The continuous increase in the level of green-house gas emissions and the depletion of fossil fuels are identified, as the major driving forces behind efforts to effectively utilize different ...sources of renewable energy. Solar energy considered one of the most prospective sources of this energy. This review paper mainly focuses on the majority of heat-transfer enhancement techniques between the phase-change material (PCM) and the heat-transfer fluid (HTF) based on the application of fins embedded in the PCM. This study also investigated the geometrical dimensions, dimensionless numbers, and fin location through numerical and experimental works conducted to assess the influences of these parameters on the thermal performance of PCM-latent heat thermal energy storage (LHTES) containers. The best enhancement is achieved using the longitudinal finned configurations because of its easy design and fabrication, especially along circumference of the cylindrical PCM containers. The circular-finned tube was also more effective than the pinned-tube for different shell and tube. PCMs based on heat sinks with internal pin fins were widely used for the thermal management of various pieces of electronic products. The heat enhancement factor was effectively dependent on increasing the numbers and dimensions of these fins. Further researches still require to explore the possible geometrical designs of fins and their key findings, which have more effect on the thermal performance of the finned-LHTES system.
This study aims to develop a numerical scheme to model and optimize the solidification process within a Latent Heat Thermal Energy Storage System (LHTESS), while specific nanoparticles are employed, ...and the system is equipped with curved fins. Response Surface Method (RSM) has been used for fin geometry optimization to determine the optimum fin geometry configuration. In this regard, Full Solidification Time (FST) is considered as the objective function. After that, the impacts of nanoparticle dispersion on the thermal efficiency are studied using the Standard Galerkin Finite Element Method (SGFEM). The developed numerical scheme is benefited from a dynamic mesh adaptive method, which significantly improved the numerical accuracy and reduced the computational time. Results indicate that using 4% SWCNT-enhanced PCM accelerates the procedure by 40.9%. Moreover, optimization of the fin configuration causes the solidification to be completed in 1269 s, which leads to a reduction of 61.54% in FST of pure PCM. Employing optimized curved fin in the system is reported as a better enhancing approach as compared to nanoparticle addition. Results also demonstrate a more expedited procedure by reducing the temperature of the cold wall especially by considering at least 18 K temperature difference between the cold wall and PCM.
Latent heat thermal energy storage (LHTES) system uses a large triplex-tube heat exchanger (TTHX) with internal longitudinal fins incorporating phase-change material (PCM) was experimentally ...designed, tested, and evaluated. The PCM was entirely solidified using the both-sides freezing, as a main method under the influence of average discharging temperature was at 65°C. The changes in the mass flow rates of 16.2, 29.4, and 37.5min/kg were investigated. The solidification rate increased, as the mass flow rate increased, therefore the mass flow rate at 37.4kg/min consumed a short time, compared with the 16.2 and 29.4kg/min. Furthermore, the PCM completely solidified, as fast as at position B than position A from the entrance of the HTF-tube because of temperature variations in axial and angular direction during discharging process. Two types of extended surfaces, namely the longitudinal and triangular fins in various configuration were numerically studied. A significant enhancement was observed using internal, internal-external, and external triangular fins at 14%, 16%, and 18% respectively, compared to longitudinal fins configuration. Consequently, the external triangular finned tube has been considered the most efficient for the brief solidification PCM (630min). The total energy released for the both types of fins were compared. The simulation results were agreed well with the experimental results.
•The PCM solidification for both-sides freezing was experimentally accomplished at 65°C.•Longitudinal and triangular fins model of the TTHX were numerically studied.•The influence of change in the mass flow rates during discharging process was investigated.•External triangular fins model was the most efficient for shorter solidification time (630min).
