Fin Locations Research Articles

Effect of fin location on constrained melting heat transfer of phase change material in a spherical capsule: A numerical study

Here, the effect of fin location of a single fin on the constrained melting behavior of phase change material (PCM) in a spherical latent heat storage unit is studied by employing two dimensional transient numerical simulations. A single fin of fixed length is situated at the center 12.5 mm and 25 mm away from the center in both upward and downward direction. Different parameters such as solid-liquid interface, temperature distribution, velocity vector, melt fraction, the melting characteristics of PCM and heat transfer enhancement for different fin locations are analyzed in detail in this study. The total melting time is found to increase by 72% and 54% for case when the fin is located at 25 mm,12.5 mm and 63% and 47% for the case when the fin is located at 25 mm,12.5 mm away from the center in both upward and downward direction respectively. Compared to other cases, the maximum enhancement ratio attained is of 107.28%, when the fin is located at the center.

An experimental study of the temperature evolution of a single fin submerged in a phase changing material during melting at different heat fluxes

An experimental setup has been designed to study a single cylindrical fin placed in a cylindrical enclosure filled with phase changing material (PCM). The heat flux to the fin is measured at the top of the fin. The temperature evolution at different fin heights is measured by thermocouples placed internally in the fin. The evolution of these temperatures has been studied for different heat fluxes. This provides insight in the contribution of the different fin heights to the total heat transfer to the PCM during the different stages of the melting process. As such they can be used to assess the effectiveness of the fin over its length. After approximately 6h, the fin temperature stabilizes during melting. Due to the temperature drop over the fin, the bottom temperature reached is significantly lower than the temperature at the top and the contribution of this lower part to the total heat transfer is lower as well. For heat fluxes higher than 3805±75 W/m2, the steady-state temperatures at fin locations in contact with the melting PCM are similar. For low heat fluxes, this steady-state temperature is not reached during a 12h experiment. Longer experiments are thus needed to study the steady-state behaviour at these lower heat fluxes.

Numerical Analysis of Melting Process in a Rectangular Enclosure with Different Fin Locations

Latent thermal energy storage is regarded as an effective strategy to utilize solar energy and recover automotive waste heat. Based upon an enthalpy-porosity method, the influence characteristics and mechanism of fin location on phase change material melting behavior in vertical rectangular enclosures were explored numerically. The results show that as fin location increases, the melting time decreases before attaining the minimum at the fin location of 0.20 after which it increases and finally surpasses the no fin case, because (1) the influence range of fins for conduction is limited by the bottom surface when putting fins next to this surface, (2) the liquid flow resistance increases with moving fins up, and (3) mounting fins near the top surface accelerates melting at the upper part, facilitating thermal stratification formation and weakening natural convection. Nu is higher than the no fin case, i.e., Nu enhancement factor is a positive value, in the melting process for a lower fin location, while for other fin locations, a transition to a negative value takes place. The higher the fin location is, the earlier the transition that arises. Finally, a strategy of increasing the maximum liquid flow velocity is proposed to reinforce melting for cases with considerable natural convection.

Inhibition of biofilm formation by rough shark skin-patterned surfaces

In this study, we investigate the microscale structure of shark skin denticles at abdomen (A) and fin (F) locations, analyze the roughness and wetting properties related to their microstructures, and evaluate the effect of the surface properties on early bacterial attachment and biofilm formation. Microstructural analysis by scanning electron microscopy and confocal laser scanning microscopy confirmed the length (A: 165–180 μm vs. F: 145–165 μm), width (A: 86–100 μm vs. F: 64–70 μm), height (A: 10.5–13.5 μm vs. F: 6.2–8.8 μm), and density (A: 110–130 denticles/mm2vs. F: 80–130 denticles/mm2) of the denticles. The results showed that the roughness and hydrophobicity properties were affected with slight differences in the microscale architecture. The denticles with a larger width, higher ridge, and denser overlap provided a rougher and more hydrophobic surface. The microscale structure not only affected surface properties but also the biological attachment process. The microscale topography of shark skin slightly promoted bacterial attachment at an early stage, but prevented bacteria from developing biofilms. This systematic investigation provides insights into the effects of the surface topography of shark skin on its anti-fouling mechanism, which will enable the future development of various products related to human activity, such as healthcare products, underwater devices and applications, and water treatment applications.

