| 1. |
- Xie, Jingzhe, et al.
(författare)
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A numerical prediction on heat transfer characteristics from a circular tube in supercritical fluid crossflow
- 2019
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 153, s. 692-703
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Tidskriftsartikel (refereegranskat)abstract
- Studies on fluids at supercritical pressure have been developed in a rapid-growth manner so that geometries are not restricted to circular tube. This paper is devoted to conduct a brief review of the recent main experiments on supercritical fluids such as CO 2 , water, R134a and n-decane, and to comment the findings. In addition, this paper discusses the probability of supercritical fluids flowing across tube bundles for the frequent use in shell-and-tube heat exchangers in supercritical power cycle systems. A numerical prediction of flow patterns and heat transfer characteristics of a circular tube in supercritical water crossflow is carried out to make a fundamental investigation of the application of supercritical fluids on external flows. Results indicate that the influence of heat flux on heat transfer in crossflow is similar with that for in-tube flows. The thermal physical properties significantly affect the heat transfer and the flow patterns also show unique characteristics with the change of boundary conditions.
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| 2. |
- Xie, Jingzhe, et al.
(författare)
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The influences of sidewall proximity on flow and thermal performance of a microchannel with large-row pin-fins
- 2019
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 140, s. 8-19
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Tidskriftsartikel (refereegranskat)abstract
- Sidewall proximity, characterized by the gap distance (G) between border pin-fin column and sidewall in a pin-finned microchannel with in-line arrangement, plays a significant role on pressure drop and heat transfer characteristics. To better understand the thermal performance and explore the underlying mechanisms, a comprehensive comparison is numerically developed among three representative microchannels with gap-to-diameter ratios (G/D) of 0.6, 1.0 and 1.4, respectively. The Reynolds number investigated in this paper varies from 13 to 202. It is found that the gap distance severely influences flow distribution, streamline structure, velocity field and temperature distributions in a pin-finned microchannel. At a fixed Reynolds number, pressure drop of microchannel is continuously decreased while heat transfer is first enhanced and then reduced with the increase of gap distance. Among the three models, the microchannel with G/D = 1.0 possesses a comparatively superior heat transfer performance. In addition, extremely low local Nusselt numbers on both the base surface and the pin-fin surface near sidewall seriously deteriorate the overall heat transfer performance of the microchannel with G/D = 0.6. Furthermore, unremarkable heat transfer performance is also observed from the microchannel with G/D = 1.4 for its obvious decline of local Nusselt number on inner regions in spite of a rise on border region. Taking heat transfer and pressure drop into account simultaneously, the results show that a very small gap distance (i.e., G/D = 0.6) should be avoided for design of a pin-finned microchannel. Microchannels with middle gap distances (i.e., G/D = 0.9, 1.0, 1.1) have a relatively better overall thermal performance, which separately provide a superiority of 10.6–13.6% (G/D = 0.9), 10.0–13.5% (G/D = 1.0), 8.2–14.4% (G/D = 1.1) compared to the microchannel with G/D = 0.6. Finally, new correlations of friction factor and Nusselt number are developed by considering the effects of sidewall proximity.
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| 3. |
- Yan, Ruijuan, et al.
(författare)
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Effects of Doping Ni on the Microstructures and Thermoelectric Properties of Co-Excessive NbCoSn Half-Heusler Compounds
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:29, s. 34533-34542
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Tidskriftsartikel (refereegranskat)abstract
- The half-Heusler (HH) compound NbCoSn with 18 valence electrons is a promising thermoelectric (TE) material due to its appropriate electrical properties as well as its suitable thermal and chemical stability. Nowadays, doping/substitution and tailoring of microstructures are common experimental approaches to enhance the TE performance of HH compounds. However, detailed theoretical insights into the effects of doping on the microstructures and TE properties are still missing. In this work, the microstructure of NbCoSn was tailored through precipitating the full-Heusler phases in the matrix by changing the nominal ratio of Co and Ni on the Co sites, focusing on the resulting TE properties. Further, first-principles calculations were employed to understand the relationship between the microstructure and the TE properties from the thermodynamic point of view. Detailed analysis of the electronic structure reveals that the presence of excess Co/Ni contributes to the increasing carrier concentration. Through an increase in the electrical conductivity and a reduction in the thermal conductivity, the TE performance is improved. Therefore, the present work offers a new pathway and insights to enhance the TE properties by modifying the microstructure of HH compounds via tailoring the chemical compositions.
