Fin Tip Research Articles

Feasibility Study of Fluidic Sealing in Turbine Shroud.

This paper analyses the methods for manufacturing turbine blades, focusing on the possibility of manufacturing slots in the region of the shroud. The reason for this analysis is the new flow control technique that can be used to limit the shroud leakage flow in a turbine—the air curtain. The air curtain uses a bypass slot to connect the upstream cavern of a shroud seal with the tip of a shroud fin. The bypass slot is an essential part of the solution, while at the same time introducing difficulties in the manufacturing process. Additionally, a parametric study on the bypass slot dimensions is performed using numerical simulations. The features of the numerical model and its validation against experimental data are presented. The parametric study includes the inlet and outlet dimensions, as well as the width of the slot. The most effective dimensions are shown, along with a possible explanation as to why they are the most effective. Interestingly, a slot that does not cover the whole span of the fin is more effective than a slot covering the whole span of the fin. This is caused by additional streamwise vortices that are created in the proximity of the bypass slot.

Analysis of Transient Teat Conduction in a 2-D Rectangular Fin with Constant Heat Flux.(Dept.M)

The objective of this work is to investigate the 2-D heat conduction in a convectively cooled rectangular fin whose base is subjected to constant heat flux with different fin tip conditions. For this purpose an analytical steady-state solution is obtained based on the traditional approach [separation of variables), Solution of the transient case of this problem isobtained by applying a new developed dimensionless finite difference technique.

Analysis of a concave parabolic fin with vertically cutting fin tip and variable fin base thickness

A concave parabolic fin with vertically cutting fin tip and variable fin base thickness is analyzed using a two-dimensional analytic method. Heat loss is presented as a function of the actual fin length, the ratio of the actual fin length to the imaginary fin length, the fin base height, and the convection characteristic number. Also, heat loss is shown as a function of the fin base thickness for both the fixed actual fin length and the fixed actual fin tip length. For equal amounts of heat loss, the relationships are presented between 1) the convection characteristic number and the fin base height, 2) the fin base thickness and the fin base height, and 3) the fin base thickness and the actual fin tip length. One of the results shows that the heat loss for the fixed actual fin tip length decreases more remarkably than that for the fixed actual fin length as the fin base thickness increases.

Etelis boweni sp. nov., a new cryptic deepwater eteline snapper from the Indo-Pacific (Perciformes: Lutjanidae).

A new species of Etelis is described based on 16 specimens collected from the Red Sea and Western Australia, with confirmed genetic records throughout the Indo-West Pacific. It is similar to and was often misidentified as Etelis carbunculus Cuvier, with both species sharing the diagnostic character of low number of developed gill rakers. Nonetheless, the two species are genetically divergent and differ morphologically in adult body length; proportions of eye, snout, cheek and caudal fin; shape of head, opercular spine and sagittal otolith; and coloration of the tip of the upper caudal fin. Etelis boweni has a wide Indo-west Pacific distribution that largely overlaps with E. carbunculus, and the two species are often caught on the same fishing line.

An approach based on the porous media model for numerical simulation of 3D finned-tubes heat exchanger

Developing efficient and compact heat exchangers is of important significance to improve the energy utilization efficiency of entire society. 3D finned-tubes, as a kind of passive enhanced heat exchange technology, are widely used for improving the thermal-hydraulic performance of the heat exchanger. In the numerical study of 3D finned-tube heat exchanger, on account of the limit by computing capacity, it is very hard to carry out the full-size numerical simulation, so the method based on porous media model becomes a common approach for numerical simulation of the heat exchanger. In the present study with the discrete 3D finned-tube heat exchanger as the study object, a kind of approach based on the porous media model under the cylindrical coordinate system is proposed. In this approach, only the fin region on the surface of base tube is simplified to the annular porous media zone while the region beyond the fin tips is still regarded as the pure gas flow region. The resistance coefficients of annular porous media, which are used to represent the retardation effects of the fin on the fluid motion, are given under the cylindrical coordinate system. Based on serialized numerical simulations of the fin configuration model seen by the air when it flows in the circumferential, axial and radial direction, the viscous resistance coefficients and inertial resistance coefficients of the annular porous media zone in each direction are obtained through fitting. Through comparison of simulated values between the porous media model and 3D finned-tube practical physical model, it is found that the pressure drop calculated by the method based on porous media model proposed in this study agree well with that based on the real physical model. The pressure drop predicted by the porous media model also agree well with the experimental results. In the approach based on porous media model, the grid number and calculation cost are smaller than those in practical physical model. Especially in case of tube bundles, number of grids applied in the simulation based on porous media model is far less than the grid quantity in the practical physical model simulation, but the pressure drop obtained by the porous media model is almost equal to the result obtained from the practical physical model. Besides, in the present method, only the fin zone is deemed as the porous media, so the flow field in the region beyond the fin tips will still be solved as same as that in the full-size simulation. Thus more flow details within the heat exchanger can be captured. The approach based on porous media model under the cylindrical coordinate system proposed can be used in the simulation study of the internal flow field of 3D finned-tube heat exchangers in actual scale. On this basis, this approach can contribute to optimization design of the 3D finned-tube heat exchanger.

