The knowledge of the hydraulic characteristics of rill flows is needed to improve the understanding and the accurate modelling of upland erosion processes. Flume investigations are developed to ...schematize conditions useful to analyze the influence of a unique variable significant for modelling rill hydraulics, while field investigations are used to simulate morphological and hydraulic conditions of natural cases. The main aim of this investigation is to compare flow resistance measurements carried out using a rectangular rill channel (flume data) and manually generated and naturally shaped rills (plot data) for the same soils and hydraulic conditions. The two data sets allowed for establishing how the soil grain roughness and rill cross‐section shape affect flow resistance using a theoretical equation deduced by applying dimensional analysis and self‐similarity theory. The analysis developed for a fixed‐bed channel with a rectangular cross‐section demonstrated that the influence of different soil roughness on the Darcy‐Weisbach friction factor is approximately equal to ±1%, while for a rill with an irregular cross‐section the same effect is almost equal to ±2%. Therefore, for an open‐channel flow on a fixed bed, the effect of the grain size roughness on the friction factor is limited. For each examined soil, the investigation also demonstrated that the rill cross‐section shape leads to a variability of the friction factor from −20% to +30%. This result highlights that, for a fixed‐bed channel, the effect of the cross‐section shape on the Darcy‐Weisbach friction factor is much greater than that due to the soil grain size roughness. The main implication of this work is that the results deduced by laboratory measurements with regular cross‐sections, thus neglecting a complex geometry, can be affected by relevant discrepancies from those obtained by the field measurements, which better simulate natural conditions.
Graphical abstarct
Flow resistance measurements performed for the same soils and hydraulic conditions using a rectangular rill channel (flume data) and manually generated and naturally shaped rills (plot data) were compared. For an open‐channel flow on a fixed bed, the analysis demonstrated that the effect of the grain size roughness on the Darcy‐Weisbach friction factor is limited (±2%), while that of the cross‐section shape is significant (from −20% to +30%).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In the present study, fluid flow and heat transfer in microchannel heat sinks with different inlet/outlet locations (I, C and Z-type), header shapes (triangular, trapezoidal and rectangular) and ...microchannel cross-section shapes (the conventional rectangular microchannel, the microchannel with offset fan-shaped reentrant cavities and the microchannel with triangular reentrant cavities) are numerically studied with computational domain including the entire microchannel heat sink. Detailed three-dimensional numerical simulations are useful in identifying the optimal geometric parameters that provide better heat transfer and flow distribution in a microchannel heat sink. Results highlight that flow velocity uniformity is comparatively better for I-type and poor for Z-type. The flow distribution is found to be symmetrical for I-type. It is seen from the header shapes analysis that the rectangular header shapes provides better flow velocity uniformity than the trapezoidal and triangular headers. The fluid flow mechanism can be attributed to the interaction of the branching of fluid and the friction offered by the walls of the header. Effects of microchannel cross-section shapes emphasize that the microchannel with offset fan-shaped reentrant cavities and the microchannel with triangular reentrant cavities of the heat sinks enhance the heat transfer compared to the conventional rectangular microchannel. The heat transfer mechanism can be attributed to the jetting and throttling effect, the additional flow disturbance near the wall of the reentrant cavities and the form drag of the reentrant cavities. The heat sink C has better heat transfer characteristic for qv=150ml/min and is able to prolong the life of the microelectronic devices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The influence of inlet cross-sectional shape on the flow pattern, pressure drop, and cut-off diameter of a gas cyclone was studied using the CFD model. Accordingly, five different inlet ...cross-sectional shapes, namely, circle, ellipse, rectangle, square, and trapezoid, for the double-inlet gas cyclone were studied. It was observed that the maximum tangential velocity was about 1.95 times the corresponding inlet velocity for primary and secondary rectangle inlets. Furthermore, the computed tangential velocity in the cyclone with the primary and secondary rectangle inlets (R-R) was considerably greater than those obtained by the other inlet shapes. In this case, the axial gas velocity reached its highest values at the bottom of the vortex finder and the cyclone center. It was also determined that the inlet shape significantly affected the cyclone pressure drop. The Circle-Square and the Rectangle-Ellipse configurations of inlet cross-sectional shape generated, respectively, the lowest pressure drop and the highest efficiency.
