Phase Change Materials For Thermal Storage Research Articles

PoDIT: Portable Device for Indoor Temperature Stabilization: Concept and Theoretical Performance Assessment

This work introduces the concept of a new Portable Device for Indoor Temperature Stabilization (PoDIT), to be considered as a low-cost, quick and easy to implement remediation strategy when, for social, economic, or technical reasons, the improvement of the building envelope and/or the adoption of air conditioning are not possible. The main goal is to attenuate the maximum indoor temperature during summer and/or heat waves. The system, which is modular, consists of a certain mass of encaged phase change material (PCM) that stays indoors during the daytime and is transported to the outdoors (e.g., a balcony) during the night to discharge the heat accumulated during the daytime. Both natural convection and forced convection variants were considered. The results showed that, in the configurations and for the reference room and weather considered, the adopting 4 modules of the device can lead to reductions in the maximum room air temperature close to 3 °C, with natural convection. Adopting a fan to impose forced convection at the surfaces of the device can lead to temperature attenuations in excess of 4 °C, as it ensures full solid–liquid commuting and therefore optimal use of the PCM thermal storage capability.

Performance investigation and sensitivity analysis of shell-and-tube phase change material thermal energy storage

This paper presents the development, experimental testing, and numerical investigation of water-based phase change material (PCM) thermal energy storage (TES) using the shell-and-tube design with different tube layouts including single serpentine, double serpentine, and spiral. Sodium acetate trihydrate (SAT) with a melting temperature of 58 °C was used as the storage medium. The major contribution of this study is the sensitivity analysis and performance comparison of the shell-and-tube PCM TES units with different tube layouts. A quasi-three-dimensional dynamic model of the PCM TES unit was developed and used to predict the performance of the TES unit under different design and operating conditions, which was validated against the experimental data. A global sensitivity analysis was implemented to quantify the influence of the design parameters on the performance of the PCM TES unit. The results showed that the inlet water temperature was the most influential parameter, followed by the tube length, water flow rate, tube layout, and PCM thermal conductivity. The PCM TES module with the spiral tube layout and the double serpentine tube layout generally outperformed that with the single serpentine tube layout. The time required to charge the PCM to a liquid fraction of 0.95 was reduced by 16.0% if changing the tube layout from single serpentine to spiral and when the tube length was 4,055 mm. The findings obtained from this study could be potentially used to guide and facilitate the design of the shell-and-tube PCM TES units.

Metal-Organic Phase-Change Materials for Thermal Energy Storage.

The development of materials that reversibly store high densities of thermal energy is critical to the more efficient and sustainable utilization of energy. Herein, we investigate metal-organic compounds as a new class of solid-liquid phase-change materials (PCMs) for thermal energy storage. Specifically, we show that isostructural series of divalent metal amide complexes featuring extended hydrogen bond networks can undergo tunable, high-enthalpy melting transitions over a wide temperature range. Moreover, these coordination compounds provide a powerful platform to explore the specific factors that contribute to the energy density and entropy of metal-organic PCMs. Through a systematic analysis of the structural and thermochemical properties of these compounds, we investigated the influence of coordination bonds, hydrogen-bond networks, neutral organic ligands, and outer-sphere anions on their phase-change thermodynamics. In particular, we identify the importance of high densities of coordination bonds and hydrogen bonds to achieving a high PCM energy density, and we show how metal-dependent changes to the local coordination environment during melting impact the entropy and enthalpy of metal-organic PCMs. These results highlight the potential of manipulating order-disorder phase transitions in metal-organic materials for thermal energy storage.

Experimental investigation and two-level model-based optimisation of a solar photovoltaic thermal collector coupled with phase change material thermal energy storage

This paper presents an experimental investigation of an air-based solar photovoltaic thermal (PVT) collector coupled with a centralised phase change material (PCM) thermal energy storage (TES) system, and the development of a model-based strategy to facilitate optimisation of the PVT-PCM systems. The originality of this study includes using statistical analysis to reveal the practical deficiencies of PVT-PCM systems, and orientating the system optimisation using a two-level model-based strategy. A set of experiments were designed and performed based on a lab-scale experimental facility to examine both electrical and thermal performance of the PVT-PCM system with various air flow rates, and different slopes and orientations of the PVT collector. The optimisation strategy was developed to identify the optimal design and at the same time to generate a performance map that can be used for control optimisation. The experimental results showed that there existed an optimal air flow rate for the PVT-PCM system under a given solar radiation for maximal overall system efficiency. To better utilise the PCM latent heat storage capacity, both the useful thermal energy generated from the PVT collector and the heat transfer within the TES unit need to be optimised. Compared to a baseline case without optimisation, the average overall system efficiency increased from 37.6% to 40.2%, and the average daily utilisation ratio of the latent TES capacity improved from 13.3% to 79.5%.