R1234ze(E) Flow Boiling inside a 2.5 mm ID Smooth Tube and Comparison against an Equivalent Microfin Tube

The air conditioning and refrigeration industry is now dealing with an imminent substitution of widely implemented refrigerants having a non-negligible global warming impact. Among the proposed hydrofluoroolefins, R1234ze(E) has thermodynamic and transport properties close to those of R134a, and thus it can be one of its substitutes. This paper experimentally analyzes R1234ze(E) flow boiling inside a smooth tube with an internal diameter of 2.5 mm. Mass velocity is investigated from 200 to 600 kg m−2 s−1, for vapor quality from 0.15 to 0.99. The test tube is electrically heated by the Joule effect, by supplying heat fluxes from 12 to 60 kW m−2. Heat transfer coefficients and frictional pressure drops were evaluated from the experimental tests, and compared against values estimated by empirical correlations. Additional experimental tests permitted the comparison between the thermal and hydraulic characteristics of the smooth tube and those of a microfin tube with an inner diameter at the fin tip of 2.4 mm. The comparison revealed the higher contribution of convective boiling for the microfin tube compared to the smooth tube for all of the investigated working conditions.

PERFORMANCE OF RECTANGULAR PIN-FIN HEAT SINK SUBJECT TO AN IMPINGING AIR FLOW

The heat sink is used to enhance heat rejection from heated surface to air. The seize and the geometry of the heat sink with the shape of the extended surfaces have a great influence on the heat transfer coefficient. The first step to get the optimal design is to predict the heat transfer by conduction in solid walls of heat sink and then by convection between the solid and air flow. The purpose of the present study is to predict the effectiveness of closely spaced parallel rectangular fin array arrangement. The electronic processor was represented by the copper heat sink base with thermal conductivity of 401 W/m.K. The 72 fins with the geometry above mentioned were exposed to heat transfer with conduction and convection along all the boundaries except the bottom from which heat flow toward air flow domain. Mesh generation at a specific cells, number of element and number of nodes were taken under temperature difference validation. The experiments were done under impinging air flow rate with Reynolds number ranged between 4000-16000. The flow was turbulent so the k-Ԑ turbulence model needed to simulate mean flow characteristics. Constant heat fluxes boundary conditions were proposed with range between 10000-70000 kW/m2. The Results of temperature contour lines depicted a heat trend from the hot base through the extended surfaces to the fin tips. The fins were aligned in the core of heat sink showed higher temperature gradient compared with the fins existed in lines surrounded the core. The thermal resistance decreased as the Reynolds number increased and the Nusselt number increased as the Reynolds number increased and also when the heat flux increased. The Reynolds number depicted increasing as the Nusselt number increased and so the heat rejected from the heat sink base increased. There is a good agreement between the experimental and simulating results at error percentage not exceed 2%.

