Heat Thermal Energy Storage System Research Articles

Stacked ensemble learning approach for PCM-based double-pipe latent heat thermal energy storage prediction towards flexible building energy

Dynamic performance prediction of the PCM-based double-pipe latent heat thermal energy storage (LHTES) system plays an important role for building peak load shifting. This study presents a stacked ensemble learning framework for the phase change performance prediction of LHTES systems. The proposed model has a two-layer structure involving base and meta models: Regression Tree, Support Vector Regression and Linear Regression. Sensitivity analysis has been utilized for the feature extraction considering possible geometrical and physical parameters of LHTES systems with a fixed PCM volume that can store 0.94 kWh of energy within 255 min. Case studies show that the proposed model outperforms the base models in terms of both prediction accuracy and robustness. Compared with base models, the proposed model has a maximum 7.82% (charging) enhancement in Mean Absolute Percentage Error (MAPE) over all-range data sets and a maximum 16.43% enhancement in MAPE for the initial discharging stage, and has more stable predictive results within the high accuracy zone (accuracy > 95%) with a maximum 7.3% (charging) increase in the distribution density over all-range data sets and a maximum interquartile range reduction of 25.6% (middle discharging stage) in Mean Absolute Error. Application of the proposed model achieved more building peak load reduction.

Study of melting behavior of phase change material in a square enclosure with constant and variable heat flux at different wall heating conditions: A numerical approach

Latent heat thermal energy storage system offers the most promising cost-effective solution in thermal energy storage applications like solar water heaters to building air conditioning, textile industries, pharmaceutical industries, etc. In this article, the melting process of phase change material (PCM) in a square enclosure with constant, linearly increasing, linearly decreasing and sinusoidal heat flux on different sides of the wall is studied. The result shows that double-wall heating has the highest melting rate followed by side-wall heating and bottom-wall heating. This happens because double-wall heating increases the heat transfer area. Between side-wall heating and bottom-wall heating with uniform heat flux, side-wall heating gives a higher melting rate due to the higher length of solid–liquid interface promoting the heat transfer to solid PCM, thus increasing the melting rate. Again, for different heat distributions of side-wall heating the linearly decreasing heat flux provides the highest melting rate. This type of heat distribution actually transfers more heat to the lower part of the container, which counters the effect of convection, resulting in an enhanced melting process. On the other hand, in the case of distributions at bottom-wall heating, linearly increasing heat flux shows the highest melting rate. In addition, for linearly increasing heat flux, the shape of the liquid cavity is triangular, which gives more space and thereby intense natural convective circulation. This enhanced convection heat transfer leads to a higher melting rate.

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Development of snow removal system using embedded pipes inside road with solar thermal energy collector and packed bed latent heat thermal energy storage

To enhance winter safety for drivers and pedestrians, this study developed and assessed an efficient snow removal system. Utilizing a packed bed latent heat thermal energy storage system with a solar thermal energy collector and phase change material (PCM), the research demonstrated performance over sensible thermal energy storage, offering increased storage capacity, isothermal characteristics, and efficient charging and discharging processes. In this study, a packed bed PCM container was proposed for the improved heat transfer performance of latent heat thermal energy storage (LHTES). The heat and fluid flow inside LHTES was numerically and experimentally analyzed for the optimization. The snow removal system comprised solar thermal energy collectors, a packed bed LHTES, and concrete pavement. As a results, the phase change material temperature increases from 30 °C to 75 °C during a 27-hour charging process, accumulating 58 MJ of thermal energy. The system's snow removal effectiveness was validated in an experiment, affirming the efficient transfer of stored heat to melt 10 cm-thick snow at −5 to 13 °C. Notably, no snow accumulation occurred on the concrete pavement surface.

