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An alternative calculation procedure for real mixture fluid properties demonstrated with a Kalina cycle.

Number: pap. n. 217

Author(s) : SOMDALEN R., SCHULZE C., KOEHLER J.

Summary

In order to continuously increase efficiency, simulation tools are utilized to design and optimize all kinds of thermodynamic cycles. For a realistic simulation of such a cycle it is essential to have reliable fluid property data in order to produce useful results. For this purpose, multiparameter equations of state (EOS) are often employed in process calculations due to their high accuracy over a wide working area. Such multiparameter EOS are evaluated using programs like REFPROP. Nevertheless, the available fluid property libraries sometimes fail to calculate vapour-liquid equilibrium properties, e.g. near the critical region. For a reliable design and optimization of thermodynamic cycles a new calculation procedure for fluid properties for the mixture of ammonia and water has been developed and embedded in a dynamic simulation software. It allows to access the numerical solvers directly and better customize the library to meet different requirements. As the calculation procedure is capable of utilizing predecessor values, the speed and robustness of the calculation is increased. Moreover, accuracy and speed of each solver can then be adjusted as needed, which further enhances the stability of simulations in the vapour-liquid region. The functionality of the calculation procedure for mixture fluid properties is demonstrated by simulations of a transient Kalina cycle. In the past ten years, this new technology based on the Rankine cycle has been commissioned as an alternative in geothermal power plants. It uses a mixture of ammonia and water as a working fluid and takes advantage of a temperature glide in the vapour-liquid region to better adapt the cycle to a heat source and sink. For an existing Kalina plant in Husavik, Iceland, steady-state simulations exist in literature. Based on the design of the Kalina plant in Husavik a dynamic model of the fluid side of a Kalina cycle has been implemented and transient simulations were performed successfully. Thus, the calculation procedure is able to handle a mixture of ammonia and water with variable composition. Furthermore, the new procedure is also capable of simulating e.g. transient absorption refrigeration cycles. Existing uncertainties in design and handling of refrigerant mixture cycles due to a free variation of the mixture composition can be analysed using dynamic simulation and maybe support its technical development and degree of implementation.

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Details

  • Original title: An alternative calculation procedure for real mixture fluid properties demonstrated with a Kalina cycle.
  • Record ID : 30004530
  • Languages: English
  • Source: 10th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2012). Proceedings. Delft, The Netherlands, June 25-27, 2012.
  • Publication date: 2012/06/25

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