•Industrial waste semicoke ash is recycled to fabricate phase change composites.•Optimal mass fraction of semicoke ash is obtained to be 50% without leakage.•Reducing the heating rate during the ...sintering benefits the forming of composites.•Uniform distribution of both materials is observed in optimal mass ratio.•Maximal thermal energy storage density of 325.91 J/g is obtained.
The use of industrial semicoke ash as skeleton material is proposed in this study to fabricate low-cost thermal energy storage materials and shape-stable phase change composites as well as recycle industrial solid waste for building heating. Eight samples with different mass ratios of semicoke ash to NaNO3 are manufactured. Key performance of NaNO3/semi-coke ash shape-stable phase change composite is then investigated using differential scanning calorimetry, laser flash analysis, scanning electron microscopy, X-ray diffraction, and constant-speed pressurization method. Results showed that the sample CC2 with a mass ratio of semicoke ash to NaNO3 of 5:5 demonstrates the absence of visual leakage and deformation and reaches a maximum thermal energy storage capacity of 325.91 J/g in the range of 100 °C to 380 °C, mechanical strength of 96.98 MPa, and maximum thermal conductivity of 1.004 W/(m∙K). In addition, semicoke ash is chemically compatible with NaNO3. Both thermal energy storage capacity and thermal conductivity of sample CC2 increase slightly after 4027 heating/cooling cycles.
•MgO particle size and density effects on CPCMs microstructure and thermoproperties were studied.•The CPCMs consisted of an MgO as CSM, a carbonated salt as PCM, graphite flakes as TCEM.•Light MgO ...particle achieved a much denser composite structure and better PCM containment than the heavy ones.•Smaller MgO particles yielded a uniform particle distribution and more compact structure.•Increasing size-similarity gave a better combination of thermal conductivity and mechanical strength.
MgO has been used as a popular ceramic skeleton material (CSM) for shape-stablising inorganic salt based composite phase change materials (CPCMs) for medium to high temperature thermal energy storage applications. This work aims to understand the effects of particle size and density of MgO on the microstructures, and thermophysical and mechanical properties of the CPCMs. A eutectic carbonate salt of NaLiCO3 was used as the phase change material (PCM) with a melting temperature of around 500 °C and graphite flakes as the thermal conductivity enhancement material (TCEM). Two types of MgO were used in the work with one being light MgO and the other heavy MgO. The results demonstrated clear evidence of salt migration within the CPCMs made from both types of MgO during thermal cycling, leading to a more homogenous distribution of the salt as well as the CSM and TCEM. For a given particle size and TCEM loading, the light MgO (with a higher surface energy) gave a more considerable extent of particles migration and rearrangement than the heavy MgO (with a lower surface energy). Due to the higher surface energy, a much denser structure and better PCM containment of the CPCMs were observed with the light MgO formulations. For a given MgO type, smaller MgO particles yielded smaller internal pores and a more rigid structure, leading to a better containment of the PCM and more stable composite structure during thermal cycling. The microstructural characteristics observed were also found to be closely related to the thermophysical and mechanical properties of the CPCMs; a CPCM composite made with ingredients of a similar size gave a more compact structure and hence a better combination of thermal conductivity and mechanical strength.
•Nano-bromides were examined for heat pipes in concentrated solar power plants.•Heat of fusion and decomposing point were improved by 99.19% and 68.4 °C respectively.•Inapparent effect on melting ...point was observed.•Interaction between nanoparticle and salt molecule account for the enhancement.•Dense dendritic-like structure networks were observed by microstructure analysis.
Thermal performance of molten salts can be enhanced by nanostructured materials, which can enhance the heat transfer capacity of heat pipes and further improve the global efficiency of Concentrated Solar Power plants. In this work, a eutectic mixture of sodium bromide, potassium bromide, lithium bromide and calcium bromide acted as the base salt, into which nine SiO2 nanoparticles in three diameters were dispersed to form twenty-two nano-bromides in total. The thermodynamic properties of the base salt and nano-bromides, e.g. the thermal stability and the phase change performance were investigated experimentally and analytically. It was observed that the size and the mass concentration of the SiO2 nanoparticles exhibited significant influence on the heat of fusion and the decomposing temperature but little on the melting point. By adding 0.7 wt% of 10 nm SiO2 particles, the heat of fusion and the decomposing point of the base salt were increased by maximum 99.19% and 68.4 °C respectively. In addition, densely dendritic-like networks were observed with Scanning Electron Microscopy in the nano-bromides and considered to be responsible for the improvement of the heat of fusion and the decomposing point. The authors believed these findings would contribute to enhance the heat transfer performance of heat pipes furtherly.
