Two-blade Paddle Research Articles

QUANTIFICATION OF KINEMATIC AND MOTOR VARIABLES IN PARACANOEING THROUGH THE ACTION CAMERA: A STUDY EXPLORATORY

Paracanoeing is a speed boating sport, practiced by men and women, who seek to cover a distance of 200 meters in the shortest possible time. To generate the propulsion of the vessel and overcome the aerodynamic and hydrodynamic drags, the athletes perform the stroke motor gesture, which consists of bilateral cyclic and symmetrical movements with a two-blade paddle. Since, the motor performance in the modality can be influenced by motor aspects related to rowing and the athlete's ability to produce and maintain high speed indexes. Thus, the objective of the present study was to explore the different ways of quantifying variables through GPS and action camera technologies, as well as programs that systematize this information, being able to transform it into graphs through commonly used statistical programs. With this, it is possible to perform the interpretation and quantification of the variables through technological equipment, GPS and action camera, the data of a volunteer, a beginner athlete of paracanoeing, were analyzed, the speed, paddling index, paddling phases were analyzed ( water and air) and paddling frequency. In this way, the study opens the possibility to use the technique in paracanoeing training programs, with the objective of evaluating the athlete, since through the quantification of the variables it is possible to map the athlete's performance in each variable. Received: 2024/02/17 Reformulated: 2024/04/23 Accepted: 2024/04/23

Mixing Performance of Inner Baffle in Shear Thinning Fluid

A mixing performance of an inner baffle was investigated in shear thinning fluid. The inner baffle was placed with a clearance between baffle and vessel wall. A traditional two-bladed paddle impeller was used. Four planar baffles were vertically placed in two ways: 1) standard baffle condition 2) inner baffle condition. The standard baffle condition was that the baffle was placed on the mixing vessel wall. A mixing pattern was visualized by decolorization method based on an oxidation-reduction reaction with sodium thiosulfate and iodine. Flow field for shear thinning fluid in mixing vessel was measured by particle image velocimetry and was shown as stream line. A pair of isolated mixing regions (IMR) like doughnut-ring formed above and below the impeller under standard baffle condition. However, IMR dissipated under inner baffle condition. As a result, a mixing time under the inner baffle condition was drastically decreased. This study suggested that inner baffle promoted mixing in shear thinning fluid.

Ice growth on the cooling surface in a jacketed and stirred eutectic freeze crystallizer of aqueous Na 2 SO 4 solutions

Abstract Eutectic freeze crystallization (EFC) has been pronounced a promising separation technique to recover ice and salt simultaneously in an energy-efficient manner. Alike other freeze concentration methods, the accumulation of an ice layer, commonly known as ice-scaling, on the heat exchanger surface during operation thwarts the commercial application of EFC as the advantage of low energy requirement is outstripped by high investment cost, scaling up and operational complexities associated with the use of a scraper blade to remove the ice-scaling. Therefore, the aim of this research work is to investigate the ice-scaling phenomenon on a subcooled heat exchanger surface in the absence of mechanical scrapping. For a continuous EFC system, the influence of temperature driving force (ΔT) and the degree of agitation on the onset/induction time (tind) of ice-scaling are considered while keeping the other parameters, e.g., solution concentration (4 wt% Na2SO4 (aq) solution), the level of initial undercooling (0.28 °C) and the residence time (30 min) constant. The experimental results show that at a certain level of agitation, tind is inverse proportional to ΔT. At a low level of ΔT (i.e., 6.0 °C), the effect of the degree of agitation on tind becomes substantial. At the eutectic condition, the heat transfer coefficient of the solution (hsol) in the crystallizer prevails over that of mass transfer (kl). In the experimental setup, the overall heat transfer coefficient for a jacketed vessel type crystallizer is restricted by the heat transfer coefficient of the jacket side coolant (hj). The power number (Np) and pumping number (Nq) for a two-blade paddle type impeller and a crystallizer of specific dimensions and orientation are estimated by means of computational fluid dynamics (CFD) modeling and are used to calculate the specific power input (e) and impeller pumping capacity (Q) at different levels of agitation. Furthermore, CFD simulations of heat transfer from the coolant to the bulk solution are performed to investigate the effect of the agitation level on solution cooling in the non-crystallizing condition.

