| National economic development and national defense are both heavily dependent on energy.With the short supply of petroleum resources, how to utilize fossil resources in an efficient andenergy-saving way becomes an imperative task. Modern gas turbine is regarded as an efficient andclean technology to make use of fossil resources. Specifically, Humid Air Turbine (HAT) cycle isregarded as a new type of dynamic cycle in the21stcentury. The working medium of HAT cycle isformed by injecting water or steam into traditional working medium. After humidification, thepower rate and efficacy of the dynamic cycle can be improved, and the formation of pollutantsmay be reduced as well.The working condition for HAT is at high temperature and high pressure, which alreadyreaches1773K and40atm respectively for current HAT in operation. To date, there is still nosatisfactory calculation model for humid working medium (i.e. humid air and humid combustiongas mixture) in such wide temperature and pressure ranges. The researches on humid workingmedium are not adequate. Specifically, scientists don’t comprehend the behaviors of traditionalworking medium and water vapor in the humid mixture very well. Both study and simulation ofHAT cycle are tightly reliant on accurate thermodynamic properties of humid working medium.However, the current researches on humid working medium do not meet the requirement of suchwide temperature and pressure ranges.Two types of models are usually applied by past researchers. The first type is the ideal gasmixture model. It fully utilizes the properties of each gas component (e.g. dry air, water vapor andCO2). However, it omits the interactions between different gas components. The thermodynamicproperties obtained by this type of model may not be accurate due to such omissions. The secondtype includes empirical and semi-empirical models. They regard the gas mixture as a pseudo-puregas, which has its own state equation. The results are more accurate because the interactionsbetween different gas components are taken into account. However, the establishment of suchmodel requires a large number of experimental data. This type of model can only be applied inthose experiment-proved temperature and pressure ranges. It cannot be extended to other widerranges.This thesis studies the thermodynamic properties of humid working medium in HAT cycle,demonstrates the behaviors of dry working medium (i.e. dry air and dry combustion gas mixture)and water vapor in the humid gas mixture, and proposes a new calculation model for humidworking medium in the above-mentioned wide temperature and pressure ranges in HAT cycle. Theerror of my proposed model is less than0.1%compared to existing experimental data, so it fullymeets the engineering standard. The main contributions of this thesis are in the following fouraspects.First, this thesis focuses on saturated humid air. It establishes the semi-permeable membranemodel and the concept of “actual effective pressure”. It is for the first time to prove the “actualeffective pressure” of water vapor in the saturated humid air exactly equal to the saturationpressure of existing alone saturated water vapor at the same temperature. Furthermore, it isdiscovered that although the saturated water vapor in the saturated humid air is at “CorrespondingState” to the saturated water vapor existing alone in the same volume at the same temperature, themol numbers of two types of saturated water vapor are different. The mol number of saturatedwater vapor in the saturated humid air is always larger than the mol number of the saturated watervapor existing alone. The difference of mol numbers are attributed to the interaction between dryair and water vapor.“Improvement Factor” is proposed to describe the “Improvement Effect” ofmol number increase of the existing alone water vapor caused by dry air quantitatively. Then theRevised Dalton’s Partial Pressure Law proposes that the summation of “actual effective pressures”of each gas component equals the total pressure. This law is proved on two hands. On the onehand, it is proved by the macro physical meaning of pressure. On the other hand, it is proved bythe numerical calculation results of my model compared to existing experimental data.Second, this thesis extends the Revised Dalton’s Partial Pressure Law to unsaturated humidair. In accordance to the physical meaning of “Improvement Effect”, the “Improvement Factors”for unsaturated humid air can be obtained in reasonable ways. Through the study of “Improvement Factors” in unsaturated humid air with the increase of temperature, it is discovered that “CuttingOff Temperature” is a crucial benchmark.“Cutting Off Temperature” is proposed for the first time,the value of which is exactly equal to the saturation temperature of the existing alone saturatedwater vapor corresponding to the total pressure of humid air. When the temperature of humid airincreases and approaches the “Cutting Off Temperature”, the “Improvement Factors” will movetowards1.0000. When the temperature is equal to or higher than the “Cutting Off Temperature”,the “Improvement Factor” will always be1.0000. It is for the first time to discover that theinteraction between dry air and water vapor may be omitted when the temperature of humid air ishigher than “Cutting Off Temperature”. Under such circumstances, it is only required to considerthe existing alone status of each gas component. Thus, thermodynamic properties of all kinds ofhumid air are able to be calculated smoothly.Third, this thesis studies humid combustion gas mixture and obtains its “Cutting OffTemperature”. Humid combustion gas mixture contains not only dry air but also large amount ofwater vapor and CO2, both of which are real gas components and deviate from ideal gas behaviorsnotably. Through in-depth research, it is found out that when the total pressure of humidcombustion gas mixture is fixed, the saturation temperature of existing alone saturated water vaporcorresponding to the fixed total pressure is always much higher than the saturation temperature ofexisting alone saturated CO2corresponding to the same total pressure. In other words, in thehumid combustion gas mixture, the “Improvement Factor” of CO2always approaches1.0000much earlier than that of water vapor. Therefore, the “Cutting Off Temperature” of humidcombustion gas mixture can be determined by the saturation temperature of existing alonesaturated water vapor corresponding to the total pressure. When the temperature of humidcombustion gas mixture is higher than the “Cutting Off Temperature”, Revised Dalton’s PartialPressure Law can be applied. Under such circumstances, the interaction between different gascomponents may be omitted. As long as the existing alone status of each gas component isobtained, the thermodynamic properties of humid combustion gas mixture can be thoroughlysolved.Fourth, this thesis applies the thermodynamic properties of humid air developed by my modelto the saturator calculation and applies the thermodynamic properties of humid combustion gasmixture to the turbine calculation. The calculation results obtained by my model are compared tothe results by ideal gas mixture model in detail. It is found that the selection of an accurate modelfor thermodynamic properties of working medium is of vital importance. By means of differentmodels, the simulation results of many output parameters in HAT cycle will be different to variousextents.In conclusion, this thesis studies saturated humid air, unsaturated humid air and humidcombustion gas mixture step by step. The semi-permeable membrane model is fully utilized toexplain the thermodynamic behaviors of humid air and humid combustion gas mixture. Suchconcepts as “actual effective pressure”,“Improvement Factor” and “Cutting Off Temperature” areproposed for the first time. This thesis describes the interaction between different gas componentsin detail. The proposition and proof of Revised Dalton’s Partial Pressure Law and the importantdeductive relationship of this law are both crucial. They provide the theoretical foundation to linkthe thermodynamic behavior of the humid gas mixture and the thermodynamic behaviors of its gascomponents. Thus, we can may full use of the well-equipped thermodynamic properties of eachexisting alone gas component to get the thermodynamic properties of humid gas mixture. Thisthesis provides a complete model for calculation of thermodynamic properties of humid air andhumid combustion gas mixture. The results of this thesis may also be fit for other types ofthermodynamic process simulation whose working mediums are humid air or humid combustiongas mixture. |
PDF Full Text Request