A novel transcritical CO2 refrigeration cycle with two ejectors

In recent years, CO2 is being revisited as a fully environmentally friendly and safe refrigerant. However, basic CO2 transcritical refrigeration cycle suffers from large expansion loss due to high pressure difference between gas cooler and evaporator. Then, it is crucial to find effective and economic way to reduce the expansion loss. Here, a novel cycle with two ejectors is proposed for the first time. Compared with conventional ejector-expansion CO2 cycle with only one ejector, this novel cycle with two ejectors is able to recover more expansion loss, thus improving the system performance further. A computational model is designed to simulate the double ejector CO2 cycle. Simulation results show its high system COP. Effects of parameters, such as ejector nozzle efficiency, gas cooler pressure, entrainment ratios of the two ejectors, gas cooler outlet temperature, on the cycle performance are also analyzed by using the computational model. (C) 2012 Elsevier Ltd and IIR. All rights reserved.</p

Numerical study of vapor bubble effect on flow and heat transfer in microchannel

Flow boiling in a microchannel is characterized by nucleation and dynamic behavior of vapor bubbles in the channel. In the present study, the effect of vapor bubble on fluid flow and heat transfer in a microchannel is investigated via lattice Boltzmann (LB) modeling. With respect to boiling flow in a single microchannel, the bubble nucleation, growth, and departure are simulated by using an improved hybrid LB model. Relating bubble behavior with fluid flow and boiling heat transfer provides some insight into the relevant fundamental physics on flow boiling in the microchannel. It is found that the bubble growth before its departure from the wall induces an obvious resistance to the fluid flow. The processes of nucleation and motion of different bubbles interact, leading to an alternate, either enhanced or weakened, effect of bubble behavior on the flow boiling. (C) 2011 Elsevier Masson SAS. All rights reserved.</p

Heat Pump-Based Novel Energy System for High-Power LED Lamp Cooling and Waste Heat Recovery

Unlike incandescent light bulb, which radiates heat into the surroundings by infrared rays, light emitting diode (LED) traps heat inside the lamp. This fact increases the difficulty of cooling LED lamps, while it facilitates the recovery of the generated heat. We propose a novel energy system that merges high-power LED lamp cooling with the heat pump use; the heat pump can cool the LED lamp and at the same time recover the waste heat. In this way, a high percentage of the energy consumed by the LED lamp can be utilized. In this work, we developed a prototype of this energy system and conducted a series of experimental studies to determine the effect of several parameters, such as cooling water flow rate and LED power, on the LED leadframe temperature, compressor power consumption, and system performance. The experimental results clearly indicate that the energy system can lead to substantial energy savings

Cytosolic PLA2 is required for CTL-mediated immunopathology of celiac disease via NKG2D and IL-15

IL-15 and NKG2D promote autoimmunity and celiac disease by arming cytotoxic T lymphocytes (CTLs) to cause tissue destruction. However, the downstream signaling events underlying these functional properties remain unclear. Here, we identify cytosolic phospholipase A2 (cPLA2) as a central molecule in NKG2D-mediated cytolysis in CTLs. Furthermore, we report that NKG2D induces, upon recognition of MIC+ target cells, the release of arachidonic acid (AA) by CTLs to promote tissue inflammation in association with target killing. Interestingly, IL-15, which licenses NKG2D-mediated lymphokine killer activity in CTLs, cooperates with NKG2D to induce cPLA2 activation and AA release. Finally, cPLA2 activation in intraepithelial CTLs of celiac patients provides an in vivo pathophysiological dimension to cPLA2 activation in CTLs. These results reveal an unrecognized link between NKG2D and tissue inflammation, which may underlie the emerging role of NKG2D in various immunopathological conditions and define new therapeutic targets

