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An important element of a solar installation is the storage tank. When properly selected and operated, it can bring numerous benefits. The presented research relates to a project that is implemented at the Solar Energy Research Center of the University of Almeria in Spain. In order to improve the operation of the solar cooling and heating system of the Center, it was upgraded with two newly designed storage tanks filled with phase change materials (PCM). As a result of design works, commercial material S10 was selected for the accumulation of cold, and S46 for the accumulation of heat, in an amount of 85% and 15%, respectively. The article presents in detail the process of selecting the PCM material, designing the installation, experimental research, and exergy analysis. Individual tasks were carried out by research groups cooperating under the PCMSOL EUROPEAN PROJECT. Results of tests conducted on the constructed installation indicate that daily energy saving when using a solar chiller with PCM tanks amounts to 40% during the cooling season.

The phase behavior of equimolar mixtures of oppositely charged colloidal systems with similar absolute charges is studied experimentally as a function of the salt concentration in the system and the colloid volume fraction. As the salt concentration increases, fluids of irreversible clusters, gels, liquid−gas coexistence, and finally, homogeneous fluids, are observed. Previous simulations of similar mixtures of Derjaguin−Landau−Verwey−Overbeek (DLVO) particles indeed showed the transition from homogeneous fluids to liquid−gas separation, but also predicted a reentrant fluid phase at low salt concentrations, which is not found in the experiments. Possibly, the fluid of clusters could be caused by a nonergodicity transition responsible for the gel phase in the reentrant fluid phase. Liquid−gas separation takes a delay time after the sample is prepared, whereas gels collapse from the beginning. The density of the liquid in coexistence with a vapor phase depends linearly on the overall colloid density of the system. The vapor, on the other hand, is comprised of equilibrium clusters, as expected from the simulations. [ABSTRACT FROM AUTHOR]