Influence Of Geometry Parameters Research Articles

Numerical simulation on heat transfer enhancement of free piston Stirling engine heater with composite cross section mini channels

Integral fin with micro-channels have been widely used in small free piston Stirling engines heater due to their high heat transfer rate, low flow loss, and high machining accuracy. A β-type free piston Stirling engine heater with composite cross section mini channels(CCSMH) is designed for heat transfer enhancement applying to solar dish power generation system. Investigation on heat transfer performance of the heater under oscillating flow is carried out by CFD method, which is compared with smooth annular tube heater. The influence of geometry parameters on the performance of heat transfer and pressure loss is investigated. A improved performance evaluation criteria PEC is proposed for the condition of equal flow velocity to evaluate the enhanced heat transfer performance of the heater. The results show that the maximum value of the comprehensive performance evaluation index PEC can reach 3.14, the maximum mean pressure drop increment of CCSMH compared with the smooth tube heater is 38.4 Pa, which is much lower than the minimum pressure of 2.3 MPa and can be neglected.

Effects of scavenging port angle and combustion chamber geometry on combustion and emmission of a high-pressure direct-injection natural gas marine engine

ABSTRACT HPDI natural gas (HPDI-NA) engines can improve nitrogen oxides and PM emissions while getting better in-cylinder combustion in the comparison of the conventional engines fueled with diesel. In this paper, a three-dimensional (3D) of a HPDI natural gas marine engine is set up. The influence of geometry parameters on mixture flow, combustion, and emissions were presented and discussed. The geometry parameters include scavenging port angle (SPA) and three combustion chamber geometries (shallow-basin-shaped (SBC), shallow-ω-shaped (SWC), and deep-pit-shaped combustion chamber (DPC)). The results show that increasing the SPA can significantly swell the swirl ratio, but too large the swirl ratio is not conducive to improving the scavenging effect. As SPA is varied from 30° to 60°, a richer-than-flammable region gets greater, and the penetration distance is shortened by the larger vortex. Then, the mixing and combustion process get worse. With the increase of the SPA, the emissions of soot, carbonic oxide (CO), and unburned hydrocarbons (HC) can be optimized. Also, a larger scavenge port angle is not conducive to improving nitrogen oxides emission and the fuel consumption efficiency. The combustion chamber geometries have fewer effects on the mixture flow and the pressure profiles and temperature than that of SPA. The CO/HC and soot emissions of the three tested combustion chamber geometries are similar. The effect of the shallow basin-shaped combustion chamber (SBC) is much better than that of the other combustion chamber geometries with respect to NOx emission.

Comparison between the cooling performances of micro-jet impingement systems using liquid metal and water as coolants for high power electronics

Liquid metals are attractive coolants for MEMS with a high heat flux. However, most existing studies on liquid metals were focused on micro- and mini-channel heat sinks. In the present work, we applied liquid metals into three micro-jet impingement systems, i.e., jet impingement surface cooling (JISC), jet impingement body cooling (JIBC) and hybrid body cooling (HBC) systems. Analytic and numerical models were established, based on which the thermal resistances of these systems using water and liquid gallium (Ga) as coolants were compared and analyzed. The results indicated that the systems using liquid Ga always achieved a smaller thermal resistance compared to water, showing a maximum decrease of 29.8% in thermal resistance and a largest drop of 12.6 K in chip temperature. The minimum thermal resistance using liquid metals reaches as low as 0.033 K/W. In addition, JIBC system always had the smallest thermal resistance when water was used. However, in the case of liquid Ga, HBC system performs best at small flow rates. The influences of geometry parameters on the system cooling performance were analyzed. It was shown that an optimal nozzle spacing of 4.7 mm existed. Moreover, the thermal resistances of the three systems increased with an increasing nozzle diameter, and the thermal resistance of JIBC system would exceed that of HBC system at an enough large nozzle diameter (e.g., ∼0.28 mm for Ga). Regardless of the coolant used, the thermal resistances of JIBC system kept nearly constant with the variation of side gap height. For HBC system, the thermal resistance increased obviously with an increasing side gap height when water was used as coolant, while barely changed for liquid Ga. The findings in this study provide a guidance for the design and operation of micro-jet impingement systems employing liquid metals as coolant.

