Thermal Energy Storage Using Horizontal Shell-Tube Heat Exchanger: Numerical Investigation on Temperature Variation of HTF (original) (raw)
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Thermal energy storage improves the efficiency and eliminates the mismatch between the energy supply and energy demand of solar thermal energy applications. Among the different types of thermal energy storage, latent heat thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. The current study numerically investigates the solidification of a phase change material (PCM) in a triplex tube heat exchanger with and without internal and external fins to enhance heat transfer during the charging and discharging of PCM. The effects of PCM freezing from the inside tube, the outside tube, and both tubes were investigated using a 2D numerical model developed with the Fluent 6.3.26 software. The pure conduction and natural convection were considered for the simulation. Different design parameters, such as the numbers of fins, fin length and thickness, and PCM unit geometries, were considered. Results indicate that Case G (8-cell PCM unit geometry) achieved complete solidification in a short time; that is, 35% of the finned tube. Experiments were conducted to validate the proposed model. Simulated results agree with the experimental results.
A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD simulations. This study aims at identifying the convective flows produced within the melted phase by temperature gradients and gravity. Simulations were carried out on experimental devices for applications to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat trans- fer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is examined by solving the unsteady Navier–Stokes equations for HTF and PCM and conduction for the tube. In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about 30% the time needed to charge the heat storage. A detailed description of the convective motion in the melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the mushy zone constant is also investigated.
Effect of Twisted Fin Array in a Triple-Tube Latent Heat Storage System during the Charging Mode
Sustainability
This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mas...
Journal of Energy Storage, 2021
A combination of heat transfer augmentation techniques is highly necessary to enhance the performance of Thermal Energy Storage (TES) systems employed in a wide range of applications. The major issue is that many of the Phase Change Materials (PCMs) possess low thermal conductivity (k ≤ 0.2 W/m K), resulting in an inefficient melting process. Triplex Tube Heat Exchanger (TTHX) based TES system is both numerically and experimentally studied using Paraffin (RT82) with Alumina (Al 2 O 3) nanoparticles that has a charging temperature in the range of 78.15-82.15 ∘ C. The experimental findings indicate that the Paraffin is not completely melted within the required time of four hours for the inside heating method at 97 ∘ C. The Paraffin is successfully melted for both sides heating at 90 ∘ C in lesser time and average temperature than the outside heating. With different charging temperatures, the Paraffin melting was consumed a short time for the non steady state at the mass flow rate of 29.4 kg/min, compared with the 16.2 and 37.5 kg/min for inner and outer tubes. Other outcomes were that with the fins-nanoparticle combination, an improved performance for melting the Paraffin, compared with those that occurred without nanoparticle. Furthermore, in the numerical study, compared with the pure Paraffin case, the melting time was minimized for TTHX with longitudinal fins (12%) and TTHX with triangular fins (22%) for the PCM having 10% nanoparticle, respectively. Close agreement is found between the numerical and experimental findings.
This study designed, tested, and evaluated an experimental energy storage system that uses a horizontal triplex tube heat exchanger (TTHX) with internal longitudinal fins incorporating phase-change material (PCM), with melting point in the range of 78.15–82.15 °C. The PCM did not entirely melt within the charge time (4 h) for the inside heating at 97 °C. The PCM melting for both-sides heating was successfully accomplished at 90 °C in lesser time than the outside heating method. The changes in the mass flow rates of 16.2, 29.4, and 37.4 min/kg on the PCM average temperature in the axial direction were investigated. The mass flow rate for the non-steady state at 29.4 kg/min consumed a short time to achieve PCM melting , compared with the 16.2 and 37.5 kg/min with different charging temperatures. However, two-types of extended surfaces, namely the longitudinal and triangular fins, were studied numerically. A significant enhancement was achieved using internal, internal-external, and external triangular fins at 11%, 12%, and 15% respectively, compared with the cases with longitudinal fins. Therefore, the external triangular finned tube has been considered the most efficient for the brief melting of PCM (193 min). The total energy stored capacities for the PCM with longitudinal and triangular fins were compared. The simulation agreed well with the experimental results.