Maximum Bubble Diameter Research Articles

Void fraction and incipient point of boiling during the subcooled nucleate flow boiling of water

Void fraction has been determined with high-speed photography for subcooled nucleate flow boiling of water. The data obtained and the data of various investigators for adiabatic flow of stream-water mixtures and saturated bulk boiling of water have yielded a correlation which covers the following conditions: geometry: vertically orientated circular tubes, rectangular channels and annuli; pressure: 2–15.9 MN/m 2; mass velocity: 388–3500 kg/m 2 s; void fraction: 0–99%; hydraulic diameter: 0.0047–0.0343 m; heat flux: adiabatic and 0.01–2.0 MW/m 2. The accuracy of the correlation is estimated to be 12.5%. The value of the so-called distribution (or flow) parameter has been experimentally determined and found to be equal to 1 for a vertical small-diameter circular tube. The incipient point of boiling for subcooled nucleate flow boiling of water has been determined with highspeed photography. The data obtained and the data available in the literature have yielded a correlation which covers the following conditions: geometry: plate, circular tube and inner tube-heated, outer tubeheated and inner- and outer tube heated annulus; pressure: 0.15–15.9MN/m 2; mass velocity: 470–17355 kg/m 2s; hydraulic diameter: 0.00239–0.032 m; heat flux: 0.13–9.8 MW/m 2; subcooling: 2.6–108 K; material of heating surface: stainless steel and nickel. The accuracy of the correlation is estimated to be 27.5%. Maximum bubble diameters have been measured at the incipient point of boiling. These data and the data from literature have been correlated for the pressure range of 0.1–15.9 MN/m 2.

Maximum bubble diameter, maximum bubble-growth time and bubble-growth rate during the subcooled nucleate flow boiling of water up to 17.7 MN/m 2

A heat transfer controlled bubble model has yielded three semi-empirical correlations to predict bubble-growth rate, maximum bubble diameter and maximum bubble-growth time for the subcooled nucleate flow boiling of water. Our data for maximum bubble diameter for 13.9, 15.8 and 17.7 MN/m 2 obtained by the use of a highspeed photographic technique and the data available in the literature were found to fit the correlations. The range of data used is as follows: pressure: 0.1–17.7 MN/m 2; heat flux: 0.47–10.64 MN/m 2; velocity: 0.08–9.15m/s; subcooling: 3–86K; maximum bubble diameter: 0.08–1.24 mm; maximum bubble-growth time: 0.175–5 ms.

Estimation of bubble diameter in gaseous fluidized beds

AbstractBubble size is one of the most important parameters in the design and simulation of a fluidized‐bed reactor.A correlation of the bubble size and growth in fluidized beds of various diameters is developed. A maximum bubble diameter determined from the bubble coalescence is incorporated in the correlation to relate the effect of the bed diameter on the bubble size.Experimental data of bubble size reported are used to develop and test the validity of the correlation. The bubble diameters calculated using this correlation show good agreement with the observed bubble diameters.

Heat transfer from teflon‐treated surfaces under flow conditions

AbstractThe effect of Teflon spot treatment of the heating surface on nucleate boiling under flow conditions has been investigated. This effect is found to be complicated, varying strongly with temperature difference and degree of sub‐cooling. In general, for high degrees of subcooling, there is some improvement in the heat transfer coefficient for Teflon‐treated surfaces at low temperature differences, and an opposite effect at high temperature differences. Teflon spot treatment does not produce any appreciable effect at very low degrees of subcooling. An attempt has been made to explain this complex effect of Teflon treatment, taking into account maximum and minimum bubble diameters and insulating effect of Teflon spots.