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•Different inlet shapes of the multi-inlet gas cyclone were studied by the CFD model.•The inlet cross-sectional shape affects the cyclone performance.•Circle-Square inlets showed the lowest ΔP (18.23% lower than the highest case).•Rectangle-Ellipse inlets showed the highest efficiency (8.77% more than the lowest case).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Four types of micro pin fins heat sinks were developed.•Flow boiling performance were accessed and compared.•The optimum micro pin fin is the square one in flow boiling.•Two-phase pressure drop and ...flow instabilities were explored.
Micro pin fin heat sinks show their great merits of thermal management in high heat flux devices in microelectronic, energy, aerospace, and military areas. The design optimization of micro pin fin shapes is a critical issue for their applications, especially in two-phase flow boiling conditions. In this study, four types of staggered micro pin fins with different cross-section shapes, i.e., square, circular, diamond and streamline, were fabricated by a laser micromilling method, and constructed for heat sinks cooling systems. Flow boiling performance of the micro pin fin heat sinks (MPFHSs) was characterized using deionized water as coolant. The effect of cross-section shape on flow boiling characteristics of MPFHSs was examined. Test results showed that the square micro pin fins presented the best boiling heat transfer, followed by circular and streamline ones. The diamond micro pin fins performed worst in boiling heat transfer and suffered severe two-phase flow instabilities at moderate to high heat fluxes, whereas they introduced the smallest pressure drop. The streamline micro pin fins presented the largest two-phase pressure drop. The square and circular micro pin fins showed their superiority in the mitigation of two-phase flow instabilities. The square micro pin fins seem to be the optimum choice and should be selected for heat sink cooling systems. The results in this study provide critical information for the design optimization of micro pin fins heat sinks for the high heat-flux applications, and are of considerable practical importance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
To analyze the effects of void on transverse tensile properties of composites considering thermal residual stress (TRS), finite element models with different distribution patterns and shapes for ...voids are established. Two different void modeling methods, with voids explicitly established and with voids modeled within elements, are compared first. For the method with voids explicitly established, circular, elliptical and arbitrary voids are considered. To reveal the effects of TRS, two different TRS analysis methods are evaluated. Results show that for the models without considering voids and TRS, the interface debonding is the dominant failure mechanism. After considering the voids, the effects of matrix damage on the crack initiation become more important. There are more variations in tensile strengths of models with voids explicitly established than those from the models with voids modeled within elements. It is also found that higher TRS values are obtained when the change of matrix properties with temperature is considered. After considering the TRS, the matrix damage contributes more to the crack initiation and the interface debonding is inhibited. Besides, the TRS results in thermal residual matrix plasticity around the void, which contributes to the premature initiation of crack around the void.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Generalized incipient deposition models are suggested.•A cross-section shape factor is incorporated into the models.•MARS and RF are hybridized with MNLR.•MARS-MNLR outperforms its alternatives.
It ...has been known that the channel cross-section shape impacts on flow velocity at sediment deposition condition; however, existing models only apply to specific cross-section shapes and there has been a lack of a general incipient deposition model applicable for all types of cross-section shapes. To this end, this study is designed to generalize incipient deposition models by including of a cross-section shape factor into the model parameters. Experimental data collected from channels of five different cross-sectional shapes namely; trapezoidal, rectangular, circular, U-shape and V-bottom are used for the modeling. Two machine-learning models, multivariate adaptive regression splines (MARS) and random forest (RF); and an empirical multi non-linear regression (MNLR) model, are developed. The accuracy of the stand-alone models is improved by hybridizing the MARS and RF models with the MNLR equation to generate robust models of MARS-MNLR and RF-MNLR. Comparison of these models with those existing in the literature indicates that cross-section-specific models may have poor performances on varied cross-section channels. MARS, RF and MNLR models as general incipient deposition models outperform cross-section-specific models, which may be attributed to the considering of shape factor as an input parameter. Hybridization of the MARS and RF models with the MNLR equation results in improving their performances in MARS-MNLR and RF-MNLR models by a factor of 25% in contrast to MNLR model. Although the MARS-MNLR model gives better results than MNLR-RF model, they both perform better than their stand-alone counterparts in terms of different statistical indices. Explicit formulae are suggested which may be applied as practical tools for channel design.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This research investigates the effect of building cross-section shape on the air pollutant dispersion around an isolated building. A Computational Fluid Dynamic (CFD) model was developed and ...validated based on detailed wind tunnel experimental data. Both Large Eddy Simulation (LES) and Realizable k-ε models were used for turbulence closure and LES was found to provide a better agreement with experimental results than the RANS model, particularly in replicating pollutant dispersion characteristics associated with wind-structure interaction. The LES model was then utilized to study the effect of building cross-section shape. Four building cross-section shapes, square, chamfered, curved and circular, along with different air pollutant emission locations were studied. It has been found that the area around an isolated building can be categorized into three emission regions, namely the windward critical emission region, the leeward critical emission region and the side non-critical emission region. The air pollutant emissions from the leeward critical emission region affect the building the most. Furthermore, the size of this region depends on the building cross-section shape, with the circular and curved buildings having a smaller leeward critical emission region than those for the chamfered and square buildings. Evidently, air pollutant dispersion around a building is dominated by wind-structure interaction which in turn is dependent on the building cross-sectional shape. These characteristics can be utilized to mitigate air pollutant dispersion in urban environments in conjunction with careful consideration of the air pollutant emission location relative to a building.
