2015 Volume 2 Issue 2 Pages 14-00300
The exhaust gas from energy system consists of non-condensable gas and steam with sensible and latent heat, respectively. When a lot of latent heat is included in the exhaust gas, its recovery is very important to improve the system efficiency. For condensation from steam-gas mixture, analogy correlation of heat and mass transfer has been used as an approximation. The analogy method is eagerly expected for the design of heat exchangers where the heat transfer correlation has been empirically established. However, at the high concentration of steam, some modification is necessary on the mass transfer correlation because it is originated and estimated from the heat transfer correlation without condensation. Condensation heat transfer on a row of horizontal stainless steel tubes was investigated experimentally and new analogy relation taking account of the mass absorption effect on the wall was proposed. Based on this basic study, a thermal hydraulic prediction method for latent heat recovery exchangers was proposed. Furthermore two kinds of compact heat exchanger with staggered banks of small bare tubes were designed with the prediction method. The more compactness was obtained with the smaller tubes at a designed heat recovery. The thermal hydraulic behavior in the compact heat exchangers was experimentally studied with air-steam mixture gas. The experimental results agreed well with the prediction proposed in this study and the more compactness with the smaller tubes was proved. Finally the prediction method was used in the commercial design of home hot water supply system using natural gas and the thermal efficiency was raised by 17 % with the latent heat recovery technology.