Mist Jet Research Articles

Experimental study of a water-mist jet issuing normal to a heated flat plate

A parametric experimental study on the development of a round jet spray impacting a smooth, heated, flat plate has been accomplished. The main objective of this effort was to provide information characterizing the flow structure of a developing mist jet, issuing vertically towards an upward facing, horizontal heated plate, by means of simultaneous droplet size and velocity measurements. Phase Doppler Anemometry was used, providing also information on liquid volume flux. The fine spray of small atomized droplets (0.5-5.0 μm), was generated using a medical nebulizer. Two low Reynolds number jets (Re=2952, 3773) issuing from a cylindrical pipe have been tested. The distance between the jets’ exit and the plate was 50 cm. A stainless steel non-magnetic flat plate of dimensions 1000x500x12mm3 was used as target wall. Constant heat flux boundary conditions were established during measurements. Results indicate that the heat flux from the plate is influencing the evolution of the spray jet, diminishing its velocity and turbulence. Average droplet sizes are affected little by the heat flux, although for the non-heated sprays, droplet sizes increase at locations very close to the plate. A significant effect on droplet volume flow rate is also reported.

RANS modeling of flow structure and turbulent heat transfer in pulsed gas-droplet mist jet impingement

The turbulent flow structure and heat transfer of a pulsed gas-droplet impinging mist jet with low mass fraction of droplets (not more than 2%) are numerically carried out. A set of non-steady-state RANS equations for the two-phase flow is utilized. The dispersed phase is modeled by the Eulerian approach. Gas turbulence is computed with the Reynolds stress model for two-phase flow. The interaction between phases (two-way coupling) is considered by the addition of extra terms in equations for the mean and fluctuating motion. The effects of pulse frequencies, ratio of on time to total cycle time, distances between pipe outlet and impinging flat plate and Reynolds number on heat transfer are numerically studied. It is shown that both the increase (up to 45%) and the suppression (up to 25%) of heat transfer are characteristic of pulsed gas-droplet jet impingement, differently from the steady-state one. Reduced heat transfer in comparison with the steady-state impinging jet is typically in the low frequency range. The impingement heat transfer initially increases with distance from the pipe edge and target surface and the heat transfer decreases at distance from the pipe edge and flat plate.

급속 열처리 시스템을 위한 물/공기 액적류 충돌 제트의 냉각 특성에 관한 연구

ABSTRACT In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.KeyWords : Mist Flow( ), Jet Impinging( ), Hot Plate( ), Mist-jet Cooling Map액적류 충돌 제트 고온 평판 (액적충돌기준선도) # Corresponding Author : jklee99@kyungnam.ac.kr Tel: +82-55-249-2613, Fax: +82-55-249-2617

Tool wear in milling Ti40 burn-resistant titanium alloy using pneumatic mist jet impinging cooling

Ti40 burn-resistant titanium alloy (Ti-25V-15Cr-0.2Si) is used to manufacture key components in aero-engines owing to its outstanding burn resistant and mechanical properties. However, Ti40 alloy has poor machinability due to its high-temperature strength and low thermal conductivity. Pneumatic mist jet impinging cooling (PMJIC) is a high-efficiency cooling/lubrication technology, which could reduce tool wear and improve production efficiency during cutting titanium alloys. This paper investigates the cooling effect of PMJIC during milling Ti40 alloy using Ti(C,N)–Al2O3 coated cemented carbide tools. The tool wear behavior and mechanisms were studied. Results obtained show that, in comparison to the traditional flood cooling (TFC), PMJIC lowers cutting temperature and tool wear rate; improvement in both tool life and material removal volume (MRV) is obtained for PMJIC. Abrasion and adhesion are the dominant wear mechanisms during the wear of cutting tools. Notch wear, micro chipping, coating delamination and fatigue cracks are the main failure modes. The tool wear is reduced significantly for PMJIC during milling Ti40 alloy.

