scholarly journals The pulsating nature of bubble boiling of subcooled water flow during cooling of a metal heater

2021 ◽  
Vol 321 ◽  
pp. 01013
Author(s):  
Levin A.A
Keyword(s):  
Water Flow ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Annular Channel ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Quantitative Prediction ◽  
Subcooled Water ◽  
Interphase Interactions ◽  
Temperature Levels

This paper presents the results of an experimental study of the subcooled water flow boiling on the surface of a metal rod 12 mm in diameter. As a result of the rapid heat release that occurs when an electric current is pulsed through a metal heater, the latter reaches certain temperature levels above the saturation temperature of water at the corresponding pressure (p = 0.17 MPa). In a system formed by a cold liquid and a heated solid body, the process of intense heat exchange begins, the cooling rate of the metal in which reaches its maximum when the nucleate boiling is realized. Interest in such scenarios is remaining high and is caused by the need for quantitative prediction of the characteristics of nucleate boiling and the existence boundaries of this boiling mode. As well-known, nucleate boiling is limited from above by the onset of film boiling and from below by the required surface temperature for which a significant number of nucleation centers are activated. The pressure waves arising during film boiling have a significant amplitude, as a result of which special conditions of interphase interactions may occur. The results of the study showed that self-oscillating pressure pulsations may occur which is associated with the nucleate boiling in an annular channel.

Non-Linear Characteristics of Subcooled Water Flow Boiling CHFS Versus Outlet Subcoolings for Flow Velocities at Pressures in Various Tubes

2008 ◽  
Author(s):  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Flow Velocity ◽  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Twisted Tape ◽  
Outlet Pressure ◽  
Subcooled Water ◽  
Twisted Tapes ◽  
Non Linear ◽  
Bare Tube

Non-linear characteristics of the subcooled water flow boiling CHF versus outlet subcooling for a flow velocity with outlet pressure as a parameter in a horizontal or vertical tube with a twisted tape having flowing subcooled water was clarified using the existing databases expanding quite recently derived the CHF correlations based on two CHF mechanisms for the bare tubes with various inside diameters and length-to-diameter ratios for a flow velocity with outlet pressure as a parameter. The databases were applied measured using, the horizontal tubes with inside diameters of 8 and 12 mm, having length-to-diameter ratios of 6.25 and 4.17 respectively with twisted-tapes having a twist ratio of 2.0, for flow velocities of 7 and 10 m/s, at pressures ranging from 0.2 to 1.1 MPa. The nonlinear characteristics of subcooled water flow boiling CHFs for outlet subcoolings in the tubes having helically coiled 1 mm diameter wires of the coil pitches of 12, 24 and 36 mm, with flowing subcooled water of a flow velocity of 7 m/s at outlet pressures of 0.2, 0.3 and 1.1 MPa were investigated based on the subcooled water flow boiling CHF correlations for bare tubes previously derived. The following results were derived that (1) the non-linear characteristic of CHF versus outlet subcooling, for a horizontal or vertical tube having a twisted tape, divided into three regions for middle, transition, and high outlet subcooling was clarified. The characteristics were similar to that for a identical bare tube, with higher CHF values for middle and high outlet subcooling values respectively, and (2) the enhanced CHF values for middle and high outlet subcooling values being dependent on outlet pressuret and being independent of one respectively, were described by the same CHF correlations derived for a identical bare tube, with higher coefficients of the correlations depending on the tubes with twisted tapes of twist ratios.

scholarly journals Critical Heat Fluxes of Subcooled Water Flow Boiling against Inlet Subcooling in Short Vertical Tube

2004 ◽  
Vol 47 (2) ◽  
pp. 306-315 ◽  
Author(s):  
Koichi HATA ◽  
Hirokazu KOMORI ◽  
Masahiro SHIOTSU ◽  
Nobuaki NODA
Keyword(s):  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Heat Fluxes ◽  
Subcooled Water

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.

Modeling of Film Boiling and Film Vaporization on Engine Piston Tops

2012 ◽  
Author(s):  
Timothy H. Lee ◽  
Dimitrios C. Kyritsis ◽  
Chia-fon F. Lee
Keyword(s):  
Heat Flux ◽  
Liquid Fuel ◽  
Combustion Process ◽  
Infinite Plate ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Spark Ignition Engine ◽  
Film Boiling ◽  
Engine Fuel ◽  
Boiling Regime

Engine-out HC emissions resulting from liquid fuel, which escapes from the combustion process, provides the motivation to better understand the film vaporization in a combustion chamber. Previous work theorized that the removal of liquid fuel from the combustion cycle was a result of the increase in film vaporization time due to the Leidenfrost phenomenon. Currently, KIVA 3V predicts a continuous decrease in vaporization time for piston top films. The objective of this work is to improve the KIVA 3V film vaporization model through the inclusion of established boiling correlations, and thus, the Leidenfrost phenomenon. Experimental results have been reviewed from which expressions encompassing high acceleration effects for the nucleate boiling regime and the film boiling regime were investigated, implemented, and validated. Validation was conducted using published experimental data sets for boiling heat flux. As a result of the implementation, a noticeable increase in heat flux occurred due to high accelerations for films in saturated film boiling in both nucleate and film boiling. Computational simulations were conducted using a semi-infinite plate and a direct-injection spark-ignition engine. The semi-infinite plate provided a controlled environment which could separate the effects of pressure and acceleration on film boiling heat flux, film vaporization rates, and film vaporization times. The effect of decreased film vaporization rates, during the Leidenfrost phenomenon, was observed to decrease with increasing acceleration. Finally, the engine computations were used to provide the first film boiling and film vaporization rates for engine fuel films at temperatures above saturation temperature. As a result of this work, a film vaporization model capable of improved prediction of vaporization rates of piston top films in saturated boiling conditions has been created.

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