On prediction of heat exchanger performance for latent heat recovery using flue gas

Abstract

The new type heat exchanger, in which fuel gas flows inside thin tubes and water is shell-side, was proposed to develop the performance and compactness of shell & tube type heat exchanger for latent heat recovery from flue gas. The effects of tube diameter (1.0~5.0 mm) and heat exchanging length (7~100 mm) on the heat transfer characteristics of a single tube were systematically investigated. Moreover, the variations of gas inlet temperature or velocity conditions are studied considering the diverse usage of the gas water heater. It was shown that the usage of thinner tubes was remarkably effective to achieve high performance. That is, since the steep temperature drop near inlet occurred and high heat transfer rate was realized for thinner tubes of 1.0mm and 2.0mm in inner diameter compared with thicker tubes. In addition, the increase in the volumetric heat transfer area in thin tube type heat exchanger contributed to the compactness. Furthermore, the non-dimensional correlations concerning non-dimensional bulk mean temperature and specific enthalpy are proposed by using the ratio of effective tube length and thermal entrance region and correlate well with the measurement data regardless of diameter or inlet conditions. It is possible to predict the heat exchanger performance by using the correlations. As a result, it was elucidated that the using mini-tubes is remarkably effective to reduce the size of heat exchanger. For example, the volume with 1 mm inner diameter of tubes is approximately 4 percent of that with 5 mm in diameter.