Fluid In Pool Research Articles

Experimental study of pool boiling heat transfer on hybrid surface coupled micro-pin-finned

The performance of identical hydrophilic-hydrophobic coupled micro-pin-finned surfaces was evaluated using FC-72 as the working fluid in pool boiling experiments. Three hydrophilic and hydrophobic coupled rectangular copper column surfaces (HH4, HH9, and HH16) were constructed to analyze their boiling heat transfer properties. By integrating the micro-pin-finned surface (PF) and the smooth surface (SS), the impact of various subcoolings (0 K, 15 K, and 25 K) on the critical heat flux (CHF) was explored. Surface HH16 showed the greatest sensitivity to subcooling effects on CHF, followed by HH9 and HH4, respectively. For HH9, the CHF at ΔTsub = 0 K, 15 K, and 25 K, reached 69.6 W·cm−2, 84.2 W·cm−2, and 93.7 W·cm−2, respectively. In comparison to other surfaces (PF, HH4, HH16), the CHF of HH9 climbs by 19.32 %, 8.75 %, and 10.8 % at saturated boiling, respectively. A high-quality camera captured bubble dynamics during the experiments. The results reveal that the hydrophilic and hydrophobic coupled micro-pin-finned copper surface has a greater critical heat flux (CHF) than the standard rectangular micro-pin-finned surface, although heat transfer performance (HTC) drops marginally (both saturated and subcooled boiling). Visual monitoring demonstrates that these coupled surfaces effectively prevent bubble coalescence during subcooled boiling. Additionally, this novel surface design may serve as an effective strategy to reduce drying and delay the onset of boiling crises. The CHF improvement of the HH9 on SS surface was 313.06 %, significantly higher than the 246.17 % of PF on SS, marking a performance increase of 66.89 %. The influence mechanism of the Lattice width coefficient and the Vapor column spacing coefficient on CHF were analyzed. Fluid replenishment and bubble formation behavior were applied to clarify the strengthened heat transfer and CHF triggering mechanism on the surface of the hydrophilic and hydrophobic coupled rectangular micro-pin-finned copper column surface.

Effects of Electromagnetic Fields on the Microstructure of Laser Cladding.

The fast heating and quenching of laser cladding increase the internal stresses in the cladding layer. Moreover, the quick condensation of the molten pool leads to an uneven distribution of the internal elements and coarse grains of the structure. To address the above defects and increase the molding quality of laser cladding, an electromagnetic field was introduced into the laser cladding technique, and the effects of the external assisted electromagnetic field on the mixed metal fluid in the molten pool were explored. On this basis, the action of the electromagnetic field on the flow states of the molten pool was further analyzed. The results demonstrate that after introducing electromagnetic assistance, the material flow in the molten pool accelerated as a response to the periodic changes in electromagnetic forces and the influences of the electromagnetic field on crystallization, thus refining the grains and improving the grain distribution uniformity in the cladding layer. The dendritic crystals in the cladding layer decreased, while the isometric crystals and the cellular-like dendrites increased. The element distribution in the cladding layer increased in uniformity. Additionally, this method can decrease the dilution rate of the cladding layer and improve its overall hardness. A laser-cladding test of the Ni-based powder was carried out on the AISI 1045 steel surface under the coaxial powder-feeding mode. Moreover, the influences of the electromagnetic field on the microstructure of the laser-cladding layer were compared, and the causes of the changes were disclosed.

Instabilities of thermocapillary-buoyant-Coriolis flow of medium Prandtl fluid in a slowly rotating annular pool

In differently heated slowly rotating annular pools, the thermocapillary force, buoyancy force, and Coriolis force drive fluid flows and induce various flow instabilities. To understand these complex flow instabilities, the linear stability of axisymmetric thermocapillary-buoyant-Coriolis flow was investigated for medium Prandtl number fluid in an annular pool slowly rotating in a counter-clockwise direction. The neutral states for the incipience of instabilities were determined by a linear stability analysis, and the underlying mechanisms were clarified using energy budgets. Three types of flow instabilities were identified for Taylor numbers ranging from 0 to 60. The results showed that the sign of the temperature perturbation in the bulk and that on the surface right above it governed the mechanisms of the stationary and oscillatory instabilities. This work can be helpful for understanding the combined effects of thermocapillary force, buoyancy force, and Coriolis force on flow instabilities.

