Triangular Protrusions Research Articles

Field synergy and thermodynamic evaluation of a mini-duct with several protrusions utilizing the cross-flow method: A numerical exercise

The field synergy and entropy generation analysis of turbulent flow in a mini rectangular duct featuring surface protrusions has been numerically explored in a finite volume approach. The governing differential is solved iteratively using adequate numerical boundary conditions and a second-order upwind technique. In the post-processing, entropy generation, and irreversibilities are measured. The duct Reynolds number (ReDh, duct) has been varied from 17,831 to 53,492 at a fixed nozzle Reynolds number (ReDh, nz) of 5104. The effects of the duct Reynolds number on the thermal and frictional irreversibility have been quantified. Thermal, frictional, and total irreversibilities have been reported to rise with ReDh, duct. Furthermore, it is discovered that thermal irreversibility dominates over frictional irreversibility. It has been found that conducting triangular protrusions creates more entropy than conducting rectangular protrusions. Filed synergy analysis has also been carried out by integrating the energy equation. Heat transfer rate has been seen to increase with synergy angle (α). Triangular protrusions have a greater field synergy angle (α) than rectangular protrusions.

ДОСЛІДЖЕННЯ ТЕЧІЇ ГАЗОВОГО ПОТОКУ МЕТОДОМ ВІЗУАЛІЗАЦІЇ

The article describes the test conducted to study the patterns of gas flow for a channel with triangular protrusions using the visualization method to clarify the physical flow pattern. The proposed method makes it possible to obtain fixed patternsof the flow in different regimes and flow parameters. The obtained flow patterns are justified by theoretical dependencies

Cooling of Heated Blocks with Triangular Guide Protrusions Simulating Printed Circuit Boards

There is no study that investigates triangular guide protrusions including their systematical geometrical changes together with the effects of channel height in the open literature in the context of the authors’ knowledge. Moreover, the number of laminar studies is less than turbulent studies, whereas low velocity or natural convection cases are still important, especially for small devices in small PCB passages. The objective of this study is to investigate numerically the effects of triangular guide protrusions for the enhancement of heat transfer from the blocks’ simulated electronic components in laminar flow conditions. Two-dimensional, incompressible, steady, and laminar flow analysis was performed to predict fluid flow and heat transfer characteristics for three heated blocks in a PCB (printed circuit board) passage with triangular guide protrusions mounted on the upper wall. The Galerkin finite element method of weighted residuals was used to discretize conservation equations. The effects of the channel expansion ratio and inlet velocity were investigated for five geometrical cases. If the size of the protrusions is increased, the existence of protrusions starts to affect the flow patterns on the lower wall. The size of the last protrusion controls the flow structure downstream of the last block. On the upper wall, after the last protrusion, a recirculation is formed and the length of the recirculation increases with an increasing Re number. Moreover, the reattachment length of recirculation after the last block increases with an increasing Reynolds number for a fixed expansion ratio. Expansion ratio and inflow conditions caused by blocks and protrusions have a great influence on the formation of secondary recirculation in addition to the Reynolds number. Heat transfer increases with increasing sizes of upper triangular protrusions. Maximum overall heat transfer enhancement is provided as 47.7% with the geometry of the maximum sized protrusions for the channel height of 3 h. In the case of 4 h, the maximum overall heat transfer enhancement is 24.21%. These enhancements in heat transfer that can be encountered in PCB cooling applications may help the PCB cooling designers.

Armchair graphene nanoribbon-based spin caloritronics

Armchair graphene nanoribbons are considered unsuitable for spin caloritronic applications, due to the lack of intrinsic magnetism. Inspired by the progress on fabricating carbon nanotubes with Janus edges Bets et al. (2019) [26], we construct graphene nanoribbons with Janus edges, where one edge is armchair type and the other one possesses triangular protrusions with zigzag-armchair or zigzag-zigzag sub-edges. By first-principles calculations, Spin Seebeck effect is found. Further analysis shows that, it is resulted from the difference of Fermi distributions between the two electrodes, which is triggered by temperature difference, and the peculiar transmission spectra, where two transmission peaks with opposite spins reside discretely on both sides of EF. These two peaks are contributed by the corresponding bands with opposite spins above and below EF respectively, which are induced by the sub-edges. We believe our findings would be useful in developing graphene-based spin caloritronics.