A theoretical analysis and parametric study of filmwise condensation on three-dimensional pin fins

In this paper, a theoretical model of filmwise condensation of steam on three-dimensional pin fins fabricated by selective laser melting (SLM), an additive manufacturing (AM) technique, is developed. The model considers the effects of surface tension and gravity on the liquid film flow over the pin fin surface. The three-dimensional nature of the liquid film flow over the fin flank and the unique features of the fin structures as a result of the laser melting process are modeled. Visualization studies are performed to verify the assumptions made in the model. From the modeling results, the local heat transfer coefficient and length-averaged heat transfer coefficient are obtained. The liquid film thickness at various locations of the pin fin is analyzed. The effects of fin tip dimensions, fin stem radius and fin pitch on the liquid film characteristics and heat transfer coefficient are systematically investigated. Our results showed that a thin film region exists in the flat and circular segments of the fin tip which cover approximately 25 – 30% of the fin surface. For a fixed fin diameter, it is found that the length-averaged heat transfer coefficient can be optimized by varying the dimensions of the flat and circular segments. A locally thin film region resulting from the suction effect is observed near the fin base for small fin spacings. However, the suction effect reduces with increasing fin spacing. Due to the three-dimensional nature of the pin fins which induces surface tension in the circumferential direction, the liquid film distribution is uniform. The differences in the length-averaged heat transfer coefficient at different circumferential locations are smaller than 5%. Finally, a comparison with existing experimental results demonstrates that a relatively accurate prediction of the average heat transfer coefficient can be achieved by our model with a maximum deviation of 8.3%.

Natural convection heat transfer performance of additively manufactured tube bundle heat exchangers with novel fin design

We studied the heat transfer of finned heat exchanger configurations with a novel design. These novel fin designs use integrated pins to enhance the heat conduction from the fin base to the fin tip as well as the air-side heat transfer on the fin surface. Oval tubes with conventional circular plain fins (CPF) as well as novel circular integrated pin fins (CIPF) and serrated integrated pin fins (SIPF) were additively generated by a Selective Laser Melting (SLM) process and installed at the bottom of a 6.5 m long chimney. All heat exchanger designs were tested in a 2-row and 3-row configuration with Rayleigh numbers between 25,000 and 120,000. We found the average Nusselt number of SIPF to be higher and the Nusselt number of the CIPF to be lower than for the CPF. Moreover, the 2-row configuration achieved a higher Nusselt number compared to the 3-row configuration for all heat exchanger designs. The analysis of the individual tube rows showed the highest Nusselt numbers at the first tube row and the lowest one at the last tube row for both configurations. However, for the SIPF the difference between the first and second tube row is smaller compared to the CPF and CIPF. In order to evaluate the compactness of the heat exchanger, the volumetric heat flux density was considered. Similar to Nusselt number the volumetric heat flux density enhanced for the SIPF and reduced for the CIPF compared to the conventional design. Also the 2-row configuration reached greater thermal performance compared to the 3-row configuration. Additionally, the volume and the surface area of the heat exchanger are 6.9% and 30.7% lower for the SIPF compared to the CPF. The experimental data were used to develop an empirical heat transfer correlation between Nusselt number, Rayleigh number, fin design and tube row number.

Application of Metaheuristic Algorithms for Optimizing Longitudinal Square Porous Fins

The objectives of this study involve the optimization of longitudinal porous fins of square cross-section using metaheuristic algorithms. A generalized nonlinear ordinary differential equation is derived using Darcy and Fourier’s laws in the energy balance around a control volume and is solved numerically using RFK 45 method. The temperature of the base surface is higher than the fin surface, and the fin tip is kept adiabatic or cooled by convection heat transfer. The other pertinent parameters include Rayleigh number (100 ≤ <i>Ra</i> ≤ 10⁴), Darcy number, (10⁻⁴ ≤ <i>Da</i> ≤ 10⁻²), relative thermal conductivity ratio of solid phase to fluid (1000 ≤ <i>k</i>_<i>r</i> ≤ 8000), Nusselt number (10 ≤ <i>Nu</i> ≤ 100), porosity (0.1 ≤ <i>φ</i> ≤ 0.9). The impacts of these parameters on the entropy generation rate are investigated and optimized using metaheuristic algorithms. In computer science, metaheuristic algorithms are one of the most widely used techniques for optimization problems. In this research, three metaheuristic algorithms, including the firefly algorithm (FFA), particle swarm algorithm (PSO), and hybrid algorithm (FFA-PSO) are employed to examine the performance of square fins. It is demonstrated that FFA-PSO takes fewer iterations and less computational time to converge compared to other algorithms.

