Radial Micro Research Articles

Experimental investigation on flow boiling characteristics of a radial micro pin–fin heat sink for hotspot heat dissipation

The rapid development of integrated circuit technology has led to an increasing chip-level heat flux, which poses a difficult challenge to cooling techniques. A radial micro pin–fin heat sink that combines the merits of micro pin–fin structure and central inlet jet configuration is proposed in this study for heat dissipation of high-heat-flux hotspot. Flow boiling experiments with ammonia are conducted for mass fluxes of 34–182 kg/m2s, heat fluxes of 752–1397 W/cm2, saturation temperatures of 26 and 30 °C, and inlet conditions of near-saturated and two-phase inlet. The rectangular parallel microchannel structure is also tested for comparison. The effects of heat flux, mass flux, saturation temperature, and inlet condition on the heat transfer and pressure drop characteristics are investigated. The governing heat transfer mechanisms of microchannel flow boiling are identified for different experimental conditions. Experimental results indicate that the radial micro pin–fin heat sink can maintain stable and outstanding heat transfer performance over a wide range of experimental conditions, which verifies its application prospect in the heat dissipation of high-heat-flux hotspot.

Improvement in the working life of a micro journal bearings with an electroless Ni–P coating

The improvement of working life is the main purpose of this paper to evaluate the mechanical properties of the electroless Ni–P coatings of radial micro journal bearings. The study was carried out using different plating parameter combinations, namely, pH values of the plating solution (6, 7, and 8), deposition time (10, 20, and 30 min), and bath temperature (60, 80, and 95 °C). The structure, surface morphology, hardness, and wear resistance of the electroless Ni–P coatings were measured and analyzed. The optimum combination of plating parameters for minimum wear is a pH value of 8, deposition time of 30 min, and bath temperature of 95 °C. When the Ni–P film is annealed at 400 °C, the hardness, wear and surface roughness can get the best values of 960 HV, 0.1 mg, and 0.177 μm, respectively, and this is because the Ni–P coating has changed from an amorphous phase to a crystalline composite phase (Ni + Ni3P) structure. However, as the annealing temperature continues to increase; the hardness, wear, and surface roughness begin to deteriorate. The coherent relationship of the crystalline composite phase is broken, the grains of the Ni–P coating will grow, and the tensile stress of the Ni–P coating will increase.

Combustion characteristics of hydrogen‐air mixture in a radial micro combustor for using in thermophotovoltaic devices

Combustion characteristics of hydrogen‐air mixture in a radial micro combustor for using in thermophotovoltaic devices

Coefficient of Rayleigh Index based performance evaluation of radial micro jet injection technique for thermo-acoustic instability control

This study proposes a coefficient of Rayleigh Index (CRI) obtained by normalizing the acquired data which can circumvent the problem of arbitrary scale and unit while quantifying the Rayleigh Index. CRI is estimated from the simultaneous measurements of luminescence of a flame as an indicator of unsteady heat release and pressure fluctuation near the burner head. Experiments were carried out for six different mixture equivalence ratios ranging from 0.75 to 1.0 and a burner positioned at x/L = 0.2. The control technique of micro jets is found to completely suppress the thermo-acoustics by decoupling the pressure waves and unsteady heat release waves as indicated by increasing phase difference between them. The coefficient of Rayleigh Index is found to reduce to nearly zero with the use of radial micro jets for suppressing the thermo-acoustic instability. In such case, the flame luminescence was observed to significantly reduce. The proposed coefficient of Rayleigh index is very useful in quantifying the effectiveness of control technique for the thermo-acoustic instability.

Preliminary design and performance analysis of a radial inflow turbine for a large-scale helium cryogenic system

Large-scale helium cryogenic systems are widely used in superconducting systems, nuclear fusion engineering, space exploration and large scientific engineering, etc. However, its energy efficiency is quite low due to the extremely low operation temperature. The helium turbine constitutes the most vital component of a large-scale helium cryogenic system. Thus, it is essential to develop a high efficiency helium turbine in order to improve the energy efficiency of the cryogenic helium system. In this paper, a high speed radial micro turbine with the splitter blade was designed for a 40 L/h helium liquefier with Claude cycle. The turbine is designed for inlet and outlet temperatures of 14.4 K and 9.4 K respectively. The design speed of the turbine is 223570 rpm due to the small mass flow rate and impeller diameter. A one-dimensional mean line optimal design approach for radial inflow turbine is adopted in this study. Furthermore, detailed three-dimensional viscous numerical simulations are conducted in order to verify the one-dimensional optimal approach in design condition and predict the performance of the designed turbine in off-design conditions. The results indicate that the optimal helium radial inflow turbine for the design and off-design conditions can be designed through applying the proposed analysis method.

