•Liquid-gas heat transfer of I-CAES based on spray injection was analyzed.•Spray effectively suppresses air temperature change due to high heat transfer rate.•Spray flow rate determines the dominant ...heat transfer mechanism.•Slow compression/expansion with enough heat transfer duration leads to high RTE.•High air storage pressure deviates CAES from isothermal system leads to low RTE.
Isothermal compressed air energy storage (I-CAES) could achieve high roundtrip efficiency (RTE) with low carbon emissions. Heat transfer enhancement is the key to achieve I-CAES, thus the liquid-gas heat transfer characteristics of near I-CAES system based on spray injection was analyzed in this paper. The liquid-gas heat transfer model and thermodynamic model were established and the effects of design variables on heat transfer rate and energy efficiency were analyzed. The results showed that spray injection can produce considerable heat transfer capacity and effectively suppress air temperature change, but spray injection at initial compression stage will not bring much heat transfer enhancement. Increasing spray flow rate shifts the dominant heat transfer contribution from water bulk to spray heat transfer and increases total heat transfer rate and RTE, however the increase effect of spray injection is more obvious in small-scale CAES. Low water flow rate and large working cylinder volume are recommended to achieve slow compression and expansion processes with enough liquid-gas heat transfer duration, realizing near I-CAES with high RTE. High air storage pressure increases heat transfer rate, but deviates CAES from isothermal system, resulting in low RTE. This research will provide scientific basis for heat transfer enhancement, system design and performance optimization of I-CAES.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Novel deep GSHP system using abandoned oil well was presented.•Heat supply of unit depth by the system reached to 192 kW/m.•There was an optimal inlet temperature obtaining largest system COP.•The ...order of parameters’ intensity of effect on COP was obtained.•Flow rate showed the strongest influence on the system COP.
As one of the most important geothermal applications, ground source heat pump (GSHP) systems have been applied for spacing heating and cooling of buildings, and the abandoned oil wells (AOW) with deep depth contain abundant geothermal energy. Therefore, this study proposed a new GSHP system using single AOW, and the deep coaxial borehole heat exchanger (BHE) with insulation is introduced to retrofit the wellbore of AOW for heat extraction. At first, a comprehensive heat transfer model for the deep coaxial BHE combing fluid, borehole and ground was built to evaluate the performance of the proposed GSHP systems during annual run. Then, Monte Carlo method was used for parameters sensitivity analysis to obtain the PRCC determining the intensity of parameters effect on total system COP. Lastly, the optimization of injection parameters was performed. The results indicated that flow rate showed the strongest influence on the total system COP. During the annual operation, it was found that the mean heat supply by the AOW-GSHP system was about 384 kW, and reached to 192 kW/m for unit depth which was obviously higher than that in conventional GSHP. And the mean heat extraction from AOW by the AOW-GSHP system reached to 294 kW, more than that by directing heating using AOW. By the optimization, it was found there was optimal inlet temperature getting maximum system COP and it existed a minimum injection pressure supporting system operation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In consideration of droplet flash evaporation and film flash evaporation, a comprehensive mathematical model of vacuum flash evaporation cooling (VFEC) was presented in this paper. Pure water was ...considered to be the working fluid. The droplet flash evaporation was modeled based on the diffusion-controlled evaporation model, while the film flash evaporation was modeled based on the film penetration theory. The droplet flash model coincided well with the experimental results reported in the literature and the comprehensive mathematical model was validated by experiment results in this paper. The droplet temperature and diameter after droplet flash evaporation were obtained numerically, and then analyzed. The effect of droplet flash evaporation on the surface temperature distribution, heat flux density, and heat transfer ratio of different mechanisms was studied based on the model. It can be concluded that the droplet flash evaporation, which can be expressed by the ratio of droplet-wall impaction heat transfer, had a great effect on vacuum flash evaporation cooling heat transfer. The droplet-wall impaction and film flash heat transfer were dominant in the vacuum flash evaporation cooling. The spray characteristics such as droplet diameter and temperature decreased a lot after droplet flash evaporation, compared to the initial parameters (measured by the PDA). After taking droplet flash into account, the surface temperature decreased and the heat flux increased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In recent years, due to the rapid development of high-performance small molecule acceptor (SMA) materials, the researches on
