Heat Release Performance Research Articles

Thermal energy and thermo-economic analysis of PCM-TES for space heating based on low-temperature waste heat: An experimental and numerical study

Great potential for using low-temperature waste heat for energy savings has been revealed in recent years. In this study, a novel PCM-TES unit integrated into a fresh air system was proposed to effectively utilize low-temperature waste heat to address shortcomings of preheating outdoor air for space heating. An experimental setup was built to investigate the heat storage and release performance of proposed unit. Well-validated CFD simulations further parametrically studied PCM thermal characteristics to HTF’s velocity and temperature changes. Energy and thermo-economic analyses were employed to evaluate unit potentials across three Chinese cities with different climate zones. The results showed that charging process was completed in 142–253 min at water temperatures of 55–60 °C; discharging process efficiency increased by 36.10% as the air velocity increased from 2 to 4 m/s. EPI revealed that, theoretically, the system could handle up to 28.2% of the heating demand. Energy and economic analysis indicated the system’s significant potential in colder climates, with Harbin achieving average energy savings of 7.93% and 13.48% over Qingdao and Chongqing, respectively, and cost savings up to 67.65% and 229.61% compared to those cities. This study is expected to shed light on the utilization of low-temperature waste sources for indoor space heating.

Experimental study on the heat storage characteristics of rock bed heat storage system with different packing structure

Establishing energy storage systems can provide an effective solution to the challenges posed by the variability and intermittency of renewable energy sources. Among the available options for energy storage, rock-packed bed thermal energy storage systems are widely favored for their performance, cost-effectiveness, and reliability. The more compact the rock packing, the more adequate the heat exchange of the system; however, poorer permeability increases fluid friction losses and pressure drop, which is detrimental to heat transport within the system. The permeability and heat exchange of the system jointly determines its thermal energy storage performance. This study proposes a composite packing scheme utilizing intact rock slabs and broken rock to enhance the thermal energy storage performance of the packed bed. This approach aims to augment heat exchange efficiency and elevate energy storage density while maintaining the bed's commendable permeability. Heat injection and heat extraction experiments of rock beds were conducted to study the heat storage characteristics of the rock-packed bed thermal storage system under different packing structure. In addition, this study investigates the effect of different injection pressures on the storage and release of heat in the system. The results show that the volume of the pore space of the filled bed, serving as the primary domain for gas flow and gas-rock heat exchange, is a decisive factor affecting the packed bed's permeability and heat exchange performance. When the porosity of the packed bed increased from 5.5 % to 9.9 %, its permeability increased from 1.42 × 10−13 m2 to 3.20 × 10−13 m2, yet the thermal exchange efficiency declined from 67.2 % to 65.3 %. Reasonably arranging intact rock slabs and broken rock fill can alter the path of heat transfer within the packed bed, thereby effectively enhancing its heat storage and release performance. For the same pore volume conditions, the heat exchange efficiency of the packed bed is increased by about 10 % by increasing the number of layers of broken rock fill. Additionally, high gas injection pressures can facilitate heat storage and release processes, but it does not mean that this is more efficient. The research findings can guide the selection of packing and injection schemes in packed bed thermal energy storage systems.

Experimental Study on Phase Change Energy Storage Flooring for Low-Carbon Energy Systems in Grassland Pastoral

Phase change energy storage technology enhances the integration of renewable resources into low-carbon energy systems for grassland pastoral settlements, further addressing the balance between energy needs and environmental sustainability. This study examines a heating system using an experimental platform in an environmental chamber, where the thermal storage and release processes of phase change energy storage flooring were monitored. The results revealed that phase change energy storage flooring exhibits higher heat transfer efficiency and faster heating rates. Under 40 °C heating conditions, the heating rate of the thermal storage layer increased by 12.5% within 1 h. The flooring also demonstrated superior heat release performance, with the peak heat flux of the thermal storage layer delayed by 15 min. Higher heating temperatures shortened the heating time and extended the heat release duration of the phase change energy storage flooring. Under 45 °C heating conditions, the heat transfer efficiency of the surface temperature of the thermal storage layer increased by 38% within 1 hour and by 24.7% over 4 h. In addition, energy consumption in different tests was analyzed, and thermal conductivity was discussed according to the heat transfer model. Phase change energy storage flooring, when coupled with the abundant solar energy resources available in grassland pastoral areas, presents a viable option for the construction of low-carbon energy systems in grassland pastoral settlements.

