Latent Heat Storage Unit Research Articles

Numerical simulation of fin arrangements on the melting process of PCM in a rectangular unit

Innovative fin arrangements were proposed to enhance the thermal performance of latent heat storage units. The enthalpy-porosity approach was employed to optimize the fin distribution and predict the transient melting behaviors of N-octadecane. The unit with horizontal fins of uniform length was set as the base condition for comparison. It was found that the dead space of heat transfer and melting due to natural convection was not effectively eliminated by the conventional fin set. The region persisted at the bottom of the unit until the end of the melting process. In light of these observations, the fins were repositioned and resized. Three alternative fin configurations were proposed and evaluated: angled fins, asymmetrically located fins, and stepped fins. Results illustrated that fin structures significantly influenced the heat transfer characteristics and melting behaviors of latent heat storage units. Generally, greater enhancements were attained with downward angles and downward offset distances. The downward angle −20°led to an accelerated melting rate of 18.3 % compared to the base condition. In case 9, where the fins were moved down by 12 mm, the heat transfer enhancement ratio reached 32.5 %. However, introducing inhomogeneity in the fin length had only a minimal impact on the melting process.

Eco-friendly synthesis of chemically cross-linked chitosan/cellulose nanocrystal/CMK-3 aerogel based shape-stable phase change material with enhanced energy conversion and storage

Phase change materials (PCMs) have attracted numerous attention owing to their high energy storage density, cost-effective and operationally simple, however, the “solid-liquid” leakage and limited solar absorbance seriously hinder their widespread applications. Herein, an innovative chitosan/cellulose nanocrystal/CMK-3 (CS/CNC/CMK-3) aerogel based shape-stable PCM (SSPCM) was successfully synthesized, in which chemically cross-linked CS and CNC acted as three-dimensional supporting skeleton, CMK-3 endowed solar-to-thermal energy conversion ability and the impregnating polyethylene glycol (PEG) acted as the latent heat storage unit. The as-synthesized CS/CNC/CMK-3 aerogel/PEG (CCCA/PEG) showed ultrahigh melting/crystallization enthalpy of 178.5/171.1 J g−1 and excellent shape stability. The PEG was effectively embedded into the hierarchical porous architecture and the composite PCM could preserve its original shape without any leakage even compressed above the melting point of PEG. Meanwhile, the CCCA/PEG exhibited robust thermal reliability with an ultralow enthalpy fading rate of 0.030 ± 0.012 % per cycle over 100 thermal cycles. Intriguingly, the introduction of CMK-3 also significantly improved the solar-to-thermal energy conversion performance of CCCA/PEG, and a high solar-to-thermal conversion efficiency of 93.1 % could be realized. This work provided a potential strategy to design and synthesize high-performance sustainable SSPCM, which showed tremendous potential in the practical solar energy harvesting, conversion and storage applications.

Design, development and performance investigations of a latent heat storage with PCM encapsulation

Encapsulation of phase change material (PCM) in cylindrical capsules has been proven to be one of the promising techniques for improving the heat transfer characteristics in latent heat storage (LHS) systems. The distribution of the capsules has a great impact on the thermal performance of these LHS systems. Therefore, in the present study, an LHS unit with cylindrical PCM encapsulation is developed numerically using COMSOL Multiphysics software. Various models (Model A, Model B, Model C, and Model D) with varying spacing between the capsules are modeled to optimize the capsule distribution inside a cylindrical shell. For this high-temperature investigation, Sodium nitrate with a phase transition temperature of 305 °C is selected as PCM, and ambient air is used as the heat transfer fluid (HTF). The performance of these models is assessed by comparing temporal variation of temperature, phase fraction in the PCM and HTF velocity in the outer shell. It is observed that the distribution of capsules greatly influences the flow dynamics of HTF which crucially altered the thermal performance of the LHS models. Model C is found to be an optimum configuration with a minimum charging/discharging time of 364/337 min. LHS module with an optimum distribution of capsules was fabricated and its charging and discharging performances were investigated in the temperature range of 270–330 °C. The heat transfer behaviour in the PCM is studied by plotting the temperature evolution at different locations in the capsules. It was observed that the LHS module with approximately 14 kg of PCM mass, stored/discharged a total heat of 3.97/3.94 MJ in the given temperature range.

