High Fin Research Articles

Numerical Simulation of Flow and Heat Transfer in LPD Type Misaligned Fins

With the rapid development of all walks of life, heat exchangers have been used all over the various fields. Plate fin heat exchanger was concerned, because of its high heat transfer rate and the small size. Among them, the offset strip fin is called “high efficiency fin” because its special staggered arrangement structure can increase the turbulent flow of fluid and enhance heat transfer. In order to study the influence of flow and heat transfer in dislocation fins, the three-dimensional numerical simulation of LPD dislocation fins is carried out by numerical simulation. Firstly, the accuracy of the standard laminar flow model is verified by using the dislocation fins and experimental data provided by the literature. The average error between the calculated value of the heat transfer factor and the experimental value is 5.95%, and the average error between the calculated value and the experimental value of the friction factor is 2.02%. On this basis, the influence of flow parameters and structural parameters on the internal flow and heat transfer in the dislocation fins is analyzed.The results show that: (1) the smaller the fluid velocity, the lower the height of the dislocation fin; the smaller the tooth angle, the shorter the cut length; the greater the heat transfer factor j, the better the heat transfer performance;(2) The higher the fluid velocity, the higher the height of the dislocation fin, the smaller the tooth angle; the shorter the cut length, the smaller the friction factor f, the better the resistance characteristic;(3) the lower the fin height, the smaller the tooth angle; the shorter the cut length, the greater the temperature difference and the pressure drop with the length of the heat transfer section; the fin height has little effect on the velocity field, The flow distribution of the fluid flow in the flow channel is affected, the shorter the cutting length is, the faster the velocity field changes.

A New Genus and Species of Scombrid Fish (Perciformes, Scombroidei, Scombridae) from the Lower Oligocene of the Caucasus

A new genus and species of scombrid fish Caucombrus histiopterygius gen. et sp. nov. is described from the Lower Oligocene (Lower Maikopian, Pshekha regional state) of the north-western Caucasus (Russia) and Abkhazia (rivers Belaya, Pshekha and Gumista). The new taxon differs from the other known Scombridae, both fossil and Recent, by the high and sail-like first dorsal fin. Osteological characters of Caucombrus gen. nov. indicate its relationship with the Spanish mackerels (subfamily Scomberomorinae). It is assumed that either C. histiopterygius gen. et sp. nov. or the related species of Caucombrus gen. nov. inhabited the Mid-Oligocene sea basin in the territory of the Rhine Graben (Germany).

Effect of aspect ratio variation on subsonic aerodynamics of cascade type grid fin at different gap-to-chord ratios

ABSTRACTThis paper dwells upon investigating the effect of aspect ratio (AR) variation on the aerodynamic performance of unconventional control surfaces called grid fins by virtue of a series of subsonic experiments on a simplified grid fin variant called the cascade fin. Wind tunnel tests were performed for differentAR(variable span) grid fins. The same had been investigated for different gap-to-chord ratio (g/c) variants. Results demonstrated a tangible increase in the aerodynamic efficiency as well as stall angle reduction for higherAR. Moreover, higherARleads to increased pitching moment, which emphasizes elevated hinge moment requirements. The study ensued the presence of higher deviation between the lowARfins, that is$AR<2$compared to the pertinent deviations between the highARfins, that is$AR\geq2$. The effect associated with these variations was termed as span effect in this paper. It was established that, the deviations arising due to this phenomena were lesser for higherg/cand higherAR. The analysis ofARvariation for differentg/cpresented a limiting value ofARreduction for stall performance enhancement. Thus, optimised selection of theg/candARvalues can lead to enhanced aerodynamic efficiency alongside an improved stalling characteristic.