Formation of mosaic diamonds from the Zarnitsa kimberlite

Mosaic diamonds from the Zarnitsa kimberlite (Daldyn field, Yakutian diamondiferous province) are morphologicaly and structurally similar to dark gray mosaic diamonds of varieties V and VII found frequently in placers of the northeastern Siberian craton. However, although being similar in microstructure, the two groups of diamonds differ in formation mechanism: splitting of crystals in the case of placer diamonds (V and VII) and growth by geometric selection in the Zarnitsa kimberlite diamonds. Selective growth on originally polycrystalline substrates in the latter has produced radial micro structures with grains coarsening rimward from distinctly polycrystalline cores. Besides the formation mechanisms, diamonds of the two groups differ in origin of mineral inclusions, distribution of defects and nitrogen impurity, and carbon isotope composition. Unlike the placer diamonds of varieties V and VII, the analyzed crystals from the Zarnitsa kimberlite enclose peridotitic minerals (olivines and subcalcic Cr-bearing pyropes) and have total nitrogen contents common to natural kimberlitic diamonds (0 to 1761 ppm) and typical mantle carbon isotope compositions (-1.9 to -6.2%c 513C; -4.2%c on average). The distribution of defect centers in the Zarnitsa diamond samples fits the annealing model implying that nitrogen aggregation decreases from core to rim.

Investigation into the lubricating gap between the ring gear and the case in internal gear pumps

PurposeThe purpose of this paper is to propose a simulation model for studying the lubricating gap between the ring gear and the case in internal gear pumps.Design/methodology/approachThe pressure distribution of the wedge-shaped oil film between the ring gear and the case is obtained based on the theory of film lubrication using the Reynolds equation implemented with MATLAB. After that, the balance of the ring gear is achieved by the radial micro motion of the ring gear. The power loss due to the leakage and the shear stress is then calculated for optimized design of the radial clearance.FindingsThe hydrodynamic effect and the squeezing effect of the wedge-shaped oil film play a role in the hydrodynamic balance of the ring gear, and they become more intense when the operating speed gets lower and the pressure gets higher. The optimal radial clearance should stay between 20 and 25 µm for the minimum power loss.Originality/valueThe present research provides the first simulation model that treats the oil film between the ring gear and the case as wedge-shaped oil film and explains why the ring gear stays balanced. Furthermore, the simulation model can be regarded as a tool for optimized design of the radial clearance.

Radial Micro Cracks in Pile-Up Region of Single Crystal Cu in Spherical Indentation: Experimental Observation and Crystal Plastic Simulation

Radial Micro Cracks in Pile-Up Region of Single Crystal Cu in Spherical Indentation: Experimental Observation and Crystal Plastic Simulation

Expander selection for an on board ORC energy recovery system

Abstract This paper deals with the comparison between volumetric expanders (screw, scroll and rotary vane) and an Inlet Forward Radial (IFR) micro turbine for the exploitation of an on board Organic Rankine Cycle (ORC) energy recovery system. The sensible heat recovered from a common bus engine (typically 8000 cc) feeds the energy recovery system that can generate sufficient extra power to sustain the air-conditioning system and part of the auxiliaries. The concept is suitable for all kind of thermally propelled vehicles, but the application considered here is specific for an urban bus. The ORC cycle performance is calculated by a Process Simulator (CAMEL Pro) and the results are discussed. A preliminary design of the considered expanders is proposed using ad-hoc made models implemented in MATLAB; the technical constraints inherent to each machine are listed in order to perform the optimal choice of the expander based on efficiency, reliability and power density. Last step will be the selection of the expander that suites the specific technical and design requests. The final choice relapsed on the screw motor, for it is the best compromise in terms of efficiency, lubrication and reliability.

