Latent Heat Storage Tank Research Articles

Performance evaluation of composite phase change materials with varying expanded graphite content in a drawer-type latent heat storage tank

The poor thermal conductivity of single-component phase change materials (PCMs) significantly impacts the operational efficiency of solar combi-systems. There is still a gap in the research on the heat release behavior of composite phase change materials (CPCMs). Therefore, this study investigated the heat release behavior of a self-developed drawer-type heat storage tank by varying the content of expanded graphite (EG) in the CPCMs used in it. Simulation was carried out using COMSOL Multiphysics 6.1, followed by experimentation on a test bench. The average outflow temperature, effective energy conversion (EEC), and heat release rate were used to evaluate the performance of the tanks. Comparing the simulation with experimental results, a maximum error of 8.75 % was obtained, indicating the accuracy of the study. The results indicate that adding EG can significantly improve the thermal conductivity of CPCM, with superior heat release behavior observed when the mass fraction of EG reaches 5 %. Under similar temperatures, the average outflow temperature from a 5 % EG tank is approximately 4.4 °C higher, EEC is 84 % higher, and heat release rate is 1.63 times higher than that from an ordinary thermal tank. Under different temperatures in a 5 % EG tank, increasing by 5 °C results in an average outflow temperature increase of 4.1 °C, EEC increase by a factor of one and an increase in heat release rate by 36 %. This study provides valuable insights for subsequent research on operation strategies for solar combined systems.

Combined solar and ground source heat pump heating system with a latent heat storage tank as a sustainable system to replace an oilfield hot water station

Present study focuses on a clean energy replacement for an oilfield hot water station and develops a combined solar and ground source heat pump (GSHP) heating system with a latent heat storage tank (LHST). The effects of LHST and heat replenishment on energy and coefficient of performance (COP) are quantitatively analyzed during short-term or long-term operation of the system. The suitability of three different phase change materials for the system is compared, and the optimal one is identified. Results show that the LHST with 70 °C melting point can increase the collector efficiency to 53.91 % and reduce the total energy consumption of the system by 52344 kWh. Heat replenishment could effectively mitigate the ground temperature drop to 0.19 °C/year, reducing the annual energy consumption of GSHP by more than 4230 kWh and providing an additional thermal energy of 72 GJ. Compared to the initial heating system, the novel system efficiency increases to 51.25 %. Gas consumption and total system energy consumption decreased by 81.7 % and 75.2 %, respectively. Annual reduction of CO2 emission is about 1150 tons, showing satisfactory performance. Outcomes of this study prove the application of clean energy in oil field industrial processes, and help in achieving the goals of emission reduction and carbon neutrality.

Thermal performance of packed-bed latent heat storage tank integrated with flat-plate collectors under intermittent loads of building heating

Packed-bed latent heat storage (PBLHS) system has been widely studied in the solar energy application area due to its properties of solving the time-space mismatch of energy supply and demand. The paper delves into the cyclic thermal performance of PBLHS tanks, seamlessly integrated with flat-plate collectors, to manage building heat loads effectively. A 1D transient mathematic model of PBLHS integrated with the solar collector for a building is established using MATLAB which is validated with the experimental results from the literature. Based on this model, the effect of different sizes, flow rates, inlet temperature thresholds and different heating months are discussed. The results show that: 1). Building heat load can have a significant influence on the thermal performance of the PBLHS system. 2). The optimal size of the tank for a 96 m2 house is 1.0*1.0 m and the optimal flow rate is 0.05 kg/s 3). The weather data can significantly affect the thermal performance of PBLHS, the storage tank heating durations for one week in different heating months are 108.4h, 73.6h,70.8h and 81.7h. These insights are pivotal for the optimal design of PBLHS tanks, paving the way for more efficient building heating solutions.

Design and assessment on a bottom-cut shape for latent heat storage tank filled with metal foam

The utilization of phase change materials (PCMs) holds tremendous potential of heat storage domain. The PCM's refractory at the latent heat thermal energy storage (LHTES) unit bottom hinders the heat storage efficiency, despite the significant improvement in thermal conductivity achieved through the addition of metal foam. This study employs numerical simulation to examine the impact of applying bottom cross-cut on PCM's spatial distribution in a horizontal LHTES unit. The manuscript analyzes parameters including melting fraction, complete melting time, Rayleigh number, natural convection heat transfer gain, melting phase interface, velocity and temperature distributions, and heat storage. The findings indicate that the proximity to the heating tube results in a reduction of solid volume at the LHTES unit bottom. A 0.6 bottom cross-cut ratio leads to an 18.84 % faster heat storage rate compared to a concentric-circle unit. Furthermore, a bottom cross-cut ratio of 0.5 enhances natural convection heat transfer gain by 3.28 times.