p
-type electron donor materials for matching with current efficient SMAs ...have become important. By means of asymmetric strategies to optimize the energy levels and inter/intramolecular interactions of molecules, we designed and synthesized an asymmetric aromatic side chain quinoxaline-based polymer donor TPQ-0F. Meanwhile, we took advantage of F atom which could form noncovalent interaction and strong electron-withdrawing property, to obtain the optimized quinoxaline-based polymer donors TPQ-1F, TPQ-1Fi and TPQ-2F. Eventually, the binary device based on TPQ-2F achieved an efficient power conversion efficiency (PCE) of 16.27%, which attributed to balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Our work demonstrates the great potential of asymmetric aromatic side chain quinoxaline-based polymer donors on optimizing the morphology of blending films, improving inter/intramolecular interactions, and subtly tuning energy level, finally for more efficient organic solar cells.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•PCM/aluminum honeycomb composite was used for thermal control.•A numerical model was established and validated for further study.•The composite material performs well in both thermal and mechanical ...properties.•The composite expands the application range for phase change thermal control.
A new kind of composite material combined the shape-stabilized phase change material with aluminum honeycomb used in thermal control was prepared and investigated both theoretically and experimentally. The shape-stabilized PCM prepared in this paper was experimentally validated to have stable phase change temperature, latent heat and thermal conductivity after several cycles of melting and solidification. The metal honeycomb structure could enhance the thermal conductivity and structural strength of organic PCM effectively with adding little weight to the system. The stress tolerance limit (STL) of the composite material was measured and compared with that of the shape-stabilized PCM. The results showed that the STL was promoted by 25.2%. A performance test experiment of the PCM thermal control unit was accomplished and a numerical model was established for further study. The temperature variations of the numerical model were in good agreement with the experimental data. Results showed that the addition of aluminum honeycomb structure could make the temperature variation of the heating source in a much smaller range, compared with the result that without aluminum honeycomb. The shape-stabilized PCM/aluminum honeycomb composite material showed the best combination properties of heat transfer and mechanical behavior.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•High alcohol surfactant has a significant effect on spray cooling.•Each surfactant has optimal concentration value to have the best performance.•Effect of surfactant on physical properties is mainly ...on surface tension.•Effect of surfactant on spray characteristics is mainly on droplet number.•Correlations to predict droplet diameter and droplet velocity are proposed.
The addition of surfactant is considered as an important method for heat transfer enhancement in spray cooling based on numerous advantages such as less demand, significant effect and stable performance. Recent studies have found that high alcohol surfactant has a significant effect on the heat transfer in spray cooling. In this study, the effect of four kinds of high alcohol surfactants, 1-heptanol, 1-octanol, isooctanol and n-decanol, on spray cooling heat transfer using water as the working medium was studied experimentally. It was found that there exists an optimal concentration for each surfactant to achieve the best heat transfer performance. Under the experimental conditions, the optimal value of 1-heptanol was 0.3‰, heat dissipation flux reached 180.9 W/cm2, and the heat transfer increased by 20.9%; the best value of 1-octanol was 0.3‰, heat dissipation flux reached 200.8 W/cm2, and the heat transfer increased by 34.2%; the best value of isooctanol was 0.5‰, heat dissipation flux reached 185 W/cm2, and the heat transfer increased by 23.7%; the best value of n-decanol was 0.1‰, heat dissipation flux reached 180.7 W/cm2, and the heat transfer increased by 20.8%. To further analyze the enhancement mechanism, this paper also studied the influence of surfactant concentration on physical properties of working fluid and the spray characteristics. The experimental results showed that the effect of surfactant on saturated vapor pressure was small, and the change became obvious at higher temperature. The tension changed obviously with the surfactant concentration, and the surface tension decreased rapidly at lower concentration. The dynamic viscosity did not vary much with the type and concentration of the surfactant. The relationship between physical properties and concentration was also obtained in experiments. After adding surfactant, droplet number was lower than that of water, the distribution of droplets at different heights was more even. Droplet diameter reduced in certain area, however it increased in the edge of the area due to local impact and fusion. The change of droplet velocity was not obvious. This paper also put forward relations between the physical properties of different working fluids and their concentration and correlations which can predict diameter and velocity of spray droplet.