Summary
Experimental studies have been carried out to evaluate the thermophysical properties and thermal performance of thermal energy storage (TES) systems. The TES system was filled with 0%‐0.025% ...vol. fractions multiwalled carbon nanotubes (MWCNT)‐based lauric acid (LA), paraffin wax (PW), and stearic acid (SA) nanoparticle‐enhanced phase change materials (NEPCMs). The T‐History method has been used to explore the thermophysical parameters, i.e., solid‐liquid specific heat capacity, solid‐liquid thermal conductivity, and heat of fusion. Results revealed that the solid thermal conductivity of the 0.02% MWCNT in lauric acid, paraffin wax, and stearic acid increased by 37.8%, 24.4%, and 13.5% than LA, PW, and SA phase change materials (PCMs), respectively. Also, an improvement in liquefying and solidification time has been observed for 0.02% vol. fraction MWCNT‐based NEPCMs. However, the dimensionless numbers justified that the combined conduction and natural convection effect occurred in the PCMs/NEPCMs thermal energy storage. The coefficient and rate of heat transfer have been compared among 0%‐0.025% vol. fraction of MWCNT‐based pure lauric acid, paraffin wax, and stearic acid PCMs/NEPCMs. Also, the maximum heat transfer rate for 0.02% MWCNT in lauric acid, paraffin wax, and stearic acid NEPCMs has been increased by 61.16%, 87%, and 26.4%, respectively, compared to LA, PW, and SA phase change materials. Hence, the 0.02% MWCNT/PW‐NEPCM‐based TES system has higher performance than the mentioned TES systems.
Composites comprising MgO nanoparticles as the dispersed phase and solid phase solar salt as the matrix have been prepared through solid-state mixing. The inclusion of MgO nanoparticles had very ...little influence on the solid-liquid phase change temperature and the latent heat of solar salt. However, the solid phase thermal conductivity of MgO-solar salt was elevated by 17.5% with the dispersion of 0.25 wt% MgO nanoparticles. The clustered nature of MgO nanoparticles and their presence at the interface between solar salt particles with reduced resistance might have contributed to the solid phase thermal conductivity enhancement for this composition of the composite. The maximum enhancement in specific heat of MgO-solar salt composite (14%) was observed at another composition (1 wt%), revealing the requirement of different composition for optimum thermal conductivity and optimum specific heat. The solidification time for 0.25 wt% composite was 30% lower than that of the solar salt. Also, the rate of discharge from 0.25 wt% composite was 42.4% higher than that of solar salt. The corresponding data for the composite containing 2 wt% MgO are 13.8% and 33.8% respectively. These composites can be used in latent heat thermal energy storage systems.
•MgO-solar salt composite phase change material prepared and characterized.•0.25 wt% composite showed needle-like structures at the MgO-solar salt interface.•Different optimum MgO concentrations for maximum ‘k’ and ‘cp’ enhancement.•Maximum thermal conductivity enhancement of 17.5% for composite with 0.25 wt% MgO.•30% reduction in solidification time for 0.25 wt% MgO-solar salt composite.
The thermal energy storage and release application of water- phase change material- (SnO2-TaC) and (SnO2–SiC) nanoparticles system has been investigated for cooling and heating applications. The ...water - polyethylene glycolwith (SnO2-TaC) and (SnO2–SiC) nanoparticles have been used. The results showed that the melting and solidification times for storage and release of thermal energy of water - polyethylene glycoldecrease with increase in(SnO2-TaC) and (SnO2–SiC) nanoparticles concentrations. The melting and solidification times decrease with increasing of TaC nanoparticles concentrations to water-polyethylene glycol/SnO2nanofluidand SiC nanoparticles concentrations to water-polyethylene glycol/SnO2nanofluid.
