Energy recovery from domestic radiators using a compact composite metal Foam/PCM latent heat storage

© 2020 Elsevier Ltd With the increasing demand for energy consumption in domestic buildings and consequent CO2 emission, there is a need to provide proper products to reduce energy loss. Domestic radiators for space heating can be improved by using a Compact Latent Heat Storage (CLHS) unit mounted on the wall side surface in order to offer energy saving and peak-shaving. The unit offers the potential to save otherwise wasted energy from the back surface of the radiator to the walls in the charging mode of the energy storage system. When the heating system is turned off, the CLHS unit discharges the stored heat towards the room to provide a uniform temperature on the surface of the radiator. An aluminium foam embedded inside the bulk Phase Change Material (PCM) can modify the heat storage/retrieval rate. A PCM is selected depending on the radiator's surface temperature, which is almost equal to the hot water temperature delivered to the radiator. Different metal foam porosities are examined and compared with the PCM-only alternative (i.e. without metal foam enhancement). The results show the porous-PCM CLHS alternative provides an almost constant temperature during the discharging process equal to 54 °C. However, for the PCM-only alternative, the temperature of the surface reduces continuously. Using the porous medium results in a shorter melting time, about 95% of what is needed for the PCM-only alternative. Increasing the metal foam porosity results in shorter charging/discharging time; however, since the surface temperature of the porous-PCM unit is almost constant for different metal foam porosities, a system with higher porosity (97%) is desirable

Elastic Wave Characteristics of Graphene Reinforced Polymer Nanocomposite Curved Beams Including Thickness Stretching Effect

This work aims at analyzing elastic wave characteristics in a polymeric nanocomposite curved beam reinforced by graphene nanoplatelets (GNPs). GNPs are adopted as a nanofiller inside the matrix to enhance the effective properties, which are approximated through Halpin-Tasi model and a modified rule of mixture. A higher-order shear deformation theory accounting for thickness stretching and the general strain gradient model to have both nonlocality and strain gradient size-dependency phenomena are adopted to model the nanobeam. A virtual work of Hamilton statement is utilized to get the governing motion equations and is solved in conjunction with the harmonic solution procedure. A comparative study shows the effects of small-scale coefficients, opening angle, weight fraction, the total number of layers in GNPs, and wave numbers on the propagation of waves in reinforced nanocomposite curved beams. This work is also developed for two different distribution of GNPs in a polymeric matrix, namely uniformly distribution and functionally graded one

Numerical study of circular-elliptical double-pipe thermal energy storage systems

Solar energy is one of the unlimited sustainable energy resources that can be stored for different applications by using latent heat thermal energy storage systems. These systems utilize the phase change process (melting/solidification) of a phase change material (PCM) for the store and release energy. In the present study, an annulus with an inner ellipse as a thermal energy storage system was numerically investigated. This study investigated the effects of various aspect ratios of the inner ellipse diameters (1, ¾, ½ and 1/3) as well as the angular position of the inner ellipse (90°, 60°, 45°, 30° and 0°) during both melting and solidification processes. The results show that the lowest aspect ratio (W=1/3H) has the best performance during charging (minimum melting time); however, the aspect ratio has no considerable effect on the solidification process. On the study of the ellipse angle, the results reveal that lower melting time is achieved for a higher angle while the solidification time is not varied significantly. The melting time reduces by almost 61% and the efficiency enhances by 26 % for the case of W=1/3H with the angle of 90º compared with the case of aspect ratio=1 (circular case)

Phase Change Process in a Zigzag Plate Latent Heat Storage System during Melting and Solidification

Applying a well-performing heat exchanger is an efficient way to fortify the relatively low thermal response of phase-change materials (PCMs), which have broad application prospects in the fields of thermal management and energy storage. In this study, an improved PCM melting and solidification in corrugated (zigzag) plate heat exchanger are numerically examined compared with smooth (flat) plate heat exchanger in both horizontal and vertical positions. The effects of the channel width (0.5 W, W, and 2 W) and the airflow temperature (318 K, 323 K, and 328 K) are exclusively studied and reported. The results reveal the much better performance of the horizontal corrugated configuration compared with the smooth channel during both melting and solidification modes. It is found that the melting rate is about 8% faster, and the average temperature is 4 K higher in the corrugated region compared with the smooth region because of the large heat-exchange surface area, which facilitates higher rates of heat transfer into the PCM channel. In addition to the higher performance, a more compact unit can be achieved using the corrugated system. Moreover, applying the half-width PCM channel accelerates the melting rate by eight times compared to the double-width channel. Meanwhile, applying thicker channels provides faster solidification rates. The melting rate is proportional to the airflow temperature. The PCM melts within 274 s when the airflow temperature is 328 K. However, the melting time increases to 460 s for the airflow temperature of 308 K. Moreover, the PCM solidifies in 250 s and 405 s in the cases of 318 K and 328 K airflow temperatures, respectively

Discharge Enhancement in a Triple-Pipe Heat Exchanger Filled with Phase Change Material

This study aims to study the discharging process to verify the influence of geometry modifications and heat transfer flow (HTF) patterns on the performance of a vertical triplex-tube latent heat container. The phase change material (PCM) is included in the middle tube, where the geometry is modified using single or multi-internal frustum tubes instead of straight tubes to enhance the discharging rate. The effects of the HTF flow direction, which is considered by the gravity and opposite-gravity directions, are also examined in four different cases. For the optimal geometry, three scenarios are proposed, i.e., employing a frustum tube for the middle tube, for the inner tube, and at last for both the inner and middle tubes. The effects of various gap widths in the modified geometries are investigated. The results show the advantages of using frustum tubes in increasing the discharging rate and reducing the solidification time compared with that of the straight tube unit due to the higher natural convection effect by proper utilization of frustum tubes. The study of the HTF pattern shows that where the HTF direction in both the inner and outer tubes are in the gravity direction, the maximum discharging rate can be achieved. For the best configuration, the discharge time is reduced negligibly compared with that for the system with straight tubes which depends on the dimensions of the PCM domain