Horizontal Water Layer Research Articles

Echo grid integration: A novel method for preprocessing multibeam water column data to quantify underwater gas bubble emissions

AbstractWater column imaging multibeam echo sounder systems (MBESs) are a promising technology for quantitative estimates of the gas bubble volume flow within large gas seepage areas. Considerable progress has been made in recent years toward applicable calibration methods for MBESs as well as developing inversion models to convert acoustically measured backscattering cross sections to gas bubble volume flow. However, MBESs are still not commonly used for quantitative gas flow assessments. A reason for this is the absence of published processing methods that demonstrate how MBES data can be processed to quantitatively represent bubble streams. Here, we present a novel method (echo grid integration) that allows for assessing the aggregated backscattering cross section of targets within horizontal water layers. This derived value enables quantifying bubble stream gas flow rates using existing acoustic inversion methods. The presented method is based on averaging geo‐referenced volume backscattering coefficients onto a high‐resolution 3D voxel‐grid. The results are multiplied with the voxel volume to represent measurements of the total backscattering cross‐section within each voxel cell. Individual gridded values cannot be trusted because the beam pattern effects cause the values of individual targets to “smear” over multiple grid‐cells. The true aggregated backscattering cross‐section is thus estimated as the integral over the grid‐cells affected by this smearing. Numerical simulation of MBES data acquisition over known targets assesses the method's validity and quantify it's uncertainty for different, realistic scenarios. The found low measurement bias (< 1%), and dispersion (< 5%) are promising for application in gas flow quantification methods.

Linear and non-linear stability analyses of Rayleigh-Bénard convection in water–copper and water–alloy nanoliquids

In this paper, we perform linear and non-linear stability analyses of Rayleigh-Bénard convection in a horizontal layer of water–copper and water–alloy nanoliquids. The corresponding eigen values for the problems involving the two nanoliquids are obtained and compared. The thermophysical properties of nanoliquids have been modelled as a function of the properties of water as base liquid, copper and alloy as nanoparticles. A non-linear analysis is performed using the energy method. The subcritical instability does not exist. As a limiting case the results of water are discussed with results of previous investigations, and a good agreement is found. The effect of nanoparticles is to destabilise the system. The results are depicted graphically.

Effect of microorganisms on the stability analysis in magnetic nanofluids

A study of onset of convection of a new type of fluid, a fluid that contains both magnetic nanoparticles and microorganisms, is presented in this paper. We consider an infinite horizontal layer of water based magnetic nanofluids (MNF) containing gyrotactic microorganisms, heated from below, in the presence of uniform vertical magnetic field. Here we utilize the Chebyshev pseudospectral method to solve the eigen value problem in gravitational environment. The effect of various important parameters which are conducive for the stability of the system is shown graphically.

Convection in a horizontal layer of water with three diffusing components

Triple diffusive convection in water is modelled with properties like density, specific heat, thermal conductivity, thermal diffusivity and thermal expansion, modified in the presence of salts. The Ginzburg–Landau equation is derived to study heat and mass transports of different combinations of salts in water. A table is prepared documenting the actual values of thermophysical properties of water with different salts and the critical Rayleigh number is calculated. This information is used in the estimation of Nusselt and Sherwood numbers and their relative magnitudes are commented upon. A detailed study on different single, double and triple diffusive systems is done and comparison is made of the results. The local nonlinear stability analysis made via a Ginzburg–Landau model mimics many properties of the original governing equations, namely, Hamiltonian character and a bounded solution.

Hilbert diagnostics of convective structures and phase transition in super cooled water

The evolution of the crystallization wave front and convective structures in a horizontal layer of supercooled water bounded by tempera- ture-controlled flat surfaces is visualized using methods of Hilbert optics. The phase transition is manifested by the occurrence of a crys- tallization wave and is accompanied by a positive energy release, which, in turn, affects the dynamic distribution of the optical phase density gradient in supercooled water and induces phase perturbations in the probing light field. The results of measurements of the phase velocity and the shape of the crystallization front approximated by Bezier curves are presented. The wave front velocity is obtained using modified time-of-fight method. The phase velocity field is found to exhibit spatio-temporal quasi-periodicity that can be related to the existence of oscillatory phenomena in the crystallization process.

Liquid-surface entrainment induced by shocked air stream

Recently, we experimentally studied, in a shock tube environment, shock waves propagating over horizontal free water layers having depths of 10, 20, and 30 mm for shock wave Mach numbers $$M_\mathrm {is}$$ equal to 1.1 and 1.4. The qualitative interaction process was observed by means of high-speed visualizations, and the pressures arising in the air and in the water layer were measured and interpreted in terms of the various incident and refracted shock waves in air and water; in particular, it was concluded that the compression wave in the water is driven by the planar shock wave in the air. Additional experiments have been conducted and the novel contributions of the present technical note are quantitative results regarding the liquid-surface entrainment. At low Mach number ( $$M_\mathrm {is}=1.1$$ ), we show that the velocity of the droplets ejected into the air is independent of the water depth, unlike the wavelength of initial ripples and the angle of ejection. When the shock wave strength increases ( $$M_\mathrm {is}=1.4$$ ), the dispersion of a very thin droplet mist and a single large wave take place. We show that the thickening of the water mist and the velocity of the subsequent large wave decreases with the water-layer depth.