Rewetting of a hot horizontal surface through mist jet impingement cooling

An experimental investigation has been carried out to study the rewetting behaviour of a hot horizontal stainless steel surface during the mist jet impingement cooling. The experiments have been performed to study the rewetting behaviour for three different initial surface temperatures viz. 255, 355, 565°C. An axis-symmetric nozzle has been used to develop the mist jet of constant flow rate. The variation in surface temperature has been acquired up to 20mm downstream spatial locations away from the stagnation point. It has been observed that unlike liquid jet impingement cooling the rise in surface initial temperature increases the rewetting temperature and the wetting delay increase with rise in the initial surface temperature but the rewetting velocity reduces. Further, the maximum surface heat flux is the highest at 20mm spatial location for 565°C initial surface temperature. Whereas, at the stagnation point, the maximum surface heat flux is not affected by the change in surface initial temperature.

Heat transfer and flow in an atomizing mist jet: a combined hot film and shadowgraph imaging approach

This paper presents research in the area of heat transfer and fluid dynamics in an impinging atomizing air/water mist jet. Time averaged and fluctuating local surface heat transfer results obtained by microfoil and hot film sensors are correlated with flow field measurements of droplet diameter and velocity obtained by shadowgraph imaging and droplet tracking velocimetry. This paper seeks to understand the linkage between the atomization process in the nozzle, the two-phase flow dynamics and the surface heat transfer characteristics.

The effect of confinement on the flow and turbulent heat transfer in a mist impinging jet

Numerical study of the effect of confinement on a flow structure and heat transfer in an impinging mist jets with low mass fraction of droplets ( M L 1 ⩽ 1%) were presented. The turbulent mist jet is issued from a pipe and strikes into the center of the flat heated plate. Mathematical model is based on the steady-state RANS equations for the two-phase flow in Euler/Euler approach. Predictions were performed for the distances between the nozzle and the target plate x/(2 R) = 0.5–10 and the initial droplets size ( d 1 = 5–100 μm) at the varied Reynolds number based on the nozzle diameter, Re = (1.3–8) × 10 4. Addition of droplets causes significant increase of heat transfer intensity in the vicinity of the jet stagnation point compared with the one-phase air impinging jet. The presence of the confinement upper surface decreases the wall friction and heat transfer rate, but the change of friction and heat transfer coefficients in the stagnation point is insignificant. The effect of confinement on the heat transfer is observed only in very small nozzle-to-plate distances ( H/(2 R) < 0.5) both in single-phase and mist impinging jets.

Experimental study on turning of TC9 titanium alloy with cold water mist jet cooling

Titanium alloys, as difficult-to-cut materials, have poor machinability due to their superior mechanical properties, heat resistance and corrosion resistance. High cutting temperature that will greatly accelerate tool wear often occurs in titanium alloy cutting process. In this paper, cold water mist jet (CWMJ) cooling method, an eco-friendly cooling method, was used to obtain a lower cutting temperature during TC9 titanium alloy turning process. The effects of CWMJ were mainly discussed as compared with cold air jet and flood cooling methods. A comprehensive evaluation on the cooling effects of CWMJ was carried out by hydrodynamic tests, heat transfer tests and turning tests, respectively. Experimental results indicated that CWMJ had better cooling effects as compared with other two cooling methods. Cutting temperature was greatly reduced, and tool life was improved with CWMJ during TC9 turning process. Machined surface quality and chip morphology were also acceptable.

Enhancement of turbulent heat transfer during interaction of an impinging axisymmetric mist jet with a target

The flow structure and heat transfer of a mist jet with a low mass concentration of droplets (within 1%) impinging onto a flat surface aligned normal to the jet are studied numerically. The mathematical model is based on solving a system of Reynolds-averaged Navier-Stokes equations for a two-phase flow with the kinetic equation of the probability density function for coordinates, velocity, and temperature of particles. Addition of droplets is demonstrated to enhance heat transfer substantially, as compared with an impinging single-phase air jet in the region directly adjacent to the stagnation point of the jet.