Lagrangian simulation and analysis of the power-law fluid mixing in the two-blade circular mixers using a modified WCSPH method

Abstract In the present study, we introduce a robust modified Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method in order to examine miscible mixing within a two-blade paddle mixer. Since it has a Lagrangian nature and it is based on particles, Smoothed Particle Hydrodynamics (SPH) is an appropriate and convenient method for simulating the moving boundary problems and tracking the particles in the mixing process. The present study thus introduces a convenient SPH method for modelling the mixing process for the power-law fluids. Two geometries for the mixer are examined and the effects of the power-law index on the fluid mixing are investigated. The results show that the geometric change from circular chamber to twin chamber considerably increases the mixing rate (by at least 49%). The results also indicate that the twin chamber mixer is more efficient for the fluids with higher power-law index.

Visualization of partially mixed region by use of periodical reaction

Mixing time and pattern in the impeller-agitated vessel with two-bladed paddle were investigated at various mixing Reynolds numbers by use of two chemical reactions: ordinary decolorizing experiment with iodine and sodium thiosulfate and Beloousov–Zhabotinskii (BZ) periodical reaction experiment. The periodical steady color-variation in BZ reaction system remained after the sufficient time required for the complete decolorization (that is, ordinary mixing time). The sequential spatial color-patterns obtained in steady periodical variation process were similar to the transitional color patterns observed in the decolorization process. The color-patterns obtained in BZ periodical reaction were consistent with the outline of partially mixed regions where the exchange of substance is relatively slow in the vessel and they depended on mixing Reynolds number. The phase of periodical concentration oscillation in each partially mixed region was shifted with one another in spite of the same period of oscillation. Whether the period and/or phase synchronize or not in each partially mixed region would depend on the relative speed between the exchange of substance and the synchronization of periodical oscillation of concentration there. The periodical reaction could become an available tool for the visualization of distribution of those partially mixed regions containing well and bad mixing regions in impeller-agitated vessel.

Mechanism of mixing enhancement with baffles in impeller-agitated vessel, part I: A case study based on cross-sections of streak sheet

Enhancement mechanism of mixing with baffle in agitated vessel using rotated two-bladed paddle impeller was investigated under a laminar condition. In mixing pattern, the toroidal isolated mixing region in the baffled vessel becomes distortive and much smaller than that of unbaffled vessel. From the visualization of streak cross-sections in the baffled vessel, interestingly, the renewed streak folds (streak lobes) are generated at the vicinity of baffles in both the vertical and horizontal cross-sections. These behaviors of streak are unlike the unbaffled case that the streak stretches straightforwardly. The streak lobe is known as the mixing template that its number and size are key factor for laminar mixing in agitated vessel. The results suggest that baffles can effectively transform the circumferential flow to vertical and/or radial flows. Consequently, in the baffled vessels, not only the vicinity of vessel wall but also the tip of baffles can become the origination of streak lobe formation, and folds of streak in the vertical and circumferential directions are further enhanced with baffles.

Experimental study on geometric structure of isolated mixing region in impeller agitated vessel

Isolated mixing region in agitated vessel with rotated two-bladed paddle impeller and no baffle was visualized experimentally and its structural property was investigated in detail. A set of thin filaments spirally wrapping around the core of the toroidal isolated mixing region is observed under low Reynolds number conditions, which is smaller than 60. Three-dimensional geometrical structure of filament in isolated mixing region depends on the periodical perturbations caused by the rotating impeller. We have succeeded in the determination of three-dimensional geometrical structure of filament in isolated mixing region based on relation between the movement of fluid particle and filament numbers and/or wire turns. Interestingly, the wire turns of filaments are opposite to movements of fluid particles.

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 °C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100–500 rpm) and time ( 15 / 60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of “honeycomb” particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20–22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5–7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Performance characteristics of mechanical foam‐breakers fitted to a stirred‐tank reactor

AbstractIn a stirred‐tank reactor (STR), a comparison of the performance of mechanical foam‐breakers: a six‐blade turbine (F‐B), a six‐blade vaned disk (V‐D), a two‐blade paddle (T‐P), a conical rotor (C‐R), a fluid‐impact dispersion apparatus (FIDA) and a rotating disk mechanical foam‐breaker (MFRD) was carried out using defined foaming media. The foam‐breaking ranges (relative to the gas superficial velocity, Ug) of the T‐P, C‐R and FIDA were inferior to that of the F‐B, V‐D and MFRD. The power consumption, Pkc, for foam‐breaking in the MFRD was the lowest among the F‐B, V‐D and MFRD. Operation of the F‐B and V‐D in the STR caused a considerable amount of liquid droplets from the collapsed foam to be entrained with the exhaust air.© 2002 Society of Chemical Industry

Development and Mixing Characteristics of a Multistage Impeller for Agitating Highly Viscous Fluids.