An additively manufactured novel polymer composite heat exchanger for dry cooling applications

The work presented in this paper focuses on the design and thermal characterization of a novel polymer composite heat exchanger (HX) produced by an innovative additive manufacturing process. The heat exchanger represents a gas to liquid configuration in which the gas side removes heat from the liquid side in a cross-flow arrangement. The novel HX utilizes a cross media approach in which, unlike the conventional HXs, the hot and cold sides are directly connected to each other through high conductivity metal fiber fins on the gas side protruding through the walls of the liquid side, thus eliminating the wall resistance separating the hot and cold sides. The HX demonstrates superior thermal performance at reduced pressure drops while also benefiting from the lighter weight and the lower cost that the polymer structure introduces. A 350-W water-to-air heat exchanger was fabricated using a fused filament fabrication (FFF) technique with a novel/patent pending printer head which was developed to produce the metal fiber composite structure of the heat exchanger. The results of the heat exchanger characterization tests show that it yields up to 220% and 125% improvement in heat flow rate over mass (Q/m) and heat flow rate over volume (Q/V), respectively, when compared to comparable state-of-the-art plate fins HX configurations. This study in particular demonstrates the impact of additive manufacturing in realizing potentially transformative heat exchanger technologies that may otherwise be very difficult to achieve with conventional fabrication methods.

High performance Fin-FET electrochemical sensor with high-k dielectric materials

In this work we combine a Fin Field Effect Transistor (Fin-FET) characterised by a high height to width aspect ratio with high-k dielectric materials to study the optimized design for chemical-FETs to provide higher transconductance (and thus a better signal to noise ratio), increased dynamic range and chemical stability. We used pH sensing to verify the design. We explored the sensitivity and linearity of the response of silicon dioxide, alumina and hafnium oxide as dielectric materials sensing pH, and compared their chemical stability in different acids. The high aspect ratio fin geometry of the sensor provides high currents, as well as a planar conduction channel more reliable than traditional silicon nanowires. The hafnium oxide Fin-FET configuration performed the best delivering the most linear response both for the output and transfer characteristics, providing a wider dynamic range. Hafnium oxide also showed the best chemical stability. Thus we believe that the developed high aspect ratio Fin-FETs/high-k dielectric system can offer the best compromise of performance of FET-based sensors.

Non-Linear Model for a Spiral Porous Fin Subjected to Darcy Flow

In this study, the temperature distribution equation for a spiral porous fin is presented. Based on Darcy’s model, a mathematical equation of the energy is derived and a suitable dimensionless form is outlined to highlight some characteristic parameters, namely, the spiral fin pitch, the porosity, and the modified Rayleigh number. The behavior of the solution is analyzed for two cases of interest, taking into account the temperature-dependent thermal conductivity of the fin encountered in a hostile environment. A Numerical method is applied to solve this non-linear problem. It is found that the thermal transfer is not affected by the change of the spiral fin pitch, whereas increasing the porosity or the parameter β* makes higher fin temperature and improve the fin efficiency.

Spatio-temporal patterns in fin whale Balaenoptera physalus habitat use in the northern Gulf of St. Lawrence

Significant ecosystem changes in the Gulf of St. Lawrence (GSL), Canada, have had far-reaching effects at all trophic levels. The abundance of fin whales Balaenoptera physalus has declined significantly in the northern GSL over the past decade. This study aimed to test the hypothesis that the observed decline was correlated to changing environmental conditions. Cetacean sightings data from 292 surveys, resulting in 2986 fin whale encounters from 2007 to 2013, were used to fit 2 separate generalised additive models in terms of (1) bathymetric and oceanographic variables (the proxy model) and (2) modelled krill biomass (the prey model). The concept of ‘handling time’ was introduced to correct for time off search effort, applicable to other studies relying on opportunistically sampled data. While a positive correlation between krill biomass and fin whale numbers was found, the performance of the proxy model (24.2% deviance explained) was overall better than the prey model (11.8%). Annual predictive maps derived from the final proxy model highlighted 2 key areas with recurrently high relative fin whale abundance and a significant overlap with shipping lanes. While both models provided evidence for an annual decline in relative fin whale abundance, static bathymetric features were the most important predictors of habitat use, and no correlation between dynamic variables and the decline was found. High resolution prey data and a better understanding of the feeding ecology of fin whales are proposed to further investigate the predator-prey relationship and decline of fin whales in the GSL.

