Modeling fluid flows is a general procedure to handle engineering problems. Here we present a systematic study of the flow and heat transfer around a circular cylinder by introducing a new ...representative appropriate drag coefficient concept. We demonstrate that the new modified drag coefficient may be a preferable dimensionless parameter to describe more appropriately the fluid flow physical behavior. A break in symmetry in the global structure of the entire flow field increases the difficulty of predicting heat and mass transfer behavior. A general simple drag model with high accuracy is further developed over the entire range of Reynolds numbers met in practice. In addition, we observe that there may exist an inherent relation between the drag and heat and mass transfer. A simple analogy model is established to predict heat transfer behavior from the cylinder drag data. This finding provides great insight into the underlying physical mechanism.
The development of display technology has continuously increased the requirements for image resolution. However, the imaging systems of many cameras are limited by their physical conditions, and the ...image resolution is often restrictive. Recently, several models based on deep convolutional neural network (CNN) have gained significant performance for image super-resolution (SR), while extensive memory consumption and computation overhead hinder practical applications. For this purpose, we present a lightweight network that automatically searches dense connection (ASDCN) for image super-resolution (SR), which effectively reduces redundancy in dense connection and focuses on more valuable features. We employ neural architecture search (NAS) to model the searching of dense connections. Qualitative and quantitative experiments on five public datasets show that our derived model achieves superior performance over the state-of-the-art models.
The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated ...numerically in this paper. Deionized water and Al2O3–water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.
The entrance region constitutes a considerable fraction of the channel length in miniaturized devices. Laminar slip flow in microchannel plate fin heat sinks under hydrodynamically developing ...conditions is investigated semi-analytically and numerically in this paper. The semi-analytical model for the pressure drop of microchannel plate fin heat sinks is obtained by solving the momentum equation with the first-order velocity slip boundary conditions at the channel walls. The simple pressure drop model utilizes fundamental solutions from fluid dynamics to predict its constitutive components. The accuracy of the model is examined using computational fluid dynamics (CFD) simulations and the experimental and numerical data available in the literature. The model can be applied to either apparent liquid slip over hydrophobic and superhydrophobic surfaces or gas slip flow in microchannel heat sinks. The developed model has an accuracy of 92 percent for slip flow in microchannel plate fin heat sinks. The developed model may be used to predict the pressure drop of slip flow in microchannel plate fin heat sinks for minimizing the effort and expense of experiments, especially in the design and optimization of microchannel plate fin heat sinks.
The technology of hydrogen generation from biomass has attracted more and more attentions nowadays. In this work, three biomass-based chemical looping hydrogen generation systems, Systems A, B and C, ...are comprehensively studied. System A is mainly composed of biomass hydrogasification, methane reformation and the calcium-looping based CO2 absorption. System B is mainly composed of biomass steam gasification and Fe2O3/FeO-looping based hydrogen generation circulation. System C is mainly composed of biomass steam gasification and Fe3O4/FeO-looping based hydrogen generation circulation. The three systems are modeled and their characteristics are analyzed and compared thermodynamically. System A has the highest cold gas efficiency (CGE) which is 72%; System B has the lowest CGE of 54% but it can generate additional nitrogen as byproduct; System C has the highest hydrogen generation ratio and its CGE is moderate and is 60%. The carbon dioxide sequestration rates of the three systems are all above 90%.
•Three chemical looping systems are proposed for biomass based hydrogen generation.•The CO2 discharge is minimized with the utilization of both CLG and CLP technologies.•The cold gas efficiencies of Systems A, B and C are 72, 54 and 60%, respectively.•The values of Rhtb of Systems A, B and C are 0.73, 0.66, and 0.76 Nm3/kg.•The values of Rcs of Systems A, B and C are found to be 92, 95 and 96%.
Hydropyrolysis of coal is considered to be a third coal conversion technology between the coal liquification and gasification technologies. It is also the primary process for coal hydrogasification ...(CHG). However, the detailed kinetic characteristics of coal hydropyrolysis (CHP) are still rarely studied, which is adverse to the further development of the CHP and CHG technologies. In this work, the hydropyrolysis kinetics of a lignite coal is studied in a pressurized thermogravimetric analyzer (P-TGA). The non-isothermal thermogravimetric method is used and the effect of pressure on the pyrolysis kinetics of the lignite coal is detected. Finally, some useful results are found from the analyses for the lignite hydropyrolysis under P-TGA. With the increment of the pyrolysis pressure, the initial pyrolysis temperature increases when the pressure is higher than 1 MPa; the temperature span of the pyrolysis process shrinks; the weight loss peak value position of the derivative thermogravimetric (DTG) curve shifts rightwards when the pressure is lower than 1 MPa, while it shifts leftwards when the pyrolysis pressure is higher than 1 MPa; the reaction process will be restrained when the pressure is lower than 2 MPa. In addition, the kinetic triplets including the pre-exponential factor, the activation energy and the kinetic mechanism function are defined for the hydropyrolysis process under different pressures.
•The hydropyrolysis kinetics of a lignite coal is studied in a P-TGA.•The effect of pressure on the pyrolysis kinetics is studied and analyzed.•The way to determine the most probable kinetic mechanism is developed.•The RNLGM with n = 4 is found to be proper to reflect the hydropyrolysis process.•The kinetic parameters of the hydropyrolysis processes at different pressures are calculated.