Organization and Ontogeny of a Complex Lateral Line System in a Goby (Elacatinus lori), with a Consideration of Function and Ecology

Gobies (family Gobiidae) have a complex mechanosensory lateral line system characterized by reduced lateral line canals and a dramatic proliferation of small superficial neuromasts (on “sensory papillae”), which are arranged in lines on the head, trunk, and tail. A suite of morphological methods was used to describe the distribution and morphology of canal and superficial neuromasts in the neon goby, Elacatinus lori, and to describe the ontogeny of the lateral line system for the first time for any gobiiform fish. Portions of only three cranial lateral line canals are retained and they contain a total of eight canal neuromasts. In addition, 128–155 superficial neuromasts are found in six head series (comprising 33 neuromast lines or rows). Superficial neuromasts are found in one body series (65–80 neuromasts arranged in three groups of vertical lines or “stitches”) and one caudal fin series (3 lines, each located between fin rays and comprised of many small neuromasts; total of 27–53 neuromasts) extending to the tip of the caudal fin. The general distribution of neuromasts is established early during the larval stage, and neuromast numbers increase within and among lines resulting in an increase in overall complexity of the system. On day-of-hatch, a total of 22 neuromasts are present. At ∼15 days post-hatch, all eight cranial canal neuromasts are present, and, in post-settlement juveniles (“settlers”), they are enclosed in canals and a total of ∼185 neuromasts are found on the head, trunk, and tail. All neuromasts are small (∼40 lm long) and diamond-shaped, but three subpopulations (canal neuromasts, canal neuromast homologs, superficial neuromasts) are defined based on their location and their arrangement within lines (“tip-to-tip” or “side-by-side”). The ontogeny of the lateral line system and distinctions among neuromast subpopulations help to reveal the structural and functional organization of the complex lateral line system in Elacatinus and will contribute to the interpretation of neuromast patterns in other gobiiforms. A comparison of superficial neuromast number in 12 species of Elacatinus and Tigrigobius (sister genera) revealed variation among species that live in different reef microhabitats, which suggests that adaptive evolution in the lateral line system is evident among closely related taxa.

Stolephorus acinaces, a new anchovy from northern Borneo, and redescription of Stolephorus andhraensis Babu Rao, 1966 (Clupeiformes: Engraulidae)

Stolephorus acinaces sp. nov. is described from 14 specimens from the northern coast of Borneo, Malaysia. The new species is closely related to Stolephorus andhraensis Babu Rao, 1966, which is redescribed, both species having a long upper jaw with the posterior tip beyond the posterior margin of the preopercle, no predorsal scutes, the posterior preopercular margin indented and concave, the posterior tip of the depressed pelvic fin not reaching to a vertical through the dorsal-fin origin, no dark lines on the dorsum, and no black spots below the eye. However, the former is distinguished from S. andhraensis in having higher gill raker counts on the first and second gill arches (14–16 + 21–23 = 36–38 and 9–11 + 18–20 = 27–31, respectively vs. 14–16 + 19–21 = 33–37 and 8–11 + 16–19 = 26–29, respectively in S. andhraensis), a longer caudal peduncle (19.7–21.9% SL vs. 16.9–19.9%), longer pectoral fin (14.3–15.2% SL vs. 12.8–14.4%), and shorter pelvic fin (6.7–7.6% SL vs. 7.4–8.9%). A molecular analysis showed that S. acinaces sp. nov. is the sister group of the clade (S. andhraensis, Stolephorus tamilensis Gangan, Pavan-Kumar, Jahageerdar & Jaiswar, 2020, and S. acinaces sp. nov. has about 7% mean p-distance divergence in the mitochondrial cytochrome oxidase I (COI) gene with each of the two species of this clade.

Active Tip Fins for Box Wing Aircraft

Background: Induced drag accounts for significant percentage of cruise and total aircraft drag. In agreement with Prandtl’s theorem, the ideal arrangement for minimum induced drag is a closed biplane design. Past studies have implemented fixed tip fins for closed biplane design, with the reduction of induced drag associated with fixed tip fin found to be less than optimal. A review of patents related to the box-wing aircraft was carried out. Methods: In an attempt to further reduce the induced drag for box wing aircraft, this study proposed the implementation of Active Tip Fins (ATF) for aircraft design. Athena Vortex Lattice (AVL) software was used to simulate the induced drag associated with AFT in comparison with that of a fixed tip fin. Results: From the result, the ATF design shows a superior induced drag reduction. Conclusion: ATF design is a novel concept that has the potential of improving box wing aircraft performance.