Influence of the Fluctuating Velocity Field on the Surface Pressures in a Jet/Fin Interaction

The mechanism by which aerodynamic effects of jet/fin interaction arise from the flow structure of a jet in crossflow is explored using particle image velocimetry measurements of the crossplane velocity field as it impinges on a downstream fin instrumented with high-frequency pressure sensors. A Mach 3.7 jet issues into a Mach 0.8 crossflow from either a normal or inclined nozzle, and three lateral fin locations are tested. Conditional ensemble-averaged velocity fields are generated based upon the simultaneous pressure condition. Additional analysis relates instantaneous velocity vectors to pressure fluctuations. The pressure differential across the fin is driven by variations in the spanwise velocity component, which substitutes for the induced angle of attack on the fin. Pressure changes at the fin tip are strongly related to fluctuations in the streamwise velocity deficit, wherein lower pressure is associated with higher velocity and vice versa. The normal nozzle produces a counter-rotating vortex pair that passes above the fin, and pressure fluctuations are principally driven by the wall horseshoe vortex and the jet wake deficit. The inclined nozzle produces a vortex pair that impinges the fin and yields stronger pressure fluctuations driven more directly by turbulence originating from the jet mixing.

Effect of Fin Location on the Latent Heat Storage: A Numerical Study

Latent heat thermal energy storage (LHTES) utilizing phase change materials (PCMs) is an appealing approach for the industrial waste heat recovery. However, due to the PCMs’ low thermal conductivity, the heat transfer enhancement methods like inserting metal fins have been widely adopted to fasten the PCMs’ melting. This paper numerically investigates the effect of the single fin location on the PCM’s melting process in a rectangular LHTES unit. The melting fraction contours and evolution curves under the three different fin locations were presented for the comparative analysis. The experiment data from one literature was applied to validate the numerical model and good agreement was found between the numerical results and the experimental data. A series of two-dimensional transient numerical simulations with three different fin locations were then carried out. It was found that the fin location would affect the natural convection process and thus generating the different PCM’s melting speeds. Besides, the fin at the bottom location has the best heat transfer enhancement performance, reducing 3.6 % melting time than the top fin location case. What’s more, the effect of fin location becomes more significant when locating at the bottom half of surface. It was concluded that the fin location could be optimized to improve the overall latent heat storage efficiency.

Development of Low Wake Wash Hull Form

Wake wash has become a significant issue in the ship design industry due to its impact on the environment in terms of erosion of natural shoreline wetlands. Many ideas for reducing wake wash have been introduced. This research work presents the development of a low wake wash catamaran hull form. In particular, the study is focused on the effectiveness of specially designed fin in order to reduce the wake wash produced by the ship. The fin was attached vertically along the centerline of the catamaran model and the model was tested in the towing tank of Marine Technology Center (MTC) to assess its wake wash. The fin was located at three different positions, which are at bow, center and stern of the ship. The results based on wave height measurements at the various fin locations showed that the fin located at the stern position produces lower wake wash compared to other positions.

Testing of High-Performance Concrete as a Thermal Energy Storage Medium at High Temperatures

Concrete is tested as a sensible heat thermal energy storage (TES) material in the temperature range of 400–500 °C (752–932 °F). A molten nitrate salt is used as the heat transfer fluid (HTF); the HTF is circulated though stainless steel heat exchangers, imbedded in concrete test prisms, to charge the TES system. During charging, significant cracking occurs in both the radial and longitudinal directions in the concrete prisms. The cracking is due to hoop stress induced by the dissimilar thermal strain rates of concrete and stainless steel. A 2D finite element model (FEM) is developed and used to study the stress at the prism/exchanger interface. Polytetrafluoroethylene (PTFE) and a heat-curing, fibered paste (HCFP) are tested as interface materials to mitigate the stress in the concrete. Significant reduction in the size and number of cracks is observed after incorporating interface materials. A heat exchanger with a helical fin configuration is incorporated to improve the heat transfer rate in the concrete. Testing confirms that the fins increase the rate of heat transfer in the concrete; however, large cracks form at each of the fin locations. Only the HCFP is tested as an interface material for the finned heat exchanger. The HCFP decreases the number and size of the cracks, however, not to the desired hairline levels.

