Investigation On Some Key Problems Of Saturator Of HAT Cycle

HAT (Humid Air Turbine) cycle is known for high efficiency, high specific power, low NOx emissions, excellent off-design performance etc. The saturator is the key unit in HAT cycle and its performances of heating and humidifying have a great effect on the efficiency of the HAT cycle. A lot of previous research on the saturator including the theory and the experiment has been done and some valuable data has been obtained. However, there are many key and difficult problems of saturator left. This paper aims to solve these problems with theory analysis, experiment and mathematical simulation methods. The main objects of this work are to understand the complicated gas-liquid two-phase flow by investigating the flow performance and exploring the mechanism of heat and mass transfer between water droplets and air. The obtained information will benefit to improve the quality of humidifying process and design high performance saturator.Main content and conclusions are followed:The experimental system for investigating the thermodynamic performance of saturator is set up. The obtained data from the experiment is analyzed with exergetic method. The exergetic equilibrium model is established and the criterion of performance, i.e. exergetic efficiency, is put forth. The exergetic performance of saturator is also discussed. The results show the exergetic efficiency increases with the increasing inlet relative humidity and the increasing water/air ratio, but decreases with the increasing inlet water temperature (or the temperature difference of water and air). Furthermore, the exergetic efficiency and specific power between STIG and HAT cycle is compared and the advantage of the latter is revealed. The both cycles have the optimized pressure ratio that is corresponded to the highest exergetic efficiency. The optimized pressure ratio of HAT cycle is lower than that of STIG so it is easier to be carried out in practice. The specific power of HAT is lower than that of STIG when the pressure ratio of the cycle is low and the tendencies of them are also obvious different.An effective device of temperature on-line measuring system for gas-liquid two-phase flow is invented. It contains three components: the particle detecting system based on light-fluctuation theory, the device for temperature measuring and the wavelet analysis method. It can separate the gas and liquid phase and get the individual temperature effectively. The experimental results show that the mesh can prevent the water droplets entering the shield. The gas and liquid temperature can be measured accurately if the vacuum pump is adopted. The initial laser light intensity will attenuate quickly so the vacuum pump is necessary to put the infiltrated water out of the shield. The fluctuation numbers of the light intensity and wavelet analysis decrease with the increasing the mesh number, but increase when the inlet air velocity increases.The transient process of spraying in saturator is simulated with FLUENT software. The distribution of parameters of the gas-liquid two-phase flow is calculated with Realizable k ?εturbulent model. This research makes up for the shortcoming of previous results that only show the steady results. The results show the air temperature doesn't always increase within the saturator in the condition of lower water/air ratio. Actually the air temperature decreases at first stage, then increases at higher stage of the saturator. The relative humidity, the content of humidity and the enthalpy of air at the higher stage are much higher than that of lower stage of the saturator. With UDF function, the problem of humidity exceeding 100% is solved. The situation is resulted from the limitation of FLUENT who can't analyze the coagulation phenomenon when the humidity exceeding 100%.On the basis of theory analysis, the one-dimension model of saturator is established with the difference of humidity which is considered as the potential force of mass transfer. By introducing three dimensionless parameters: dimensionless height z|- , dimensionless temperature t|- and dimensionless humidity x|- , the dimensional equations can be transformed to dimensionless equations. With similitude theory and the dimensionless analysis method, three crucial dimensionless parameters have been obtained( Re, Eu ,D|- ). The parameter Re describes the flow field similitude condition; the parameter Eu describes the spraying field similitude condition and the parameter D|- stands for the geometry similitude condition. With the above three dimensionless parameters, the similitude between the real operation condition and experimental condition is assured. It is very helpful to deal with the raw data from the experiment.The complex two-phase flow and the heating and mass transferring process in the saturator are studied in detail in this paper. The data and the conclusions are very important to develop the high performance saturator.