Effect of eccentricity and V-shaped fins on the heat transfer performance of a phase change heat storage system

Thermal energy storage plays a crucial role in the efficient use of solar energy and the recovery of waste heat from plants. This paper introduces an eccentric V-shaped fin latent heat storage unit. The influence of multiple geometric parameters including eccentricity, fin angle, height and thickness, on the system performance was studied, and the influence of four new fin arrangement and distribution on the melting process was proposed and compared. Finally, the fin structure was optimized by the response surface method. The results show that when the inner tube moves downward (the eccentricity is positive), the natural convection in the system is enhanced, the melting rate increases, and the optimal eccentricity is +3 mm. In addition, with the increase of the fin angle, the total melting time first decreases and then increases, and the total melting time is the shortest when the fin angle is 75°. Increasing the fin height can shorten the total melting time by up to 22.25 %; the fin thickness has less influence on the melting process. It is worth noting that after changing the fin arrangement and distribution mode, the total melting time is shortened by 4.91 %. Moreover, the optimal fin parameters under the most finned arrangement and distribution mode were obtained by the response surface test, and the total melting time was shortened by 60.67 % compared with the concentric tube without fins on the surface under the above parameters. Combining eccentricity and V-shaped fins can greatly shorten the total melting time, and reasonable changes in the arrangement and distribution of fins can further accelerate the melting rate.

Discharge performance assessment of a vertical double-pipe latent heat storage unit equipped with circular Y-shaped fins

This paper aims to study the effect of circular Y-shaped fin arrangement to improve the low thermal response rates of a double-tube heat exchanger containing Paraffin phase change material (PCM). ANSYS software is employed to perform the computational fluid dynamic (CFD) simulations of the heat exchanger, including fluid flow, heat transfer, and the phase change process. The optimum state of the fin configuration is derived through sensitivity analysis by evaluating the geometrical parameters of the Y-shaped fin. For the same height of the fins (10 mm), the solidification time is reduced by almost 22%, and the discharging rate is enhanced by almost 26% using Y-shaped fins compared with the straight fins. The results demonstrate that the solidification time is inversely proportional to the fin's length. The heat release rate for the case with the longest fins (stem length of 10 mm) is 39 W, almost 2.8 times higher than that with the fins' stem length of 5 mm. The case with the tributary's angle of 22.5o solidified in 55 min, faster than the other studied angles. Increasing the number of fins significantly affects the solidification time and discharging rate. By increasing the number of fins from 3 to 9, the heat transfer rate improves by 194%. The advantages of circular Y-shaped fins are well known in heat transfer applications and therefore are characterized toward higher performance in this study for the first time during the solidification process.

Enhancing thermal performance of latent heat storage unit for solar cooling: A hybrid approach with C-shaped fins and nano-additives

The performance of solar cooling systems is significantly affected by the intermittent nature of solar energy. To address this problem, thermal energy storage systems such as sensible and latent heat storage systems can be a viable option. Among these, the latent heat storage systems are promising due to their high energy storage density and nearly isothermal charging/discharging characteristics. However, the low thermal conductivity of the phase change material used within the storage unit hinders heat transfer, leading to longer charging and discharging periods. To overcome this problem, a hybrid approach that uses fins and nano additives is proposed in this study. A novel C-shaped fin design is introduced that effectively utilises the natural convection current in the molten phase change material. A comprehensive geometrical and material optimisation study is performed to determine the optimal shape, position, and material of the fins. The study also investigates the effect of the inclusion of graphene nanoplatelets (GnP) on the latent heat storage units. An experimental study is conducted to characterise the composite phase change material, and empirical correlations for viscosity and thermal conductivity are developed. The performance of an optimally designed LHS stacked with nano PCM composite of varying mass fractions is also evaluated. The study reveals that the C-shaped fins can reduce melting time by up to 59% compared to conventional fin designs, while PCM dispersed with 1% GnP reduces melting time by 27% when compared to the base PCM. Finally, a two-bed solar vapour adsorption cooling system with a 500 W capacity is considered to conduct a case study for demonstrating the performance of the proposed LHS. The result shows that the solar adsorption system integrated with the proposed heat storage unit can operate up to 3.3 h longer than it currently does. Thus the study presents a promising solution to overcome the obstacles limiting the widespread utilisation of solar cooling systems.

