Liquid Film Separation Research Articles

GAS-LIQUID FILM DISTRIBUTION AND SEPARATION OF CONDENSATION FROM A DOWNWARD-FLOWING STEAM-NONCONDENSABLE GAS MIXTURE ONTO A HORIZONTAL TUBE AT SUBATMOSPHERIC PRESSURE

Based on the boundary layer, a mathematical model was established to investigate the thicknesses of liquid and gas films and the steam condensate distribution in the presence of noncondensable gas outside a horizontal tube at pressures lower than atmospheric pressure. The model accurately predicts the steam condensation heat transfer with noncondensable gas. The influences of the noncondensable gas mass fraction, pressure, velocity, and surface subcooling upon the condensation heat transfer, the thicknesses of liquid and gas films, and condensate distribution around the horizontal tube have been studied. The liquid film thickness rises as the surface subcooling raises but reduces with raising pressure and mass fraction of noncondensable gas. The gas film thickness rises with rising surface subcooling and noncondensable gas mass fraction, reducing as the pressure rises. The thicknesses of gas and liquid films and condensate distribution significantly affect the local heat transfer. The liquid film separation velocity reduces with raising pressure, surface subcooling, and mass fraction of noncondensable gas, which is most influenced by pressure.

Influence of Surface Preparation on Cracking Phenomena in TIG-Welded High and Medium Entropy Alloys

Multi-element systems with defined entropy (HEA—high entropy alloy or MEA—medium entropy alloy) are rather new material concepts that are becoming increasingly important in materials research and development. Some HEA systems show significantly improved properties or combinations of properties, e.g., the overcoming of the trade-off between high strength and ductility. Thus, the synthesis, the resulting microstructures, and properties of HEA have been primarily investigated so far. In addition, processing is crucial to achieve a transfer of potential HEA/MEA materials to real applications, e.g., highly stressed components. Since fusion welding is the most important joining process for metals, it is of vital importance to investigate the weldability of these materials. However, this has rarely been the subject of research to date. For that reason, in this work, the weldability depending on the surface preparation of a CoCrFeMnNi HEA and a CoCrNi MEA for TIG welding is investigated. The fusion welding of longer plates is described here for the first time for the CoCrNi alloy. The welds of both materials showed distinct formation of cracks in the heat affected zone (HAZ). Optical and scanning electron microscopy analysis clearly confirmed an intergranular fracture topography. However, based on the results, the crack mechanism cannot be conclusively identified as either a liquid metal embrittlement (LME) or hot cracking-like liquid film separation.

Experimental investigations on atomization characteristics of dual-orifice atomizers part I: Optimization method formation

In this paper, influences of structure parameters on mass flow and atomization characteristics (spray cone angle, SMD, liquid film fusion and separation) of dual-orifice atomizers were investigated using Fraunhofer diffraction optical instrument and high-speed shadowgraph technique. The main influential structure parameters are obtained by structural parameter sensitivity analysis. Liquid film fusion and separation is an important atomization characteristic lacking of in-depth research. Results of liquid film fusion and separation illustrate that three patterns (separation-fusion-secondary separation) of main stage liquid film and pilot stage liquid film appear with the increase of Δ P. Liquid film fusion makes SMD larger, and there is a delay in liquid film separation when reduce Δ P after liquid film fusion. In addition, mass flow and spray cone angle are key factors which affect liquid film fusion pressure, liquid film secondary separation pressure and distance between two liquid films. The smaller the pilot stage mass flow is, the larger the effect of the main stage on pilot stage spray cone angle will be. Results in this paper could be used to the design and optimization of new dual-orifice atomizers.

