Effect of Orientation on Performance of The Refrigerant Distributor

Maldistribution of refrigerant two-phase flow in a DX evaporator is almost inevitable in real application because of the different properties of liquid and vapor. One of the main reasons for this is phase separation due to the effect of gravity. For vertical orientation, the influence of gravity on the operation of distributors is small. However, horizontal installation is more likely to be affected by gravity when the flow is not homogeneous. This paper presents an evaluation of the performance of a refrigerant distributor at three different orientations: horizontal, vertical upwards, and downwards. For each direction, the expansion device, distributor, and evaporator are connected in the same way to reduce the effect of test facility on the flow distribution. A transparent distributor with identical geometry of an original version is built for the purpose of visualization. Both distributors are tested under the same working conditions to investigate the individual difference. Results show that two-phase distribution at the horizontal orientation is similar to the vertical results, indicating no effect of gravity for the tested working conditions. However, the difference in individual distributor circuit due to manufacture will result in maldistribution in some degree

Effect of Flow Regime Before Distributor on Two-phase Flow Distribution

Conical refrigerant distributors are usually used to improve the distribution of two-phase flow to each circuit of the DX evaporators. A nozzle is commonly added before a cone to homogenize two-phase flow and that way unify distribution among channels. However, when the nozzle is not properly sized or, in some cases, there is no nozzle, the distributor performance is much affected by the flow regimes at the distributor inlet. This paper presents the effect of the flow regime at the distributor inlet on the uniformity of two-phase flow distribution. In this case, the flow regime is determined by mass flux, quality, and distance from the expansion device. A high-speed camera is used to visualize the two-phase flow regimes between the expansion valve and distributor. The same technique is also used to interrogate the flow regime inside the distributor. We relate the distributor performance with flow regimes at the distributor inlet to understand the two-phase distribution behavior. The experiments using the distributor with the original design is set as the baseline. After acquiring results for the baseline situation, we implemented two approaches to change the flow regime at the distributor inlet besides changing the operating conditions. The first is adding an orifice to remix the two-phase flow, and the second is increasing the distance between the distributor and the expansion valve to make the two-phase flow fully developed. The average deviations of capacity for each branch are 6-10% for the baseline case, less than 2% for the distributor with an orifice, and 20% for the distributor with a 600mm inlet tube

Evaluation and visualization of refrigerant two-phase flow in distributor

This study aims at understanding flow distribution exiting thermostatic expansion valve and through distributor. It is well known that when two-phase flow goes through separation devices such as distributors and headers, mal-distribution is unavoidable due to different properties of liquid and vapor. However, it is possible to reduce mal-distribution by better design or creating proper working conditions. In this study, several parameters that may influence the flow distribution such as mass flow rate, distributor inlet quality, and orientation are studied. Refrigerant mal-distribution is quantified by comparing mass flow rate, quality, and cooling capacity in each circuit. To make the experiment results more applicable to real system, several aspects in this facility which are not exactly the same with real air conditioning system are analyzed, including the extra pressure drop due to mass flow meter and the different design of evaporator. What’s more, two-phase flow exiting thermostatic expansion valve and through distributor is visualized by high-speed camera to get a deeper understanding about what happened in this region. It was found that better distribution can be achieved at higher mass flow rate and lower distributor inlet quality, because flow velocity increases as mass flow rate gets higher, which contributes to form more homogeneous flow. And decrease in quality makes the two-phase flow closer to single phase. Orientation was found to have no influence on distribution, since the distributor is installed quite close to the exit of thermostatic expansion valve where the phase separation does not happen. The pressure drop due to mass flow meter was proved helpful to achieve better distribution, which means the performance of distributor was a little overestimated by experiments in this study. According to the visualization, flow regime at the inlet of distributor is somewhere between annular flow and homogeneous flow with variation of mass flow rate

'Don't Get Too Technical with Me': A Discourse Structure-Based Framework for Science Journalism

