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Title: THE EFFECT OF SURFACE TENSION ON BOILING HEAT TRANSFER (thesis)

Abstract

The static and dynamic surface tension were measured for aqueoils solutions of eleven surface active agents for the purpose of studying the effect of surface tension upon boiling heat transfer. The surfactants were chosen from the Tween, Aerosol, and Hyonic series. The phenomenon of dynamic or nonequilibrium surface tension arises because of the finite time required ior a surfactant molecule to become oriented at an interface. It is demonstrated by the existence of an apparent surface tension somewhere between the value for pure solvent and the static or equilibrium value. Dynamic surface tension was investigated by observing the volume and frequency for air bubbles forming from a submerged orifice. In all cases, the dynamic surface tension for solutions of these surface active agents was less than the value for pure water, greater than the static value for the same concentration, and was a smoothly decreasing function of concentration. The static values were measured using a duNouy tensiometer. Values were recorded at temperatures approaching T = l00 deg C; the value at this temperature was obtained by extrapolation. Results show that the static surface tension at 100 deg C may have a positive or negative value for d sigma /dT dependingmore » upon the solute-concentration combination chosen. Further, it was shown that although in general the static surface tension decreases with increases in concentration, there are instances where static surface ten sion increases with increases in concentration. The heat transfer data were taken in three groups. The first group of data was used to construct plots of the steady- state heat transfer coefficient versus the superheat. The Tween series showed results which could be interpreted quite successfully on the basis of a decrease in the critical radius for nucleation. The Hyonic series resulted in a fouling of the surface, perhaps due to some decomposition of polymerization product. The Aerosol series showed a cleansing action which kept the surface free of fouling and may even have increased the micro-roughness such that the heat transfer coefficient increased. The second group of data was obtained by observing the immediate temperature response upon addition of a surface active agent. In this way the time-related surface effects described above were eliminated. Analysis of these data indicated that the value of the surface tension which gave the best correlation with the liquid superheat was an arithmetic average of the static and dynamic values. Calculations based upon mass transfer to the growing bubble demonstrated why this was so. The final group of data was obtained using high speed photography. In this manner, quantities such as bubble volume, delay time, and growth time could be measured for the various solutions. A model is presented to describe the manner in which surface tension changes these variables. Results from this model show that surface tension is effective because it changes the nucleating properties of the liquid and not because it alters its hydrodynamic character. Results obtained using this model, as well as data from the films, show that the previously accepted concept of the sr-gnificance of the balance between buoyancy and surface tension forces at bubble break-off'' is in error. The three sets of data all tend to confirm the hypothesis that surface tension is a factor in boiling heat transfer only because it affects the nucleating properties of the liquid. Hydrodynamic effects, such as bubble volume and frequency, are the direct results of the nucleation effects and are not themselves changed significantly by the surface tension. (auth)« less

Authors:
Publication Date:
Research Org.:
Purdue Univ., Lafayette, Ind.
OSTI Identifier:
4827339
Report Number(s):
TID-15920
NSA Number:
NSA-16-022303
Resource Type:
Technical Report
Resource Relation:
Other Information: Orig. Receipt Date: 31-DEC-62
Country of Publication:
Country unknown/Code not available
Language:
English
Subject:
ENGINEERING AND EQUIPMENT; ADDITIVES; AEROSOLS; AIR; BOILING; BUBBLE GROWTH; BUBBLES; CHEMICALS; CLEANING; DECOMPOSITION; DETERGENTS; EFFICIENCY; EXPANSION; FLOW MODELS; FLUID FLOW; FREQUENCY; HEAT TRANSFER; HYDRODYNAMICS; IMPURITIES; MASS; MATHEMATICS; MEASURED VALUES; MOLECULES; NUCLEATE BOILING; ORIFICES; PERFORMANCE; PHOTOGRAPHY; POLYMERIZATION; QUANTITY RATIO; RECORDING SYSTEMS; SOLUTIONS; SOLVENTS; STABILITY; SUPERHEATING; SURFACE TENSION; SURFACES; TEMPERATURE; VOLUME; WATER

Citation Formats

Roll, J B. THE EFFECT OF SURFACE TENSION ON BOILING HEAT TRANSFER (thesis). Country unknown/Code not available: N. p., 1962. Web.
Roll, J B. THE EFFECT OF SURFACE TENSION ON BOILING HEAT TRANSFER (thesis). Country unknown/Code not available.
Roll, J B. Wed . "THE EFFECT OF SURFACE TENSION ON BOILING HEAT TRANSFER (thesis)". Country unknown/Code not available.
@article{osti_4827339,
title = {THE EFFECT OF SURFACE TENSION ON BOILING HEAT TRANSFER (thesis)},
author = {Roll, J B},
abstractNote = {The static and dynamic surface tension were measured for aqueoils solutions of eleven surface active agents for the purpose of studying the effect of surface tension upon boiling heat transfer. The surfactants were chosen from the Tween, Aerosol, and Hyonic series. The phenomenon of dynamic or nonequilibrium surface tension arises because of the finite time required ior a surfactant molecule to become oriented at an interface. It is demonstrated by the existence of an apparent surface tension somewhere between the value for pure solvent and the static or equilibrium value. Dynamic surface tension was investigated by observing the volume and frequency for air bubbles forming from a submerged orifice. In all cases, the dynamic surface tension for solutions of these surface active agents was less than the value for pure water, greater than the static value for the same concentration, and was a smoothly decreasing function of concentration. The static values were measured using a duNouy tensiometer. Values were recorded at temperatures approaching T = l00 deg C; the value at this temperature was obtained by extrapolation. Results show that the static surface tension at 100 deg C may have a positive or negative value for d sigma /dT depending upon the solute-concentration combination chosen. Further, it was shown that although in general the static surface tension decreases with increases in concentration, there are instances where static surface ten sion increases with increases in concentration. The heat transfer data were taken in three groups. The first group of data was used to construct plots of the steady- state heat transfer coefficient versus the superheat. The Tween series showed results which could be interpreted quite successfully on the basis of a decrease in the critical radius for nucleation. The Hyonic series resulted in a fouling of the surface, perhaps due to some decomposition of polymerization product. The Aerosol series showed a cleansing action which kept the surface free of fouling and may even have increased the micro-roughness such that the heat transfer coefficient increased. The second group of data was obtained by observing the immediate temperature response upon addition of a surface active agent. In this way the time-related surface effects described above were eliminated. Analysis of these data indicated that the value of the surface tension which gave the best correlation with the liquid superheat was an arithmetic average of the static and dynamic values. Calculations based upon mass transfer to the growing bubble demonstrated why this was so. The final group of data was obtained using high speed photography. In this manner, quantities such as bubble volume, delay time, and growth time could be measured for the various solutions. A model is presented to describe the manner in which surface tension changes these variables. Results from this model show that surface tension is effective because it changes the nucleating properties of the liquid and not because it alters its hydrodynamic character. Results obtained using this model, as well as data from the films, show that the previously accepted concept of the sr-gnificance of the balance between buoyancy and surface tension forces at bubble break-off'' is in error. The three sets of data all tend to confirm the hypothesis that surface tension is a factor in boiling heat transfer only because it affects the nucleating properties of the liquid. Hydrodynamic effects, such as bubble volume and frequency, are the direct results of the nucleation effects and are not themselves changed significantly by the surface tension. (auth)},
doi = {},
url = {https://www.osti.gov/biblio/4827339}, journal = {},
number = ,
volume = ,
place = {Country unknown/Code not available},
year = {1962},
month = {8}
}

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