An Innovative Azobenzene-Based Photothermal Fabric with Excellent Heat Release Performance for Wearable Thermal Management Device.

Azobenzene (azo)-based photothermal energy storage systems have garnered great interest for their potential in solar energy conversion and storage but suffer from limitations including rely on solvents and specific wavelengths for charging process, short storage lifetime, low heat release temperature during discharging, strong rigidity and poor wearability. To address these issues, an azo-based fabric composed of tetra-ortho-fluorinated photo-liquefiable azobenzene monomer and polyacrylonitrile fabric template is fabricated using electrospinning. This fabric excels in efficient photo-charging (green light) and discharging (blue light) under visible light range, solvent-free operation, long-term energy storage (706 days), and good capacity of releasing high-temperature heat (80-95 °C) at room temperature and cold environments. In addition, the fabric maintains high flexibility without evident loss of energy-storage performance upon 1500 bending cycles, 18-h washing or 6-h soaking. The generated heat from charged fabric is facilitated by the Z-to-E isomerization energy, phase transition latent heat, and the photothermal effect of 420nm light irradiation. Meanwhile, the temperature of heat release can be personalized for thermal management by adjusting the light intensity. It is applicable for room-temperature thermal therapy and can provide heat to the body in cold environments, that presenting a promising candidate for wearable personal thermal management.

Remediation of seawater polluted by oil spills via integrating porous materials with phase-change materials

The cleanup of viscous oil spills, especially in frigid regions, presents significant challenges due to the low fluidity of the oil. While the integration of absorption materials with photo/electric thermal conversion has shown significant promise, its effectiveness can be greatly influenced by environmental factors. To address these challenges, this study introduces an innovative solution: three-dimensional porous materials (3D-PMs) combined with phase change materials (PCMs). By utilizing energy pre-stored in PCMs through sunlight irradiation or electric heating, heat can be efficiently released when 3D-PMs come into contact with crude oil. A novel superhydrophobic melamine sponge (PPCPP@MS), composed of polypyrrole (PPy) and polyethylene glycol (PEG), has been developed for this purpose. The PPy polymerization layer reliably converts light/electricity into heat, while the PEG‑carbon nanotube (CNT) composite coating layer facilitates heat storage and release. This innovative design significantly enhances safety, energy utilization efficiency, and operational effectiveness. Furthermore, COMSOL simulation was employed to the interfacial heat transfer and phase transformation process of PPCPP@MS during crude oil absorption. Demonstrating stable heat release and oil-adsorbing performance in simulated low-temperature marine environments, PPCPP@MS exhibits great potential for addressing oil spills in extreme climates. The innovative design of PPCPP@MS offers crucial insights for managing viscous oil spills, particularly in frigid regions, providing a promising approach in environmental protection and remediation efforts.

A new reactor with porous baffle for thermochemical heat storage: Design and performance analysis

The Ca(OH)2/CaO reaction system presents broad development prospects for thermochemical heat storage. However, the poor thermal conductivity of heat storage material and the complex internal flow limit the performance of the reactor. To improve the performance of the reactor, this work designs a new improved fixed bed reactor with baffle. The comparison with and without baffle, as well as the effects of operation conditions and structural parameters of the improved reactor on heat storage and release performance, are numerically investigated. The results show that the improved reactor can enhance heat transfer and flow inside the reactor, resulting in performance improvement. After baffle installation, there is a 64% decrease in the pressure drop, a 29.14% reduction in the heat storage time, and a 35.45% reduction in the heat release time. Besides that, the improved reactor can maintain the high temperature for longer at the outlet during heat release. The orthogonal test design analysis reveals that the inlet velocity of direct heat transfer fluid has the greatest impact on heat storage, while the inlet velocity of indirect heat transfer fluid has the smallest impact, and the same applies to heat release. The thermal conductivity and permeability of the porous baffle have minor impacts, but the air distribution chamber has a noticeable influence. This work can guide the optimization design and operation adjustment of the reactor.