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| 4. |
- Chen, Peiyu, et al.
(författare)
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Thermal design and performance prediction of a shell condenser for closed-cycle underwater vehicles
- 2018
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Ingår i: Energy. - 9780791852071 ; 6A
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Konferensbidrag (refereegranskat)abstract
- The shell condenser is a key component for the underwater vehicles. To study its heat transfer performance and flow characteristics and to design a more efficient structure, a mathematical model is generated to simulate condensation inside the straight and helical channels. The model combines empirical correlations and MATLAB based on an iterative algorithm. Here, quality is used as a sign of the degree of condensation. The computational model is verified by comparison of simulations and experiments. Several cases are designed to reveal the effects of the initial condition. The inlet temperature varies from 160 to 220°C and the inlet mass velocity ranges between 133 and 200 kg/m 2 ·s. The results show that the inlet temperature and mass velocity significantly affect flow and heat transfer in the condensation process. In addition, comparisons of the straight channel and helical channel with different Dh/R indicate that the heat transfer capability of the helical channel is obviously better than that of the straight channel, and the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide useful information for performance prediction and structure design of shell condensers, and provide a relatively universal computational model for condensation in channels.
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| 5. |
- Jin, Xin, et al.
(författare)
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Comparative evaluations of thermofluidic characteristics of sandwich panels with X-lattice and Pyramidal-lattice cores
- 2018
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 127, s. 268-282
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Tidskriftsartikel (refereegranskat)abstract
- This study compares the thermo-fluidic characteristics of sandwich panels with the X-lattice and the Pyramidal lattice at a given porosity and surface area density. The numerical model is validated against available experimental data at first. At a given Reynolds number in the range of 3100–5700, numerical results reveal that the X-lattice sandwich panel provides a 47–60% higher average overall Nusselt number. The special topology of the X-lattice induces counter-rotating spiral primary flow and more complex secondary flows, including one which becomes a longitudinal vortex later. The flow in the Pyramidal lattice sandwich panel is composed of a parallel primary flow and a counter-rotating vortex pair entrenched in the zone behind ligaments of the Pyramidal lattice. Compared with the Pyramidal lattice sandwich panel, endwall heat transfer of the X-lattice sandwich panel is enhanced by 75–97% and the ligaments surface heat transfer is enhanced by 85–97% at a given Reynolds number. It is also found that the friction factor of the X-lattice sandwich panel is about 2 times higher for the spiral primary flow and more complex secondary flows induced by the staggered ligaments. Finally, at a given pumping power, the cooling performance of the X-lattice is much better, too. Taking the identical fabrication method and cost into account, apparently the X-lattice is superior in engineering applications.
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| 6. |
- Mansouri, Kamel, et al.
(författare)
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CoMPARA : Collaborative Modeling Project for Androgen Receptor Activity
- 2020
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Ingår i: Journal of Environmental Health Perspectives. - 0091-6765 .- 1552-9924. ; 128:2, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Endocrine disrupting chemicals (EDCs) are xenobiotics that mimic the interaction of natural hormones and alter synthesis, transport, or metabolic pathways. The prospect of EDCs causing adverse health effects in humans and wildlife has led to the development of scientific and regulatory approaches for evaluating bioactivity. This need is being addressed using high-throughput screening (HTS) in vitro approaches and computational modeling.OBJECTIVES: In support of the Endocrine Disruptor Screening Program, the U.S. Environmental Protection Agency (EPA) led two worldwide consortiums to virtually screen chemicals for their potential estrogenic and androgenic activities. Here, we describe the Collaborative Modeling Project for Androgen Receptor Activity (CoMPARA) efforts, which follows the steps of the Collaborative Estrogen Receptor Activity Prediction Project (CERAPP).METHODS: The CoMPARA list of screened chemicals built on CERAPP's list of 32,464 chemicals to include additional chemicals of interest, as well as simulated ToxCast (TM) metabolites, totaling 55,450 chemical structures. Computational toxicology scientists from 25 international groups contributed 91 predictive models for binding, agonist, and antagonist activity predictions. Models were underpinned by a common training set of 1,746 chemicals compiled from a combined data set of 11 ToxCast (TM)/Tox21 HTS in vitro assays.RESULTS: The resulting models were evaluated using curated literature data extracted from different sources. To overcome the limitations of single-model approaches, CoMPARA predictions were combined into consensus models that provided averaged predictive accuracy of approximately 80% for the evaluation set.DISCUSSION: The strengths and limitations of the consensus predictions were discussed with example chemicals; then, the models were implemented into the free and open-source OPERA application to enable screening of new chemicals with a defined applicability domain and accuracy assessment. This implementation was used to screen the entire EPA DSSTox database of similar to 875,000 chemicals, and their predicted AR activities have been made available on the EPA CompTox Chemicals dashboard and National Toxicology Program's Integrated Chemical Environment.