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Using abandoned oil wells for geothermal power generation can relieve energy problem, save drilling cost, and govern the pollution caused by the residual oil of the abandoned oil wells. In this ...paper, a novel method for enhancing the geothermal utilization efficiency by developing thermal reservoirs is presented. A 2-D thermal reservoirs coupling with 1-D wellbore heat transfer model was set up to simulate geothermal energy production, and the effects of the thermal reservoirs on the geothermal production and electric power output were analyzed. The study results showed that the geothermal well with thermal reservoirs could produce about 4 times the heat and electric power output as that without thermal reservoirs. Moreover, the thermal reservoirs parameters would impact the heat production and power generation significantly. Especially, the heat production and electric power output increased with the thermal reservoirs depth and the fluid injection rate, however increased with the thermal reservoirs length firstly, and then decreased, which indicated that there was a maximal heat production and power generation at an optimal reservoir length. Simultaneously, the fluid loss in the thermal reservoirs increased with the thermal reservoirs depth and length as well as thermal reservoirs porosity.
•A 2-D thermal reservoirs coupling with 1-D wellbore heat transfer model was set up.•The simplified model greatly shortened the simulated calculation time.•The effects of porosity, fluid loss and permeability on production were considered.•The thermal reservoirs could enhance the heat and electric power output observably.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The thermal conductivity of supercritical fluids is a crucial parameter for many applications in the field of energy conversion. However, the drastic nonlinear variations of gas properties near the ...pseudo-critical line make it difficult to determine the real characteristic temperatures, leading to large deviations between measurements. A cluster data processing method is proposed to determine thermal conductivity variations at the actual temperatures near the pseudo-critical line. Based on this method, the thermal conductivities of supercritical CO2 near the pseudo-critical line were measured using the measurement system constructed with the short-hot-wire apparatus. The data in this article confirm the existence of thermal conductivity peaks close to pseudo-critical points. The results show that the literature data and the NIST Standard Reference Database agree well with the experiments in this paper away from the pseudo-critical points, but there are large deviations near the pseudo-critical points. The differences are caused by the identification of the characteristic temperatures, demonstrating the rationality and superiority of the proposed method. This article enriches the measurement data of supercritical CO2 near the pseudo-critical line and proposes a new data processing method that lays the foundation for the accurate measurements of other fluids with temperature-sensitive properties.
•A data process is proposed to avoid the error caused by characteristic temperature.•A system to measure gas thermal conductivity in pseudo-critical region is set up.•The data processing method is verified by testing CO2 away from the critical point.•Results well show the change in thermal conductivity at CO2 pseudo-critical points.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A tidal stream energy resource assessment can be achieved through direct measurements of tidal elevations or flow velocities, theoretical formulas, and numerical models. This paper first described ...the development of renewable energy in China. Then, the tidal stream energy resource in the Qiantang River Estuary was assessed. The present work established a 2D numerical model for calculating the power density in the estuary and validated it with in situ water level, tidal current, and suspended sediment concentration measurements. Three possible sites found near the Hangzhou Bay Bridge were selected for detailed resource assessment. The results indicated that if only 50 turbines are deployed to each site, the tidal stream energy output by all turbines would be 7.5 GWh/year. Finally, building a tidal stream power generation device into an existing bridge structure was proposed at the Qiantang River Estuary.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
