Elliptical Micro Research Articles

Multiple hot spot cooling with flow boiling of HFE-7000 in a multichannel pin fin heat sink

Electronics cooling applications require a high cooling performance due to increasing power consumption. Phase change heat transfer is a popular approach for offering high heat flux cooling. Controlling temperature distribution and mitigating boiling instabilities under high heat flux conditions present a significant challenge. While numerous studies investigated the effect of pin fins in a minichannel with single hotspots on boiling enhancement, few research studies are available for minichannels with multiple segmented hotspots. This study's primary objective is to dissipate high heat (1.4 kW) using flow boiling of a dielectric fluid, namely HFE-7000, which has lower thermophysical properties than water, to achieve a uniform temperature distribution, and to suppress boiling instabilities. The boiling performance of a pin fin multichannel heat sink with dimensions of 3 × 14 × 300 mm (H × W × L) subjected to 8 hotspots with uniform heating was investigated in this regard. Flow boiling experiments were performed over a wide range of input heat power from ∼0.1 to ∼1.4 kW with a coolant mass flux of 500 kg/m2 s in the three parallel minichannels having staggered elliptical pin fins with no tip clearance on each hotspot and distribution pins at the inlet. High-speed visualization was used to relate the heat transfer coefficient variations along the channel to flow patterns. The heat transfer performance and flow regimes at different locations were obtained and discussed. Thanks to the mixing effect of elliptical micro pin fins with optimum geometrical parameters along the heat sink, the presence of distribution pin fins at the inlet for suppressing boiling instabilities and early transition to stable annular flow, the temperature uniformity (∼2.3 °C, temperature difference between the inlet and outlet hotspots) could be achieved at the highest heat input. Heat transfer coefficient reduction upto 27 % was reported along the channel when comparing inlet (1st) and outlet (8th) hotspots.

Hybrid photonic crystal fiber with elliptical micro air hole as an efficient supercontinuum source

Abstract A unique design of a pure silica hybrid photonic crystal fiber consisting of three circular rings and one octagonal ring lattices of air holes bounding silica core has been simulated for the generation of wide super continuum spectrum extending from ultraviolet to near infrared. Further modifications of the fiber core with elliptical air hole, manipulated the dispersion profile of the fundamental mode and it generated two zero dispersion wavelengths. The insertion of air hole enhanced the value of nonlinear coefficient, typically from 75 W−1km−1to 466 W−1km−1 (at 1550 nm) for an optimum PCF with ellipticity 0.93, keeping the single mode guidance. Numerical aperture of the fibers was found to increase substantially from 0.56 to 0.86 correspondingly to the ellipticity 0.72 to 0.93 at 1550 nm. Pumping with femtosecond pulses in the anomalous dispersion regime made the spectrum broad. At 1000 W pump, a bandwidth of ≈1472 nm (491 to 1963 nm) was obtained for a fiber of 1 m length with pulse duration of 200 fs. The characteristics of the proposed fiber indicate that it can find numerous applications in a variety of fields, especially in ophthalmology, dentistry and imaging using optical coherence tomography.

Application of a non-conforming tetrahedral element in the context of the three-dimensional strain gradient elasticity

In the size-dependent continuum theories such as the strain gradient theory, the higher-order derivatives of displacement field appear in the energy functional of the structure which leads to the employment of C1 continuous shape functions within the finite element discretization procedure. Although a wide range of one- and two-dimensional small-scale finite elements were developed to analyze the structural behavior of micro- and nano-structures, a few studies can be found on the development of size-dependent three-dimensional (3D) finite elements. Hence, the main purpose of this work is the introduction of a four-node tetrahedral element to analyze the size-dependent mechanical behavior of micro- and nano-structures based on the three-dimensional strain gradient theory (SGT). In the proposed element, the values of displacement components and their related first-order derivatives are considered as degrees of freedom at each node. To present the governing equations, the matrix form of kinetic and strain energies and the work of external forces are derived based on the 3D elasticity theory and strain gradient model. To show the efficiency of the proposed model, the size-dependent linear vibration analysis of circular and elliptical micro- and nano-plates is presented. Various numerical results including comparative and convergence studies are reported to check the accuracy and performance of the introduced finite element.

