Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

This is an open access article distributed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International license (CC BY-NC-ND 4.0) https://creativecommons.org/licenses/by-nc-nd/4.0/Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional (2D) numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.Peer reviewe

Modeling of heat transfer for energy efficiency prediction of solar receivers

© 2019 Elsevier. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). Please see https://creativecommons.org/licenses/by/4.0/ for further details.In this article, a new heat transfer model for solar receivers with metal foam is developed for design optimization. The proposed model facilitates analysis of heat transfer processes in terms of forced convection, natural convection, heat conduction and radiation, accurately predicting the energy efficiency and percentage contribution of each form of heat loss. The results show good agreement between the predicted results and the experimental data. Specifically, sensitivity analysis is performed to predict the energy efficiency of solar receivers under different operating conditions. To explore the influence of inlet temperature, a series of simulations under high inlet temperature are carried out, resulting in poorer energy performance and heavier radiant heat loss. Non-radiant heat loss, however, accounts for less than 1.1% of the total energy loss in all cases. The results reveal that reduction of radiant loss is conducive to energy efficiency improvement.Peer reviewe

Experimental and Analytical Study of Dual Compensation Chamber Loop Heat Pipe under acceleration force assisted condition

In this article, a combined experimental and theoretical study has been conducted to investigate the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) with ammonia as the working fluid under acceleration force conditions. The DCCLHP with nickel wick consists of a cylindrical evaporator and dual compensation chambers at both ends of evaporator. In the current study, a new DCCLHP test rig is set up which can provide the acceleration up to 11 g. Two types of loading mode are utilized for applying heat load prior to acceleration. The heat load ranges from 25 W to 300 W. Comparisons of operating performance of the DCCLHP are carried out under both gravity and acceleration conditions. A novel acceleration force assisted concept is proposed to address the observed operating behavior. Experimental results show that: (i) the acceleration effect with the proposed orientation can improve the operating performance of the DCCLHP which may operate at the centrifugal force driven mode and capillary-centrifugal force co-driven mode. The operating temperature profile at different heat loads shows “/-shape” oblique line with the increase of the acceleration; (ii) the transition heat load from centrifugal force driven mode to capillary-centrifugal force co-driven mode changes with the variation of acceleration magnitude at both loading modes; (iii) the acceleration effect on the operating temperature is remarkably significant as the heat load is less than 100 W. The operating temperature under acceleration conditions is apparently lower than that under terrestrial gravity; (iv) the coupling change of the loop pressure, vapor-liquid distribution, two-phase flow and heat transfer caused by acceleration effect leads to the unique operating performance of the DCCLHP.Peer reviewe

Large eddy simulation of supercritical heat transfer to hydrocarbon fuel

Accepted for publication in a forthcoming issue of International Journal of Heat and Mass Transfer.In this article, a large eddy simulation (LES) method for the heat transfer of the hydrocarbon fuel flowing through the uniformly heated miniature round pipe at supercritical pressure has been formulated and validated. The four species surrogate model was used to simulate the real thermophysical properties of the fuel. Validation of the developed LES model was carried out through comparisons of the wall temperature and pressure drop with available experimental data and other turbulence model results. Results show that the LES gave the best prediction. Further calculations based on the proposed LES for three cases including subcritical, transcritical and supercritical temperature ranges were numerically investigated in a systematic manner. It was found that the entrance effect occurred among the subcritical, transcritical and supercritical temperature cases that caused by the developing thermal boundary layer. The significant variation of the thermophysical properties near the pseudo-critical temperature would weaken the heat transfer in the transcritical case where the velocity fluctuation affected more on turbulent heat transfer than the temperature fluctuation did.Peer reviewe

Numerical and experimental investigations into protection net icing at the helicopter engine inlet

© 2020, Emerald Publishing Limited. This is the accepted manuscript version of an article which has been published in final form at . https://doi.org/10.1108/AEAT-09-2019-0190The ice shapes of the protection net at different times are firstly simulated by a 2D icing calculation, then the porous media parameters are calculated based on the 2D ice shapes. Afterwards, a three-dimensional (3D) flow fields of the engine inlet with the iced net are simulated using the porous media model instead of the real protection net. The transient pressure losses of the iced protection net are calculated and tested through an icing wind tunnel test rig under different icing conditions. Overall the numerical results and experimental data shows a good agreement. The effects of several control parameters such as liquid water contents (LWC), water droplet diameters, and airflow velocities on the pressure loss of the protection net during the icing process are analyzed in a systematic manner. The results indicate that the pressure loss increases with the increase of the LWC at the same icing time. The same trend occurs when the water droplet diameter and the airflow velocity increase.Peer reviewe

