The origin of thermocapillary convection in subcooled nucleate pool boiling

Publisher Summary Condensation plays a significant role in the heat rejection parts of the rankine power generation cycle and the vapor compression refrigeration cycle, which generally involve single components. Condensation is initiated by a nucleation process either in a bulk vapor or on a solid surface. Condensation heat transfer can be studied from either the macroscopic or the microscopic point of view. The macroscopic viewpoint considers matter as a continuum and requires the introduction of certain phenomenological laws, the macroscopic transport equations, in addition to the conservation equations of mass, energy, and momentum, in order to deal with rate processes. The microscopic viewpoint deals with molecules, atoms, and subatomic particles.

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Condensation Heat Transfer

Diffusion layer modeling for condensation in vertical tubes with noncondensable gases

Condensation in the presence of noncondensable gases

The forced convection heat transfer with water vapor condensation is studied both theoretically and experimentally when wet flue gas passes downwards through a bank of horizontal tubes. Extraordinarily, discussions are concentrated on the effect of water vapor condensation on forced convection heat transfer. In the experiments, the air–steam mixture is used to simulate the flue gas of a natural gas fired boiler, and the vapor mass fraction ranges from 3.2 to 12.8%. By theoretical analysis, a new dimensionless number defined as augmentation factor is derived to account for the effect of condensation of relatively small amount of water vapor on convection heat transfer, and a consequent correlation is proposed based on the experimental data to describe the combined convection–condensation heat transfer. Good agreement can be found between the values of the Nusselt number obtained from the experiments and calculated by the correlation. The maximum deviation is within ±6%. The experimental results also shows that the convection–condensation heat transfer coefficient increases with Reynolds number and bulk vapor mass fraction, and is 1∼3.5 times that of the forced convection without condensation.

J. M. Marchello

Papers

Film Condensation in the Presence of a Noncondensable Gas