Accelerated charging dynamics in shell-and-multi-tube latent heat storage systems for building applications

Thermal energy storage (TES) is an emerging technique to store the surplus energy generated during periods of excess supply and utilise it when demand arises. Phase change material (PCM) stands out as a highly efficient TES system. Enhancing heat transfer during phase change is a major challenge in creating effective PCM-based TES systems. This study focuses on enhancing the melting performance of a shell-and-tube latent heat thermal energy storage (LHTES) system. This improvement is achieved by conducting an extensive parametric study involving various geometric factors including tube position from the bottom, vertical tube spacing, tube diameter, different heat exchanger shell aspect ratios, PCM temperature, tube temperature, and PCM type. A three-dimensional model is simplified to a two-dimensional geometry for numerical simulation. The results indicate that the PCM melting time decreased by 20.6 % and 4.4 % with a 20 mm vertical tube distance compared to 15 mm and 25 mm. Among the considered scenarios, the configuration with a doubled number of tubes in width consistently exhibits a higher melt fraction throughout the entire duration. Regarding the aspect ratio, the square-shaped system demonstrates both quicker melting times and a higher energy storage rate. When comparing PCM types, it is evident that RT 35 exhibits a 3.2 % higher heat storage rate and a 44.7 % shorter melting time compared to RT 35 HC.

Experimental investigation of thermal performance of vertical multitube cylindrical latent heat thermal energy storage systems.

The multitube design in the shell-and-tube type latent heat thermal energy storage (LHTES) system has received intensive attention due to its promising benefits in enhancing heat storage efficiency. In this paper, single and multi-tube shell LHTES systems were experimentally investigated. First, this study experimentally compared the thermal characteristics between a multiple-tube heat exchanger (MTHX) and a single-tube heat exchanger (STHX). The STHX's geometrical parameters coincided with a virtual cylindrical domain in the MTHX, being similar to the single-tube model formulated by simplifying the numerical solution to investigate the MTHX. The experimental data was then used to validate the simplified numerical model commonly used in the literature that converted the multi-tube problem to a single-tube model by formulating a virtual cylindrical domain for each tube in the MTHX system. The results showed that there was a noticeable difference in the thermal characteristics between the actual STHX and the virtual cylindrical STHX domain in the MTHX system. The comparison indicated that the simplified numerical model could not accurately reflect the thermal performance of the MTHX system. An experimental study or three-dimensional numerical modelling was required for the thermal analysis of the multi-tube problems. Second, the effect of tube number in the MTHX was experimentally investigated. It was found that an increase in tube number boosted both charging and discharging rates without inhibiting the natural convection. The five-tube configuration decreased the total charging and discharging duration by 50% compared to the two-tube one. Finally, the effect of heat transfer fluid (HTF) operating parameters on the system performance was evaluated on the five-tube MTHX system. The results revealed that the adoption of higher HTF temperature considerably improved the charging performance. The charging time decreased by up to 41% with the HTF temperature increasing from 70 to 80°C. Meanwhile, a variation in the HTF flow rate from 5 to 20 L/min showed a more pronounced influence on charging than on discharging due to the different dominant heat transfer mechanisms.

Development and experimental investigation of full-scale phase change material thermal energy storage prototype for domestic hot water applications

The paper presents an experimental analysis of the full-scale phase change material (PCM) thermal energy storage (TES) prototype that is designed for use in domestic hot water preparation systems. The PCM-TES prototype is based on the external arrangement of organic PCM and a custom-made compact fin-and-tube type of heat exchanger. The prototype has been designed, constructed, and tested according to the Ecodesign Directive requirements for water heaters and hot water storage tanks. Several parameters have been analysed, including the heat transfer fluid (HTF) temperature and mass flow rate, heat transfer rate, accumulated and released energy, and quantity of domestic hot water (DHW) delivered. Additional attention was paid to the reliability and repeatability of the results. Experimental research allowed to determine the quantity and temperature of DHW at a constant mass flow rate of 0.1 kg/s. The prototype unit showed that it can deliver 99.1 l of hot water at 40 °C for up to 15 min and 39 s, while the use of lower temperature DHW (up to 37 °C) allows to increase the quantity of hot water delivered up to 156.2 l. Experimental results showed the viability of the prototype, areas for improvement and further possibilities for its optimization. Overall, the study results are relevant for developing latent heat thermal energy storage systems using fin-and-tube heat exchangers in tanks and the feasibility of integrating such systems into DHW systems.