Free vibration of piezoelectric FGM sandwich beam with porous core embedded in thermal environment and elastic foundation

This paper aims to present thermo-electrical free vibration characteristics of functionally graded material (FGM) sandwich beam placed on the two-parameter elastic foundation. The beam is constructed of a foam core, two middle FGM layers, and two outer piezoelectric layers. It is assumed that the beam is subjected to a constant voltage and a uniform/linear temperature distribution. Physical properties of the core and two middle layers vary smoothly through the thickness according to the cosine and power-law forms, respectively. Lagrange equations in conjunction with the Reddy third-order beam theory is employed to derive the governing equations of motion. A simple polynomial trial function-based Ritz method is adopted for the approximation of the displacement field to obtain the vibration response. The correctness of the study is verified by comparisons with other authors’ published results. Influences of geometry parameters, material property distribution, applied voltage, elastic foundation, temperature distribution, temperature change, porosity coefficient, span-to-height ratio, and boundary conditions are investigated through parametric studies.

Analysis of the influence of the geometry of the input part of the matrix on the formation of the edge part of the cylindrical bill

The formation of an uneven geometry of the end part of cylindrical products is quite common after the implementation of drawing of sheet blanks. It occurs due to the imbalanced orientation of the crystallographic structure of the material, that is, due to the anisotropy of the mechanical properties. As different elements of the sheet bill have different speed of movement relative to the tool during the drawing, so-called scallops, or protrusions, appear. This causes a problem during the production, since it takes additional time and resources to bring the geometry of the products to the norm. Therefore, the actual task is to minimize this phenomenon. The article discusses an approach to eliminating or minimizing scallop formation by means of scientifically grounded selection of the geometry of the input part of the matrix. The influence of geometry parameters on the uneven geometry of products and their stress state is described.

Computational Investigation of Flow Control Methods in the Impeller Rear Cavity

In typical median and small aeroengines, the air used to realize the functions such as cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, adjusting of rotating assembly axial load is normally drawn through the rear cavity of centrifugal impeller, so the thorough understanding of flow characteristics and pressure distribution and the proposal of the corresponding control methods in the cavity are the key to design the rational secondary air system. With an impeller rear cavity in a small turbofan engine as an object, the current study was dedicated to the investigation of flow control methods in the cavity. Two methods, namely, baffle and swirl-controlled orifice, were proposed to regulate the pressure loss and distribution in the cavity. Furthermore, the influence of geometry parameters of the two methods such as the length of baffle, the space between the baffle and rotating disk wall, the orientation, and radial position of swirl-controlled orifice was investigated. The CFD results show that the swirl-controlled orifice which could deswirl the flow is more effective in regulating the pressure loss and its distribution in cavity than baffle. The variation of the radial position of the swirl-controlled orifice had little influence on pressure loss but obvious influence on pressure distribution; therefore, decreasing the radial position could reduce the axial load on the rotating disk without changing the outlet pressure.

Broadband light absorption with doped silicon for the terahertz frequency

The broadband absorption effect with patterned doped silicon for terahertz (THz) frequency is investigated. It is achieved by patterning the doped silicon substrate with a two-dimensional grating and covered by a layer of anti-reflective coating. The bandwidth with the polarization-insensitive absorption above 95% covers a frequency range of 0.79–4.115 THz. Moreover the broadband absorption performance can be maintained for the incident angle up to 70°. The electromagnetic field distributions at the resonant frequencies are illustrated to disclose the underlying mechanism of such broadband absorption phenomenon. Last, the influence of geometry parameters on the absorption performance is investigated to provide a guide for practical fabrication. It is hoped that the designed broadband absorber may found applications in the area of thermal emitter, cloaking and biosensor.

Design and optimization of DETF resonator based on uncertainty analysis in a micro-accelerometer

Boundary structure and geometry parameters of the Double-Ended-Tuning Fork (DETF) resonator in a micro-accelerometer are investigated. The theoretical vibration model of a DETF resonator is established and verified by the simulation results obtained by finite element method. Uncertainty analysis incorporating the parametric uncertainty distribution is conducted by establishing the sample-based stochastic model to systematically investigate the influence of different geometry parameters of the DETF resonator on the natural frequency and the sensitivity of DETF resonator. The results reveal the different influences of geometry parameters, which can be used as reference for design and optimization of the DETF resonator of the micro-accelerometer.