On the design of a solar heat storage tank at 120°C

ABSTRACT This work presents the materials selection process, the design and the dimensioning process of a latent heat storage tank that works between a high temperature heat pump and an Organic Rankine Cycle unit. The selected heat storage material is the S117 Phase Change Material that has a melting point at 117°C matches the operational temperature of the system at approximately 120°C. The tank configuration is selected for optimised heat transfer process, resulted from practical experience of the project partners and it is described in details in the document. The simulation results from the Computational Fluid Dynamic study of the tank are also presented here. This work should be useful for engineers designing compact heat storage tanks for medium temperature applications.

Effect of phase change heat storage tank with gradient fin structure on solar energy storage: A numerical study

In this paper, the heat storage process of a latent heat thermal energy storage (LHTES) tank is studied numerically. A new type of gradient fin is added to the heat storage process in a latent heat storage tank to improve the heat transfer performance of the internal phase change material (PCM). The numerical model is verified by the experimental data. The influences of different structures on the melting rate, temperature distribution, velocity distribution, and maximum melting rate of PCM in LHTES tank are investigated, and the influence of natural convection on the energy storage system is further quantified. The results show that the melting time can be significantly reduced by 16.9% by using the four straight fins with gradient shape, and the melting time can be further reduced by 41.1% by reconstruction of the gradient fin position. The deformation in the opposite direction will slow down the melting speed and extend the melting time by more than 4.66 times. The convection criterion for judging the buoyancy convection of the melt in this paper shows that natural convection is dominant in both the upper and lower part of the melt. The closer the convection coefficient is to the overall heat transfer coefficient, the better the melting efficiency and energy efficiency will be.

Machine learning and multilayer perceptron enhanced CFD approach for improving design on latent heat storage tank

Solid-liquid phase change heat storage is an important method to solve the mismatch of the generation and usage of waste heat, which is conducive to decarbonization and energy conservation. However, there always exists inhomogeneity for the melting and temperature of the phase change material (PCM) in solid–liquid phase change heat storage. Changing the shape of the heat storage tank will change the distance of heat transfer to the phase change material, thus changing the heat storage performance. Therefore, this paper designed ten shapes of trapezoidal tank with different proportions of upper and lower radius. And the heat storage performance of ten cases were investigated through the designed numerical model, whose accuracy is convinced through comparison with experimental results. Many indexes are proposed to evaluate the properties of the latent heat thermal energy storage (LHTES) from the view of whole region, uniformity among subregions, and the storage heat performance of integrity. Except for drawing mass fraction, temperature, and streamline contours, the temperature proportion and the average velocity are proposed to quantitatively evaluate the temperature distribution and convection intensity. The results showed that the cases with larger upper radius are shorter than cases with larger lower radius. In addition, the shortest melting time is 17210 s, which is about 39.2% shorter by 11080 s than that of basic case. The evaluation from the view of uniformity also indicated that properly increasing the PCM amount is beneficial for improving the melting uniformity. The most uniform temperature and mass fraction are case 5 and case 4, respectively, with 12.92% and 38.28% improvement. Finally, one multilayer perceptron (MLP) network model is built to predict the melting fraction and total heat storage. After training, one model with a deviation lower than 10% between simulation and prediction is set up.

Simulation of a composite latent heat storage tank with horizontal baffles and two phase-change temperatures

A composite latent heat storage tank (CLHST) is fabricated using baffles and two phase-change materials (PCMs) with different phase-change temperatures. The performance of the tank is optimized based on both structure and material. This optimization approach is a new integrated method differing from those developed in previous studies, where only a single aspect of the structure/material is considered. Experimental verification and simulation analysis are used to analyze the difference between the integrated and single-structure/material optimization methods and their influence on the thermal properties of the traditional latent heat storage tank (TLHST). The results show that the CLHST exhibits the best characteristics. Compared with the TLHST, the CLHST’s charging quantity increases by 13.6%, the outlet temperature can be increased by 6.5°C, and the utilization rate of PCM exceeds 85%. Moreover, the PCM in the CLHST melts more completely than unilaterally adding baffles. The charging and discharging quantities of the CLHST increase by more than 10% than just using two PCMs. Furthermore, adding baffles can increase the charging quantity by 11% compared to using two PCMs. Evidently, the tank design must be improved considering several aspects, and structural optimization plays a more important role in improving tank performance.