A combination of fins-nanoparticle is essential for a wide range of technologies using to enhance the performance of Thermal Energy Storage (TES) systems. Major problem is that most Phase-Change ...Materials (PCMs) have low thermal conductivity (k ≤ 0.2 W/m K), resulting in an incomplete melting and solidification processes. Triplex-Tube Heat Exchanger (TTHX) was numerically studied with Alumina nanoparticle (Al2O3) and Paraffin (RT82) that has melting and solidification temperatures of 82 °C and 65 °C, respectively. The findings indicate that the isothermal and liquid fraction contours of PCM obtained using external triangular fins entirely achieved at 193 min and 630 min, respectively. Furthermore, other important findings were that the external triangular fins-nanoparticle model has fins number (8), fins length (141 mm) and fins aspect ratio (18%) considered the most efficient to minimize the melting and solidification times to 163 min and 425 min, respectively. A close agreement has proved between numerical and experimental results. Keywords: Thermal energy storage, Triangular fins, Nanoparticle, Melting time, Solidification time
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•Oxidised molten droplet-solid surface interaction outcomes studied for We < 150.•A critical Weber number (We ∼ 79) noted for rebound to disintegration transition.•A power law ...correlation obtained to quantify droplet spreading time with We.•A kinetic model derived to determine the transient droplet spreading rate.•Maximum droplet spread increased with We resulting in decreased solidification time.
Molten metal droplet impingement and subsequent solidification phenomena in both inert and non-inert gas environment exist widely in various industrial applications. Exposing a molten droplet to air allows to form an oxide layer on the droplet surface which greatly influences the thermophysical properties of the droplet. While previous studies demonstrated the influence of oxide layer on the spreading dynamics, understanding of the impact dynamics is still missing when solidification is involved. To address this issue, in the present study, high-speed imaging was used to determine the interaction dynamics and solidification behaviour of a molten droplet of three different compositions onto a solid surface over a range of Weber numbers (We < 150) in an open atmosphere. Two distinct outcomes were noted – (1) rebound and (2) disintegration demarcated by a critical Weber number. Upon impingement, each droplet exhibited periodic spreading and recoiling behaviour which was subsequently dampened by the simultaneous solidification process. The maximum droplet spread area and droplet spreading time were shown to increase and decrease with Weber number, respectively following a power law form. It was shown that in all cases, oscillation and solidification time decreased with Weber number. Finally, a recovery type exponential profile was utilised to describe the droplet spreading kinetics.
Abstract
In order to further improve the efficiency of concrete in engineering application, the influence of vibration mixing intensity on the solidification efficiency and performance of concrete is ...studied. Four vibration intensity levels of 0g, 2g, 3g and 4g were selected to explore the initial and final solidification time and working performance of concrete under different vibration intensity. The test results show that when the vibration strength is 2g, 3g and 4g, the initial solidification time decreases by 4.9%, 7.5% and 8.7%, the final solidification time decreases by 1.5%, 1.9% and 2.7%, and the slump increases by 3.9%, 5.9% and 15.7%, respectively, compared with the vibration strength of 0g. Compared with 0g vibration strength, the compressive strength of concrete with 4g vibration strength is increased by 5.48%, 4.11% and 7.04% respectively at the age of 3D, 7d and 28d. The results show that with the increase of vibration intensity, the initial solidification time and final solidification time shorten, the slump increases, the compressive strength increases. Vibration mixing is of great significance to the application and expansion of concrete engineering.
Buildings account for 39% of global GHG emissions. In any building, space cooling/heating consumes the maximum electricity. Recently, encapsulated phase change materials (PCMs)-based cool thermal ...energy storage (CTES) systems have gained huge attention due to its numerous advantages in meeting building space cooling demand. Energy is stored inside these capsules in the form of latent heat. Considering the relevance of PCM solidification in capsules, two novel correlations are proposed to determine the inward and outward solidification time of phase change material (PCM) inside/around a spherical capsule based on its thermal conductivity and thickness. Further, an experimental investigation is also performed to validate the correlation. The correlation agrees closely to the experiment with a maximum inaccuracy of around 6.6%. Thereafter, a parametric analysis is also carried out to analyse the impact of both the parameters on inward solidification time of PCM. The results showed a significant reduction in solidification time up to a capsule thermal conductivity value of 0.3 W/mK. Beyond 10 W/mK thermal conductivity, capsule thickness did not affect solidification. The incorporation of these correlations into software will benefit engineers working in the fields of CTES, refrigeration, food processing, and plastics industries.
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