scholarly journals Mechanism of Film Boiling Elimination and IQ Process Design for Hardening Steel in Low Concentration of Water Polymer Solutions

2020 ◽  
pp. 39-56
Author(s):  
Nikolai I. Kobasko
Keyword(s):  
Heat Transfer ◽  
Polymer Solutions ◽  
Heat Treating ◽  
Nucleate Boiling ◽  
Steel Part ◽  
Point Of View ◽  
Film Boiling ◽  
Slow Cooling ◽  
Low Concentration ◽  
Boiling Process

The paper considers a mechanism of the elimination of the film boiling process during intensive quenching (IQ) of steel parts in water polymer solutions of low concentration. The use of the IQ process results in improvement of material mechanical properties and steel part performance characteristics. Evaluation of ways of eliminating of the film boiling process using a modern physics point of view allows significant improvement of the IQ equipment making it less costly and more efficient. All of this cardinally simplifies the implementation of the IQ technology in heat treat practice. The paper shows how creation of a thin insulating surface layer during quenching of steel parts in low concentration of inverse solubility polymers results in eliminating of film boiling processes that makes the quench process intensive. Historically in heat treating industry, an effective heat transfer coefficient was widely used for evaluating of the nucleate boiling process. And quenching during the nucleate boiling mode of heat transfer was considered as slow cooling.

scholarly journals Intense Quench Process in Slow Agitated Water Salt and Polymer Solutions

2021 ◽  
Vol 3 (3) ◽  
pp. 6-12
Author(s):  
Nikolai Mykola Kobasko
Keyword(s):  
Polymer Solutions ◽  
Water Solution ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Liquid Media ◽  
Slow Cooling ◽  
Low Concentration ◽  
Boiling Process ◽  
Water Salt

In the paper it is shown that quenching in slow agitated water salt solution of optimal concentration and in low concentration of inverse solubility polymers is intensive quenching creating maximal temperature gradients at the beginning of cooling. The evidence to support such idea were collected by analyzing quenching process in liquid media where any film boiling process was completely absent. In this case, surface temperature at the beginning of cooling drops closely to saturations temperature of a liquid within the interval 1–2 seconds, independently on nature of water solution, and then during transient nucleate boiling process maintains at the level of boiling point of a liquid which is often called self–regulated thermal process. The computer modeling of such cooling processes provided Kondrat’ev numbered Kn which are strongly linear function of time. At the beginning of cooling Kondrat’ev number is almost equal to 1 while average Kondrat’ev number Kn≥0.8. According to US Patent, intensive quenching starts when Kn=0.8. Based on achieved results, it is possible to perform intensive quenching in slow agitated of low concentration water salt and polymer solutions, usually initiated by hydrodynamic emitters. Along with liquid agitation, emitters generate resonance wave effect which destroys film boiling processes making cooling very uniform and intensive. The proposed IQ process works perfectly when martensite starts temperature Ms>Ts. If saturation temperature Ts≥Ms, intensive austempering process via cold liquids can be successfully performed to replace slow cooling of molten salts and alkalis by intensive quenching in liquid media.

scholarly journals INVESTIGATION OF BATCH INTENSIVE QUENCHING PROCESSES WHEN USING HYDRODYNAMIC EMITTERS IN QUENCH TANKS

2016 ◽  
Vol 6 ◽  
pp. 29-36 ◽  
Author(s):  
Nikolai Kobasko
Keyword(s):  
Heat Transfer ◽  
Resonance Effect ◽  
Heat Treating ◽  
Nucleate Boiling ◽  
New Method ◽  
Film Boiling ◽  
Boiling Process ◽  
Part Distortion ◽  
Water Tanks

The paper discusses patented in Ukraine a new intensive quenching IQ–2 technology based on film boiling resonance effect [1]. Namely, the paper discusses improving of the batch intensive quenching (IQ) process known as IQ-2 method by the use of hydrodynamic emitters installed in quench tanks. The hydrodynamic emitters produce oscillating waves in the quench media with the frequency of the film boiling process creating a resonance effect. Two- and three-step IQ-2 processes are considered. Specifics of the heat transfer during the IQ-2 process are presented with focusing on the first stage of quenching where film and nucleate boiling processes are taking place. Examples of production IQ-2 equipment and loads processed are also presented. Application of hydrodynamic emitters in the IQ water tanks in addition to currently used propellers is considered in details. It is shown that the proposed new method can fully eliminate the film boiling process resulting in significant reduction of part distortion during quenching. Further evaluation of the proposed method is needed for its implementation in heat treating practice.

scholarly journals Unusual Phenomenon of Forced Heat Exchange Taking Place during Quenching Silver Probe in Cold Electrolyte