Convective boiling of R-410A in 5.0 and 7.0 mm outer diameter microfin tubes

ABSTRACTAlthough microfin tubes are widely used in refrigeration and air-conditioning industries, relatively little data are available for small diameter tubes. In the present study, 7.0 and 5.0 mm outer diameter (O.D.) microfin tubes were tested for a range of mass flux (from 50 to 250 kg/m2s) and vapor quality (from 0.2 to 0.8). The saturation temperature was 8°C and the heat flux was 3.0 kW/m2. This heat flux is quite small, and existing investigations have not been gone to this low heat flux. Results showed that an optimum behavior was observed for the enhancement factor. It increased as mass flux increased up to 150 kg/m2s, and then decreased with a further increase of mass flux. The penalty factors were larger than 1.0 except at the lowest mass flux of 50 kg/m2s. Possible reasoning was provided based on flow patterns of the microfin and the smooth tube. The enhancement factor ranged from 1.24 to 1.93 for the 7.0 mm microfin tube, and 1.63 to 3.26 for the 5.0 mm microfin tube. The penalty factor ranged from 0.82 to 1.11 and from 0.48 to 1.39 for the 7.0 mm and the 5.0 mm microfin tube, respectively. Larger high fin height of the 5.0 mm microfin tube may be responsible for the larger enhancement and penalty factor of the 5.0 mm microfin tube. Comparison with predictions by existing correlations revealed that 7.0 mm microfin tube data were reasonably predicted. However, 5.0 mm microfin tube data were generally underpredicted, probably due to the large fin height of the 5.0 mm microfin tube.

Morphological and functional diversity of piscivorous fishes on coral reefs

Piscivory is a significant ecosystem function on coral reefs, with up to 53% of species on reefs being regarded as piscivorous. Despite this ecological importance, the species that contribute to this function have not been assessed in a broad comparative, morphological context. We therefore conducted a morphological assessment of piscivorous coral reef fishes based on a comparative analysis of 119 species, linking morphology with ecological traits (habitat and activity). After accounting for phylogenetic relationships, we found that head length, premaxilla–maxilla (pmx–mx) length, body depth, and eye size mark the primary axis of variation among species. Pmx–mx length is strongly correlated with both vertical and horizontal gape size. We identify three distinct ecomorphotypes: diurnal benthic, nocturnal, and pelagic piscivores. Benthic diurnal and nocturnal piscivores display a wide array of pmx–mx lengths, potentially reflecting the large array of prey sizes and shapes in benthic habitats. This diversity highlights the potential for niche partitioning based on maximum ingestible prey sizes. By comparison, pmx–mx lengths in pelagic piscivores are more restricted, suggesting limited variance in prey sizes or restrictions associated with their feeding mode. Fin shape was also a primary driver of variation between benthic and pelagic predators. The ecomorphotype of nocturnal piscivores suggests that although they are benthic-associated during daytime, these forms leave the reef at night to feed in more open habitats. When analyzing diurnal benthic piscivores alone, we found a major axis of variation between deep-bodied piscivores with large gapes and large head lengths versus fusiform piscivores with high fin aspect ratio values. This continuum appears to describe the relative strength of benthic associations. Overall, we provide a broad quantitative framework for understanding the morphology and potential functions of piscivorous fishes on coral reefs.

Practical approaches to assess thermal performance of a finned heat sink prototype for low concentration photovoltaics (LCPV) systems: Analytical correlations vs CFD modelling

The performance of a low-cost extruded heat sink prototype for a Low Concentration Photovoltaics system is studied using various analytical correlations and CFD simulations. An experimental test, with temperature measurements at different monitoring points of heat sink surface, was carried out in order to select the most appropriate approach. Large deviations (of up to 20 °C) in the estimation of base plate temperature from correlations were found when compared to experimental results, probably due to the specific geometry characteristics of the heat sink, with variable fin thickness and high fin length. Furthermore, discrepancies of up to 48% have been found among the different correlations. The numerical CFD results of temperature at monitoring points and at the base plate showed relative errors of about 1%, which were at least 15 times smaller than the results given by analytical correlations. Also, numerical simulations allowed the identification of stagnation zones due to the great length of the heat sink and characteristic air flow patterns, which help to explain its performance under different operating conditions. Thus, results showed that multiple chimney flow pattern and air stagnation zones seem to disappear for inclination angles greater than 30°.