Photothermal properties and photothermal conversion performance of nano-enhanced paraffin as a phase change thermal energy storage material

The paraffin incorporation in device of glass envelope allows the thermal regulation, increasing the thermal comfort and energy efficiency of buildings. Addition of nanoparticles has an advanced application prospect in the field of solar energy collection and storage capacity of glass envelope systems filled with paraffin. The present study conducts an experimental and numerical investigation in order to study photothermal properties of the paraffin incorporated ZnO or CuO nanoparticles. An experimental and theoretical model is also established to analyze the effect of nanoparticles on the thermophysical and optical properties of nano-enhanced paraffin. The results show that due to the presence of the nanoparticles, the transmittance of nano-enhanced paraffin decreases. On the other hand, temperature increment results in a small rise in the transmittance of nano-enhanced paraffin. The results also indicate that the utilized nanoparticles exhibit a higher attenuation to light, and the scattering effect cannot be avoided, where the maximum scattering proportion is 6.3%. Improvements of 5.87 and 13.12% in thermal conductivity of nano-enhanced paraffin at the volume fraction of 5 × 10−4 vol% are obtained using ZnO and CuO nanoparticles, respectively. The evaluation of the photothermal performance based on the temperature variations shows that the CuO/paraffin can absorb more solar energy. The optimum photothermal performance can be satisfied by the nanoparticle volume fraction ranging from 5 × 10−4 to 1.5 × 10−3 vol%.

Interfacial thermal conductance across hexagonal boron nitride & paraffin based thermal energy storage materials

It is of vital importance to understand the interfacial thermal conductance between the high thermal conductivity fillers and the phase change thermal energy storage materials in order to enhance the energy storage efficiency. The interfacial thermal conductance across low-dimensional hexagonal boron nitride layers (h-BN) and n-octadecane was calculated with reverse non-equilibrium molecular dynamics methods in this paper. The influences of size effect, molecular arrangement of n-octadecane, layer number of h-BN as well as the defects modified with various functional groups on the interfacial thermal conductance within the temperature range from 273.15 to 373.15 K were investigated, respectively. The results showed that the interfacial thermal conductance of all systems increase with rising temperature and the size effect is inconspicuous. And systems with n-octadecane molecules parallel to the h-BN surface possess the highest interfacial thermal conductance with respect to the vertical and amorphous arrangements. In addition, the interfacial thermal conductance will reduce when the layer number of h-BN increases. In terms of the effect of defects, the systems with h-BN containing the defects modified with hydrogen atoms, i.e., lighter atom, possess higher interfacial thermal conductance. At last, for interpreting deeper mechanism, the vibration power spectrum of the velocity autocorrelation function and the components in different directions were also calculated.

Conceptualization and analysis of a novel combined sorption and phase-change material thermal storage system

Abstract A new sorption-based thermal storage cycle is proposed. Energy is stored chemically by separating the constituents of highly non-ideal solutions, yielding much lower stand-by losses than in conventional approaches. The cycle avoids limitations of previously proposed sorption-based storage cycles by using a liquid-liquid mixer, and does not require a thermal source during discharge. A criterion based on a second law analysis is developed to evaluate potential working fluids for the cycle. Different cycle configurations are analyzed. An enhanced combined sorption and phase-change material (PCM) cycle is also investigated and compared with conventional thermal storage systems. For delivering 100 GJ of energy after 8 months, the combined cycle has an efficiency of 11% and lower storage volumes (down to 0.1 ×) than conventional thermal storage technologies. The energy density of the combined sorption-PCM system is 30 kWh m − 3.

Photovoltaic Greenhouse Load Control Based on Phase Change Thermal Storage Method

Aiming at the problem of unstable grid connection of photovoltaic power source, an in-situ consumption strategy was proposed, and a photovoltaic energy and phase change energy storage method was proposed to provide energy for greenhouse loading. Design an agricultural greenhouse power supply system with complementary solar energy and phase change thermal storage materials, including constant temperature control center, detection circuit, input circuit and display circuit. It could be seen through software programming and simulation analysis that phase change and photovoltaic combined energy supply could to meet the load demand of agricultural greenhouses, it provided a reference for the local consumption of photovoltaic energy.