2020 ◽  
pp. 29-37
Author(s):  
Nikolai I. Kobasko
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Short Film ◽  
Contemporary Theory ◽  
Boiling Process ◽  
Unusual Phenomenon ◽  
Electrical Layer ◽  
Careful Investigation ◽  
Very High

It is shown in the paper that forced heat transfer exchange during quenching silver probes in cold electrolytes is explained by periodical replacement of short film boiling process by shock boiling. The frequency of such process is very high that increases cardinally heat transfer exchange. This phenomenon doesn’t fit contemporary theory concerning nucleate boiling processes and needs further careful investigations. The reason for existing periodical process is a double boundary electrical layer where are acting increased electrical forces during quenching in electrolytes. In contrast of quenching steel, silver generates higher heat flux density during quenching; however full film boiling cannot be developed due to presence of high electrical forces in a double electrical layer caused by increased electrical conductivity of silver. The discovered phenomenon can be used in the practice in the future after its careful investigation to force heat transfer exchange by external electrical forces to eliminate any film boiling process during batch quenching.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

Predicting heat extraction due to boiling in the cooling channels during the pressure die casting process

2000 ◽  
Vol 214 (3) ◽  
pp. 465-482 ◽  
Author(s):  
L D Clark ◽  
I Rosindale ◽  
K Davey ◽  
S Hinduja ◽  
P J Dooling
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Die Casting ◽  
Casting Process ◽  
Nucleate Boiling ◽  
Heat Extraction ◽  
Film Boiling ◽  
Cooling Channels ◽  
Die Casting Process ◽  
Pressure Die Casting

The effect of boiling on the rate of heat extraction by cooling channels employed in pressure die casting dies is investigated. The cooling effect of the channels is simulated using a model that accounts for subcooled nucleate boiling and transitional film boiling as well as forced convection. The boiling model provides a continuous relationship between the rate of heat transfer and temperature, and can be applied to surfaces where forced convection, subcooled nucleate boiling and transitional film boiling are taking place in close proximity. The effects of physical parameters such as flow velocity, degree of subcooling, system pressure and bulk temperature are taken into account. Experimental results are obtained using a rig that simulates the pressure die casting process. The results are compared with the model predictions and are found to show good agreement. Instrumented field tests, on an industrial die casting machine, are also reported. These tests show the beneficial effects of boiling heat transfer in the pressure die casting process, including a 75 per cent increase in the production rate for the test component.

An Experimental Study on Cryogenic Spray Quenching of a Circular Metal Disk II. Chilldown Efficiency and Effects of Coating and Flow Pulsing

2021 ◽  
Author(s):  
Jun Dong ◽  
Hao Wang ◽  
Samuel Darr ◽  
Jason Hartwig ◽  
Jacob Chung
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Liquid Nitrogen ◽  
Mass Flow ◽  
Flow Rate ◽  
Continuous Flow ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Teflon Coating ◽  
Bare Surface

Abstract This is the second part of a two-part series that presents the results of liquid nitrogen spray quenching of a Stainless Steel disc. The results of continuous-flow spray chilldown of a bare surface disc are summarized first that serves as the baseline information for evaluating the effects of disc surface coating and pulse flow. We found that for continuous-flow spray chilldown of a bare surface disc, the chilldown efficiency is mainly a function of the average mass flow rate with the trend of decreasing efficiency with increasing mass flow rate. Additional experiments were performed to evaluate the enhancement of cryogenic spray quenching by three techniques: 1. Using intermittent pulse sprays on SS bare surface, 2. Coating the SS surface with a layer of low thermal conductivity Teflon film, and 3. Spraying liquid nitrogen intermittently on the coated SS surface. In general, the results indicate that all three methods effectively produced higher spray thermal efficiencies and reduced liquid nitrogen mass consumption. However, it was also found that the Teflon coating was more effective than the flow pulsing due to that the Teflon coating induced a large surface temperature drop at the beginning of the chilldown that allowed the quenching to move quickly from poor heat transfer film boiling to efficient heat transfer transition and nucleate boiling regimes. This quick transition shortens the film boiling period, thus facilitates the switch to much higher heat transfer transition boiling and nucleate boiling periods earlier to complete the chilldown process faster.

Flow Boiling on Heterogeneous Wetting Surface in a Vertical Narrow Microchannel

2020 ◽  
Author(s):  
Yuhao Lin ◽  
Junye Li ◽  
Kan Zhou ◽  
Wei Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Working Fluid ◽  
Hydrophilic Surface ◽  
Structured Surfaces ◽  
Boiling Process

Abstract The micro structured surfaces have significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. The hydrophobic surface promotes bubble nucleation while the hydrophilic surface supplies liquid to a heating surface, thus there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surface on flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surface was conducted with deionized water as the working fluid. The heat transfer characteristics of flow boiling in the microchannel was studied and the flow pattern was photographed with a high-speed camera. The onset of flow boiling and heat transfer coefficient were discussed with the variation of heatfluxes and mass fluxes, the trends of which were analyzed along with the flow patterns. During the boiling process, the dominated heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes and on the hydrophobic ones. In the meantime, after the merged bubbles were constrained by the channel walls, it would be difficult for them to expand towards upstream since they were restricted by the contact line between hydrophilic/hydrophobic stripes, thereby reduce the flow instability and achieve remarkable heat transfer performance.

