目的设计一种打印规则,在喷墨技术作为一种高效的生产工具被用于先进制造时提高其喷墨打印精度。方法通过墨滴观测系统分析喷点火频率对喷射状态的影响;分析串扰对喷嘴间的影响,获得高频连续喷射参数,并用高精度打印平台对不同模式进行测试。表征方法包括传统的图像质量分析方法以及喷墨制造获得的导电网格的导电性能对比。结果使用提出的打印规则,喷墨点火频率达到78 k Hz,打印样张网点面积率误差小于1%,竖线粗糙度方差约等于3μm2。宏观和微观的视觉效果得到提升,打印制作的柔性触摸屏网格线条均匀线宽约65μm,导电性良好。结论优化后的打印规则可以弱化残余振动和串扰对其他喷嘴的影响,在提升打印效率的同时提高打印精度和点火频率,有效地促进压电喷头在喷墨制造领域的应用。 相似文献
The objective of the present numerical study is to investigate the heat transfer enhancement, entropy generation, and thermal performance of turbulent nanofluids inside double-pipe heat exchangers equipped with novel perforated cylindrical turbulators. Effects of inflow velocity, CuO nanoparticles volume fraction and perforated index are evaluated on the Nusselt number, friction loss, thermal performance factor (η), and viscous irreversibilities of the double-pipe heat exchangers. The newly proposed perforated turbulators with CuO nanopowder with ϕ = 1.5% provide the thermal performance of η = 1.931, which is considerably higher than the other previous studies. The results show that raising PI reduces the turbulent kinetic energy, especially in outer regions of the cylindrical turbulator. The jet formation near the walls and the perforations is the primary physical reason for this. The viscous entropy generation is increased up to 153.0% by increasing the Re number from 6,000 to 17,000 for PI = 8% and DR = 0.7. Thermal boundary layer disruption is the primary physical reason for heat transfer enhancement. 相似文献
Most of the research work applied to the intensification of heat transfer through convection in turbulent flow, has been devoted to local heat flow and local friction losses. Intensification is obtained by means of turbulators inside smooth channels (fins, steps).In the re-sticking zone of the boundary layer, the heat transfer is maximum and the friction factor is minimum, the latter being maximum in the free flow zone. Maximum values are more than ten times higher than those observed in an undisturbed analogous stream.As early as 1958, those results have been applied to the construction of heat exchangers by which the heat transfer coefficient rises faster than the hydraulic resistance (discovery No 242).Such heat exchangers (water-air) are built from ribbed fin-plates and cross-tubes. The ribs act as turbulators inside the channels which are allowed between plates and tubes.The present paper deals with the influence of geometrical shape and distribution of the turbulator on thermal and hydraulic efficiencies of heat transfer surfaces.The results are presented as graphs where:Nu,NuR = Nusselt number for channels with and respectively, without, turbulators; ε,εR=friction loss factor for channels with, and respectively, without, turbulators; l'/d = pitch of trottling=ratio between the length of smooth piece l' and its hydraulic diameter d; d1/d=rate of throttling=ratio between hydraulic diameter of the throttled section d1, and that of the smooth piece d.Experimentations have been performed with 16 different combinations of l'/d and d1/d, in channels of the same triangular section and Reynolds number varying between 400 and 5500; in channels with different triangular sections; in channels with rectangular sections.Main results are: the heat transfer intensification depends on the parameters l'/d and d1/d; the maximum intensification depends on the shape of the channel section, the highest values being obtained with triangular shaped channels; the most efficient turbulators consist of two dimensioned surfaces generated along the channel radius.New radiators for farm tractor-engines have been developed. Their volume and weight are half those of conventional radiators. Their construction does not require any significant modification of the traditional manufacturing technique of such type of equipment and their utilization in dusty environments does not raise any particular difficulty. 相似文献