Thermal analysis of a binary base fluid in pool boiling system of glycol–water alumina nano-suspension

The main aim of the present research is to measure the nucleate boiling heat transfer coefficient (BHTC) of aqueous glycol nano-suspension as a coolant around a horizontal heater. Alumina nanoparticles were added to the base fluid at a volumetric concentration of 1% to improve the thermal conductivity of the nano-suspension. The pressure of the system was set to the atmospheric pressure, and the coolant was tested at different applied heat fluxes (HF) ranged from 0 to 90 kW m−2 and volumetric concentration of 0–40% of the heavier component. Two zones of heat transfer were identified, including a natural convection zone and nucleate boiling one mixed with bubble formation and bubble interactions. Results also showed that the HTC of the nano-suspension is smaller than those recorded for the pure water. A rough comparison was made to examine the accuracy of the developed equations for estimating the BHTC value against the experimental data. It was found that the developed equations are not accurate for the data measured in the free convection region. Thus, the Churchill-Chu correlation was recommended for estimating the BHTC in the free convection area of heat transfer. Also, the effect of operating parameters such as HF and volumetric concentration on the pool boiling HTC of the solution was studied.

Effect of Heat Dissipation on Thermocapillary Convection of Low Prandtl Number Fluid in the Annular Pool Heated from Inner Cylinder

This paper presents a series of numerical simulations on the effect of heat dissipation on the thermocapillary convection of a low Prandtl number (Pr = 0.011) fluid in an annular pool heated from its inner cylinder. The radius ratio and the aspect ratio of the annular pool set as η = 0.5 and e = 0.1, respectively. The results show that with the increase of Biot number, the isotherms of the two-dimensional basic flow are seriously compressed near the hot inner cylinder and the thermocapillary flow pattern will be impaired. With the increase of Marangoni number, the thermocapillary convection first evolves from the basic flow to a three-dimensional stationary flow with longitudinal stationary stripes on the free surface, and then to a three-dimensional oscillatory flow featured with the combination of stationary stripes and azimuthal waves, which is caused by the mutual effect of the radial convection, azimuthal local flow and heat dissipation. After the flow destabilization, the amplitude of temperature fluctuation increases and the wave number decreases with the increase of Marangoni number when the free surface is adiabatic. Furthermore, the temperature fluctuation pattern is changed due to the surface heat dissipation. In addition, with the increase of Biot number, the wave number almost keeps constant when Marangoni number is small, but it increases significantly at a large Marangoni number.

A CFD Model for Simulating the Electron Beam Welding of TRIP‐Matrix‐Composites

AbstractThe purpose of the presented model is the numerical simulation of the electron beam welding of metal matrix composites regarding heat transfer, phase change, and fluid and particle flow in the weld pool. The governing equations for the 3D, transient, incompressible heat and fluid flow are therefore extended by a phase change model and a heat source. Furthermore, Lagrangian particle tracking is used for the dispersed particle phase. The implementation of this model into OpenFOAM ensures reusability and expandability for further applications and refinements.