The spatial distribution patterns of Caligus rogercresseyi and C. elongatus on Atlantic salmon hosts (Salmo salar)

The location of attached and mobile stages of Caligus rogercresseyi and C. elongatus on Atlantic salmon Salmo salar hosts was compared with that of the distribution patterns of Lepeophtheirus salmonis. The distribution of C. rogercresseyi was also compared in experimental and natural infections, and there were no significant differences for either attached or mobile stages between infection routes. Most C. rogercresseyi chalimi were located on the abdomen and post anal areas. Although the distribution of mobile stages was more homogenous there was a significantly higher percentage on the post anal area, 35% of all mobiles, compared with the salmon surface in the post anal region of only 3%. Significantly more attached stages, from 70 to 75%, of both Caligus species were located on the fins compared with mobiles. The mobile stages of both Caligus species had a predilection for the abdominal body. A higher percentage of attached stages of C. elongatus was located on the ventral fins and tail compared with C. rogercresseyi and, in contrast,significantly more were present on the body in C. rogercresseyi. However, there was no difference in the distribution of mobile stages of the two Caligus species with a significantly higher percentage located on the abdomen. In contrast, mobile L. salmonis were predominantly located on the back and head. Significantly more attached stages of L. salmonis were present on the dorsal fins and adjoining basal epidermis, 30% comparedwith <2% in the Caligus species. These results suggest that C. rogercresseyi and C. elongatus show similar preferences for the host ventral body and fin locations and there is no direct competition for host substrate between C. elongatus and L. salmonis.

Indirect adaptive output feedback control of a biorobotic AUV using pectoral-like mechanical fins

This paper treats the question of servoregulation of autonomous underwater vehicles (AUVs) in the yaw plane using pectoral-like mechanical fins. The fins attached to the vehicle have oscillatory swaying and yawing motion. The bias angle of the angular motion of the fin is used for the purpose of control. Of course, the design approach considered here is applicable to AUVs for other choices of oscillation patterns of the fins, which produce periodic forces and moments. It is assumed that the vehicle parameters, hydrodynamic coefficients, as well the fin forces and moments are unknown. For the trajectory control of the yaw angle, a sampled-data indirect adaptive control system using output (yaw angle) feedback is derived. The control system has a modular structure, which includes a parameter identifier and a stabilizer. For the control law derivation, an internal model of the exosignals (reference signal (constant or ramp) and constant disturbance) is included. Unlike the direct adaptive control scheme, the derived control law is applicable to minimum as well as nonminimum phase biorobotic AUVs (BAUVs). This is important, because for most of the fin locations on the vehicle, the model is a nonminimum phase. In the closed-loop system, the yaw angle trajectory tracking error converges to zero and the remaining state variables remain bounded. Simulation results are presented which show that the derived modular control system accomplishes precise set point yaw angle control and turning maneuvers in spite of the uncertainties in the system parameters using only yaw angle feedback.

Characteristics of fin buffeting over delta wings

Characteristics of fin buffeting over various delta wings was investigated by measurements of fin tip acceleration, particle image velocimetry measurements, and flow visualization. For slender wings, there is a strong asymmetry with regard to the effect of fin location on the buffeting response, and largest response occurs for the inboard fin locations. For outboard fin locations, the buffeting is small, even at high angles of attack when vortex breakdown is well upstream. For inboard fin locations, the largest fin vibrations were found for breakdown locations well upstream of the fin, and when the shear layer of the breakdown region impinges on the fin. The results show that single-fin buffeting may be as important as twin-fin buffeting. For a wing with low sweep angle, vortex shedding rather than vortex breakdown may become the responsible mechanism, and large buffeting excitation for outboard fin locations at a specific incidence is possible. For a double-delta wing, the interaction of strake vortices with the wing flow has a major influence on the buffeting characteristics. Finally, it was found that a nonzero fin angle did not have much effect on the conclusions arrived in this study.

