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Thermochemical energy storage (TCES) has attracted significant attention in recent years due to some unique features of the technology such as very high energy density and negligible heat loss during storage. The TCES, however, is still at its early stage of development currently at a technology readiness level of 1–3. Major technical challenges of the TCES include materials stability, charge/discharge kinetics and limited temperature lift. Here we firstly studied the application of shell-and-tube thermochemical reactor with silica gels as heat storage material in open TCES system by experimental method. And then validated model (the maximum root mean square percentage error of 13.62% between the modeling and experiments) of single tube reactor containing 0.29 kg silica-gel was established to numerically investigate the discharging behavior of the thermochemical reactor under different operating conditions and flow directions of air and water. The numerical simulation results showed inverse heat transfer occurred for a counter-flow of air-water. The problem could be solved by changing the counter-flow of air and water to the parallel-flow. Thus, the water outlet maximum temperature limit was broken through. The total heat uptake increased by at least 24.14% when water flow rate was less than 0.36 kg/h and 11.93% when air flow rate was more than 1.07 kg/h, respectively. By increasing the inlet temperature of air and water from 23 °C to 38 °C, the maximum temperature lift could be significantly increased by 79.94% for air and 80.81% for water, respectively. Meanwhile, the total heat uptake increased by 107.44%. For a completely charging and discharging process, the discharging rate of parallel-flow was faster than that of counter-flow.

Distributed generation (DG) has gradually become significant in the power system owing to energy shortages and environmental pollution. However, the traditional structure of power systems is change...

The present study considers sand saturated with thermal conductive fluid as a new low-cost thermal storage material that can have better heat transfer than using concrete or sand alone and also avoids issues of heat transfer degradation associated with the mismatch of thermal expansion in concrete. The new thermal storage material (sand saturated with Xceltherm ® 600 heat transfer oil) was tested in a lab-scale experimental setup from 27 °C to 55 °C to show the concept and also validate a 1D transient enthalpy-based model for simulation of thermal storage. The model was then applied to study and compare the thermal storage performance of sand saturated by Hitec ® (heat transfer fluid) and concrete for a 600MW ele CSP power plant at a thermal efficiency of 35% and thermal storage temperatures ranging from 400 °C and 500 °C. It was found that more energy can be stored and extracted if Hitec ® -saturated sand is used as storage media, which may result in appreciable cost reduction than using concrete thermal storage system based on a study for a 600 MW ele CSP system in operation for one year. As a result, Hitec ® -saturated sand can be used to replace concrete as the thermal storage media in high temperature operating range (>400 °C). It is expected that such a new approach of sensible heat storage is of significance to solar thermal energy storage technologies.

Although ceramic-based oxygen transport membranes (OTMs) have irreplaceable advantages over traditional oxygen production technologies, their oxygen permeability and stability need to be further improved. Based on the theoretical starting point of increasing the three-boundary reaction zone and reducing blocking effect, a set of new dual-phase membranes 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%-Sm0.8Sr0.2Co0.8Fe0.2O3-δ (CSC-8282) and 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%Sm0.3Sr0.7Co0.8Fe0.2O3-δ (CSC-3782) with different strontium contents were prepared by a one-pot sol-gel method ensuring that each element has the same chemical potential. The surface morphology, crystal structure and element distribution are systematically studied by SEM, XRD and EDS, which confirms that the synthesized membranes have an obvious dual-phase structure and excellent compactness. The results of the oxygen permeability experiment show that the oxygen permeability of CSC-3782 is always higher than that of CSC-8282 under any conditions due to the inducing effect of strontium on oxygen vacancies, and flow rate of CSC-3782 at 960°C reached 0.64 and 0.22mL⋅cm-2⋅min-1 for He and CO2 as a sweep gas, respectively. The final long-term stability test confirmed that the dual-phase composite membrane with great prospects for development has high temperature stability and CO2-tolerant property, and the doping of strontium to A-site of perovskite contributes to the improvement of its performance.