Natural convection during melting in vertical finned tube latent thermal energy storage systems

Natural convection can have a major impact on the melting process during charging in a latent heat storage system. Heat transfer enhancement by natural convection depends strongly on the dimensions, material properties and boundary conditions of the storage system. In complex geometries, such as shell-and-tube storage systems with extended fins, a good approximation of the impact of natural convection on the melting process is very difficult. There are no correlations for such geometries, and simulations of these storage systems require extensive computational effort. In the present work, we analyzed the impact of natural convection in four vertical shell-and-tube extended fin systems with a common tube height. To investigate the influence of the tube height, one of the fins was additionally modeled with two further tube heights. We scaled the resulting liquid fraction evolutions into a dimensionless form and used a convective enhancement factor to assess the strength of natural convection. A linear fit function for the mean convective enhancement factor was derived to estimate the melting process considering natural convection. With it, natural convection may be incorporated into the design process of storage systems to optimize the charging time. The results indicate a negligible impact of natural convection in fins with a small tube spacing and a high fin fraction. There is a considerable impact from natural convection in fins designed with a large tube spacing and a low fin fraction. However, large fin heights lead to decreased heat transfer enhancement by natural convection.

Ceramic high temperature plate fin heat exchanger: Experimental investigation under high temperatures and pressures

Ceramic materials enable operation in high temperature and harsh environments and can so exceed the capabilities of comparable metal heat exchangers. For the use in power plant applications and high temperature processes a heat exchanger has to operate under both high temperature and high pressure levels. So far, the operation of a ceramic heat exchanger under such conditions has not been investigated. This work presents a ceramic heat exchanger prototype with modified offset-strip-fin design, which was experimentally investigated in a specifically designed test environment. Experimental tests were conducted with air as a heat transfer fluid at temperatures up to 800 °C, absolute pressures up to 5 bar and norm volume flows up to 160 N m3 h−1. The functionality under high temperatures and absolute pressures could be proven. The paper reports measured performances of the heat exchanger prototype, for which heat transferred up to six kilowatt and effectiveness up to 97% has been achieved. A comparison of Colburn and friction factors with correlations from literature was conducted, too. Good agreement for Colburn prediction of the flue gas channels could be shown, but the investigation also reveals a limited applicability for the friction factor and the Colburn factor of the process gas channel.

Effect of magnetic field on the hydrodynamic and heat transfer of magnetite ferrofluid flow in a porous fin heat sink

Abstract The present study numerically investigates the effects of a uniform external magnetic field and porous fins on convective heat transfer and pressure drop of magnetite ( F e 3 O 4 /water) nanofluid in a heat sink. Effects of volume fraction, porosity, Reynolds number, and magnetic field strength on the performance of the heat sink are studied. Results indicate that heat transfer increases at high volume fractions, fin porosities and magnetic field intensities and decreases with the Reynolds number. A 13% enhancement of heat transfer is obtained for the heat sink with solid fins by using ferrofluid compared to the pure water flow. This value grows up to 35% by using porous fins and imposing magnetic field to the heat sink. Moreover, using porous fins is shown to decrease the pressure drop while the magnetic field effect is not considerable. Therefore, it is concluded that the proposed methods result in a remarkable heat transfer enhancement while decreasing the pressure drop.

Functional morphology of endurance swimming performance and gait transition strategies in balistoid fishes.