Condensation of an Azeotropic Mixture inside 2.5 mm ID Minitubes

The ongoing miniaturization of air conditioning and refrigeration systems, in order to limit, as much as possible, the refrigerant charge, calls for smaller and smaller heat exchangers. Besides, the new environmental regulations are calling for new pure refrigerants or refrigerants mixtures with lower values of global warming potentials (GWPs). In this context, this paper analyzes the possible implementation of minitubes during condensation of the azeotropic mixture R513A. Two minitubes are tested: a smooth tube with an inner diameter of 2.5 mm, and a microfin tube with an inner diameter at the fin tip of 2.4 mm. The effects of vapor quality (varied in the range 0.10–0.99), of mass velocity (varied in the range 200–1000 kg m−2 s−1), and of saturation temperature (30 °C and 40 °C) on the heat transfer coefficient are investigated. The experimental results indicate that the heat transfer coefficient increases as both vapor quality and mass velocity increase, both in the case of the smooth tube and of the microfin tube, but the slope of the heat transfer coefficient trend respect to vapor quality is higher in the case of the microfin tube. The microfin tube shows, on average, heat transfer coefficients are 79% higher than those of the smooth tube under the same working conditions. Since R513A is a possible substitute of R134a, some experimental data during condensation heat transfer are also compared against those for R134a. Finally, the experimental results are compared against values estimated by empirical correlations available in the open literature.

Analysis of Cooling Efficiency Using the Biot Number of a Rectangular Fin

The performance of a rectangular fin, the relative value of the performance for L=0.1, and the ratio of the heat transfer from the fin tip to the total heat transfer from the rectangular fin were investigated using a two-dimensional analytical method. The variables are the Biot number and non-dimensional fin length. The relative resistance, effect, and efficiency increase as the non-dimensional length increases for a small Biot number (Bi≤0.1). On the other hand, the relative resistance and effect decrease and the relative efficiency increases as the non-dimensional length increases for a large Biot number (Bi≥0.7).

Experimental investigation and COMSOL modeling for different geometrical configurations of extended surfaces

AbstractThe current work presents and analyzes an experimental and three‐dimensional COMSOL simulation to address and quantify the influence of different geometric cross‐sectional shapes and types of materials (ie, brass and stainless steel) on the thermal performance of extended surfaces. Three cross‐sectional shapes (ie, circular, square, and hexagonal) were examined under various base temperatures (ie, 40°C, 50°C, 60°C, and 70°C). Additionally, two types of fin materials, brass and stainless steel, were investigated to address the impact of thermal conductivity on the temperature distribution, local heat transfer coefficient, heat dissipation rate, efficiency, and effectiveness of extended surfaces. The experimental results showed a significant increase in the heat transfer coefficient and heat dissipation rates for hexagonal brass fins over other shapes and stainless steel fins. The simulation results were validated with the experimental temperature distributions for different geometries and materials under differing operating conditions (ie, different base temperatures, with and without an insulated fin tip). The validation and evaluation of the current COMSOL simulation indicated that the simulated results had high accuracy, with less than a 6% deviation, compared with the experimental data. The current validated COMSOL model can serve as a useful tool to facilitate the design and optimization of fins under various design and operating parameters.

Single-Camera Three-Dimensional Velocity Measurement of a Fin-Generated Shock-Wave/Boundary-Layer Interaction

The three-dimensional (3-D) shock-wave/boundary-layer interaction (SBLI) between a fin-generated shock and a turbulent boundary layer is examined using plenoptic particle image velocimetry (PIV): a 3-D diagnostic technique that uses a single camera to obtain direct 3-D velocity measurements. A sharp, unswept fin at a 15 deg angle of attack in Mach 2 flow generates a 45 deg oblique shock that interacts with the boundary layer on the tunnel floor. This type of SBLI has been extensively studied in quasi-two-dimensional representations, but no work up to this point has been done to capture true 3-D measurements. This work represents the first 3-D velocity field measurements in supersonic flow using plenoptic PIV, as well as the first 3-D velocity measurements of a fin-generated SBLI. Flow features including the -shock structure and slip region expected from this SBLI were able to be resolved, and the 3-D imaging allowed for better visualization of the overall flow topology. Plenoptic PIV enabled the visualization of features not considered in previous literature, particularly the 3-D curvature of the inviscid shock and effects from an expansion region emanating from the fin tip due to the finite fin height. Plenoptic PIV results are compared with inviscid shock theory and stereoscopic PIV for validation purposes.

