Heat and mass transfer characteristics of simulated high moisture flue gases

Abstract

The heat transfer process occurring in a con- densing heat exchanger where noncondensible gases are dominant in volume is different from the condensation heat transfer of the water vapor containing small amount of noncondensible gases. In the process the mass transfer due to the vapor condensation contributes an important part to the total heat transfer. In this paper, the Colburn-Hougen method is introduced to analyze the heat and mass transfer process when the water vapor entrained in a gas stream condenses into water on the tube wall. The major influential factors of the convec- tive-condensation heat transfer coefficient are found as follows: the partial pressure of the vapor pv, the tem- perature of the outer tube wall Tw, the mixture tem- perature Tg, Re and Pr. A new dimensionless number Ch, which is defined as condensation factor, has been proposed by dimensional analysis. In order to determine the relevant constants and investigate the convection- condensation heat and mass transfer characteristics of the condensing heat exchanger of a gas fired condensing boiler, a single row plain tube heat exchanger is de- signed, and experiments have been conducted with va- por-air mixture used to simulate flue gases. The experimental results show that the convection-conden- sation heat transfer coefficient is 1.532 times higher than that of the forced convection without condensa- tion. Based on the experimental data, the normalized formula for convention-condensation heat transfer coefficient is obtained.