Thermocapillary convection of moderate Prandtl number fluid in a shallow annular pool heated from inner cylinder with surface heat dissipation

This paper presents a series of three-dimensional numerical simulations on thermocapillary convection of moderate Prandtl number (Pr = 6.7) fluid in a shallow annular pool heated from the inner cylinder with surface heat dissipation. The aspect ratio and radius ratio of the annular pool are respectively fixed at ε = 0.05 and η = 0.5. Biot number varies from 0 to 40 and Marangoni number varies from 0.1 × 105 to 6.0 × 105. Results show that there is a large temperature drop near the heated cylinder and the flow becomes more intense than those when the outer cylinder is heated at adiabatic free surface. With the increase of Marangoni number, the flow will transit from the axisymmetric steady flow to the three-dimensional oscillatory flow. The critical Marangoni number decreases first, and then increases with the increase of Biot number. After the flow destabilization, thermocapillary convection with adiabatic free surface exhibits the multicellular wave pattern when the inner cylinder is heated, which is different from that when the outer cylinder is heated. The temperature fluctuation pattern depends on the coupling effect of thermocapillary convection and heat exchange on the free surface. The wave number increases first, and then decreases with the increase of Marangoni number at a fixed Biot number. Furthermore, as Marangoni number increases, the temperature fluctuation on the free surface will radially extend from the inner cylinder to the outer cylinder gradually, and the amplitude of temperature fluctuation increases obviously.

Three-Dimensional Numerical Simulation on Thermocapillary Convection of Moderate Prandtl Number Fluid in an Annular Shallow Pool with Surface Heat Dissipation

In order to understand the effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in an annular shallow pool, we performed a series of three-dimensional numerical simulations by using the finite volume method. An annular shallow pool is full of 0.65cSt silicone oil with Prandtl number of 6.7. The radius ratio and the aspect ratio of the pool are respectively fixed at 0.5 and 0.1. Surface heat dissipation Biot number is varied from 0 to 50. Results indicate that the critical Marangoni number of flow destabilization mainly depends on the coupling effect of the thermocapillary force and surface heat dissipation on the free surface, which decreases first, and then increases gradually. When Biot number is small, the steady axisymmetric flow after the flow destabilization will bifurcate to the hydrothermal wave. With the increase of Marangoni number, the flow pattern evolution at a small Biot number is similar to that of an adiabatic free surface, and the fundamental oscillatory frequency increases gradually. With the increase of Biot number, the radial roll cells near the outer cylindrical wall gradually extend to the inner wall, and eventually occupy the whole liquid pool. When Biot number is large, the flow pattern after the flow destabilization is a radial rolling cell pattern with alternating azimuthal direction. Then it gradually evolves into azimuthal waves, and the fundamental oscillatory frequency has a slight decrease.

Effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in a shallow annular pool

This paper presents a series of three-dimensional numerical simulations on the effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in a shallow annular pool. The annular pool with a fixed aspect ratio of 0.05 and radius ratio of 0.5 is filled with 0.65 cSt silicone oil. Its Prandtl number is 6.7. Biot number of surface heat dissipation ranges from 0 to 50. The results show that when Marangoni number is small, thermocapillary convection is the axisymmetric steady flow. When Marangoni number exceeds the critical value, the basic flow will destabilize and transit to the hydrothermal waves that propagate along the clockwise or anticlockwise direction. The critical Marangoni number of the flow destabilization increases with the increase of Biot number. Furthermore, when Biot number increases, the radial temperature gradient on the free surface decreases near the inner cylindrical wall, but increases near the outer cylindrical wall, which results in the thermocapillary convective cell moving gradually from the inner to the outer cylindrical walls. After the flow destabilizes, the temperature fluctuation on the free surface mainly appears near the outer cylinder at a large Biot number.

Surface Heat Dissipation Dependence of Thermocapillary Convection of Moderate Prandtl Number Fluid in an Annular Pool

