Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

Some Possible Critical Conditions in Nucleate Boiling

1963 ◽  
Vol 85 (2) ◽  
pp. 89-99 ◽  
Author(s):  
Yan-Po Chang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Maximum Rate ◽  
Unit Area ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Critical Conditions ◽  
Bubble Generation ◽  
Basic Ideas

The primary purpose of this paper is to introduce into boiling heat transfer certain basic ideas from which several critical conditions are derived. The heat transfer in nucleate boiling is considered as being limited by the maximum rate of bubble generation from a unit area of the heating surface. With certain simplified assumptions, an equation is obtained for the first critical heat flux of nucleate boiling with and without forced convection and subcooling.

A New Correlation of Pool-Boiling Data Including the Effect of Heating Surface Characteristics

1969 ◽  
Vol 91 (2) ◽  
pp. 245-250 ◽  
Author(s):  
B. B. Mikic ◽  
W. M. Rohsenow
Keyword(s):  
Heat Transfer ◽  
Heating Surface ◽  
Surface Characteristics ◽  
Nucleate Boiling ◽  
Surface Characteristic ◽  
Organic Liquids ◽  
Cavity Size ◽  
New Correlation ◽  
Wall Superheat ◽  
Wide Range

The standard approach which relates heat transfer in nucleate boiling to heat transfer to the superheated layer averaged over the time between two successive departures of a bubble from a given site is extended in order to relate the heat flux to the wall superheat through the heating surface characteristic. It was found that the q/A versus ΔT relation depends on the cavity size distribution over the surface. For a known distribution of cavity size, the q/A versus ΔT relation may be predicted, or for unknown characteristics of the boiling surface it is sufficient to have boiling data at one pressure in order to predict the q/A versus ΔT relation of other pressure levels for the same surface and the same liquid. The latter was tried on a wide range of experimental data including water and three organic liquids with good results.

Variation of Superheat With Subcooling in Nucleate Pool Boiling

1991 ◽  
Vol 113 (1) ◽  
pp. 201-208 ◽  
Author(s):  
R. L. Judd ◽  
H. Merte ◽  
M. E. Ulucakli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Constant Heat Flux ◽  
Heat Transfer Process ◽  
Heater Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Microlayer Evaporation

An analysis is presented that explains the variation of superheat with subcooling that has been observed by a number of researchers investigating nucleate boiling heat transfer at constant heat flux. It is shown that superheat initially increases with increasing subcooling near saturated conditions because of the way in which changes in active site density and average bubble frequency with increasing subcooling affect the rate of heat removal from the heater surface by enthalpy transport and microlayer evaporation. As subcooling increases further, natural convection begins to play an increasingly important role in the heat transfer process. Ultimately, natural convection is able to accommodate the entire imposed heat flux, after which superheat decreases as subcooling increases. The success of the analysis in explaining the variation of superheat with subcooling suggests that the rate of the heat removal from the heater surface is completely determined by the mechanisms of enthalpy transport, natural convection, and microlayer evaporation.

A Comprehensive Model for Nucleate Pool Boiling Heat Transfer Including Microlayer Evaporation

1976 ◽  
Vol 98 (4) ◽  
pp. 623-629 ◽  
Author(s):  
R. L. Judd ◽  
K. S. Hwang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Methylene Chloride ◽  
Significant Proportion ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Evaporation Heat ◽  
Microlayer Evaporation

The results of an experimental investigation are presented in which dichloromethane (methylene chloride) boiling on a glass surface was studied using laser interferometry and high-speed photography. New data for active site density, frequency of bubble emission, and bubble departure radius were obtained in conjunction with measurements of the volume of microlayer evaporated from the film underlying the base of each bubble for various combinations of heat flux and subcooling. These results were used to support a model for predicting boiling heat flux incorporating microlayer evaporation, natural convection, and nucleate boiling mechanisms. Microlayer evaporation heat transfer is shown to represent a significant proportion of the total heat transfer for the range of heat flux and sub-cooling investigated.

scholarly journals Convective flow boiling heat transfer in an annular space: N-heptane/water case in a bubbly sub-cooled flow

2020 ◽  
Vol 3 (2) ◽  
pp. 33
Author(s):  
M. M. Sarafraz ◽  
H. Arya
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

The subcooled flow boiling heat transfer characteristics of n-heptane and water is conducted for an upward flow inside the vertical annulus with an inner gap of 30 mm, in different heat fluxes up to 132kW.m-2, subcooling max.:30C, flow rate: 1.5 to 3.5lit.min-1 under the atmospheric pressure. The measured data indicate that the subcooled flow boiling heat transfer coefficient significantly increases with increasing liquid flow rate and heat flux and slightly decreases with decreasing the subcooling level. Although results demonstrate that subcooling is the most effective operation parameter on onset of nucleate boiling such that with decreasing the subcooling level, the inception heat flux significantly decreases. Besides, recorded results from the visualization of flow show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing the flow rate and slightly decreases with decreasing the subcooling level. Meanwhile, comparisons of the present heat transfer data for n-heptane and water in the same annulus and with some existing correlations are investigated. Results of comparisons reveal an excellent agreement between experimental data and those of calculated by Chen Type model and Gungor–Winterton predicting correlation.

