Latent Heat Thermal Energy Storage Device Research Articles

Charging/discharging performance and corrosion behavior of a novel latent heat thermal energy storage device with different fin plate materials

The use of low-grade industrial waste heat for building heating could facilitate the decarbonization of heat sector, which accounts for a large share of energy consumption worldwide. However, the uncontrollable fluctuation characteristics of heat source and mismatch between energy supply and demand greatly limit its large-scale application. Notably, latent heat thermal energy storage (LHTES) technology, showing remarkable advantages in terms of energy storage density, heat storage temperature (nearly constant), technology maturity and cost, could effectively solve the above problem. Hence, this work specially focused on LHTES device that utilized fin plate for improving performance of heat harvesting and reuse. Furthermore, charging/discharging performance and corrosion behavior of a novel device with different fin plate materials (brass, aluminum and stainless steel) were investigated. Results showed that temperature difference between plate surface and melting point above 10 °C effectively shortened charging time more than 45.7 %. A higher thermal conductivity of fin material contributed to a better thermal performance. Aluminum and stainless steel preferred to be used as fin plate materials of targeted hydrated salt owing to their low corrosion rate of 0.016 and 0.002 mg/(cm2·yr), respectively. This work was expected to provide a guidance on designing a LHTES device applied in building heating.

Metal foam reinforced phase change material energy storage device: A collaborative optimization strategy for porosity and container shape

Latent heat thermal energy storage (LHTES) is often employed in solar energy storage systems to improve efficiency. This method uses phase change materials (PCM) as heat storage medium, often augmented with metal foam to optimize heat transfer. In this paper, we introduce a novel approach of altering the container shape to enhance the heat storage effectiveness. LHTES tank with different coning coefficients (C) is designed by reducing the hard-to-melt bottom region. Based on the finite volume, volume averaging, and enthalpy porosity method, the transformation process of a simplified two-dimensional model of the LHTES tank is numerically simulated. Analysis focuses on the evolution of liquid-solid interface, liquid fraction, temperature field, and heat storage performance. The results indicate that the bottom region area enhances the heat storage performance when C < 0.375, whereas for C ≥ 0.375, it hinders heat transfer. When the porosity is 0.93, the newly deformed LHTES tank demonstrates a reduction of up to 6.2% in melting time compared with the basic model. Additionally, it achieves 98% of the basic thermal energy storage. Furthermore, metal foams with varying porosity are analyzed, and a cooperative optimization matching strategy between porosity and shape is obtained. By reducing the porosity to 0.87, the melting time can achieve a 61% reduction at C = 0.125. This study is expected to provide new insights and references for optimizing the design of LHTES devices.

Environment-friendly efficient thermal energy storage paradigm based on sugarcane-derived eco-ceramics phase change composites: From material to device

Latent heat thermal energy storage (LHTES) technology can well alleviate the imbalance between intermittent energy supply and demand. However, the low thermal conductivity and poor shape stability of phase change materials (PCMs) seriously limit their practical applications. Here, sugarcane-derived biomimetic SiC ceramics are proposed for fast and efficient thermal energy storage. After loading paraffin, the composite phase change materials (CPCMs) demonstrate a high thermal conductivity of 10.34 W/mK and a high energy density of 151.20 kJ/kg at a porosity of 85%, outperforming state-of-the-art ceramics-based CPCMs. This benefits from continuous SiC skeletons composed of tightly stacked grains, so that both boundary and contact thermal resistances are reduced even at a high porosity. No prominent decay of thermal conductivity and energy storage density after 500 charging-discharging cycles, as well as good leakage resistance, confirm the good cyclic stability of proposed CPCMs. High-performance CPCMs are further packed into a fixed-bed LHTES device and investigated both experimentally and numerically. The melting time of LHTES device is prominently reduced by 44.3% benefiting from synergy of high thermal conductivity and non-coaxial arrangement of packed CPCMs cells. This work opens a new route for rapid thermal energy storage based on sugarcane-derived biomimetic materials.

