Dimensionless Numbers
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2022 ◽  
Vol 73 (1) ◽  
pp. 1-18
Y.E.A. RAJ ◽  

The diurnal variation of north east monsoon rainfall of coastal Tamil Nadu represented by four coastal stations Chennai Nungambakkam (Nbk), Chennai Meenambakkam (Mbk), Nagapattinam (Npt) and Pamban (Pbn)  was  studied in detail based on hourly rainfall data of rainy days only, for the period 1 Oct-31 Dec for the 47/48  year period 1969-2016/2017.  Mean Octet rainfall and its anomaly were computed for the 8 octets  00-03,…., 21-24 hrs of the day and the anomaly was tested for statistical significance. Various analysis for the individual months of Oct, Nov, Dec and the entire period Oct-Dec were separately conducted.  The basic technique of evolutionary histogram analysis supplemented by harmonic analysis of octet mean rainfall anomaly was used to detect the diurnal cycle signal. Two indices  named as  diurnal variation of  rainfall index and coefficient of mean absolute octet rainfall anomaly representing the intensity of diurnal variation  in dimensionless numbers were defined,  computed  and interpreted. The analysis based on the above techniques revealed that the diurnal signal which shows an early morning maximum and late afternoon minimum of octet rainfall is well defined in Oct, decreases in Nov and further decreases in Dec for all the 4 stations. Though the diurnal variation manifests a well defined pattern in Dec the signal is not statistically significant in most cases. For Nbk and Mbk there is a weak secondary peak of octet rainfall anomaly occurring in the forenoon and afternoon respectively in Oct and Dec suggesting the presence of semi-diurnal variation of rainfall. Stationwise, the diurnal signal is most well defined for each month/season in Pbn followed by Npt, Nbk and then Mbk.   The physical causes behind the diurnal signal and its decrease as the north east monsoon season advances from Oct to Dec have been deliberated. The well known feature of nocturnal maximum of oceanic convection influencing a coastal station with maritime climate and the higher saturation at the lower levels of the upper atmosphere in the early morning hours have been advanced as some of the causes. For the much more complex feature of decrease of diurnal signal with the  advancement of the season, the decrease of minimum surface temperature over coastal Tamil Nadu from Oct to Dec causing an early morning conceptual land breeze has been shown as one of the plausible causes  based on analysis of temperature and wind.  Scope for further work based on data from automatic weather stations, weather satellites and Doppler Weather Radars has been discussed.

2022 ◽  
Vol 10 (1) ◽  
pp. 85
Hongbo Shi ◽  
Xikun Wang ◽  
Qingjiang Xiang ◽  
Gonghe Zhang ◽  
Lin Xue

In the marine fire suppression system, continuous delivery of dry chemical powder to the fire source with long powder discharge range and high dispersion concentration is essential. The work is devoted to experimental and numerical studies of the flow characteristics of the dry chemical powder jet from a horizontal injector with a wide range of Stokes numbers between 6 to 30 and Reynolds numbers between 4792 to 23,960 by considering the effect of gravitational acceleration. A CFD-based Eulerian–Eulerian multiphase model combined with Standard k-ω turbulence model was used to predict flow characteristics of particle-laden jet using dimensionless numbers, including the solid volume fraction, the normalized velocity magnitude, and the turbulent viscosity ratio. Experimental studies have been carried out for three different inflow velocities (2.06, 2.45, and 2.81 m/s). The results indicate that the particle density plays a significant role in the dispersion of the particles in the radial and axial directions. The transition from U-shaped to V-shaped solid dispersion structure on the ground can be captured with the increase of particle density. Moreover, the higher level turbulence intensity enhances the solid dispersion concentration. Finally, it was found that the Portland cement powder exhibits better discharge performance in terms of solid discharge range and dispersion concentration in comparison with other dry powders. These results have implications in the design of powder-based fire suppression system. Further studies should aim to the in-depth research on the fire extinguishing mechanism of the Portland cement powder, especially the fire suppression effectiveness and thermal decomposition process.