Performance of a large-scale greenhouse solar dryer integrated with phase change material thermal storage system for drying of chili

ABSTRACT Large-scale greenhouse solar dryers have been used for drying various products and this type of dryer is usually equipped with LPG burner as auxiliary heater, which creates more operating cost. To overcome this problem, phase change material (PCM) thermal storage was proposed to substitute for the LPG burner. In this work, the performance of a large-scale greenhouse solar dryer integrated with a PCM as a latent heat storage for drying of chili was investigated. Experimental studies were conducted to compare the performance of this dryer with that of another large-scale greenhouse solar dryer without the PCM thermal storage and open sun drying. Chili with an initial moisture content of 74.7% (w.b.) was dried to a final moisture content of 10.0% (w.b.) in 2.5 days, 3.5 days, and 11 days using the solar dryer integrated with the PCM thermal storage, the solar dryer without the PCM thermal storage and the open sun drying, respectively. The performance of the solar dryer integrated with the PCM thermal storage was also evaluated using exergy analysis. The exergy efficiency of the drying room of the solar dryer integrated with the PCM thermal storage and the solar dryer without the PCM thermal storage for drying of chili was found to be 13.1% and 11.4%, respectively and the thermal storage helps to dry chili during adverse weather conditions. The results of exergy analysis implied that the exergy losses from the dryer with the PCM should be reduced.

Enhancing Heating Performance of Low-Temperature Air Source Heat Pumps Using Compressor Casing Thermal Storage

Air source heat pumps (ASHPs) are widely recognized as energy-saving and environmentally friendly heating and air-conditioning equipment with broad applications. However, when conventional ASHPs are operated at a low ambient temperature, they suffer from problems such as high discharge temperature and low heating efficiency. To address these problems, this study designed a new type of dual evaporator combined with a compressor casing thermal storage heat pump system (DE-CCTS) on the basis of a low-temperature air source heat pump water heater with enhanced vapor injection (EVI). The proposed DE-CCTS used thermal storage phase change material (PCM), which was filled in the secondary evaporator (the thermal storage heat exchanger), to recover the waste heat of the compressor casing. Unlike that in the original system under different ambient temperatures, the suction temperature increased by 0.1–1 °C, the discharge temperature decreased by 0.1–0.5 °C, and the coefficient of performance (COP) of DE-CCTS increased by 0.85–4.72% under the proposed system. These effects were especially evident at low temperatures.

Study on the effect of glass on the properties of Na2CO3-K2CO3 eutectic salt/MgO composite as phase change thermal storage materials

ABSTRACT The salt/ceramic phase change materials (PCMs) have a good thermal storage performance and high application temperature. In this paper, we studied the effect of glass as additive on the mechanical properties, thermal storage, and morphology of the Na2CO3-K2CO3 eutectic salt/MgO composite PCMs. The results show that glass can effectively improve the compressive strength of MgO matrix material. When the mass ratio of glass and MgO is 7:3, the compressive strength of the composite body can be up to 104.3 MPa. When the mass ratio of Na2CO3-K2CO3 eutectic salt, MgO, and glass is 55:25:20, the composite PCM body has a good stable form, and its total heat storage is 788 J/g, which increased by 6.7% compared with the total heat storage of composite PCMs without glass in the range of 150°C~750°C. When the mass ratio of Na2CO3-K2CO3 eutectic salt, MgO, and glass is 55:15:30, the composite PCM body cannot maintain stable form.

Hybrid cooling system integrating PCM-desiccant dehumidification and personal evaporative cooling for hot and humid climates

Hot and humid climates present a challenge for implementing passive cooling practices in office spaces, due to the inherent small temperature difference between day and night, which affects the utilization of thermal storage systems. Moreover, added means are required to maintain the humidity in the space at an acceptable level for comfort. The novelty of this study is to design and implement a feasible hybrid cooling system for office spaces in such climates by uniquely combining several sustainable cooling, thermal storage, and dehumidification solutions. The proposed system integrates a phase change material (PCM) thermal storage layer with a melting temperature of 25 °C to cool the supply air and a personalized evaporative cooler (PEC) to provide cooling for the occupants. The supply air humidity is controlled using a solid desiccant wheel regenerated via an auxiliary heater assisted with a Trombe wall. Mathematical models were adopted for each system component/process, solved numerically and integrated to size the system components, simulate their operation and predict the overall system's performance in an office space during the summer months of Beirut climate. The proposed system was found to achieve acceptable thermal comfort levels in the space. Moreover, it reduced the total energy cost by 87% compared with a conventional air conditioning unit over the summer period. In addition, the Trombe wall provided energy savings of 55% compared to relying only on the auxiliary heater. Hence, integrating several sustainable solutions succeeded in implementing an effective cooling system of office spaces in hot humid climates.

