Mirko Stijepovic

Multi-level Design and Selection of Optimum Working Fluids and ORC Systems for Power and Heat Cogeneration from Low Enthalpy Renewable Sources

This work presents a multi-level method for the design and selection of heat exchange working fluids tailored for Organic Rankine Cycle (ORC) systems used in power and/or heat cogeneration from renewable, low enthalpy sources. A systematic methodology is employed supporting the design of optimum working fluid candidates using Computer Aided Molecular Design (CAMD). The performance of the designed fluids is evaluated using ORC models that enable simulation and economic design optimization. In addition to chemical/physical properties the performed evaluation considers working fluid characteristics such as safety (toxicity and flammability) and environmental properties (ozone depletion potential and global warming potential) that are equally important to economic efficiency. The proposed approach is illustrated through a case study involving varying geothermal field conditions employed as energy sources for greenhouse power and heat co-generation.

Molecular Design of Working Fluid Mixtures for Organic Rankine Cycles

Abstract This work presents a Computer-Aided Molecular Design (CAMD) method for the synthesis and selection of binary working fluid mixtures used in Organic Rankine Cycles (ORC). The method consists of two stages, initially seeking optimum mixture performance targets by designing molecules acting as the first component of the binaries. The identified targets are subsequently approached by designing the required matching molecules and selecting the optimum mixture concentration. A multi-objective formulation of the CAMD-optimization problem enables the identification of numerous mixture candidates. A non-linear sensitivity analysis method is employed to address model-related uncertainties in the mixture selection procedure. The proposed approach remains generic and independent of the considered mixture design application.

Magnetic and Dynamic Mechanical Properties of Nd-Fe-B Composite Materials with Polymer Matrix

At the end of the last century whole variety of technical-technological achievements occurred. Cars overflow the streets, air-conditions coated the facades, everyday life became unimaginable without computers and cell phones; kitchens are filled with assorted appliances, and industry has been improved and enforced by high technology in order to achieve higher manufacturing products, with less energy and manpower consumption. If a deeper look is taken, behind modern design exteriors, inside all of these appliances, it is noticeable that one of the key roles in their performance is engaged by permanent magnets. These materials have very important role as functional components within the wider spectra of contemporary devices in different industrial branches, as well as in the wider consumption. One of the most important applications of the permanent magnets are: spare parts in AC and DC engines production (Slusarek & Dudzikowski, 2002), as well as synchronized motors, transformers, actuators, magnetic buffers, stationary fields, etc. (Gutfleisch et al., 2011). Information storage (hard discs), communications, medical appliances and scanners, automobile and aircrafts industries, could also be emphasized as important applications (Matsuura, 2006; Brown et al., 2002). The nanocrystalline Nd-Fe-B alloys are one of the most superior magnetic materials with high value of maximum energy production (app 50 MGOe) (Herbst, 1991). Besides their high values of the remanence and coercivity, as well as relatively high Curie temperatures (app 312 °C) (Sagawa et al., 1984) this type of magnetic alloys are identified suitable for research and further development of magnetic composite materials with polymer matrix, so called bonded magnets (Brown et al., 2006; Ma et al., 2002). Contemporary research in the field of magnetic composite materials on the basis of Nd-Fe-B alloys are directed into four basic directions: increase of magnetic energy, meaning optimisation of magnetic capacities; improving corrosion resistance; optimisation production process of process parameters; and reduction of the subtle rare earth content (Nd), targeting decreasing the price of the final magnetic material, keeping high values of the maximum magnetic energy. Application of

Synthesis of NiFe2O4 nanofibers by joint sol-gel and electrospinning technique

In this study, electrospinning combined with sol-gel technique is applied in order to produce magnetic nickel ferrite (Ni-ferrite) nanofibers. The prepared Ni-ferrite gel was mixed with poly(vinylpyrrolidone) (PVP) solution which was used as a spinning aid to enable spinnability of the mixture. Structural and morphological characteristics of the as-spun ferrite gel/PVP composite web structure and calcinated Ni-ferrite nanofibers were analyzed using scanning electron microscopy (SEM). Phase composition analysis was carried out by Fourier-transform infrared (FT-IR) spectroscopy, X-Ray diffraction analysis (XRD) and 57 Fe Mossbauer spectroscopy (MS). The obtained results suggest that the pure nanocrystalline NiFe 2 O 4 dense mat to the almost coral-like structure of fibers with diameters ranging from hundreds of nanometers to few micrometers was obtained. The results of MS analysis revealed the existence of a crystallite size distribution within the material as well as the existence of a superparamagnetic fraction with very small crystallite sizes (<13nm). Magnetic behavior of the obtained material at elevated temperatures was also scrutinized using thermomagnetic measurements (TM) up to 800 °C.

Modeling of pure components high pressures densities using CK-SAFT and PC-SAFT equations

SAFT equations of state have been widely used for the determination of different thermo-physical and phase equilibria properties. In order to use these equations as predictive models it is necessary to calculate the model parameters. In this work CK-SAFT and PC-SAFT equations of state were applied for the correlation of pure compounds densities in the wide ranges of temperature and pressure (288.15–413.15 K and 0.1–60 MPa, respectively). The calculations of densities for n-hexane, n-heptane, n-octane, toluene, dichloromethane and ethanol, under high pressure conditions, were performed with the new sets of parameters determined in this paper by CK-SAFT and PC-SAFT. Very good agreement between experimental and calculated density values was achieved, having absolute average percentage deviations lower than 0.5 %.

Targeting and Design of Organic Rankine Cycle Systems for Multiple Heat Sources with Simultaneous Working Fluid Selection

Abstract We propose a systematic model for the optimum design of Organic Rankine Cycles (ORC) used for power generation from multiple heat sources available at different temperatures. The model enables the automated generation of inclusive and flexible ORC cascades and is optimized using a global optimization algorithm. Design parameters include the number of ORC cascades, the shared structure of the heat exchanger network, the operating conditions and the working fluid used in each cascade in order to identify an overall ORC structure that maximizes the power output. Results indicate significant operating improvements from using a double ORC cascade with different working fluids.

Design of Multi-pressure Organic Rankine Cycles for Waste Heat Recovery in Site Utility Systems

This work addresses the design of Organic Rankine Cycle (ORC) processes used for power generation from low-grade heat available in site utility systems. The Exergy Composite Curves approach is used within a systemic optimization framework to explore various complex ORC configurations. The method facilitates interconnectivity at several temperature and pressure levels, considering different types and numbers of turbines as design decision parameters simultaneously with other operating ORC features. It is employed to investigate the performance of two generic ORC configurations, namely one considering independent pressure loops with expansion turbines and the other considering pressure loops contacted through induction turbines. To optimize the number of pressure levels, ORC structural configuration, and operating parameters an inclusive objective function is used considering thermodynamic criteria. The application of the method is demonstrated by a case study on waste heat recovery and reuse in a utility plant.