Study on Flame Expansion Phenomenon in Pool Fire Extinguished by Water Mist

The theoretical and experimental studies on the phenomenon of flame expansion in pool fire extinguishment with water mist are presented in the paper. Firstly, the theoretical analysis on fire expansion phenomenon is made. It's found that, both the interaction of water mist with flame and hot fuel lead to the flame expansion phenomenon in liquid pool fire extinguishment with water mist. The impacting on fuel vapor by water mist jet flow, which corresponding to the interaction of water mist and flame, and the azeotropic effects, which corresponding to the interaction of water mist and hot fuel, are these two kinds of root causes for fire expansion phenomenon. And the theoretical analysis also indicates that the flame characteristics, the interaction of water mist and pool fire, the momentum of water mist are the key factors to leading to an expanded fire. Then, three groups of experiments are set to study the above factors. The experimental results show that the impacting effects of the water mist jet flow to fuel vapor and the azeotropic effects of the mixtures of water and hot fuel are the main causes for fire expanding. And the flame characteristics, the momentum of water mist are important to the size of expanded fire. The existence of a certain amount of fuel vapor in the fuel vapor rich core of pool fire and the impacting of water mist with adequately large momentum are the prerequisites for fire expansion. It's also found in the experiments that the fire expansion start from the bottom of the pool fire and not much related to the far-end of the flame. The experimental results indicate that the theoretical analysis are fit the fire expansion phenomenon well.

A new technology on enhancing heat transfer during grinding of titanium alloy

Purpose – Grinding may generate high temperature along the arc of grinding zone, especially during the grinding process of difficult‐to‐machine materials. It can cause thermal damage to the ground surface and poor surface integrity. Conventional cooling methods based on large amounts of water‐oil emulsions can be both ineffective and environmentally unacceptable. The purpose of this paper is to offer a new high efficiency cooling method – cryogenic pneumatic mist jet cooling (CPMJ) to enhance heat transfer in the grinding zone during grinding of difficult‐to‐machine materials.Design/methodology/approach – CPMJ equipment is a set up, which can produce water mist of −5°C with jet velocity above 150 m/s and mean particle size below 20 μm at the impingement distance of 10‐40 mm on the symmetry axis. To validate the cooling efficiency of CPMJ equipment, heat transfer experiments were carrying out on it. Finally, CPMJ was applied to the grinding of titanium alloy to verify its cooling effects.Findings – With hi...

Enhancement of an impingement heat transfer between turbulent mist jet and flat surface

The work presents the results of numerical investigation of the flow structure and heat transfer of impact mist jet with low concentration of droplets ( M L 1 ⩽ 1%). The downward gas-droplets jet issued from a pipe and strikes into at a center of the circular target wall. Mathematical model is based in the solution to RANS equations for the two-phase flow in Euler approximation. For the calculation of the fluctuation characteristics of the dispersed phase equations of Zaichik et al. (1997) [35] model were applied. Predictions were performed for the distances between the nozzle and target plate x/(2 R) = 1–10 and the initial droplets size ( d 1 = 5–100 μm) at the fixed Reynolds number based on the nozzle diameter, Re = 26,600. Addition of droplets causes significant increase of heat transfer intensity in the vicinity of the jet stagnation point compared with the one-phase air impact jet.

The Theoretical Analysis and Experimental Study on Heat-Transfer in Cryogenic Pneumatic Mist Jet Cooling

Based on the pool film boiling, the paper discusses the heat transfer coefficient of fogdrop jet into cutting zone to cool high temperature wall and then founds the model. It can be concluded by transient test in cryogenic pneumatic mist jet cooling high temperature titanium surface with different water flow, that when reaching the best cooling effect, the water flow of cryogenic pneumatic mist jet cooling as well as the materials vaporizing and involving phase change heat-transfer under certain temperature must be equivalent, and at that time, the heat transfer coefficient of cryogenic pneumatic mist jet cooling will reach the maximum.

Effectiveness of the Swirl Mist Jet Method to Remove Spider Mites on the Surface of Apples

Effectiveness of the Swirl Mist Jet Method to Remove Spider Mites on the Surface of Apples

Belt Grinding of TC4 Based on the Technology of Cryogenic Mist Jet Combined MQL

To solve the problems of the reduces in belt life、low in metal removal rate and environmental pollution by using conventional grinding fluid, a new high efficiency and green cooling technology—— The Technology Of Liquid Nitrogen Cryogenic Wind Jet Combined MQL(LNCWJCM), It was used in belt grinding of TC4. The effect of LNCWJCM on grinding performance of TC4 was analyzed to compare with cold air 、liquid nitrogen and conventional flood cooling method. The experimental results indicate that LNCWJCM can improve metal removal rate and the life of belt, in addition , impacting on abrasive belt grinding from which the flow of liquid nitrogen, grinding temperature, the flow of oil droplets and other key parameters is studied.