Performance study and heating simulation on novel latent heat thermal energy storage device suit for air source heat pump

Latent heat thermal energy storage (LHTES) technology can solve the problem of limited performance improvement of air source heat pump (ASHP) systems due to the time mismatch between building energy demand and operational efficiency in low temperatures. Therefore, this paper proposes a LHTES device suitable for the ASHP system. Firstly, the internal structure is obtained by ANSYS numerical simulation. Furthermore, experiments are carried out to verify the heat storage and release performance of the proposed device under different inlet water temperatures and flow rates. Finally, the operational effects of the ASHP-LHTES combined heating system are analyzed by TRNSYS. The design results show that a liquid phase ratio of 97.24 % is achieved with a pipe diameter of 16 mm, tube pitch of 70 mm, and 1/2 horizontal tube fins. Experiment results exhibit that the proposed device performs excellently under optimal conditions, with 89.7 % effective heat storage efficiency and 92.5 % available heat release efficiency. TRNSYS results indicate that the annual operating cost of the combined heating system saves 32.9 % compared with the single ASHP heating system, although the power consumption increases by 24.4 %. This study can provide theoretical support for the application of low-temperature LHTES devices in the ASHP system.

Performance investigation of a biomimetic latent heat thermal energy storage device for waste heat recovery in data centers

Improving the power usage effectiveness of data centers has become a significant challenge for carbon peaking and carbon neutrality. To address this, here we propose a single-phase immersion cooling system with latent heat thermal energy storage (LHTES) devices to recover waste heat. Furthermore, an innovative LHTES device with palmate leaf-shaped fins is designed by bionic techniques. The phase change behavior and thermal transport patterns of biomimetic and traditional LHTES devices are investigated, and the effects of the arrangement and working conditions are revealed. Additionally, the proposed solution's application prospect and economy are presented. The results indicate that the performance of palmate leaf-shaped finned LHTES devices is significantly enhanced compared to traditional ones, whose charge and discharge durations reduce by 21.0 % and 38.2 %, respectively. Moreover, the natural convection development enhances the melting performance, but its effect on solidification processes is insignificant. Considering the trade-off between power consumption and LHTES efficiency, a horizontal biomimetic LHTES device with a flow rate of 20 L/min and a large heat-transfer temperature difference is suggested in practical engineering. Notably, the maximum reduction in annual power consumption for using biomimetic LHTES devices is 2397.4 kW·h, and the minimum payback period is only 2.0 years.

Development of multilayer interacted characteristic melting region for large-scale horizontal latent heat storage investigation

The development of thermal energy storage (TES) technology has aroused extensive attentions due to its considerable energy-saving benefits. In the current work, the strategy of multilayer interacted characteristic melting region (MCR) was established to characterize large-scale horizontal latent heat thermal energy storage (LHTES). Based on the shell-and-tube configuration, the influence of multilayer interaction was numerically investigated and the single-tube approach was found to be inapplicable to characterize the melting performance of horizontal LHTES devices. Furthermore, the characterization strategy with MCR was applied to reexamine typical eccentric design and quite different rules were concluded. The melting performance of cases with intersection angles ranging from 60° to 120° and the tube eccentricity ranging from 0 to 0.6 were established and compared. For the design of eccentric side fins, horizontally spreading heat transfer structures was found to be a better choice, which extended the area dominated by the natural convection above the tubes. The full melting time of the case with the intersection angle of 90° was reduced by 2.9 % and 6.2 % compared with the case with intersection angles of 60° and 120°, respectively. The eccentric tube arrangement was found to have negative influence on the melting performance for large-scale horizontal LHTES devices. The full melting time of the case with the fin-tubes eccentricity of 0.6 was increased by 23.3 % compared with the concentric design.