PONDERING THE CHOICE OF PCM AND MATHEMATICAL MODEL IN AUTOMOTIVE LHTS

Phase change materials are latent heat storage materials. As the source temperature rises, the chemical bonds within the PCM break up as the material changes phase. Upon storing heat in the storage material, the material begins to melt when the phase change temperature is reached. The temperature then stays constant until the melting process is finished. The heat stored during the phase change process of the material is called latent heat. Ideally, automotive engine cooling is undesirable from the thermodynamic point of view. If the heat transfer rates from the gas to metal could be reduced, then more power could be produced at a particular fuel flow rate, i.e. the thermal efficiency of the engine would increase. Also the heat removed out via radiator could be reduced and hence smaller radiator size. That is why powertrain thermal management is extremely necessary for good engine reliability and durability with a compromise of the thermal efficiency. One of the most technically and commercially available options for this is the use of latent heat thermal energy storage system. Despite the fact that there are numerous works and reviews covering this topic, the author hopes to draw attention to some aspects of the choice of material and mathematical model for such systems. Keywords: phase-change materials, latent heat, energy storage systems, thermal conductivity, thermo-physical properties, kinetic properties.

Improving heat storage performance of shell-and-tube unit by using structural-optimized spiral fins

Spiral fins have been widely used to enhance the heat transfer of latent heat thermal energy storage (LHTES) systems. However, owing to the inhomogeneous melting of solid-liquid phase change materials (PCMs) driven by convective heat transfer, the uniform spiral fins always have poor enhancing performance. In the present work, we proposed structural-optimized spiral fins, including optimized fin thickness, optimized fin height, and optimized fin pitch, to uniformly and efficiently transfer the heat from fins to PCM. By comparing their melting results with the original-uniform model, we found that negative models with larger fin volume at the bottom are more efficient in accelerating the melting process, and they can maximally reduce the complete melting time of PCM by 15.01% compared with the original one. On the contrary, the positive model with a smaller fin volume at the bottom slows down the melting of the LHTES unit. The heat transfer mechanism along the whole melting process is analyzed by comparing the thermal parameters (including liquid fraction, average temperature, average liquid velocity, and heat flux) of the original and optimized models. The enhancements of the negative models are owing to their benefits to the developments of convective heat transfer in the top region and conductive heat transfer at the bottom. According to the results of this paper, researchers can design novel high-performance LHTES systems using optimized spiral fins.

Effect of orientation and nanoparticle addition of a encapsulated phase change material on heat transfer in a packed bed thermal energy storage system – A numerical analysis