Experimental and numerical investigation on the melting behavior of paraffin in a shell and tube latent heat storage unit

In order to reduce the melting time of an improved shell and tube latent heat energy storage unit, the melting behaviors of phase-change material (paraffin) in the unit are investigated through visualization experiments. And a two-dimensional simulation model is established to explore the strengthening mechanism of the melting process by distinct heating methods and non-heat source wall. Results show that the complete melting time of outside heating method is 70.2% less than that of inside heating method at same heat flux. Eliminating the influence of heat transfer area (equal total heat input), the outside heating can generate more extensive and stronger natural convection, and the complete melting time can be shortened by 20.2%. In addition, the heat transfer bridge built by the non-heat source wall between the high temperature liquid phase-change material zone and the dead zone can effectively enhance the natural convection and accelerate the melting process. Especially considering the non-heat source wall, the melting time can be reduced by 44.2% through using the inside heating method.

Simultaneously improved heat storage rate and specific power for efficient thermal management via optimizing latent heat storage units

The latent heat storage unit (LHSU) is crucial for effective heat regulation in high-power heat dissipation systems. However, it encounters the challenge of simultaneously increasing the heat storage rate and specific power. In light of this, a comprehensive evaluation of thermal performance for LHSU with different heat storage enhancement techniques is essential in the design and optimization of LHSU. Here, numerical and experimental investigations are conducted to compare performances of single-tube, aluminum foam, fin and multi-tube LHSUs. The multi-tube LHSU has the largest heat storage rate and specific power because it increases the heat transfer area of both fluid-side and PCMs-side and reduces the amount of heat transfer fluid. The fin LHSU has the second best performance, with the aluminum foam LHSU ranking behind it. Furthermore, based on the synergy of multi-tube and fin, a multi-tube-fin LHSU for significantly improving the heat storage rate and specific power is proposed, which can reduce the melting time of PCMs by 92.4% and improve the specific power by 1091.2%, compared to single-tube LHSU. This study deepens the understanding for the characteristics of different LHSUs and provides a guide for their selection and optimization in specific situations.

Influence of heat transfer fluid on thermal performance improvement of latent heat storage unit with helical fins

The helical fins can improve the hampering effect of classical fins on the convection flows of latent heat storage units (LHSU) as an innovative design, but their thermal performance improvement was largely affected by the operational conditions of heat transfer fluid (HTF), especially for fluid temperature and velocity. Based on this, an experimental system was established to measure thermal performance of latent heat storage units with perforated and solid helical fins (PHF-LHSU and SHF-LHSU). Two inlet temperatures were considered as 65 °C and 75 °C in the charge process and 20 °C and 30 °C in the discharge process, while three velocities were employed as 0.5 L/min, 1.0 L/min and 1.5 L/min. Experimental results showed PHF-LHSU exhibited the higher thermal performance than SHF-LHSU, especially in temperature response and average Nusselt number. Increasing HTF temperature from 65 °C to 75 °C increased melting rate, the average heat flux, Nusselt number and thermal efficiency by 25.4%–31.6%, 65.9%–70.6%, 15.9–25.9% and 9.7%–11.6% in the charge process, while reducing HTF temperature from 30 °C to 20 °C lowered the solidifying rate, the average heat flux and thermal efficiency by 39.3%–47.4%, 52.5%–56.6%, and 30.7%–35.3% in the discharge process. The HTF velocity had the certain effects on thermal properties and with the HTF velocity increasing from 0.5 L/min to 1.5 L/min, the thermal efficiency was increased by 3.9%–4.7%.