This study focuses on altering the diffusion combustion characteristics of the self-reflux burner by optimizing the burner nozzle structure. By adjusting the jet angle of each nozzle, enhancing the diffusion effect of fuel and air in the combustion chamber, a low-oxygen combustion atmosphere is formed in the high-temperature zone of the combustion chamber, avoiding local high temperature caused by fuel accumulation and combustion, reducing the combustion rate of nitrogen, and then the thermal NOx emission is reduced. Parallel, inwardly inclined, and outwardly inclined jet angles are studied in simulation, and five working conditions (-10°, -5°, 0°, 5°, and 10°) are calculated, compared, and analyzed. The cooperative coupling mechanism between multiple fields (velocity, concentration, and temperature) is compared and analyzed. We use the diffusion effect to reduce the oxygen concentration in the central axis and achieve the goal of reducing NOx by reducing the maximum combustion temperature. The simulation results show that the maximum and average temperatures of the combustion chamber are reduced by 28.9 K and 15.38 K, respectively, when the jet angle is outwardly tilted by 5°, which reduces the local high temperature; and NOx emissions are in turn reduced by 104.72 ppm.

Based on the design concept of a fourth-generation smart pipe network system, this paper innovatively proposes a new TOTS (Two-supply/One-return, triple pipe structure) arrangement method for district heating systems. Moreover, to accurately predict the heat loss due to the pipeline operation of the multi-pipe system, based on the multipole calculation method, a new heat loss theoretical analytical model for the TOTS was created; additionally, a corresponding three-dimensional numerical simulation model was established, which was analyzed and numerically solved. The results showed that in comparison with thermal loss data measured by Danfoss et al., the above analytical and numerical models have a high accuracy, and the deviation is within 2%. Additionally, through calculations, it was found that the distance between the heating pipes is an important factor that affects the total heat loss from the new multi-control heating system and the actual heat exchange between pipes.

Based on the 1MWt parabolic trough concentrating solar power (CSP) pilot plant, the operation characteristics are investigated in three typical weather conditions around the vernal equinox. A simplified performance prediction model is proposed, and the simulation results are compared with the measured data. The results show that the change of the heat transfer oil temperature at the loop inlet will be transferred to the loop outlet after a while. The fluctuation of direct normal irradiance (DNI) has little effect on the outlet temperature. The model is able to accurately predict the performance of the parabolic trough systems at stable flow rate and stable inlet temperature. Installation accuracy of parabolic trough collectors as well as the cleanliness of mirrors has a great influence on the collectors’ solar-to-thermal efficiency, therefore, high standard of installation and maintenance is necessary.

With an extended lumped capacitance method applied to account for the internal heat conduction resistance in a solid (for Biot number larger than 0.1), a general model of thermal energy storage with various solid–fluid structural combinations is presented and verified using numerical results. The thermal energy storage system has a heat transfer fluid (HTF) flowing through a packed bed of solid materials structured in different configurations, such as in the form of solid pebbles, parallel plates, solid rod-bundles, or solids with fluid tubes imbedded through them. The model of energy conservation in the liquid and solid is transient, one-dimensional in nature, due to the introduction of a modified lumped capacitance method that counts for the effect of three-dimensional heat conduction in the solid structures. The computational workload using this modified model is significantly less compared to that of a comprehensive CFD analysis. Numerical results obtained from a CFD analysis of the thermal energy storage in the solid and liquid are used to verify the model. The CFD simulated results of temperatures of HTF are compared with the 1D model results, and they show excellent agreement. In conclusion, the 1D model is recommended as a convenient and accurate tool for general analysis and sizing of thermal energy storage containers that have various solid–fluid structural combinations.

Because of the capability of large capacity thermal storage, concentrated solar power (CSP) technology is getting more attentions in the recent years. The energy storage allows power generation using solar energy during the late afternoon and evening time. For a large capacity of thermal energy storage, a dual-media system is typically adopted for reducing the use of the heat transfer fluid (HTF), which is usually expensive. In a dual-media system, the solid material must have large heat capacity and be inexpensive. One type of configuration for a dual-media system is that HTF flowing in pipes which are imbedded into the solid material. The present study considers sands, a major component of concrete, as low-cost solid thermal storage materials. The novel approach is that the sand is saturated with high thermal conductive fluid. Compared to using concrete for thermal storage, this method avoids issues of heat transfer degradation associated with the mismatch of thermal expansion of pipes and concrete. Since only sands are porous materials and the heat transfer performance is low, a high conductive fluid (XCELTHERM® 600 hot oil) was used to saturate sands, which then forms a new thermal storage material that can have better heat transfer. Results of thermal storage process with sands only and with the oil-saturated sands are presented and discussed.Copyright © 2014 by ASME