Science journalism refers to the task of reporting technical findings of a scientific paper as a less technical news article to the general public audience. We aim to design an automated system to support this real-world task (i.e., automatic science journalism) by 1) introducing a newly-constructed and real-world dataset (SciTechNews), with tuples of a publicly-available scientific paper, its corresponding news article, and an expert-written short summary snippet; 2) proposing a novel technical framework that integrates a paper's discourse structure with its metadata to guide generation; and, 3) demonstrating with extensive automatic and human experiments that our framework outperforms other baseline methods (e.g. Alpaca and ChatGPT) in elaborating a content plan meaningful for the target audience, simplifying the information selected, and producing a coherent final report in a layman's style.Comment: Accepted to EMNLP 202

NECE: Narrative Event Chain Extraction Toolkit

To understand a narrative, it is essential to comprehend the temporal event flows, especially those associated with main characters; however, this can be challenging with lengthy and unstructured narrative texts. To address this, we introduce NECE, an open-access, document-level toolkit that automatically extracts and aligns narrative events in the temporal order of their occurrence. Through extensive evaluations, we show the high quality of the NECE toolkit and demonstrates its downstream application in analyzing narrative bias regarding gender. We also openly discuss the shortcomings of the current approach, and potential of leveraging generative models in future works. Lastly the NECE toolkit includes both a Python library and a user-friendly web interface, which offer equal access to professionals and layman audience alike, to visualize event chain, obtain narrative flows, or study narrative bias

Pretreating poplar cuttings with low nitrogen ameliorates salt stress responses by increasing stored carbohydrates and priming stress signaling pathways

Soil salinity is a widespread stress in semi-arid forests worldwide, but how to manage nitrogen (N) nutrition to improve plant saline tolerance remains unclear. Here, the cuttings of a widely distributed poplar from central Asia, Populus russikki Jabl., were exposed to either normal or low nitrogen (LN) concentrations for two weeks in semi-controlled greenhouse, and then they were added with moderate salt solution or not for another two weeks to evaluate their physiological, biochemical, metabolites and transcriptomic profile changes. LN-pretreating alleviated the toxicity caused by the subsequent salt stress in the poplar plants, demonstrated by a significant reduction in the influx of Na+ and Cl- and improvement of the K+/Na+ ratio. The other salt-stressed traits were also ameliarated, indicated by the variations of chlorophyll content, PSII photochemical activity and lipid peroxidation. Stress alleviation resulted from two different processes. First, LN pretreatment caused a significant increase of non-structural carbohydrates (NSC), allowed for an increased production of osmolytes and a higher potential fueling ion transport under subsequent salt condition, along with increased transcript levels of the cation/H+ ATPase. Second, LN pretreatment enhanced the transcript levels of stress signaling components and phytohormones pathway as well as antioxidant enzyme activities. The results indicate that early restrictions of N supply could enhance posterior survival under saline stress in poplar plants, which is important for plantation programs and restoration activities in semi-arid areas.This research was supported by Natural Science Foundation of China ( 31770644 and 31270660 ), Project of Innovation research team in Sichuan Education Administration in China (No. 13TD0023 )

An intelligent neural stem cell delivery system for neurodegenerative diseases treatment

Transplanted stem cells constitute a new therapeutic strategy for the treatment of neurological disorders. Emerging evidence indicates that a negative microenvironment, particularly one characterized by the acute inflammation/immune response caused by physical injuries or transplanted stem cells, severely impacts the survival of transplanted stem cells. In this study, to avoid the influence of the increased inflammation following physical injuries, an intelligent, double‐layer, alginate hydrogel system is designed. This system fosters the matrix metalloproeinases (MMP) secreted by transplanted stem cell reactions with MMP peptide grafted on the inner layer and destroys the structure of the inner hydrogel layer during the inflammatory storm. Meanwhile, the optimum concentration of the arginine‐glycine‐aspartate (RGD) peptide is also immobilized to the inner hydrogels to obtain more stem cells before arriving to the outer hydrogel layer. It is found that blocking Cripto‐1, which promotes embryonic stem cell differentiation to dopamine neurons, also accelerates this process in neural stem cells. More interesting is the fact that neural stem cell differentiation can be conducted in astrocyte‐differentiation medium without other treatments. In addition, the system can be adjusted according to the different parameters of transplanted stem cells and can expand on the clinical application of stem cells in the treatment of this neurological disorder