2021 ◽  
Vol 61 (12) ◽  
pp. 2897-2903
Yuichi Tsukaguchi ◽  
Kodai Fujita ◽  
Hideki Murakami ◽  
Roderick I. L. Guthrie

GALIASSI Gabriela Regina Rosa ◽  
RAMIREZ Maribel Valverde

Background: Heat treatment is one of the most used methods to preserve food, such as orange juices, which are an excellent source of ascorbic acid. To avoid vitamin C degradation and reduce loss, fast heating is recommended. However, little is known about heat transfer during juice pasteurization. Aim: Therefore, this work aimed to determine the vitamin C content and the convective heat transfer coefficient in the pasteurization of orange juice. Methods: To perform the experiment, in the juice container, two regions were analyzed: the central region and near the wall. For the time-temperature control, thermometers were installed in the two regions mentioned. Every 120 seconds, the temperature was measured. The vitamin C content in the juice was evaluated before and after pasteurization using the iodometric method. The convective coefficient was evaluated using the method of dimensionless numbers and the experimental method. Results and Discussion: In pasteurization, the solution was heated to 80 °C, where heating lasted 3000 seconds and cooling for 2520 seconds. The graph showing the relationship of the convective heat transfer coefficient and temperature follows the same trend of the literature. The convective coefficient is higher in the region near the wall. As time passes and temperature decreases, the central region tends to equilibrium, and the coefficient becomes more constant. The vitamin C content remained constant before and after pasteurization. The values of the dimensionless numbers used in the calculations are in the same order of magnitude as the literature. Conclusions: The pasteurization did not cause ascorbic acid degradation since the heating step was fast in the heat treatment. The graphic showed that there is a dependence of the dimensionless of temperature with the dimensionless Biot and Fourier. It was noted that studying the thermal behavior in the cooling of orange juice is extremely important to ensure its quality.

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7601
Beatriz Arauzo ◽  
Álvaro González-Garcinuño ◽  
Antonio Tabernero ◽  
María Pilar Lobera ◽  
Jesús Santamaría ◽  

A new approach based on the atomization of non-Newtonian fluids has been proposed to produce microparticles for a potential inhalation route. In particular, different solutions of alginate were atomized on baths of different crosslinkers, piperazine and barium chloride, obtaining microparticles around 5 and 40 microns, respectively. These results were explained as a consequence of the different viscoelastic properties, since oscillatory analysis indicated that the formed hydrogel beads with barium chloride had a higher storage modulus (1000 Pa) than the piperazine ones (20 Pa). Pressure ratio (polymer solution-air) was identified as a key factor, and it should be from 0.85 to 1.00 to ensure a successful atomization, obtaining the smallest particle size at intermediate pressures. Finally, a numerical study based on dimensionless numbers was performed to predict particle size depending on the conditions. These results highlight that it is possible to control the microparticles size by modifying either the viscoelasticity of the hydrogel or the experimental conditions of atomization. Some experimental conditions (using piperazine) reduce the particle size up to 5 microns and therefore allow their use by aerosol inhalation.

2021 ◽  
Xiaoyu Xie ◽  
Wing Kam Liu ◽  
Zhengtao Gan

Abstract Dimensionless numbers and scaling laws provide elegant insights into the characteristic properties of physical systems. Classical dimensional analysis and similitude theory fail to identify a set of unique dimensionless numbers for a highly-multivariable system with incomplete governing equations. In this study, we embed the principle of dimensional invariance into a two-level machine learning scheme to automatically discover dominant and unique dimensionless numbers and scaling laws from data. The proposed methodology, called dimensionless learning, can be treated as a physics-based dimension reduction. It can reduce high-dimensional parameter spaces into descriptions involving just a few physically-interpretable dimensionless parameters, which significantly simplifies the process design and optimization of the system. We demonstrate the algorithm by solving several challenging engineering problems with noisy experimental measurements (not synthetic data) collected from the literature. The examples include turbulent Rayleigh-Bénard convection, vapor depression dynamics in laser melting of metals, and porosity formation in 3D printing. We also show that the proposed approach can identify dimensionally homogeneous differential equations with minimal parameters by leveraging sparsity-promoting techniques.

