Development and evaluation of electronically controlled precision seed-metering device for direct-seeded paddy planter

Nusselt number-friction characteristic for a twisted rib roughened rectangular duct using liquid crystal thermography

Experimental investigation has been performed to investigate the influence of inclination angle on the film cooling performance of two typical diffuser shaped hole configurations, including laidback hole and laidback fanshape hole, using transient liquid crystal measurement technique. Under very small blowing ratio, increase of inclination angle has very small influence on the film cooling effectiveness of laidback fanshape hole configuration. With the increase of blowing ratio, large inclination angle notably reduces its film cooling effectiveness, especially in the upstream region. For film cooling of laidback hole configuration, the increase of inclination angle reduces the film cooling effectiveness under small blowing ratio due to the lift-off of film jets, while produces better film coverage and higher film cooling effectiveness under larger blowing ratios in the downstream region due to the reattachment of lift-off film jets. The increase of inclination angle reduces the heat transfer coefficient for film cooling of laidback fanshape hole configuration in the upstream region. For film cooling of laidback hole configuration, heat transfer coefficient is higher in the upstream region for large inclination angle case due to the enhancement effect of strong counter-rotating vortex pair, while laidback hole with small inclination angle has relatively higher heat transfer coefficient in the downstream region. Under very large blowing ratio, the counter-rotating vortex pair produce two intensely enhanced heat transfer region of spindle shape for film cooling of holes with large inclination angle. From the aspect of heat flux ratio, increase of inclination angle is beneficial to the thermal protection of laidback hole film cooling under large blowing ratio. For both diffuser shaped hole configurations, holes with large inclination angle have larger discharge coefficient due to smaller aerodynamic loss in the hole.

Steam condensation with non-condensable gas exists widely in petro-chemical, power plant and seawater desalination processes. Super-hydrophobic surfaces with high contact angle could be an promising condensing surface to promote DWC and enhance heat transfer. As pure steam condensing droplet completely occupies micro/nano-structures of super-hydrophobic surfaces, super-hydrophobic function becomes “invalid”. For stream-air mixture vapor, the non- condensable gas would occupy the micro/nano-structures instead of water. Droplets form Cassie or transition wetting mode, holding or partly holding super-hydrophobic feature. Inclination angle of the tube can influence the shape, size and dynamic characteristics of the condensing droplets, thus changing the heat transfer performance. Therefore, for getting deeply insights of the effect of the non-condensable gas on condensation heat transfer, it is necessary to study the condensing drops characteristics on super-hydrophobic tube for different inclined angles. According to dropwise condensation model, increasing contact angle hysteresis, departure droplet size, sweeping period would reduce the condensation heat transfer efficiency. In this paper, dropwise condensation is performed on super-hydrophobic copper tube, departure droplet size, sweeping period and the phenomenon of contact angle hysteresis are thoroughly studied and are compared with the case of hydrophobic surface or pure steam to explore the influence of inclined angle and surface wettability on droplet dynamics to achieve condensation heat transfer enhancement. The experimental result shows: (1) On the top of copper tube, for the condensation of steam with 10% non-condensable gas, the contact angle hysteresis on super-hydrophobic surface is smaller than that on hydrophobic surface. Compared with pure steam condensation on super-hydrophobic surface, the contact angle hysteresis of mixed steam is smaller because the non- condensable gas fills the micro/nano-structures. However, on the middle and bottom parts of the tube, the contact angle hysteresis on super-hydrophobic surface is greater than that on hydrophobic surface for the condensation of both pure steam and mixed steam. This phenomenon indicates that the contact angle hysteresis is determined by surface wettability instead of inclination angle. (2) The departure droplet size on super-hydrophobic surface increases with the inclination angle and the opposite trend is found on hydrophobic surface. With the increase of inclination angle, the support force provided by the tube would increase and change direction. So the wettability of the surface and departure droplet size would be changed. (3) The sweeping period of droplet on super-hydrophobic surface is longer because the micro/nano-structures increase the adhesion between the surface and the droplets. With the increase of the inclination angle, the sweeping period decreased slightly, shorter than the sweeping time when the tube is vertical. The sweeping period of vapor with non-condensable gas condensation is greater than that of pure steam. The presence of non-condensable gas increases thermal resistance, thus slowing down the drop growth rate and increasing the sweeping period. To sum up, on the top of copper tube, the contact angle hysteresis on super-hydrophobic surface is smaller than that on the hydrophobic surface. However, the totally opposite trend is found on the middle and bottom parts of the tube. The departure droplet size on super-hydrophobic surface increases with the inclination angle. The sweeping period of droplet on super-hydrophobic surface is longer. This work offers a new avenue to further enhance heat transfer of condensation with non-condensable gas.