Optical Hilbert diagnostics of convective structures and phase transition in a horizontal layer of supercooled water

Methods of Hilbert optics are used to visualize evolution of convective structures and wave front of crystallization in a horizontal layer of supercooled water bounded by thermally stabilized plane surfaces. Measured phase velocities and shapes of the crystallization front approximated with the aid of the Bezier curves are presented. The spatiotemporal quasi-periodicity of the phase-velocity field can be related to oscillatory modes of the crystallization front as a dynamic surface of the water–ice interphase transition.

Dynamics of the crystallization front induced by the temperature gradient at the upper boundary of a horizontal layer of a fluid

The dynamics of the crystallization front induced by the temperature gradient at the upper boundary of a horizontal layer of water bounded by flat thermostatted surfaces is studied. The formation and evolution of convective structures are visualized by methods of the Hilbert optics and digital video recording. The difference in the temperatures of the upper (T1) and lower (T2) thermostats satisfies the condition T1 < T2. In this system, the temperature of the cooled upper surface is an order parameter. Reaching a critical value of this parameter leads to a bifurcation phase transition from the liquid state (supercooled water) to the solid state (ice). The velocity and shape of the crystallization wave front are determined. The spatial-temporal state of the crystallization wave is found, in which the wave front shape is a line of equal velocities. The dynamic profile of the isothermal surface bounding the spatial shape of the solid phase is visualized.

Planar shock wave sliding over a water layer

In this work, we conduct experiments to study the interaction between a horizontal free water layer and a planar shock wave that is sliding over it. Experiments are performed at atmospheric pressure in a shock tube with a square cross section ( $$200\times 200\,\hbox {mm}^2$$ ) for depths of 10, 20, and 30 mm; a 1500-mm-long water layer; and two incident planar shock waves having Mach numbers of 1.11 and 1.43. We record the pressure histories and high-speed visualizations to study the flow patterns, surface waves, and spray layers behind the shock wave. We observe two different flow patterns with ripples formed at the air–water interface for the weaker shock wave and the dispersion of a droplet mist for the stronger shock wave. From the pressure signals, we extract the delay time between the arrival of the compression wave into water and the shock wave in air at the same location. We show that the delay time evolves with the distance traveled over the water layer, the depth of the water layer, and the Mach number of the shock wave.

Thermocapillary deformation of a water layer at local heating

A horizontal water layer of 0.29-0.44 mm thickness, locally heated from the substrate, is investigated. The value of thermocapillary deformation occurring at local heating is measured by an inverted laser scanning confocal microscope Zeiss LSM 510 Meta. The heater in the form of strip of 0.5-mm width, 40-mm length, and 0.5-mm height made of indium oxide is sputtered on a sapphire substrate. The water temperature from the side of the substrate is measured using the infrared scanner Titanium 570M. We studied in detail the effect of the initial layer thickness and heating power on the value of thermocapillary deformation and temperature field. It is shown that deformation increases with an increase in thermal capacity and decrease in the layer thickness. Results of numerical simulation are in good qualitative agreement with the measurement results.

Capillary waves at microdroplet coalescence with a liquid layer

The quickly damped capillary waves generated at coalescence of microdroplets (diameter of up to 100 µm), formed in a gas atmosphere at water vapor condensation, with the horizontal layer of water are studied experimentally. Evaporation takes place at intensive local heating of liquid from the substrate side. To visualize and measure the deformations, the Schlieren technique and high-speed video (up to 54000 f/s) are applied. The measured wave amplitude varies within 1-6 μm, and this is consistent with the magnitude of the surface energy of coalescing microdroplets. The waves are generated by the energy of droplet surface.

The Effect of Contact Angle on Dynamics of Dry Spots Spreading in a Horizontal Layer of Liquid at Local Heating

The effect of equilibrium contact angle on dynamics of dry spot spreading at disruption of a horizontal water layer heated locally from the substrate was studied using the high-speed Schlieren technique. Different methods of working surface processing were applied; this allowed variations of the equilibrium contact angle from 27±6° to 74±9° without a change in thermal properties of the system. It is found out that substrate wettability significantly affects the propagation velocity of dry spot and its final size. It is also found out that the velocity of contact line propagation is higher in the areas of substrate with a higher temperature.

On the role of capillary waves in the mechanism of coalescence of a droplet cluster

Packets of capillary waves on the surface of a horizontal water layer generated at coalescence with a layer of microdroplets (with a characteristic diameter of 50–100 μm) of the dissipative structure “droplet cluster” have been detected by high-speed video recording and the schlieren method. The shortest experimentally observed waves have a length of about 130 μm and their phase velocity exceeds 1.8 m/s. It has been found that the coalescence of a single drop initiates a self-sustained wave process, which induces the coalescence of hundreds of droplets in a time shorter than 1 ms, which form a cluster.