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1466
Jana Sonnenschein ◽  
Pascal Friedrich ◽  
Moloud Aghayarzadeh ◽  
Otto Mierka ◽  
Stefan Turek ◽  

The Archimedes Tube Crystallizer (ATC) is a small-scale coiled tubular crystallizer operated with air-segmented flow. As individual liquid segments are moved through the apparatus by rotation, the ATC operates as a pump. Thus, the ATC overcomes pressure drop limitations of other continuous crystallizers, allowing for longer residence times and crystal growth phases. Understanding continuous crystallizer phenomena is the basis for a well-designed crystallization process, especially for small-scale applications in the pharmaceutical and fine chemical industry. Hydrodynamics and suspension behavior, for example, affect agglomeration, breakage, attrition, and ultimately crystallizer blockage. In practice, however, it is time-consuming to investigate these phenomena experimentally for each new material system. In this contribution, a flow map is developed in five steps through a combination of experiments, CFD simulations, and dimensionless numbers. Accordingly, operating parameters can be specified depending on ATC design and material system used, where suspension behavior is suitable for high-quality crystalline products.

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Mohammed S. Ismail ◽  
Mohamed R. Berber ◽  
Ziyad A. Alrowaili ◽  
Mohamed Pourkashanian

Purpose This paper aims to numerically solve fully developed laminar flow in trapezoidal ducts with rounded corners which result following forming processes. Design/methodology/approach A two-dimensional model for a trapezoidal duct with rounded corners is developed and conservation of momentum equation is solved. The flow is assumed to be steady, fully developed, laminar, isothermal and incompressible. The key flow characteristics including the Poiseuille number and the incremental pressure drop have been computed and tabulated for a wide range of: sidewall angle (θ); the ratio of the height of the duct to its smaller base (α); and the ratio of the fillet radius of the duct to its smaller base (β). Findings The results show that Poiseuille number decreases, and all the other dimensionless numbers increase with increasing the radii of the fillets of the duct; these effects were found to amplify with decreasing duct heights or increasing sidewall angles. The maximum axial velocity was shown to increase with increasing the radii of the fillets of the duct. For normally used ducts in hydrogen fuel cells, the impact of rounded corners cannot be overlooked for very low channel heights or very high sidewall angles. Practical implications The data generated in this study are highly valuable for engineers interested in estimating pressure drops in rounded trapezoidal ducts; these ducts have been increasingly used in hydrogen fuel cells where flow channels are stamped on thin metallic sheets. Originality/value Fully developed laminar flow in trapezoidal ducts with four rounded corners has been solved for the first time, allowing for more accurate estimation of pressure drop.

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Jifeng Cui ◽  
Umer Farooq ◽  
Ahmed Jan ◽  
Murtada K. Elbashir ◽  
Waseem Asghar Khan ◽  

The practice of flowing effort is participating in various industries especially in nutrition productions all around the world. These fluids practices are utilized extensively in nutrition handling productions by making use of sticky liquids to produce valuable food manufactured goods in bulk. Nevertheless, such productions ought to guarantee that involved equipment such as pipelines are maintained clean as well as are cleared out for the efficient movement of fluids. The nonsimilar characteristics of involuntary convection from circular cylinder stretching in the axial direction subjected to an external flow of Sisko fluid characterized by the freely growing boundary layers (BL) are presented in this research. A circular cylinder is submerged in a stationary fluid. The axial stretching of the cylinder causes external fluid flow. The magnetic force of strength ″ B 0 ″ is enforced in the transverse direction. Because of the fluid's high viscosity, frictional heating due to viscous dissipation is quite significant. The flow is three dimensional but with no circumferential variations. The governing equations for axisymmetric flow that include the mass balance, x -momentum, and heat equation are modeled through conservation laws. The dimensionless system is developed by employing appropriate nonsimilar transformations. The numerical analyses are presented by adapting local nonsimilarity via finite-difference (FDM)-based MATLAB algorithm bvp4c. The characteristics of dimensionless numbers are determined by graphs that are plotted on momentum and heat equations. The nonsimilar simulations have been compared with the existing local similar solutions. Fluid velocity is increased as the material and curvature parameters are increased, resulting in improved heat transfer. The deviation in skin friction and local Nusselt number against the various dimensionless numbers is also analyzed.

Vălu Gheorghe-Orlando ◽  
Susan-Resiga Daniela

Abstract In this paper we investigated from rheological point of view some samples of ferrofluid-based magnetorheological fluids (FF-MRFs) with different volumic fractions of Fe microparticles, but with the same ferrofluid used as carrier liquid. We correlated the dimensionless flow curves, measured at different values of the magnetic field induction, using either Mason number or Casson number. It has been shown that in this approach, data sets measured under different conditions collapse on a single curve. This master curve is useful for controlling the concentration of Fe particles, so that the magnetic and magnetorheological properties of FF-MRF to be adapted to obtain high-performance applications.

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