Sewage sludge and red mud, as common industrial waste, have become a research hotspot in the field of achieving carbon peaking and carbon neutrality, reducing carbon emissions, and solving ...environmental problems. However, their treatment and disposal have always been a difficult problem in the environmental field. Utilizing these two materials for thermal energy storage can not only improve energy utilization efficiency but also further reduce carbon emissions during their treatment process, providing a new approach for sustainable development in the industrial sector. This article summarizes the research progress for the resource recovery of sewage sludge and red mud for direct thermal energy recovery and composite phase change energy storage. After proper treatment, sludge and red mud can be directly used as energy storage materials. In addition, sludge and red mud can be combined with phase change materials to prepare composite materials with an excellent energy storage performance. This composite has broad application prospects in fields such as solar energy utilization and building energy efficiency. However, there are still some challenges and issues in this resource recovery and utilization, such as potential environmental pollution during the treatment process, the long-term stability of energy storage materials, and cost-effectiveness, which require further research and resolution. The purpose of this paper is to evaluate the potential of sewage sludge and red mud as energy storage materials, to explore their feasibility and advantages in practical applications, and to reveal the research progress, technical challenges, and future development directions of these two materials in the field of thermal energy storage.
Massive accumulation of solid waste semi-coke ash (SCA) produced in industrial processes will damage local environment. To recycle SCA and fabricate low-cost thermal energy storage materials, the ...idea of fabricating the form-stable phase change materials (FSPCMs) with SCA as skeleton material and solar salt (SS) as phase change material was proposed innovatively. Seven FSPCMs with different SS content were prepared by compression and sintering method, and key performances were investigated by differential scanning calorimetry, constant-speed pressurization method, scanning electron microscopy, sessile drop method and X-ray diffraction. The research found that the sample A55 with 50 wt% SS showed the best performance; the thermal energy storage density of sample A55 was 483 J/g in the range of 100 to 450 °C; the compressive strength of sample A55 reached 86.12 MPa; the sample A55 had excellent chemical compatibility and thermal stability.
•A novel system which can recover pressure energy as well as regulate pressure is proposed.•Round trip efficiency of the whole system (including gas source) reaches up to 25%.•Isentropic efficiency ...of expander has great influence on round trip efficiency.•Wide installation of the system bring about rich economic and environmental benefit.
Natural gas (NG) is delivered with abundant pressure energy from the gas station to various industrial users and residents. The commonly used Throttle Valve Pressure Regulation configuration can achieve stable downstream pressure, but the gas pressure loss is great. Additional turbines could be employed to recover the pressure energy, but hard to present a high efficiency. This work innovatively proposes an Expander-Depending Natural Gas Pressure Regulation configuration, which can regulate the NG pressure and harvest the pressure energy as well. A single screw expander is used to recover the pressure energy, whereby an air-source heat pump acts as a heat source to warm the cold gas. A thermodynamic model is established to evaluate the energy and exergy performance. Thermodynamic analyses show that the daily round-trip efficiency of the system, including both the NG source sector and the expander-depending NG pressure regulation sectors, can be more than 25% while the daily exergy efficiency and the daily power output of the expander-depending gas pressure regulation sector come up to 37.02% and 60.9 kWh respectively under the inlet NG pressure of 0.6 MPa and the outlet NG pressure of 0.1 MPa, and the volume flow rate from 30 Nm3/h to 350 Nm3/h. The round-trip efficiency, the exergy efficiency and the net power output dramatically increase with the isentropic efficiency improvement of the single screw expander. The proposed expander-depending natural gas pressure regulation unit can produce rich economic and environmental benefits and promise a bright future in the engineering application.
•Industrial carbide slag is suitable as skeleton material for SSPCM fabrication.•Sample CC6 with mass fraction 50% of carbide slag reached the optimal performance.•Carbide slag has chemical ...compatibility with sodium nitrate.•Sample CC6 achieved a TES density of 447 KJ/kg in the range of 100–400 °C.•Sample CC6 remains excellent thermal stability after the 3700 heating/cooling cycles.