Coarse particle-laden flows in inclined pipes are commonly encountered in a wide range of industrial processes. A fully coupled CFD-DEM model considering various fluid-particle interphase forces and turbulence-particle interactions is used to simulate coarse particles transported in inclined pipes. The energy dissipation is calculated from both the macro and micro perspectives. The effects of pipe’s inclination angle, particle concentration, conveying speed and particle diameter on the hydraulic transport characteristics and the energy dissipations are analyzed. The results showed that, with the increase in inclination angle, the deposited particles were gradually dispersed. Pressure drop and energy dissipation displayed a peak at 60°. Both the parameters increased with the increases in particle concentration and conveying speed in 60° inclined pipe. The energy dissipation was mainly due to the turbulent dissipation, wall friction, mean velocity field and particles’ gravity. The results further showed that the modulations in the fluid due to particle distribution could significantly change the energy dissipation caused by the fluctuating velocity, thus resulting in the maximum pressure drop and energy dissipation at 60°. The particle-fluid energy dissipation increased almost linearly with the increase in conveying speed, while it varied nonlinearly with the increase in inclination angle and particle parameters.

Investigation was carried out on the application of coefficient of friction in the separation of cocoa beans–husk mixture. An inclined plane at angles 20, 25 and 35°rotating at different speeds (215, 250 and 260 rpm) and receiving the mixture at heights 30, 60 and 90 mm, was used for the study. The result indicates that within the range of factors considered, the separation efficiency of the beans from the mixture increases with increase in speed of rotation and height of fall, while it decreases with increase in angle of inclination. Statistical analysis shows that the effects of each of the factors and that of their interaction are significant at 99%. The best separation efficiency (99%) was observed at a speed of 250 rpm, an angle of inclination of 25° and a height fall of 90 mm.PRACTICAL APPLICATIONSSeparation of cocoa beans from the husks has been a serious problem in cocoa processing. Handpicking is still being used to separate the mixture of cocoa beans–husk even with the mechanical pod breaker available. This therefore constitutes a tedious operation. An inclined plane mechanism tested for the separation of the mixture in this study can be incorporated into the design of the cocoa pod processor to reduce the drudgery involved in cocoa processing and improve the quality of the product.

Film cooling performances of laidback hole and laidback fan-shaped hole have been investigated using transient liquid crystal measurement technique. For film cooling of laidback hole, the increase of inclination angle reduces the film cooling effectiveness under small blowing ratio, while produces better film coverage and higher film cooling effectiveness under larger blowing ratios. Heat transfer coefficient is higher in the upstream region of laidback hole film cooling with large inclination angle, while laidback hole with small inclination angle has relatively higher heat transfer coefficient in the downstream region. The increase of inclination angle reduces the film cooling effectiveness and heat transfer coefficient of laidback fan-shaped hole film cooling, especially in the upstream region. Increase of inclination angle is beneficial to the thermal protection of laidback hole film cooling under large blowing ratio. Film hole with large inclination angle has larger discharge coefficient due to smaller aerodynamic loss in the hole.