Field Trials of Marking Stream Salmonids by Dye Injection and Coded-Wire-Tagging

In the summers of 1993 and 1994, we conducted trials in natural streams to assess the performance of dye marks and full-length coded wire tags (CWTs) when used simultaneously. Brook trout Salvelinus fontinalis and juvenile Atlantic salmon Salmo salar (fork length ≥55 mm) were marked with jet injection of Alcian Blue dye (in the base of the pectoral, pelvic, or caudal fins) and CWT (snout implant). All Alcian Blue marks remained clearly visible for at least 4 weeks. After 8 weeks, 3.1 % of brook trout and 11.4% of Atlantic salmon had lost at least one mark. Although loss rates did not differ significantly among marking locations, 86% of mark losses were from the caudal fin. Marking in pelvic or pectoral fin locations induced high mortality in smaller fish. Dye retention was low for individuals recaptured 10–14 months after injection, presumably because interannual growth caused dilution of the mark. Loss rates of CWT in summer were 2.5% for brook trout and 8.4% for Atlantic salmon; for either species, loss rates did not differ significantly among size-classes. Marked fish did not differ from unmarked fish in growth or condition in summer.

Base drag prediction on missile configurations

New wind-tunnel data have been taken, and a new empirical model has been developed for predicting base drag on missile configurations. The new wind-tunnel data were taken at NASA Langley Research Center in the unitary wind tunnel at Mach numbers from 2.0 to 4.5, angles of attack to 16 deg, fin control deflections up to 20 deg, fin thickness-to-chord ratio of 0.05 to 0.15, and fin locations flush with the base to two chord lengths upstream of the base. The newly developed empirical model uses these data along with previous wind-tunnel data. It estimates base drag as a function of all the preceding variables along with boattail and power-on or power-off effects. In comparing the new empirical model to that used in the former aeroprediction code, the new model gives improved accuracy compared to wind-tunnel data. The new model also is more robust due to inclusion of additional variables. On the other hand, additional wind-tunnel data are needed to validate or modify the current empirical model in areas where data are not available.

Individual marking of Atlantic salmon: evaluation of cold branding and jet injection of Alcian Blue in several fin locations

Individual marking of Atlantic salmon: evaluation of cold branding and jet injection of Alcian Blue in several fin locations

Resonant characteristics and end effects of a slot resonator in unilateral fin line

The resonant characteristics and end effects of a rectangular-slot resonator in unilateral fin line are presented for centered as well as off-centered fin locations in the guide. Sample theoretical results on the resonant frequency are verified through experiment at the Ka-band.

Phenotypic affinities of 11 species of Australian mullet (Pisces : Mugilidae)

The phenotypic affinities of 11 species of Australian mullet are examined using, principally, canonical variate analysis of 32 external body characteristics measured on individuals of each species. The body forms of four species of Liza and two of Mugil are compared within genera. All species proved to be distinct on the basis of the measured variables and the major discriminators proved to be the locations and relative sizes of the caudal, pectoral and first dorsal fins. Some degree of sexual dimorphism was evidenced in the analyses. In a combined analysis of all 11 species, no generic groupings of species were noted. One species, Rhinomugil nasutus: proved to be substantially different in body shape from the remainder. The Mahalanobis distance between Myxus elongatus and Liza argentea was not significant although the distances between all other species were. As shown by a minimum spanning tree analysis, M. elongatus occupies a central position and its relationships require further elucidation. The major discriminators in the combined analysis were again fin locations and relative sizes although some other body depth and width characteristics served to separate R. nasutus from the remaining species.