Study on the Behavior of a Wetted Area Right After Liquid-Wall Contact in Pool Film Boiling

2000 ◽  
Author(s):  
Hiroyasu Ohtake ◽  
Hiroyuki Satoh ◽  
Yasuo Koizumi
Keyword(s):  
Temperature Fluctuation ◽  
Contact Angles ◽  
Film Boiling ◽  
Vapor Film ◽  
Saturated Water ◽  
Wall Superheat ◽  
Liquid Injection ◽  
Wetted Area ◽  
Superheated Surface ◽  
Liquid Wall

Abstract The behaviors of the rewetting on pool film boiling, focusing on observations of a collapse of a vapor film, a wetted area and a contact angle on a superheated surface were investigated experimentally. Using a U-shaped platinum wire with 2 mm diameter and 140 mm long, pool film-boiling experiments were performed for saturated water at atmospheric pressure. After a stable film-boiling state at a prescribed initial wall temperature was established, saturated water from a nozzle, set above the test wire, was injected on the superheated surface in the stable film-boiling, then artificial rewetting was forced on the superheated surface. During forming the artificial rewetting, the temperature fluctuation right under the liquid injection and the behavior of the rewetting were obtained for the initial wall temperatures of 600, 420, 400 and 300 degree-C, respectively. The present experimental results showed that the propagative collapse of the vapor film occurred when the initial wall superheat was below 300 K. On the other hand, above the initial wall superheat of 320 K, the rewetting declined after liquid injection was finished then film boiling recovered. The temperature was related to the thermodynamic limit of superheat, according to the measured temperature fluctuation during supplying the liquid. The wetted area right after liquid-wall contact and the advancing velocity of the rewetting front increased as the initial wall superheat decreased. The measured angles between the liquid-vapor interfacial line and the heated wall corresponded to dynamic contact angles were close to the dynamic advancing contact-angles in room temperature.

Effect of the Bottom and Top Configurations on Pool Film Boiling Around a Vertical Finite-Length Cylinder

2011 ◽  
Author(s):  
Satoru Momoki ◽  
Kenichi Araki ◽  
Toru Shigechi ◽  
Takashi Yamada ◽  
Kaoru Toyoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Finite Length ◽  
Lateral Surface ◽  
Film Boiling ◽  
Bottom Surface ◽  
Flat Bottom ◽  
Surface Area Ratio ◽  
Test Cylinder ◽  
Saturated Water ◽  
Wall Superheat

The bottom configuration of a vertical finite-length cylinder is an important factor to examine the convective heat transfer by film boiling around a vertical finite-length cylinder, as the vapor generated under the bottom surface grows thicker during flowing upward along the vertical lateral surface and finally leaves the top surface as bubbles. In this study, four types of silver cylinder with a vertical lateral length equal to the diameter of 32mm were prepared for the possible combinations of bottom and top configurations: with a flat bottom and a flat top, with a flat bottom and a curved top, with a curved bottom and a flat top, and with a curved bottom and a curved top, where “flat” refers to “horizontal” and “curved” to “convex hemispherical”. Quenching experiments have been carried out for the test cylinders for saturated and subcooled water at atmospheric pressure. The initial temperature in the measurement is 600 °C. Boiling curves were obtained from the cooling curves measured using a K-type thermocouple inserted near the center on the axis of the test cylinder and the film boiling process was observed by still and high speed video cameras. The following results were obtained from the experiments using four types of test cylinder. 1. For saturated water, the test cylinders are entirely covered with a thick continuous vapor film, however, the effect of bottom configuration on film boiling heat transfer is appeared within 18% in terms of the wall heat flux averaged over the entire surface depending on the vapor fluid flow on the bottom and vertical lateral surfaces. 2. For the cylinders with a flat bottom surface, the wall heat flux averaged over the entire surface increases significantly with an increase in liquid sub cooling. This is attributed to that the convective heat transfer and the surface area ratio on the vertical lateral surface are predominant and govern the total heat transfer. 3. The effects of the cylinder top configurations on the film boiling heat transfer are small as the heat transfer on the top surface is small compared with that on the vertical lateral surface. 4. The differences between film boiling characteristics due to the bottom and top configurations are explained by examining the average heat transfer coefficient composed of the heat transfer coefficient and the surface area ratio on each surface. 5. The minimum wall superheat corresponding to the vapor-film-collapse is almost constant at 133K for four types of test cylinder in saturated water. In subcooled water, the minimum wall superheat for the cylinders with a flat bottom surface is larger than that for the cases with a convex hemispherical bottom surface.

