Abstract
This paper deals with the condensation of water vapour in the presence of non-condensable air. Experimental and theoretical solutions of this problem are presented here. A heat exchanger for the condensation of industrial waste steam containing infiltrated air was designed. The condenser consists of a bundle of vertical tubes in which the steam condenses as it flows downwards with cooling water flowing outside the tubes in the opposite direction. Experiments with pure steam and with mixtures of steam with added air were carried out to find the dependence of the condensation heat transfer coefficient (HTC) on the air concentration in the steam mixture. The experimental results were compared with the theoretical formulas describing the cases. The theoretical determination of the HTC is based on the Nusselt model of steam condensation on a vertical wall, where the analogy of heat and mass transfer is used to take into account the behaviour of air in a steam mixture during the condensation process. The resulting dependencies obtained from the experiments and obtained from the theoretical model have similar results. The significant decrease in the condensation HTC, which begins at very low air concentrations in a steam mixture, was confirmed.
Highlights
Waste steam produced in many industrial processes has typically low parameters and it may contain infiltrated air limiting its following utilization
The significant decrease in the condensation heat transfer coefficient (HTC), which begins at very low air concentrations in a steam mixture, was confirmed
For the air concentration in the steam mixture of 1%, the condensation HTC decreases according to the experiments to 62% and according to the theoretical model even to 75% of the value for the condensation of pure steam
Summary
Waste steam produced in many industrial processes has typically low parameters and it may contain infiltrated air limiting its following utilization. This paper deals with the influence of non-condensable gases (air) in a steam mixture on the utilization of its condensation heat. An evaluation of this effect is based on experiments with a condenser designed for the utilization of atmospheric pressure steam with a small content of infiltrated air. The dependence of the condensation heat transfer coefficient (HTC) on the air concentration in a steam mixture is given. The influence of non-condensable gas on heat transfer is an important factor for the design of waste vapour heat condensers whose use may increase the energy efficiency of processes producing waste steam [1], [2]. The tubes are made from stainless steel 1.4301 (AISI 304)
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