Thermal energy storage technology research is growing globally due to the increased awareness of the clean energy demand and limitations of fossil fuel commodities. The packed bed latent heat thermal energy storage (PBLHTES) system is one among it promising a greater number of applications like solar water heating, industrial waste heat recovery process, thermal power generations, thermal comfort of buildings etc., Due to the high latent heat capacities, available in wide temperature ranges and minimal volume change, solid-to-liquid phase change materials (PCMs) are more attractive than any other latent heat materials to use in the PBLHTES system. Although, the low conductivity of PCM restricts the heat transfer while the charging and discharging periods. Therefore, it is necessary to incorporate thermal enhancement techniques in a PBLHTES system to improve the melting rate of the PCM. In this work, it is attempted to carry the 2-D numerical analysis of PBLHTES system provided with encapsulated PCM staggered in the flow direction of heat transfer fluid. The numerical results are validated with the experimental work. The effect of the inclination of PCM capsules with the flow direction (0°, 2.5°, 5°, 7.5°, and 10°), the addition of Multi-walled carbon nanotubes (MWCNT) nanoparticles (0 %, 1 %, 2 %, 3 %, 4 %, and 5 %) on energy absorbed by the PCM are studied. Also, the contours of temperature distribution and liquid fraction of the PCM with time are presented. The results revealed that the temperature distribution of HTF rises when PCM spheres orientated to the HTF shifted from 0 to 2.5° later it reduces. Though HTF temperature rises, the PCM temperature, liquid Fraction and energy absorbed decline when the capsules inclined to the flow direction. This is mainly due to the reason that the HTF moves outwards from the flow direction and towards the edges of the container, which makes the HTF carry a more amount of heat without sharing with the PCM capsules. Therefore, these arrangements will be helpful to switch over the ideal high-temperature HTF at the outlet without charging the TES system and vice versa. An improvement of 13.16 % melting rate is observed from 0 to 3 % of a nanoparticle addition and only 4 % enhancement is noted from 3 to 5 % MWCNT deposition. The effect of nanoparticles on energy absorbed by the PCM is nearly constant after 3 % of Multi-walled carbon nanotubes (MWCNT) addition. Therefore, this is the optimum MWCNT volume concentration to be added. The maximum energy absorbed with 3 % MWCNT for 60 min of time is 98.7 kJ and 97 kJ which are 3.5 % and 3.65 % more than the pure PCM for the standard case (0°) and 2.5° angle of attack of EPCMs with the flow direction.

Experimental study of a latent heat thermal energy storage system using erythritol for medium temperature applications

Using solar energy and waste heat for medium-temperature thermal applications depends on efficient and economical heat storage development. Developing a compact thermal energy storage system is essential to use excess thermal energy from a source in a process or to shift the utilisation time of solar thermal energy or recovered waste heat. Phase change materials are commonly used for energy storage applications globally. In this work, a latent heat thermal energy storage (LHTES) system with 2.37 kg of Erythritol as the phase change material (PCM) has been studied. A shell and tube heat storage system is selected due to its effectiveness in heat transfer. Synthetic silicone oil Hi-Tech Therm-60 was used as heat transfer fluid. Thermal stability tests in a differential scanning calorimeter (DSC) for a small sample mass and a specifically designed experiment for a larger sample mass were performed to assess the stability of the PCM. The time-dependent temperature distribution inside the storage system and the effect of heat transfer fluid (HTF) inlet temperature on the charging behaviour were studied during the charging process. Charging time and melt fraction have been calculated. No significant change in melting temperature and a 10% reduction in latent heat of PCM was observed in the thermal stability test for a small sample mass in DSC. The charging time of the storage device was observed to be 91–97 min and 195 min for 140 °C and 130 °C HTF inlet temperatures, respectively. The total stored energy in the system was 922 kJ with a Stefan number of 0.59. Temperature variation during the charging process inside the storage also suggests a buoyancy effect, leading to increased natural convection during the melting process.

Investigation on the performance of a natural convection solar dryer with novel palmitic and sebacic acid eutectic phase change material for thermal energy storage applications

Solar drying has got enormous opportunity in the agricultural sector for hygienic processing of various crops which leads to value addition and high return to farmers. One of the drawbacks associated with solar drying is its usage during non-solar hours. This demerit could be effectively alleviated by integrating latent heat thermal energy storage system based on PCM with the solar dryer and extend its usage beyond sunshine hours. The present study encompasses the development of a novel eutectic phase change material (PCM) consisting of palmitic and sebacic acids (PA-SA) with an individual composition of 80 wt% and 20 wt%, respectively. Using a differential scanning calorimeter, the melting point and enthalpy of fusion of the PA-SA eutectic mixture were determined as 61.10 °C and 161.14 J g−1, respectively. Fourier transform infrared spectroscopy analysis ensured the chemical durability of the fresh eutectic materials and 1000 thermal cycled samples, which proved the suitability of the material for long-term applications. Accelerated thermal cycles up to 1000, and thermal conductivity tests accentuated the superior thermal reliability, and competency of the developed PA-SA PCM. Thermo-gravimetric analysis observed a degradation temperature of 215.13 °C, which is >3 times higher than the operating temperature and hence qualifies the thermal stability test. Corrosion analysis carried out as per ASTM G O1 using three metals such as stainless steel, aluminium and copper revealed the compatibility of using stainless steel as heat exchanger material. Corrosion rates were found to be zero, 0.4015 and 8.6505 mg cm−2 year−1 over 365 cycles respectively for stainless steel, aluminium and copper. Extensive experimental analysis was undertaken to compare the effectiveness of a natural convection solar dryer with and without PA-SA eutectic PCM. The study conducted with 3 kg of eutectic PCM encapsulated in stainless steel cylindrical tubes as heat exchanger elucidated the use of solar with PCM for a duration of four and half hours after sunshine. For solar drying applications, an organic PA-SA eutectic PCM has been developed with a melting range of 61.1 °C and a latent heat of 161.14 J g−1.