Effects of binary hybrid nanofluid on heat transfer and fluid flow in a triangular-corrugated channel: An experimental and numerical study

The flow and heat transfer over a modulated surface in the form of triangular protrusions using MWCNTs-TiO2 nanohybrids were investigated, and its results are detailed in this paper. The nanomaterials were functionalized and prepared at weight concentrations of 0.025%-wt., 0.05%-wt., 0.075%-wt., and 0.1%-wt., then had its morphology elucidated using the high-resolution transmission electron microscopy (HR-TEM), field emission transmission electron microscopy (FE-SEM), and Energy Dispersive X-Ray Analysis (EDX). The mixture's thermophysical properties at 303 K were determined and utilized in the investigation's numerical aspect. A steady-state 2D analysis of flow over a modulated surface was solved in ANSYS-FLUENT with turbulent flow at 5000 ≤ Re ≤ 15,000. The model was validated using the Dittus-Boelter Eq., and its average error was 9.840%. The heat transfer was enhanced by 13.181%, 18.056%, 22.033% and 26.107% for nanoparticles' weight concentrations of 0.025%-wt., 0.05%-wt., 0.075%-wt., and 0.1%-wt., respectively. The water flow and MWCNTs-TiO2 nanohybrids' turbulent kinetic energy, pressure, velocity, turbulence intensity contours, and velocity vectors were determined, and correlations were formed from the results to predict the average Nusselt number for the DW and MWCNTs-TiO2 as a function of the nanoparticles' weight concentrations.

Flat surfaces machining by the magneto-abrasive method with permanent magnet end-type heads. The influence of the design of the working surfaces of the heads on the effectiveness of the magneto-abrasive machining

Investigation of the magneto-abrasive machining process of flat surfaces of parts made of ferromagnetic material steel 45 by the end heads based on high-power permanent magnets, which form the magneto-abrasive tool of the "brush" type, was carried out. For ensuring the high efficiency of the magneto-abrasive machining process, an analysis of the machining by heads on the working surfaces of which located protrusions of various shapes, sizes and configurations was carried out. Twelve types of working surfaces were investigated. The control of magneto-abrasive machining process efficiency was curried for the changing of the parameter Ra, the value of the relative roughness and the rate of its change, the size of the surface's relative reference profile length from the section level of the formed microprofile and the parameter of geometric heredity obtained during the machining. It has been determined that the most rational design of the working surface of the end head with the magneto-abrasive tool of the "brush" type was the surface with 9-12 radial triangular protrusions located on it. Using of such heads provides a highly efficient form of the roughness of machined surfaces with Ra < 0.03 µm with an initial Ra of 0.8 µm obtained after face milling. At the same time, microwaves had been formed after milling was almost eliminated. The kinetics formation of the relative reference profile length from the section level was analyzed by the nature of its size change. It has been shown that at the initial stage, the predominant removal of micro peaks had occurred, and then micro valleys were actively machined with further smoothing of the microprofile.

Flow analysis of a rectangular channel with triangular and semi-spherical protrusions

Thermo-flow analysis of an internal cooling channel with turbulators is carried out pertinent to gas turbine blade cooling. Two-pass rectangular channel with 180° bend is adopted to assess the effect of geometric configurations of turbulators on heat transfer enhancement and pressure drop. Two-pass rectangular channel features triangular straight turbulators having ratio of 1/8 rib height to hydraulic diameter, while semi-spherical protrusion has radius of 1/8 hydraulic diameter. Protrusions are introduced along the flow path to promote mixing of flow. Influence of Reynolds number on heat transfer rates and pressure drop is also incorporated. The Reynolds number ranges in between 19,500 and 69,000, which produce same effect of the land-based air breathing engines which operate at high air speeds. To simulate flow and thermal fields in the channel, 3-dimensional configuration of channel is adopted in numerical computations. Predictions are validated with the experimental work. It is found that by introducing triangular and semi-spherical prostrations at channel wall, heat transfer rates improves significantly while pressure drop reduces. Influence of turbulators on heat transfer enhancement becomes more apparent as the heating performance is compared to smooth channel.