Experimental Research on the Cooling Effects of a New High Efficiency Green Cooling Method

With more attention paying to the environment, green manufacturing (GM) has become inevitable trends in 21st century. Green cooling technology as one branch of GM always was one research hotspot in manufacturing. In this paper, a new high efficiency cooling technology based on GM is proposed, called as CPMJ. In this technology, a little quantity of 0 °C water is carried by high pressure cryogenic air (–20 °C) and reaches the grinding zone in the form of high speed mist jet to enhance heat transfer and gain the best cooling effect. Heat transfer experiments and grinding experiments were carried out to evaluate the cooling effects of CPMJ. Experimental results indicated that CPMJ can offer better cooling effects compared with cold air jet and flood cooling method. Grinding temperature was effectively reduced during grinding of titanium alloys with CPMJ.

Experimental study on the cooling effects of cryogenic pneumatic mist jet impinging cooling method

Grinding, characterised by its high specific energy consumption, may generate high grinding zone temperature. These can cause thermal damage to the ground surface and poor surface integrity, especially in the grinding of difficult-to-machine materials. Conventional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. Here a new high efficiency cooling technology – Cryogenic Pneumatic Mist Jet Impinging (CPMJI) cooling technology is offered. It utilises the high penetrative power of fast cryogenic air jet combined with a little quantity of water of 0°C to greatly improve heat transfer effects in the machining zone. Experimental results, including heat transfer experiments and grinding experiments, indicate that CPMJI has strong cooling ability and can offer better cooling effects compared to cold air jet and traditional flood cooling method in the grinding of titanium alloy.

Research on Cryogenic Pneumatic Mist Jet Impinging Cooling and Lubricating of Grinding Processes

Grinding, characterized by its high specific energy consumption, may generate high grinding zone temperature. These can cause thermal damage to the ground surface and poor surface integrity, especially in the grinding of difficult-to-machine materials. Conventional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. Here a new high efficiency cooling technology—cryogenic pneumatic mist jet impinging cooling technology is offered. It utilizes the high penetrative power of fast cryogenic air jet combined with a little quantity of 0°C water to greatly improve heat transfer effects in the machining zone. The experimental results indicated that CPMJI could offer better machining effects compared to cold air jet and traditional flood cooling method in the grinding of titanium alloy.

The Application of Cryogenic Pneumatic Mist Jet Impinging in High-Speed Milling of Ti-6Al-4V

To solve the problems caused by high temperature in the cutting zone during high-speed milling of Titanium alloys, some cooling methods are employed, such as cold air cooling, high pressure coolant jet impinging, MQL, etc. But all have their shortfalls, both in cooling efficiency and environmental pollution. Here a new high efficiency cooling technology-cryogenic pneumatic mist jet impinging (CPMJI) cooling technology is offered. In this technology, a little quantity of coolant is carried by high pressure cryogenic air (-20) and reaches the machining zone in the form of mist jet. This paper mainly focuses on the cooling effects of CPMJI in high-speed milling of Titanium alloy Ti-6Al-4V, as compared with dry, cold air cooling and MQL conditions. CPMJI greatly reduced the temperature in cutting zone and flank wear of tool.

The Cooling Effects of Cryogenic Pneumatic Mist Jet Impinging in Grinding of Titanium Alloy

Grinding is inherently characterized by high specific energy requirements, a high grinding zone temperature. Many methods have been employed in grinding high grinding zone temperature. But all have their shortfalls, both in cooling environmental pollution. Here a new high efficiency cooling technology—cryogenic mist jet impinging (CPMJI) cooling technology is offered. In this technology, coolant is carried by high-pressure cryogenic air (–20°C) and reaches the machining form of mist jet to enhance heat transfer in machining zone. This paper mainly cooling effects of CPMJI in surface grinding, compared with grinding with compressed flood cooling. CPMJI seems to have better effects than other cooling methods.