Thermal Performance Assessment for an Active Latent Heat Storage Tank by Using Various Finned-Coil Heat Exchangers

Paraffin-based latent heat storage has a higher thermal capacity than sensible heat storage. Despite that, the actual implementation of paraffin as an active latent heat storage (ALHS) system is limited due to low charging and discharging rate with unequal temperature distribution as the impact of mushy region formation. The present study evaluates the finned-coil heat exchanger for the ALHS tank to overcome the related problems. Three finned-coil configurations are tested experimentally: straight-fin, branched-fin and height-fin. The evaluation uses the ALHS arrangement to assess each configuration's charging/discharging rate. The branched fin provides an equal thermal distribution, promoting a higher final temperature of 112.3°C. It also achieves the highest power rate of 250.5 Watts. The height-fin minimizes the effect of void formation, which maintains a sufficient heat transfer rate during the discharging. However, the average power rate for each model is relatively low. The finding indicates that it is essential to provide adequate heat transfer for the center part of the tank, including adding a branched fin along with coil turn to provide a better heat transfer rate. It boosts the charging/discharging rate, making the system's response time desirable to achieve effective power during the operation.

Thermal performance analysis and optimization of cascaded packed bed latent heat storage tank

The packed bed tank with multiple phase change materials (PCMs) is one of the most efficient latent heat energy storage techniques. This study presents insight into the influence of the latent heat arrangements on the cascaded packed bed tank, providing a new idea for designing multi-PCM packed bed tank, which concerns the screening of PCMs. In this study, a parametric study is conducted to optimize the latent heat of the multi-PCM packed bed tank for the charging and discharging process. A developed two-dimensional model is used to predict the thermal behaviors of the heat transfer fluid and PCMs in packed bed tanks, which is verified by experiment. The results showed that the case with uniform latent heat arrangement exhibits the best overall thermal performance, which obtains the lowest standard deviation of average heat-exchange zone travel velocities for the charging and discharging cycle process. Moreover, the relationship between the efficiency and the standard deviations of the heat-exchange-zone travel velocities is unearthed, and its effectiveness is verified by an actual cascaded PCMs packed bed tank. The charging/discharging/overall efficiency increases with a decrease in the standard deviation of the heat-exchange-zone travel velocities of the PCM layers. This relationship can be used as a new PCM selection method for the cascaded latent heat storage tank. In addition, the actual cascaded packed bed unit with a different latent heat is optimized by variable capsule diameters.

Thermal hysteresis analysis of finned-heat-pipe-assisted latent heat thermal energy storage application for solar water heater system

This work numerically investigates the performance of an innovative compact-design solar water heater (SWH) using evacuated tube heat pipe solar collectors (ETHPSCs) coupled with a latent heat storage tank (LHS tank). This system is thought to be an unwritten fourth generation of solar water heaters known as heat-pipe-assisted thermal batteries. The basic and explicit hypothesis is to store energy than a bulk of hot water, which is the key distinction in compared to the prior classical sorts. Using three phase change materials (PCMs) for high and low solar intensity categories in the tropical region of South East Asia, a computational effort is conducted to model the system and the given temperature headed for the supply output hot water. This research is validated by two interrelated experimental and analytical investigations. According to the results of 12-h charging (melting) process, the maximum mean temperature of the PCMs belongs to PCM C, Rubitherm (RT70HC), which indicates 101 °C during the defined typical high daily solar radiation. This value implies 2.02% error in compared to the reference study. Referring to the solid-liquid interface parameter, the maximum liquefied thickness is also for PCM C with 76 mm thickness. However, reaching the complete melting is required by further studies.

Charging and discharging characteristics of cascaded latent heat storage (CLHS) tank for low-temperature applications

The cascaded latent heat storage (CLHS) system effectively enhanced the thermal and exergy performance in the low-temperature range (e.g. less than 100 °C), wherefore it was particularly significant to reveal effects of system configurations and thermophysical parameters on charging and discharging characteristics. However, few studies focused on the thorough performance analysis and optimization of the CLHS system, especially for the multi-tube and multi-stage latent heat storage tank. In this study, one-tube and four-tube CLHS tanks were built, thermophysical parameters of three kinds of paraffin were characterized, and temperature change trends of PCMs in CLHS tanks were measured. Moreover, the equivalent heat capacity model was used to simulate the three-dimensional unsteady-state CLHS system. Effects of heat transfer fluid (HTF) flow rates, HTF inlet temperatures, number of PCMs stages and layouts of HTF tubes on thermodynamic performance were studied, and the overall energy and exergy performance were evaluated. Compared with one-tube tank, the heat charge/discharge efficiency of four-tube tank increased by 13.4%/12.8%, and the exergy charge efficiency increased by 18.8%. While compared with the one-stage tank, the maximum heat charge efficiency of three-stage tank increased by 9.0%, and the maximum exergy charge efficiency increased by 20.5%. The four-tube three-stage CLHS tank under 80 °C-2 lpm and 10 °C-2 lpm were taken as the optimal heat charge and discharge condition, respectively. In addition, the four-tube three-stage tank with layout 2 had a shorter heat charge/discharge time and higher heat charge/discharge rate, and PCMs with thermal conductivity of 2 W/(m‧K) resulted in better heat charging and discharging performance. Above findings demonstrated that the four-tube three-stage CLHS system owned excellent latent heat storage potential, and provided a theoretical basis for its popularization and application.

