Critical Heat Flux for Nearly Saturated Water Flowing Normal to a Cylinder

1964 ◽  
Vol 86 (1) ◽  
pp. 59-66 ◽  
Author(s):  
G. C. Vliet ◽  
G. Leppert
Keyword(s):  
Heat Flux ◽  
Atmospheric Pressure ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Companion Paper ◽  
Critical Flux ◽  
Steel Wires ◽  
Saturated Water ◽  
Peak Flux ◽  
Heater Wall

Visual and photographic observations are used to construct a physical model of the mechanism of transition from nucleate to film boiling on a cylindrical heater. In this paper, interest is focused on forced-convection boiling of a liquid which is near its saturation temperature, while a companion paper deals with the effects of various degrees of liquid subcooling on the peak flux. An approximate analysis is presented of the saturated nucleate-boiling model which predicts the critical flux, and comparisons are made with experimental observations. Measurements of the peak nucleate-boiling heat flux are reported for water at atmospheric pressure over a velocity range of 1.2 to 9.5 feet per second. Resistively heated, stainless-steel wires and tubes of 0.010 to 0.189-inch diameter, the latter with wall thicknesses of 0.006 to 0.028 in., were used. Within these ranges of variables, the critical flux is found to increase with the square root of the velocity and to be independent of heater wall thickness. Only a weak dependence on the heater diameter is observable, but the tendency is for the peak flux to diminish for larger tubes.

Critical Heat Flux for Subcooled Water Flowing Normal to a Cylinder

1964 ◽  
Vol 86 (1) ◽  
pp. 68-74 ◽  
Author(s):  
G. C. Vliet ◽  
G. Leppert
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Atmospheric Pressure ◽  
Marked Effect ◽  
Fractional Power ◽  
Nucleate Boiling ◽  
Water Velocity ◽  
Critical Flux ◽  
Vapor Cavity ◽  
Saturated Water

Empirical data are presented which show the effects of diameter, water velocity, and subcooling on the critical heat flux from an electrically heated, cylindrical lube or wire. The maximum flux which can be accommodated in subcooled nucleate boiling is found to vary directly with the water velocity and subcooling and inversely with a fractional power of the heater diameter. The exponent which describes the diameter dependence is itself a function of both velocity and subcooling. Measurements of the critical flux are reported for water at atmospheric pressure over a range of subcooling from 3 to 100 deg F, velocity from 0.5 to 11 ft/sec, and heater diameter from 0.010 to 0.189 in. Visual and photographic observations indicate a marked effect of subcooling on the flow mechanism near the critical heat flux. High subcooling prevents the formation of the vapor cavity which was described in the previous paper [1] for nearly saturated water, although the failure of nucleate boiling still occurs at the rear of the cylinder and is accompanied by a concentration of vapor in that region.

Evaporation and Nucleate Boiling of an Individual Droplet on Surfaces

2005 ◽  
Author(s):  
X. D. Wang ◽  
G. Lu ◽  
X. F. Peng ◽  
B. X. Wang
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Imaging System ◽  
Dynamical Behavior ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Dynamical Process ◽  
Boiling Regime ◽  
Film Evaporation

A visual study was conducted to investigate the evaporation and nucleate boiling of a water droplet on heated copper, aluminum, or stainless surfaces with temperature ranging from 50°C to 112°C. Using a high-speed video imaging system, the dynamical process of the evaporation of a droplet was recoded to measure the transient variation of its diameter, height, and contact angle. When the contact temperature was lower than the saturation temperature, the evaporation was in film evaporation regime, and the evaporation could be divided into two stages. When the surface temperature was higher than the saturation temperature, the nucleate boiling was observed. The dynamical behavior of nucleation, bubble dynamics droplet were detail observed and discussed. The linear relationships of the average heat flux vs. temperature of the heated surfaces were found to hold for both the film evaporation regime and nucleate boiling regime. The different slopes indicated their heat transfer mechanism was distinct, the heat flux decreased in the nucleate boiling regime more rapidly than in the film evaporation due to the strong interaction between the bubbles.

Simple Model of Boiling Heat Transfer on Tubes in Large Pools

1997 ◽  
Vol 119 (2) ◽  
pp. 376-379 ◽  
Author(s):  
Y. Parlatan ◽  
U. S. Rohatgi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Exchanger ◽  
Atmospheric Pressure ◽  
Boiling Heat Transfer ◽  
Saturation Temperature ◽  
Flow Dynamics ◽  
Simple Method ◽  
Vertical Tubes

A simple method has been developed to model boiling heat transfer from a heat exchanger to pools using the experimental data available in the literature without modeling the flow dynamics of the pool. In this approach the heat flux outside vertical tubes is expressed as a function of outside wall temperature of the tubes and saturation temperature of the pool at or near atmospheric pressure.

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.

Effect of Velocity on Heat Transfer to Boiling Freon-113

1980 ◽  
Vol 102 (1) ◽  
pp. 26-31 ◽  
Author(s):  
Salim Yilmaz ◽  
J. W. Westwater
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Film Boiling ◽  
Square Root ◽  
Peak Heat Flux

Measurements were made of the heat transfer to Freon-113 at near atmospheric pressure, boiling outside a 6.5 mm dia horizontal steam-heated copper tube. Tests included pool boiling and also forced flow vertically upward at uelocities of 2.4, 4.0 and 6.8 m/s. The metal-to-liquid ΔT ranged from 13 to 125° C, resulting in nucleate, transition, and film boiling. The boiling curves for different velocities did not intersect or overlap, contrary to some prior investigators. The peak heat flux was proportional to the square root of velocity, agreeing with the Vliet-Leppert correlation, but disagreeing with the Lienhard-Eichhorn prediction of an exponent of 0.33. The forced-flow nucleate boiling data were well correlated by Rohsenow’s equation, except at high heat fluxes. Heat fluxes in film boiling were proportional to velocity to the exponent 0.56, close to the 0.50 value given by Bromley, LeRoy, and Robbers. Transition boiling was very sensitive to velocity; at a ΔT of 55° C the heat flux was 900 percent higher for a velocity of 2.4 m/s than for zero velocity.