Transient Response of Longitudinal Fins under Step Changes in Base Temperature and Heat Flux using Lattice Boltzmann Method

The present article reports the transient response of longitudinal fins having linear and non-linear temperature dependent thermal conductivity, convection coefficient and internal heat generation under two cases of base boundary condition, (i) step change in base temperature and (ii) step change in base heat flux. The fin tip is assumed to be adiabatic. Both, linear and non-linear, temperature dependency of thermo-physical properties is addressed in the mathematical formulation and the solution for the above cases is obtained using Lattice Boltzmann method (LBM) implemented in an in-house source code. LBM, being a dynamic method, simulates the macroscopic behavior by using a simple mesoscopic model and offers enormous advantages in terms of simple algorithm to handle even the most typical of boundary conditions that are easy and compact to program even in case of complicated geometries too. Although the transient response of longitudinal fins has been reported earlier, however power law variation of thermo physical properties for the above two base condition has not been reported till date. The present article first establishes the validity of LBM code with existing result and then extends the code for solving the transient response of the longitudinal fin under different sets of application-wise relevant conditions that have not been treated before. Results are reported for several combination of thermal parameter and are depicted in form of graphs.

Characteristics of R513A evaporation heat transfer inside small-diameter smooth and microfin tubes

This paper investigates the characteristics of R513A during flow boiling. R513A is an azeotropic mixture made of R1234yf and R134a (0.56/0.44 by mass), and it has been proposed as a direct drop in of the common R134a. Experimental tests were run in a wide range of operative conditions: mass velocity in the range 200-800 kg m−2 s−1, heat flux in the range 12-60 kW m−2, for saturation temperatures of 15, 20 and 25°C. Two different mini tubes were tested: a smooth tube with an inner diameter of 2.5 mm, and a microfin tube with an inner diameter at the fin tip of 2.4 mm. Heat transfer coefficients and frictional pressure drops were evaluated from the experimental measurements. The approximately same diameter of the two tubes permitted to highlight the effect of the microfins on the thermal and hydraulic behavior during R513A flow boiling. Finally, experimental heat transfer coefficients and frictional pressure drops were compared against values predicted by correlations available in the literature.

Taxonomic revision of the Menticirrhus americanus (Linnaeus, 1758) and M. littoralis (Holbrook, 1847) (Percomorphacea: Sciaenidae) species complexes from the western Atlantic.

The genus Menticirrhus is widely distributed in the Neotropical region, where its species are common and abundant in shallow coastal waters and estuaries. The diversity, biogeography, and evolutionary relationships of the Menticirrhus species are still poorly known, due primarily to the difficulty of differentiating the species, given the broad similarities in their external morphology. The present study is based on the analysis of morphological and molecular data, with the examination of type specimens and a comprehensive collection of non-type specimens from an ample geographic range. These analyses indicated that two widely distributed Western Atlantic species, Menticirrhus americanus and M. littoralis, represent species complexes. The M. littoralis species complex is characterized by the absence of dark bars on body side, and a smaller, light-colored pectoral fins, that barely reaching the tip of the depressed pelvic fins, with fewer pectoral-fin rays. This complex includes three species: M. littoralis, found in the Gulf of Mexico, M. gracilis, from the southeastern and southern coast of South America, and a new species, described here, from the northern to eastern Brazilian coast. The M. americanus species complex is characterized by the presence of dark bars on body side, and a large, dark pectoral fin, that surpass the tip of the depressed pelvic fin, with more pectoral-fin rays. This complex has two species, M. americanus, which occurs on the east coast of the United States and in the Gulf of Mexico, and M. martinicensis, found from Caribbean to Argentina, that represents a cryptic allopatric species. An identification key to all species of the genus is presented.