INTERPHASE MATTER TRANSFER, THE CONDENSATION COEFFICIENT AND DROPWISE CONDENSATION

On interphase matter transfer, the condensation coefficient and dropwise condensation

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1987.0068 ◽

1987 ◽

Vol 411 (1841) ◽

pp. 305-311 ◽

Cited By ~ 19

Keyword(s):

Heat Transfer ◽

General Theory ◽

Water Molecule ◽

Temperature Difference ◽

Interface Temperature ◽

Dropwise Condensation ◽

Condensation Coefficient ◽

Upper Limit ◽

Approximate Nature ◽

Matter Transfer

It is argued that heat-transfer measurements for dropwise condensation cannot be used to determine the condensation coefficient accurately. It is shown that, when recent data for dropwise condensation of steam are re-evaluated, taking account of polyatomicity of the water molecule in the calculation of the interface temperature difference, an upper limit for the value of the condensation coefficient is found to be 0.93 rather than 0.6, as reported earlier. In view of the approximate nature of the polyatomicity correction and uncertainties in the general theory of dropwise condensation, it is considered that these data do not show conclusively that the condensation coefficient is less than unity.

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DROP-SIZE DISTRIBUTIONS AND HEAT TRANSFER IN DROPWISE CONDENSATION - CONDENSATION COEFFICIENT OF WATER AT LOW PRESSURES

Proceeding of International Heat Transfer Conference 8 ◽

10.1615/ihtc8.120 ◽

1986 ◽

Cited By ~ 6

Author(s):

Hiroaki Tanaka ◽

Shigeo Hatamiya

Keyword(s):

Heat Transfer ◽

Drop Size ◽

Size Distributions ◽

Dropwise Condensation ◽

Condensation Coefficient ◽

Drop Size Distributions ◽

Low Pressures

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Further Developments of Dropwise Condensation Theory

Journal of Heat Transfer ◽

10.1115/1.3451044 ◽

1979 ◽

Vol 101 (4) ◽

pp. 603-611 ◽

Cited By ~ 18

Author(s):

H. Tanaka

Keyword(s):

Critical Size ◽

Nucleation Site ◽

Dropwise Condensation ◽

Condensation Coefficient ◽

Characteristic Parameters ◽

Nusselt Numbers ◽

Site Density ◽

Nucleation Sites ◽

Basic Equations ◽

Nucleation Site Density

The high rates of heat transfer of dropwise condensation as well as its limits are explained on the basis of the behaviors of submicroscopic active drops. The expression for the substantial growth rate of a single drop valid down to the thermodynamic critical size is incorporated into a set of basic equations from [8] whose capability to describe the process of coalescence and growth of drops in dropwise condensation has been demonstrated in [9]. Consideration of the nondimensionalized forms of the basic equations with the aid of numerical analysis results in an expression of the Nusselt number for dropwise condensation in terms of a few characteristic parameters. Comparison of the predicted Nusselt numbers with available experimental data suggests that the condensation coefficient of water is around 0.2 provided the nucleation site density is infinitely high. Otherwise, if the condensation coefficient should be unity, we have to accept that the nucleation sites are fairly scattered.

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Interphase matter transfer: an experimental study of condensation of mercury

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1981.0154 ◽

1981 ◽

Vol 378 (1774) ◽

pp. 305-327 ◽

Cited By ~ 22

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Vapour Pressure ◽

Temperature Drop ◽

Vertical Plane ◽

Film Condensation ◽

Interface Temperature ◽

Condensation Coefficient ◽

Condensation Rate ◽

Matter Transfer

Comparisons between interphase matter-transfer theory and measurements have, in the past, been hindered by uncertainties about the ‘condensation coefficient’. Large experimental errors have often been misinterpreted as indicating low values of the condensation coefficient. Condensation experiments with metals are convenient for the study of interphase matter transfer since, owing to the high thermal conductivity of the liquid, the temperature drop across the condensate film is small and, particularly at low pressures and high condensation rates, the temperature discontinuity at the vapour-liquid interface is of measurable magnitude. Condensation rate, and vapour and condenser surface temperature measurements have been made during film condensation of mercury on a vertical, plane, square (side 40 mm), nickel-plated, copper surface. Thermocouples, accurately located and spaced through the copper condenser block, served to measure, by extrapolation, the temperature of the copper-nickel interface and, from the temperature gradient, the heat flux from which the condensation mass flux was determined. Special care was taken to ensure that the results were not vitiated by the presence in the vapour of noncondensing gases. The observations cover wider ranges of vapour pressure (temperature) and condensation rate (heat flux) than hitherto studied, i.e. 50-4300 Pa (378-493 K) and 0.2- 3.6 kgm ~2 s- 1 (56-1062 kW m -2 ) respectively. The results are considered to have enhanced accuracy. In particular, after the accuracy of calibration and positioning of the thermocouples, and th at of the thermoelectric measurements has been considered, it is estimated that the condenser surface temperature was measured to within around ± 0.1 K. Interface temperature discontinuities up to around 70 K have been observed at low vapour pressure and high condensation rate. The results lend support to recent theoretical studies and indicate that the condensation coefficient exceeds 0.9.

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