4E analysis and multi-objective optimization of compression/ejection transcritical CO2 heat pump with latent thermal heat storage

To promote the goal of peak carbon dioxide emissions and carbon neutrality, low-energy consumption buildings require innovative technologies and efficient energy management. In this paper, the multi-objective optimization and the energy, exergy, economic and environmental (4E) analyses of the compression/ejection transcritical CO2 heat pump with latent thermal storage (TPE-LTES) system are conducted, and the influences of crucial parameters on the system performance are evaluated. The results show that the optimal comprehensive COP and annual hot water production (mDHW) of the TPE-LTES system are 3.59 and 3110 tons, respectively. Then, the comprehensive exergy efficiency of the TPE-LTES system owns 48.93 % higher than that of the heat pump unit. Furthermore, the optimal life-cycle cost (LCC) and life-cycle CO2 emissions (LCCE) of the TPE-LTES system are 708,073 CNY and 575,512.79 kg, respectively. Moreover, with constant discharge pressure, the evaporative superheat can be preferentially increased to reduce the system LCC and LCCE. Finally, the comprehensive COP and exergy efficiency of the system can be improved by increasing the inlet water temperature, while the increasing inlet water flow rate is the least desirable. This work is helpful to promote the research and application of latent heat storage unit integrated into air source heat pump.

Numerical study on melting process and heat transfer analysis of a multitube combination latent heat storage unit with innovative harpoon-type fins

The heat transfer rate of a coupled system combining a passive residual heat removal system and a latent heat thermal energy storage system is directly related to worker safety in nuclear power plants. To enhance the heat transfer performance of the coupled system, in this study, the melting process of phase change material in the latent heat thermal energy storage system is numerically investigated by inserting innovative harpoon-type fins. A new assessment index is also proposed to evaluate the comprehensive heat transfer performance of fins. More than thirty cases with different harpoon-type fins are designed, and the impacts of various efficient structural parameters of the harpoon-type fin on the melting process are evaluate. The response surface method is used to optimize the structure. The results demonstrated that the handle length and the number of fins significantly improve the heat transfer performance of the harpoon-type fin. The optimal geometrical parameters (arc angle θ = 45°, handle length Lha = 10 mm, fin number Nf = 8, and arc number Na = 1) of harpoon-type fins are obtained. The heat transfer rate of the optimal fin structure is six times that without fins, and the total melting time is shortened by 85.9%. Furthermore, the longitudinal extension of the fins is more important than the complex horizontal extension of fins. The harpoon-type fin not only shows better performance in the coupled system but can also be used in shell-and-tube latent heat thermal energy storage systems.

Effect of fin length and angle on the melting process of phase change materials in vertical latent heat storage unit

The installation of fins offers an effective solution for addressing the poor thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems. This paper aims to investigate the combined effects of unequal fin length arrangements and the inclination angle of fins on the performance of an LHTES system during the charging process. The LHTES system consists of a cylindrical container filled with paraffin (RT55) serving as the PCM. Numerical models are established and validated, followed by simulating various fin structures to analyze the complete melting time of the PCM. The characteristics of the melting process are further examined in four representative cases, including the full melting time, evolution of the melt fraction, average maximum velocity, streamline contours, temperature uniformity, and average Nusselt number. The results reveal that the optimal case, featuring unequal length and downward annular fins, achieves a significant 49.8% reduction in the complete melting time of the PCM compared to the benchmark case with ordinary annular fins. Moreover, the optimal configuration increases the largest average maximum velocity of the PCM by 35.36%, resulting in a more uniform temperature distribution and a higher Nusselt number.