Melting and solidification characteristics of a semi-rotational eccentric tube horizontal latent heat thermal energy storage

• Effect of eccentricity was investigated for the latent heat thermal energy storage. • Bottom eccentricity significantly improved the melting process. • Top eccentricity showed the potential to enhance the solidification process. • A novel semi-rotation of the storage system was proposed. • An optimum eccentricity was justified, and key parameters were investigated. Research showed that bottom eccentricity improved the melting performance in the horizontal shell-and-tube latent heat thermal energy storage (LHTES) system. However, it largely reduced the solidification performance. To solve this problem, this study investigated the effects of different eccentric positions of the inner heat transfer fluid (HTF) tube on the thermal performance of a horizontal shell-and-tube LHTES system during the melting and solidification processes. A novel technique with the intermittent rotation of the LHTES device was proposed to take the advantage of eccentric tube configurations for enhancing both the melting process during charging and the solidification process during discharging. Numerical simulations were conducted and validated in the FLUENT application of ANSYS software by utilizing the enthalpy-porosity method. Liquid fraction, average temperature, energy storage rate, and velocity distribution were used to evaluate the LHTES system thermal performance. Results showed that the bottom eccentricity significantly improved the melting process, however, it slowed down the solidification process. But the further study found that the top eccentricity could enhance the solidification process. Based on the average energy storage rate, the optimum bottom eccentricity laid between 0.60 and 0.75 for the charging process, which improved the melting rate by 64–74%. However, the optimal top eccentricity was between −0.15 and −0.30 for the discharging process. The proposed novel rotational technique well adapted the bottom eccentricity to improve the melting process during charging and the top eccentricity to enhance the solidification process during discharging. It was found that an optimal eccentricity of 0.30 could well tradeoff between the bottom eccentricity for charging and top eccentricity for discharging process in the proposed approach. Both the HTF cooling temperature and shell-to-tube radius ratio did not show a significant impact on the optimal eccentricity of the LHTES system.

Technical assessment of phase change material thermal expansion for passive solar tracking in residential thermal energy storage applications

Phase changing materials (PCMs) have been widely investigated for Latent Heat Thermal Energy Storage (LHTES) applications in the last decades, due to their inherently high volumetric storage density and thermal control features. Nonetheless, PCMs and their related LHTES systems still require significant scientific and technical advancements and more efficient market penetration strategies, to be able to play a key role in the massive transition towards renewable energy that is expected to take place in EU in the near future. Some of the most investigated PCMs for low to medium temperature LHTES belong to the alkanes/paraffins family, which is characterized by a relatively high volumetric expansion solid-to-liquid phase transition. This is generally considered a side effect, which should be accounted for to avoid damaging the containment structure. However, it could also represent an opportunity to add extra functionalities and increase the overall efficiency of LHTES systems.In this paper, we evaluate the feasibility of using the mechanical work generated by the volumetric expansion cycles in a paraffin-based LHTES device for photovoltaic (PV) solar tracking purposes, thus assuming a novel paradigm for the efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical approach. Accurate charge/discharge profiles of the TES are implemented, considering data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this analysis allow to estimate the tracking capability of the chosen PCM in terms of number/surface of actuated PV panels.

Numerical investigation of melting enhancement for paraffin in an innovative finned-plate latent heat thermal energy storage unit

Latent heat thermal energy storage (LHTES) is essential for eliminating the discrepancy between energy supply and demand as well as for improving the utilization rate of low-grade industrial waste heat. This paper aims to solve the problem of long energy charge time in finned-plate LHTES device. In the present study, the LHTES unit is designed with three different orientations of the fin plates: A denotes a horizontal unit with fins; B and C denote vertical units with transverse and longitudinal fins, respectively. First, the melting process with different sizes and distributions of fins is investigated and the effect of fin thickness on the melting time is analysed. When obtaining the optimized fin parameters, two potential strengthening strategies (rippling fins and fins of non-equal length) are applied to further improve the melting performance of the device. The results show that long and thick fins can remarkably ameliorate the melting performance of paraffin, and the melting rate for the three orientations is of the order A>C>B. Compared with the finless structure, the melting rate increased by 4.52, 3.63, and 3.62 times for the three orientations of A, B, and C, respectively, for a fin length of 50 mm and fin number equal to 10. The use of rippling fins can reduce the melting time up to 4.1%, 5.4%, and 10.7% for the three orientations of A, B, and C, respectively, compared to using equal-length homogeneous fins with a thickness of 3 mm. Moreover, for orientations A and B, by adjusting fin length arrangement or using full fins, 11.4 and 46% reduction in melting time could be achieved compared with the configuration with a fin length of 50 mm and a thickness of 3 mm. The proposed innovative finned-plate LHTES device provides a useful reference and groundwork for the future large-scale utilization of the LHTES system.