Influence of System Pressure on Microlayer Evaporation Heat Transfer

1978 ◽  
Vol 100 (1) ◽  
pp. 49-55 ◽  
Author(s):  
H. S. Fath ◽  
R. L. Judd
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Methylene Chloride ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
System Pressure ◽  
Evaporation Heat ◽  
Microlayer Evaporation

Evaporation of the microlayer underlying a bubble during nucleate boiling heat transfer is experimentally investigated by boiling dichloromethane (methylene chloride) on an oxide coated glass surface using laser interferometry and high speed photography. The influence of system pressure (51.5 kN/m2—101.3 kN/m2) and heat flux (17 k W/m2—65 kW/m2) upon the active site density, frequency of bubble emission, bubble departure radius and the volume of the microlayer evaporated have been studied. The results of the present investigation indicate that the microlayer evaporation phenomenon is a significant heat transfer mechanism, especially at low pressure, since up to 40 percent of the total heat transport is accounted for by microlayer evaporation. This contribution to the overall heat transfer decreases with increasing system pressure and decreasing heat flux. The results obtained were used to support the model propounded by Hwang and Judd for predicting boiling heat flux incorporating microlayer evaporation, natural convection and transient thermal conduction mechanisms.

Characteristics of Nucleate Boiling With Gold Nanoparticles in Water

2006 ◽  
Author(s):  
Jenny E. Jackson ◽  
Brian V. Borgmeyer ◽  
Corey A. Wilson ◽  
Peng Chen ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Gold Nanoparticles ◽  
Pure Water ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Gold Particles ◽  
Before And After ◽  
The Heat Transfer Coefficient ◽  
Scanning Electron

An experiment was designed to test the pool boiling performance of 3 nm gold nanofluid on a flat circular copper coupon. Compared to pure water, an increase of up to 175% in the critical heat flux was seen with gold nanofluids. However, a 25-30% deterioration in the heat transfer coefficient was also observed. The heating surface was observed before and after boiling with a scanning electron microscope. A thin, dark film was observed on the surface, which was due to the deposition of gold particles.

A Near-Wall Interfacial Area Concentration Model to Predict Departure From Nucleate Boiling Critical Heat Flux Based on High Speed Video From Boiling Water Flows

2009 ◽  
Author(s):  
Evan T. Hurlburt ◽  
Helene A. Krenitsky ◽  
Richard C. Bauer
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Speed ◽  
Interfacial Area ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Interfacial Area Concentration ◽  
High Speed Video ◽  
Near Wall

In nucleate boiling as the heat flux from the wall to the fluid is increased the heat transfer coefficient initially increases. At a sufficiently high heat flux called the critical heat flux (CHF) the heat transfer mechanism suddenly becomes less effective resulting in a rapid jump in wall temperature. In bubbly subcooled (or near-subcooled) conditions the CHF mechanism is referred to as departure from nucleate boiling. Departure from nucleate boiling (DNB) refers to the transition from nucleate boiling where liquid contacts the wall to film boiling in which a vapor layer contacts the wall. Various hypotheses have been used in modeling and predicting CHF. High speed video images of boiling water flows taken at Bettis Laboratory at the critical heat flux visually captured sufficient evidence of the DNB mechanism that improved insight into DNB modeling may be possible. This paper summarizes high speed video image analysis and the development of a new DNB critical heat flux model based on the image analysis findings. Using short window averages of image data, a significant increase in transmitted light intensity is seen near the wall just prior to CHF. The increase suggests that at CHF there is a transient reduction in the interfacial area concentration, ai, or bubble number density near the wall. This is believed to be the result of a sudden increase in bubble coalescence rates near the wall. The increase in coalescence rates results in a reduction in the interfacial area concentration causing it to reach a maximum at CHF. This near-wall maximum in ai at CHF under flow boiling conditions is consistent with recent pool boiling data in the literature. The image based observations motivated development of an interfacial area based CHF model to predict the maximum in the interfacial area concentration at CHF. The model predicts that a critical nucleation site density or a near-wall critical void fraction can be used as a DNB CHF criterion. This is a valuable simplification that can be directly implemented in three-dimensional thermal hydraulic codes. The critical nucleation site density result was used as an input to a simple wall heat transfer partition model to predict the critical heat flux. The model relies on correlation based estimates for the superheat temperature, bubble departure diameter, and bubble departure frequency. Model predictions are compared to CHF values taken from Groeneveld’s 2006 CHF look-up table.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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