Triggerfishes and filefishes (Balistoidea) use balistiform locomotion to power steady swimming with their dorsal and anal fins, and transition to a gait dominated by body and caudal fin (BCF) kinematics at high speeds. Fin and body shapes are predicted to be strong determinants of swimming performance and gait transitions. The goal of this study was to combine morphometrics and critical swimming tests to explore the relationships between fin and body shapes and swimming performance in a phylogenetic context in order to understand the evolution of balistiform swimming. Among 13 species of balistoid fishes, those with high aspect ratio fins tended to achieve higher critical swimming speeds than fishes with low aspect ratio fins. Species with long, large median fins and wide caudal peduncles used the balistiform gait alone for a larger percentage of their total critical swimming speed than fishes with short, small median fins and narrow caudal peduncles. Although analyses revealed overall positive relationships between median fin aspect ratios and gait transition speeds, fishes on both ends of the aspect ratio spectrum achieved higher swimming speeds using the balistiform gait alone than fishes with median fins of intermediate aspect ratios. Each species is specialized for taking advantage of one gait, with balistiform specialists possessing long, large median fins capable of the large power requirements of high-speed swimming using the median fins alone, while BCF specialists possess short, small median fins, ill-suited for powering high-speed balistiform locomotion, but narrow caudal peduncles capable of efficient caudal fin oscillations to power high-speed locomotion.

3D GaN Fins as a Versatile Platform for a‐Plane‐Based Devices

GaN fins on GaN‐on‐sapphire templates are fabricated by continuous mode selective area metalorganic vapor phase epitaxy. The fins exhibit high aspect ratios and smooth nonpolar a‐plane sidewalls with an ultra‐low threading dislocation density of a few 105 cm−2 making them ideally suited for optoelectronic to electronic applications. A detailed analysis of the inner structure of GaN fins is provided by the help of marker layer experiments and correlation of results from fins fabricated under different growth conditions, leading to the development of a growth model to explain the final geometry and optical as well as electrical properties of these high aspect ratio fins. Distinctly different material properties for the central and outer parts of the fins are detected. Whereas the outer sidewalls represent high quality GaN surfaces with very low defect densities, a strong quenching of near band edge emission (NBE) in the central part of the fins is accompanied by heavy compensation of free electrons. A possible explanation is the incorporation of excessive point defects, like intrinsic defects or carbon impurity. The sidewall regions, however, prove to be highly suitable for device applications due to their strong NBE emission, low dislocation density, and high free carrier concentration.

Estimation of thermal performance and design optimization of finned multitube latent heat thermal energy storage

Abstract This paper presents the effectiveness of finned multi-tube latent heat thermal energy storage system (LHTES) for medium temperature (∼200 °C) solar thermal power plant in reducing the fluctuations in heat transfer fluid (HTF) temperature caused due to the intermittent solar radiation. Commercially available phase change material (PCM) of melting temperature 168.7 °C is used as the storage material in the shell of LHTES, whereas a thermic oil based HTF passes through the tubes. Majority of the available PCMs have very low thermal conductivity (∼0.2–0.5 W/m.K), which drastically affects the thermal performance of the thermal storage system. Hence, in this study, thermal conductivity enhancer (TCE) in the form of fin is used to enhance heat transfer in the PCM. The fluid flow and heat transfer behaviour latent heat thermal energy storage system in the LHTES is studied by using a numerical model coupled with the enthalpy technique to account for the phase change process in the PCM. The developed numerical model, which is validated with the lab-scale experimental setup, is used to investigate the effect of number of fin, fin thickness and fin height on the HTF temperature at the outlet of the storage system. It is found that the number of fins and fin thickness significantly affect the thermal performance of the storage system, whereas the enhancement in heat transfer for high thermal conductivity material fin is marginal. Further, optimization of LHTES is performed for a defined objective function to identify the best configuration.