Parametric Effects of Heater Size, Contact Angle, and Surrounding Vessel Size On Pool Boiling Critical Heat Flux From Horizontal Surfaces

2021 ◽  
Author(s):  
Zhenyu She ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Nucleate Boiling ◽  
Flat Plates ◽  
Vessel Size ◽  
Saturated Water ◽  
Nucleate Boiling Heat Transfer ◽  
Parametric Effects ◽  
Glass Tubes

Abstract Saturated water at one atmosphere pressure was boiled on horizontal copper discs of diameters 1.0,1.5 and 2.0 cm. respectively. The contact angle was varied from 10 to 80 degrees by controlling thermal oxidation of the discs, while the surrounding vessel size was changed by placing glass tubes of different inner diameters around the discs. Nucleate boiling heat transfer data were obtained up to critical heat flux (CHF), where vapor removal patterns were photographed. Dominant wavelengths at vapor jet interface and vapor jet diameters were measured from the photographs of the well wetted discs. For a well wetted surface, the magnitude of CHF increased when the heater size was reduced from 2.0 to 1.0 cm. Improving the wettability enhanced the CHF substantially, whereas the increased size of the liquid holding vessel had a smaller effect. The highest measured CHF is 233 W/cm2 or 2.11 times Zuber's CHF prediction for infinite horizontal flat plates. It was obtained on a 1.0 cm. disc of contact angle about 10 degrees surrounded by a large vessel. The CHF for this surface was increased from 201 to 233 W/cm2 when the ratio of heater size to surrounding vessel size was reduced from 1 to about 0.

Boiling Heat-Transfer Data at Low Heat Flux

1967 ◽  
Vol 89 (3) ◽  
pp. 235-242 ◽  
Author(s):  
W. C. Elrod ◽  
J. A. Clark ◽  
E. R. Lady ◽  
H. Merte
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Convection Heat Transfer ◽  
Solid Material ◽  
Nucleate Boiling ◽  
Suspended Solid ◽  
Dissolved Gas ◽  
Horizontal Tubes ◽  
Saturated Water

Data are presented for natural and forced convection heat transfer from the outside of a single 3/4-in-dia tube to saturated water in the pressure range from 535 to 1550 psia. Nonboiling and nucleate boiling at low heat flux are considered for vertical and horizontal tubes. Water chemistry control is shown to be important in obtaining reproducible data. A new factor, suspended solid material in the boiling medium, is found to influence the nucleate boiling data in a manner similar to that of a dissolved gas.

Lattice Boltzmann Simulations of Macro/Microscale Effects on Saturated Pool Boiling Curves for Heated Horizontal Surfaces

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Ping Cheng ◽  
Chaoyang Zhang ◽  
Shuai Gong
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Lattice Boltzmann ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Correlation Equation ◽  
Nucleate Boiling ◽  
Nucleate Boiling Heat Transfer

Results of lattice Boltzmann (LB) simulations of macroscale effects (heating modes, heater size, and saturation temperature) as well as microscale effects (wettability and roughness) on saturated pool boiling from superheated horizontal surfaces are summarized in this paper. These effects on pool boiling curves from natural convection through nucleate boiling to critical heat flux (CHF) and from transition boiling to film boiling are illustrated. It is found that macroscale effects have negligible influence on nucleate boiling heat transfer, and Rohsenow's correlation equation fits well with the simulated nucleate boiling heat transfer on smooth hydrophilic and hydrophobic horizontal surfaces. Both macroscale and microscale effects have important influence on critical heat flux and transition boiling heat transfer.

Assessment of CFD Models for Multiphase Heat Transfer in Different Boiling Regimes

2021 ◽  
Author(s):  
Cosimo Bianchini ◽  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
Giuseppe Caggiano ◽  
Maddalena Angelucci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Full Range ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
High Energy ◽  
Operating Conditions ◽  
Liquid Oxygen ◽  
Cfd Models

Abstract Cryogenic propellant rockets, designed to exploit the high energy densities of liquid hydrogen and liquid oxygen, are equipped with turbopumps that deliver liquid fuel to the engine at high pressure levels. Due to the very low saturation temperature of the cryogenic propellant, it is common during the transient operation to have portion of pump walls that achieve boiling conditions. The effect of boiling on the heat transfer between the solid and the fluid needs to be well characterized in order to correctly predict the pump metal temperature evolution and the necessary amount of propellant. This paper presents an investigation about the capabilities of currently available CFD models for boiling to reproduce correctly the phenomenon under various flow conditions. The analysis, conducted with Ansys Fluent CFD solver, focuses on the Eulerian multiphase approach coupled with the mechanistic nucleate boiling model extended to consider the wall boiling regime transition from the nucleate boiling to the critical heat flux regime (CHF). Several test cases are presented to cover the full range of boiling regimes and flow characteristics: the first test focuses on nucleate boiling of sub-cooled water in an upward heated cylindrical pipe, second one deals with 3D boiling water in a rectangular-sectioned duct, the third one considers again nucleate boiling but with a different fluid, namely the R-113 refrigerant, whereas the last investigates the critical heat flux and post dry-out regimes in vertical pipes. Selected tests span over different operating conditions and consider alternative fluids in order to provide a preliminary validation propaedeutic for future investigations focused on more complex applications representative of cryogenic turbopumps.

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