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1H NMR-based metabolic profiling combined with multivariate data analysis was used to explore the metabolic phenotype of functional dyspepsia (FD) in stressed rats and evaluate the intervention effects of the Chinese medicine Weikangning (WKN). After a 7-day period of model establishment, a 14-day drug administration schedule was conducted in a WKN-treated group of rats, with the model and normal control groups serving as negative controls. Based on 1H NMR spectra of urine and serum from rats, PCA, PLS-DA, and OPLS-DA were performed to identify changing metabolic profiles. According to the key metabolites determined by OPLS-DA, alterations in energy metabolism, stress-related metabolism, and gut microbiota were found in FD model rats after stress stimulation, and these alterations were restored to normal after WKN administration. This study may provide new insights into the relationship between FD and psychological stress and assist in research into the metabolic mechanisms involved in Chinese medicine

Effects of Astragalus Polysaccharides on Associated Immune Cells and Cytokines in Immunosuppressive Dogs

AbstractThe aim of this study was to determine the effects of Astragalus Polysaccharide (APS) on associated Immunity Cells and Cytokines in the immunosuppressive dogs and its dose-effect correlation. One hundred two-month-old male Chinese Countryside Dogs were randomly assigned to five groups: Control group (CG), immunosuppressive group (IG), APS low dose group (50mg/kg, LDG), APS median dose group (100mg/kg, MDG), and APS high dose group (200mg/kg, HDG), each group with twenty animals. After successfully established the dexamethasone-induced immunosuppressive models, with intravenous administer the CG and IG groups were daily dosed with saline, and the other three groups were daily dosed with APS for 7 days. On day 4 and 11 venous blood samples were collected and analyzed to determine the percentages of peripheral blood ANAE+ T lymphocytes, CD4+, CD8+ cells and CD4+/CD8+ ratio; the phagocytic index and percentage of the peritoneal macrophages; and the contents of INF-γ and IL-2. After 7 days administration, the measured parameters as described above in three treated groups increased significantly (P<0.05). Our findings show that the dosage of 200mg/kg APS can significantly enhance the cellular immune level of the immunosuppressive dogs. This study has provided evidence and basis for Astragalus polysaccharides development as companion animal health products as well as for its clinical application

Experimental Study of the Energy and Exergy performance for a Pressurized Volumetric Solar Receiver

This document is the Accepted Manuscript of the following article: Jianqin Zhu, Kai Wang, Guoqing Li, Hongwei Wu, Zhaowu Jiang, Feng Lin, and Yongliang Li, 'Experimental study of the energy and exergy performance for a pressurized volumetric solar receiver', Applied Thermal Engineering, Vol. 104, July 2016, pp. 212-221. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/. The Version of Record is available online at doi: https://doi.org/10.1016/j.applthermaleng.2016.05.075. © 2016 Elsevier Ltd. All rights reserved.This article presents an experimental investigation of the heat transfer characteristics as well as energy and exergy performance for a pressurized volumetric solar receiver under variable mass flow rate conditions. During a two-hour period of continuous operation in the morning, the solar irradiance is relatively stable and maintained at approximately 600 W/m2, which is beneficial for analyzing the energy and exergy performance of the solar receiver. Experimental results show that the mass flow rate fluctuation has insignificant effect on the solar receiver outlet temperature, whereas the mass flow rate plays an important role in the solar receiver power, energy efficiency and exergy efficiency. The efficiency of the solar receiver is normally above 55% with the highest efficiency of 87%, and under steady state operating conditions the efficiency is maintained at approximately 60%. A very low value of the heat loss factor (0.014 kW/K) could be achieved during the current steady state operating conditions. The highest exergy efficiency is approximately 36%. In addition, as the temperature difference increases, the impact of the exergy factor increases. The highest exergy factor is 0.41 during the entire test.Peer reviewe

Diameter effect on the heat transfer of supercritical hydrocarbon fuel in horizontal tubes under turbulent conditions