Novel method for evaluation of stress assisted corrosion through compact tension specimens to assess material compatibility in latent heat thermal energy storage systems

The next generation Concentrated Solar Power (CSP) plants integrated with Thermal Energy Storage (TES) offer a promising solution for dispatchability, reliability, and economic concerns associated with renewable energy technologies. However, the expected operational life of up to 30 years proves to be a major challenge due to the impact of high temperatures and corrosive eutectic salts utilised in the latent heat TES systems. Additionally, the system is under varying degrees of stress that can accelerate corrosion mechanisms. Unfortunately, this stress corrosion relationship is often neglected during the material compatibility assessment. This study utilises a novel static immersion testing approach with three designs of modified Compact Tension (CT) specimens manufactured from AISI 316L to investigate the interaction of alloys under stress with various eutectic salts at up to 750 °C for up to 1000 Hours. The results indicate that oxidation is accelerated up to four times and Intergranular Corrosion (IGC) up to two times in the high-stress region of the test samples. Furthermore, the findings suggest that static immersion testing using CT specimens can be regarded as an effective approach to assess the influence of stress on corrosion and conduct a reliable material assessment for latent heat TES systems and CSP plants.

Cascading latent heat thermal energy storage in parabolic trough solar collector as a promising solution: An experimental investigation

Solar energy system can be considered as a reliable energy source if it connects to a latent heat thermal energy storage (LHTES) system using phase change materials (PCMs). To tackle the low thermal conductivity coefficient of PCMs, the cascaded latent heat storage (CLHS) configuration is a promising solution. This study aims to illustrate the improvement of CLHS setup comparing with non-cascaded arrangement, performing a whole-scale experimental investigation. A compact parabolic trough collector (PTC) unit equipped with a LHTES module is designed and constructed for a residential purpose. Experimental results reveal that the average thermal efficiency of PTC is 73.5 %. Three paraffin waxes with melting ranges of (64–68 ℃), (57–60 ℃) and (46–48 ℃) are injected in three same series of shell-tube heat exchangers. For comparing cascaded and non-cascaded PCM performance, three experimental series, namely (Exp.1, Exp.2 and Exp.3) are performed. The experimental findings show that the deployment of the CLHS configuration improves the latent heat storage of non-CLHS-Exps.1, 2, and 3 by more than 10, 47, and 5 %, respectively. In addition, CLHS system has a potential to increase the exergy storage of non-CLHS setup by up to 27.4 %. Furthermore, impact of increasing heat transfer fluid (HTF) flow rate is examined and it is observed that the melting process is shortened by almost 39 %. Accordingly, increasing flow rate improves energy stored in PCMs1, 2, and 3 by 60 %, 59.62 %, and 72.04 %, respectively. Consequently, the latent thermal exergy storage of the PCM experiences a twofold increase. Conducting an experimental evaluation of thermal performance of the storage module integrated with PTC setup can be valuable, particularly in the realm of residential applications.