Evaluation of suction force focusing on suction cup area of elliptical micro suction cup array

Evaluation of suction force focusing on suction cup area of elliptical micro suction cup array

Tribological aspects of various geometrically shaped micro-textures on cutting insert to improve tool life in hard turning process

The present study investigates the effect of three different geometrically shaped micro-textures, namely horizontal micro-texture (WH), vertical micro-texture (WV) and elliptical micro-texture (WE) impregnated with MoS2 dry lubricant on the rake surface of the cutting inserts on the machining performance of hard turning. The results of the experiments carried out with and without micro textures were compared. Experimental results showed the improvement in reducing coefficient of friction resulting into reduction of cutting force and increase in shear angle when machining with horizontal, vertical and elliptical micro textures impregnated with MoS2 as compared to the results of machining without micro textures or without solid lubricant. Reasons for micro-textures reducing the tribology action at the chip-tool interface were investigated. The theoretical model developed here to determine the coefficient of friction by incorporating actual chip-tool contact length confirms the patterns of improvement observed during the experiments and offers a basis for explaining the reasons for it. Novelty of the study involves in predicting actual chip-tool contact length corresponding to forces in cutting speed direction, feed force in axial direction. This study has taken care of validating the theoretical model with experimental results. Errors in the results of chip-tool contact length was within 12% and that of chip reduction coefficient was within 5%. Optimum value of shear angle for maximum chip reduction coefficient was found to be approximately 39°. A maximum reduction of 11.9% in coefficient of friction was obtained using vertically oriented micro texture.

Suction force evaluation of elliptical micro suction cup array

Suction force evaluation of elliptical micro suction cup array

The impact of contact angle on flow resistance reduction in hydrophobic micro pin fins

The pressure drops and the friction factors are measured when ultra pure water flows through the elliptical, diamond and circular hydrophobic micro pin fins with different contact angles of θ=99.5°, 119.5° and 151.5°, and the coefficients of pressure drop reduction dp_coe and friction factor reduction df_coe are calculated respectively. It is found that the value of dp_coe becomes large with the increase of θ in elliptical and diamond micro pin fins, but for circular micro pin fins it increases at first and then decreases. With the increase of θ, both values of dp_coe and df_coe are reduced with the increase of the flow rate in elliptical micro pin fins, but the values are reduced at first and then become almost constants in diamond and circular micro pin fins. Besides, the minimal value of df_coe is over 50% in diamond and circular micro pin fins with contact angle of θ=151.5°. When θ⩾119.5°, the values of dp_coe and df_coe in diamond and circular micro pin fins are both larger than those in elliptical test sections, but for θ=99.5° the former are slightly smaller than the latter at Re<600.

Computer Simulation and Modelling of 3D Travelling Wave Ultrasonic Motor Using a Flexural Vibration Ring Transducer

This paper presents a 3D piezoelectric ultrasonic motor using a single Flexural Vibration Ring Transducer. The motor consists of three main parts, the rotor, the stator and the housing unit. The stator is a piezoelectric transducer ring made from PZT S42 material. Three steel rods and a magnet were designed to support the rotor. The rotor is a sphere of metal that rests on the stator intersecting at the tips of the steel rods and the magnet. The housing unit is made of Perspex, a transparent thermoplastic material. Longitudinal and bending vibration modes, of oscillating structures are superimposed in the motor, generating elliptical micro motions at the driving tips. Pressing the rotor against the stator tips the micro motions are converted into a 3D rotational motion, via the friction between the tips of the three rods and the rotor. The motor structures, working principles, design and finite element analysis are discussed in this paper. A prototype of the motor was fabricated and its characteristics measured. Experimental tests show typical speed of movement equal to 35 revolutions per minute, a resolution of less than 5μm and maximum load of 3.5 Newton.

Ultra Precision Diamond Shaping of an Elliptical Micro-Lens Array

Micro lens array is widely used in photonics and telecommunication products, including back-light module of flat panel display devices and white-light LED illumination. The ultra precision diamond shaping method together with tool servo technique was studied and developed in this research to generate elliptical micro lens array. Each elliptical micro lens has radii in X and Y direction of 1.0 mm and 1.5 mm respectively. A high filling-factor (100 %) elliptical micro lens array with form accuracy better than 0.15μm and surface roughness around 5nm Ra was successfully fabricated.

Ultra Precision Diamond Shaping of an Elliptical Micro-Lens Array

Micro lens array is widely used in photonics and telecommunication products, including back-light module of flat panel display devices and white-light LED illumination. The ultra precision diamond shaping method together with tool servo technique was studied and developed in this research to generate elliptical micro lens array. Each elliptical micro lens has radii in X and Y direction of 1.0 mm and 1.5 mm respectively. A high filling-factor (100 %) elliptical micro lens array with form accuracy better than 0.15μm and surface roughness around 5nm Ra was successfully fabricated.