It is well known that a genetic link exists between the formation of ultramafic-rocks-hosted PGE-Cu–Ni sulfide deposits and the eruption of associated continental flood basalts. We here present a new ...model for the relationship between the Cu–Ni deposits located along the northeastern margin of Tarim and the internal Tarim basalt. Sr–Nd isotope and Hf isotope two-stage crust model ages TDMc indicate that whereas the Cu–Ni deposits along the northeastern margin of Tarim have Neoproterozoic and Mesoproterozoic lithology contamination, the surrounding rocks of Cu–Ni deposits in Beishan (Pobei) and Central Tianshan do not have Neoproterozoic lithologies. We propose that this is the result of mixing with the Neoproterozoic rocks in the interior of Tarim block. There is also an east–west trending positive magnetic anomaly belt in the central Tarim Basin, while Early Permian mafic–ultramafic rocks found along the northeastern margin of Tarim probably have a relationship with the Tarim Basin basalt. According to the Bouguer gravity map, the Bachu area near the center of Early Permian plume has high gravity values, with the northeastern high gravity belt in the central Tarim Basin possibly the result of a tilt of the mantle plume to the southwest below the Tarim block, which could be consistent with the earlier uplift and denudation in northeastern Tarim and later in southwestern Tarim from the Early Carboniferous to the Late Permian, as well as with observed uplift in the Bachu area in the Permian. We infer that the tilt of a mantle plume to the southwest below the Tarim block led to the inclined attitude of overlying rocks, with Early Permian magma flowing toward the northeast margin of Tarim. Based on this model, new PGE-Cu–Ni magmatic sulfide deposits related to Early Permian mafic–ultramafic intrusions may be found in the southwest area of Beishan, although this area is covered by Mesozoic and Cenozoic sediments.
•We inferred that the tendency of Tarim Early Permian mantle plume was southwest.•Tarim plume magma possibly flowed toward the northeastern margin of the Tarim Basin.•New Cu–Ni deposits in Early Permian may be found in the southwest area of Beishan.
Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical ...model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.
The performance of impingement air cooled plate fin heat sinks differs significantly from that of parallel flow plate fin heat sinks. The impinging flow situations at the entrance and the ...right-angled bends of the plate fin heat sink are quite involved. Flow characteristics of a plate fin heat sink with elliptic bottom profiles cooled by a rectangular impinging jet with different inlet widths are studied by numerical simulations. The results of pressure drop of numerical simulations and experimental results match quite well. The numerical results show that at the same flow rate, the pressure drop decreases with the increase of the impingement inlet width, and the pressure drop increases significantly with the increase of the fin height. The larger the impingement inlet width of air-cooled plate fin heat sink, the milder the pressure drop changes with velocity. Pressure drop for an impinging plate fin heat sink without elliptic bottom profiles is larger than that with elliptic bottom profiles at the same inlet width and velocity. Based on the fundamental developing laminar continuum flow theory, an improved model which is very concise and nice for quick real world approximations is proposed. Furthermore, this paper verifies the effectiveness of this simple impinging pressure drop model.
Yeast culture (YC) is a yeast-fermented product of enzymolysis soybean protein with plenty of small peptide and nucleotide. This study aimed to investigate the effects of YC as a substitute for fish ...meal (FM) on the growth, serum biochemical parameters, intestinal histology and microorganisms of hybrid snakehead (Channa argus ♂ × C. maculate ♀). In a basal diet containing 250 g/kg FM, YC was included at the levels of 0, 40, 80, 120 g/kg to replace 0, 29.5, 59.0 and 88.5 g/kg FM to form four isonitrogenous diets (CON, YC-40, YC-80 and YC-120). The four diets were fed to hybrid snakehead with initial body weight (9.2 ± 0.1 g) for 70 days. The results showed that there were no significant differences in weight gain (WG), feed conversion ratio, protein efficiency ratio (PER), protein retention (PR) and lipid retention (LR) among the three groups of CON, YC-40 and YC-80 groups (P > 0.05). However, the WG, PER, PR and LR in YC-120 group were significantly lower than those in the CON group (P < 0.05). No significant differences in body indexes and whole fish proximate composition were detected among all the groups (P > 0.05). In serum biochemical parameters, superoxide dismutase activity and total antioxidant capacity in YC-40 and YC-80 groups were significantly increased, and total cholesterol content in YC-120 group was significantly decreased when compared to the control (P < 0.05). In foregut morphology, YC-120 group showed significantly lower muscle thickness and villus height than the control (P < 0.05), but there was no significant difference in villus width among all the groups (P > 0.05). Intestinal microbial analysis showed that the major intestinal microorganisms in all groups were Firmicutes, Spirochaetota, Proteobacteria and Actinobacteria. The relative abundance of Brevinema in YC-120 group was significantly higher than that in CON group (P < 0.05). In conclusion, in a basal diet containing 250.0 g/kg FM, 80 g/kg YC could successfully replace 59.0 g/kg FM without adverse effects on growth performance, nutrient utilization, serum biochemical indices, intestinal histology and microorganisms of juvenile hybrid snakehead.
•In a diet containing 250 g/kg fish meal (FM), 80 g/kg yeast culture (YC) could successfully replace 59 g/kg FM for hybrid snakehead.•Dietary inclusions of 40, 80 g/kg YC promoted serum superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC).•High replacement of FM with YC negatively affected intestinal morphology and microorganism.
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