825 Study on the Behavior of a Wetted Area Right after Liquid-Wall Contact in Pool Film Boiling

2001 ◽  
Vol 2001.7 (0) ◽  
pp. 237-238
Author(s):  
Hiroyasu OHTAKE ◽  
Akira MURAKAMI ◽  
Yasuo KOIZUMI
Keyword(s):  
Film Boiling ◽  
Wetted Area ◽  
Liquid Wall

scholarly journals Incipience of the intensive heat transfer regime at cooling high-temperature bodies in subcooled liquid

2021 ◽  
Vol 2057 (1) ◽  
pp. 012049
Author(s):  
P K Kanin ◽  
V V Yagov ◽  
A R Zabirov ◽  
M A Lexin
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Solid Wall ◽  
Longitudinal Velocity ◽  
Vertical Plane ◽  
Film Boiling ◽  
Vapor Film ◽  
Subcooled Liquid ◽  
Wall Superheat ◽  
Good Agreement

Abstract Cooling in film boiling is usually an unwanted process in many technologies due to low intensity of heat transfer. Thus, predicting the solid wall superheat at vapor film destabilization is useful to avoid this phenomenon. In the present paper, two new semi-empirical models for evaluation of the wall superheat at destabilization of vapor film around the metallic body cooled in saturated or in subcooled liquid are proposed. Both models with fitted empirical multipliers are in good agreement with an experimental dataset. To evaluate the contribution of the natural convection in the model for temperature head at cooling in subcooled liquid, a problem about the natural convection near the vapor film, occurring during film boiling along the vertical plane, is numerically solved by means of ANES20XE CFD-code. The computational results of longitudinal velocity are in good agreement with the theoretical velocity of natural convection used in the model.

Subcooled Pool Film Boiling Heat Transfer From Spheres With Superhydrophobic Surfaces: An Experimental Study

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Li-Wu Fan ◽  
Jia-Qi Li ◽  
You-You Su ◽  
Huan-Li Wang ◽  
Ting Ji ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Atmospheric Pressure ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Superhydrophobic Surfaces ◽  
Film Boiling ◽  
Vapor Film ◽  
Wall Superheat ◽  
Static Contact

Pool film boiling was studied by visualized quenching experiments on stainless steel spheres in water at the atmospheric pressure. The surfaces of the spheres were coated to be superhydrophobic (SHB), having a static contact angle greater than 160 deg. Subcooled conditions were concerned parametrically with the subcooling degree being varied from 0 °C (saturated) to 70 °C. It was shown that film boiling is the overwhelming mode of heat transfer during the entire course of quenching as a result of the retention of stable vapor film surrounding the SHB spheres, even at very low wall superheat that normally corresponds to nucleate boiling. Pool boiling heat transfer is enhanced with increasing the subcooling degree, in agreement with the thinning trend of the vapor film thickness. The heat flux enhancement was found to be up to fivefold for the subcooling degree of 70 °C in comparison to the saturated case, at the wall superheat of 200 °C. A modified correlation in the ratio form was proposed to predict pool film boiling heat transfer from spheres as a function of the subcooling degree.

Free Convection Film Boiling Heat Transfer From a Rotating Surface

1992 ◽  
Vol 114 (3) ◽  
pp. 695-702 ◽  
Author(s):  
J. Orozco ◽  
H. Francisco
Keyword(s):  
Free Convection ◽  
Surface Flux ◽  
Film Boiling ◽  
Integral Approach ◽  
Vapor Film ◽  
Experimental Facility ◽  
Layer Model ◽  
Rotating Surface ◽  
Minimum Heat ◽  
Good Agreement

A boundary layer model of laminar, subcooled, free convection film boiling from a rotating sphere has been developed. The conservation equations for the vapor and liquid were simplified, transformed into ordinary differential equations using an integral approach, and solved numerically. The theoretical variation of vapor film thickness with heater temperature and the resulting boiling fluxes were investigated. An experimental facility was built for the purpose of verifying the validity of the theoretical model and good agreement was found between the model and the experimental data at low rpm. The instability of the vapor film near the minimum heat flux for a rotating surface flux was also investigated.

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