Effect of porosity, density and temperature on microstructure and mechanical behavior of hybrid premix sponge ferrous compact

This study on hybrid premix sponge ferrous sintered materials is focused on its mechanical properties and microstructure with respect to the amount of porosity. The pressure of 430 MPa and sintering temperatures 1090?C, 1115?C, and 1130?C in a Nitrogen atmosphere for an hour is followed to produce this hybrid premix sponge ferrous compact. Radial crush strength, dimensional change and micro hardness test were performed on these samples to determine the mechanical properties. Scanning electron microscope (SEM) was used for fractured surface analysis, while light optical microscopy (LOM) is used to study the structure and pore formation. The study infers, as porosity percentage increased, tendency of irregular pore formation increased with simultaneous decrease in mechanical properties of the sample. Temperature of sintering has a vital role in decreasing the porosity of powder materials.

Fluid Flow within Radial Micro Channel Heat Sink: A Review

Objectives: Micro channels are characterized as stream sections that have pressure driven measurements in the scope of 10 to 200 micrometers. Methods/Statistical Analysis: It is assumed that the present work would provide new direction to the researcher in the field of Micro Channel Heat Sink. Findings: Subsequent to looking into the progression in warmth exchange innovation from a verifiable point of view, the benefits of utilizing micro channels as a part of high warmth flux cooling applications is examined and research done on different parts of micro channel heat exchanger execution is assessed. Application/Improvements: The present condition of manufacture innovation is looked into, taxonomically sorted out and found to offer numerous new potential outcomes for building micro channels.

Suppression of thermo-acoustic instability using air injection in horizontal Rijke tube

The thermo-acoustic instability arising out of coupling between the pressure fluctuation and the unsteady heat release, when grows sufficiently, is known to cause serious structural damage thereby reducing the life span of systems having combustor for example, jet engines, gas turbines and industrial burners. The present work involves experimental study of thermo-acoustic instabilities occurring in a Rijke tube and their suppression by means of diverting a very small fraction of the incoming air flow in the form of radial injection from the wall of the tube through micro jets. A horizontal quartz tube with pre-mixed burner is used as the test model of Rijke tube. The coefficient Rayleigh Index (RI) is estimated from simultaneous measurement of chemiluminescence using a PMT and pressure in the plane of burner head. Experiments were carried out at the equivalence ratio of Φ = 1 for a range of the burner position inside the tube, velocity of micro jets, and total mass flow rate through the tube. The control technique of micro jets was found to completely suppress the thermo-acoustics in a range of jet velocity depending on the burner position and the total air mass flow rate. For complete suppression of the thermos-acoustics, the phase difference between the pressure and chemiluminescence waves was found to significantly increase and the RI was found to reduce to nearly zero. In such case, the flame luminescence was observed to significantly reduce. The proposed technique of air injection into the flame through radial micro jets is simple yet very effective in controlling the thermos-acoustic instability.

Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.

Characterization of Doped Titanium Oxide Varistor Powder Processed with Latex Binder

In the processing of semiconducting electro ceramic materials the use of appropriate binder can lead to improve characteristics of powder which will reduce density gradient in the green body during compaction. The binder system is anticipated to have an influence on the grain growth and microstructure which in turn affect the electrical performance. To investigate this phenomenon, TiO2 powder doped with tungsten oxide (WO3), silicon oxide (SiO2) and bismuth oxide (Bi2O3) was processed with and without various percent of latex binder. The prepared samples were characterized by evaluating the physical properties like green density, fired density, axial and radial shrinkage, micro hardness and compressive strength. It was observed that TiO2 processed with latex binder exhibited higher green density and less axial and radial shrinkage compared to powder processed without binder. However, the binder level did not have any significant influence on the other characteristics of varistor discs. SEM analysis indicated that the average grain size was also influenced by the percent of binder used and but the higher average grain size was obtained for discs without any binder.

Fluid-Thermal-Structural Coupled Analysis of a Radial Inflow Micro Gas Turbine Using Computational Fluid Dynamics and Computational Solid Mechanics

A three-dimensional fluid-thermal-structural coupled analysis for a radial inflow micro gas turbine is conducted. First, a fluid-thermal coupled analysis of the flow and temperature fields of the nozzle passage and the blade passage is performed by using computational fluid dynamics (CFD). The flow and heat transfer characteristics of different sections are analyzed in detail. The thermal load and the aerodynamic load are then obtained from the temperature field and the pressure distribution. The stress distributions of the blade are finally studied by using computational solid mechanics (CSM) considering three cases of loads: thermal load, aerodynamics load combined with centrifugal load, and all the three types of loads. The detailed parameters of the flow, temperature, and the stress are obtained and analyzed. The numerical results obtained provide a useful knowledge base for further exploration of radial gas turbine design.