A new multistage impeller developed for mixing highly viscous fluids (0.1-10.0 Pa.s) in a stirred tank provides several advantages: excellent axial circulation flow, hardly any stagnant zones, and low power consumption. The impeller is composed of a vertical rotating shaft to which are attached, from top to bottom, a pair of two-bladed gate-impellers and one two-bladed paddle impeller. Four baffles are employed to accelerate the axial circulation flow in the tank. In this paper, the geometrical configuration of the multistage impeller is described, and its mixing characteristics for fluids of high viscosity - i.e. the power consumption, flow pattern, mixing time, circulation time, and mixing efficiency - are clarified. For comparison, the same characteristics were also examined in the stirred tanks using anchor, double-helical ribbon, and single-gate impellers. The results showed the multistage impeller to be superior to the other types in that the time required for complete mixing is relatively short and almost no stagnant zones are created. The relationship between the Reynolds and Nusselt numbers for the multistage impeller, as well as for single-gate and four-pitched paddle impellers, was clarified from the laminar to turbulent regions.

Mechanical suppression of the dynamic foam head in bubble column reactors

The necessity of suppressing foam formation arises in many industrial operations and in sewage treatment plants. Mechanical foam breakers are used for such a purpose when the use of chemical antifoams and defoaming agents is prohibited by the process. Two new foam breakers were used to control a dynamic foam head generated in a bubble column containing foamable liquid: a comb-type two-blade paddle with three slits, and a brush-type two-blade paddle with 168 needles. In comparison with more conventional foam breakers, both foam breaker designs gave significantly reduced critical speeds for foam control. Their performance was characterised under various experimental conditions including different foam-base liquid properties, gas sparger types, surfactant concentrations, and foam breaker clearances above the liquid surface level. The control of dynamic foams generated continuously in a bubble column was found to depend on the foam characteristics such as bubble size and liquid holdup, and the foamability of the base liquid. Foams generated in stirred tank reactors were found to be have different characteristics and hence different control requirements.

Performance characteristics of novel mechanical foam breakers in a stirred tank reactor

Unlimited foam formation and insufficient foam collapse can have serious effects in an aerated system such as a fermentation process. Mechanical foam breakers are used in foam control to avoid the drawbacks associated with the use of chemical antifoams and defoaming agents. In this paper, two new foam breakers consisting of a two-blade paddle with three slits, and a two-blade paddle with 168 thin needles have been tested. They gave significantly reduced critical speeds and power consumption for foam control in a stirred vessel, compared with some conventional foam breakers. The effects of various parameters, namely the physical properties of the foaming solution, type of gas sparger, surfactant concentration, and foam-breaker clearance above liquid level, have been investigated. The degree of difficulty of controlling dynamic foams generated continuously in a stirred vessel is found to be a function of the nature of the foam, ie its bubble size, its liquid holdup, and the degree of foamability of the system. © 1999 Society of Chemical Industry

Performance Characteristics of Mechanical Foam-Breakers with Rotating Parts Fitted to Bubble Column

The characteristics of four mechanical foam-breakers (a six-blade turbine (F-B), a six-blade vaned disk (V-D), a two-blade paddle (T-P) and a conical rotor (C-R) having six-blades fixed internally) with rotating parts fitted to a bubble column (BC) treating various foaming liquids were examined. In the BC with different foam-breakers, the average liquid hold-up in foam, ϕL, was both a typical parameter reflecting the foaming intensity of the BC, and a parameter related to the difficulty or ease of foam-breaking. The value of power consumption, Pkc, for foam-breaking in the C-R was the largest amongst the foam-breakers. Furthermore, it was demonstrated that in the four foam-breakers with rotating parts a considerable amount of very small liquid droplets was entrained with the exhaust air. © 1997 SCI.