Incipient Boiling Superheat Research Articles

Electrolytic Bubble Nucleation Activation in Pool Boiling of Water: Heat Transfer Enhancement and Reduction of Incipient Boiling Superheat

The effects of the electrolytic activation of bubble nucleation on heat transfer in the saturated boiling of water were experimentally investigated. A copper heated surface is used as a cathode in the electrolysis circuit in this study. The hydrogen bubbles electrolytically generated at the heated surface are used as boiling bubble nuclei to increase the nucleation site density. This paper is the first report on the heat transfer characteristics in boiling activated by electrolysis. In the experiment, the generated hydrogen bubbles were confirmed to actually act as boiling bubble nuclei through the visualization of bubble behavior. The electrolytic supply of boiling bubble nuclei significantly enhanced the boiling heat transfer, as intended. The electrolytic boiling activation was found to be more effective at a lower heat flux with fewer bubbles at the heated wall. Finally, it was demonstrated that this method is also useful for reducing/controlling incipient boiling superheat.

An analysis of incipient boiling superheat in alkali liquid metals

Studies on the incipient boiling superheat (IBS) in alkali liquid metals have revealed that many factors can have effects on IBS. However, existing results about the effects of most variables are inconsistent and even conflicting. It is possible that effects of many variables are only apparent and the complex results can be explained with several simple factors. Three basic variables, i.e. the effects of inert gas diffusion, oxide layer and dynamic process were involved in our model to show their effects on IBS. Analysis showed that the inert gas diffusion should be carefully considered because it may result in large variation of IBS in a short time. Existence of oxide layer could help reducing IBS by keeping large cavities un-wetted and enhancing nucleation contact angle. The effect of dynamic process on IBS which may cause apparent velocity and heat flux effects may be explained with the variation of apparent nucleation contact angle caused by interface speed, and a correlation with some empirical coefficients was proposed to describe its effect. To verify the model several sets of experimental data were carefully selected. Predictions considering these effects were compared with these experimental data and good agreements were gained.

Incipient Boiling of Sodium Flowing in a Single-Pin Annular Channel

This paper deals with an experimental study on incipient boiling of sodium flowing in an annular channel electrically heated by a pin forming the channel core. In the present experiment, the inlet temperature and flow rate were held constant, and the heat flux was gradually increased up to inception of boiling. Measurements were made of the incipient-boiling superheat, and the boiling patterns were observed. The experimental results were compared with analytical calculations The incipient-boiling wall superheat decreased exponentially with increase in flow rate. The boiling patterns observed in the present experiment were not the single-bubble slug expulsion model, as assumed in calculational code, but more similar to multiple-bubble slug expulsion or homogeneous two-phase flow models.

Incipient-boiling superheat for sodium in turbulent, channel flow: Effects of heat flux and flow rate

An experimental study was carried out in which the effects of heat flux and velocity on the incipient-boiling superheat were determined for turbulent flow of sodium in an annular channel. The heating surface was polished type-316 stainless steel having a profilometer roughness of 14–18 μin. (rms). The rate of temperature rise of the heating surface was maintained constant in each incipient-boiling run, by gradually increasing the inlet sodium temperature to the test section, while the heat flux on the heater was held constant. In this way, the independent variables of heat flux and rate of temperature rise were separated. For a finite rate of temperature rise, it was found that the greater the heat flux, the greater was the incipient-boiling superheat, other things being equal. It was also found that the greater the rate of temperature rise, the greater was the effect of heat flux. The flux was varied over the range 25 000–300 000 Btu hft 2 . In general agreement with published results of previous investigators, the incipient-boiling superheat was found to have a strong dependence on the flow rate, falling off exponentially as the flow rate was increased. The axial location of boiling inception was determined by means of a series of voltage taps spaced along the outer wall of the test section; and the results presented herein represent superheat values for, and nucleations at, the upper end of the heater, or at the highest heating-surface temperature in the testsection channel.

Incipient-boiling Superheats for Sodium in Turbulent Channel Flow: Effect of Rate of Temperature Rise

Using sodium, an experimental study was carried out to determine the effect of rate of temperature rise on the incipient-boiling superheat for fully developed, forced turbulent flow. Three different methods of achieving boiling inception were used. The magnitude of the incipient-boiling superheat was found to be quite reproducible and independent of the experimental method as long as the rate of temperature rise (temperature ramp) was kept constant and kept the same. Moreover, the value of the superheat was found to have a strong dependency on the temperature ramp—the greater the ramp, the larger the superheat. The failure to carefully measure and control temperature ramp is apparently one reason why incipient-boiling-superheat data generally show so much scatter, and those from different laboratories so much disagreement.

Closure to “Discussion of ‘Incipient-boiling Superheats for Sodium in Turbulent Channel Flow: Effect of Rate of Temperature Rise’” (1973, ASME J. Heat Transfer, 95, p. 165)

Closure to “Discussion of ‘Incipient-boiling Superheats for Sodium in Turbulent Channel Flow: Effect of Rate of Temperature Rise’” (1973, ASME J. Heat Transfer, 95, p. 165)

Closure to “Discussions of ‘Incipient Boiling Superheat in Liquid Metals’” (1969, ASME J. Heat Transfer, 91, pp. 198–200)

Closure to “Discussions of ‘Incipient Boiling Superheat in Liquid Metals’” (1969, ASME J. Heat Transfer, 91, pp. 198–200)

Incipient Boiling Superheats in Liquid Metals

Measurements were obtained of the superheat required to initiate incipient boiling of potassium in forced convective flow. Emphasis was placed on determining the effect of preboiling, deactivation conditions on subsequent incipient-boiling superheat. Data were obtained with deactivation subcoolings of 10 to 380 deg F, boiling temperatures of 1295 to 1600 deg F, and boiling pressures of 8 to 24 psia. Measured superheats ranged from 17 to 117 deg F. Sufficient data were obtained to indicate the functional dependence of incipient-boiling superheats on each of the three independent variables: deactivation pressure, deactivation temperature, and boiling pressure. The experimental results were found to be in substantial agreement with an analytical model developed herein. The proposed correlating equation was generally correct in predicting both the magnitude of the superheat and in its functional dependence on each of the independent variables.