Analysis of conditions of the quartz surface photochemical polishing by way of profile optimization

PurposeThe purpose of this paper is to show the possibility of using the quartz regular surface profile in the form of protrusions and troughs of a triangular shape instead of a random surface profile characterized by a Gaussian correlation function when analyzing the electromagnetic field parameters above the quartz surface to determine the conditions of the effective surface subnano-polishing.Design/methodology/approachThe numerical determination of the evanescent field optimal configuration formed near the quartz rough surface coated with an aqueous solution of calcium hypochlorite when illuminated from the side of the solution has been considered. The finite-element approach is used to solve the Helmholtz two-dimensional vector equation.FindingsConditions of effective photochemical polishing of rough surface with profile in the form of triangular protrusions and troughs to a sub-nanometer level of roughness are found. These optimal conditions are achieved when the light falls normally on the quartz surface and the height of the surface protrusions is small (up to 20 nm).Originality/valueThis paper shows the possibility of simplifying electrodynamic calculations and analyzing an evanescent field near a quartz surface for the purpose of photochemical polishing by replacing the random profile function with a deterministic periodic function. That is, the novelty of this paper, which supplements the works published earlier [Journal of Modern Optics, 67(3) (2020):242–251; Optik, 207 (2020):164438].

Electrodynamic analysis of light-assisted subnano-polishing of a quartz surface under conditions of total internal reflection by using surface profile optimization

The solution of the electrodynamic problem for determining the optimal configuration of the evanescent field formed near the rough quartz surface coated with an aqueous solution of sodium hypochlorite when illuminated from the side of quartz has been considered in order to ensure effective photochemical polishing of this surface to a sub-nanometer level of roughness. It was found that for a quartz surface profile in the form of triangular protrusions and troughs, which periodically repeat, the optimal conditions for photochemical polishing are achieved when the angle of incidence of light is critical and the height of the surface protrusions is small (up to 20 nm). It has been shown that in this case, the incident electromagnetic wave forms significantly higher values of the electric field in the protrusion region than in the trough region, creating optimal conditions for the subnano-polishing of this surface. Criteria are described for the possibility of using a regular profile in the form of protrusions and troughs of a triangular shape instead of a random surface profile characterized by a Gaussian correlation function when determining the optimal field parameters above the quartz surface.

Wind energy harvesting performance of tandem circular cylinders with triangular protrusions

This study evaluated the performance of wind energy harvesters with multiple shape-optimized circular cylinders in tandem via computational fluid dynamics simulations. The circular cylinders were optimized by attaching triangular protrusions on their surface. The circumferential location of the protrusion plays a crucial role in the efficiency of this kind of wind energy harvester. The protrusions at the circumferential angles of α = 60°and 90°significantly extend the wind velocity range with remarkable energy generation. When the reduced wind velocity is lower than 10, the harvester with three plain cylinders in tandem generates the most power. However, when the speed is higher than 10, the most power is generated by the harvester having three cylinders in tandem with protrusions at α = 60°. Therefore, in a low wind velocity environment, the harvester with three plain circular cylinders in tandem is superior to other tested configurations, whereas in a high wind velocity environment, the harvester with three circular cylinders with protrusions at α = 60°in tandem outstands from other tested configurations. The associated flow mechanisms are detailed as well.

Heat transfer correlation for a triangular protruded surface with a cross-flow jet

In this paper, the fluid flow and heat transfer characteristics of a small rectangular channel fitted with triangular protrusions have been studied in a three-dimensional computational domain. A hybrid cooling strategy employing forced convection air stream with jet impingement on the protruded surface has been numerically studied by solving the conservation equations for mass, momentum, energy as well as turbulent kinetic energy and its dissipation rate in the frame work of finite volume method. The duct and nozzle Reynolds numbers and Prandtl number are varied in the range of \( 17,827 \le \text{Re}_{Dh,duct} \le 53,480 \), \( 5,135 \le \text{Re}_{Dh,nz} \le 12,044 \) and \( 0.7 \le \Pr \le 12 \), respectively. The effects of the duct Reynolds number, nozzle Reynolds number and Prandtl number on heat transfer rate have been quantified. Extensive numerical computation has also been executed to collect the data for Nusselt number by varying each of the independent parameters. A non-linear regression analysis based on Lvenberg–Marquardt (L–M) method has been used to fit a correlation for Nusselt number utilizing the data captured from CFD analysis.

