A desirable feature of concentrated solar power (CSP) with integrated thermal energy storage (TES) unit is to provide electricity in a dispatchable manner during cloud transient and non-daylight hours. Latent heat thermal energy storage (LHTES) offers many advantages such as higher energy storage density, wider range of operating temperature and nearly isothermal heat transfer relative to sensible heat thermal energy storage (SHTES), which is the current standard for trough and tower CSP systems. Despite the advantages mentioned above, LHTES systems performance is often limited by low thermal conductivity of commonly used, low cost phase change materials (PCMs). Research and development of passive heat transfer devices, such as heat pipes (HPs) to enhance the heat transfer in the PCM has received considerable attention. Due to its high effective thermal conductivity, heat pipe can transport large amounts of heat with relatively small temperature difference. The objective of this research is to study the charging and discharging processes of heat pipe-assisted LHTES systems using computational fluid dynamics (CFD) and experimental testing to develop a method for more efficient energy storage system design. The results revealed that the heat pipe network configurations and the quantities of heat pipes integrated in a thermal energy storage system have a profound effect on the thermal response of the system. The optimal placement of heat pipes in the system can significantly enhance the thermal performance. It was also found that the inclusion of natural convection heat transfer in the CFD simulation of the system is necessary to have a realistic prediction of a latent heat thermal storage system performance. In addition, the effects of geometrical features and quantity of fins attached to the HPs have been studied. / Mechanical Engineering

This thesis deals with computer modeling of temperature hysteresis during phase change, namely complete and partial phase change. There is performed a review of methods for modeling temperature hysteresis based on the enthalpy method and the effective heat capacity method. In the case of complete phase change, there are several methods that use the effective heat capacity method, as well as the heat source method, which, on the contrary, is a certain analogy of the enthalpy method. The following are works dealing with modelling of partial phase change, the most interesting of which is due to the validation method of static hysteresis and the method designed by Bony and Citherlet. The second part of this thesis deals with the hysteresis behavior of the material with phase change, which is organic paraffin RT 27. The input data obtained by differential scanning calorimetry was converted to the dependence of the enthalpy on temperature. These curves was represented by piecewise linear function. In the case of partial phase transformations, a modeling method based on the methods proposed by Bonym and Citherlet was designed. An one-dimensional model enabling thermal simulation of the material was implemented in the MATLAB software environment. The results obtained with this simulation are finally compared with a model that does not consider thermal hysteresis.