Controller Evaluation for Solar-Latent Thermal Energy Applications

In this study, the performance of a self-sufficient controller used for a solar-latent heat domestic hot water (DHW) production unit under real-world operating conditions was analyzed. The unit consists of a flat-plate solar collector and a latent heat storage tank. The controller is powered by a small solar panel and governs the charging and discharging of the system, ensuring maximum solar energy absorption, desired hot water temperature, and constant monitoring of the heat-storage tank’s capacity. The system is compact and can be installed on flat and curved roofs as a direct replacement of conventional solar collectors with heat-energy storage tanks. During testing, all internal and external parameters were monitored using a monitoring system that was also used for emulating user profiles. The controller uses self-learning techniques to adjust its parameters and improves its performance by fine-tuning the control equations to the peculiarities of the specific system and installation location. The system was installed and operated for an extended period to allow for the learning equations to train the system. The results for the first, fifth, and twentieth days of operation are presented in this paper. On the 20th operating day, the controller effectively regulated the heat transfer fluid temperature difference in the charging circuit within the efficient band of 2°C–5°C following the irradiance conditions at the testing area. During discharge, the DHW temperature was regulated between 37°C–40°C, with the user’s set temperature as 38°C. The regulation hysteresis time for the DHW temperature regulation was approximately 5 min. The tests were conducted under real-world operating conditions for the charging of the system, while for the discharging, the user profile was emulated using a test rig.

An experimental investigation of the Evacuated Tube solar collector in conjunction with a latent heat storage tank

An experimental investigation of the Evacuated Tube solar collector in conjunction with a latent heat storage tank

Solidification and melting of sugar alcohol with additives in a latent heat storage tank

Solidification and melting of sugar alcohol with additives in a latent heat storage tank

Influence investigation of hot molten salt temperature on operation and mechanical behaviours of latent heat storage tank

This paper presents an effect evaluation of initial hot molten salt temperature on behaviours of a thermally stratified latent heat storage (LHS) tank using phase change material (PCM) capsules. The influence of initial hot molten salt temperature on the heat storage, heat release and mechanical behaviours of the LHS tank are evaluated. The simulation results show that the initial hot molten salt temperature has relatively great influences on both the heat storage and heat release behaviours of the LHS tank. A higher initial hot molten salt temperature can reduce both the thermocline thickness and total heat storage duration of the tank in the heat storage process, and can increase the maximum heat storage and heat release powers, final effective heat storage and heat release quantities and peak maximum mechanical stress of the tank. When the initial hot molten salt temperature reaches 873.0 K, the peak maximum mechanical stress of the tank is 141.7 MPa. Therefore, to achieve a better operation behaviour of the LHS tank, the initial hot molten salt temperature should be appropriately increased while ensuring that the peak maximum mechanical stress of the tank does not exceed the yield stress and a certain margin can be kept.

An experimental and numerical analysis of an improved thermal storage tank with encapsulated PCM for use in retrofitted buildings for heating

In the building sector, 40% of final energy is used for heating and cooling. Up to 75% of this is used in residential buildings. It is necessary to take a step forward and reduce this share of energy consumption, in particular through the use of efficient technologies and their integration into the system of renovation of residential buildings, which is a major challenge for future research in this field. An important technology for achieving this goal is heat storage, where the use of phase change materials as heat storage material allows for a higher energy density. The main advantage of using heat storage technologies is the solution of the problem of the temporal divergence of energy demand and the possibility to use a higher share of energy from renewable sources, e.g. such as solar energy. Solar energy as a resource can be used during the day, when production is higher than demand, which allows storing energy for a later period of demand. This also improves the efficiency of the heat generators in the system in which the thermal storage is integrated. The focus of the present study is on the investigation of phase change materials (PCM) as thermal storage in the conventional water tank storage. A comparison was made between a conventional sensible thermal energy storage tank and a hybrid latent heat storage tank, where the PCM was encapsulated in cylindrical nodules and integrated into the water tank to improve the energy density of the conventional water heat storage tank. The results of the experiment showed that 15% of the PCM inside the water storage tank increases heat storage for 70% over conventional heat storage tank with water only inside. The measured experimental data were compared with the simulation results from TRNSYS model to enable further analysis and improvement of the heat storage tank with PCM integration.