Heat storage and release performance of solar greenhouses made of composite phase change material comprising methyl palmitate and hexadecanol in cold climate

Solar greenhouses play a crucial role in winter crop cultivation in the cold regions of China. However, adverse weather conditions such as low temperatures can negatively affect their production. Therefore, improving the greenhouse thermal environment and energy utilisation is crucial for optimising greenhouse productivity. One effective method of storing energy is phase change technology. In this study, melt blending was used to prepare composite phase change materials (CPCMs), with methyl palmitate and hexadecanol as raw materials. In addition, ceramsite was encapsulated with a styrene-acrylic emulsion to form a shape composite phase change material (SCPCM). The results showed that the latent heat of phase change of the CPCMs was 221 J/g, with an initial phase change temperature of 23.48 ℃. The encapsulation of the SCPCM with a styrene-acrylic emulsion significantly reduced leakage. Phase-change ceramsite concrete slabs were developed by integrating the SCPCM into concrete. These slabs were used to construct phase-change and non-phase-change greenhouses. A temperature-testing system was installed in the greenhouses to examine the temperature variations and distributions under typical sunny and cloudy conditions. Results revealed that compared with the control greenhouse, the phase-change greenhouse exhibited a decrease of 3.0 ℃ in the maximum indoor temperature during sunny days and an increase of 3.2 ℃ in the minimum indoor temperature at night. This study highlights the effective temperature control capabilities of phase-change ceramsite concrete slabs for improving energy utilisation and provides valuable theoretical and technical insights for the future utilisation and widespread adoption of phase-change greenhouses.

Experimental Study on Heat Release Performance for Sorption Thermal Battery Based on Wave Analysis Method

Recent developments in water-based open sorption thermal batteries (STBs) have drawn burgeoning attention due to their advantages of high energy storage density and flexible working modes for space heating. One of the main challenges is how to improve heat release performance, e.g., longer stable heat output and effective output temperature. This paper aims to explore the heat release performance of sorption thermal batteries based on wave analysis methods. Zeolite 13X is used for the experimental investigation in terms of the relative humidity of inlet gas, system air velocity, and the length of the reactor. The results demonstrate that the optimal stable temperature output time of the sorption thermal battery experimental rig is 80 min, and heat release per unit volume reaches 115.6 MJ for the most appropriate reactor length. Thus, the optimal heat release time of the STB under the condition of various relative humidity and air velocities is 152 min and 182 min, respectively, and the corresponding stable heat release could reach 161.1 MJ and 136.5 MJ, respectively. Therefore, the heat release performance of STBs could be adjusted by adopting the wave analysis method, which would facilitate the reactor design and system arrangement.

Novel modular PCM wall board for building heating energy efficiency: Material preparation, manufacture and dynamic thermal testing

With the comprehensive implementation of China’s “dual carbon” goals, the building heating sector, characterized by high energy consumption and emissions, urgently requires low-carbon transformation. However, energy-saving measures for plateau regions are scarce and face challenges due to harsh climates. This study proposes an innovative heating method utilizing composite phase change materials. A new modular phase change thermal storage electric heating terminal integrated with a photovoltaic thermal system has been designed to address issues of high building energy consumption and problems related to heating system freezing and leakage in the Tibetan Plateau (Qinghai-Xizang Plateau). Laboratory tests were conducted on six groups of samples with different structures and placements to examine their heat storage and release characteristics. Results indicate: The system’s temperature stabilization time totals 14.6 h; Horizontally placing the terminal reduces melting time by up to 2.7 h, enhancing heat storage performance; Structure three shortens solidification time by up to 2.2 h compared to structure one, improving heat release performance; Vertically placed terminals have better heat release performance than horizontally placed ones, resulting in more effective indoor heating. This study proposes a modular design for phase change heat storage electric heating walls, simplifying installation and maintenance while maintaining aesthetic appeal. Detailed temperature measurements of different wall surfaces revealed excellent cyclic heat storage and release performance. The developed phase change heat storage electric heating terminal is expected to significantly reduce heating energy consumption in the Tibetan Plateau (Qinghai-Xizang Plateau), enhancing building energy efficiency and providing valuable insights for further applications of phase change materials in building design.