In order to understand surface heat dissipation dependence of thermocapillary convection for moderate Prandtl number fluid in a deep annular pool, a series of three-dimensional numerical simulations have been carried out by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are fixed at 0.5 and 1.0, respectively. The working fluid is 0.65cSt silicone oil with Prandtl number of 6.7. Surface heat dissipation Biot (Bi) number is varied from 0 to 50. Results indicate that with the increase of Biot number, the radial temperature gradient near the inner cylindrical wall decreases, and near the outer cylindrical wall it increases, so the flow is enhanced. When 0 < Bi < 10, with the increase of Marangoni number, the axisymmetric steady flow first transits to the standing wave, and then to the azimuthal waves. The standing wave should be attributed to Marangoni-Benard instability. However, the azimuthal waves should be corresponded to hydraulic instability, which is mainly driven by the azimuthal motion of temperature fluctuation from the sudden change of flow direction near the bottom and the inner cylindrical wall. When Bi ≥ 10, when the flow destabilizes, the axisymmetric steady flow transits directly to the azimuthal waves. With the increase of Biot number, the critical Marangoni number of the flow destabilization increases. Furthermore, the fundamental frequency and the wave number of three-dimensional oscillatory flow increase gradually with the increase of Biot number.

Flow pattern transition and destabilization mechanism of thermocapillary convection for low Prandtl number fluid in a deep annular pool with surface heat dissipation

In order to understand clearly the flow pattern transition and the destabilization mechanism of thermocapillary convection for low Prandtl number fluids in a deep annular pool with surface heat dissipation, we carried out a series of three-dimensional numerical simulations by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are respectively fixed at 0.5 and 1.0. Prandtl number of the working fluid is 0.011. Because the total heat dissipation coefficient on the free surface for low Prandtl fluids is small, Biot number is varied from 0 to 1.0. Results indicate that thermocapillary convection experiences the transitions from axisymmetric steady state flow into three-dimensional steady flow, and then into three-dimensional oscillation flow with the increase of Marangoni number. The critical Marangoni number of flow pattern transition decreases slightly with the increase of Biot number, and the maximum temperature and velocity fluctuations appear near the lower part of outer wall. The azimuthal temperature fluctuation on the free surface gradually shrinks to the inner wall, and the temperature fluctuation region decreases. However, it remains almost unchanged near the bottom of the annular pool, but the fluctuation amplitude increases.

Piezoelectric driven self-circulation micromixer with high frequency vibration

Active micromixers have been widely used in chemistry, biomedicine and many micro analyses as it offers low reagent consumption, controllable mixing process, safe, and reliable. Based on piezoelectric (PZT) drive technology and numerical simulation results, a self-circulation micromixer with high frequency vibration has been designed and fabricated. The micromixer is composed of PZT micropump, vibration substrate, mixing pool with double U-shaped inlet and outlet, upper cover plate and lower substrate. The performance of the micromixer’s self-circulation and high frequency vibration is evaluated by experimental tests. Experimental results show that: When the drive voltage and frequency of the self-circulation reflux micropump are set to 100 V and 100 Hz, respectively, a significant vortex flow is generated in the mixing pool, and the vortex flow speed is as high as 320 r min−1. When the driving frequency of the vibration substrate is set to its first resonance frequency, the displacement of its center point is the largest up to 28.1 µm. Furthermore, the vortex flow speed of the fluid in the mixing pool and the vibration intensity of the vibration substrate can be adjusted separately by regulating the driving voltage of the PZT micropump and vibration substrate.

Functional difference equations in the problem on the forced oscillations of a fluid in an infinite pool with conical bottom

Functional difference equations in the problem on the forced oscillations of a fluid in an infinite pool with conical bottom

Flow bifurcation routes to chaos of thermocapillary convection for low Prandtl number fluid in shallow annular pool with surface heat dissipation

In order to understand clearly the transition characteristics of thermocapillary convection of low Prandtl number fluid in shallow annular pool with surface heat dissipation, some bifurcation routes to chaos of thermocapillary convection have been numerically investigated by using the finite volume method in this paper. The annular pool was filled with the low Prandtl (Pr) number fluid of Pr = 0.011. The range of Biot number is from 0 to 1. Results indicate that the flow bifurcation route of thermocapillary convection depends intensively on surface heat dissipation. When surface heat dissipation is smaller, with the increase of Marangoni number the flow bifurcation sequence of thermocapillary convection is two-dimensional axisymmetric steady flow → three-dimensional steady flow → coexisting hydrothermal waves and radial moving waves → radial moving waves → chaos. When surface heat dissipation is larger, the bifurcation sequence becomes simple as two-dimensional axisymmetric steady flow → hydrothermal waves → chaos. Furthermore, every bifurcation of thermocapillary convection is always accompanied by the variations of the wave number and the oscillatory frequency. Furthermore, the temperature fluctuation amplitude on the free surface increases gradually with the increase of Marangoni number.