Physical Characterization and Microstructure Evaluation of Titanium Dioxide Semiconductor Discs Processed with Binders

The processing of TiO2 semiconducting materials has a long route with numerous contributing variables. The binder plays an important role in the development of this electro-ceramic material. Higher density and strength of a green body are critical not only for handling at its green state but also to avoid the causes of flaw formation during sintering. Use of appropriate binder can lead to improve characteristics of powder which will reduce density gradient in the green body during compaction. Enhanced green properties can consequently lead to higher fired strength of the varistor discs. The binder system is anticipated to have an influence on the grain growth and microstructure which in turn affect the electrical performance. To investigate this phenomenon, TiO2 powder doped with 0.2% of Ta2O5 was processed with and without binder polyvinyl alcohol. The prepared samples were characterized by evaluating the physical properties like green density, fired density, axial and radial shrinkage, micro hardness and compressive strength. It was observed that TiO2 processed with binder exhibited better properties compared to powder processed without binder. The higher percent of binder enhanced the properties further. XRD revealed that the diffraction angle peak was similar to that of pure TiO2. SEM analysis indicated that the average grain size was larger for discs prepared with higher percent of binder. It is anticipated that the larger grain size will improve varistor properties in terms of low voltage applications.

Filamentary Micro Sensors with Predetermined Breaking Points

Abstract Filamentary polymer sensors with predetermined breaking points have been developed. These sensors are produced by radial micro patterning of conductive polymer filaments by ultrasonic hot embossing. Micro structures in the filaments are generated by this fabrication process in less than a second. The dimensions of radial micro grooves in a filament tune the strain at which the filament breaks. This way, overload sensors for ropes or fuses can be realized. For example the discard status or the residual life time of ropes can be controlled with a simple measurement of the electric resistance of sensor filaments. By using different sensors in one rope it is possible to indicate different load cases of the rope.

Investigations on the Blade Vibration of a Radial Inflow Micro Gas Turbine Wheel

This paper demonstrates the investigations on the blade vibration of a radial inflow micro gas turbine wheel. Firstly, the dependence of Young's modulus on temperature was measured since it is a major concern in structure analysis. It is demonstrated that Young's modulus depends on temperature greatly and the dependence should be considered in vibration analysis, but the temperature gradient from the leading edge to the trailing edge of a blade can be ignored by applying the mean temperature. Secondly, turbine blades suffer many excitations during operation, such as pressure fluctuations (unsteady aerodynamic forces), torque fluctuations, and so forth. Meanwhile, they have many kinds of vibration modes, typical ones being blade-hub (disk) coupled modes and blade-shaft (torsional, longitudinal) coupled modes. Model experiments and FEM analysis were conducted to study the coupled vibrations and to identify the modes which are more likely to be excited. The results show that torque fluctuations and uniform pressure fluctuations are more likely to excite resonance of blade-shaft (torsional, longitudinal) coupled modes. Impact excitations and propagating pressure fluctuations are more likely to excite blade-hub (disk) coupled modes.

Micro-spot, UV and wetting patterning pathways for applications of biofunctional aminosilane-titanate coatings

The micropatterning of functional films for biomedical applications is a key part of the process leading to a precise application. In the present work we present three different methodologies to micro-design biofunctional aminosilane-titanate coatings. The chemical functionality of the surface immobilized amino groups was initially tested by surface characterization techniques. X-ray photoelectron spectroscopy was used to analyze the films before and after derivatization with Trifluoromethylbenzaldehyde while atomic force microscopy was used to study the adsorption kinetics onto these hybrid films. The three micropatterning pathways were selected for three different kinds of applications: (1) 300 microm spots were satisfactorily used for oligonucleotide immobilization, (2) Masked regions protected from UV irradiation were intensively coated by colloidal gold nanoparticles creating a drastic contrast with respect to the UV exposed areas, and (3) radial micro stripes, used afterwards for culturing cells, were created onto Si substrates by wetting from modified precursor solutions. The results are a clear indication of the versatility of hybrid aminosilane-titanate coatings for biomedical applications requiring micropatterned biofunctional surfaces.