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Saturated thermodynamic properties for the air-water system at elevated temperature and pressure
KTH, Superseded Departments, Chemical Engineering and Technology.
KTH, Superseded Departments, Chemical Engineering and Technology.
2003 (English)In: Chemical Engineering Science, ISSN 0009-2509, Vol. 58, 5069-5077 p.Article in journal (Refereed) Published
Abstract [en]

A new thermodynamic model is proposed to calculate the thermodynamic properties for the air-water system in which the dry air was assumed to be a mixture of nitrogen and oxygen with the mole fractions of 0.7812 and 0.2188, respectively. For the vapor phase, fugacity coefficients were calculated with the modified Redlich-Kwong equation of state in which a new interaction parameter of oxygen and water was correlated from the experimental data of oxygen-water system. The dissolved gas followed Henry's law. Henry's constant of nitrogen was calculated with the Helgeson equation of state and that for oxygen was correlated from the experimental data of oxygen-water system. The proposed model was verified by comparing the calculated results with the available experimental data. It is shown that the proposed model is suitable for predicting saturated thermodynamic properties for the air-water system up to 300°C and 200 atm. Furthermore, the prediction results of the proposed model are better than those calculated with the model of Rabinovich and Beketov (Moist Gases, Thermodynamic Properties. Begell: House, 1995), and the application range is wider than that of the model of Hyland and Wexler (ASHRAE Trans. 89(2A) (1983a, b) 500-519, 520-535) which are among the best of today's models

Place, publisher, year, edition, pages
2003. Vol. 58, 5069-5077 p.
Keyword [en]
Air-water system, Gases, Humid air, Modelling, Phase equilibria, State equation
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6205DOI: 10.1016/j.ces.2003.08.006ISI: 000186677800011OAI: oai:DiVA.org:kth-6205DiVA: diva2:10850
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-12-06Bibliographically approved
In thesis
1. Thermodynamic properties of humid air and their application in advanced power generation cycles
Open this publication in new window or tab >>Thermodynamic properties of humid air and their application in advanced power generation cycles
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Water or steam is added into the working fluid (often air) in gas turbines to improve the performance of gas turbine cycles. A typical application is the humidified gas turbine that has the potential to give high efficiencies, high specific power output, low emissions and low specific investment. A heat recovery system is integrated in the cycle with a humidifier for moisturizing the high-pressure air from the compressor as a kernel. Based on today’s gas turbines, the operating temperature and pressure in the humidifier are up to about 523 K and 40 bar, respectively. The operating temperature of the heat exchanger after the humidifier is up to 1773 K. The technology of water or steam addition is also used in the process of compressed air energy storage (CAES), and the operating pressure is up to 150 bar.

Reliable thermodynamic properties of humid air are crucial for the process simulation and the traceable performance tests of turbomachinery and heat exchanger in the cycles. Several models have been proposed. However, the application range is limited to 400 K and 100 bar because of the limited experimental data for humid air. It is necessary to investigate the thermodynamic properties of humid air at elevated temperatures and pressures to fill in the knowledge gap.

In this thesis, a new model is proposed based on the modified Redlich-Kwong equation of state in which a new cross interaction parameter between molecular oxygen and water is obtained from the fitting of the experimental data of oxygen-water system. The liquid phase is assumed to follow Henry’s law to calculate the saturated composition.

The results of the new model are verified by the experimental data of nitrogen-water and oxygen-water systems from ambient temperature and pressure to 523 K and 200 bar, respectively. Properties of air-water system are predicted without any additional parameter and compared with the available experimental data to demonstrate the reliability of the new model for air-water system. The results of air-water system predicted using the new model are compared with those calculated using other real models. The comparison reveals that the new model has the same calculation accuracy as the best available model but can be used to a wider temperature and pressure range. The results of the new model are also compared with those of the ideal model and the ideal mixing model from ambient temperature and pressure to 1773 K and 200 bar to investigate the effect of the models on the thermodynamic properties of humid air.

To investigate the impact of thermodynamic properties on the simulation of systems and their components, different models (ideal model, ideal mixing model and two real models) are used to calculate the thermodynamic properties of humid air in the simulation of the compressor, humidification tower, and heat exchanger in a humidified gas turbine cycle. The simulation reveals that a careful selection of a thermodynamic property model is crucial for the cycle design. The simulation results provide a useful tool for predicting the performance of the system and designing the humidified cycle components and systems.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 75 p.
Series
Trita-KET, ISSN 1104-3466 ; 229
Keyword
air-water mixture, humid air, properties, wet cycles, dry air, water, enthalpy, entropy, heat capacity, density, evaporative gas turbine, compressed air energy storage
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4129 (URN)91-7178-437-3 (ISBN)
Public defence
2006-10-23, F3, KTH, Lindstedtsvägen 26, Stockholm, 13:30
Opponent
Supervisors
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-09-02Bibliographically approved

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