Solidification Enhancement in a Triple-Tube Latent Heat Energy Storage System Using Twisted Fins

This work evaluates the influence of combining twisted fins in a triple-tube heat exchanger utilised for latent heat thermal energy storage (LHTES) in three-dimensional numerical simulation and comparing the outcome with the cases of the straight fins and no fins. The phase change material (PCM) is in the annulus between the inner and the outer tube, these tubes include a cold fluid that flows in the counter current path, to solidify the PCM and release the heat storage energy. The performance of the unit was assessed based on the liquid fraction and temperature profiles as well as solidification and the energy storage rate. This study aims to find suitable and efficient fins number and the optimum values of the Re and the inlet temperature of the heat transfer fluid. The outcomes stated the benefits of using twisted fins related to those cases of straight fins and the no-fins. The impact of multi-twisted fins was also considered to detect their influences on the solidification process. The outcomes reveal that the operation of four twisted fins decreased the solidification time by 12.7% and 22.9% compared with four straight fins and the no-fins cases, respectively. Four twisted fins improved the discharging rate by 12.4% and 22.8% compared with the cases of four straight fins and no-fins, respectively. Besides, by reducing the fins’ number from six to four and two, the solidification time reduces by 11.9% and 25.6%, respectively. The current work shows the impacts of innovative designs of fins in the LHTES to produce novel inventions for commercialisation, besides saving the power grid.

Parametric Study of the Solidification Process Between Vertical Parallel Plates of a Storage System

A conduction model is developed to describe the phase change between the plates of a thermal storage system. The diffusion equation and the associated boundary, initial, and interface conditions are approximated numerically by finite differences and implicit approach with variable time-step. The developed computational code is validated against data and good agreement was found. It is found that the reduction of the surface temperature of the cold plate increases the interface advance rate and reduces the full solidification time. Opposite effects are found due to the increase of the spacing between plates. Further, fractions of Al2O3 nanoparticles are mixed with the phase change material (PCM) to enhance the thermal conductivity of the PCM. For 7% volumetric fraction of Al2O3, the full solidification time and latent heat values decreased by 25.5% and 4.5%, respectively.

Influence of Riser Necking Ratio and Taper on the Solidification of Heavy Ingots by Numerical Simulation

The effect of riser necking ratio and taper on solidification process of 96T steel ingot have been studied numerically using the software package ProCAST. The results show that the solidification time decrease with the increase of riser necking ratio, and the position of shrinkage porosity moves up and the secondary porosity presents a tendency of increase, and the inclusions on the shoulder of body ingot decreases. The riser taper has little effect on the solidification process of heavy ingots.

Microstructural Characterization and Mathematical Modeling for Determination of Volume Fraction of Eutectoid Mixture of the Cu-8.5wt% Sn Alloy Obtained by Unidirectional Upward Solidification

The Cu-8.5wt % Sn alloy presents an extensive microsegregation during its solidification. That microsegregation results in the formation of a eutectoid mixture, which is detrimental to subsequent forming processes. This study deals with the influence of solidification time and cooling rate on the microstructure of that alloy. The unidirectional solidification technique allowed the acquisition of thermal data. The optical microscopy enabled the microstructural characterization of the material, the measurement of dendrite arm spacings and the quantification of the volume fraction of the eutectoid mixture. A semi-analytical mathematical model was proposed to estimate the volume fraction of the eutectoid mixture. The model expresses the volume fraction as an implicit function of the Fourier number. The results showed that the microstructure is dendritic and that the characteristic spacings increase with the solidification time between the liquidus and the peritectic temperatures. The data also showed that for higher cooling rates the dendrite arm spacings are smaller and that there is a tendency for the volume fraction of eutectoid mixture in the columnar zone to increase with the Fourier number and to decrease with the cooling rate. The proposed model allowed obtaining values of volume fraction with the same order of magnitude of the experimental data, but with behavior tendency opposite to that observed.