Effect of surface heat dissipation on thermocapillary convection of low Prandtl number fluid in a shallow annular pool

In order to understand the effect of surface heat dissipation on thermocapillary convection of low Prandtl number in a shallow annular pool, a series of three-dimensional numerical simulations were carried out by using the finite volume method. Results indicate that with the increase of surface heat dissipation, the thermocapillary convection intensity increases at first, and then decreases slightly; furthermore, the center of the thermocapillary convective cell moves gradually to the hot outer wall. With the increase of Marangoni number, the stable axisymmetric flow bifurcates orderly to the three-dimensional steady flow and the three-dimensional oscillatory flow at a weak surface heat dissipation. However, it bifurcates directly to the three-dimensional oscillatory flow at a strong heat dissipation. After thermocapillary convection destabilizes, the hydrothermal waves appear at the weak surface heat dissipation, but the longitudinal rolls near the outer wall are dominant at the strong heat dissipation. The flow pattern transition is always accompanied by the variations of the temperature fluctuation amplitude, the oscillatory frequency and the wave number.

Application research of computational mass-transfer differential equation in MBR concentration field simulation.

After conducting the intensive research on the distribution of fluid’s velocity and biochemical reactions in the membrane bioreactor (MBR), this paper introduces the use of the mass-transfer differential equation to simulate the distribution of the chemical oxygen demand (COD) concentration in MBR membrane pool. The solutions are as follows: first, use computational fluid dynamics to establish a flow control equation model of the fluid in MBR membrane pool; second, calculate this model by adopting direct numerical simulation to get the velocity field of the fluid in membrane pool; third, combine the data of velocity field to establish mass-transfer differential equation model for the concentration field in MBR membrane pool, and use Seidel iteration method to solve the equation model; last but not least, substitute the real factory data into the velocity and concentration field model to calculate simulation results, and use visualization software Tecplot to display the results. Finally by analyzing the nephogram of COD concentration distribution, it can be found that the simulation result conforms the distribution rule of the COD’s concentration in real membrane pool, and the mass-transfer phenomenon can be affected by the velocity field of the fluid in membrane pool. The simulation results of this paper have certain reference value for the design optimization of the real MBR system.

浄水場における傾斜板沈降装置のスロッシング被害対策に関する研究

High rate plate settler modules are solid and liquid separation devices to improve precipitation efficiency of purification in settling tanks in purification plants. In the 2011 off the Tohoku Pacific coast Earthquake, the high rate plate settler module fell off and it was damaged. As a result, supply of the water stopped for a long time. It is considered that liquid sloshing by long period ground motion caused these damages. There are examples of damage as liquid sloshing in the past, fire of an oil tank, and damage of device in a tank, overflow of fluid in storage pool for spent nuclear fuel in a nuclear power plant. From these backgrounds, there are a lot of researches of sloshing for those oil tanks and those nuclear power plants. On the other hand, there are few researches for settling tank in purification plant. Settling tank in purification plant is an important lifeline essential to economy and activity. Therefore, it is necessary to take measures so such kind of damage will not occur again. The purpose of this study is to propose high rate plate settler module with mechanism, which can suppress damage by liquid sloshing and has good repairability. In this paper, we examined that the sloshing occurred by purification plant inclined plates were moved in a long period ground motion. When the inclined plates damaged and falling off, its have became a problem. Therefore, we proposed vibration control devices. Authors performed the sloshing experiment by the miniatures, and investigated the effect of the vibration control devices. Authors carried out the identification of the result based on Housner theory, construction of the analysis model by mass system. Examination of sloshing damage carried out by using the analysis model.