A first principles framework to predict the transient performance of latent heat thermal energy storage

Thermal energy storage (TES) is increasingly recognized as an essential component of efficient Combined Heat and Power (CHP), Concentrated Solar Power (CSP), Heating Ventilation and Air Conditioning (HVAC), and refrigeration as it reduces peak demand while helping to manage intermittent availability of energy (e.g., from solar or wind). Latent Heat Thermal Energy Storage (LHTES) is a viable option because of its high energy storage density. Parametric analysis of LHTES in terms of dimensionless numbers is highly desired as a tool to model LHTES systems. One approach is to develop a model equation so as to minimize the error between the model and data obtained from experiments or simulations. While this approach can produce an accurate correlation applicable within the range of data used for its creation, it does not provide physical understanding of the rate-limiting process controlling the transient behavior of the device. In this paper we present an alternative approach whereby the potential rate-limiting processes are identified from first principles and then the key process is determined as a function of time as a LHTES device is charged. For example, in a simple geometry, the melt-fraction can be expected to vary linearly in time if the heat transfer rate is limited by natural convection of the phase changing material and we show it scales with the PCM Grashof number asGrp1 and PCM Prandtl number asPrp(1∕3). On the other hand, if surface area of solid PCM limits the heat transfer rate, the melt fraction increases asymptotically to reach full melting. The existence of these linear and asymptotic regions and theGrp1Prp1∕3 shape of the melt fraction curve is verified using our database of 64 simulations. Of practical importance in designing LHTES devices is the melt fraction at which the heat transfer rate ceases to be limited by convection, after which the heat storage rate deteriorates. For our geometry, this is found to be about 90%. This test case of our methodology shows the value of our approach, that predicting heat storage rate based on the rate-limiting physical phenomenon as a function of time is an effective approach to modeling LHTES devices.

Numerical investigation on latent heat thermal energy storage in a phase change material using a heat exchanger

AbstractThe use of a heat exchanger using phase change material (PCM) is an example of latent heat thermal energy storage (LHTES). In this study, the charging of PCM (RT50) is studied in a double pipe heat exchanger. The designing of the heat exchanger needs to be optimized for operating and boundary conditions to store latent heat efficiently. The size of the equipment and the amount of PCM are also important to calculate the latent heat storage capacity of the LHTES device. In this study, the amount of PCM taken is quite high to avoid sensible heat transfer and to maximize the heat content of PCM. The charging process of PCM is numerically simulated using an enthalpy‐porosity model. The study includes the effect of inlet temperature and flow rate of high‐temperature‐fluid (HTF) and concludes that both play an important role in determining the charging time. The continuous increase in inlet temperature of HTF can decrease the charging time of PCM in the heat exchanger. However, the continuous increase in the HTF flow rate cannot show the same effect. The charging time can only be minimized with a specified flow rate regime for a specific inlet temperature of HTF. These factors consequently affect the efficiency of the heat exchanger.

Numerical analysis and improvement of the thermal performance in a latent heat thermal energy storage device with spiderweb-like fins