Theoretical and numerical investigation on the fin effectiveness and the fin efficiency of printed circuit heat exchanger with straight channels

Theoretical and numerical studies were conducted on the fin effectiveness and the fin efficiency of printed circuit heat exchanger (PCHE). A heat conduction equation for the fins of PCHE with straight channels was derived, from which the longitudinal temperature distribution of the fins can be obtained. And the expressions of the fin effectiveness and the fin efficiency were developed. Based on their expressions, an understanding of the heat transfer process between the fin surface and the bulk fluid was improved. Results show that the PCHE fin effectiveness is enhanced by the choices of high fin thermal conductivity, decreasing the ratio of the fin thickness to the radius of the channels, or under conditions for which the convective coefficient is small. As for the fin efficiency of PCHE, it's improved with high fin thermal conductivity, thick fin and low convective coefficient of the working fluid. For the cases with large Biot number, the PCHE fin effectiveness and the PCHE fin efficiency can be weakened up to 20%, which should be considered in the modeling of thermal-hydraulic. Moreover, the theoretical investigations were validated against the numerical simulation, and they agree with each other very well.

The fate of the most threatened order of elasmobranchs: Shark-like batoids (Rhinopristiformes) in the Arabian Sea and adjacent waters

Shark-like batoids (Rhinopristiformes) represent of some of the most threatened families of sharks and rays. In certain regions, they are a relatively important component of elasmobranch fisheries, commonly taken as bycatch in gillnets and longlines, but also increasingly targeted for their high value fins and meat. This demand, combined with intense fishing pressure, has resulted in global population declines as well as localized extinctions of many rhinopristoids. Yet, information on the life-history, ecology, and conservation status remains scarce for most species. From 2010–2012, data was opportunistically collected from thirteen rhinopristoid species, including four endemic to the Arabian Sea and adjacent waters, landed from fisheries in the United Arab Emirates or transported from Oman. Four taxa dominated and comprised 92% of total shark-like batoid landings by number, namely Rhynchobatus spp., the Halavi guitarfish (Glaucostegus halavi), bowmouth guitarfish (Rhina ancylostoma), and Bengal guitarfish (Rhinobatos annandalei). Details of the biological characteristics, including size composition and sex ratios, are presented for each species. While there remain identification challenges related to some unresolved taxonomic issues, with several likely undescribed species occurring in the region, the first regional checklist of rhinopristoids is provided. Evidence of significant declines in landings combined with increasing fishing effort over a short time period raises concern about the status and long-term persistence of many species. Increased research to understand the biology, ecology, diversity, and resilience to harvest by fisheries is critical to the effective management of these species and an urgent precautionary approach to their conservation is warranted.

Review of the fish genus Epinnula Poey (Perciformes: Gempylidae), with description of a new species from the Pacific Ocean.

The gempylid fish genus Epinnula is reviewed and two species are recognized. The type species E. magistralis is considered restricted to the western Atlantic Ocean and a new species from the Pacific Ocean is described. The new species, Epinnula pacifica sp. nov., can be distinguished from E. magistralis by 17 or 18 dorsal-fin rays (vs. 15 or 16 in E. magistralis), 15 or 16 anal-fin rays (vs. 13 or 14), 247-268 total scales on lower lateral line (vs. 285-330), a deeper body, relatively high dorsal fin as reflected by the relatively long fin spines and rays, longer dorsal-fin and anal-fin bases, longer pectoral fin, and longer pelvic fin and pelvic spine.

A Si-Compatible Fabrication Process for Scaled Self-Aligned InGaAs FinFETs

We have developed a scalable gate-last process to fabricate self-aligned InGaAs FinFETs that relies on extensive use of dry etch. The process involves F-based dry etching of refractory metal ohmic contacts that are formed early in the process. The fins are etched in a novel inductive coupled plasma process using BCl3/SiCl4/Ar. High aspect ratio fins with smooth sidewalls are obtained. To further improve the quality of the sidewalls and shrink the fin width, digital etch is used. Through this process flow, we have demonstrated FinFETs with ${L} _{{g= 20}}$ nm and fin width as narrow as 7 nm with high yield. Good electrostatic characteristics are obtained in a wide range of device dimensions. In devices with 7 nm fin width, record channel aspect ratio, and transconductance per unit footprint are obtained.