Massive accumulation of industrial carbide slag tend to cause ecological environment pollution and greenhouse gas emission. This innovative work proposed to fabricate shape-stable phase change materials (SSPCMs) with carbide slag to utilise industrial solid waste and protect precious natural resources. Seven SSPCMs were fabricated with different mass ratios of industrial carbide slag to sodium nitrate by cold-compression hot-sintering method, and key performance was investigated on the SSPCMs. Results showed that the SSPCM (sample CC6) with the mass ratio of 5:5 of carbide slag to sodium nitrate presented the best performance: sample CC6 achieved a high thermal energy storage density of 447 J/g in the range of 100–400 °C and reached a mechanical strength of 73.6 MPa; sample CC6 demonstrated a good thermal stability and chemical compatibility between carbide slag and sodium nitrate during the heating/cooling cycles; the thermal conductivity of sample CC6 was 0.93 W/(m•K), and elements distributed uniformly in sample CC6.
To establish an accurate model to optimize the vertical cooling process of the sinter, the inverse problem method is used to calculate the gas-solid heat transfer coefficient based on the gas outlet ...temperature, which is fitted into the correlation. The research indicates that the increase in the gas velocity is beneficial to the enhancement of the gas-solid heat transfer. With the gas velocity ug increasing from 0.8 m·s-1 to 1.6 m·s-1, the heat transfer coefficient hv increases by about twice. But this effect will weaken with the increase in the particle size. Besides, the reduction of the particle size is conducive to improving the convective heat transfer intensity between the gas and solid. With the particle size decreasing, this enhancement effect is progressively evident. At ug of 0.8 m·s-1, the increasing extent of hv is 1142.25 W·m-3·K-1 with the particle size decreasing from 20~25 mm to 15~20 mm, while that is 3152.65 W·m-3·K-1 with the particle size decreasing from 15~20 mm to 10~15 mm. In addition, the variation of the measured value of the Nusselt number with the Reynolds number has the same trend as predicted values obtained by other works. However, there is a considerable deviation in the value. Among them, the minimum value of the mean relative error is 26.81%. It is proved that the previous empirical correlations are no longer applicable, while the predicted value of this work is in good agreement with the measured value with the mean deviation of only 7.61%. Therefore, the modified correlation can accurately predict the gas-solid heat transfer characteristics in the sinter bed, which lays a foundation for the numerical design and optimization of the new process.
In gas transmission, the regulator needs to adjust the gas pressure from high to low. The pressure energy can be then recovered by an expander, and the expander can drive a generator to produce ...electricity. However, the gas pressure regulator system and generator torque process often present difficult adjustment of PI parameters, and strong non-linearity of the hysteresis comparator and switching table in the traditional direct torque control (DTC) cause difficulties in the controller design and lead to large fluctuations of the generator torque. This paper designs a model predictive controller (MPC) for the gas pressure regulator process to reduce generator torque fluctuations. Simultaneously, a fuzzy PI controller is designed for the generator rotational speed process, and an MPC controller is exploited for the torque process; they operate in a cascaded manner. The fuzzy PI controller is used to calculate the torque set point. And the MPC controller is designed to obtain the optimal voltage vector of the generator for improving control performance through time delay compensation. The simulation experimental results highlight that the fluctuation of the regulator outlet gas pressure is reduced by 7.9% and 8.1%, and the output torque range is reduced by 3.4% and 2.1% compared with the traditional PI control and fuzzy PI control, respectively. The generator torque fluctuation range is reduced by 82.3%, the rotational speed fluctuation range is reduced by 76.9%, and the three-phase current fluctuation range is reduced by 76.6% compared with the traditional DTC.
To recycle industrial wastes sufficiently, this work innovatively proposed a mixture of desulfurization gypsum and carbide slag as skeleton material to fabricate phase-change composites with NaNO3 as ...phase change material in a mass ratio of 5 to 5. Four phase-change composites were fabricated with different ratio of desulfurization gypsum to carbide slag by the cold compression-hot sintering method, and then key thermal and mechanical properties, microscopic morphology and chemical compatibility between components were investigated in detail. Results show that the mixture of desulfurization gypsum and carbide slag as skeleton material is feasible and reliable and an optimal mass ratio of desulfurization gypsum to carbide slag was obtained to be 3.5 to 1.5; the phase-change composite with the optimal mass ratio possesses good mechanical strength of up to 134.116 MPa and an energy storage capacity of 483.151 J/g in the range of 100 to 400 °C, as well as excellent thermal stability and chemical compatibility between components, inside which the NaNO3 is well encapsulated. Moreover, the phase-change composites fabricated in this work have far low energy consumption and carbon dioxide emission.
•PCC encapsulates well at a 3.5 : 1.5 : 5 mass ratios of DG, CS, and NaNO3.•NaNO3 has favorable chemical compatibility with CS and DG.•SP3 reached a TES density of 483.151 J/g and compressive strength of 134.116 MPa.•SP3 shows the good thermal stability through the 2094 heating/cooling cycles.