Self-cleaning assisted photovoltaic system with thermal energy storage: Design and performance evaluation

This study experimentally investigates the potency of the designed and developed a photovoltaic thermal energy storage with self-cleaning (SC) sub-systems in improving the electrical efficiency of a solar photovoltaic system with thermal energy storage (PV-TES). The photovoltaic system with thermal energy storage (PV-TES) absorber is called double serpentine-flow channel, wherein phase change materials (PCM) thermal storage system has been integrated for better temperature control. An automatic self-cleaning system has been mounted on PV glass cover to clean the dust and ensure higher absorption of incident solar energy. The performance of self-cleaning assisted photovoltaic system with thermal energy storage (PV-TES-SC) has been studied under varied flow rate of 0.5 to 4 L per minute (LPM). Results shows that the PV-TES-SC attained a maximum thermal efficiency of 77.60% at a mass flow rate of 2 LPM. Else ways, the average maximum electrical efficiency of 11.91% was found at a mass flow rate of 4 LPM, whereas a PV alone system could deliver only 9.89% electrical efficiency. From the experimental results it can be confirmed that the PV-TES-SC system is efficient than a PV alone as a result of the newly introduced PCM thermal energy storage and self-cleaning system.

Improving the melting performance of PCM thermal energy storage with novel stepped fins

Abstract Numerical investigation on latent heat thermal energy storage (LHTES) systems with phase change materials (PCMs) vertically heated from one side with novel stepped fins is presented. Transient numerical simulation by using the enthalpy-porosity method is performed to investigate the heat transfer rate and melting behaviors, while the natural convection is considered. To improve the PCM melting process, different upward and downward stepped fins with the step ratios (b/c) of 0.66, 1, 1.5, 2.33 and 4 are employed. The melt fraction and temperature contours by consideration the natural convection effects are presented. The results show that at the beginning of the melting process, the fins in the downward direction with b/c = 0.66 improve the PCM melting rate than the other cases, as the part of the heat is well transferred to the bottom of container along the fins and heat is trapped between the heated wall and the fins. The results show that the melting process in all of the tested stepped fins is faster than the conventional horizontal fins. The results show that by using downward stepped fins (b/c = 0.4) instead of conventional horizontal fins, the melting process could be enhanced up to 56.3% at t = 800 s and 65.5% at t = 3600 s.

Thermo-economic analysis of a solar-driven multi-stage desalination unit equipped with a phase change material storage system to provide heating and fresh water for a residential complex

• A new multi-stage desalination using solar energy for production of fresh water and heat was investigated. • A PCM thermal energy storage system was included for continuous operation. • TRNSYS, HYSYS, and MATLAB software were employed to simulate the integrated structure. • Exergy and economic analyses for the entire integrated structure were carried out. • Overall exergy efficiency of the cycle was determined as 62.79%. In this paper, a novel integrated structure for the production of fresh water and heat for residential complexes in Yazd is introduced and analyzed. The proposed process consisted of flat plate solar collectors, the thermal energy storage system (TES) with phase change material (PCM), and a multi-stage desalination unit. These sub-units were used to provide the required thermal energy, energy storage, and desalinating unconventional waters, respectively. To do so, HYSYS and MATLAB software were employed to simulate the integrated structure. The proposed process produced 4500 kg/h hot water at 64.26 °C and 379.6 kg/h fresh water at 25.35 °C. Effect of the different process parameters such as mass flow rate (MFR) of the inlet water into the solar collectors and number of collectors on the collector efficiency and solar fraction as well as the amount of solar and boilers energy accumulated during the year were broadly assessed and discussed. Comprehensive exergy analysis of the whole system was scrutinized to evaluate the efficiency of the system and to find out the exact location of the exergy losses and ultimately to provide practical solutions to reduce the losses. Solar collectors had the highest exergy destruction rate, which accounts for 344.05 kW. The effect of the cost of product on the period of return and the net annual benefit was also studied.

