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Abstract:Exergy analysis is used as a tool for the evaluation of exergy losses in a two-phase steam-water injector in an effort to improve its overall performance in respect to exit pressure. The aim of this paper is to study irreversible losses in the component parts of the injector, including the steam nozzle, water nozzle and diffuser as well as the two-phase region comprising the mixing chamber and the condensation shock wave. Calculations based on experimental data revealed the regions with the greatest irreversibilities, namely in the two-phase region and in the steam nozzle. Particular attention was paid to the steam nozzle, for which a procedure was developed to determine the overall velocity coefficient, including all irreversibilities in the steam nozzle during steam expansion. The study indicated the most important factors influencing the injector's performance. Finally, the exergy efficiency was calculated for the two investigated steam injectors. Keywords

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Paper deals with theoretical analysis of possible efficiency increase of compression refrigeration cycles by means of application of a twophase ejector. Application of the two phase ejector in subcritical refrigeration system as a booster compressor is discussed in the paper. Results of exergy analysis of the system operating with various working fluids for various operating conditions have been shown. Analysis showed possible exergy efficiency increase of refrigeration compression cycle.Keywords: Two-phase ejector; Compression refrigeration system; COP; Exergy Nomenclature b -specific exergy, J/kġ B -exergy rate, W h -specific enthalpy, J/kg h f g -specific enthalpy of vaporisation, J/kġ m -mass flow rate, kg/s p -pressure, Pa P -driving power, W

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The implementation of low-energy construction includes aspects related to technological and material research regarding thermal insulation. New solutions are sought, firstly, to reduce heat losses and, secondly, to improve the environment conditions in isolated rooms. The effective heat resistance of insulating materials is inversely proportional to temperature and humidity. Cement composites filled with lightweight artificial aggregates may be a suitable material. Selecting a proper method for measuring the thermal conductivity of concrete is important to achieve accurate values for calculating the energy consumption of buildings. The steady state and transient methods are considered the two main thermal conductivity measurement approaches. Steady state is a constant heat transfer, whereby the temperature or heat flow is time independent. In the transient method, temperature changes over time. Most researchers have measured the conductivity of cement-based materials based on transient methods. The availability and cost of equipment, time for experimental measurements and measurement ability for moist specimens may be some of the reasons for using this method. However, considering the accuracy of the measurements, the steady state methods are more reliable, especially for testing dry materials. Four types of composites were investigated that differed in filler: natural aggregate, sintered fly ash filler, sintered clay and granular foam glass aggregate. The method of preparing the samples for testing is especially important for the obtained results. The samples, with a specific surface roughness, will show a lower coefficient of thermal conductivity by 20–30%; therefore, the selection of the type of contact layer between the plate of the measuring device and the sample is of particular importance.