumentation using a developed Faraday shield for the sensor. The sensor was used in an oil degradation experiment. to verify the in-situ capability. These measurements of the relative permittivity and conductivity yielded values such as a degree of oxidation and acidity number. For the first time: it was possible to measure in-situ the complex dielectric properties of liquids at temperatures between 20 °C to 140 °C using interdigitated sensors.</p>

The Physics of Interdigitated Dielectrometry Sensors and Application as In-Situ Oil Oxidation Monitoring

<p>Monitoring of hydrocarbon oxidation is of great importance in many industry applications and reliable in-situ measurements are a challenge. In literature, it was shown that new versus degraded hydrocarbons show a change in their dielectric properties. In this thesis, the degradation of the oil was investigated by means of two thermal oil degradation experiments and the Fourier transform infrared spectroscopy. In addition, the impact. on the dielectric properties were determined using a novel type of a dielectric test cell that is temperature compensated. It was found that ketones, acids and moisture were generated through a thermal oil aging process. These products have been found to change in the dielectric properties of the liquid which are reflected through the complex permittivity. Ketones increased largely the real part of the permittivity and organic acids affected predominantly the imaginary part of the complex permittivity in a nonlinear fashion, which could be described using a modified polaron theory model. These measurements served as the base for the development of a novel kind of interdigitated sensor that can measure the dielectric properties such as the relative permittivity and the intrinsic conductivity with high accuracy and precision, without being affected by temperature. This is a crucial step in the development of a suitable in-situ sensor, as it does not need to undergo a complicated temperature curve compensation or calibration using calibration-liquids. The interdigitated sensor, made using cost efficient printed circuit board technology, exhibited an accuracy in measuring the complex permittivity of about 99%. The sensing precision was practically limited by the measurement instrumentation using a developed Faraday shield for the sensor. The sensor was used in an oil degradation experiment. to verify the in-situ capability. These measurements of the relative permittivity and conductivity yielded values such as a degree of oxidation and acidity number. For the first time: it was possible to measure in-situ the complex dielectric properties of liquids at temperatures between 20 °C to 140 °C using interdigitated sensors.</p>

Kinematics of steam film wetting while quenching cylindrical samples in thermal oils

The paper presents the determination of the velocity of the vapor front along the outer wall of a cylindrical specimen in the process of two-dimensional axisymmetric quenching of the samples in thermal oils. One thermal oil is Isorapid 277 HM heated to 40°C and the other thermal oil is Marquench 722 heated to 90°C. The experimental setup of the work consists of heating to a temperature of 850°C, then quenching three dimensionally different cylindrical probes. The dimensions of the probe were: ϕ25x100 ϕ50x150 and ϕ75x225 mm. All quenchings were done in strictly controlled conditions of the flow rate of the quenchant around the cylinder as well as maintaining the temperature of the quenchant within the maximum 40±2.5°C or 90d3°C, during the quenching of the samples. The velocity of movement of the steam front on the outer surface of the cylinder was determined from the time-measured values of temperatures at the marked points of each sample. The analysis of the steam front movement velocity along the cylinder wall starts from the moment the lower base of the probe touches the quenchant. During the process of immersing the test probe in the quenchant, in addition to measuring the temperatures in time, the time of lowering the probe to contact with the quenchant sample was also measured. The approximate average velocity of the vapor front was determined based on the indications of the lower and middle thermocouples located 1.5 mm below the outer surface of the cylinder wall. Based on the distance of one half the height of each probe and time, the velocity of the steam film movement or the kinematics of the steam film wetting was obtained. The obtained results were compared with the results of quenching in water and aqueous solutions of the same probes under the same strictly controlled conditions.