Analysis on the effect of novel topological optimization fin structures considering eccentricity on the heat storage and release characteristics of shell and tube phase change heat accumulator

Shell and tube phase change accumulator (STPCA), as a common type of heat accumulator, can effectively solve the mismatching of time and space in solar thermal power generation by using phase change storage technology. However, the low thermal conductivity of phase change materials (PCMs) reduces its heat storage and release rate. To achieve a rapid latent heat energy storage and release, it needs to carefully modify the structure of STPCA. In the existing literature, insufficient attention has been given to simultaneously addressing the heat storage and release processes, while there is a scarcity of topological optimization methods employed in fin design. On one hand, it is difficult to find the optimal structure. On the other hand, the optimized structure is suitable for melting process but may not be suitable for solidification process. In this contribution, we initially integrated topological optimization and eccentricity to derive fin structures suitable for respective melting and solidification processes. Then, we compared and analyzed the effects of eccentricity and objective function on melting and solidification processes. Finally, we summarized the topology optimization process, objective function and eccentricity suitable for fast heat storage and release. The findings indicated that as the eccentricity increases, the rate of heat storage and release initially rises before subsequently declining. In this work, it is found that an eccentricity of 5 mm is the best. From the whole heat storage and release cycle, when the eccentricity is 5 mm, the objective function is the minimum temperature difference and the topological optimization fin structure calculated during solidification process shows the best heat storage and release performance. Compared with the topology optimization structure without eccentricity, the heat storage speed is increased by 36.43 %, and the heat release speed is increased by 15.53 %. The design law of the STPCA based on combined with the eccentricity influence and topology optimization method is summarized to help improve its heat storage and release performance.

Influence of Ambient Pressure on the Jet-Ignition Combustion Performance and Flame Propagation Characteristics of Gasoline in a Constant Volume Combustion Chamber

Based on a constant volume combustion chamber, the initial ambient pressure effect on gasoline combustion performance and flame propagation of the active and passive pre-chamber ignition systems were studied. Compared with the passive pre-chamber, the active pre-chamber can significantly expand the lean combustion limit from 1.2 to 1.5, enhance the ignition and combustion performance, and speed up the combustion of the main combustion chamber. At slightly lean combustion conditions, the heat release performance has a positive correlation with the initial ambient pressure. As the premixed λ increases, the heat release performance and the initial ambient pressure begin to become negatively correlated. Ignition delay can be decreased by approximately 50% at an initial pressure of 0.75 MPa, premixed lambda of 1.2 with APC compared with PPC. The high ambient pressure (1.0 MPa) in the constant volume chamber greatly reduces the mixture entrainment ability of the jet flame at lean combustion conditions, thereby reducing the combustion speed and peak heat release rate.

Edible squid ink proteoglycans as a multifunctional sustainable additive for silk coatings: Fire protection, UV shielding and as a colorant

Today, marine biomolecules have attracted great interest in the field of flame-retardant (FR) science due to their sustainability and charring properties. Squid ink is mixed bio-colloid rich in proteoglycans, melanin, and metal ions. Here, squid ink was applied to endow silk with outstanding FR performance and ultraviolet protection through surface coating. After coating with 40 g/L squid ink, silk displayed excellent ultraviolet shielding performance with a high UV protection factor (UPF) of 71.5, attributing to powerful ultraviolet absorption ability of melanin. Besides, the coated silk also exhibited outstanding FR performance, characterized by a shorter char length (7.1 cm) and a higher FR-Index (2.5). The heat release performance of the treated silk dramatically decreased, and the peak heat release rate (pHRR) and heat release capability (HRC) both decreased by 49.1 %. Moreover, a significant reduction in total smoke production (TSP ∼ 60 %) was also observed in cone calorimetry test. A reduction in these fire parameters indicated a great improvement in the fire safety of silk. Interestingly, due to the natural adhesiveness of the proteoglycan mixed colloid, the coated silk could withstand 10 washing cycles while maintaining FR properties. Subsequently, further analyses of the cone residues confirmed the formation of a compact and stable char layer. The squid ink coating exerted an intumescent FR action on silk.