A multimodal cell census and atlas of the mammalian primary motor cortex

ABSTRACT We report the generation of a multimodal cell census and atlas of the mammalian primary motor cortex (MOp or M1) as the initial product of the BRAIN Initiative Cell Census Network (BICCN). This was achieved by coordinated large-scale analyses of single-cell transcriptomes, chromatin accessibility, DNA methylomes, spatially resolved single-cell transcriptomes, morphological and electrophysiological properties, and cellular resolution input-output mapping, integrated through cross-modal computational analysis. Together, our results advance the collective knowledge and understanding of brain cell type organization: First, our study reveals a unified molecular genetic landscape of cortical cell types that congruently integrates their transcriptome, open chromatin and DNA methylation maps. Second, cross-species analysis achieves a unified taxonomy of transcriptomic types and their hierarchical organization that are conserved from mouse to marmoset and human. Third, cross-modal analysis provides compelling evidence for the epigenomic, transcriptomic, and gene regulatory basis of neuronal phenotypes such as their physiological and anatomical properties, demonstrating the biological validity and genomic underpinning of neuron types and subtypes. Fourth, in situ single-cell transcriptomics provides a spatially-resolved cell type atlas of the motor cortex. Fifth, integrated transcriptomic, epigenomic and anatomical analyses reveal the correspondence between neural circuits and transcriptomic cell types. We further present an extensive genetic toolset for targeting and fate mapping glutamatergic projection neuron types toward linking their developmental trajectory to their circuit function. Together, our results establish a unified and mechanistic framework of neuronal cell type organization that integrates multi-layered molecular genetic and spatial information with multi-faceted phenotypic properties

A numerical study of EGS heat extraction process based on a thermal non-equilibrium model for heat transfer in subsurface porous heat reservoir

With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process

A review on passive and active strategies of enhancing the safety of lithium-ion batteries

Lithium-ion battery (LIB) becomes the dominant candidate for electric vehicles (EVs) and energy storage systems (ESSs); nevertheless, as its popularization, the number of safety (fire) accidents regarding with LIB thermal runaway increases, undermining the public confidence. Safety turns into one of the main concerns in the widespread usage of LIBs. In this review paper, various faults in LIBs which have a potential risk leading to safety accidents are scrutinized firstly, followed by the presentation of recent progress in strategies of improving the safety of LIBs. Faults in large-scale LIB-based systems like EVs and ESSs for power grids include battery faults, sensor faults and actuator faults. The battery faults can be triggered by mechanical abuse, electrical abuse, thermal abuse as well as aging or degradation. This paper classifies the safety strategies into active safety strategies and passive safety strategies. Passive safety strategies pursue inherent safety in LIBs via material modification and alleviate the hazard level of faults through taking timely countermeasure like fire suppression or extinguishment once the LIB fire accident occurs. On the contrary, the active safety strategies aim to prevent the abuse conditions from developing into uncontrollable thermal runaway or fire accidents by effective state estimation and monitoring, fault diagnosis and early warning, thermal management, equalization technology, etc. (c) 2021 Elsevier Ltd. All rights reserved

Simulated annealing reconstruction and characterization of the three-dimensional microstructure of a LiCoO2 Lithium-ion battery cathode

We adapt the simulated annealing approach for reconstruction of the 3D microstructure of a LiCoO2 cathode from a commercial Li-ion battery. The real size distribution curve of LiCoO2 particles is applied to regulate the reconstruction process. By discretizing a 40 x 40 x 40 mu m cathode volume with 8,000,000 numerical cubes, the cathode involving three individual phases: 1) LiCoO2 as active material, 2) pores or electrolyte, and 3) additives (polyvinylidene fluoride + carbon black) is reconstructed. The microstructural statistical properties required in the reconstruction process are extracted from 2D focused ion beam/scanning electron microscopy images or obtained by analyzing the powder mixture used to make the cathode. Characterization of the reconstructed cathode gives important structural and transport properties including the two-point correlation functions, volume-specific surface area between phases, tortuosity and geometrical connectivity of individual phase. (C) 2013 Elsevier Inc. All rights reserved

Elucidating the Performance Limitations of Lithium-ion Batteries due to Species and Charge Transport through Five Characteristic Parameters

Underutilization due to performance limitations imposed by species and charge transports is one of the key issues that persist with various lithium-ion batteries. To elucidate the relevant mechanisms, two groups of characteristic parameters were proposed. The first group contains three characteristic time parameters, namely: (1) t(e), which characterizes the Li-ion transport rate in the electrolyte phase, (2) t(s), characterizing the lithium diffusion rate in the solid active materials, and (3) t(c), describing the local Li-ion depletion rate in electrolyte phase at the electrolyte/electrode interface due to electrochemical reactions. The second group contains two electric resistance parameters: R-e and R-s, which represent respectively, the equivalent ionic transport resistance and the effective electronic transport resistance in the electrode. Electrochemical modeling and simulations to the discharge process of LiCoO2 cells reveal that: (1) if te, ts and tc are on the same order of magnitude, the species transports may not cause any performance limitations to the battery; (2) the underlying mechanisms of performance limitations due to thick electrode, high-rate operation, and large-sized active material particles as well as effects of charge transports are revealed. The findings may be used as quantitative guidelines in the development and design of more advanced Li-ion batteries