• A bionic spiderweb-like fin is designed and optimized for latent heat storage. • A solidification model with consideration of free convection is developed. • Free convection is conducive to the overall energy discharging performance. • Spiderweb-like fin with a bifurcation number of 8 maximizes thermal performance. • Solidification time reduces by 47.9% and discharging rate increases by 1.44 times. Solidification enhancement is an essential topic for sustainable energy development. An innovative latent heat thermal energy storage (LHTES) device employing spiderweb-like fins is designed to improve solidification efficiency. The numerical solidification process of the current LHTES device is performed and compared to that with plate fins occupying an identical fin volume. Moreover, the solidification strengthening mechanism is revealed as well as the role of free convection in the heat release performance. Finally, the configuration of the spiderweb-like fin is improved, and the solidification efficiency of LHTES devices is evaluated. The results imply that the LHTES device with spiderweb-like fins improves the solidification performance by eliminating the heat transfer hysteresis zone. The dominant heat transfer mechanism of the solidification process shifts from convective heat transfer in the early stages to heat conduction in the later stages. More significantly, the free convection strengthens the solidification performance of the LHTES device with plate fins but has little effect on that with spiderweb-like fins. A spiderweb-like fin with the bifurcation number of 8 is suggested for maximizing the discharging performance. Compared to the plate fin, the full solidification time of the improved LHTES device with spiderweb-like fins is shortened by 47.9%, and its corresponding time-averaged heat release rate increases by 1.44 times.

Numerical and experimental investigations of latent thermal energy storage device based on a flat micro-heat pipe array–metal foam composite structure

Latent heat thermal energy storage (LHTES) is crucial in the application of renewable energy and waste heat recovery. A novel LHTES device with a flat micro-heat pipe array (FMHPA)–metal foam composite structure is designed in this study to obtain excellent heat transfer performance. An evaluation standard called integrated power is proposed to assess and compare the structural advantages of the LHTES device with others. Performances of FMHPA, temperature distribution, effort of inlet temperature and velocity of heat transfer fluid (HTF) are also studied in the experiments. A three-dimensional numerical model is developed to investigate the effort of porosity and pore density of metal foam on the charging process. Results show that the FMHPA–copper foam composite structure improves the performance of the LHTES device. This structure exhibits stronger heat transfer performance than that of other devices. The increasing inlet temperature of HTF has a better promotion effect on power than raising HTF velocity. High porosity is conducive to natural convection but detrimental to heat conduction. High pore density is disadvantageous to natural convection and does not affect heat conduction. • Strengthen of flat micro-heat pipe arrays and metal foam are studied. • The temperature distribution of PCM are experimentally studied. • The effect of temperature and velocity of HTF are experimentally studied. • The porosity and pore density of copper foam are numerically studied. • An evaluation standard is proposed to evaluate the structural advantages.

Numerical Investigation on a Packed-Bed LHTES System Integrated into a Micro Electrical and Thermal Grid

Currently, energy storage systems are considered a key solution when mismatch occurs between energy supply and demand, allowing a more efficient energy deployment and use. The present paper is focused on the study of a latent heat thermal energy storage (LHTES) system based on a packed bed of encapsulated phase change material (PCM) of spherical shape, conceived as an auxiliary component of a micro-grid to be built in a Research Center located in southwestern Sardinia (Italy). The main purpose of this work was to perform numerical simulations for predicting the performance of the TES system, designed to store the surplus thermal energy produced during the weekend by a heat pump fed by a photovoltaic (PV) plant. The stored energy would then be utilized during the weekdays to integrate the air-conditioning system supply. The numerical simulations were based on a one-dimensional (1-D) two-equation transient model, able to return the thermocline profile of the water and the PCM separately. The behavior of the LHTES device during charge and discharge phases was reproduced, as well as during the standby periods. Finally, two characteristic indexes of the PV system were evaluated, to investigate the effect of TES on grid interchanges, self-consumption, and self-sufficiency.

Silicon as a Phase Change Material: Performance of h-BN Ceramic During Multi-Cycle Melting/Solidification of Silicon

Silicon has recently been recognized as a potentially attractive phase change material for ultra-high-temperature latent heat thermal energy storage (LHTES) and conversion systems. It has been proposed that the utilization of silicon’s latent heat should drastically increase the performance of LHTES devices in terms of operational temperatures and available energy density. Nevertheless, in order to ensure a high reliability and long lifetime of the system, proper ceramic materials that are able to withstand contact heating and cooling cycles during consecutive melting/solidification steps need to be examined and selected. Previously, we have documented that hexagonal boron nitride (h-BN) is the only ceramic that shows non-wettability and limited reactivity in contact with molten silicon at temperatures up to 1650°C. In this work, we present for the first time the results of experimental research on the performance of a Si/h-BN system upon cycling melting/solidification processes. For this reason, the Si/h-BN couple was subjected to a sessile drop experiment containing 15 cycles of heating/cooling between 1300°C and 1450°C. During the test, temperatures of specific events as well as contact angle values were recorded. After the test, the structure and surface morphology of the solidified Si/h-BN couple were characterized by means of scanning electron microscopy.