Application of phase change material on solar-greenhouse back wall and its effects on indoor thermal environment and cucumber production in winter

The configuration of the solar greenhouse building wall and the thermal properties of the building materials directly impact wall insulation, heat storage characteristics, and, consequently, the thermal environment within the greenhouse. To address the variations in wall heat storage during the design and construction of solar greenhouses, this study aims to integrate solar energy effectively with phase change heat storage technology. Utilizing Energy Plus, the study simulates and verifies the heat storage and release performance of phase change materials on the greenhouse's back wall. The research also explores the warming effect of these materials on cucumber growth. The findings reveal that the composite phase change greenhouse (PC) wall exhibits an average heat release of 60.47 W/m2, maintaining an average temperature of 21.09 °C. In comparison, the heat release from the back wall of the traditional greenhouse (CK) increases by 14.03 W/m2, resulting in a temperature rise of 1.91 °C. Additionally, the substantial heat released by the phase change wall raises the average ground temperature to 18.26 °C through heat conduction, exceeding CK by 3.07 °C. Despite this, the maximum temperature remains below 25 °C, creating an ideal growth temperature for cucumbers and fostering vigorous growth. Furthermore, cucumber quality indicators, such as soluble sugar and VC content, significantly improve, demonstrating a 28.5 % increase in the single fruit weight of cucumbers. In conclusion, the composite phase change greenhouse outperforms the traditional greenhouse in heat storage capacity. The heat storage wall effectively enhances the overall thermal environment, insulation, and heat storage performance, ultimately leading to increased cucumber yield and quality.

Development of Macro-Encapsulated Phase-Change Material Using Composite of NaCl-Al2O3 with Characteristics of Self-Standing

Developing thermal storage materials is crucial for the efficient recovery of thermal energy. Salt-based phase-change materials have been widely studied. Despite their high thermal storage density and low cost, they still face issues such as low thermal conductivity and easy leaks. Therefore, a new type of NaCl-Al2O3@SiC@Al2O3 macrocapsule was developed to address these drawbacks, and it exhibited excellent rapid heat storage and release capabilities and was extremely stable, significantly reducing the risk of leakage at high temperatures for industrial waste heat recovery and in concentrated solar power systems above 800 °C. Thermal storage macrocapsules consisted of a double-layer encapsulation of silicon carbide and alumina and a self-standing core of NaCl-Al2O3. After enduring over 1000 h at a high temperature of 850 °C, the encapsulated phase-change material exhibited an extremely low weight loss rate of less than 5% compared with NaCl@Al2O3 and NaCl-Al2O3@Al2O3 macrocapsules, for which the weight loss rate was reduced by 25% and 10%, respectively, proving their excellent leakage prevention. The SiC powder layer, serving as an intermediate coating, further prevented leakage, while the use of Al2O3 ceramics for encapsulation enhanced the overall mechanical strength. It was innovatively discovered that the Al2O3 particles formed a network structure around the molten NaCl, playing an important role in maintaining the shape and preventing leakage of the composite thermal storage phase-change material. Furthermore, the addition of Al2O3 significantly enhanced the rapid heat storage and release rate of NaCl-Al2O3 compared to pure NaCl. This encapsulated phase-change material demonstrated outstanding durability and rapid heat storage and release performance, offering an innovative approach to the application of salt phase-change materials in the field of high temperature rapid heat storage and release and encapsulating NaCl as a high-temperature thermal storage material in a packed bed system. Compared with conventional salt-based phase-change materials, the developed product is expected to significantly improve the reliability and thermal efficiency of thermal storage systems.