Mechanism of stabilization of location of a droplet cluster above the liquid-gas interface

We studied the influence of sizes of droplets, forming the “droplet cluster” dissipative structure, on their levitation height in the vapor-air flow, which appears when free surface of horizontal water layer is locally heated. A sharp decrease in the velocity of the vapor-air flow takes place at a distance from the surface comparable with the droplet diameter. Allowing for the aerodynamic nature of the droplet levitation, this peculiarity of the flow determines the high stability of location of the droplet cluster above the interface. Existence of droplets that are anomalously heavy in the slope of the Stokes levitation mechanism is described.

The underground application of Magnetic Resonance Soundings

Abstract The potential application of MRS technology in locating waterbearing fractures in underground mines is studied. The determination of the presence of water ahead of mining is important to prevent accidents and to ensure higher efficiency in mining operations. In the usual surface based measurements, with horizontal loop and water layer, the geometry of the problem can be summarized by the value of the inclination of the Earth magnetic field. For MRS measurements under the geometric conditions associated with underground mining, where the loop is non-horizontal, the geometry can be described in an effective inclination that can be expressed in terms of the Earth magnetic inclination and declination, together with two further parameters that characterize the orientation of the mine wall. We examine the consequences of the different geometries on the MRS signal. Since the loop size is severely restricted in underground conditions, the feasible target depth is also severely limited. The consequences of the fractured hard rock aquifer conditions, typical of deep mining or tunneling environments, are also examined. The overall conclusion is that in underground MRS applications the signal strength is too small to enable the practical identification of fractures containing large volumes of water ahead of the mining face.

Analysis on the onset of microwave induced convection within a horizontal water layer

This work is concerned with the onset of convection due to microwave incidence in a horizontal water layer. The onset characteristics in terms of critical Rayleigh (Rac) and wave (kc) numbers have been determined for various regimes of microwave heating, namely thin, sinusoidal and thick samples. It has been shown that both Rac and kc exhibit oscillatory patterns in sinusoidal regimes of microwave heating, while they attain asymptotes in thin and thick sample regimes. The variation patterns of critical Rayleigh and wave numbers from thin to thick samples have been correlated with the degree of asymmetry in internal heat source profiles. The analysis is carried out over the entire spectrum of microwave source configurations. It has been shown that there exists a one-to-one correlation between the variation patterns of Rac and kc with the degree of symmetry in internal heat source profiles. The total power required to initiate the convection has also been analysed in terms of the modified Rayleigh number .

Turbulent Natural Convection in a Horizontal Water Layer at High Rayleigh Numbers

The fluid flow and heat transfer of the turbulent natural convection in a horizontal water layer, with heated from below, were investigated experimentally. The experiment was performed for the Rayleigh number Ra in the range of 1.5×105 up to 3.9×1010. As Ra increases above107, the circulating large-scale flow was gradually replaced by isolated rising and sinking plumes and then heat transfer was controlled by only those plumes. At Ra>109, a three-dimensional vortex in addition to those plumes was released from the thermal boundary layer. Consequently, this vortex appeared at high Rayleigh numbers seems to enhance the heat transfer process. For high Rayleigh numbers, the correlation between Ra and Nu is as follows : Nu=0.093 0 Ra0.326(1.5×105<Ra<3.9×1010).

201 水平流体層における自然対流場の形成挙動および乱流自然対流に関する研究(熱力学1)

201 水平流体層における自然対流場の形成挙動および乱流自然対流に関する研究(熱力学1)

Upward Heat Flux Through the Horizontal Fluid Layer of Water with Sinusoidal Wall Temperature at the Top or Bottom Boundary

Either top or bottom wall temperature of an infinite horizontal fluid layer at Pr = 6 is sinusoidally oscillated with constant average temperature on the opposing horizontal wall. This is a system with no temperature difference between the top and bottom walls in a time-averaged sense, as studied by Kalabin et al. for a square channel. The fluid is water, and the Boussinesq approximation is made. The computational region of height 1 and horizontal width 1 is adopted and numerical computation is carried out. The results show that the fluctuating Nusselt numbers computed at both the top and bottom walls give positive time-averaged values for two different frequencies computed. Time-dependent convection plumes occur when the bottom wall temperature becomes higher than the top wall temperature. The time-averaged heat flux is always positive, i.e., upward, even if the time-averaged temperature difference is zero between the top and bottom walls. This holds even if the oscillating temperature is on either the top or bottom wall. Two periods of temperature oscillation give one period of oscillation in flow and Nu, at least for the parameters studied.

Average heat transfer rates measured in two different temperature ranges for magnetic convection of horizontal water layer heated from below

The average heat transfer rates of gravitational and magnetic convection of water heated from below and cooled from above are measured for two cases of cold wall temperature θ c at 10 °C and 30 °C. The height of the cylindrical enclosure is 2 mm with 40 mm in diameter. The magnetic field is imposed in a vertical direction to increase or decrease 29% of the gravitational acceleration in a bore space of a super-conducting magnet of 10 T at the solenoid center. The group of data at θ c = 30 °C gives a better agreement with the classical heat transfer rate of Silveston than that at θ c = 10 °C. This is probably due to the almost constant value in the volumetric magnetic susceptibility of water at about 10 °C.