Numerical and experimental study of spray impingement and liquid film separation during the spray/wall interaction at expanding corners

The liquid film separation at expanding corners during the spray/wall interaction is usually encountered in internal combustion engines, which has significant influence on the fuel/air mixing and combustion processes, and consequently the engine-out emissions. However, fundamental investigations on the film separation during the spray/wall interaction at expanding corners are very limited, especially under the relevant operating conditions of engines. In the present study, a new film separation and atomization model was proposed, including the sub-models of film separation criterion, film separation mass ratio, and the film atomization model derived from the Rayleigh-Taylor instability theory. By implementing the proposed model into a computational fluid dynamics (CFD) code, the reliability of the new model was validated by the experimental measurements conducted in this study. The results indicate that the effects of the injection pressure, impingement distance, and corner angle of the expanding corner on the evolution of the impinging spray and the wall film dynamics after the corners are satisfactorily reproduced by the present model. Moreover, the predicted size distribution of the detached droplets formed by the film separation is in good agreement with the measurement. It is also found that the expanding corner angle remarkably affects the impinging spray structure and the film separation characteristics, and the predictions of the new film separation model agrees better with the measurements than the previous model.

Effect of nanotextured array of conical features on explosive boiling over a flat substrate: A nonequilibrium molecular dynamics study

Nonequilibrium molecular dynamics simulations were performed to investigate the effects of size of nanocone array and types of wall material, i.e., aluminum and silver, on the explosive boiling of ultra-thin liquid argon film on nanostructure. An Embedded Atom Method (EAM) potential is used in describing the interatomic interaction between metal atoms. The results showed that the cone-like nanostructures drastically enhance heat transfer from solid to liquid and they have significant effects on temperature and pressure histories, net evaporation number, as well as the density distribution in the system. In all cases studied, the liquid molecules above the solid surface go into explosive boiling and a cluster of liquid is observed to move upward. It was also observed that the separation temperature associated with separation of liquid film from solid surface strongly depends on size of nanostructure while it is not sensitive to the type of materials. Furthermore, in all cases in a specific time after beginning of boiling, the evaporation on the hot wall stopped and a non-evaporating layer will form on the surface.

Characteristics of Liquid Film Flowing around Side Wall of a Horizontal Circular Cylinder (Separation of Liquid Film)

Characteristics of Liquid Film Flowing around Side Wall of a Horizontal Circular Cylinder (Separation of Liquid Film)

Solidification crack susceptibility of aluminum alloy weld metals

AbstractThe susceptibilities of the three aluminum alloys to solidification crack were studied with trans-varestraint tests and tensile tests at elevated temperature. Their metallurgical characteristics, morphologies of the fractured surface and dynamic cracking behaviors at elevated temperature were analyzed with a series of micro-analysis methods. The results show that dynamic cracking models can be classified into three types. The first model has the healing effect which is called type A. The second is the one with deformation and breaking down of metal bridge, called type B. The last one is with the separation of liquid film along grain boundary, called type C. Moreover, the strain rate has different effects on crack susceptibility of aluminum alloys with different cracking models. ZL101 and 5083 alloys belong to type A and type C cracking model respectively, in which strain rate has greater effect on eutectic healing and plastic deformation of metal bridge. 6082 alloy is type B cracking model in which the strain rate has little effect on the deformation ability of the liquid film.

Characteristics of Liquid Film Flowing around Side Wall of a Horizontal Circular Cylinder (Separation of Liquid Film)

A standing wave with a peak line toward downstream appears on the surface of a liquid film flowing around a horizontal circular cylinder. The amplitude of the wave grows in the downward direction and finally a part of the wave separates from the film at certain position on the cylinder. A theoretical model was proposed to explain the physical mechanism of separation. The wave peak would separate when the resultant of the centrifugal force, gravitational force, surface tension and negative pressure acting on the wave root is not sufficient to supply the flow rate necessary to maintain the wave amplification. The points of separation on the cylinder were theoretically calculated from the above condition for three kinds of test liquids, i. e., water, ethanol and glycerin solutions. The results agree with those from experiments for various flow rates of the film flow.

Critical heat flux and exit film flow rate in a flow boiling system

Critical heat flux and liquid film flow rate at exit end of the test tube are measured with Freon 113 upward flow in a uniformly heated tube. The exit film flow rate at the critical heat flux condition is near to zero in all cases of the exit qualities higher than 50%, however, the exit film flow rate tends to increase as the heat flux is increased and the exit quality decreases less than 50%. A correlation is proposed for the critical condition with high heat fluxes, suggesting that the liquid film separation from the heated surface by vapor generation takes an important part of the critical phenomenon.