Numerical Investigation of Heat Transfer Characteristics of Trapezoidal Fin Phase Change Thermal Energy Storage Unit

Abstract: In order to enhance the heat transfer performance of a phase change thermal energy storage unit, the effects of trapezoidal fins of different sizes and arrangement modes were studied by numerical simulation in the heat storage and release processes. The optimal enhancement solution was obtained by comparing the temperature distribution, instantaneous liquid-phase ratio, solid–liquid phase diagram and comprehensive heat storage and release performance of the thermal energy storage unit under different fin sizes. During the heat storage process, the results show that when the ratio of the length of the upper and lower base of the trapezoid h1/h2 is 1:9, the heat storage time is shortened by 9.03% and 18.21% compared with h1/h2 = 3:7 and 5:5, respectively. During the heat release process, the optimal heat transfer effect is achieved when h1/h2 = 5:5. To further improve the heat transfer effects, the energy storage unit is placed upside down; then, the least time is achieved when h1/h2 = 2:8. When heat storage and release are considered together, the energy storage unit with h1/h2 = 2:8 takes the shortest time to melt in upright placement and then to solidify in upside-down placement.

In situ construction of iron-rich metal-organic frameworks on wool surface for enhanced flame retardancy and low smoke generation

The incorporation of metal-organic frameworks (MOFs) on textile materials to enhance flame retardancy is of interest and challenge. In this study, an iron-rich MOF (Fe-MOF) was constructed in situ on wool fabric surface through the alternating assembly of ferric metal salt and the carboxylic acid ligand 1,3,5-benzenetricarboxylic acid. The surface morphology, flame retardancy, smoke and heat release performance, thermal stability, and flame-retardant mechanism of the Fe-MOF coated wool fabric were investigated. Square-shaped crystals were observed on the coated wool fabric, indicating successful construction of Fe-MOF on the wool surface. The coated wool fabric with an add-on of 6.8% exhibited excellent flame retardancy, as evidenced by its self-extinguishing ability during the vertical burning test and a significantly enhanced limiting oxygen index of 32.6%. Moreover, the coated wool fabric demonstrated a remarkable reduction in heat and smoke production of 23.8% and 68.4%, respectively, indicating enhanced fire safety. The analysis of char residue, including thermal stability, surface morphology, iron content, and graphitization degree, supported the formation of ferric oxides as a protective layer, contributing to the improved flame retardancy of the Fe-MOF coated wool in the condensed phase. The in situ construction of Fe-MOF on wool macromolecules offers a promising and innovative approach for developing nonhalogen and nonphosphorus flame-retardant systems.

Design optimization on solidification performance of a rotating latent heat thermal energy storage system subject to fluctuating heat source

The combination of latent heat storage (LHS) technology with the Organic Rankine Cycle represents a widely recognized solar thermoelectric conversion means. However, this technology is hindered by the instability of solar energy and the poor thermal conductivity of thermal storage materials. This study addresses the challenges posed by solar energy fluctuations by implementing a sinusoidal heat source condition during the heat release process of LHS system. Furthermore, a comprehensive approach is taken to enhance heat transfer, incorporating both active methods such as rotational conditions, and passive methods using metal nanoparticles and high-performance fins. The Taguchi method is employed to optimize rotation speed, heat source amplitude, and half-period of the latent heat storage unit, and the resulting heat release performance is compared between different structures and the optimized structures. The findings from optimal design analysis reveal that rotation speed has the most significant influence on mean heat discharging rate and solidification time, followed by the heat source amplitude and half-cycle period. There is a notable interaction between heat source amplitude and half-cycle period. Compared to the initial structure, the optimal structure identified through the optimal design shortens the solidification time by 11.18%, increases the mean heat discharging rate by 13.04% and raises the average temperature response by 18.82%. Furthermore, the addition of Al2O3 nanoparticles further enhances heat discharging properties. Specifically, the presence of 2.5% and 5% Al2O3 nanoparticles shortens unit solidification time by 9.52% and 18.83% and increases the mean heat release rate by 7.69% and 17.26%. It is noted that the incorporation of rotating-fit nanoparticles partly compensates for the limitations of increased viscosity and particle settlement associated with metal nanoparticles, although it does not fully address the challenges related to reduced heat storage/release.

