Dependence of heat transfer intensity on foam flow direction

Two-phase flows of water and water vapour (liquid and gas) are very frequent in thermal energy systems where evaporation or condensation processes take place. The intensity of many technological processes depends on the inter-contact surface size of both phases (liquid and gas). Foam is distinguished by especially large inter-phase contact surface and can be applied for the conduction of different purpose heat and mass exchanges. Apparatus with foam flow are suitable for use in different technologies like heat exchangers, the food industry, and the chemical and oil processing industry. Statically stable liquid foam until now has been used in technologic systems rather seldom, although the usage of this type of foam as a heat transfer agent in foam equipment has a number of advantages in comparison with one phase liquid equipment: a small quantity of liquid is required, the heat transfer rate is rather high, the mass of equipment is much smaller, energy consumption for foam delivery into heat transfer zone is lower. It is known that the structure of statically stable foam flow and heat transfer is different for horizontal and vertical flows. Directions of the foam flow motion in vertical channels also influence heat transfer intensity. Investigation of the heat transfer process from statically stable foam flow to horizontal tube bank in a vertical channel was performed. Dependency of heat transfer on flow direction, velocity and volumetric void fraction of foam was analysed and estimated by empirical formulas. A significant difference of heat transfer intensity for front and back tubes of the tube row in laminar foam flow was noticed. Analysis of the reasons for this is performed in this paper. The obtained relations can be applied to the design of foam type heat exchangers.