Comparison of different approaches for thermal performance improvement of a phase change energy storage system

Performance improvement of a phase change material (PCM) thermal storage system is numerically investigated. A finite volume solver is employed to simulate the melting process of the PCM in different geometrical and boundary conditions. The numerical predictions are initially validated against available experimental data. Afterward, four different scenarios are investigated to improve the thermal characteristics of the phase change process. These scenarios include insertion of radial fins with different radial lengths, insertion of a porous layer on the PCM side of the heat transfer fluid (HTF) tube, doubling the HTF mass flow rate, and also increasing the HTF inlet temperature. The results indicate that all of these scenarios expedite the melting process, but at different rates. The insertion of the porous medium is shown to be more effective than using of radial fins. Moreover, according to the second-law analysis of the thermal storage system, using the porous layer provides a superior exergy efficiency compared to other enhancement scenarios. Overall, the addition of a metallic porous layer around the HTF tube is proven to be the most effective as well as the most efficient approach to improve the thermal characteristics of the energy storage system.

Performance enhancement of PCM latent heat thermal energy storage system utilizing a modified webbed tube heat exchanger

In this study, a novel modified webbed tube heat exchanger was introduced and numerically investigated, to enhance the thermal performance of phase change material (PCM) thermal energy storage (TES) system. To evaluate the thermal performance for this heat exchanger its performance was compared with two types of heat exchanger. These heat exchangers included: the webbed tube heat exchanger and the triple tube heat exchanger. Two-dimensional numerical models were developed. The models enabled us to simulate conduction and natural convection heat transfer mechanisms. The process of solidification (discharging) was monitored during the simulation. The results showed that the PCM solidification process accelerates by 41% when utilizing the modified webbed tube heat exchanger compared to the webbed tube heat exchanger.

Study on the influence of glass encapsulating on the hygroscopicity of high temperature phase change heat storage materials

In this paper, Na2CO3-K2CO3 / MgO phase change composite was coated on the surface of glass by spray plating, which solved the problem of absorbing moisture and pulverizing of molten salt / MgO phase change thermal storage material in high humidity environment, and reduced the absorbing moisture and pulverizing rate from 31% to 19% without affecting the latent heat of phase change thermal storage material.

Design, realization, and tests of a portable solar box cooker coupled with an erythritol-based PCM thermal energy storage

Solar radiation is a variable energy source and the mismatch between the availability of such source and the domestic energy demand is a paramount challenge to deal with. For this reason, in this work a 4.08 concentration ratio portable solar box cooker coupled with a thermal energy storage (TES) based on a phase change material (PCM) was characterized through outdoor experimental tests. The TES is a double-wall stainless steel vessel, with the annular volume filled with 2.5 kg of erythritol. The portable solar box cooker was tested under 4 different experimental conditions: without load, with water, with silicone oil, and with silicone oil inserted in the erythritol-based TES. The load tests were divided into a heating and a cooling phase, in order to evaluate the cooker performance in absence of solar radiation. Results showed that equipping the portable solar box cooker with the erythritol-based TES allowed to extend the average load cooling time, in the range 125–100 °C, of around 351.16%.

Forecasting the performance of a district solar thermal smart network in desert climate – A case study

The present paper investigates the performance of a district solar thermal smart network capable of providing the cooling, heating, and domestic hot water needs for a group of 100 villas in the desert climate of Riyadh, Saudi Arabia. Evacuated tube solar collectors are distributed over the villas’ roofs, while the hot water Lithium Bromide absorption chillers and hot phase change material thermal storage tanks are located in a centralized plant. Electrical heating elements embedded in the thermal storage tanks are considered as back up auxiliary sources in case of shortages. Using the “Design Builder” energy simulation program, a typical villa constructed as per the local thermal standard has been modeled to calculate the hourly thermal loads. These hourly profiles are the initial inputs for a Transient System Simulation (TRNSYS) model integrated with the Generic Optimization Program (GenOpt). The interaction between these two programs is used to find the optimized sizing of the solar collectors’ area and the hot thermal storage volume which could achieve the maximum thermo-economic performance with a 100% solar fraction. The hourly transient simulations over a one-year period show that this system can achieve up to 82.67% reduction in the annual electrical consumption as well as carbon dioxide emissions if compared to conventional district thermal plants. Furthermore, the smart network benefits have been revealed from three different aspects: generation source, transmission loop network, and end-user consumer. The feasibility analysis performed shows that adopting the smart network can enhance the profitability of the project by 34.89% if compared to central solar plants. Also, it gives the end-user the opportunity to participate in energy production through buying the solar collectors installed on their roofs, and thus further enhancing the reduction in their annual thermal bills from 23.13% to 82.88% in a payback period of 4 years and 11 months.