The Effect of Triangular Protrusions on Geothermal Wellbore Heat Exchanger from Retrofitted Abandoned Oil Wells

The cost to implement geothermal energy is extremely high, due to the requirement of drilling production and reinjection wells. One method to overcome this problem is to retrofit abandoned oil wells with a closed loop system, eliminating the need for drilling entirely. This study is conducted to evaluate the heat transfer performance of the wellbore heat extractor with the triangular protrusions. A two-dimensional axis-symmetry computational model for fluid flow and conjugate heat transfer in the wellbore is developed. The effect of protrusion height, pitch and volume flow rate are evaluated and discussed in view of numerical results. The results suggest that triangular protrusions offer higher heat transfer rate. However, careful consideration should be taken as the pumping power required is higher due to higher pressure drop. The outcome of this study provides a new insight into the development of geothermal energy, especially on the utilization of abandoned oil wells.

Large-Area Preparation of Robust and Transparent Superomniphobic Polymer Films.

Transparent superamphiphobic surfaces that repel various liquids have many important applications, but there are critical challenges in their fabrication, such as expensive or complicated fabrication methods, contradictions between the rough surface for superamphiphobicity and smooth surface for transparency, large-area fabrication, etc. Herein, we report a simple and effective strategy for large-scale fabrication of robust, transparent, and superomniphobic polymer films by combined unidirectional rubbing and heating-assisted assembly technology. The obtained polymer films display two kinds of special structures of monolayer ordered re-entrant geometries with either hexagonally triangular protrusions or with hexagonally rectangular micropillars, depending upon the sphere diameters of silica templates, and demonstrate excellent repellence to water and low-surface-tension liquids, as well as high transparency.

Interplay between morphological and shielding effects in field emission via Schwarz-Christoffel transformation

It is well known that sufficiently strong electrostatic fields are able to change the morphology of Large Area Field Emitters (LAFEs). This phenomenon affects the electrostatic interactions between adjacent sites on a LAFE during field emission and may lead to several consequences, such as: the emitter's degradation, diffusion of absorbed particles on the emitter's surface, deflection due to electrostatic forces, and mechanical stress. These consequences are undesirable for technological applications, since they may significantly affect the macroscopic current density on the LAFE. Despite the technological importance, these processes are not completely understood yet. Moreover, the electrostatic effects due to the proximity between emitters on a LAFE may compete with the morphological ones. The balance between these effects may lead to a non trivial behavior in the apex-Field Enhancement Factor (FEF). The present work intends to study the interplay between proximity and morphological effects by studying a model amenable for an analytical treatment. In order to do that, a conducting system under an external electrostatic field, with a profile limited by two mirror-reflected triangular protrusions on an infinite line, is considered. The FEF near the apex of each emitter is obtained as a function of their shape and the distance between them via a Schwarz-Christoffel transformation. Our results suggest that a tradeoff between morphological and proximity effects on a LAFE may provide an explanation for the observed reduction of the local FEF and its variation at small distances between the emitter sites.

Enhancement of heat transfer in solar air heater duct having different pitch of triangular protrusions as roughness elements on absorber plate

Objective: This paper elucidates the experimentation based on improving the heat transfer rate in the solar air heating apparatus of triangular protrusions designed in a zigzag pattern on the aluminum plate surface. Method: Triangular protrusions of varying pitch of 10, 15, 20, 25 and 30 mm facilitates artificial roughness on the outer surface of the aluminum plate. These protrusions possess an angle of 45; the relative thickness of each protrusion is 0.11mm respectively. The operating parameters are developed by the various researches for roughed ducts of the solar based air heater. Air flow parameter value has to be maintained between ‘0.017-0.0182 Kg/Sec. The air flow corresponds to Reynolds number (Re) between 10300 to 12000, and the Nusselt number ranges from 50 and 110, and friction factor of air lines at 4.5-6.8x10-3’. Findings: It was observed that when the thickness of triangular protrusions over the aluminum collector is 25 mm, it has the highest rate of heat transfer of 104, for which the rate of airflow is 0.0182 kg/Sec and thermo hydraulic performance is 1.71. Applications: The setup can be used to trap solar energy for various thermal applications, it can be used in heat exchangers for effective heat transfer, it can also be effectively used for space heating and curing of materials and for drying of agricultural products etc. Keywords: Artificial Roughness, Friction-Factor, Heat-Transfer Enhancement, Nusselt Number, Solar Based Air-Heater, The Pitch of Triangular Protrusion

Interplay between Steps and Oxygen Vacancies on Curved TiO2(110).