Analysis and Simulation of an Absorption Cooling System Using a Latent Heat Storage Tank and a Tempering Valve

The energy consumption for space cooling is growing faster than for any other end-use in buildings, more than tripling between 1990 and 2016. Energy efficiency is an important topic in the drive to reduce the consumption of electricity, particularly in air conditioning. This paper presents a simulation of an absorption cooling system with a parabolic trough collector under dynamic conditions using TRaNsient SYstem Simulation (TRNSYS) software. The thermal analysis seeks to evaluate a storage tank at three different configurations: (1) sensible heat, (2) latent heat, and (3) latent heat incorporating a tempering valve. The latent heat storage tank is a rectangular heat exchanger using MgCl2·6H2O as the phase change material, programmed in EES software; in addition, water and synthetic organic fluid were analyzed as heating fluids. The process was analyzed while varying the solar collector area from 20 to 40 m2 and the storage tank volume from 0.25 to 0.75 m3. The results showed that the solar collector of configuration 1 is unable to satisfy the energy demand. Configuration 2 can satisfy the demand with water and a storage tank volume above 0.50 m3 and 30 m2, while configuration 3 can satisfy the demand above 0.50 m3 and 20 m2 with water.

Integration of solar latent heat storage towards optimal small-scale combined heat and power generation by Organic Rankine Cycle

Abstract Thermal energy and distributed electricity demand are continuously increased in areas poorly served by a centralized power grid. In many cases, the deployment of the electricity grid is not economically feasible. Small-scale Organic Rankine Cycle (ORC) appears as a promising technology that can be operated by solar energy, providing combined heat and power (CHP) generation. Additionally, thermal energy storage can ensure stable and continuous operation in case of scarce thermal energy availability. This paper evaluates the potential application of latent heat storage to enhance solar ORC performance at operating temperatures between 80 °C and 140 °C, aiming at improving the efficiency and capacity of ORC for low-cost non-concentrating solar-thermal collectors. Three thermal energy storage scenarios are considered. Scenario 1 and 2 consist of reference cases based on a solar ORC system integrated with a conventional hot water tank and a pressurised water tank. Scenario 3 implements a storage unit based on a phase change material. The simulation was carried out through models developed in TRNSYS for solar energy balance and ASPEN for ORC system performance. The results show that solar latent heat storage tank can provide 54% of useful collector gains with a higher and narrower temperature range in the evaporator, increasing the annual thermal energy capacity by 19%, reducing annual heat losses by 66% and decreasing the investment cost by 50% in comparison with a pressurised water tank. It also allows increasing the efficiency of ORC cycle by approximately 18% (from 8.9% to 10.5%) with a higher net generated power than a conventional water tank integration, scaled up from 498 W to 1628 W. These results highlight the potential benefits that latent heat integration provides to improve the low-cost solar ORC performance for powering electricity and thermal energy supply.

Peripheral Isothermal System of Heat Gain Storage for Thermal Stability in Low-Energy Buildings

The problem of heat storage in low- or ultra-low-energy houses is becoming a crucial issue. The general purpose of this study was to determine the potential for utilising heat gain recovery in a building. The proposed solution is based on an auxiliary latent heat storage tank using paraffin RT24. The tank is connected to an integrated heat recovery system that supplies heat from the internal loop of a mechanical ventilation system. The storage capacity of the tank was determined using the proposed parameter “excess of heat gains” of the thermal zone, and was obtained by measurement. The detailed construction of the tank, the phase change material properties and the quantity were proposed. The data that was collected allowed for the calculation of the temporary charging level as well as the overall seasonal energy stored in the tank. It was shown that during the heating season, the temperature could rise above the set-up value of 20 °C by as much as 8 K at maximum. Although the analysed building was characterised by heavy construction and high thermal mass, the additional heat could be effectively stored and utilised to cover the energy demand of the zone at the level of 88 MJ/a and 208 MJ/a, depending on the airflow rate between the rooms and the heat exchanger, for 140 and 420 m3/h, respectively. The expected energy effect for a low thermal mass construction, e.g., a timber frame was much higher and the results obtained by using the numerical simulation were 116 MJ/a for 140 m3/h, and 273 MJ/a for 420 m3/h, respectively.