Numerical energy and exergy evaluation for a multiple-layer latent heat storage unit enhanced with nanoparticles under different seasons

Latent heat thermal energy storage unit alleviates the mismatch between energy supply and demand. However, the sole melting temperature of a phase change material in a single-layer heat storage unit does not adapt well to the environment. Therefore, the mechanisms associated with the better environmental adaptability of a multiple-layer heat storage unit are explored in this study based on energy and exergy evaluations via comparison with single-layer units. An innovative methodology is proposed to discuss transient thermal energy and exergy, and exergy distribution of these heat storage units in different seasons. Results show that the multiple-layer units address the limitations of single-layer units by exhibiting excellent heat storage capacity and quality, as well as uniform melting and exergy distribution. Compared with the single-layer unit with a melting temperature of 49 °C, the multiple-layer unit exhibits a 56.64% higher energy in the winter. Moreover, the exergy is 57.14% higher than that of the single-layer unit with a melting temperature of 33 °C in the summer. This study reveals the mechanism of excellent thermal energy storage performance of the multiple-layer latent heat storage unit in different seasons.

Experimental and numerical studies of thermal transport in a latent heat storage unit with a plate fin and a flat heat pipe

Experimental and numerical studies of thermal transport in a latent heat storage unit with a plate fin and a flat heat pipe

Experimental and numerical investigation of a rectangular finned-tube latent heat storage unit for Carnot battery

Latent heat storage technology has a great potential in Carnot battery systems, and its thermal performance directly affects the system performance. In this paper, a rectangular phase change heat storage unit with finned-tube structure is designed and manufactured, and polyethylene wax/expanded graphite is adopted as the composite phase change material. The thermophysical properties of the polyethylene wax are characterized by experiments first, and then the heat transfer performance of the unit is investigated through varying inlet mass flow rates and inlet temperature on the test rig. Meanwhile, the detailed evolution of the phase change process is visualized and obtained by corresponding numerical simulations. Furthermore, the effects and selection principle of fin number, thickness, and material on the melting process are clarified by numerical simulations. Results shows that the influence of the inlet temperature is more significant than the mass flow rate on the melting/solidification time, however, changing the inlet temperature and mass flow rate has little effect on melting/solidifying the last 10 % of PCM. Heat conduction dominated the heat transfer process due to the high viscosity of polyethylene wax, inducing little stratification of the temperature distribution in the regions bounded by fins. The regions close to the corners and sidewalls are the primary factors delaying melting/solidification rate. Increasing fin number and thickness can effectively decrease the melting/solidification time at the expense of the heat storage capacity. Compared to selecting only high thermal conductivity fin materials, adopting fins with high thermal conductivity, low density, and low specific heat is a better approach for achieving higher heat storage capacity and shorter melting time. The present study explores candidate materials for medium-low temperature latent heat storage and potential applications of traditional finned-tube heat exchangers in medium-low temperature latent heat storage.

Parametric analysis for exergetic optimisation of a solar shell-and-tube latent heat storage unit for agricultural applications

Thermal energy storage by employing phase change materials (PCMs) has gained huge attention in many fields but despite great potential, a broader implementation in agricultural processes is yet to be achieved. Therefore, a standalone system for solar thermal energy storage using a Scheffler concentrator was developed for variety of agricultural applications. This study is aimed at the exergetic optimisation of the system by assessing the impact of various intensities of solar thermal input and flow rates on the exergetic performance and exergetic distribution inside an inversely arranged shell and tube heat storage unit. The experimental setup consisted of a cylindrical heat receiver, an inversely arranged shell and tube PCM tank and a flat plate resistive electric heater for solar irradiation simulation. The tank filled with 4 kg of RT70HC PCM was subject to various charging cycles under 2.5 LPM, 5 LPM, 7.5 LPM and 10 LPM flow rates and 450 W/m2, 575 W/m2, 700 W/m2 and 825 W/m2 of simulated solar intensities. The results indicate that increasing the mass flow rate enhances the heating uniformity within the tank but also leads to higher total exergy losses. However, the difference in the rate of exergy stored in the PCM was mostly negligible. Conversely, increasing the exergetic thermal input had a significantly positive impact on the rate of exergy stored in the PCM.. The exergetic efficiency of the PCM tank varied from 17.5% to 9.2%, with its peak value recorded at a 2.5 LPM flow rate and 1070 W of exergetic input.