A vicinal rutile TiO2(110) crystal with a smooth variation of atomic steps parallel to the [1-10] direction was analyzed locally with STM and ARPES. The step edge morphology changes across the samples, from [1-11] zigzag faceting to straight [1-10] steps. A step-bunching phase is attributed to an optimal (110) terrace width, where all bridge-bonded O atom vacancies (Obr vacs) vanish. The [1-10] steps terminate with a pair of 2-fold coordinated O atoms, which give rise to bright, triangular protrusions (St) in STM. The intensity of the Ti 3d-derived gap state correlates with the sum of Obr vacs plus St protrusions at steps, suggesting that both Obr vacs and steps contribute a similar effective charge to sample doping. The binding energy of the gap state shifts when going from the flat (110) surface toward densely stepped planes, pointing to differences in the Ti(3+) polaron near steps and at terraces.

Heat transfer enhancement from a small rectangular channel with different surface protrusions by a turbulent cross flow jet

In the present study, thermo-hydrodynamic performance of a small rectangular channel with different protruded surfaces is investigated numerically in a three–dimensional computational domain. An air jet impinging normal to the main flow is considered to enhance heat transfer rate. Conservation equations for mass, momentum and energy are solved using finite volume method with SST k−ω turbulence model. Three different protrusion shapes have been tested: rectangular, trapezoidal and triangular, respectively. The duct and nozzle Reynolds numbers are varied in the range of 17,831 ≤ ReDh,duct ≤ 53,490 and 5,136 ≤ ReDh,nz ≤ 11,980, respectively. Also, three different nozzle positions (X/Dh,duct = 8.717, 11.597 and 14.258) along the axial direction of rectangular duct have been considered to choose the best location for heat transfer enhancement. A higher heat transfer enhancement rate is observed at the nozzle position 2 (X/Dh,duct = 11.597) as compared to the other positions considered in this study. Flow recirculation in inter-protrusion spaces has also been discussed. In this hybrid cooling strategy, the pumping power requirement with protrusions is observed to be higher than that of without protrusions. The heat transfer enhancement rate with triangular protrusions is found to be more as compared to other protrusion shapes.

CFD simulations to study the effects of wall protrusions on microfluidic mixing

In this study the effects of different types of wall protrusions on microfluidic mixing are studied using computational fluid dynamics (CFD) simulations. Two new protrusions, single first bracket protrusions and double opposite first bracket protrusions (DOFBPs), are conceptualized, evaluated through CFD simulations and compared to protrusions having standard geometrical shapes, e.g. rectangular protrusions, triangular protrusions and semicircular protrusions. In the range of Reynolds numbers covered in this study, the microchannel having an opposed T-junction and DOFBPs is found to provide good mixing. A hybrid approach relying on the modification of microfluidic junctions as well as wall protrusions for enhancing microfluidic mixing is also evaluated. The microchannel based on the hybrid approach of an OA 10°–20°–165° WY-junction and DOFBPs is also found to provide very good mixing for a wide range of Reynolds numbers.

THERMO HYDRAULIC PERFORMANCE OF SOLAR AIR DUCT HAVING TRIANGULAR PROTRUSIONS AS ROUGHNESS GEOMETRY

An experimental investigation has been carried out for a range of system and operating parameters in order to analyze effect of artificial roughness on heat transfer and friction in solar air heater duct having triangular protrusions as roughness geometry. An increase in heat transfer and friction loss has been observed in solar for duct having roughened absorber plate. Experimental data have been used to develop Nusselt number and friction factor correlations as function of system and operating parameters for predicting performance of the system having investigated type of roughness geometry.

Wet purification of air from dust in innovative irrigated nozzle of regular structure for ventilation of cabins of wheeled and tracked vehicles

It was studied the mechanism of wet purification of air from dust in innovative irrigated nozzle of regular structure made from porous plastic plates and equipped with triangular protrusions in airducts that are located across the stream for artificial turbulence. Functional link between the effi- ciency of air purification from dust and reduction of temperature in adiabatic humidification was drawn out.