•Air pollutant dispersion around different building shapes was studied by CFD.•Three emission regions were defined for different building shapes.•Circular building shape has the smallest critical emission region.•Building shape can be optimised to mitigate air pollutant dispersion.•Reattachment lengths predicted by LES are 50%–60% shorter than the RANS model.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The pressure drop exiting in three hybrid modules were comparatively analyzed.•The cooling performance of three hybrid modules were comparatively analyzed.•The cause of the difference in the cooling ...performance were analyzed.•The cooling performance of trapezoid channel module was further improved by changing the geometrical parameters.
This paper investigates the effect of channel shape on the micro-channel and slot-jet module with the realizable k-ε turbulent model. Cooling performance of three channels with a same cross-section area but different shapes (rectangular, trapezoid and circular) are comparatively discussed. The hybrid module with circular channel has the maximum pressure drop at the same flow rate. While the hybrid module with trapezoid channel achieves the best cooling performance. Its superiority in the cooling performance enlarges with the heat flux rising and the pump power increasing, as compared with the other two hybrid modules. The local thermal resistance in the trapezoid channel exhibits peak-shape distribution, which is very different from the other two shapes channel. In addition, the cooling performance of the trapezoid channel module can be further improved by the optimization of the three geometric parameters (channel height, channel bottom width, and channel corner angle). When the optimal value for the three parameters is respectively adopted, the temperature on the bottom surface of the module can be reduced by 12.22%, 14.85% and 7.15% as compared with the worst design, and the temperature difference can also be reduced by 63.60%, 74.86% and 57.16%. What's more, the influence level of these parameters is also compared. Before the reference value, the channel height has the greatest influence on the module bottom surface temperature, whereas after the reference value, the corner angle becomes the largest influence factor. As for the temperature difference on the module bottom surface, it is just opposite.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Composite corrugation is a structure transformed from traditional corrugation to improve the thermal-hydraulic comprehensive performance (THCP) of corrugated tubes. However, compared to simple ...corrugations, the mechanism by which composite corrugations enhance THCP is still unclear. Therefore, in this work, numerical simulations are performed within the Reynolds number (Re) range of 5000–20,000 to evaluate the mechanism of composite corrugation strengthening THCP. The distributions of flow velocity, streamline, turbulent kinetic energy (TKE), pressure, and normalized force are used to reveal the differences in the effects of simple and composite corrugations on THCP. In addition, the influence of composite corrugation cross-sections and distribution forms on THCP has been explored in detail. The results indicate that increasing the impingement of the fluid on the tube wall, disrupting the fluid boundary layer, and expanding the range of secondary flow are the main mechanisms by which composite corrugations further strengthen THCP compared to simple corrugations (CT-SC). The THCP of composite corrugation (CT-CC-A-F) can be increased by 31.5% at Re = 20,000 compared to CT-SC. Composite corrugations with different cross-sections cause differences in THCP due to their varying effects on the distribution of secondary flow and the impingement of the fluid on the tube wall. The difference in the influence of composite corrugation distribution forms on THCP is still caused by the difference in the impingement of the fluid on the tube wall. This work can provide a reference for the design of composite corrugations to achieve better THCP.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, the cross section shape of fabric rubber seal is designed and optimized. First, the cross section shape optimization design method is introduced based on the structural features of ...fabric rubber seal. Then, according to the key performance of fabric rubber seal, the optimization constraints, optimization objective and corresponding calculation methods are determined. Finally, the optimal cross section shapes of fabric rubber seal are obtained under different gas pressure differences, temperatures and multi-objective optimization design. The results indicate that the shape optimization method has an important guiding for the design and manufacture of the fabric rubber seal.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