Evaluation of Mixing Effect on Coupled Heat Release and Transfer Performance of a Novel Segregated Solid Rocket Motor

The effect of mixing on coupled heat release and transfer performance of a novel segregated solid motor is numerically evaluated with a transient two-dimensional combustion model. The results show that vortex structures are formed and evolved in the combustion chamber. Quantitative calculation of the mixing effect shows the inhomogeneous distribution of oxidant and fuel species. The well-mixing area is located in a narrow belt-like coupled combustion region near the burning surface of the propellant. Heat transfer coefficient decreases greatly due to lower combustion reaction rate and enlarged flow channel area. Heat transfer coefficients near the two ends of the propellant grain are higher than other parts due to the influence of vortex mixing. Raising the inlet mass flow rate leads to enhanced mixing and heat transfer, which results in a lower temperature and regression rate of the propellant with combustion time. Temperature and oxidation rates of H2 and CO are unevenly distributed in the boundary layer of coupled combustion. Increasing the mass flux of inlet oxidizer gas leads to a higher combustion heat release rate. Therefore, the gas-phase temperature increases significantly. The heat release rate reaches the maximum near the ends of the propellant grain, where vortex mixing strengthens the coupled combustion process in the motor.

Research on creating the indoor thermal environment of the solar greenhouse based on the solar thermal storage and release characteristics of its north wall

Improving the solar thermal storage capacity of the north wall of the solar greenhouse can effectively enhance the indoor thermal environment during the night-time in winter. However, the indoor thermal environment is also influenced by the interaction between the spatial parameters of the solar greenhouse and outdoor meteorological conditions. Additionally, the heat storage and release performance of the north wall are dynamically affected by changes in the indoor thermal environment. This complicates the quantitative assessment of the impact of solar active–passive heat storage methods applied to north walls on the indoor thermal environment. Therefore, in this study, we develop a mathematical model that considers simplified calculations of the solar greenhouse’s spatial parameters and the design method of an active–passive ventilation wall with latent heat storage, which was proposed in the early stage, for evaluating the impact of the solar thermal storage and release characteristics of the north wall on the indoor thermal environment of the solar greenhouse. This model is validated against measured data from the experimental solar greenhouse with high accuracy. Using this model, we analyze the quantitative reinforcement effects of a phase change composite wallboard and a solar collector system on the solar energy utilization of the north walls and its effects on the indoor thermal environment. Compared to ordinary solar greenhouses in Wuzhong, the application of a GH-20 composite phase change thermal storage wallboard to improve the passive solar energy utilization of the north wall can increase the solar energy contribution rate by 90.9%. Furthermore, integrating a multi-surface solar air collector with double-receiver tubes on the phase change composite wall can increase the solar energy contribution rate by 95.4%. Also, the experimental results reveal that the solar active–passive heat storage methods applied to the north wall can enhance the indoor thermal environment during night-time and increase cucumber yield by more than 10% in winter. This study provides a method reference for optimizing the active–passive solar thermal utilization of the solar greenhouse.

Numerical investigation of the heat-release performance of a metal hydride reactor-integrated phase change material

Metal hydride (MH) heat storage has a relatively high energy density and can be used in concentrated solar power (CSP) plants. However, in this system, the outlet temperature of the heat transfer fluid (HTF) has large fluctuations while discharging heat, which cannot satisfy the requirement of CSP plants. Therefore, this study proposes an MH-based heat storage system integrated with phase change materials (PCMs). A mathematical model was established to investigate the effects of the thickness of PCMs, HTF velocity, and the initial state of PCMs on heat-release performance. The results showed that the fluctuations can be effectively attenuated, and the fluid outlet temperature can be kept stable for a certain period by integrating PCMs. Plateaus in the curves of the MH bed and HTF outlet temperatures were observed, and the platform temperature and time are defined as the average temperature of two inflection points of the curve and their corresponding time difference, respectively. Increasing the thicknesses of PCMs can extend the platform time. Furthermore, the liquid phase of PCMs is conducive to improving the heat-release performance of the MH reactor with PCM.