Numerical study on the discharging performance of a latent heat thermal energy storage system with fractal tree-shaped convergent fins

In this paper, an innovative fractal tree-shaped convergent fin (FTSCF) is embedded into a latent heat thermal energy storage system (LHTESS) to numerically investigate the parametric influences of FTSCF including FTSCF number N, maximum branching level m, length ratio α, branch convergence β, level convergence γ, rotation angle δ of the branch at the outermost level and branching angle θu on the discharging performance of the LHTESS under the fixed total fin volume. The results imply that increasing N, m, and α significantly reduces the complete solidification time τ of the phase change material (PCM). Further, the τ of the PCM demonstrates a pattern of initial decrease followed by an increase under the influences of β, γ, and δ, indicating the presence of an optimal FTSCF structure maximizing the discharging efficiency of LHTESS. Compared to the fins without branch convergence, the minimum τ of PCM within the LHTESS reduces by 4.33 %, 5.03 %, and 12.42 % by the branch convergence β when γ = 0.5, 0.707, and 1. In addition, the minimum τ of PCM monotonically decreases when θ1 = θ2 increases from 50° to 90°. The present work provides a technique to improve the discharging performance of the LHTESS by using fin convergence.

Experimental study on the thermal characteristics of a visualized shell-and-tube LHTES system at different endothermic and exothermic temperatures

This research developed a novel medium-temperature (up to 300 °C) latent heat thermal energy storage (LHTES) system, utilizing a compact shell-and-tube thermal exchange system containing spiral finned tubes, 220 kg of phase change material (PCM) was employed, enabling 44.52 MJ of heat storage, a visible window allowed to observe the phase change process and investigate the temperature variations in conjunction with thermocouples. The study analyzed the thermal traits and explored the impact of charging and discharging temperatures on the system's thermal performance.The outcomes indicated that natural convection gradually supplants heat conduction in the charging process as the primary heat transfer mechanism and a temperature stratification phenomenon emerges within the TES; during the discharging process, a contrasting behavior is observed. Employing charging-discharging temperature configurations of 290-170, 280-160, and 270-150 °C, the cumulative energy input to complete the cycle process is 63.59, 56.43, and 54.87 MJ, correspondingly, the released energy is 33.64, 33.41, and 33.57 MJ, yielding cycle efficiencies of 52.90, 59.20, and 61.20 %, respectively, with the charging temperature rising from 270 to 290 °C, storage time decreased 25.6 %, but lead to an 8.49 % decrease in heat storage efficiency, while the discharging temperature has a relatively minor influence on the system.

Investigation of the thermal exchange mechanism of PCM melting process in an LHTES with elliptic tube configurations inside a cylindrical shell

This study presents a comprehensive 2D numerical investigation into the heat transfer mechanisms and melting time estimation for a phase change material melting process in latent heat thermal energy storage systems. The energy storage system of interest employs an elliptic tube configuration within a cylindrical shell. This study primarily aims to decipher the impact of spatial arrangement and its geometrical intricacies on melting time and the associated heat transfer mechanisms. First, this study examines the transition in the dominant heat transfer mechanisms, from conduction to natural convection, throughout the progression of the melting process. The examination is facilitated using the enthalpy porosity method, which can articulate an additional momentum term by leveraging the porosity at the melting interface and the local liquid fraction. Conduction dominance characterizes the early stages of the melting process; however, a transition toward a complex interplay of natural convection and conduction is observed as the process evolves. When the distance between the heat source and the outer covering is changed from a measure of 0.95 to 0.7, the time it takes for phase change material to melt increases by 73.2%. Additionally, when the shape of a certain heat transfer fluid carrier cylinder and the space between them in angles (from 1/8 to 8 and from 30° to 150°) are adjusted, the melting time changes by 31.1% and 38.9% respectively. In addition to the numerical analysis, this study introduces an innovative predictive model based on artificial neural networks to forecast the melting time of the phase change material in the energy storage system. This predictive model is trained and validated using the data derived from the numerical study and shows good accuracy in predicting the melting time, which is a critical factor for the efficiency and performance of systems.