Buoyancy-driven melting and solidification heat transfer in finned latent heat storage units

The thermal expansion and contraction property of phase change materials (PCMs) is a significant factor in affecting the buoyancy-driven melting/solidification heat transfer performance in latent heat storage (LHS) units. To reveal the intrinsic mechanisms, a mathematical model of buoyancy-driven melting/solidification processes in finned LHS units is constructed. The phase-change behaviors, thermal transport properties of different PCMs, and roles of heat transfer fluid (HTF) direction and fin layout in melting/solidification performance are explored. The results indicated that when compared to conduction-dominated cases, the buoyancy-driven melting duration of gallium and n-octadecane increases by 1.8% and decreases by 32.6%, respectively, while the corresponding solidification times decrease by 8.4% and increase by 15.2%, respectively. The downward HTF enhances the melting rate of gallium with thermal-contraction properties and the solidification rate of n-octadecane with thermal-expansion properties. Conversely, the upward HTF enhances the melting rate of n-octadecane with thermal-expansion properties and the solidification rate of gallium with thermal-contraction properties. For finned LHS units with upward HTF, the ladder-type and reverse ladder-type fins facilitate the melting performance of n-octadecane and gallium, respectively. Moreover, the ladder fins with non-uniform layouts weaken the solidification performance of PCMs with different thermal characteristics.

Multi-objective optimization of fin shape in a cylindrical encapsulated phase change material for thermal energy storage applications

This study presents a novel fin design for a latent heat storage unit that improves its thermal performance through a methodology that integrates numerical simulation, the response surface method, and a multi-objective genetic optimization algorithm. The stored latent energy per mass (Em) and mean power (Pt) are chosen as the objectives for the optimization process. The fin parameters are optimized using the NSGA-II (non-dominated sorting genetic algorithm) to achieve the objectives of maximizing both the stored latent energy per mass (Em) and mean power (Pt). The proposed design is evaluated through simulations and the results are analyzed to determine the optimal fin configuration and the effect of the fin design parameters on the stored energy and power of the unit. The results show that the implementation of full-fin in the latent heat storage unit leads to a 7.2% reduction in total stored energy, but a 34% increase in power in comparison to the finless case. However, the use of an optimization approach results in a substantial increase in power output while maintaining minimal compromise to the stored latent energy. In particular, the optimal fin configuration, Design B, is recommended when power and stored energy are given equal importance, as it results in a 90.1% increase in power and a negligible 4.3% decrease in stored energy per mass.

MAXIMIZATION THE LATENT HEAT STORAGE UNIT (LHSU) ENERGY SAVING USING SIMULATED ANNEALING ALGORITHM

An integration between latent heat storage unit (LHSU) and an air cooler was studied to reduce the space cooling energy consumption in telecommunications base stations (TBSS). A mathematical model was developed to address the heat transfer processes within energy storage modules and air cooler. Furthermore, a solid works simulation was used to simulate the real system virtually. A simulated annealing algorithm (SA) was utilized to maximize annual energy savings ratio which was considered a performance criterion for the proposed system. The calculations included comparisons the relative errors of air and temperature difference between the optimized using simulated annealing algorithm and tested (virtual) results which were calculated for both operation modes energy charging and energy discharging. The obtained results illustrated a remarkable improvement both relative errors and annual energy savings ratio for the study case.

Numerical study on thermal and melting performances of a horizontal latent heat storage unit with branched tree-like convergent fins

Numerical study on thermal and melting performances of a horizontal latent heat storage unit with branched tree-like convergent fins