Heat transfer enhancement induced by the geometry of a LHTES device

In the present contribution the authors investigate by means of numerical simulations the thermal performance of two geometries of Latent Heat Thermal Energy Storage (LHTES). The numerical model takes into account the mass, momentum and energy equations for the PCM together with an Entalphy-Porosity model for the phase change and a Bussinesq approximation for the buoyancy force. Indeed in such a system the convective motion within the melted PCM plays an important role, as confirmed by several studies. The scope of the research has been the enhancement of heat transfer performance of LHTES increasing the convection by means of modifications on the shape of the PCM enclosure. In particular, in this study two geometries have been considered to investigate the influence of the convective motion on the overall melting time. The first case consists of two concentric cylinders with the axis aligned with the vertical direction, in order to realize an internal heating of the Phase Change Material (PCM) that is confined between the internal and the external cylinder. It is a well-known ”shell-and-tube” configuration, generally adopted in LHTES systems, even in CSP applications. In the second case, the authors propose a simple cylindrical geometry filled with the PCM, with the cylinder axis aligned with the vertical position. Thus, the heated surface corresponds to the external lateral surface of the cylinder. The PCM volume (V) and the net heat transfer surface (A) have been kept constant in the two cases, in order to be able to compare them under the same operative conditions. The tests reveal a sensible difference between the thermal performance of the two proposed solutions. The external heating configuration shows an important enhancement of the convective motion within the PCM that induces a more efficient heat transfer with respect to the standard ”shell-and-tube” configuration. The complete melting time of the PCM with external heating is reduced by about 50%.

Experimental investigation and modelling of a low temperature PCM thermal energy exchange and storage system

A real-scale latent heat thermal energy storage (LHTES) device has been designed and set up for air-cooling in the housing sector. This system uses the thermal gap between night-time and daytime outdoor air to refresh the indoor air. The air passes along a box-section horizontal tube bundle filled with paraffin wax (phase change material). To develop a design tool, a one-dimensional model is proposed which describes the thermal behaviour of the LHTES device as the paraffin wax melts. This model takes into account the close-contact exchange between the PCM and the surface of the tubes due to the decreasing density of the PCM as it melts, and the corresponding buoyancy phenomenon. An enthalpy formulation is used for the PCM energy balance equation. An experimental study is performed which validates the modelling approach. This model will be used to simulate the LHTES devices of two single family houses (Napevomo, Sumbiosi). Finally, a first illustrative application of the simulation model of LHTES device is developed by coupling it with a basic mono-zone building performance programme.

Free cooling of a building using PCM heat storage integrated into the ventilation system

This article presents a study of the free cooling of a low-energy building using a latent-heat thermal energy storage (LHTES) device integrated into a mechanical ventilation system. The cylindrical LHTES device was filled with spheres of encapsulated RT20 paraffin, a phase-change material (PCM). A numerical model of the LHTES was developed to identify the parameters that have an influence on the LHTES’s thermal response, to determine the optimum phase-change temperature and to form the LHTES’s temperature-response function. The last of these defines the LHTES’s outlet-air temperature for a periodic variation of the inlet ambient-air temperature and the defined operating conditions. The temperature-response function was then integrated into the TRNSYS building thermal response model. Numerical simulations showed that a PCM with a melting temperature between 20 and 22 °C is the most suitable for free cooling in the case of a continental climate. The analyses of the temperatures in a low-energy building showed that free cooling with an LHTES is an effective cooling technique. Suitable thermal comfort conditions in the presented case-study building could be achieved using an LHTES with 6.4 kg of PCM per square metre of floor area.