Solar Driven Gas Phase Advanced Oxidation Processes for Methane Removal - Challenges and Perspectives.

Methane (CH4 ) is a potent greenhouse gas and the second highest contributor to global warming. CH4 emissions are still growing at an alarmingly high pace. To limit global warming to 1.5 °C, one of the most effective strategies is to reduce rapidly the CH4 emissions by developing large-scale methane removal methods. The purpose of this perspective paper is threefold. (1) To highlight the technology gap dealing with low concentration CH4 (at many emission sources and in the atmosphere). (2) To analyze the challenges and prospects of solar-driven gas phase advanced oxidation processes for CH4 removal. And (3) to propose some ideas, which may help to develop solar-driven gas phase advanced oxidation processes and make them deployable at a climate significant scale.

Enhanced thermal and mechanical performance of 3D architected micro-channel heat exchangers.

Many crystals in nature have simple interatomic microstructures, such as simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) lattice symmetries, making these structures extremely stable. Inspired by these arrangements, a series of architected micro-channel heat exchangers with rationally designed 3D microstructures were established. A multi-physics mathematical model using thermal-fluid-structure interaction (TFSI) was employed to investigate the coupled heat transfer performance and mechanical properties of these architected heat exchangers. When compared with the corrugated straight plate (CSP) microchannel heat exchanger, the thermal-hydraulic performance factors (TPC) of FCC and BCC microchannel heat transfer were 2.20 and 1.70 times that of SC microchannel heat exchanger, respectively. The micro-channel heat exchanger with FCC architectures could enhance the convective heat transfer performance by 201.0%, while the micro-channel heat exchanger with SC architectures reduced the Von-Mises equivalent (VME) stress by 20.0% when compared with the conventional 2D CSP heat exchanger. The proposed architected micro-channel heat exchangers could find a wide range of potential applications ranging from power electronics in electric vehicles to concentrated solar power systems, where both good convective heat transfer performance and high mechanical strength are simultaneously pursued.

The simulated cooling performance of a thin-film thermoelectric cooler with coupled-thermoelements connected in parallel.

The thermoelements of the traditional thin-film thermoelectric cooler (TEC) are connected electrically in series, thus the performance of traditional thin-film TEC reduces sharply when there is something wrong with any thermoelement. On account of this deficiency, we proposed a novel thin-film TEC with a couple of thermoelements electrically connected in parallel and then electrically connected in series to the next couple of thermoelements. The performance and reliability of the novel thin-film TEC is compared with the traditional thin-film TEC. The maximum cooling capacity, the maximum cooling temperature, and the coefficient of performance of the novel and the traditional thin-film TEC are systematically studied and compared when 0, 2, and 4 thermoelements are disabled, respectively. The results show that the performance and reliability of the novel thin-film TEC are superior to that of the traditional thin-film TEC, while the optimal electric current of the novel thin-film TEC current is 2.14 times of that for the traditional thin-film TEC. This work is of great significance to improving the performance and reliability of thin-film thermoelectric devices consisting of dozens of small thermoelements.

Feasibility of Solar Updraft Towers as Photocatalytic Reactors for Removal of Atmospheric Methane-The Role of Catalysts and Rate Limiting Steps.

Due to the alarming speed of global warming, greenhouse gas removal from atmosphere will be absolutely necessary in the coming decades. Methane is the second most harmful greenhouse gas in the atmosphere. There is an emerging technology proposed to incorporating photocatalysis with solar updraft Towers (SUT) to remove methane from the air at a planetary scale. In this study, we present a deep analysis by calculating the potential of methane removal in relation to the dimensions and configuration of SUT using different photocatalysts. The analysis shows that the methane removal rate increases with the SUT dimensions and can be enhanced by changing the configuration design. More importantly, the low methane removal rate on conventional TiO2 photocatalyst can be significantly improved to, for example, 42.5% on a more effective Ag-doped ZnO photocatalyst in a 200 MW SUT while the photocatalytic reaction is the rate limiting step. The factors that may further affect the removal of methane, such as more efficient photocatalysts, night operation and reaction zone are discussed as possible solutions to further improve the system.

Efficient Gas Adsorption Using Superamphiphobic Porous Monoliths as the under-Liquid Gas-Conductive Circuits.

The gas-liquid membrane contactor forms a gas-solid-liquid interface and has a high potential for the applications in gas adsorption, catalysis, energy exchange, and so on. Porous superhydrophobic membranes show a great gas separation/adsorption ability. However, the complicated device architecture and the durability issue are normally concerned especially for the continuous circulation of gas and liquid. In this work, we present a free-standing gas-conductive circuit simply formed by connecting the superamphiphobic porous monoliths (SAPMs) to achieve an efficient under-liquid gas adsorption. The porous worm-like SAPM is prepared with low-temperature expandable graphite and polyvinylidenefluoride, exhibiting superamphiphobicity and superaerophilicity after fluoridation. The as-made SAPM circuits can be used as a reliable gas conductor under numerous liquids, such as water, alkaline, acidic, and oily solutions. In this work, the CO2 adsorption capacities of the SAPM circuits are evaluated under NaOH and methyldiethanolamine solutions and the mass transfer rate can reach up to 9.61 mmol m-2 s-1. Moreover, the effective human blood oxygenation process is also demonstrated using SAPM circuits. Thus, the reported SAPM provides an alternative gas-liquid exchanging method and the simplified process could be of great benefit to the cost-effectively large-scale CO2 capture or gas exchanging applications.

Fighting global warming by greenhouse gas removal: destroying atmospheric nitrous oxide thanks to synergies between two breakthrough technologies.

Even if humans stop discharging CO2 into the atmosphere, the average global temperature will still increase during this century. A lot of research has been devoted to prevent and reduce the amount of carbon dioxide (CO2) emissions in the atmosphere, in order to mitigate the effects of climate change. Carbon capture and sequestration (CCS) is one of the technologies that might help to limit emissions. In complement, direct CO2 removal from the atmosphere has been proposed after the emissions have occurred. But, the removal of all the excess anthropogenic atmospheric CO2 will not be enough, due to the fact that CO2 outgases from the ocean as its solubility is dependent of its atmospheric partial pressure. Bringing back the Earth average surface temperature to pre-industrial levels would require the removal of all previously emitted CO2. Thus, the atmospheric removal of other greenhouse gases is necessary. This article proposes a combination of disrupting techniques to transform nitrous oxide (N2O), the third most important greenhouse gas (GHG) in terms of current radiative forcing, which is harmful for the ozone layer and possesses quite high global warming potential. Although several scientific publications cite "greenhouse gas removal," to our knowledge, it is the first time innovative solutions are proposed to effectively remove N2O or other GHGs from the atmosphere other than CO2.