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Metal foam (MF) and nano-sized particles (NSP) are regarded as patent tools for enhancing the thermal performance of phase change materials (PCM)-based latent thermal energy storage unit (LTES), but data on this issue for large-scale installations is very scarce. This study provides a comprehensive computational analysis of the effects of MF and NSP on the solidification process of RT82 paraffin (PCM matrix) in a large-scale shell-and-tube latent thermal energy storage unit (of heat exchanger form). The developed 2D transient model developed on Ansys Fluent 15.0 software was initially verified using available literature experimental data. The process performance was tested for 5% Al2O3 nanoparticles and various MFs [i.e. aluminum (Al), copper (Cu), nickel (Ni) and titanium (Ti)] with varied porosity (96–100%). The computed mean and spatial temperature and solidified degree of the PCM block showed a drastic acceleration of the solidification process with the b MF technique rather than with the nanoparticles system. The solidification performance increased in the direction of MF-thermal conductivity increase, i.e. Cu > Al > Ni > Ti, and material porosity decrease. These conditions allow rapid HTF heat recovery and then stocking considerable thermal energy. However, the MF porosity could not decrease below 95% to avoid a huge loss of material storage (PCM), thereby diminishing the thermal storage capacity of the LTES unit. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have recently been coupled with metal hydride storage tanks (MHSTs) to store adsorption heat and subsequently deliver it for hydrogen desorption through melting and solidification cycles. This method might reduce process costs by eliminating the use of HTF (i.e. heat transfer fluid). However, thermodynamics and kinetic data are scarce for large-scale MH-PCM applications, particularly when PCM is loaded in metal foams (MFs) to promote heat transfer. The current work aimed to develop a 2D model for simulating H 2 -absorption in a LaNi 5 -metal bed integrating a PCM-MF unit in a large-scale tube-and-shell heat exchanger. The constructed model (via Fluent 15.0 CFD-platform) was first-validated using referenced experimental data. The resulting heat transfer was analyzed for different MFs [aluminum, copper, nickel and titanium] of different porosities (0.1–1.0). Excellent outcomes were retrieved. By trapping the H 2 -absorption heat, the MF-PCM unit improved the LaNi 5 hydriding. The LaNi 5 charging was achieved after ∼500 s, independently of the MF type and porosity. The PCM melting rate depends on tube position, porosity and the MF type. It increased with MFs incorporation (order of enhancement: Cu > Al > Ni > Ti) and MF-porosity decrease (from ε = 100% to 10%). Besides, the PCM tube above the H 2 -feeding pipe melts more quickly than the other tubes, presumably to the gravitational-force effect. Longer times (i.e. 9 000 s to >16 000 s, depending on tube position) were recorded for complete melting of the PCM when ε MF = 100%; however, when ε MF is less than 80%, the required time for total melting was tremendously reduced to less than 500 s. Nevertheless, the MFs porosity could not be decreased considerably to avoid a huge loss of material storage (PCM), thereby diminishing the thermal storage performance of the PCM matrix. • Hydrogen absorption in large-scale MH-MF-PCM reactor is studied. • Mass and heat transfer are deepthly analyzed in the MH-MF-PCM bed. • The MF-PCM system absorb efficiently the reaction heat. • MFs considerably increases the melting rate of the paraffin. • PCM-tube position and the MF type play a crucial role in PCM melting. [ABSTRACT FROM AUTHOR]

The thermal analysis of melting process of phase change material in rectangular latent thermal energy storage unit is presented herein. To resolve the low heat transfer rate due to the low thermal conductivity of pure paraffin (the phase change material of this study), the nano-paraffin approach has been numerically investigated. Four nano-metal oxides (Al2O3, MgO, SiO2 and SnO2) with high thermal conductivity are dispersed into the pure paraffin at different concentrations (1 %, 3 % and 5 %, v/v). The adopted mathematical model that has been used to study the mass, momentum, and energy transport processes inside the nano-paraffin systems has been firstly validated by available literature data. The obtained results showed that both heat transfer and solid melting rate are significantly improved in the presence of nanomaterials, with an independent relation to the particles concentration for a long melting time, i.e. up to 10 000 s. However, above 10 000 s, high particles concentration slightly enhanced the liquid fraction. Besides, it is found that the type of particles did not affect appreciably the heat transfer and the solid melting rate. Nevertheless, the enhancing effect of the nano-paraffin system is strongly melting time dependence. For the four investigated metal oxides, the temperature system attained 351 K at 1000 s of operation, whereas that recorded for the pure paraffin at the same time is 345 K, which yields an improvement of 1.7 %. For the same conditions, the liquid fraction passes form 0.04 for pure paraffin to 0.1 for nano-paraffin system, showing 150 % of enhancement in the melting yield. [ABSTRACT FROM AUTHOR]