Flame spread over cables in a utility tunnel: Effect of longitudinal wind and inclination angle

Excavation unloading is a primary stress condition for engineering rock mass in deep underground. Based on the unloading stress condition during the excavation operation, this paper employed a distinct element method (DEM) to simulate the unloading responses of intact and preflawed rock specimens. The simulation results revealed that the unloading failure strength, unloading damage thresholds, and cracking characteristics were largely dependent on the inclination angle α of the preflaws. With the increase in the flaw inclination angle, the unloading failure strength of a preflawed specimen exhibited a sigmoidal curve increasing trend, and it decreased by 5.5%-20% compared to the unloading failure strength of an intact specimen. Based on the crack accumulation in specimens, three damage thresholds were identified under unloading condition and two damage thresholds σci and σdi were found to be increased with the increase in the flaw inclination angle. Furthermore, when the flaw inclination angle was smaller, cracks were initiated around the preflaws, and there were obvious axial splitting cracks in the failure modes of preflawed specimens, while axial splitting cracks were few in the preflawed specimen with a larger flaw inclination angle and none in the intact specimen. These unloading responses indicate that inducing preflaws can reliably reduce the unloading failure strength and promote the cracking process of hard rock during an excavation unloading process. Moreover, inducing preflaws with a smaller inclination angle (e.g., vertical to the unloading direction) will be more helpful for the unloading failure and rock cracking during an excavation unloading process.

Droplet impinging on an inclined cylinder is different from that on a horizontal one in some ways. However, there is still a lack of in-depth study on its dynamic behavior. In this study, a numerical model of droplet impinging on a superhydrophobic inclined cylindrical surface was established by incorporating a dynamic contact angle model. Droplet motion patterns, sliding behavior, spreading and shrinking behavior, and contact time after droplet impinging were discussed under the influences of inclination angle and Weber number. Results show that under different conditions, droplets may exhibit four motion patterns: full rebound, pure slide, fragmentation, and oscillation. Pure slide is an inherent motion pattern for droplet impinging on an inclined surface, and full rebound is caused by the different sliding velocities of leading and trailing edges. Leading edge's sliding distance curve is convex and trailing edge's one is concave. The dimensionless sliding distance of the droplet rises with Weber number and inclination angle, and the effect of Weber number on it lessens at small inclination angles. The time for the droplet to reach maximal spreading length in axial direction gradually exceeds that in circumferential direction with the increase in inclination angle, and the non-monotonicity of the axial spreading length during the shrinking process disappears when an inclination angle is introduced. When the Weber number is less than 15.28 and the inclination angle rises from 0° to 80°, the contact time increases by 58.8%. This growth is even more pronounced when the Weber number is larger.

Micro end milling is a main method for the fabrication of microgroove parts which are widely applied in biology, electronics, precision machinery, and other fields. However, the machining quality of microgroove is difficult to meet requirements due to size effect, and the machined grooves easily produce high surface roughness and poor form accuracy during micro milling. In this paper, in order to investigate the effects of machining inclination angles on the performance of micro ball end milling, the micro milling experiments on Ti-6Al-4V are carried out by setting the micro ball end mill with different inclination angles in feed direction, cross-feed direction, and the combination of the two directions, respectively. The results show that the tool orientation strategy has significant influences on the quality of microgroove and can reduce the roughness and improve the form accuracy. With increase of the absolute value of inclination angle along feed direction from 0° to 45°, the surface roughness has a decreasing trend, and the chips adhesion and texture becomes inconspicuous. When inclination angle along feed direction is 30° and 45°, the combination inclination angle strategy has no obvious influences on the surface roughness with increase of inclination angle along cross-feed direction. However, the combination inclination angles strategy can reduce the maximum form deviation and improve the form accuracy of the groove. Based on the results, an optimal combination inclination angles with feed direction 45° and cross-feed direction 20° strategy is proposed to machining the microgroove.

