Combined Heat and Mass Transfer during Condensation of Vapours Mixture and Non-Condensable Gas in a Vertical Tube

Abstract

The problem of laminar film condensation from binary vapours mixture with the presence of non-condensable gas (air) flowing in a vertical tube is numerically investigated. The set of the non-linear parabolic equations expressing the mass conservation, momentum, energy, and species diffusion in both phases with the boundary conditions are resolved by using a finite difference numerical scheme. A comparative study between the results obtained for three cases (water-ethanol-air, water-methanol-air, and ethanol-methanol-air) under the same conditions is made. The impact of varying the wall temperature, the inlet vapour mass fractions, and the inlet liquid mass flow rate on the conjugate the heat and mass transfer during the condensation of the studied mixtures are examined. It is found that the condensation of water-methanol-air corresponds to a higher latent heat flux QL2 and accumulated condensation rate Mr2 when compared with water-ethanol-air and ethanolmethanol-air. Moreover, the nature of the fluid plays an important role in the heat and mass exchanges.

Hybrid Wettability-Induced Heat Transfer Enhancement for Condensation with NonCondensable Gas

“…Ji et al 11 used the steam jet to destroy the mixed boundary layer of steam and NCG, indicating that the steam jet injection can improve the average heat transfer efficiency by about 118%. Charef et al 12 numerically analyzed the condensation from mixed vapors in the presence of the NCG inside a vertical tube. They found that the accumulated condensation rate of water− methanol−air is more enhanced by increasing the mass fraction of the NCG and for a lower wall temperature.…”

“…With the development of surface engineering, hydrophobicity is widely employed to enhance the heat transfer efficiency by removing the condensate more efficiently, where a lot of work is made to realize some special condensate-removal mechanisms, for example coalescence-induced droplet jumping. − However, except for the thermal resistance of the accumulated condensate, noncondensable gas (NCG), widely existing in industry, brings significant resistance for the heat transfer process. There have been some investigations focusing on this topic. − Tang et al developed theoretical models for film condensation heat transfer with the NCG. Their results present reasonable agreement with the available experimental data.…”