Heat transfer coefficients for quenching process simulation

2004 ◽  
Vol 120 ◽  
pp. 269-276
Author(s):  
M. Maniruzzaman ◽  
R. D. Sisson
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Process Simulation ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Quenching Process

Quenching heat treatment in a liquid medium is a very complex heat transfer process. Heat extraction from the part surface occurs through several different heat transfer mechanisms in distinct temperature ranges, namely, film boiling, partial film boiling (i.e. transition), nucleate boiling and convection. The maximum heat transfer occurs during the nucleate boiling stage. Experimental study shows that, the effective surface heat transfer coefficient varies more than two orders of magnitude with the temperature during the quenching. For quenching process simulation, accurate prediction of the time-temperature history and microstructure evolution within the part largely depends on the accuracy of the boundary condition supplied. The heat transfer coefficient is the most important boundary condition for process simulation. This study focuses on creating a database of heat transfer coefficients for various liquid quenchant-metallic alloy combinations through experimentation using three different quench probes. This database is a web-based tool for use in quench process simulation. It provides at-a-glance information for quick and easy analysis and sets the stage for a Decision Support System (DSS) and Data Mining for heat-treating process.

Subcooled Pool Boiling Experiments on Horizontal Heaters Coated With Carbon Nanotubes

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
V. Sathyamurthi ◽  
H-S. Ahn ◽  
D. Banerjee ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Heat Flux ◽  
Pool Boiling ◽  
Type A ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Test Fluid ◽  
Type B ◽  
Coated Surfaces

Pool boiling experiments were conducted with three horizontal, flat, silicon surfaces, two of which were coated with vertically aligned multiwalled carbon nanotubes (MWCNTs). The two wafers were coated with MWCNT of two different thicknesses: 9 μm (Type-A) and 25 μm (Type-B). Experiments were conducted for the nucleate boiling and film boiling regimes for saturated and subcooled conditions with liquid subcooling of 0–30°C using a dielectric fluorocarbon liquid (PF-5060) as test fluid. The pool boiling heat flux data obtained from the bare silicon test surface were used as a base line for all heat transfer comparisons. Type-B MWCNT coatings enhanced the critical heat flux (CHF) in saturated nucleate boiling by 58%. The heat flux at the Leidenfrost point was enhanced by a maximum of ∼150% (i.e., 2.5 times) at 10°C subcooling. Type-A MWCNT enhanced the CHF in nucleate boiling by as much as 62%. Both Type-A MWCNT and bare silicon test surfaces showed similar heat transfer rates (within the bounds of experimental uncertainty) in film boiling. The Leidenfrost points on the boiling curve for Type-A MWCNT occurred at higher wall superheats. The percentage enhancements in the value of heat flux at the CHF condition decreased with an increase in liquid subcooling. However the enhancement in heat flux at the Leidenfrost points for the nanotube coated surfaces increased with liquid subcooling. Significantly higher bubble nucleation rates were observed for both nanotube coated surfaces.

scholarly journals Wetting layer evolution and interfacial heat transfer in water-air spray cooling process of hot metallic surface

2021 ◽  
pp. 318-318
Author(s):  
Lidan Ning ◽  
Liping Zou ◽  
Zhichao Li ◽  
Huiping Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Film Boiling ◽  
Metallic Surface ◽  
Interfacial Heat Transfer Coefficient ◽  
Interfacial Heat Transfer ◽  
Cooling Process ◽  
Inverse Heat Transfer

Spray cooling experiments on the hot metallic surfaces with different initial temperatures were performed. This paper adopts a self-developing program which is based on the inverse heat transfer algorithm to solve the interfacial heat transfer coefficient and heat flux. The temperature-dependent interfacial heat transfer mechanism of water-air spray cooling is explored according to the wetting layer evolution taken by a high-speed camera and the surface cooling curves attained by the inverse heat transfer algorithm. Film boiling, transition boiling, and nucleate boiling stages can be noticed during spray cooling process of hot metallic surface. When the cooled surface?s temperature drops to approximately 369?C - 424?C; the cooling process transfers into the transition boiling stage from the film boiling stage. The wetting regime begins to appear on the cooled surface, the interfacial heat transfer coefficient and heat flux begin to increase significantly. When the cooled surface?s temperature drops to approximately 217?C - 280?C, the cooling process transfers into the nucleate boiling stage. The cooled surface was covered by a liquid film, and the heat flux begins to decrease significantly.

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