This document is the Accepted Manuscript version of the following article: Zeyuan Cheng, Zhi Tao, Jianqin Zhu, and Hongwei Wu, ‘Diameter effect on the heat transfer of supercritical hydrocarbon fuel in horizontal tubes under turbulent conditions’, Applied Thermal Engineering, Vol. 134: 39-53, April 2018. Under embargo until 31 January 2019. The final, definitive version is available online at: https://doi.org/10.1016/j.applthermaleng.2018.01.105This article presented a numerical investigation of supercritical heat transfer of the hydrocarbon fuel in a series of horizontal tubes with different diameters. The Reynolds averaging equations of mass, momentum and energy with the LS low-Reynolds number turbulence model have been solved using the pressure-based segregated solver based on the finite volume method. For the purpose of comparison, a four-species surrogate model and a ten-species surrogate model of the aviation kerosene RP-3 (Rocket Propellant 3) were tested against the published experimental data. In the current study, the tube diameter varied from 2 mm to 10 mm and the pressure was 3 MPa with heat flux to mass flux ratios ranging from 0.25 to 0.71 kJ/kg. It was found that the buoyancy has significant effect on the wall temperature non-uniformity in the horizontal tube. With the increase of the diameter, the buoyancy effect enhances and the thermal-induced acceleration effect reduces. The buoyancy effect makes wall temperature at the top and bottom generatrices of the horizontal tube increase and decrease, respectively. Due to the coupled effect of the buoyancy and thermal-induced acceleration caused by the significant change of the properties, as the diameter increases, the heat transfer deteriorates dramatically at the top generatrix but remains almost unchanged at the bottom generatrix at high heat flux to mass flux ratio. Heat transfer enhancement is observed at low heat flux to mass flux ratio when the tube diameter is less than 6 mm. Moreover, the safety analysis has been performed in order to optimally design the supercritical cooling system.Peer reviewe

The prebiotic effects of oats on blood lipids, gut microbiota, and short-chain fatty acids in mildly hypercholesterolemic subjects compared with rice: a randomized, controlled trial

20openInternationalInternational coauthor/editorPhytochemicals derived from oats are reported to possess a beneficial effect on modulating dyslipidemia, specifically on lowering total and LDL cholesterol. However, deeper insights into its mechanism remain unclear. In this randomized controlled study, we assigned 210 mildly hypercholesterolemic subjects from three study centers across China (Beijing, Nanjing, and Shanghai) to consume 80 g of oats or rice daily for 45 days. Plasma lipid profiles, short chain fatty acids (SCFAs), and fecal microbiota were measured. The results showed that total cholesterol (TC) and non-high-density lipoprotein cholesterol (non-HDL-C) decreased significantly with both oats and rice intake after 30 and 45 days. The reduction in TC and non-HDL-C was greater in the participants consuming oats compared with rice at day 45 (p = 0.011 and 0.049, respectively). Oat consumption significantly increased the abundance of Akkermansia muciniphila and Roseburia, and the relative abundance of Dialister, Butyrivibrio, and Paraprevotella, and decreased unclassified f-Sutterellaceae. In the oat group, Bifidobacterium abundance was negatively correlated with LDL-C (p = 0.01, r = −0.31) and, TC and LDL-C were negatively correlated to Faecalibacterium prausnitzii (p = 0.02, r = −0.29; p = 0.03, r = −0.27, respectively). Enterobacteriaceae, Roseburia, and Faecalibacterium prausnitzii were positively correlated with plasma butyric acid and valeric acid concentrations and negatively correlated to isobutyric acid. HDL-C was negatively correlated with valeric acid (p = 0.02, r = −0.25) and total triglyceride (TG) was positively correlated to isovaleric acid (p = 0.03, r = 0.23). Taken together, oats consumption significantly reduced TC and LDL-C, and also mediated a prebiotic effect on gut microbiome. Akkermansia muciniphila, Roseburia, Bifidobacterium, and Faecalibacterium prausnitzii, and plasma SCFA correlated with oat-induced changes in plasma lipids, suggesting prebiotic activity of oats to modulate gut microbiome could contribute towards its cholesterol-lowering effect.openXu, Dengfeng; Feng, Meiyuan; Chu, YiFang; Wang, Shaokang; Shete, Varsha; Tuohy, Kieran M; Liu, Feng; Zhou, Xirui; Kamil, Alison; Pan, Da; Liu, Hechun; Yang, Xian; Yang, Chao; Zhu, Baoli; Lv, Na; Xiong, Qian; Wang, Xin; Sun, Jianqin; Sun, Guiju; Yang, YuexinXu, D.; Feng, M.; Chu, Y.; Wang, S.; Shete, V.; Tuohy, K.M.; Liu, F.; Zhou, X.; Kamil, A.; Pan, D.; Liu, H.; Yang, X.; Yang, C.; Zhu, B.; Lv, N.; Xiong, Q.; Wang, X.; Sun, J.; Sun, G.; Yang, Y