• The approach of the sono-PCM reactors was revealed herein for the fist time. • The analysis was made on sonicated water in ultrasonic reactor operating at 300 kHz using three powers. • Promising thermal energy performance of the sono-PCM reactors was obtained. • The PCM absorb the ultrasonic-generated heat and stabilize the sonicated liquid temperature. To keep sonochemical reactors at a constant temperature, cryothermostat systems (equipped with a pump, cooling fluids and tubing) are commonly used. The cryothermostat serves a dual purpose, supplying both heating and cooling as needed to keep the temperature stable. However, this device is an energy consumer, especially when the sonochemical reaction is carried out over an extended period of time (hours to days). As a result, alternative systems are required to reduce the operating cost of sonosystems. The present work introduces a new approach of incorporating phase change materials (PCMs) for the recovery and storage of heat dissipated from ultrasonic reactors (i.e. the sono-PCM reactor approach). The purpose of the project is to go as far as replacing the circulating fluid-based cooling system with a small PCM unit capable of absorbing the generated heat flux and storing it in the form of latent heat (with phase change). The analysis was made on sonicated water (300 mL) in a standing wave ultrasonic reactor operating at 300 kHz, where the dissipated heat flux was measured calorimetrically. After that, using a computational fluid dynamics (CFD) model (implemented in ANSYS Fluent® software), the energetic performance of the PCM unit was assessed by tracking the system (i.e. the sono-PCM reactor) response (i.e. average and spatial evolutions of temperature, enthalpy, total energy, velocity and PCM-melting kinetics) to the imposed acoustic energy. Paraffin RT31 was selected as PCM because of its suitable characteristics such as low melting point (27–31 °C) and high thermal energy storage capacity (165 kJ kg−1). Despite the relatively low thermal conductivity of the used PCM (0.2 W m − 1 °C − 1), promising results have been obtained in terms of thermal energy management and storage using a phase change material (PCM) instead of a water-cooling system. [ABSTRACT FROM AUTHOR]

• The approach of the sono-PCM reactors was revealed herein for the fist time. • The analysis was made on varying water volume sonicated in 300 kHz ultrasonic reactor. • Promising thermal energy performance of the sono-PCM reactors was obtained. • The PCM absorb the ultrasonic-generated heat and stabilize the sonicated liquid temperature. As an alternative to a water-based cooling system for a sonoreactor, the present work presents for the first time the use of a phase change material for the management and storage of the dissipated heat within the sonicated water. The performance of the PCM is analyzed as a function of liquid height (LH = 5.1, 10.2, 15.3, and 20.4 cm) at a frequency of 300 kHz and two electric powers (P E = 20 and 60 W). The effective powers dissipated in the irradiated water were determined by the calorimetric technique. A computational fluid dynamics (CFD) model (implemented in ANSYS Fluent® software), was used for the analysis of the combined system (sonoreactor + PCM-thermal unit) at different operating conditions (liquid height and electric power). By analyzing the different outputs (variation of temperature, velocity, enthalpy, liquid fraction of PCM) of the used CFD model, more clarifications are provided about the behaviour of the combined system (sonoreactor + PCM-thermal unit) as function of the liquid height (5.1 – 20.4 cm) and electric power (20 and 60 W). In terms of temperature, velocity, enthalpy and liquid fraction of the PCM, promising results were obtained in spite of the low thermal conductivity of the employed PCM. The best performance of the combined system (sonoreactor and thermal unit) was obtained at the liquid height of 15.3 cm (corresponding to a water volume of 300 mL) with a similar behaviour (evolution of temperature, velocity, enthalpy, and liquid fraction of the PCM) at both electric powers (i.e., 20 and 60 W) with an intensified response at the P E = 60 W. [ABSTRACT FROM AUTHOR]

Due to the scarcity of data on the industrial use of energy storage technology based on material phase change (PCM), a complete computational assessment is done in this work, where a nano-PCM technique is used to enhance the thermal energy storage in a big-scale shell-and-tube heat exchanger. Four high thermal conductive nano-oxides (i.e., Al 2 O 3 , MgO, SiO 2 , and SnO 2) are added at various concentrations (1–5% v/v) into the PCM (i.e., paraffin RT82). A two-dimensional mathematical model is used to study the produced nano-PCM systems' heat transfer and melting rate. The model accurately predicted the PCM-melting data's observed behavior, showing that it is adequate for simulating PCM problems. The addition of nano-oxides, for up to 5%, in the PCM solid matrix dramatically enhances heat transmission and melting rate during the first melting stage. However, after a long melting period, the melting performance of the nano-PCMs decreased and became equivalent to that of the pure PCM. Furthermore, increasing the concentration of nanoparticles from 1 to 5% did not significantly improve the temperature and liquid fraction evolutions for the four studied nano-PCMs. Therefore, the use of nano-PCMs in the adopted LTES unit can effectively improve heat recuperation and melting rate, but only for a short charging time during which a part (up to 60%) of the PCM's latent heat is recovered. Consequently, the present paper's data is considered a guideline for increasing the efficacy of thermal energy storage in big-scale shell-and-tube heat exchangers using nano-PCM technology. [Display omitted] • The melting process of pure-PCM (paraffin) and various nano-PCMs was compared. • Heat transfer and solid melting rate were analyzed for diverse cases of nano-PCMs dosage. • Nano-PCMs accelerated the melting rate over the pure-PCM at the initial melting period. • After a period of melting, the performance of the pure-PCM overlaps those of non-PCMs. • Nanoparticles allow rapid recovering of up to 60% of the latent heat of the PCM at short time. [ABSTRACT FROM AUTHOR]