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In this study, tubes filled with PCM as a thermal energy storage unit with an indirect air heater are used to store and recover solar thermal energy. Two different configurations of PCM-filled tubes (inline and staggered) in the unit are considered and compared with the PCM-filled plate unit. In all cases, the amount of the PCM is the same. The effects of airflow rate, diameter of tubes and inlet temperature on the charging and discharging rates are studied. Results showed that the PCM tube unit is more efficient than the PCM plate unit. The thermal performance is enhanced with the increase of the air mass flow rate. Results also revealed that the phase change rate in staggered configurations is between 7% and 36% (depending on the airflow rate) greater than that in the inline ones. By reducing the tube diameter, the melting and solidification processes are performed more quickly due to the rise of the overall heat transfer surface area. The influence of the temperature difference between the inlet air and PCM is more effective than the other considered effects where the 10 °C increase of the temperature difference enhances the charging rate by a factor of 2. [ABSTRACT FROM AUTHOR]

The aim of this work is to study laminar mixed convection heat transfer characteristics within an obstructed enclosure by using the Lattice Boltzmann method. Flow is driven by a top cold lid while other walls are stationary and adiabatic. Hot cylinders are located at different places inside the cavity to explore the best arrangement. Comparison of streamlines, isotherms, average Nusselt number are presented to evaluate the influence of Richardson number and location of cylinders on flow field and heat transfer. Results indicate that heat transfer decreases with a rise of Richardson number for all considered arrays of cylinders. Among them, horizontally-located cylinders at the top of the cavity have the greatest heat transfer at all Richardson numbers. Horizontally located cylinders at the bottom of the cavity have the lowest heat transfer at Richardson numbers of 0.1 and 1 while the lowest heat transfer rate belongs to cross diagonal located cylinders at a Richardson number of 10. [ABSTRACT FROM AUTHOR]

Constrained melting around one hot cylinder inside a horizontal square cavity is inefficient from an energy-saving viewpoint because of the elevated thermal stratification and sluggish advancement of the melting front at the bottom. The situation is exacerbated by the low thermal conductivity of the phase change materials (PCM). To overcome it, four hot cylinders instead of one cylinder are selected in the same cross-section area. Besides, the base PCM is mixed with the small volumetric concentration of the nanometer-sized Cu particles to enhance the melting rate. It has to be clarified in which array the NEPCM is the most effective way. However, increasing the dynamic viscosity of the base PCM using nanoparticles may have a negative effect on the speed of the natural convection flow. Finally, the metallic porous matrix with the thermal characteristics of the Nickel-Steel alloys is inserted in the base PCM to enhance the thermal conductivity and melting rate and to abate the full melting time. The weakening of the natural convection effect within the porous structure could be worthy of attention. The enthalpy-based lattice Boltzmann method (LBM) with a D2Q9-double distribution function (DDF) model at the REV scale is used to model the ice melting in the absence of the subcooling. [ABSTRACT FROM AUTHOR]