Thermal Stability and Performance Testing of Oil based CuO Nanofluids for Solar Thermal Applications

For solar thermal systems, nanofluids have been proposed as working fluids due to their enhanced optical and thermal properties. However, nanoparticles may agglomerate over time, heating and thermal cycles. Even though pristine nanofluids have be proven to enhance performance in low temperature application, it is still unclear if nanofluids can meet the reliability requirements of solar thermal applications. To investigate this, the present study conducted experiments with several formulations of oil‐based CuO nanofluids in terms of their maximum operational temperature and their stability upon cyclic heating. In the samples tested, the maximum temperature ranged from 80oC to 150 22 oC and the number of heating cycles of ranged from 5 to 45, with heating times of between 5 to 60 minutes. The results showed that heating temperature, heating cycles, and heating time all exacerbated agglomeration of the samples. Following these experiments, orthogonal experiments were designed to improve the preparation process and the resultant thermal‐impulse stability. Thermal properties of these samples were characterized and thermal performance in an ‘on‐sun’ linear Fresnel solar collector was measured. All tests revealed that thermal performance of solar collecting system could be enhanced with nanofluids, but that thermal stability still needs to be further improved for industrial applications

Simulation and economic analysis of an innovative indoor solar cooking system with energy storage

Solar energy technology and energy storage technology are promising to make a contribution to current energy and global climate issue. The energy demand of daily cooking is enormous, and conventional cooking methods use gas or electricity with large carbon emissions. This paper proposes an innovative solar cooking system (SCS) integrated with rock-bed thermocline storage. Thermal oils transfer heat from the collectors to the rocks in the charging process and release heat in cooktop unit for cooking. The energy consumption of a household is first assessed by a reasonable hypothesis. Mathematical models and simulation models are then established to analyze the heat transfer performance of the cooktop unit and the annual running performance of the SCS. The rock-bed thermocline storage, single-tank thermocline storage and two-tank storage are compared. The simulation results indicate that the rock-bed thermocline storage unit employed to SCS will enhance the annual running performance and acquire the minimum initial investment cost. The economic analysis shows that the lowest levelized cost of cooking energy (LCOC) of the SCS is 0.3884 $/kWh, while the corresponding levelized cost of cooking a meal (LCCM) is 0.953$/Meal and the solar fraction (SF) is 71%. Compared to the electrical and natural gas cooker, the SCS saves 1.75 tons and 0.52 tons of carbon emissions annually, respectively

Confined FeNi alloy nanoparticles in carbon nanotubes for photothermal oxidative dehydrogenation of ethane by carbon dioxide

Oxidative dehydrogenation of ethane with CO2 (ODEC) is an attractive reaction for reduction of carbon footprints and ethene production. In this work, we present photothermal catalysis on confined bimetal catalysts for ODEC. Carbon nanotubes confined non-noble bimetal alloy (i.e., CoNi@CNTs and FeNi@CNTs) catalysts were prepared and FeNi@CNTs showed effective performance in photothermal catalytic ODEC to ethene. Experiments and simulations reveal that UV and visible lights (420 – 490 nm) are responsible for ODEC and non-oxidative dehydrogenation of ethane, respectively, to ethene. Additionally, ODEC to ethene is preferred to C-C cracking to methane on FeNi@CNTs in light ( \u3e 490 nm)-induced thermocatalysis. The photothermal effect turns more significant when introduced into thermocatalytic ODEC (500 °C), with ethene generation at one order of magnitude. This work advances new mechanism of photo-mediated catalysis and sheds light on utilization of full-spectrum solar energy and non-noble metallic catalysts for ethene production and CO2 recycling at moderate conditions

Numerical investigation of the heat and mass transfer performance of a two-phase closed thermosiphon based on a modified CFD model

A modified CFD model was developed to investigate the heat and mass transfer performance of a two-phase closed thermosiphon (TPCT). In this model, the phase-change temperature of the working fluid was considered to be dependent on the local pressure. Meanwhile, an auto-adjust and control strategy was established for the condensation mass transfer time relaxation parameter, which could balance the phase-change pressure to the working pressure. The modified phase-change model was verified by experiments and then used to investigate the heat and mass transfer behaviors of the TPCT under different heat flux of 12.31–15.95 kW/m2. The results indicated that the maximum relative errors of wall temperature and working pressure of the TPCT were 0.25–0.48% and 0.14–0.46%, respectively. The wall temperature gradually decreases from the bottom of evaporator to adiabatic section, and then increases from the bottom to the top of the condenser due to the temperature difference between the inlet and outlet of the cooling water. Also, as the heat flux increase, the overall thermal resistance reduces from 0.060 to 0.055 K/W. These results indicate that the proposed model can be used to predict the heat and mass transfer of the TPCT

Gasification Characteristics of High Moisture Content Lignite under CO₂ and Auto-Generated Steam Atmosphere in a Moving Bed Tubular Reactor

An external thermal high-temperature continuous feed moving bed tubular reactor was used for the gasification of high moisture content lignite (30.41 wt.%) under CO2 and an auto-generated steam atmosphere. The objectives of this study are to illustrate the synergistic gasification characteristics of high moisture content lignite and CO2 in the tubular reactor; CO2 and auto-generated steam (steam released from the lignite) were used as gasification agents for lignite gasification. The effects of temperature and CO2 flow rate were also investigated. Experimental results showed that when the gasification temperature increased from 800 °C to 1000 °C, the H2 yield also increased from 8.45 mol kg−1 to 17.86 mol kg−1. This may indicate that the H2O-CO2 gasification of semi-coke was enhanced with the rise in temperature. At 900 °C, the gas yield increased with the increase in CO2 flow rate, while the yield of char and liquid product showed an opposite trend. The lower heating value of the H2-rich syngas varied from 11.73 MJ m−3 to 12.77 MJ Nm−3. The experimental results proved that the high moisture content lignite in-situ CO2 gasification process is an effective methodology for the clean and efficient utilization of lignite

Gasification Characteristics of High Moisture Content Lignite under CO2 and Auto-Generated Steam Atmosphere in a Moving Bed Tubular Reactor

An external thermal high-temperature continuous feed moving bed tubular reactor was used for the gasification of high moisture content lignite (30.41 wt.%) under CO2 and an auto-generated steam atmosphere. The objectives of this study are to illustrate the synergistic gasification characteristics of high moisture content lignite and CO2 in the tubular reactor; CO2 and auto-generated steam (steam released from the lignite) were used as gasification agents for lignite gasification. The effects of temperature and CO2 flow rate were also investigated. Experimental results showed that when the gasification temperature increased from 800 °C to 1000 °C, the H2 yield also increased from 8.45 mol kg−1 to 17.86 mol kg−1. This may indicate that the H2O-CO2 gasification of semi-coke was enhanced with the rise in temperature. At 900 °C, the gas yield increased with the increase in CO2 flow rate, while the yield of char and liquid product showed an opposite trend. The lower heating value of the H2-rich syngas varied from 11.73 MJ m−3 to 12.77 MJ Nm−3. The experimental results proved that the high moisture content lignite in-situ CO2 gasification process is an effective methodology for the clean and efficient utilization of lignite