Study on Surface Depression of Ti-6Al-4V with Ultrahigh-Frequency Pulsed Gas Tungsten Arc Welding

Molten pool surface depression was observed with the arc welding process that was caused by arc pressure. It was supposed to have a significant effect on fluid in the molten pool that was important for the microstructure and joint properties. The impact of arc force was recognized as the reason for the surface depression during arc welding. The mathematical distribution of arc force was produced with the exponent and parabola models. Different models showed different concentrations and attenuations. The comparison between them was discussed with the simulation results. The volume of fluid method was picked up with the arc force distribution model. The surface depression was caused by the arc force. The geometry of the surface depression was discussed with liquid metal properties. The welding process was carried out with different pulsed frequencies. The results indicated the forced depression exists in molten pool and the geometry of depression was hugely due to the arc force distribution. The previous work calculated the depression in the center with force balance at one point. The other area of gas shielding was resistant by the reverse gravity from the feedback of liquid metal that was squeezed out. The article discusses the pressure effect with free deformation that allowed resistance of liquid and was easy to compare with different distributions. The curve profiles were studied with the arc force distributions, and exponent model was supposed to be more accurate to the as-weld condition.

Effect of fluid in molten pool on the welds with Ti-6Al-4V during pulsed arc welding

Titanium alloy is one of the most popular materials in engineering applications. Pulsed arc welding can obtain grain refinement of titanium that is a benefit for mechanical properties. However, the study found that the optimized effect decreased with some higher frequencies. Hence, the study of Ti-6Al-4V was carried out with higher-frequency region, and the reason was discussed. The fluid of molten pool had effect on microstructure and mechanical properties of welding joints. Simultaneously, the arc behavior with pulsing current was known as the important factor for the fluid status. Thus, the microstructural morphology, microhardness gradient, and mechanical properties were detected, which were also compared with other frequencies. With high frequency more than 50 kHz, the fluidity of molten pool decreased significantly with low ductility of joints. The mechanism simulation was produced with plane and ellipsoid assumptions, and the results indicated that the conflux caused impact region of double circulation, which was recognized as the main reason for the drops of microstructure and properties with more than 50 kHz.

Direct contact condensation of steam jet in crossflow of water in a vertical pipe. Experimental investigation on condensation regime diagram and jet penetration length

The direct contact condensation of jets in fluid has been of great importance in many industrial applications. Experiments on condensing jets in initially stagnant fluid in pool have increased significantly in sophistication over the last few decades. For condensing jets in crossflow, however, the flow and geometry characteristics of the jet might be fundamentally different due to the complex convection effect induced by the crossflow. Here, experiments are performed to investigate direct contact condensation of steam jet in crossflow of water in a vertical pipe. The condensation regime diagram and jet penetration length are investigated visually by using high-speed camera and image processing methods. The condensation regime diagram mainly contains three kinds of condensation regime, i.e., chugging, condensation oscillation and stable condensation (i.e., stable conical shape, stable cylinder shape and stable expansion shape). The condensation regime is not only affected by steam mass flux and water temperature, but also affected significantly by Reynolds number of water flow. Therefore, condensation regime diagrams for different Reynolds number of water flow are developed. Both the regions of the chugging and condensation oscillation regimes expand slightly towards higher steam mass flux as Reynolds number of water flow increases. The dimensionless jet penetration length from experimental results is found to be in the range of 0.78–6.84. It increases with increase of steam mass flux and water temperature, but decreases with increase of Reynolds number of water flow. Empirical correlation is proposed for predicting the dimensionless jet penetration length depending on three dimensionless parameters, i.e., dimensionless steam mass flux, condensation driving potential and Reynolds number of water flow. The predicted results agree well with experiments and the discrepancies are within ±20%.