Injector Nozzle Multiphase Flow Numerical Simulation of High Pressure Common Rail System

The changing of injector nozzle structure will influence the combustion and emission properties in diesel engine. Three-dimensional numerical simulation of multiphase flow of mini-sac nozzles of high pressure common rail were calculated by using the computational fluid dynamics ( CFD ) method in this paper. The results shown that this method can be more accurately obtained a lot of useful information on the flow field inside the nozzle in a relatively short period of time, and it is convenient for analysis and research the influence of geometry parameters on the flow characteristics inside the nozzle. The paper also studied the influence of nozzle inlet pressure, the angle between the axis of the hole and the axis of the injector and nozzle entrance radius to the flow characteristics inside the nozzle. It also studied the distribution of internal pressure, velocity of flow, gas-phase volume fraction and turbulent kinetic energy. These studies provided a favorable basis for the design and improvement of the nozzle structure and optimize combustion system matches.

Influence of Geometry Parameters on Critical Heat Flux in Helically Coiled Tubes: Development of Correlation

Based on 2006 look-up tables to analysis the effect of pipe diameters on CHF, the correlations are established for horizontal helically coiled tube by introducing equivalent geometrical parameter. According to experimental data, it is found that the correlation is very suitable, and the regularity of horizontal helically coiled tube geometry parameters on CHF tends to be consistent with that of a vertical tube.

Subwavelength Demagnification Imaging and Lithography Using Hyperlens with a Plasmonic Reflector Layer

Unlike the case in magnification mode, it is found that hyperlens employed in demagnification and lithography manner encounters great degradation of imaging quality especially for high-resolution image features. This problem mainly arises from the transversal magnetic polarization feature of light which delivers reduced contrast of electronic components intensity profile at the imaging region. Hyperlens with plasmonic reflector layer is designed for subwavelength demagnification imaging and photolithography. Analytical equations and numerical simulations show amplification of reflected evanescent waves in photoresist sandwiched by hyperlens and plasmonic reflectors in cylindrical geometry. The image quality features including resolution, contrast, and intensity can be improved significantly. Also presented are the dependence and influence of geometry parameters on imaging quality. Numerical demonstrations are given with about 15 nm half-pitch resolution imaging at illuminating wavelength of 365 nm.

Influence of metal contacts on the electrical properties of a UV-MSM photodetector

We have developed a two-dimensional theoretical model. This model allowed us to characterize the MSM photodetector based ZnO. It also allowed us to simulate the dark current and photocurrent of the device with different dimensions of the metal contact of structure. The simulation results were agreed with those of the experiment. We have identified the influence of geometry parameters of the metal contact on the dark current and also on the photocurrent. Calculating the ratio (photocurrent / dark current), allowed us to find the best values of finger width w and finger spacing s of the metal structure leading to a low dark current and at the same time a better absorption of the incident light. The best performance of MSM PD are obtained for the following values s = 14 µm, w = 12 microns. These values have enabled us to obtain a dark current of 25nA and a photocurrent equal to 0.78 µA at a 3V bias.

Influence of Geometry Parameters on Durability of Concrete Structures Exposed to Chloride Environment

Finite difference method (FDM) is used to numerical stimulation analysis for chloride diffusion in concrete. By numerical computing, comparison of chloride content profile in different concrete members with different sectional shapes is made. Calculation and comparison show the chloride content prolife in rectangular and circular section has obvious difference. If the side length of rectangular section is equal to the diameter of circular section, as well as the material property and environment, the chloride content in rectangular section is higher than that in that in circular section. In the calculation example, the chloride content at the depth of reinforcement of circular section is about 50-60% that of rectangular section. This tendency is more remarkable in less section dimension, as well as less cover thickness. With the increasing of section, the ratio of difference becomes to be less until to a constant value. In durability design and service life prediction of concrete structures, the section shape and dimension influence should be taken to consideration.

Analytical model of range-doppler of cone-cylinder combination

The technique of laser range-Doppler image has been intimately noticed by aerospace and national defense circles. A analytical model of laser range-Doppler image of cone-cylinder combination is proposed in this paper. The analytical model includes the contribution of disk base. The analytical model can provide the effects of geometry parameters, the roughness of the surface, attitude, and pulse duration on laser range-Doppler image. This analytical model can reduce into the analytical model of range-Doppler image of cone and cylinder. This analytical model can reduce into the analytical model of Doppler spectra for plane waves. The influences of geometry parameters, and attitude are analyzed numerically by using the analytical model. The results indicate that the laser range-Doppler image of cone-cylinder combination can show the information about geometrical shape and attitude of target. Combining the theory and measurements, the analytical model can be used for indentifying physical parameters and geometrical parameters of cylinders, cones and cone-cylinder combination. This analytical solution is of significance for the laser Doppler velocimetry and ladar applications.