Solar-driven chemisorption cogeneration system integrated with thermal energy storage

In this study, a power and cooling cogeneration system is introduced, consisting of a chemisorption cycle, a latent heat thermal energy storage (TES) system employing phase change materials (PCM), and a solar system employing compound parabolic collectors (CPC). The system is targeted at being employed in a residential area in Shiraz City and TRNSYS and MATLAB software environments are utilized to simulate and assess the system. In the system, power is generated by a turbine with the pressure difference elicited through the chemical reaction in the chemisorption cycle. Also, the cooling is produced via the evaporation of ammonia in the evaporator. The effect of the supplied hot source temperature for the reaction in the adsorbent bed was investigated. It was observed that in the 100–200 °C heat source temperature range, the total energy efficiency increased from 0.313 to 0.467 and the COP for the refrigeration process reduced from 0.71 to 0.53. Also, the maximum overall energy and exergy efficiency in this temperature range were 0.46 and 0.405, respectively. Also, at the heat source temperature of 200 °C, the average maximum electrical power and cooling capacity were gauged at 2.7 kW and 14.5 kW, respectively. In the TES system with a volume of 1.5 m3, the maximum achievable capacity was 250 kWh and the solar system showed its highest temperature in July and August. It was observed that heat source temperature augments the production capacity of the system while it reduced the coefficient of performance (COP) of the system. Sustainable development goals (SDG) impact [Display omitted]

Melting enhancement of latent heat thermal energy storage by implementing new geometric design

Latent heat thermal energy storage systems can manage peak energy demand with the unique thermo–physical properties of phase change material. However, the primary concern of using these systems is their low heat transfer rate. The present study attempts to increase the thermal performance of these systems using perforated stair fins and changing the enclosure’s geometry. For this purpose, parametric studies have been conducted to assess the effect of perforations on fins with different diameters (from dimensionless diameters of 1 to 2) and different numbers of perforations (from 6 to 24). Next, the effect of changing the enclosure's geometry to a parallelogram, trapezoid, and rectangle is investigated. Finally, by simultaneously applying the above–mentioned ideas, the performance parameters of the system are calculated and compared with the base case (enclosure with simple stair fins). The investigations are conducted using the finite volume method, and the material melting process is carried out based on the enthalpy–porosity method. All the simulations are three–dimensional and transient, with variable properties of material in solid and liquid phases. According to the results, using perforated fins intensifies the buoyancy force by increasing fluid displacement inside the enclosure. As a result, using 24 perforations on each fin with a D/δ = 2 improves the liquid fraction up to 9.7%. Moreover, the change of geometry reduces the critical area at the bottom of the system and improves the liquid fraction up to 5.4% inside the trapezoidal enclosure. By applying two ideas of using perforated fins and changing the geometry simultaneously, the mean Nusselt numbers for rectangular, trapezoidal, and parallelogram enclosures are significantly enhanced by 95, 114, and 133%, respectively. In these cases, the improvement in the heat transfer rate has led to a decrease in the melting time of the materials by 44.5, 47.5, and 51.5 min, respectively. These operational suggestions also enhance the critical performance parameters of the system, namely the stored energy and the mean charging power from 946 kJ/m and 124 W/m (in the base case) to 963 kJ/m and 211 W/m (70%) (in the rectangular enclosure with perforated fins).

Heat Transfer and Thermal Energy Storage Enhancement by Foams and Nanoparticles

The use of innovative methods for the design of heating, cooling, and heat storage devices has been mainly oriented in the last decade toward the use of nanofluids, metal foams coupled with working fluids, or phase change materials (PCMs). A network of nine Italian universities achieved significant results and innovative ideas on these topics by developing a collaborative project in the last four years, where different approaches and investigation techniques were synergically employed. They evaluated the quantitative extent of the enhancement in the heat transfer and thermal performance of a heat exchanger or thermal energy storage system with the combined use of nanofluids, metal foams, and PCMs. The different facets of this broad research program are surveyed in this article. Special focus is given to the comparison between the mesoscopic to macroscopic modeling of heat transfer in metal foams and nanofluids, as well as to the experimental data collected and processed in the development of the research.