In present study, a new type of three-dimensional pin–fin plate with elliptical cross-section was proposed. Steam condensation on the proposed plates with different geometric parameter was experimentally studied at atmospheric pressure. The effects of horizontal pin spacing, pin height and inclination angle on condensation heat transfer were investigated. The results showed that all the elliptical pin-fin plates exhibited substantially better performance than the flat plate. The highest enhancement ratio of 2.33 was achieved when the elliptical pin-fin plate was vertically placed. The geometric parameter and inclination angle showed a strong influence on the performance of elliptical pin-fin plate. The performance of elliptical pin-fin plate was enhanced when the pin height increased from 1.2 mm to 2.0 mm or the horizontal pin spacing increased from 1.2 mm to 2.0 mm. The strengthening effect of pin height became weaker with the increase of horizontal pin spacing. When the inclination angle increased from 0° to 60°, the heat flux and average condensation heat transfer coefficient decreased by 16 and 25%, respectively. With the increase of inclination angle, the gravity effect in the direction of condensate flow decreased, resulted in the deterioration of heat transfer. The results can provide reference for practical engineering applications and the further optimization design of pin-fin enhanced condensation structure.

The effect of motion patterns on edge-loading of metal-on-metal hip resurfacing

The frost heave failure mechanism of fractured rock mass is a complicated problem faced by engineering construction in cold area. In this study, low temperature frost heave test and post-freezing uniaxial compression test on sandstone samples with a water-filled flaw were carried out. The frost heave cracking mode, frost heave pressure, frost heave cracking criterion and the effect of frost heave-induced cracks on post-freezing uniaxial compression failure behavior under different flaw inclination angles (0 ~ 90°) and freezing temperatures (–10~–40 °C) were investigated. Frost heave cracks initiate and extend along the coplanar direction of flaws. The frost heave damage degree decreases with the increase of flaw inclination angle. As the freezing temperature drops, the flaw cracking length first increases greatly, and then decreases, reaching the maximum at − 15 °C. The evolution of frost heave pressure can be divided into six stages: pre-freeze stage, rapid increase stage, rapid decrease stage, stable stage, slight rebound stage and dissipation stage. The peak frost heave pressure first increases and then decreases with the increase of flaw inclination angle, and reaches the maximum at 60°, and increases as the freezing temperature drops. Formulas for calculating the critical stress intensity factor KIC for flaw frost heave cracking are provided, considering flaw inclination angle or freezing temperature. When the flaw is within a certain range of inclination angles (45 ~ 75°), cracks under uniaxial compression will extend from the frost heave-induced cracks.

In the present investigation an attempt is made to study the axial and oblique pullout capacity of monopile and belled pile embedded in geogrid reinforced sand beds by conducting tests on model piles. A model tank of size 1.2mX0.75mX1.5 m is used to study the behaviour of an aluminium model pile under axial and oblique pull-out loads in geogrid reinforced sand bed of relative density 30%. A comparative study was made between monopile and belled piles by varying parameters such as embedment ratios (L/Ds) of 5, 7.5, and 10 respectively and diameter ratios (Db/Ds) of 1.5 & 2 with bell angles of 30°, 45°, and 60° under axial and oblique inclination angle of 30˚& 45˚.The use of the optimum size of the geogrid reinforcement placed at the bottom of the short pile and at a spacing of 4.5Ds from top in case of intermediate and long pile significantly enhanced the pullout and oblique pullout capacities of both monopile and belled piles. In the case of a monopile, the pull-out capacity increases with an increase in the load inclination angle from 0˚ to 45°, whereas in the case of the belled pile, the pullout capacity decreased with an increase in the load inclination angle. A non-dimensional parameter called the Uplift Improvement Ratio was evaluated, and the results revealed that the efficiency of the geogrid reinforcement was independent of the load inclination, bell angle, Db/Ds ratio, and L/Ds ratio when the optimum size of the geogrid was placed at optimum position of the belled pile foundation. It was also found that the obtained breakout factor increases with an increase in the L/Ds ratio and load inclination angle but the influence of the bell angle on the breakout factor was found to be marginal.The obtained values of the breakout factor were compared with the existing limit equilibrium theory, and it was found that the results of the breakout factor were in good agreement with the Meyerhof and Adam theory for both unreinforced and geogrid-reinforced sand beds.

Free convection heat transfer inside vertical and inclined elliptic tubes with different axis ratio and different inclination and orientation angles