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| 7. |
- Rao, Ziyuan, et al.
(författare)
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Machine learning-enabled high-entropy alloy discovery
- 2022
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 378:6615, s. 78-84
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 x 10-6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys with optimal thermal, magnetic, and electrical properties.
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| 8. |
- Shen, Beibei, et al.
(författare)
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Forced convection and heat transfer of water-cooled microchannel heat sinks with various structured metal foams
- 2017
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 113, s. 1043-1053
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Tidskriftsartikel (refereegranskat)abstract
- The excellent performance of metal foams is well-recognized in the thermal and energy fields. This paper presents an investigation on the convective heat transfer and thermal performance of microchannel heat sinks with different structures of metal foams, such as Y-shaped, metal foam attached to fins, combined metal foams. The inlet Reynolds number is ranging from 170 to 554 and the porosity of the metal foam is ranging from 0.7 to 0.9. The detailed thermal performance and flow characteristics are presented and analyzed by using computational fluid dynamics with a verified computational model. The influences of flow velocity and porosity of the metal foam on the flow and heat transfer characteristics in a microchannel are also observed. It is found that different configurations and locations of metal foam in microchannel result in different heat transfer characteristics. The microchannel heat sinks with combined metal foams have better overall thermal performance than the other two models because it possesses the advantages of mixing fluid flow caused by Y-shaped metal foam and contacting the fins closely. Therefore, properly designed configurations of metal foams can further enhance the microchannel heat sink cooling capacity. Besides, the porosities have a small effect on the thermal performance but have a larger effect on the pressure drop.
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| 9. |
- Shen, Han, et al.
(författare)
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Convective heat transfer of parallel-flow and counter-flow double-layer microchannel heat sinks in staggered arrangement
- 2017
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Ingår i: Heat Transfer and Thermal Engineering. - 9780791858431 ; 8
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Konferensbidrag (refereegranskat)abstract
- Previous research has proved Double-layer Microchannel Heat Sinks (MHSs) to be efficient ways to improve the cooling performance of electronic devices. However, the cooling potential of the upper working liquid cannot be fully utilized to cool down the substrate with the heated elements. In this sense, a concept of staggered double-layer MHS is proposed and designed. The parallel and counter flow directions are considered to investigate the flow arrangement effect. The Reynolds number effect, Nusselt number and pressure drop are analyzed in detail and compared with those of a parallel straight double-layer MHS. It is found that the staggered double-layer MHSs exhibit much better heat transfer enhancement and overall thermal performance compared with the parallel straight double-layer MHS. For the staggered double-layer MHSs, the counter flow case is superior to the parallel flow case. This research provides a new structure design to enhance the heat transfer in microchannel heat sinks and broad application prospects for heat sinks in the thermal management of high power density electronic devices.
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| 10. |
- Shen, Han-Ming, et al.
(författare)
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Computational optimization of counter-flow double-layered microchannel heat sinks subjected to thermal resistance and pumping power
- 2017
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 121, s. 180-189
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Tidskriftsartikel (refereegranskat)abstract
- Various microchannel heat sinks are widely used to cool electronic chips, but they are often designed to be single-layer channels. To a certain extent, single-layered microchannel heat sinks can solve the problem of high heat flux. However, due to the limitation of pumping power, only a small coolant flow rate can be adopted; and the temperature of the heated plate is non-uniform. In this paper, the structure of double-layered countercurrent microchannel heat sinks is designed. The NSGA-II optimization algorithm is used to optimize the height ratio of the two layers and the length of the upper layer. The corresponding Pareto frontier is obtained. After validation of the optimization Pareto front, some validated characteristic cases are investigated numerically. The results of the optimization show that despite a conflict between reducing the thermal resistance and lowering the pumping power, there is an appropriate structure of the double-layered countercurrent microchannel heat sink optimized by the NSGA-II optimization algorithm. For the selected cases, Case 4 has the best thermal performance, because Case 4 not only has a smaller pumping power than Case 0, but also has a smaller thermal resistance than Case 0. Therefore, it is indicated that better thermal performance of microchannel heat sinks can be achieved through the optimization algorithm.
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